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Expert Opinion on Drug Delivery

ISSN: 1742-5247 (Print) 1744-7593 (Online) Journal homepage: http://www.tandfonline.com/loi/iedd20

Drug delivery from gelatin-based systems

Maytal Foox & Meital Zilberman PhD

To cite this article: Maytal Foox & Meital Zilberman PhD (2015) Drug delivery fromgelatin-based systems, Expert Opinion on Drug Delivery, 12:9, 1547-1563, DOI:10.1517/17425247.2015.1037272

To link to this article: http://dx.doi.org/10.1517/17425247.2015.1037272

Published online: 05 May 2015.

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1. Introduction

2. Gelatin sources and

crosslinking

3. Gelatin as a drug delivery

carrier

4. Gelatin-based particles

5. Gelatin-based fibers

6. Gelatin-based hydrogels and

bioadhesives

7. Conclusion

8. Expert opinion

Review

Drug delivery from gelatin-basedsystemsMaytal Foox & Meital Zilberman†

†Tel-Aviv University, Department of Biomedical Engineering, Faculty of Engineering, Tel-Aviv,

Israel

Introduction: Carriers for controlled drug release offer many advantages com-

pared with conventional dosage forms. Gelatin has been investigated exten-

sively as a drug delivery carrier, due to its properties and history of safe use

in a wide range of medical applications.

Areas covered: Gelatin was shown to be versatile due to its intrinsic features

that enable the design of different carrier systems, such as microparticles

and nanoparticles, fibers and even hydrogels. Gelatin microparticles can serve

as vehicles for cell amplification and for delivery of large bioactive molecules,

whereas gelatin nanoparticles are better suited for intravenous delivery or for

drug delivery to the brain. Gelatin fibers contain a high surface area-to-vol-

ume ratio, whereas gelatin hydrogels can trap molecules between the poly-

mer’s crosslink gaps, allowing these molecules to diffuse into the blood

stream. Another interesting area is the combination of tissue bioadhesive-

based gelatin with controlled drug release for pain management and wound

healing.

Expert opinion: The modification of gelatin and its combinations with other

biomaterials have demonstrated the flexibility of these systems and can be

employed for meeting the challenges of finding ideal carrier systems that

enable specific, targeted and controlled release in response to demands in

the body.

Keywords: fibers, gelatin, hydrogels, microparticles, nanoparticles, tissue bioadhesive

Expert Opin. Drug Deliv. (2015) 12(9):1547-1563

1. Introduction

Gelatin is a natural, biocompatible, biodegradable and multifunctional biopolymer.It is widely used in food, pharmaceutical, cosmetic and medical applications due toits unique mechanical and technological properties. In the medical and pharmaceu-tical fields, gelatin is currently used as a matrix for implants, device coatings and as astabilizer in vaccines against measles, mumps, rubella, Japanese encephalitis, rabies,diphtheria and tetanus toxin [1]. It is also used in intravenous infusions, hard andsoft capsules, plasma expanders, wound dressings, tissue bioadhesives, hemostats,sealants and in drug delivery systems [2-5]. Gelatin was first produced commerciallyin 1685 in Holland [6] and has been used for intravenous infusions since World WarI [5]. The demand for gelatin for many applications has increased over the years andhas reached an annual global output of nearly 326,000 tons [7]. Gelatin’s manyqualities, along with its ability to produce a thermoreversible gel, have turned itinto a good candidate for targeted drug delivery carriers. The collagen source, thetype of hydrolytic treatment used, the extraction method, the amount of thermaldenaturation employed and the crosslinking degree of gelatin influence the mechan-ical properties, swelling behavior, thermal properties and other physiochemicalproperties [5,8-10]. The versatility in gelatin properties enables choosing the mostsuitable conditions for desired drug-release profiles. The aim of this article is toreview the different sources and production methods of gelatin as well as its

10.1517/17425247.2015.1037272 © 2015 Informa UK, Ltd. ISSN 1742-5247, e-ISSN 1744-7593 1547All rights reserved: reproduction in whole or in part not permitted

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modification to produce different types of carries with orwithout synthetic or natural polymers in order to optimizeand specify the drug-release profile for a broad range of appli-cations in regenerative medicine.

2. Gelatin sources and crosslinking

2.1 Gelatin sourcesGelatin is a water-soluble polypeptide that can be obtainedfrom acid, alkaline or enzymatic hydrolysis of collagen, themain protein component of the skin, bones and connectivetissue of animals, including fish and even insects. Gelatinderived from an acid treatment, such as hydrochloric acid orsulfuric acid, is known as type A, whereas gelatin derivedfrom an alkaline treatment is known as type B. After bothkinds of treatments, the solutions are filtered, deionized andconcentrated by membrane filtration and/or vacuum evapora-tion. Minerals, fats and albuminoids found in bones or skinare then removed by chemical and physical treatment in orderto obtain purified gelatin [6].Porcine skin-derived gelatin is the most popular source

(46%), followed by bovine skin (29.4%), bone (23.1%) and

other sources (1.5%) [7]. However, these sources suffer frommajor constrains and concerns among consumers due toreligious issues (porcine-derived products are forbidden inboth Judaism and Islam, and Hindus do not consumebovine-derived products) as well as the increase in vegetarian-ism throughout the world. Furthermore, there is a healthconcern of transmitting pathogenic vectors such as prions [11].Other sources of gelatin, including poultry, fish, vertebratesand even recombinant gelatin, have therefore been introducedduring the past decade. Due to the fact that the commercialproduction of gelatin from poultry skin is currently limitedby low yields, it is not very popular as a source of gelatin [12].Gelatin from fish (especially warm-water fish) possesses simi-lar characteristics to porcine gelatin and may thus be an alter-native for it. Production of gelatin from fish may also serve asa means for utilizing some of the by-products of the fishingindustry. However, the primary amino acid sequence levelof fish gelatin is different from that of porcine and bovineskin gelatin. Fish gelatin (especially from cold-water fish)has a lower melting temperature, which can decrease its ther-mal stability and effectiveness at body temperature. Fishgelatin also raises a concern for possible allergic reac-tions [13,14]. Recombinant gelatins were developed in orderto overcome the disadvantages associated with animal tissue-derived material. This technology allows the production ofgelatins with specific properties to match a specificapplication [15].

2.2 Crosslinking of gelatinGelatin should be crosslinked before use in order to increaseits mechanical properties and lower its solubility and degrada-tion rate in aqueous solutions [16]. Physical crosslinking bymicrowave energy [17], dehydrothermal treatment and ultravi-olet irradiation [18], biological crosslinking by enzymes orchemical crosslinking by agents such as formaldehyde, [19],glutaraldehyde [20], glyceraldehyde [21], genipin [22] and carbo-diimide [23] have been reported.

Physical crosslinking can be achieved using environmentaltriggers (such as pH, temperature or ionic strength) or physi-cochemical interactions (such as hydrophobic interactions,charge condensation, hydrogen bonding, stereocomplexationor supramolecular chemistry). When physical crosslinking isemployed, there is no need for chemical modification or theaddition of crosslinking agents that might be toxic [24]. How-ever, it is difficult to control the crosslinking density and thecrosslinking procedure is often less efficient [25].

There are two types of chemical crosslinkers: non-zero-length and zero-length [25]. Non-zero-length crosslinkersare built into the biomaterial by bridging free amine groupsof lysine and hydroxylysine or free carboxylic acid residues ofglutamic and aspartic acid of the protein molecules.Aldehydes (formaldehyde, glutaraldehyde, glyceraldehydes),polyepoxides and isocyanates are often used as crosslinkers,with glutaraldehyde being the most commonly used. How-ever, during the biomaterial’s degradation, reactive and toxic

Article highlights.

. A great demand exists for the development ofcontrolled release of bioactive molecules. The uniqueproperties of gelatin and its extensive investigation as abiomaterial for controlled release of bioactive moleculesare discussed.

. Gelatin was shown to be versatile due to its intrinsicfeatures that enable the design of different carriersystems such as microparticles and nanoparticles, fibersand even hydrogels.

. Gelatin microparticles can serve as vehicles for cellamplification and delivery of large bioactive molecules,whereas gelatin nanoparticles have higher intracellularuptake and are better suited for intravenous delivery orfor drug delivery to the brain. Gelatin fibers contain ahigh surface area-to-volume ratio and high porosity,whereas gelatin hydrogels can trap molecules within thegaps between the polymer crosslinks, allowing the drugsto diffuse into the blood stream.

. Another interesting area is the combination of tissuebioadhesive-based gelatin with controlled drug releasefor pain management and wound healing.

. Gelatin-based systems exhibit a high ability to absorbwater. However, this can be monitored by changing thegelatin source, its molecular weight and the degree ofthe crosslinking. The challenge is to find a goodcrosslinking technique that will not change the uniqueand desired properties of the gelatin or lower itsbiocompatibility.

. It is concluded that work is continuing to allow therelease of a wider variety of biomolecules for a broadrange of applications by the modification of gelatin andits combination with other biomaterials.

This box summarizes key points contained in the article.

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1548 Expert Opin. Drug Deliv. (2015) 12(9)

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compounds might leach into the body and cause damage [26].

In contradistinction, zero-length crosslinkers activate

carboxylic acid residues to react with free amine residues,

resulting in the formation of an amide bond without incor-

poration of foreign structures into the network. Acyl azide

and water-soluble carbodiimide crosslinkers are representa-

tives of this group of crosslinkers. The acyl azide crosslinking

is a four-step reaction which requires the use of the toxic

reagent hydrazine [4]. However, a simpler and less toxic

variation of this reaction is achieved when using diphenyl-

phosphoryl azide instead of hydrazine [27,28]. Carbodiimides

are reactive organic compounds with a R-N=C=N-R struc-

ture. The R is usually alkyl, aryl, acyl, aroyl, imidoyl or

sulfonyl, but can also be nitrogen, silicon, phosphorous

and metal [29]. Nobel laureate Sheehan used water-soluble

carbodiimides in the synthesis of penicillin and was the first

to use carbodiimides to crosslink gelatin. The workhorse in

this application is the water-soluble N-ethyl-N-(3-dimethy-

laminopropyl) carbodiimide (EDC). The carbodiimide

crosslinking can be performed in one step and involves the

use of less harmful reagents [30,31].However, when using chemical crosslinkers, unreacted

crosslinker molecules might be left inside the matrix and there

is a risk of the creation of toxic products by the reaction

between the substrate and the crosslinking agent during

in vivo biodegradation. Means to lower the concentrations

of chemical crosslinkers and finding naturally derived cross-

linking agents with low cytotoxicity are therefore being

examined. One example is the use of genipin, a natural cross-

linking reagent obtained from geniposide, an iridoid

glucoside isolated from the Genipa americana and Gardeniajasminoides Ellis fruits [32]. Studies have shown that crosslink-

ing with genipin resulted in lower cytotoxicity and higher bio-

compatibility compared to glutaraldehyde, formaldehyde and

epoxy compounds. Additionally, in vivo studies showed that

lacerations treated by a genipin-crosslinked bioadhesive indu-

ced significantly fewer inflammatory responses and recovered

sooner than lacerations treated by aldehyde-crosslinked

bioadhesives [22,33-35].Gelatin dissolves rapidly in aqueous environments. Its use

as a carrier for long-term delivery systems is thus ineffective.

Crosslinking of gelatin can improve its thermal and mechan-

ical stability and its hydration potential under physiological

conditions, as well as lower its degradation in vivo, and allows

it to maintain its long-term release function as a carrier [36,37].

The increase in the resistance against degradation probably

results from the crosslinking which modifies cleavage sites of

gelatin molecules, resulting in an inhibition of the enzyme-

substrate interaction [38]. The crosslinking density of the

gelatin carrier can be altered by either prolonging the cross-

linking reaction period or increasing its concentration. As a

consequence, the period of bioactive molecule release can be

regulated [38,39].

3. Gelatin as a drug delivery carrier

Significant efforts have been made to improve formulations

for better stabilization of drugs over a sufficient storage

time. In the body, the therapeutic effect of a drug is most

effective when its concentration in the blood is above the

minimum effective level and below the toxic level. However,

every drug has its own biological half-life and can therefore

be maintained at an effective concentration for only a specific

and short time. One solution for this problem is to increase

the dose of the drug. However, it is important not to reach

the toxic response region. Another solution, which is less

convenient for the patient, is to take the drug several times

during a period of time. Extensive efforts are consequently

being made to develop dosage forms that prolong the biolog-

ical activity of a protein in the body or assist in targeting it to a

specific tissue. One possible way to achieve these goals is to

incorporate the drug into an appropriate matrix. Drug

controlled-release carriers offer many advantages compared

to conventional dosage forms, including improved efficacy,

maintenance of the desired drug concentration in the blood

for a long period of time without reaching a toxic level or

dropping below the effective level, reduced toxicity and

improvement in patient compliance and convenience.In spite of these advantages, the patient can be harmed if

the controlled drug delivery system is not properly designed.

The ideal drug delivery system must therefore be biocompat-

ible without toxic degradable products, mechanically strong

with the ability to load large amounts of drug with no concern

of accidental release, simple to fabricate and sterilize, easy to

place and remove and comfortable for the patient [29].There are several mechanisms by which the release of active

agents from drug delivery systems to the surrounding can be

controlled: i) diffusion; ii) swelling followed by diffusion

(mostly in hydrogels); iii) diffusion and degradation (erodible

systems); iv) hydrolysis of the covalent bond in case the drug

is covalently bound to the biodegradable polymer (pendant

chain systems); v) osmotic pressure; and vi) externally or

self-regulated systems.Polymeric carriers, which physically entrap molecules of

interest, need to be shielded to avoid fast recognition by the

immune system followed by rapid clearance from the body.

The physicochemical properties of drug carriers, such as size,

hydrophilicity and zeta potential have enormous effects on

their identification and phagocytosis by the macrophage

system. The suppression of nonspecific interactions with the

body, including blood components (opsonization) and activa-

tion of the complement system, would reduce blood clearance

of drug carriers. Drug delivery carriers can be coated with a

hydrophilic polymer, such as gelatin, to allow both inhibition

of opsonization and improvement of water solubility [40]. In

addition, using a biodegradable polymer as a drug carrier

would protect the drug against corrosion by gastric acid and

Drug delivery from gelatin-based systems

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disassembly by enzymes, thus preserving the efficient activityof the drug in the body [41].Gelatin has been extensively investigated as a drug delivery

carrier for many classes of drugs due to its properties as anatural biomaterial and history of safe use in a wide range ofmedical and pharmaceutical applications. Inflammatorydrugs, antineoplastic compounds, antibacterial agents andrecently nucleic acid and hydrophobic materials were reportedin the literature [42-50]. Gelatin properties can be adjusted tomaximize drug-loading efficiency [51]. Gelatin’s isoelectricpoint can be adjusted to the electrostatic properties of thechosen drug molecule by using an alkaline or an acidic treat-ment [52]. Furthermore, the hydrophilic nature of gelatin facil-itates the penetration of body fluids into the particles andthereby increases the diffusion-mediated release of bioactivemolecules [53]. Drug-release profiles from gelatin can also beoptimized by changing the gelatin source, molecular weightand the degree of crosslinking [39]. Furthermore, modificationof gelatin to different types of carriers and addition ofsynthetic or natural polymers can be optimized and the drugprofile release can be specified to a broad range of tissue engi-neering [54,55], cancer therapy (46 -- 47), and therapeuticangiogenesis [56,57] applications.As a drug delivery carrier, gelatin has been shown to be ver-

satile due to its intrinsic features that enable the design ofdifferent carrier systems. The most widely used gelatin-basedsystems are described in the sections below.

4. Gelatin-based particles

Gelatin microparticles and nanoparticles have been exten-sively studied as carrier systems for many applications. Micro-particles have the advantage of a large surface area whichenables sufficient exchange of nutrients and metabolic wastesand allows rapid cell development [58]. They can thereforeserve as vehicles for cell amplification and can simplify thedelivery of these expanded cells or other large bioactive mole-cules to the desired site [59]. The size of nanoparticles offersother advantages, including a relatively higher intracellularuptake by various areas of the body [60]. For example, nano-particles are better suited for intravenous delivery [61] or fordelivery of drugs to the brain, due to their ability to betteraccumulate in macrophage-rich organs which can easily crossthe blood--brain barrier [62]. Due to their unique design, lipo-somes have the ability to incorporate both hydrophilic andhydrophobic drugs, protect them from degradation, targetthem to the desired site and reduce the toxicity or side effectsof those molecules [63-67]. Unfortunately, liposomes have lowencapsulation efficiency, poor storage stability and water-soluble drugs can rapidly leak in the presence of bodyfluids [68]. However, some researchers showed that embeddingliposomes into a gelatin-based system resulted in an improve-ment in their stability, viscosity and the half-life of the loadeddrug and the liposome [69].

4.1 NanoparticlesNanoparticles are defined as particles with a size in the rangeof 1 -- 1000 nm [42]. They have good in vivo stability, can beeasily sterilized, scaled-up and their manufacture can be freeof contamination with pyrogens. These advantages can beused in the fields of biomaterials and medicine [70]. Nanopar-ticles can be used to deliver hydrophilic and hydrophobicdrugs, proteins, vaccines and other types of bioactive mole-cules to various areas in the body, such as the lymphaticsystem, brain, arterial walls, lungs, liver, spleen or even forlong-term systemic circulation [61]. A successful nanoparticlesystem should have high loading capacity to reduce theamount of carrier needed for administration. Depending onthe drug and carrier properties, the drug can be dissolved,entrapped, encapsulated or attached to the nanoparticle. Theloading of the drug can be performed at the time of the nano-particle production, during the polymerization process orafter the formation of the nanoparticles by incubating themwith the drug solution [68]. The amount of bound drug and

the type of interaction between the drug and the nanoparticlesdepend on the chemical structure of the drug and the polymerand the conditions of the drug-loading procedure [71].

Gelatin nanoparticles have been widely used for encapsulat-ing many bioactive molecules [72]. Li et al. encapsulatedbovine serum albumin (BSA) as a model protein drug, usinggelatin-based nanoparticles. BSA release was followed by adiffusion-controlled mechanism and was enhanced by thenanoparticles’ water uptake capacity of 51 -- 72% [73]. Nano-particles can better accumulate in macrophage-rich organswhich can easily cross the blood--brain barrier and reach thebrain, compared to other carrier systems [62].

The oral administration of didanosine, a widely used anti-HIV drug, is associated with poor gastrointestinal tolerability,narrow therapeutic index, low plasma protein binding, shortplasma half-life (30 min to 4 h) and dose-dependent sideeffects with the need for frequent dosing [74]. Therefore, gela-tin nanoparticles with a mannan coating to further enhancethe macrophage uptake and the distribution in organs thatact as major HIV reservoirs were loaded with didanosine.The ex vivo study indicated that the rate of didanosine uptakeby the macrophages was fivefold higher from mannan-coatedgelatin nanoparticles than from free didanosine in PBSsolution [70].

In order to reduce the toxic side effects of chloroquinephosphate, a well-known antimalarial drug, it was encapsu-lated in gelatin nanoparticles [75]. The results showed thatchloroquine phosphate release was controlled via diffusion,increased with increasing temperature, but decreased in thephysiological fluids and was found to be optimal near thephysiological pH (7.4). The addition of the crosslinker glutar-aldehyde to the nanoparticles decreased the drug release rate.The type of gelatin also affected the release profile. Gelatin

type B nanoparticles showed higher drug release than gelatintype A [75].

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The release of growth factors in vivo is known to be verychallenging, since a special and time-specific controlled deliv-ery of multiple factors must be obtained in order to achievemaximum efficiency. Since degradation rates of subpopula-tions of specific blocks in colloidal gels can be controlled,they can be suitable for independent release of multiplebiomaterials [54]. For this reason, colloidal gels made ofoppositely charged gelatin nanospheres were loaded withboth osteogenic bone morphogenetic protein-2 (BMP-2)and angiogenic basic fibroblast growth factor (bFGF), usinga twin syringe in order to improve control over their dualdelivery. In vitro results showed that the crosslinking degreeof gelatin has a greater effect on the delivery rates of bothBMP-2 and bFGF than the gelatin type. However, thecombined delivery of both BMP-2 and bFGF resulted in aninhibitory effect on osteogenesis under the current experimen-tal conditions. More experiments are needed in order tomaximize the ability of these nanospheres [54].

In another study, gelatin nanoparticles prepared by nano-precipitation using water and ethanol were loaded with threedifferent drugs (tizanidine hydrochloride, gatifloxacin andfluconazole). The addition of glutaraldehyde as a crosslinkerenhanced the tizanidine hydrochloride-loading efficiency,but lowered the gatifloxacin-loading efficiency due to compe-tition of activated groups [42]. No loading was achieved in thecase of fluconazole.

Ibuprofen sodium, an anti-inflammatory drug, was loadedinto PEGylated gelatin nanoparticles. The results demon-strated an improved plasma half-life of ibuprofen sodiumwhen encapsulated within the nanoparticles. These resultsmight allow lowering the rate of ibuprofen sodium neededfor treatment [45]. Targeting nano- and micro-vesicles toenhance drug uptake only in tumor cells, while sparinghealthy cells, is a unique strategy which is currently beinginvestigated. It is known that the extracellular pH of tumortissue is lower than that of normal tissue. The pH-responsivecarriers would therefore have an advantage in acceleratinglocal drug release in tumor tissue [76]. Doxorubicin, an anti-cancer drug, was encapsulated in an amphiphilic gelatin--ironoxide core/calcium phosphate shell nanoparticle. The addi-tion of a calcium phosphate shell acts as a drug reservoirand turned the nanoparticles into highly pH-responsivedrug-release carriers [76]. These nanoparticles were found tobe biocompatible and were taken up by HeLa cells [47]. Inanother study, paclitaxel-loaded gelatin nanoparticles wereshown to be effective against human bladder transitional can-cer cells with a very rapid release rate of 90% at 37�C after 2 hin PBS and urine solutions [53].

Surface-modified gelatin nanoparticles were also tested ascarriers for double-stranded DNA and RNA oligonucleotidesvia ionic interactions. The results showed that the loadingcapacity of the oligonucleotides was dependent on the parti-cle’s zeta potential and on the incubation medium [77].A new tumor-targeted small interfering RNA (siRNA) deliv-ery system using a gelatin nanocarrier was developed. The

primary amines of gelatin and the 5¢-end of the siRNA werethiol-modified in order to increase the interactions betweenthem. The encapsulation of siRNA molecules in the self-assembled thiolated gelatin nanoparticles using chemicalcrosslinking protected them from enzymatic degradation.The nanoparticles showed a great potential as a systemicsiRNA delivery system for cancer therapy, based on their char-acteristics of low toxicity, tumor accumulation and effectivesiRNA delivery [47].

4.2 MicroparticlesGelatin microparticles have been extensively studied as acarrier system for many applications [78-80]. They can beproduced by several methods: emulsion polymeriza-tion [59,81,82], solvent evaporation [58], coacervation [83] andspray-drying [84]. However, gelatin microparticles have poormechanical properties and rapid dissolution rates in aqueousenvironments which accelerate drug release at body tempera-ture [21]. Gelatin microparticles are typically crosslinked withformaldehyde, glutaraldehyde [85], genipin and/or carbodii-mides [38] in order to solve these problems. However, metha-crylation of gelatin has been reported to be less cytotoxic andto enable a larger range of crosslinking densities compared tothe traditional chemical crosslinking methods, thus offeringan alternative method to better control the extent of hydrogelcrosslinking [86]. It was shown that fewer methacrylatedmicroparticles had decreased elastic moduli and larger meshsizes but could be loaded with up to a 10-fold higher relativeamount of growth factor compared to glutaraldehyde cross-linked microparticles. Furthermore, a reduced gelatin methac-rylate crosslinking density resulted in higher release ofBMP-4 and bFGF and accelerated release rate with collage-nase treatment [78].

Solorio et al. succeeded in developing a self-assembledsystem of gelatin microspheres loaded with TGF-b1 as amean of enhancing neo-cartilage tissue formation in a humanmesenchymal stem cells (hMSCs) culture. In addition to theproduction of hMSC sheets with superior mechanical proper-ties, this system could decrease the culture time necessarybefore implanting hMSCs and might also avoid the problemof the loss of chondrogenic phenotype in vivo by providingcontinued local exposure of these hMSCs to growth factorby the microparticles [87]. Additional researches demonstratedthe efficacy of gelatin microparticles in releasing VEGF orBMP-2. Both VEGF and BMP-2 release kinetics were depen-dent on the gelatin crosslinking degree [88,89].

Gelatin microparticles showed several advantages forpulmonary delivery, such as a large distribution to lungepithelial cells and higher availability of bioactive moleculesto the infected cells. Rifampicin and isoniazid are part of thetherapeutic treatment against tuberculosis. However, thesedrugs are relatively toxic, can cause several side effects andmight cause drug resistance when not followed to completion.The use of microcarriers loaded with these drugs may allowreducing the therapeutic dose, extending the duration of

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action, ensuring sustained drug delivery to the lungs and as aresult improving patient compliance. Therefore, a new poly-meric microparticle system based on gelatin covalently boundto isoniazid and containing rifampicin was developed. Theresults showed that the microparticles demonstrated low cyto-toxicity, were able to encapsulate both rifampicin (51 ± 6%)and isoniazid (22 ± 1%) and had a good nebulizationefficiency which is important in pulmonary antituberculardrug delivery systems [90].It is known that most anticancer drugs have pharmacoki-

netic limitations such as low bioavailability and a high effec-tive dose (ED50) index. A new strategy of targetingmicrovesicles to enhance specific drug uptake by tumor cellswithout harming healthy cells is increasingly investigated. Ste-rically stabilized gelatin micro-assemblies loaded with theanticancer drug noscapine were developed for targetinghuman NSCLC. In vitro release studies indicated that thesemicro-assemblies followed first-order release kinetics andexhibited an initial burst followed by slow release of thedrug. The in vitro studies showed that the stabilized gelatinmicro-assemblies had an approximately threefold lower IC50

compared to free noscapine. The micro-assemblies extendedthe release of noscapine and increased the plasma half-life ofnoscapine by ~ 9.57-fold with an accumulation of ~ 48%drug in the lungs [46].Propolis ethanolic extractive solution (bee glue) is usually

used in wound healing, tissue regeneration, burns, neuroder-matitis, leg ulcers, psoriasis, herpes simplex and genitalis,rheumatism and sprains, periodontal diseases, candidiasis,cheilitis, stomatitis, influenza and cold [84]. Gelatin micropar-ticles loaded with propolis prepared by the spray-dryingmethod have been shown to be a feasible and inexpensivemethod. In addition, this propolis dosage form would bewithout the propolis extraction solution’s strong and unpleas-ant taste, aromatic odor and high ethanol concentration,which can cause packaging and transport difficulties andpatient inconvenience [84].In another research, novel microparticles combined with

sustained and localized delivery of bFGF and gyrus-patternedsurface were tested for both delivery systems and scaffolds forproliferation and attachment of cells. The results suggestedthat this unique system might be a good candidate for rapidcell expansion and has a potential for application in cartilagetissue engineering [59].

4.3 LiposomesLiposomes are small spheres of an aqueous core entrapped byone or more phospholipids which form closed bilayeredsystems [91]. Liposomes are widely used as an advanced tech-nology for delivering bioactive molecules due to their highbiocompatibility, ability to incorporate hydrophilic andhydrophobic drugs and their ability to deliver bioactive mole-cules directly to the desired site [64-67]. Hydrophobic drugs areusually encapsulated in the lipid bilayers of liposomes,whereas hydrophilic drugs may either be encapsulated inside

the aqueous cores of liposomes or be located in the externalaqueous phase.

A liposomal hydrogel system consisting of a PEG--gelatinhydrogel loaded with liposomes containing the antibioticciprofloxacin was developed in order to reduce bacterial adhe-sion to silicone catheter material. Liposomal hydrogel-coatedcatheters were shown to have an antimicrobial efficacy againstPseudomonas aeruginosa [92]. Another study demonstrated acontrolled release of liposomes loaded with calcein fluores-cence dye or calcein labeled with rhodamine from gelatincarboxymethyl cellulose films. The release rate of the loadedliposomes depended mainly on the amount of liposomesentrapped inside the films, the swelling degree and thenetwork density of the film, and the glutaraldehyde crosslink-ing degree [93]. A successive release of sodium periodate(oxidizing reagent) from thermal liposomes entrapped insidea stimuli-responsive gelatinous derivative hydrogel was alsodemonstrated [94]. Embedding liposomal drug deliverysystems into a polymer-based system improves the liposomestability, viscosity, half-life of the loaded drug and the embed-ded liposome. It also allows a sustained and efficient drugrelease over prolonged periods of time [69].

5. Gelatin-based fibers

Polymer fibers can be used for various biomedical applicationssuch as tissue-engineered matrices and wound-healingpatches, due to their morphological similarity to the structureof the native extracellular matrix [95,96]. In the past five deca-des, an enormous number of studies on gelatin films havebeen published [61]. Lin and Tsai developed an ultravioletcrosslinked mixture of gelatin and phenyl azide-conjugatedpoly (acrylic acids) electrospun fibers for tissue engineeringapplications. They also demonstrated that these fibers can beincorporated with bioactive substance, such as hydroxyapatitenanoparticles for enhancing osteoconductivity, which possessa great potential in bone tissue engineering [97]. The produc-tion of polymer fibers can be carried out by several methods.Large diameter fibers are usually produced by melt spin-ning [98], wet spinning [99,100], gel spinning [100-102] or dryspinning [103], whereas fabrication of nanofibers is usuallyperformed by electrospinning [104,105], centrifugal [105,106]

and solution/melt blow spinning [105,107].The development of polymer-based nanofibers using elec-

trospinning has attracted much attention in biomedical fieldsduring the past years. The fibers produced via electrospinningform a porous network with a very high surface area-to-volume ratio, high porosity and controllable pore size. Asa drug carrier, a high surface-to-volume ratio would acceleratethe solubility of the drug in the aqueous solution and enhancethe efficiency of the drug. Many parameters that can becontrolled during the procedure such as solution properties,temperature and humidity can influence the morphology ofnanofibers, which affects the release rate of the drug [108].For example, a poly (D, L-lactide-co-glycolide) (PLGA) and

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gelatin mixture was fabricated via the electrospinning tech-nique to produce nanofiber scaffolds which were loadedwith fenbufen, a NSAID. The results showed that increasedgelatin contents enhanced the hydrophilic nature of PLGA/gelatin scaffolds which increased the fenbufen release rate.As was seen in other researches, the addition of a crosslinkeragent (glutaraldehyde vapor) reduced the drug release rate [41].

The main problem with the topical application of antifun-gal agents is their uncontrolled release rate which requiresreapplication to achieve a local therapeutic concentration.Gelatin-based fibers were therefore loaded with different anti-fungal agents. The in vitro results showed that incorporationof polyene antifungals resulted in the inhibition of the growthof yeasts and filamentous fungal pathogens. It was also foundthat polyene antifungals had strong interactions with thegelatin matrix which led to a reduction in the hemolyticactivity of polyenes, making them noncytotoxic to primaryhuman corneal and sclera fibroblasts. This system mayprovide new opportunities for management of superficialskin infections [109].

Another research studied the possible potential of genipincrosslinked gelatin fibers loaded with human VEGF as asystem for inducing early angiogenesis. The studies demon-strated that the VEGF-loaded gelatin fibers induced cellviability, endothelial differentiation, chemoattractive proper-ties of hMSCs and induced an angiogenic potential in stimu-lating new vessel formation. These results may suggest a greatpotential for stimulating and inducing angiogenesis in tissueengineering applications and for improving the clinicaloutcome of implanted tissue-engineered scaffolds [110].

Clearly, a wide variety of drugs can be delivered usinggelatin particles and fibers via several routes (Figure 1).

6. Gelatin-based hydrogels and bioadhesives

Hydrogels have been of great interest to biomaterial scientistsfor many years. One of the most interesting properties ofthese polymers is the distension of polymeric chains aftercontact with a solvent (polymer swelling) [111]. Hydrogelsare considered biocompatible and their structure is similarto the macromolecular-based components in the body. Theywere therefore studied as scaffolds for various applications intissue engineering, wound dressing as well as drug deliverycarriers [112,113].

6.1 HydrogelsHydrogels are semisolid forms of hydrophilic polymers thatcan swell in water and hold a large amount of water whilemaintaining their structure [114]. They are usually crosslinkedto allow control over the swelling rate and are used in long-term applications [115,116]. This crosslinking can be carriedout by covalent bonds, hydrogen bonding, van der Waalsinteractions or physical interactions [117].

Hydrogels for tissue engineering scaffolds usually containlarge pores to accommodate living cells, or may dissolve or

degrade while releasing growth factors and as a result create

pores into which living cells may penetrate and prolifer-

ate [118]. An injectable methacrylated gelatin hydrogel was

developed, which is capable of rapid gelation via visible light

activated crosslinking in air or in an aqueous solution. The

results showed that the hydrogel supported human bone

marrow-derived mesenchymal stem cell growth and

TGF-b3-induced chondrogenesis. They, thus, offer a promis-

ing scaffold for cell-based repair and resurfacing of articular

cartilage defects [119]. In another study, a wound dressing

hydrogel produced from chitosan, honey and gelatin was

developed. The results showed a powerful antibacterial

efficacy against Staphylococcus aureus and Escherichia coli andsignificantly promoted burn healing [120].

Hydrogels can be also used as delivery carriers by trapping

molecules within the gaps between the polymer crosslinks. In

the body, due to a direct contact with water, they swell and

the gaps between the polymer crosslinks increase, thus allow-

ing the drugs to diffuse into the blood stream. Hydrogels can

protect the drug from hostile environments and also control

drug release by changing the gel structure in response to envi-

ronmental stimuli [114]. Hydrogels can be made from several

synthetic and natural polymers, including PLGA, poly

(hydroxyethyl methacrylate), polyvinyl alcohol or natural

polymers such as chitosan, gelatin and alginate. Hydrogels

consisting of gelatin, varying concentrations of polyvinyl alco-

hol and the anticancer drug cisplatin were synthesized as a

slow-release drug delivery system. In vivo results showed that

hydrogels containing a low dose of cisplatin were as effective

in inhibiting tumor growth as the conventional treatment of

intraperitoneal administration of high doses of free cisplatin.

This would allow reducing the unpleasant side effects of the

drug and improving the quality life of the patients during

the treatment [121].In another study, gelatin was chemically derivatized to give

succinylated gelatin with an anionic charge in order to

optimize stromal cell-derived factor-1 (SDF-1) release from

the hydrogel. The release profile rate of SDF-1 from the

hydrogel could be controlled by changing the water content

of the hydrogel which could be modified by changing the

hydrogel preparation conditions. When the succinylated

gelatin hydrogel loaded with SDF-1 was implanted subcuta-

neously, it significantly enhanced angiogenesis and the

mRNA level of SDF-1 receptor compared to an injection of

SDF-1 solution [56].Saito and Tabata chemically introduced ethylenediamine

into the gelatin carboxyl groups in order to obtain a cationized

gelatin. The cationized gelatin was mixed with a low-molecu-

lar-weight heparin and was dehydrothermally crosslinked to cre-

ate a gelatin hydrogel-incorporating complex. The complex did

not dissolve or release heparin in a PBS solution at 37�C.When

collagenase was added, the hydrogel was enzymatically degraded

and heparin was released from it. Increasing the time of the

crosslinking process resulted in a slower degradation and release

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rate of the heparin. The gelatin hydrogel-incorporating complexshowed an antifibrotic effect when tested in a mouse model [57].

6.2 BioadhesivesNovel tissue bioadhesives based on gelatin, with alginate as apolymeric additive and crosslinked by EDC, were developedand studied by us. These formulations were loaded with anes-thetic drugs and antibiotic drugs [122,123]. The purpose of thisstudy was to develop a bioadhesive with a therapeutic effect ofreleasing drugs to the lacerated area for pain management.Gelatin and alginate were selected for this study due to theirunique properties. Gelatin polar groups, such as amine andcarboxyl groups, enable it to bind to other compounds. Gelat-in’s ability to form physically crosslinked hydrogel struc-tures [124], its natural sticky behavior in solution along withits other qualities, such as being biocompatible, biodegradableand non-immunogenic, has made it one of the most exten-sively investigated materials for tissue bioadhesives. Alginate,a natural polysaccharide, possesses a bioadhesive nature andis classified, with its carboxyl end groups, as an anionicmucoadhesive polymer [125]. Its properties of biodegradabilityunder physiological conditions, a controllable gel porosity andallowing high diffusion of macromolecules, has turned it into

a good candidate for protein delivery. It is also known to

induce cytokine production and can thus influence the heal-

ing process [126].The incorporation of bupivacaine in the gelatin-alginate

bioadhesive improved the bioadhesive’s bonding strength,

probably due to the reinforcing effect of its crystals (Figure 2).

Bupivacaine exhibited a burst release of 44 -- 74% after 6 h

with ~ 99% release during the first 3 days. It was also showed

that the EDC concentration, which controlled the swelling

ratio, had a major effect on the burst release, whereas the

effects of gelatin and alginate concentrations were less notable.

These results suggested that the bupivacaine release profile

was controlled mainly by the swelling, allowing water penetra-

tion into the hydrogel and hydrophilic group concentration of

the bioadhesive. The drug’s hydrophilic nature and the elec-

trical interactions between the polymeric components and

the drug also had some effect on the release profile. A model

describing the dependence of the drug release profile on the

bioadhesive and drug characterization is presented

in Figure 3. The obtained release profiles are beneficial for

the treatment of wounds because pain usually decreases with

the healing process.

A.

D. E.

B. C.

Figure 1. Scanning electron microscopic images showing: (A and B) gelatin particles. (A) Gyrus-patterned surface and

(B) smooth surface. Magnification: � 3000 (A), � 2000 (B). (C) Crosslinked gelatin mat with 0.1% w/v genipin, scale bar 1 µm.

(D) Electrospun fenbufen-loaded poly (D, L-lactide-co-glycolide)/gelatin (9/1) nanofibers crosslinked by glutaraldehyde vapor

for 5 h and (E) corresponding film.A and B: Adapted from [59] with permission.

C: Adapted from [110] with permission.

D and E: Adapted from Ref. [41] with permission.

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In a continuing research, N-hydroxysuccinimide was alsoadded to the crosslinking reaction of the gelatin-alginate bio-adhesive (Figure 4) in order to enable a decrease in the EDCcontent and thereby the cytotoxic effect, without decreasingthe bonding strength. Three antibiotic drugs were incorpo-rated in these formulations: clindamycin, vancomycin andofloxacin (Table 1). However, only clindamycin was foundto be inert toward the crosslinking reaction and did notdecrease the bonding strength of the bioadhesive (Figure 5).

These results can be explained by the chemical structure ofthe drugs. Ofloxacin contains carboxyl groups, vancomycincontains both amine and carboxyl groups, whereas clindamy-cin does not contain either of these groups (Table 1). Thedrugs’ primary amine and carboxyl groups can be crosslinkedwith gelatin or alginate by the EDC crosslinking reaction,reducing the amount of EDC molecules available for thecrosslinking of gelatin and alginate, and as a result decreasingthe crosslinking degree of the bioadhesive and its bondingstrength. The results also showed low cytotoxicity of the

gelatin-alginate bioadhesive toward human fibroblasts cells.The release profile of clindamycin was highly effective againsttwo relevant bacterial strains, Staphylococcus albus andS. aureus, which were eradicated within < 48 h (Figure 5).Delivering an antibiotic or anesthetic drug locally to thelaceration area using the bioadhesive could reduce the risk ofinfections or relieve the pain caused by the wound and therebyincrease the therapeutic effect of the bioadhesive itself.

7. Conclusion

Incorporating bioactive molecules into appropriate carriersoffers many advantages compared to conventional dosageforms. It can improve patient compliance and convenienceby reducing possible toxic side effects of the drug while sus-taining the effective drug level and even allowing easy deliveryof multiple growth factors which is usually a very challengingand expensive process. Gelatin has been extensively investi-gated as drug delivery carrier due to its properties and history

100

80

60

40

20

00

10

8

6

4

2

100 µm 20 µm

A.

C. D.

B.

Cu

mu

lati

ve b

up

ivac

ain

e re

leas

e [%

]

Cu

mu

lati

ve b

up

ivac

ain

e re

leas

e [%

]C

um

ula

tive

bu

piv

acai

ne

rele

ase

[%]

10

100 mg/ml gelatin

200 mg/ml gelatin

20 mg/ml aiginate

40 mg/ml aiginate

60 mg/ml aiginate

5

Time [days] Time [days]

15

100

80

60

40

20

00 105 15

Figure 2. Drug delivery results of the bioadhesives research showing the effect of the gelatin (A) and alginate

(B) concentrations on the release profile of bupivacaine from the basic adhesive formulation (200 mg/ml gelatin, 40 mg/ml

alginate, 20 mg/ml EDC) loaded with 3% w/v bupivacaine. (C and D) ESEM fractographs showing the basic formulation loaded

with 1% w/v bupivacaine.Adapted from [122] with permission.

EDC: N-ethyl-N-(3-dimethylaminopropyl) carbodiimide.

Drug delivery from gelatin-based systems

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of safe use in a wide range of medical applications. Gelatin’s

properties can be modified and adjusted to maximize drug

loading and efficiency of release for many classes of drugs.

The release profile from gelatin carriers was shown to be opti-

mized by changing the gelatin source, its molecular weight

and the degree of its crosslinking. The amount of loaded

drug and the type of interaction between the drug and the

carrier depend on the chemical structure of the drug and the

carrier and the conditions of the drug-loading procedure. Gel-

atin versatility enabled the design of different carrier systems.

Cross-linkingdensity of the

adhesive network

The bioadhesive’shydrophilic groups

concentration

Hydrop hilicity of the drug

Durg-polymerelectrical interaction

Diffusionof the drug

The swellingrate of the bioadhesive

Minoreffect

Durgreleaseprofile

Majoreffect

Figure 3. Bioadhesive research: a schematic representation of a qualitative model describing the dependence of the

drug-release profile on the characteristics of the adhesive and of the drug.Adapted from [122] with permission.

O-Iso-Acylurea

H+

R1

R2

EDC

N

N

CC OH+ +

O

H+

C C

N

+

R2

NHSHO N

O

O

NH

N-acylurea

NH2

Nucleophilic attack

CH3CH3

CH3

NH+

Cr

R1

O

O

AI

AI

AI

GelGel Gel

Gel

AI

Gel

AI

Gel

C

O C

+

+

Urea NH-R’

NH–R’

O+

OH

C

O

NH Gel

Gel

NH2–Gel

R1

R1=

R2=

R2

NH

N

C

C

OO

C OH+

O

Gel

C OH

O

AI C OH

O

O

O

C

NHs activated carboxylic acid group

N

O

O

Figure 4. Crosslinking reaction of gelatin and alginate with EDC and NHS.Adapted from [123] with permission.

Al: Alginate; EDC: N-ethyl-N-(3-dimethylaminopropyl) carbodiimide; Gel: Gelatin; NHS: N-hydroxysuccinimide;

NHS: N-hydroxysuccinimide.

M. Foox & M. Zilberman

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Gelatin microparticles and nanoparticles have been widelyused for encapsulating many bioactive molecules. Micropar-ticles have a relatively large surface area and can thereforeserve as vehicles for cell amplification and delivery ofexpanded cells or large bioactive molecules to the desiredsite. Nanoparticles have a higher intracellular uptake and arebetter suited for intravenous or drug delivery in different areasin the body. Due to their unique design, liposomes have theability to incorporate both hydrophilic and hydrophobicdrugs, protect them from degradation, target them to thedesired site and reduce the toxicity or side effects of thosemolecules. Embedding liposomes into a gelatin-based systemresulted in an improvement in their stability and viscosityand in the half-life of the loaded drug and the liposome.

As a drug carrier, gelatin fibers contain a high surface area-to-volume ratio, high porosity and controllable pore size andcan therefore accelerate the solubility of the drug in theaqueous solution and enhance the drug’s efficiency.

Gelatin hydrogels can trap molecules within the gapsbetween the polymer crosslinks. In the body, due to a directcontact with water, they swell and the gaps between the

polymer crosslinks increase, allowing the drugs to diffuseinto the blood stream. However, work is continually beingcarried out in order to improve gelatin release technology bymodification of gelatin to allow release of a wider variety ofbiomolecules from gelatin carriers for a broad range ofapplications.

8. Expert opinion

There is a growing need for controlled release of bioactivemolecules which is becoming larger due to their productionon an industrial scale. Significant efforts have therefore beenmade in order to achieve a sustained, effective and time-specific controlled release of bioactive molecules from differ-ent carriers. It is thus important to improve efficacy, maintainthe desired drug concentration in the blood for a long periodof time without reaching a toxic level or dropping below theeffective level, reduce toxicity and improve patient compli-ance and convenience.

The unique properties of gelatin and its extensive investiga-tion as a biomaterial for controlled release of different

Table 1. The chemical structure of the antibiotic drugs used in the bioadhesives research.

Antibiotic

drug

Chemical structure Functional groups that can react with the crosslinking

agent EDC (circled in red)

Clindamycin H3C

CH3

NO HO

CI

CH3

SCH3

O

OH• HCI

OH

NH

-

Ofloxacin

N

N

F

N

O O

O

OH

Carboxyl groups

Vancomycin

HOH3C

NH2H3C

CH3

CH3

H2N CH3

OO

O

OO

CI

HO

ONH

NH

NH

NH

NH

NHO

O O

OOH

O

OHOHHO

O

OCI

• HCI

O

OH

HOHO

HOHN

Carboxyl and amine groups

Adapted from [123] with permission.

EDC: N-ethyl-N-(3-dimethylaminopropyl) carbodiimide.

Drug delivery from gelatin-based systems

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bioactive molecules are described in the current review article.

Gelatin was shown to be versatile due to its intrinsic features

that enable the design of different carrier systems. The release

of inflammatory drugs, antineoplastic compounds, antibacte-

rial agents, growth factors and even nucleic acids and

hydrophobic materials were reported in the literature.

Furthermore, modification of gelatin to different types of

carriers and the addition of synthetic or natural polymers

can enable higher flexibility and diversity in terms of system

degradation and optimized and specific drug release, while

maintaining and improving the properties of the bulk mate-

rial. These modifications enabled the development of micro-

particle- or nanoparticle-based gelatin that can be injected

subcutaneously to different areas of the body. Another unique

property of gelatin-based nanoparticles loaded with drugs

is their ability to be taken up by macrophages, pass the

blood--brain barrier and release bioactive molecules in the

brain for neural regeneration applications.The main issue regarding the use of gelatin as a carrier for

drug delivery systems is its high ability to absorb water. This

high water-absorption capacity leads to a very fast release

profile and does not allow sustained and effective release of

water-soluble drugs. The water uptake can be partially

controlled by changing the gelatin source, its initial molecular

weight and the degree of its crosslinking. Advanced solutions

may be based on new methods to crosslink gelatin. Unfortu-

nately, most of the common crosslinking agents are not highly

biocompatible. There are several techniques based on modifi-

cations of gelatin, such as methacrylation or enzymes as cross-

linking agents. However, the main challenge is to develop a

good crosslinking technique that would not change the

unique and desired properties of the gelatin or decrease its

14A.

B.

12

10

8

6

4

2

0No drug Vancomycin

Antibiotic drugOfloxacin Clindamycin

10.09

7.16

*

* *

*

6.62

10.02

Bo

nd

ing

str

eng

th (

KP

a)

C.8

7

6

5

3

4

2

1

0Lo

g10

(m

icro

org

anis

ms/

ml)

0 24 48Time (h)

72

18

16

14

1210

86

4

2

0No clind 1%

Clindamycin concentration (%w/v)3% 5% 7%

10.09 10.0211.59

12.45 12.57

Bo

nd

ing

str

eng

th (

KP

a)

D.

0

8

76

5

3

4

2

1

0Lo

g10

(m

icro

org

anis

ms/

ml)

24 48Time (h)

72

Figure 5. (A and B) Bonding strength of bioadhesives showing the effect of antibiotic incorporation on the bioadhesive’s

bonding strength: (A) the effect of drug type on the bonding strength of the basic formulation (200 mg/ml gelatin, 40 mg/ml

alginate and 20 mg/ml N-ethyl-N-(3-dimethylaminopropyl) carbodiimide) loaded with %1 w/v drug. (B) The effect of

clindamycin content on the bonding strength of the basic formulation is shown. Values are expressed as means ± SD. (C and D)

Microbiological results showing the effect of antibiotic-eluting bioadhesives on bacterial inhibition. The remaining number

of Staphylococcus aureus (C) and Staphylococcus albus (D) CFU versus time when initial bacterial concentrations of 107 CFU/ml

were used is shown. The releasing samples were derived from formulations containing 200 mg/ml gelatin, 40 mg/ml alginate

and EDC (mg/ml)--NHS (mg/ml)--clindamycin (%) concentrations of ( ) 20--0--0, ( ) 10--1--0, ( ) 20--0--3, ( ) 20--0--7, and ( )

10--1--7. Bacteria in the presence of PBS only served as control ( ).Significant differences are marked with (*).

Adapted from [123] with permission.

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biocompatibility. The balance is between biocompatibilityand effectiveness of the crosslinking reaction. New crosslink-ing methods may also enable improvement of the gelatin’smechanical properties and may lower its solubility and degra-dation rate in aqueous solutions. New methods forpreparation of gelatin-natural polymer and gelatin--syntheticpolymer mixtures may enable desired water uptake and swell-ing behavior for various applications.

Another direction that should be investigated in order toincrease the diversity and efficiency of these systems is theuse of different sources of gelatin, rather than the commonuse of porcine or bovine gelatin. Gelatin from warm waterfish possesses similar characteristics to porcine gelatin andmay thus be an alternative for it. In contradistinction, cold-water fish gelatin has a lower melting temperature which canbe beneficial when low viscosity is needed, especially in appli-cations that require injection through a catheter. Theseinjectable formulations could be administered more readilyinto the body, thereby facilitating in vivo release and biologi-cal activity. An alternative gelatin source that can eliminatethe disadvantages associated with animal tissue-derived mate-rial is the development of recombinant gelatin which shouldbe studied further. This technology allows the production ofgelatin with specific properties to match a specific application.Understanding the system’s behavior, the process parametersand their effects on the mechanical and biological propertieswill enable effective and diverse advanced gelatin-basedsystems for many applications.

Gelatin can be used for drug-release application only or beused for active implants that in addition to their regular rolealso release drug molecules in a controlled desired manner.Examples of the latter systems can be wound dressings thatalso release antibiotic or analgesic drugs to the wound siteand scaffolds for various biomedical applications that alsorelease growth factors. Both scaffolds and wound dressingsare based on films or fibers, which means that these drug-eluting structures must combine desired mechanical andphysical properties with a beneficial drug-release profile.Thus, dense and porous novel gelatin-based drug-elutingstructures may make a significant contribution to the newemerging field of active implants. Not only gelatin films andfibers are relevant to active implants. Gelatin hydrogels ormicroparticles/nanoparticles can be also used to fill the spacesin the pores of porous scaffolds designed for tissue engineer-ing. In addition, drug-loaded gelatin and mixtures of gelatinformulations with other natural or synthetic polymers canbe used to coat various implants and thus convert them intodrug-eluting implants. These new directions will require thedevelopment of novel methods for processing drug-loadedgelatin formulations.

Another interesting area is the combination of tissue bioad-hesives with controlled drug release for pain management and

wound healing. Gelatin’s ability to form physically cross-linked hydrogel structures, its natural sticky behavior in solu-tion, along with its other qualities such as beingbiocompatible, biodegradable and non-immunogenic, hasturned it into one of the most extensively investigated materi-als for tissue bioadhesives. Novel gelatin-based bioadhesivesystems with drug delivery were described in the current arti-cle and will be studied by us also in animal models.

The demand for gelatin in many applications has increasedover the years. We believe that this tendency will continue inboth the pharmaceutical and the medical fields. The next levelof research in this field should focus on in vivo models whichwill be followed by clinical trials. The animal studies relatedto the various drug-loaded gelatin systems will enable elucida-tion of the performance of gelatin systems in the fields ofregenerative medicine, neurological rehabilitation and softtissue restoration.

Overall, the search for an ideal drug delivery carrier basedon gelatin continues. For the time being, the modificationof gelatin and its combinations with other biomaterialsdemonstrate the flexibility of these systems and ensure theircontinued role as a carrier in the field of drug delivery andother areas such as tissue engineering and wound healing.Each type of gelatin carrier should be further optimized to aspecific field that it is most suitable. For example, gelatinmicroparticles have an advantage as vehicles for cell amplifica-tion and delivery of large bioactive molecules, whereas gelatinnanoparticles have higher intracellular uptake and are bettersuited for drug delivery to the brain, which is a verydemanded and important field. Gelatin fibers, as well as gela-tin hydrogels, contain a high surface area-to-volume ratio andhigh porosity and can therefore combined drug delivery withtissue engineering or wound healing systems. The future ofdrug delivery systems based on gelatin raises challenges offinding the ideal carrier systems which enable a specific,sustained, targeted and controlled release in direct responseto local microenvironment demands in the body.

Acknowledgments

The authors are grateful to the Office of the Chief Scientist inthe Israel Ministry of Industry, Trade and Labor, for support-ing research, which is briefly described in this article.

Declaration of interest

The authors have no relevant affiliations or financial involve-ment with any organization or entity with a financial interestin or financial conflict with the subject matter or materialsdiscussed in the manuscript. This includes employment,consultancies, honoraria, stock ownership or options, experttestimony, grants or patents, received or pending, or royalties.

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BibliographyPapers of special note have been highlighted as

either of interest (�) or of considerable interest(��) to readers.

1. Burke CJ, Hsu TA, Volkin DB.

Formulation, stability, and delivery of

live attenuated vaccines for human use.

Crit Rev Ther Drug Carrier Syst

1999;16:1-83

2. Karim AA, Bhat R. Fish gelatin:

properties, challenges, and prospects as

an alternative to mammalian gelatins.

Food Hydrocoll 2009;23:563-76

. A review focusing on the advantages

and challenges involved in the

production and applications of fish

gelatin as alternative to

mammalian gelatins.

3. Pollack SV. Silicone, fibrel, and collagen

implantation for facial lines and wrinkles.

J Dermatol Surg Oncol 1990;16:957-61

4. Rao KP. Recent developments of

collagenbased materials for medical

applications and drug delivery systems.

J Biomater Sci Polym Ed 1995;7:623-45

5. Saddler JM, Horsey PJ. The new

generation gelatins. A review of their

history, manufacture and properties.

Anesthesia 1987;42:998-1004

6. GMIA. Gelatin handbook. Gelatin

Manufact. Inst. Am., New York; [online]

2012. Available from: http://www.

gelatin-gmia.com/html/qanda.html

[Retrieved 22 September 2012]

7. GME. Gelatin Manufacturers of Europe.

2008. Available from: http://www.

gelatine.org/en/gelatine/overview/127.htm

[Accessed 15 March 2008]

8. Asghar A, Henrickson RL. Chemical,

biochemical, functional, and nutritional

characteristics of collagen in food

systems. Adv Food Res 1982;28:231-372

9. Farrugia CA, Farrugia IV, Groves MJ.

Comparison of the molecular weight

distribution of gelatin fractions by size-

exclusion chromatography and light

scattering. Pharm Pharmacol Commun

1998;4:559-62

10. Courts A. The N-terminal amino acid

residues of gelatin. 2. Thermal

degradation. Biochem J 1954;58:74

11. Wilesmith JW, Ryan JBM, Atkinson MJ.

Bovine spongiform encephalopathy:

epidemiological studies on the origin.

Vet Rec 1991;128:199-203

12. Schrieber R, Gareis H. Gelatine

handbook. Wiley-VCH GmbH & Co;

Weinhem: 2007

13. Aas K. Studies of hypersensitivity to fish.

A clinical study. Int Arch Allergy

Appl Immunol 1966;29:346

14. Sakaguch M, Toda M, Ebihara T, et al.

IgE antibody to fish gelatin (type I

collagen) in patients with fish allergy.

J Allergy Clin Immunol

2000;106:579-84

15. Olsen D, Yang C, Bodo M, et al.

Recombinant collagen and gelatin for

drug delivery. Adv Drug Deliv Rev

2003;55:1547-67

. A review describing tools to produce

recombinant collagen and gelatin for

biomedical applications.

16. Bigi A, Cojazzi G, Panzavolta S, et al.

Mechanical and thermal properties of

gelatin films at different degrees of

glutaraldehyde crosslinking. Biomaterials

2001;22:763-8

17. Vandelli MA, Romagnoli M, Monti A,

et al. Microwave-treated gelatin

microspheres as drug delivery system.

J Control Release 2004;96:67-84

18. Welz MM, Ofner CM. Examination of

self-cross-linked gelatin as a hydrogel for

controlled release. J Pharm Sci

1992;81:85-90

19. Digenis GA, Gold TB, Shah VP.

Cross-linking of gelatin capsules and its

relevance to their in vitro-in vivo

performance. J Pharm Sci

1994;83:915-21

20. Raymond G, Degennaro M, Mikeal R.

Preparation of gelatin: phenytoin sodium

microsphers: an in vitro and in vivo

evaluation. Drug Dev Ind Pharm

1990;16:1025-51

21. Vandelli MA, Rivasi F, Guerra P, et al.

Gelatin microspheres cross-linked with

D, L-glyceraldehyde as a potential drug

delivery system: preparation,

characterisation, in vitro and in vivo

studies. Int J Pharm 2001;215:175-84

22. Sung HW, Huang DM, Chang WH,

et al. Gelatin-derived bioadhesives for

closing skin wounds: an in vivo study.

J Biomater Sci Polym Ed

1999;10:751-71

23. Tomihata K, Ikada Y. Cross-linking of

gelatin with carbodiimides. Tissue Eng

1996;2:307-13

24. Hoare TR, Kohane DS. Hydrogels in

drug delivery: progress and challenges.

Polymer (Guildf) 2008;49:1993-2007

. A review discussing progress and

challenges regarding effectively drug

delivery using hydrogel-based system.

25. Kuijpers AJ, Engbers GH, Krijgsveld J,

et al. Cross-linking and characterisation

of gelatin matrices for biomedical

applications. J Biomater Sci Polym Ed

2000;11:225-43

26. Tomihata K, Burczak K, Shiraki K,

Ikada Y. Cross-linking and

biodegradation of native and denatured

collagen. Polym Biol

Biomed Significance 1994;540:275-86

27. Petite H, Frei V, Huc A, Herbage D.

Use of diphenylphosphorylazide for

cross-linking collagen-based biomaterials.

J Biomed Mater Res 1994;28:159-65

28. Khor E. Methods for the treatment of

collagenous tissues for bioprostheses.

Biomaterials 1997;18:95-105

29. Uhrich KE, Cannizzaro SM, Langer RS,

Shakesheff KM. Polymeric systems for

controlled drug release. Chem Rev

1999;99:3181-98

30. Olde Damink LHH, Dijkstra PJ,

Van Luyn MJA, et al. Cross-linking of

dermal sheep collagen using a water-

soluble carbodiimide. Biomaterials

1996;17:765-73

31. Lee JM, Edwards HHL, Pereira CA,

Samii SI. Crosslinking of tissue-derived

biomaterials in 1-ethyl-3-(3-

dimethylaminopropyl)-carbodiimide

(EDC). J Mater Sci 1996;7:531-41

32. Chiono V, Pulieri E, Vozzi G, et al.

Genipin-cross-linked chitosan/gelatin

blends for biomedical applications.

J Mater Sci 2008;19:889-98

33. Sung HW, Huang DM. Chang,

WH, et al. Evaluation of gelatin hydrogel

cross-linked with various crosslinking

agents as bioadhesives: in vitro study.

J Biomed Mater Res 1999;46:520-30

34. Sung HW, Huang RN, Huang LL,

Tsai CC. In vitro evaluation of

cytotoxicity of a naturally occurring

cross-linking reagent for biological tissue

fixation. J Biomater Sci Polym Ed

1999;10:63-78

35. Tsai CC, Huang RN, Sung HW,

Liang HC. In vitro evaluation of the

genotoxicity of a naturally occurring

crosslinking agent (genipin) for biologic

M. Foox & M. Zilberman

1560 Expert Opin. Drug Deliv. (2015) 12(9)

Dow

nloa

ded

by [

Tel

Avi

v U

nive

rsity

] at

03:

47 0

3 M

ay 2

016

tissue fixation. J Biomed Mater Res

2000;52:58-65

36. Esposito E, Cortesi R, Nastruzzi C.

Gelatin microspheres: influence of

preparation parameters and thermal

treatment on chemico-physical and

biopharmaceutical properties.

Biomaterials 1996;17:2009-20

37. Di Silvio L, Gurav N, Kayser MV, et al.

Biodegradable microspheres: a new

delivery system for growth hormone.

Biomaterials 1994;15:931-6

38. Liang HC, Chang WH, Liang HF, et al.

Crosslinking structures of gelatin

hydrogels cross-linked with genipin or a

water-soluble carbodiimide.

J Appl Polym Sci 2004;91:4017-26

39. Young S, Wong M, Tabata Y,

Mikos AG. Gelatin as a delivery vehicle

for the controlled release of bioactive

molecules. J Control Release

2005;109:256-74

.. A review describing gelatin as a carrier

matrix for controlled release of

bioactive molecules for several

applications.

40. Knop K, Hoogenboom R, Fischer D,

Schubert US. Poly (ethylene glycol) in

drug delivery: pros and cons as well as

potential alternatives. Angew Chem

Int Ed 2010;49:6288-308

41. Meng ZX, Xu XX, Zheng W, et al.

Preparation and characterization of

electrospun PLGA/gelatin nanofibers as a

potential drug delivery system.

Colloids Surf B Biointerfaces

2011;84:97-102

42. Lee EJ, Khan SA, Park JK, Lim KH.

Studies on the characteristics of drug-

loaded gelatin nanoparticles prepared by

nanoprecipitation.

Bioprocess Biosyst Eng 2012;35:297-307

43. Rajan M, Raj V. Formation and

characterization of

chitosan-polylacticacid-polyethylene

glycol-gelatin nanoparticles: a novel

biosystem for controlled drug delivery.

Carbohydr Polym 2013;98:951-8

44. Kumar R, Nagarwal RC, Dhanawat M,

Pandit JK. In-vitro and in-vivo study of

indomethacin loaded gelatin

nanoparticles. J Biomed Nanotechnol

2011;7:325-33

45. Narayanan D, Koyakutty M, Nair S,

Menon D. Poly-(ethylene glycol)

modified gelatin nanoparticles for

sustained delivery of the anti-

inflammatory drug Ibuprofen-Sodium:

an in vitro and in vivo analysis.

Nanomedicine 2013;9:818-28

46. Madan J, Pandey RS, Jain UK, et al.

Sterically stabilized gelatin

microassemblies of noscapine enhance

cytotoxicity, apoptosis and drug delivery

in lung cancer cells. Colloids Surf

B Biointerfaces 2013;107:235-44

47. Lee SJ, Yhee JY, Kim SH, et al.

Biocompatible gelatin nanoparticles for

tumor-targeted delivery of polymerized

siRNA in tumor-bearing mice.

J Control Release 2013;172:358-66

48. Li WM, Chen SY, Liu DM. In situ

doxorubicin--CaP shell formation on

amphiphilic gelatin--iron oxide core as a

multifunctional drug delivery system with

improved cytocompatibility, pH-

responsive drug release and MR imaging.

Acta Biomater 2013;9:5360-8

49. Wang J, Wu W, Zhang Y, et al. The

combined effects of size and surface

chemistry on the accumulation of

boronic acid-rich protein nanoparticles in

tumors. Biomaterials 2014;35:866-78

50. Bonner DK, Zhao X, Buss H, et al.

Crosslinked linear polyethylenimine

enhances delivery of DNA to the

cytoplasm. J Control Release

2013;167:101-7

51. Santoro M, Tatara AM, Mikos AG.

Gelatin carriers for drug and cell delivery

in tissue engineering. J Control Release

2014;190:210-18

.. A review highlighting some of the

latest studies performed on gelatin

modifications for immune system

evasion, drug stabilization and targeted

delivery, as well as gelatin composite

systems based on synthetic or

natural polymers.

52. Tabata Y, Ikada Y. Protein release from

gelatin matrices. Adv Drug Deliv Rev

1998;31:287-301

. A review describing protein release

from gelatin matrices and focusing on

sustained release of growth factor from

the gelatin hydrogels.

53. Lu Z, Yeh TK, Tsai M, et al.

Paclitaxel-loaded gelatin nanoparticles for

intravesical bladder cancer therapy.

Clin Cancer Res 2004;10:7677-84

54. Wang H, Zou Q, Boerman OC, et al.

Combined delivery of BMP-2 and bFGF

from nanostructured colloidal gelatin gels

and its effect on bone regeneration in

vivo. J Control Release 2013;166:172-81

55. Kim YH, Furuya H, Tabata Y.

Enhancement of bone regeneration by

dual release of a macrophage recruitment

agent and platelet-rich plasma from

gelatin hydrogels. Biomaterials

2014;35:214-24

56. Kimura Y, Tabata Y. Controlled release

of stromal-cell-derived factor-1 from

gelatin hydrogels enhances angiogenesis.

J Biomater Sci Polym Ed 2010;21:37-51

57. Saito T, Tabata Y. Preparation of gelatin

hydrogels incorporating

low-molecular-weight heparin for anti-

fibrotic therapy. Acta Biomater

2012;8:646-52

58. Tan H, Huang D, Lao L, Gao C. RGD

modified PLGA/gelatin microspheres as

microcarriers for chondrocyte delivery.

J Biomed Mater Res B Appl Biomater

2009;91:228-38

59. Huang S, Wang Y, Liang T, et al.

Fabrication and characterization of a

novel microparticle with gyrus-patterned

surface and growth factor delivery for

cartilage tissue engineering. Mater Sci

Eng C 2009;29:1351-6

60. Pinto Reis C, Neufeld RJ, Ribeiro AJ,

Veiga F. Nanoencapsulation I. Methods

for preparation of drug-loaded polymeric

nanoparticles. Nanomedicine

2006;2:8-21

61. Hans ML, Lowman AM. Biodegradable

nanoparticles for drug delivery and

targeting. Curr Opin Solid State

Mater Sci 2002;6:319-27

62. Kreuter J. Nanoparticulate systems for

brain delivery of drugs. Adv Drug

Deliv Rev 2001;47:65-81

63. Knight CG. Liposomes, from physical

structure to therapeutic applications.

Elsevier; Amsterdam: 1981

64. Mastrobattista E, Koning GA,

van Bloois L, et al. Functional

characterization of an endosome-

disruptive peptide and its application in

cytosolic delivery of immunoliposome-

entrapped proteins. J Biol Chem

2002;277:27135-43

65. Schnyder A, Huwyler J. Drug transport

to brain with targeted liposomes.

NeuroRx 2005;2:99-107

66. Immordino ML, Dosio F, Cattel L.

Stealth liposomes: review of the basic

science, rationale, and clinical

applications, existing and potential.

Int J Nanomedicine 2006;1:297

Drug delivery from gelatin-based systems

Expert Opin. Drug Deliv. (2015) 12(9) 1561

Dow

nloa

ded

by [

Tel

Avi

v U

nive

rsity

] at

03:

47 0

3 M

ay 2

016

67. Chen C, Han D, Cai C, Tang X. An

overview of liposome lyophilization and

its future potential. J Control Release

2010;142:299-311

68. Soppimath KS, Aminabhavi TM,

Kulkarni AR, Rudzinski WE.

Biodegradable polymeric nanoparticles as

drug delivery devices. J Control Release

2001;70:1-20

. A review describing methods of

preparation, drug loading and drug

release of biodegradable polymeric

nanoparticles systems.

69. Mufamadi MS, Pillay V, Choonara YE,

et al. A review on composite liposomal

technologies for specialized drug delivery.

J Drug Deliv 2011;2011:939851

70. Kaur A, Jain S, Tiwary A.

Mannan-coated gelatin nanoparticles for

sustained and targeted delivery of

didanosine: in vitro and in vivo

evaluation. Acta Pharm 2008;58:61-74

71. Shenoy DB, Amiji MM. Poly (ethylene

oxide)-modified poly (epsilon-

caprolactone) nanoparticles for targeted

delivery of tamoxifen in breast cancer.

Int J Pharm 2005;293:261-70

72. Kumari A, Yadav SK, Yadav SC.

Biodegradable polymeric nanoparticles

based drug delivery systems.

Colloids Surf B Biointerfaces

2010;75:1-18

.. A review highlighting the use of

biodegradable nanoparticles such as

poly (D, L-lactide-co-glycolide),

polylactic acid, chitosan, gelatin,

polycaprolactone and

poly-alkyl-cyanoacrylates as drug

delivery systems.

73. Li JK, Wang N, Wu XS. Gelatin

nanoencapsulation of protein/peptide

drugs using an emulsifier-free emulsion

method. J Microencapsul

1998;15:163-72

74. Yarchoan R, Mitsuya H, Thomas RV,

et al. In vivo activity against HIV and

favorable toxicity profile of 2’,

3’-dideoxyinosine. Science

1989;245:412-15

75. Bajpai AK, Choubey J. Design of gelatin

nanoparticles as swelling controlled

delivery system for chloroquine

phosphate. J Mater Sci 2006;17:345-58

76. Lee ES, Gao Z, Bae YH. Recent progress

in tumor pH targeting nanotechnology.

J Control Release 2008;132:164-70

77. Zillies J, Coester C. Evaluating gelatin

based nanoparticles as a carrier system for

double stranded oligonucleotides.

J Pharm Pharm Sci 2005;7:17-21

78. Nguyen AH, McKinney J, Miller T,

et al. Gelatin methacrylate microspheres

for growth factor controlled release.

Acta Biomater 2015;13:101-10

79. Forni F, Vandelli MA, Cameroni R.

Influence of drug loading level on drug

release and dynamic swelling of cross-

linked gelatin microspheres Journal of

microencapsulation. 1992;9:29-39

80. Ozkizilcik A, Tuzlakoglu K. A new

method for the production of gelatin

microparticles for controlled protein

release from porous polymeric scaffolds.

J Tissue Eng Regen Med 2014;8:242-7

81. Kempen DH, Lu L, Hefferan TE, et al.

Retention of in vitro and in vivo BMP-2

bioactivities in sustained delivery vehicles

for bone tissue engineering. Biomaterials

2008;29:3245-52

82. Franssen O, Hennink WE. A novel

preparation method for polymeric

microparticles without the use of organic

solvents. Int J Pharm 1998;168:1-7

83. Dinarvand R, Rahmani E, Farbod E.

Gelatin microspheres for the controlled

release of all-trans-retinoic acid topical

formulation and drug delivery evaluation.

Iranian J Pharm Res 2003;1:47-50

84. Bruschi ML, Cardoso MLC,

Lucchesi MB, Gremiao MPD. Gelatin

microparticles containing propolis

obtained by spray-drying technique:

preparation and characterization.

Int J Pharm 2003;264:45-55

85. Holland TA, Tabata Y, Mikos AG. Dual

growth factor delivery from degradable

oligo (poly (ethylene glycol) fumarate)

hydrogel scaffolds for cartilage tissue

engineering. Journal of Control Release

2005;101:111-25

86. Hoch E, Schuh C, Hirth T, et al. Stiff

gelatin hydrogels can be photo-

chemically synthesized from low viscous

gelatin solutions using molecularly

functionalized gelatin with a high degree

of methacrylation. J Mater Sci

2012;23:2607-17

87. Solorio LD, Vieregge EL, Dhami CD,

et al. Engineered cartilage via self-

assembled hMSC sheets with

incorporated biodegradable gelatin

microspheres releasing transforming

growth factor-beta1. J Control Release

2012;158:224-32

88. Patel ZS, Ueda H, Yamamoto M, et al.

In vitro and in vivo release of vascular

endothelial growth factor from gelatin

microparticles and biodegradable

composite scaffolds. Pharm Res

2008;25:2370-8

89. Patel ZS, Yamamoto M, Ueda H, et al.

Biodegradable gelatin microparticles as

delivery systems for the controlled release

of bone morphogenetic protein-2.

Acta Biomater 2008;4:1126-38

90. Manca ML, Cassano R, Valenti D, et al.

Isoniazid-gelatin conjugate microparticles

containing rifampicin for the treatment

of tuberculosis. J Pharm Pharmacol

2013;65:1302-11

91. Bangham AD, Hill MW, Miller NGA.

Preparation and use of liposomes as

models of biological membranes.

Springer; US: 1974. p. 1-68

92. DiTizio V, Ferguson GW,

Mittelman MW, et al. A liposomal

hydrogel for the prevention of bacterial

adhesion to catheters. Biomaterials

1998;19:1877-84

93. Peptu C, Popa M, Antimisiaris SG.

Release of liposome-encapsulated calcein

from liposome entrapping gelatin-

carboxymethylcellulose films:

a presentation of different possibilities.

J Nanosci Nanotechnol 2008;8:2249-58

94. Burke SA, Ritter-Jones M, Lee BP,

Messersmith PB. Thermal gelation and

tissue adhesion of biomimetic hydrogels.

Biomed Mater 2007;2:203

95. Martins A, Ara�ujo JV, Reis RL,

Neves NM. Electrospun nanostructured

scaffolds for tissue engineering

applications. Nanomedicine

2007;2:929-42

96. Li W J, Laurencin CT, Caterson EJ,

et al. Electrospun nanofibrous structure:

a novel scaffold for tissue engineering.

J Biomed Mater Res 2002;60:613-21

97. Lin WH, Tsai WB. In situ UV-

crosslinking gelatin electrospun fibers for

tissue engineering applications.

Biofabrication 2013;5:035008

98. Grigsby WJ, Kadla JF. Evaluating poly

(lactic acid) fiber reinforcement with

modified tannins. Macromol Mater Eng

2014;299:368-78

99. Ingildeev D, Hermanutz F, Bredereck K,

Effenberger F. Novel cellulose/polymer

M. Foox & M. Zilberman

1562 Expert Opin. Drug Deliv. (2015) 12(9)

Dow

nloa

ded

by [

Tel

Avi

v U

nive

rsity

] at

03:

47 0

3 M

ay 2

016

blend fibers obtained using ionic liquids.

Macromol Mater Eng 2012;297:585-94

100. Kotek R, Jung D, Tonelli AE,

Vasanthan N. Novel methods for

obtaining high modulus aliphatic

polyamide fibers. J Macromol Sci Part C

Polym Rev 2005;45:201-30

101. Fukae R, Maekawa A, Sangen O.

Gel-spinning and drawing of gelatin.

Polymer (Guildf) 2005;46:11193-4

102. Midorikawa T, Lawal OS, Sasaki Y,

Fukae R. Structure and physical

properties of gelatin fibers prepared by

gel-spinning in ethylene glycol.

J Appl Polym Sci 2012;125:E332-8

103. Stoessel PR, Raso RA, Kaufmann T,

et al. Fibers mechanically similar to sheep

wool obtained by wet spinning of gelatin

and optional plasticizers.

Macromol Mater Eng 2014;300:234-41

104. Zeugolis DI, Khew ST, Yew ES, et al.

Electro-spinning of pure collagen nano-

fibres--Just an expensive way to make

gelatin? Biomaterials 2008;29:2293-305

105. Persano L, Camposeo A, Tekmen C,

Pisignano D. Industrial upscaling of

electrospinning and applications of

polymer nanofibers: a review.

Macromol Mater Eng 2013;298:504-20

106. Valipouri A, Ravandi SH, Pishevar AR.

A novel method for manufacturing

nanofibers. Fibers Polym 2013;14:941-9

107. Mahalingam S, Edirisinghe M. Forming

of polymer nanofibers by a pressurised

gyration process. Macromol Rapid

Commun 2013;34:1134-9

108. Chakraborty S, Liao I, Adler A,

Leong KW. Electrohydrodynamics:

a facile technique to fabricate drug

delivery systems. Adv Drug Deliv Rev

2009;61:1043-54

109. Lakshminarayanan R, Sridhar R, Loh XJ,

et al. Interaction of gelatin with polyenes

modulates antifungal activity and

biocompatibility of electrospun fiber

mats. Int J Nanomedicine 2014;9:2439

110. Del Gaudio C, Baiguera S, Boieri M,

et al. Induction of angiogenesis using

VEGF releasing genipin-cross-linked

electrospun gelatin mats. Biomaterials

2013;34:7754-65

111. Conte U, Colombo P, Gazzaniga A,

et al. Swelling-activated drug delivery

systems. Biomaterials 1988;9:489-93

112. Jhon MS, Andrade JD. Water and

hydrogels. J Biomed Mater Res

1973;7:509-22

113. Jen AC, Wake MC, Mikos AG. Review:

Hydrogels for cell immobilization.

Biotechnol Bioeng 1996;50:357-64

114. Qiu Y, Park K. Environment-sensitive

hydrogels for drug delivery. Adv Drug

Deliv Rev 2001;53:321-39

. A review describing the potential of

environmentally sensitive hydrogels in

various applications such as

drug delivery.

115. Kim S, Park K. Tailor-made hydrogels

for tumor delivery. In: Kratz F, Senter P,

Steinhagen H, editors, Drug delivery in

oncology: from basic research to cancer

therapy. Wiley-VCH Verlag GmbH &

Co. KGaA, Weinheim, Germany;.

2011. p. 1071-97

116. Wolinsky JB, Colson YL, Grinstaff MW.

Local drug delivery strategies for cancer

treatment: gels, nanoparticles, polymeric

films, rods, and wafers. J Control Release

2012;159:14-26

117. Kamath K, Park K. Biodegradable

hydrogels in drug delivery. Adv Drug

Deliv Rev 1993;11:59-84

118. Hoffman AS. Hydrogels for biomedical

applications. Adv Drug Deliv Rev

2002;54:3-12

. A review describing the composition,

synthesis and properties of hydrogels

in biomedical applications such as

drug and cell carriers and

tissue engineering.

119. Lin H, Cheng AWM, Alexander PG,

et al. Cartilage tissue engineering

application of injectable gelatin hydrogel

with in situ visible-light-activated

gelation capability in both air and

aqueous solution. Tissue Eng Part A

2014;20:2402-11

120. Wang T, Zhu XK, Xue XT, Wu DY.

Hydrogel sheets of chitosan, honey and

gelatin as burn wound dressings.

Carbohydr Polym 2012;88:75-83

121. Oun R, Plumb JA, Wheate NJ.

A cisplatin slow-release hydrogel drug

delivery system based on a formulation

of the macrocycle cucurbit [7] uril,

gelatin and polyvinyl alcohol.

J Inorg Biochem 2014;134:100-5

122. Cohen B, Shefy-Peleg A, Zilberman M.

Novel gelatin/alginate soft tissue

adhesives loaded with drugs for pain

management: structure and properties.

J Biomater Sci Polym Ed

2014;25:224-40

123. Foox M, Raz-Pasteur A, Berdicevsky I,

et al. In vitro microbial inhibition,

bonding strength, and cellular response

to novel gelatin--alginate antibiotic-

releasing soft tissue adhesives.

Polym Adv Technol 2014;25:516-24

124. Bae SK, Sung TH, Kim JD. A soft-tissue

gelatin bioadhesive reinforced with a

proteinoid. J Adhes Sci Technol

2002;16:361-72

125. Gombotz WR, Wee SF. Protein release

from alginate matrices. Adv Drug

Deliv Rev 2012;64:194-205

126. Otterlei M, Sundan A, Skjak-Bræk G,

et al. Similar mechanisms of action of

defined polysaccharides and

lipopolysaccharides: characterization of

binding and tumor necrosis factor alpha

induction. Infect Immun

1993;61:1917-25

AffiliationMaytal Foox1 & Meital Zilberman†2 PhD†Author for correspondence1Tel-Aviv University, Department of Biomedical

Engineering, Faculty of Engineering,

Tel-Aviv 69978, Israel2Professor,

Tel-Aviv University, Department of Biomedical

Engineering, Faculty of Engineering,

Tel-Aviv 69978, Israel

Tel: +972 3 6405842;

Fax: +972 3 6407939;

E-mail: meitalz@eng.tau.ac.il

Drug delivery from gelatin-based systems

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