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In continuation of our study on the concurrent polymerization of acrylamide with the hydration of calcium sulphate hemihydrate to calcium sulphate dihydrate, the influence of the polymer on the compressive strength, porosity and on the microstructure of the composite products has been studied.

Strategies to engineer bone have focused on the use of natural or synthetic degradable materials as scaffolds for cell transplantation or as substrates to guide bone regeneration. The basic requirements of the scaffold material are biocompatibility, degradability, mechanical integrity, and osteoconductivity. A major design problem is satisfying each of these requirements with a single scaffold material. This study addresses this problem by describing an approach to combine the biocompatibility and degradability of a polymer scaffold with the osteoconductivity and mechanical reinforcement of a bonelike mineral film. We report the nucleation and growth of a continuous carbonated apatite mineral on the interior pore surfaces of a porous, degradable polymer scaffold via a one step, room temperature incubation process. A 3-dimensional, porous scaffold of the copolymer 85:15 poly(lactide-co-glycolide) was fabricated by a solvent casting, particulate leaching process. Fourier transform IR spectroscopy and scanning electron microscopy (SEM) analysis after different incubation times in a simulated body fluid (SBF) demonstrate the growth of a continuous bonelike apatite layer within the pores of the polymer scaffold. Quantification of phosphate on the scaffold displays the growth and development of the mineral film over time with an incorporation of 0.43 mg of phosphate (equivalent to 0.76 mg of hydroxyapatite) per scaffold after 14 days in SBF. The compressive moduli of polymer scaffolds increased fivefold with formation of a mineral film after a 16-day incubation time as compared to control scaffolds. In summary, this biomimetic treatment provides a simple, one step, room temperature method for surface functionalization and subsequent mineral nucleation and growth on biodegradable polymer scaffolds for tissue engineering.

A sulphonic cation-exchange resin, containing nitro groups in the aromatic ring, was shown to have selective properties towards the heavier of the alkali metals.

A biodegradable polyphosphate polymer (Mn = 18,000, Mw/Mn = 3.2) matrix system was developed as a potential delivery vehicle for growth factors. As a model system, release of recombinant human osteogenic protein-1 (OP-1) from this polymer was evaluated. The polyphosphate was synthesized using a triethylamine catalyst in an argon environment, and characterized using elemental analysis, gel permeation chromatography (GPC), and Fourier transform infrared spectroscopy (FTIR). Degradation kinetics of the polyphosphate polymer in phosphate-buffered saline (PBS) were represented by a second-order polynomial while degradation in bovine serum was linear with time. The polymer degraded faster in PBS than in bovine serum. In vitro release of OP-1 was also faster in PBS than in serum. Release kinetics of OP-1 in PBS and serum were represented by second-order polynomials. The OP-1 release from this physically dispersed polymeric matrix may be described by several possible mechanisms: diffusion, bulk polymer degradation, ion complexation, and interactions among the protein (OP-1), polymer, proteins, and enzymes in the media. This polyphosphate may be an effective carrier for morphogens, growth factors, or other classes of bioactive molecules.

Fractographic analyses were performed on retrieved porous and surface-coated cobalt-chromium alloy prostheses which were revised because of metallurgical fracture. Two femoral neck fractures and one fractured post of a femoral component of a total knee replacements were retrieved and analyzed via light, stereo and scanning electron microscopy (SEM). In all cases, fatigue was the mechanism of failure. The life time of these prostheses was 3-5 years. The porous coating; microstructural features, including large grains, carbides, porosity, inclusions and defects; design and manufacturing defects were all likely causative factors in these fatigue failures. In light of these and other reported fractures, further study of fatigue mechanisms and improvement of design and manufacturing processes are warranted.

A series of finite element models was developed for evaluation of the micromechanics of implant/tissue interfaces. Conventional finite element global models of a dental implant, assuming a continuum implant/bone interface, were developed so that general stress patterns in the implant and surrounding tissue could be obtained. Stresses in bone were concentrated on the alveolar crest and apex region for all global models having a direct bone/implant contact. The addition of a 100-microns-thick layer of fibrous tissue into the bone/implant interface concentrated the stresses in the middle third of the bone adjacent to the implant surface. Stresses in the middle third were ten times higher than in the cases without fibrous tissue. Interfaces modeled under the assumption of a volume-weighted average material stiffness of bone tissue and metal confirmed these general stress patterns, but provided no stress details of the interfacial zone. Finally, the equivalent material constants of the interfacial zone with and without fibrous tissue were calculated by homogenization theory. From these equivalent constants, local strains around single threads were calculated. These equivalent material properties are sensitive to the microstructure. Therefore, it is now possible for stress patterns within the interfacial zone to be quantified and the local micromechanical behavior around individual surface structures for whole implants accounted for.

Forty-two percent of the population over the age of 65 is totally edentulous. The use of dental implants as a means of treating these patients has accelerated in the last decade, and there are now 300,000 dental implants used in the United States. It is therefore imperative that a greater understanding of the parameters which govern the long-term success of implants be developed. In order for the effectiveness of implants to be better quantified, a fundamental, quantitative understanding of the physical parameters governing the complex synthetic material/tissue aggregate is needed. The design of an "optimal" implant requires the integration of material, physical, chemical, mechanical, biological, and economic factors. The approach taken for a specific property objective to be met should be based on a materials science approach, in which the synergistic relationships among processing, composition, structure, and properties are characterized. Implant success is a function of biomaterials and biomechanical factors, including: materials and material processing; mechanisms of implant/tissue attachment; mechanical properties; implant design; loading type; tissue properties; stress and strain distributions; initial stability and mechanisms of enhancing osseointegration; biocompatibility; and surface chemistry, mechanics, and bone-binding ability of the implant. This paper presents an overview of physical parameters important to implantology. Following a general presentation of implantology concepts, the physical parameters listed above are discussed in greater detail.