A calcium phosphate coating over chitin sample was produced by a process based on phosphorylation, Ca(OH)2 treatment and SBF immersion. Ca(OH)2 soaking of the fibers phosphorylated by urea/phosphorus acid (H3PO3) method is found to produce highly crystalline clusters lodged in the fibers which were calcium phosphite mono-hydrate (CaHPO3H2 O). CaHPO3H2O clusters were still present in chitin fibers even after 7 days of soaking, while after 17 days calcium phosphate was observed. While chitin fibers phosphorylated by urea and H3PO4 method and then soaked in saturated Ca(OH) 2 solution at ambient temperature, which lead to the formation of thin coatings formed by partial hydrolysis of PO4 functionalities which were found to stimulate the growth of a calcium phosphate coating on their surfaces after soaking in 1.5×SBF solution for as little as 1 day. EDX analyses of the thin coating gave Ca/P ratio of 1.29, which is speculated to be OCP. The mechanism of formation of the coating is believed to involve dissolution of the CaHPO3 H2O clusters or the OCP upon introduction of the Ca(OH) 2- treated phosphorylated chitin fibers into the 1.5×SBF solution which elevates the Ca2+ ion concentration in the vicinity of the fibers so stimulating calcium phosphate formation from the soaking medium.

Biomineralization centers on the idea that organics control the nucleation, growth and final form of inorganics. The present studies investigated the deposition or precipitation of inorganics templated by organic monolayer films, unilamellar phospholipid vesicles, and selfassembled hexadecylamine, with the emphasis on the regulation of template on phase, orientation and microstructure of minerals. The obtained calcium phosphate varied from the thin layer precipitated on the organic monolayer to the confined particles formed inside the lipid vesicles to the mesolamellar structure self-organized in the precursor sol-gel. The typically regulated features of these three systems have been revealed. Consequently, the different phases of calcium phosphate can be obtained through variation of controllable parameters.

An estimated 11 million people in the United States have at least one medical device implant [1]. Orthopaedic implants account for 51.3 % of all implants. They include fixation devices (usually fracture fixation) and artificial joints, used in 77% and 23% of the cases respectively. Among the joint replacement procedures, hip and knee surgeries represent 90% of the total, and, in 1988, were performed 310,000 times in this country [1]. Currently, somewhat more than half the joint reconstruction devices are used with bone cement, which is a polymer grout that keeps the prosthesis components in place in the bone. The fixation in the other cases depends on the bone's ability to grow in contact with the device. This can be achieved by making the prosthesis surface porous, such that bone grows into the interstices; or by making the surface chemically reactive with bone tissue such that a continuous, uninterrupted transition is formed from tissue to device. Bioactive glasses and ceramics are the materials of choice to achieve this effect on bone tissue bonding [2]. Bone growth stimulation is also sought in the treatment of difficult fractures. In the U.S. alone, there are 1.23 million fractures that require a bone plate. Of that total, approximately I million require between 10 and 100 cc of graft material to stimulate bone repair. At this time, autogenous bone graft represents the gold standard: this graft is typically bone tissue taken from the patient's own iliac crest. Given the morbidity associated with this procedure and the frequently insufficient quantities available, extensive efforts for suitable alternatives are currently underway. Calcium phosphate ceramics and glasses, either by themselves or as carriers for bone (or “osteogenic”) cells or various bone growth factors, are also prime candidate materials for these applications.

Protein adsorption to ceramic surfaces is an important early step in the function of implants. The types and amounts of adsorbed protein and the resulting conformational changes could mediate subsequent cell adhesion and inorganic deposition. Microporous silicoalumino-phosphates, which allow variations in surface composition within the same crystal structure, have been used as model surfaces. Effects of surface composition on adsorption isotherms, elutability, and biological activity of the adsorbed protein layer have been studied using lysozyme, a model protein. Control over protein adsorption mechanisms using well-characterized surface properties could be used to predict the biological properties of surfaces, and engineer coatings for a desired response.

Aggregate structures of steroids adsorbed on electrically-poled hydroxyapatite (HAp) ceramics were investigated by X-ray diffractometry (XRD) and scanning electron microscopy. Effectivity of the poled HAp on modification of the steroid assembly modes was discussed by the arrangement estimations of the steroid molecules. The dense HAp ceramics were obtained from the pelletized HAp powder precipitated from calcium hydroxide suspension and phosphoric acid using conventional sintering at 1250°C under the saturated water vapor pressure. The HAp ceramic blocks were poled in a DC electrical field of 1.0 kVcm-1 with being heated at 300°C. The HAp ceramics were immersed in ethanol solution of steroids at 37°C. The steroid crystals were overgrown onto the HAp substrates by recrystallization method. In the case of cholesterol, the tabular crystals of cholesterol monohydrate and the needle-like crystals of anhydrate were overgrown on all of the HAp ceramic surfaces. The thickness of the cholesterol layers on the positively (p) poled HAp surfaces was considerably less than those of the negatively (n) poled and non-poled (0) surfaces. The remanent chaige of the HAp ceramics altered the morphology of vitamin D3 crystals deposited on the HAp surfaces. It was revealed that the electrically-poled HAp ceramic surfaces changed the aggregate structures and the crystal growth rates of steroids.

Basic design requirements of scaffolds for bone tissue engineering applications include biocompatibility, temporally controlled degradability, osteoconductivity, mechanical integrity, and mass transport capabilities. A recent study has attempted to meet design criteria via the growth of a carbonated apatite (bone-like) mineral on the inner pore surfaces of a highly porous 85:15 poly(lactide-co-glycolide) scaffold using a biomimetic process. It has also been recently demonstrated that the mineralization strategy can be combined with sustained growth factor delivery to induce vascular tissue ingrowth. The present study examines the effect of protein presence on the mineralization process by measuring the amount of protein incorporated into the scaffold during the process of mineral formation. Surprisingly, vascular endothelial growth factor incorporates more readily into control scaffolds than into scaffolds subjected to mineralization treatment. This finding suggests that there is little incorporation of protein into the growing mineral film, and offers insight into the mechanism for sustained drug delivery from the mineralized scaffolds.

We have studied the electrostatic interactions of proteins with the calcite surfaces during its subsequent nucleation and growth on a surface. In doing so, a model system of four globular proteins (lysozyme, ribonuclease, myoglobin and α-lactalbumin), having the same size and conformation, but differing in surface properties (i.e. surface charge) was used. Depending on the nature of the charge on the protein, its morphological effect on calcite growth (inhibition of specific crystal faces) varies, with this effect becoming more pronounced as the protein is more negatively charged. To study how the adsorption of proteins affects the growth of calcite along different crystal directions, calcite plates cut with different crystallographic orientations (i.e. (001), (104), (100) and (110)) were used as substrates. The overgrowing calcite crystals show the same orientation as the substrate. The nucleation density also varies with the crystallographic orientation of the calcite substrates, increasing in accordance with the sequence: (110), (100) and (001). Finally, to study how the protein itself controls the orientation of crystals, we used amorphous substrates (glass). After incubation on the glass substrates with negatively charged proteins, an oriented nucleation of the calcite crystals was induced.