Garth W. Hastings

Handbook of biomaterial properties

Foreword. Introduction. Contributors. Part I: A1. Cortical bone J. Currey. A2. Cancellous bone T.M. Keaveney. A3. Dentine and enamel K.E. Healey. B1. Cartilage J.R. Parsons. B2. Fibrocartilage V.M. Gharpuray. B3. Ligament, tendon and fascia S.L.-Y. Woo, R.E. Levine. B4. Skin and muscle A.F.T. Mak, M. Zhang. B5. Brain tissues S.S. Margulies, D.F. Meaney. B6. Arteries, veins and lymphatic vessels X. Deng, R. Guidoin. B7. The intraocular lens T.V. Chirila. C1. Blood and related fluids V. Turitto, S.M. Slack. C2. The vitreous humour T.V. Chirila, Y. Hong. Part II: 1. Metallic biomaterials J. Breme, V. Biehl. 1a. Stainless steels. 1b. CoCr-based alloys. 1c. Titanium and titanium alloys. 1d. Dental restoration materials. 2. Composite materials L. Ambrosio, G. Carotenuto, L. Nicolais. 3. Thermoplastic polymers in biomedical applications S.H. Teoh, Z.G. Tang, G.W. Hastings. 4. Biomedical elastomers J.W. Boretos, J. Boretos. 5. Oxide bioceramics in medicine and dentistry J. Li, G.W. Hastings. 6. Properties of bioactive glasses and glass-ceramics L.L. Hench, T. Kokubo. 7. Wear M. LaBerge. 8. Degradation/resorption in ceramics in orthopaedics H. Oonishi, H. Oomamiuda. 9. Corrosion of metallic implants M.A. Barbosa. 10. Carbons A.D. Haubold, R.B.More, J.C. Bokros. Part III: 1. General concepts of biocompatibility D.F. Williams. 2. Soft tissue response J.M. Anderson. 3. Hard tissue response T. Albrektsson. 4. Immune response K. Merritt. 5. Cancer M. Rock. 6. Blood-material interactions S.R. Hanson. 7. Soft tissue response to silicones S.E. Gabriel. Index.

Preparation of a chitin-apatite composite by in situ precipitation onto porous chitin scaffolds.

Composites of chitin with calcium phosphate were obtained by in situ precipitation of the mineral from a supersaturated solution onto chitin scaffolds. The chitin scaffolds were obtained by freeze drying to give a highly porous structure possessing a polar surface favorable for apatite nucleation and growth. THe extent and arrangement of calcium phosphate deposits on the chitin and substituted chitin scaffolds were explored. Up to 55% by mass of calcium phosphate could be incorporated into chitin scaffolds. Deposits on the chitin surface were a continuous apatite carpet nature while deposits on carboxymethylated chitin surfaces displayed a spherical morphology. Carboxymethylation of chitin exerts an overall inhibitory effect towards calcium phosphate deposition, but it provides for site-specific nucleation of the mineral phase. In situ precipitation can be an important route in the future production of various polymer-calcium phosphate composites.

Promotion of calcification on carboxymethylchitin discs.

A series of water-insoluble carboxymethylchitin (CM-chitin) discs of varying degrees of substitution (d.s.) has been investigated for their interaction with calcium phosphate. Discs of d.s. 0.03, 0.11, 0.14 and 0.23 were prepared by casting from solutions of CM-chitin in 90% formic acid. Calcium uptake and calcium phosphate nucleation were found to increase with the degree of substitution of the CM-chitin discs. The results suggest that water-insoluble CM-chitin may be useful as a platform for in vivo calcification.

Hydroxyapatite modified chitin as potential hard tissue substitute material

Calcium hydroxyapatite (HA) powder was incorporated into chitin solutions to form an intimate mixture. Upon casting of this mixture into molds of fixed dimensions with subsequent removal of solvent, HAs containing chitin flexible plates were produced. The amount of (HA) was varied from 10 to 50% by mass of HA. The elastic modulus, yield stress, and elongation to fracture, measured at a crosshead speed of 5 mm/min, of these HAs containing chitin flexible plates were evaluated. The amount of HA in the HA incorporated chitin was found to not significantly change the elastic modulus or elongation to fracture. However, a decrease in the maximum tensile stress with an increase in the HA content was found.

The influence of anionic chitin derivatives on calcium phosphate crystallization.

The influence of two water-soluble anionic chitin derivatives, sodium carboxymethyl-chitin (CM-chitin) and phosphoryl-chitin (P-chitin) on the crystallization of calcium phosphate by seeded growth and turbidimetry were studied. The adsorption of these derivatives onto hydroxyapatite obtained at 37 degrees C, fitted the Langmuir isotherm. The affinity constant and number of adsorption sites were measured at 2.9 and 1.69 micromol m(-2) for CM-chitin and 11.85 and 4.23 micromol m(-2) for P-chitin. P-chitin exerted a potent inhibitory effect on the seeded growth of hydroxyapatite from a supersaturated solution, reducing the initial rate of crystallization by more than 90% at a solution concentration of 10(-4)M. Both chitin derivatives also retarded the rate of spontaneous calcium phosphate precipitation. The type of calcium phosphate precipitated was poorly crystallized, calcium-deficient apatite. The chitin derivatives were found to be incorporated into the precipitate and influenced both the phase and morphology of calcium phosphate formed.

Reversible water-swellable chitin gel

A novel, reversible, water-swellable chitin gel has been produced by the carboxymethylation of a dry chitin film. The property of this material is that unlike carboxymethyl-chitin, it takes up water but is not soluble and retains a degree of rigidity even when wet. The degree of swelling depends on the reaction conditions and alkali (sodium or potassium hydroxide) used as a co-reactant during the carboxymethylation. Upon drying, the gel returns to its dry film form. This water uptake and loss is cyclic, which is a desirable property in certain applications and is a tremendous advantage in the handling of this material.

Surface Carboxymethylation of a Chitin Hydrogel

A chitin hydrogel was modified to give a bilayer structure comprised of a surface layer of carboxymethyl-chitin and bulk chitin within. By gradually increasing the sodium hydroxide concentration used in the activation step of the reaction, thickness of the carboxymethyl layer with accompanying swellability was varied. These bilayer hydrogels showed distinct morphological differences between the surface and bulk regions, visualized with a basic dye test and verified by FT-IR. Carboxymethylation was found to increase the lysozyme susceptibility of these hydrogels. These modified hydrogels have potential in orthopedics applications where enhanced water swellability and calcium affinity imparted by surface carboxymethylation are desirable properties.

Chapter 3 Thermoplastic Polymers In Biomedical Applications: Structures, Properties and Processing

In general thermoplastic polymers are made up of long linear chain molecules which exhibit large scale chain mobility and deformation under shear forces above their softening temperature. This change is reversible. Above this temperature the thermal motions of the chain segments are sufficient to overcome inter- and intra-molecular forces. At room temperature the material is a viscoelastic solid. Their behaviour is dependent on chain morphology, structure, crystallinity and the types of additives added (often to aid processing). The materials can easily be processed into different type of products and are considered to be the most important class of plastic materials commercially available. The proeessability of this class of plastics is a key characteristic for developing biomedical applications.