Outline:

Introduction

What is HAp?

Chemistry of HAp

Techniques

Discussion

Future research

By: Younes Sina /The University of Tennessee/ MSE

Introduction

Due to its poor mechanical properties, HAp ceramics cannot be used for heavy load bearing applications.

Uses include bone graft substitution and coatings on metallic implants

The most important bioceramic materials for its unique bioactivity and stability

strong chemical bonds with surrounding bone

Unlike the other calcium phosphates, HAp does not break down under physiological conditions stable at physiological pH

Why HAp?

Why chemistry of HAp is important?

•The composition, physicochemical properties, crystal size, and morphology of synthetic HAp are extremely sensitive to preparative conditions

•the success and quality of orthopedic coatings is also largely dependent upon the HA powder characteristics

•For example spherical powders of narrow size distribution are favored in order to enhance excellent heat transfer characteristics to increase deposition efficiency and decrease coating porosity.

•Thermal processing is a function of Ca/P ratio

•One of the most important properties of HAp is porosity. The simplest way to generate porous scaffolds from ceramics such as HAp is to sinter particles, preferably spheres of equal size

Why chemistry of HAp is important?

Methods for producing and processing HAp powder:

microwave irradiationmechanosynthesisSol-gel Hydrothermal Solid state reaction Solid state reactionplasma technique hydrothermal hot pressing ultrasonic spray pyrolysis emulsion system

Acid-base method :

10 Ca (OH) 2+6 H3 PO 4→Ca10 (PO 4)6 (OH) 2+18 H 2O

only by- product is water

Temperature and PH in this route are very important factors for having a stable HAp

Precipitation reaction for synthesis nanostructure HAp

10CaCl2 + 6Na2PO4 + NaOH → Ca9+(x/2) (PO4)6(OH)2 + (18+x) NaCl + (1-(x/2)) CaCl2 (x=0,1,2)

Hydrothermal route

Hydrothermal process works at high temperature and high pressure

Environmentally benign

Chemical composition and stoichiometry of the material can be controlled

Needle-like particles between 20 - 40 nm in diameter and 100-160 nm in length

The treatment time had no effect on the particle morphology or size, within the reaction time range of 24-72 hrs

high degree of crystallinity

wide distribution of crystal sizes

Microwave irradiation route

Environment-friendly, non-polluting, clean and safe approach

Acceleration of chemical reaction

Denser HAp.

HAp processing at much lower temperature

Energy efficient densification

Ultrasonic irradiation Homogeneous HAp

Easier control on temperature, [Ca2+], Ca/P ratio and ultrasonic power

Sol-Gel technique

Low temperature synthesis

Ability of thin film formation

Easy control of chemical composition

Fluorinated hydroxyapatite (FHAp)

Ca10(PO4)6(OH)2-2xF2x (0 ≤ x ≤ 1)

FHAp has a better thermal and chemical stabilities than HAp

Better biological properties

Ca/P ratio at FHAp = 1.71 higher than 1.667 for HAp

i.e. Ca10 (PO4)6(OH) 0.7F1.3

goal

In developing new biomaterials for tissue replacement, the structure and properties of the tissue which is to be replaced must be taken into consideration

because, if properties of the new material are significantly different from those of the host tissue, the material under development will cause dynamic changes in the host tissue after implantation, as has been discussed in terms of Wolff’s Law,

and thus will not achieve the goals considered in the original conceptual design.

Wolff’s Low: If a stiff metal or ceramic implant is placed in the bone, the bone will be subjected to lower mechanical stresses, and consequently bone will resorb

Problem/ Solution

Nanopowders= powders with particle sizes not exceeding 100 nm

Nanopowders have a high specific surface area excess surface energy driving force of the sintering process

Obtaining ceramic with uniform structure from nanopowders is a quite difficult problem (Because of aggregation)

Average particle size (aggregates) in the powder is 1– 3μ m

HAp powder with particle sizes less than 100 nm results in the formation of 1 – 15 μm grains, depending on the sintering regime and the method used to prepare the power.

An obvious way out of the technological situation is to use surfactants, which modify the surface of particles, and to eliminate milling of the powder material,

Solution

Homogeneity

The increase in density is considered to be due to increase in the homogeneity in the matrix phase and the lower sintering temperature of HAp.

Conclusions

HAp is suitable for fabricating the artificial teeth & bone due to its excellent biocompability.

Improvement on Fracture Toughness & Young’s Modulus is needed.

Some materials were found that thay decrease the crystal’s size of HAp.

Numerous different types of biomaterials have been designed for human implants or prostheses, specifically for bone repair, however considerably less effort has been addressed to implants capable of tooth ingrowths

Research for future

A new generation of porous biomaterials similar to structure of natural bone