The use of skin substitute in the treatment of burns and Bone regeneration and

bioengineering.

Dr. Munira Shahbuddin

• The idea of covering the exposed burnt tissue to prevent and control fluid and heat loss.

• Treatment of burn:1. Mimicking the normal wound healing

environment using dressing2. Replicating the chemical environment of the

wound using chemokines and growth factors3. Replacing the damaged skin, utilizing skin

substitutes.

Autograph

• The use of split thickness skin graft is to transfer residual keratinocytes stem cells that aid with regeneration and faster wound epithelization.

• This is not ideal and may lead to the formation of keloid.

• Result obtained with full-thickness skin are much better aesthetically.

• The advantageous of autografts are that they are immunologically compatible with the patients.

Skin substitute

• The ideal skin substitute should be a safe, easy to apply, topical material that promotes healing and leads to good aesthetic and functional recovery.

• Should have barrier function of actual skin.• Can be derived from either naturally or

synthetically.

Examples of skin substitute

Collagen GAG scaffold for the regeneration of skin after brain tumor operation on 54 year old woman

The making of skin substitute – Tissue engineered skin

Temporary skin substitutes

1. Cadaveric skin- Can be used fresh or from a glycerol preserved

state. Both showed compatible metabolic activities.

- Glycerol dehydrates the skin and prevent oxidative and hydrolytic reaction which are detrimental to the cells.

Disadvantageous of cadaveric skins

• Low supply, substandard quality, infection and immune rejection, glycerolized cadeveric skin slows the onset of rejection by 5 weeks.

• Removal of antigenic epidermal cells is technically challenging and not successful to date.

• Although pretreated with antibiotic, certain bacteria still persist.

• Concern about virus and prion disease transmission.

Decellularized cadaveric skins.

• Eliminates any immune rejection• The method takes 4 weeks • Do not eliminate the risks of viral

transmission.

2. Amniotic membrane- The avascular nature of amnion and its thick

basement membrane containing collagen, laminin and proteinase inhibitors aid healing of burn wound.

- More successful than cadaveric skin use at preserving the excised wound bed of a burn.

- Its complex structure minimizes fluid and electrolyte loss from the wound bed underneath and maintain an aerobic environment to encourage healing.

• Disadvantageous- Risk of bacterial and virus contamination.- Not suitable for full thickness burns because it

disintegrates before entering reepithelization.- Silver ions are used with amniotic membrane

for its antimicrobial activities. But this has been found to inhibit epithelial and fibroblasts proliferation that may impair wound healing.

Xenograft

• Economically and widely available• Fresh disinfect porcine dermal grafts are used

because they similar to human cadaveric skin in the result they give to patients.

• Similar to human cadaveric, this can be decellularized to produce an acellular dermal matrix as skin substitutes.

• Concern about viral, bacterial and prion disease transmission.

Name andManufacturer or investigating group

Incorporated human cells

Primary cellular loading occur

Cell source

Scaffold source

Scaffold materials

Duration of cover

Reference

Epidermal substitute

Bioseed-SBioTissue Technologies,GmbH, Freiburg,Germany

Cultured keratinocytes (subconfluent cell sheet).

In vitro Auto Allo Fibrin sealant

Permanent (Shevchenko, James et al. 2010)

CryocealXCELLentis, Gent, Belgium merged with CellTrans Ltd, Sheffield, U.K.

Cryoreserved keratinocytes

In vitro Auto Allo Temporary (Shevchenko, James et al. 2010)

LyphodermXCELLentis, Gent, Belgium merged with CellTrans Ltd, Sheffield, U.K.

Lyophilized neonatal keratinocytes

In vitro Auto Allo Temporary (Shevchenko, James et al. 2010)

EpicelGenzyme Biosurgery,Cambridge, MA, USA.

Cultured dermal keratinocytes

In vitro Auto - - Permanent (Shevchenko, James et al. 2010)

MySkinCellTrans Ltd. Sheffield, U.K.

Cultured keratinocytes (subconfluent cell sheet).

In vitro Auto Synthetic Silicone support layer with surface coated with specific formulation.

Permanent (Shevchenko, James et al. 2010)

Commercially available or in development materials for epidermal/dermal substitute for the treatment of wound

Name andManufacturer or investigating group

Incorporated human cells

Primary cellular

loading occur

Cell source

Scaffold source

Scaffold materials Duration of cover

Reference

Dermal substitute

Collagen-GAG-Chitosan dermal matrixINSERM, U533, Universite’ Paris 7, IUH, Paris, France

Cultured dermal fibroblasts

In vitro Allo Xeno Bovine collagen 1/ Chondroitin-4/ 6-sulfate/ chitosan lyophilized dermal matrix

Temporary (Shevchenko, James et al. 2010)

Collagen-GAGFibers and Polymers Laboratory, Massachusetts Institute of Technology, Bldg. Cambridge, MA. U.S.A

- In vitro Allo Xeno Bovine collagen/ GAG

Temporary (Yannas, Lee et al. 1989; Yannas, Tzeranis et al. 2010)

Permacol™Tissue Science Laboratories Inc.Andover, MA, U.S.A

- In vitro Auto Xeno Crosslinked collagen from porcine

Temporary (MacNeil 2007)

Biodegradable polyurethaneMicrofibers, Department of Materials Science andEngineering, University of Delaware, Newark, DE, U.S.A

In vivo - Synt Biodegradable polyurethane microfibres

Permanent (Shevchenko, James et al. 2010)

Silk fibroin and alginateCollege of Veterinary Medicine andSchool of Agricultural Biotechnology,Seoul National University, Seoul,South Korea

- In vivo Xeno + Synth Silk fibroin/ Alginate blended sponge

Permanent (Shevchenko, James et al. 2010)

Name andManufacturer or investigating

group

Incorporated human

cells

Primary cellular loading occur

Cell source

Scaffold source

Scaffold materials Duration of cover

Reference

Dermal skin construct

AllodermLifeCell Corporation, Branchburg, NJ. U.S.A

- In vivo - Allo Human acellular lyophilized dermis

Temporary (Shevchenko, James et al. 2010)

SuredermHANS BIOMED Corporation, Seoul, Korea

- In vivo - Allo Human acellular dermis

Temporary (Shevchenko, James et al. 2010)

MatridermDr. Suwelack Skin and Health Care, AG, Billerbeck, Germany

- In vivo - Xeno Bovine non crosslinked lyophilized dermis, coated with α-elastin hydrolysate

Temporary (Shevchenko, James et al. 2010)

IntegraIntegra LifeSciences Corporation, Plainsboro, NJ. U.S.A.

- In vivo Synthetic+ Xeno

Silicone, collagen and glycosamino glycans

Temporary (Wolter, Noah et al. 2005)

Tegaderm – nanofibre contstructNanoscience and Nanotech Initiative, Division of Bioengineering,National University of Singapore, Singapore.

Cultured dermal fibroblasts

In vitro Allo Synthetic+ Xeno

Poly (ε-caprolactone/ gelatine nanofibrous scaffold electrospun on polyurethane dressing

Temporary (Shevchenko, James et al. 2010)

The image shows how keratinocytes are cultured from an initial skin biopsy into confluent sheet of cells.

Cells - issue

• Keratinocytes and fibroblasts are most commonly used to repopulate scaffolds intended for epidermal and dermal replacement.

• In order of living cells to be cultured, each cell type is expanded in its appropriate culture medium.

• Cytokeratin 19 (K19) has proven to be indicator of proliferative keratinocytes, expressed in stratum basale. This marker cannot be detected in skin of human individuals over 2 years of age. May be a subtype of stem cell, exclusively expressed at very young age.

• Additional with other cells like endothelial cells may improve healing by promoting vascularization.

• The use of vascular endothelial growth factor (VEGF) and fibroblast growth factor (FBF) increase angiogenesis.

Bone regeneration and Bioengineering

Bone repair – going back to the roots

Learning nature’s lesson: providing insight into bone regeneration.

Preclinical and clinical studies indicate that the use of MSC for bone reconstruction and repair is indeed feasible.MSC can be derived from various sources.Biomimetic concept: tropic and immune-modulatory effect of stem cells, scaffold resembling the natural extracellular matrix and delivered multiple growth factors: all in orchestrated fashion.

Bone remodelling after fracture.

Schematic illustration of tissue regeneration via endogenous regenerative approaches. MSC secreted growth factors can produce their effect via auticrine, telecrine and paracrine mechanisms.

• Fracture may induce mobilization of endothelial progenitor cells from the bone marrow to prepheral blood and these cells themselves can promote both neovascularization and initiate the healing process in the damaged bone.

• Peripheral blood of fracture patients expressed an increase in CD34+ and CD 133+, with high level of chemoattractant BMP and SDF-1.

• This highlight the possibility of circulating osteogenic cells related to hemapoetic stem cells and plastic adherent stem cells. (both originated from bone marrow).

Fibrodyplasia ossificants progressiva – unstoppable growth of bone.

Shown the activation of ALK2, in endothelial and chrondrocytes.

In principle, the presence of these circulating cells can hold great promise but strategies should be developed to enhance the migration of cells and promote natural endogenous repair mechanisms.

Uncontrolled bone growth: Disease??