A hydroxyapatite, HAP, film was deposited on a titanium substrate in an aqueous solution, at an ambient temperature and ambient pressure. The solution included 3 mmoldm-3 Ca(H2PO4)2 and 7 mmol dm-3 CaCl2 at pH 5.5. The temperature of the substrate surface was controlled in both methods of applying alternative current through the Ti foil and high frequency induction heating using Ti ingot. In these methods, the substrate was heated up and the temperature gradient was formed between the substrate and the solution. The effects of surface temperature, fluoride ions, additive inhibitor and heating time on the morphology of HAP crystals formed on Ti substrate were investigated in various conditions. The morphology changed from compact layer to dendrite layer with the HAP growing time in AC current method and the HAP film with the thickness of 200 μm can be obtained on Ti foil with cross section of 30 μm × 2mm by heating for 20 min at 20 A-AC. On the other hand, the deposits consisted of algae-like whisker in the induction heating method. The HAP formation is found to take place only on the substrate surface by these substrate heating methods without HAP precipitation in aqueous solution

An important inorganic phase of synthetic bone applications, calcium hydroxyapatite (HA, Ca10(PO4)6(OH)2), was prepared as a single-phase and sub-micron bioceramic powder. Carbonated HA precursors were synthesized from calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts dissolved in “synthetic body fluid” (SBF) solutions, containing urea (H2NCONH2) and enzyme urease, under the biomimetic conditions of 37°C and pH 7.4, by using a novel chemical precipitation technique.

New bone formation around implants is one of preferable conditions for the successful implantation. In this study, formable carbonate apatite ceramics were prepared and implanted in cavities (φ 400 μm, depth 400 μm) on the surface of pure titanium implant (ASTMB348-GR2) to enhance new bone formation around the titanium implant.

Pure diopside, CaMgSi2O6 and the partly modified new type of crystalline diopside, NaxCa1-xMgSi2O6, were prepared mainly by coprecipitation process These ceramics were synthesized from the inorganic nitrates and the metal alkoxide in ethanol solutions. The sodium contents in the crystal had remarkable effect on the apparent densities and improved the mechanical properties, especially when the hot-isostatic pressing was applied in the final process. The precise measurements of the X-ray diffraction patterns strongly suggested that the Ca positions in the unit cell were partly substituted by the Na atoms. SBF soaking tests showed that the porous sol-gel method diopside induced the higher apatite crystal growth rates than the hot-pressed surface of the pure or the Na-modified diopside.

The surface of the coprecipitation process diopside specimens was coated with the porous ceramics for the purpose of the formation of the bioactive diopside films.

In recent years, several research groups have pursued biomimetic or bio-inspired techniques for the synthesis of ceramic thin films from aqueous solutions at low temperatures. The substrates range from inorganic materials (metals, glass, single-crystal silicon) without special surface preparation, to functionalized organic surfaces such as self-assembled organic monolayers (SAMs). Our results on the deposition of tin (IV) oxide (SnO2, cassiterite) and hydroxyapatite (Ca10(PO4)6(OH)2) thin films on SAMs will be reviewed. The former system forms films via assembly of nano-scale particles on the substrate, while the latter system appears to form films via heterogeneous nucleation. In both cases, the role of the substrate in film formation is discussed.

Biological systems have a unique ability to control crystal structure, phase, orientation and nanostructural regularity of inorganic materials. An example is seen with the control of crystallographic phase and orientation of calcium carbonate with the polyanionic proteins isolated from shells of the marine gastropod abalone. We are currently investigating the principles of natural biological molecular recognition in materials and developing new methods to pattern useful non-biological electronic and magnetic materials on new length scales. A peptide combinatorial approach has been employed to identify proteins that select for and specifically bind to inorganic structures such as semiconductor wafers, nanoparticles and quantum confined structures. This approach utilizes the inherent self-organizing, highly selective properties of biologically derived molecules. We are currently investigating peptide recognition and interaction with III-V and II-VI semiconductor materials, magnetic materials, calcium carbonates and phosphates. We have selected peptides that can specifically bind and discriminate between zinc-blende III-V semiconductor surfaces. These peptides show crystal face specificity and are being used to organize nanoparticle heterostructures. Long term potential application of these materials would include opto-electronic devices such as light emitting displays, optical detectors, lasers, and nanometer scale computer components.

As many properties of group II-VI semiconductor nanocrystallites arise from their quantum confined nature, the synthesis of these clusters is of great interest. The challenge of synthesizing functional nanoclusters is, however, complicated by the limited stability of metalchalcogen surfaces under highly oxidizing conditions and Ostwald ripening. Our objectives are to develop methods for the synthesis of biogenic CdS semiconductor nanocrystallites that address the following issues: (1) What properties of the ligand peptide are important in stabilizing and producing CdS particles of any desired size? (2) Will hybrid peptides using nonnatural amino acids stabilize the nanoclusters while incorporating new surface functionality? (3) Is it possible to use novel peptides to modify the particle surface, thereby, controlling the photophysical properties of the CdS cluster? Our approach consists of parallel combinatorial techniques and computational methods for the discovery and optimization of peptide and peptidomimetic ligands to stabilize size-defined clusters of CdS. The effects of cysteine separation on CdS particle size by varying the number of bonds with rotational freedom within the spacer amino acids is examined. Furthermore, the properties of the resulting CdS nanoclusters are reported.

Molluscan shell is a composite made up of μm-sized CaCO3 crystals and an organic phase (matrix). This report outlines our studies on the structure and activities of matrix proteins isolated from the inner calcite layer of shell of the Eastern oyster, including their cellular origin and structure and their relationship to the crystalline mineral phase. In addition, we present results of the synthesis and commercialization of polypeptide polymers which are based on the structure and activities of the oyster proteins. Extracted shell proteins are polyanionic and range in size from relatively small soluble forms to those which are crosslinked and insoluble. The soluble forms are capable of adsorbing to calcite in vitro and in the process changing its growth habit and acting as threshold growth inhibitors. Their function in vivo is not understood, but they may serve to control shell crystal morphology. The insoluble protein forms gels readily and may serve to provide resiliency to the shell and, from in vitro and in situ observations, appears to serve as a site for nucleation of crystals. However, from studies in vitro, these gels do not lower the energy of activation for nucleation, as previously expected. Matrix protein aggregates are identifiable by AFM on the surface of crystals, but as such do not serve as nucleation sites for new crystal growth. If the aggregates are removed, then ectopic crystal growth proceeds readily revealing orientation of the underlying crystals. All the matrix proteins contain domains rich in aspartic acid, are heavily phosphorylated, crossreact in antibody studies and may belong to a limited number of gene families with individuals modified post-synthesis. The proteins are made by a specialized group of cells located primarily some distance from the growing edge of the shell and appear to be assembled into sheets soon after secretion. Soluble anti-scalants and crosslinked insoluble water absorbents have been developed based on the structure and activity of the matrix proteins. These are primarily poly(aspartates) which can be made in large scale via thermal polycondensation of aspartic acid. The soluble forms are commercially used as biodegradable water treatment chemicals among other applications.

Hard tissue regeneration (i.e. shell repair) is an important biomineralization process in mollusks. Rapid regeneration is important in avoiding loss of fluids and preventing attacks by predators. We have studied such tissue regeneration in the Queen conch (Strombus Gigas) by inserting an abiotic glass cover slide between the mantle tissue and the shell. The glass cover slides were removed after mineralization periods extending from 6 hours to 4 days, and the deposited materials on the glass substrates (“flat pearls”) analyzed by X-ray diffraction, and scanning and transmission electron microscopy.

Although the CaCO3 in native Queen conch shell is exclusively aragonite, calcite was detected in the regenerated materials grown on glass substrates. Calcite formation occurred only during the very early stage of mineralization and the initial minerals formed were soon overgrown by aragonite. The initial aragonite overgrowth had a spherulitic morphology, and was thus relatively poorly oriented; after this spherulitic transient, the microstructure was recognizable as the crossed-lamellar structure of the natural shell.

Thus, shell regeneration on abiotic substrates differs from shell formation during growth of conchs only in the very early stage. Once the crossed-lamellar microstructure has formed, further hard tissue development is identical to that occurring during natural shell growth.

Three dimensional finite element models of nacre were constructed based on reported microstructural studies on the ‘brick and mortar’ micro-architecture of nacre. 3D eight noded isoparametric brick elements were used to design the microarchitecture of nacre. Tensile tests were simulated using this model at stresses of 2 MPa which occur well within the elastic regime of nacre and thus effects related to locus and extent of damage were ignored. The reported values of elastic moduli of organic (0.005 GPa) and aragonitic platelets (205 GPa) were used in our simulations and the resulting displacements were found to be extremely large and corresponding to a very low modulus of 0.011 GPa. The reported elastic modulus of nacre is of the order of 50 GPa. The large displacements can possibly result from two possibilities. Firstly. the organic layer due to its multilayered structure is possibly composed of distinct layers of different elastic moduli. A significantly higher modulus of the organic phase may be possible near the organic-inorganic interface. Simulations using variable elastic moduli for the organic phase suggest that an elastic modulus of 15 GPa is consistent with the observed elastic behavior of nacre. A second possibility for the observed higher elastic modulus may arise from localized platelet-platelet contact. Since the observed modulus of nacre lies within the above two extremes (i.e. 15 GPa and 205 GPa) it is suggested that a combination of the two, i.e. a higher modulus of the organic phase near the organic-inorganic interface and localized platelet-platelet contact can result in the observed elastic properties of nacre.

Biological systems have evolved mechanisms that precisely control inorganic structures on both the micro- and nanoscale, operating at ambient pressures and temperatures. In both the calcium carbonate, calcium phosphate and silicon dioxide utilizing organisms, proteins and polysaccharides have been found to play integral roles in the organization of these biominerals[1–3]. The organic constituents generally have been thought to act as direct templates or modulators for the deposition of the particular mineral. We have explored the synthesis and structural control of silica by the marine sponge, Tethya aurantia. Needles of amorphous silica comprise the skeletal system of this organism, representing 75% of the dry weight of the organism. These glassy needles, called spicules, are 2 mm in length and 30 μn in width[4,5]. We have characterized the structure, genetics and functions of the proteins that form an occluded axial filament within each silica spicule. Based on our discovery, a unique structure-directing catalytic mechanism exhibited by these protein filaments, and the structural determinants responsible for the catalytic activity, we have designed novel block copolypeptides that catalyze and spatially direct he condensation of silicon alkoxides to form organized silica structures ranging from transparent spheres to lath-like structures at ambient pressure, low temperature and neutral pH.

Serine- and polysaccharide-enriched organic matrix is associated with biogenic silica such as diatom tests, sponge spicules, and phytoliths. We have used molecular orbital theory to determine the relative stability and 29Si NMR shifts of direct Si-O-C ester-like bonds versus hydrogen bonds between the monomeric silicic acid and the alcohol group on aliphatic organics such as serine and threitol (a polyacohol as proxy for polysaccharides). Preliminary results suggest that at neutral pHs, H-bonds and ester-bonds of four-fold coordinated silicon are of comparable stability. Formation of ester-like bonds with five-fold coordinated silicon is endothermic at neutral pHs but is stabilized at higher pHs. 29Si shifts of the H-bonded and ester-bonded complexes of four-fold coordinated silicon range from −55 to −73 ppm similar to monomeric inorganic silicic acid but far more positive than the −92, −102, and −110 ppm values observed experimentally in biogenic silicas. The five-coordinated silicon complexes yield shifts of −96 to −107 ppm. The latter range is within the range of inorganic, polymerized silica. If five-fold coordinated Si with direct Si-O-C bonds is present as a precursor or intermediate or stable species in biogenic silica, it could have escaped detection due to overlap with inorganic polymerized silica. Thus, 29Si NMR shifts are not necessarily diagnostic of the presence or absence of Si-O-C bonds in biogenic silica.

Through organized surfactant templating, mesoporous silica (MPS) was prepared on two different types of substrates with a hydrophilic or hydrophobic surface. In this study, a Si substrate covered with photochemically-grown surface oxide was served as the hydrophilic surface. The hydrophobic surfaces were prepared by forming an organosilane self-assembled monolayer (SAM) on Si substrates through chemical vapor deposition. Octadecyltrimetoxysilane or (heptadecafluoro-1,1,2,2-tetrahydro-decyl) trimethoxysilane was used as a precursor. The morphologies of the deposited MPS on these surfaces were found to be quite different. The MPS formed on the hydrophilic Si substrate consisted of small disk-like features of 2∼5 μm in diameter, while those on the hydrophobic SAM surfaces were continuous thin films. These morphological differences of the deposited MPS were ascribable to the differences in the supramolecular template structure formed on each of the surfaces. Furthermore, in order to study microstructure effects on the MPS growth, a micropatterned SAM/Si, on which hydrophobic regions were spaced alternately with hydrophilic regions at a 5 μm-wide interval, was employed as a sample substrate. On this substrate, MPS was preferentially grown on the hydrophobic regions while the hydrophilic regions remained almost undeposited. The spatial control of surfactant-assembling using the micropatterned SAM surface was successfully accomplished.

We traced and quantified the silicon released from bioactive glass (BG) granules in vivo (45S5, 300–355 μm). 1500 mg of BG granules were implanted in the paraspinal muscle of 7 four kg rabbits. Blood samples and 24-hour urine samples were obtained over a 24 week period. Local muscle tissue as well as the following organs were harvested for chemical and histological analyses: brain, heart, kidney, liver, lung, lymph nodes, spleen, and thymus. Flame atomic absorption spectrophotometry was used to measure the concentration of elemental silicon in all the samples after digestion. Tissues and fluids from a sham group of 7 rabbits (underwent surgical procedure but received no implants) were obtained in a similar manner.

The urinary silicon of the implanted group was significantly higher than in the control group. From the data, the calculated average excretion rate was approximately 2.4 mg/day, and as such, 100 percent of the implanted silicon was excreted in 19 weeks. No elevated concentrations of silicon were found at the implant site or in the other organs after 24 weeks. Histological appearance of all major organs was normal for all animals in the study.

The concentrations of silicon measured in the urine were well below saturation and since no significant increase in silicon was found in the kidney or in the other organs, the increased silicon excretion rate was within the physiological capacity of rabbits. Therefore, it can be concluded that the resorbed silica gel is harmlessly excreted in soluble form through the urine.

More than 80% of human kidney stones consist of calcium oxalate and/or calcium phosphate. Human urine is generally metastable with respect to these salts and their nucleation is heterogeneous. Based on: 1. ultrastructural and immunohistochemical studies of stones in which cellular degradation products and lipids were commonly seen in association with calcific crystals and 2. in vivo studies of nephrolithiasis in rat models where calcium oxalate (CaOx) and calcium phosphate (CaP) crystals almost always formed and seen in association with cell membranes, we proposed that membranes and their lipids are involved in crystallization of these salts. To test our hypothesis we isolated organic matrix of kidney stones, its lipid contents and membrane vesicles from epithelial cells of rat kidney and incubated them in metastable solution of CaOx. Both membrane vesicles and matrix from the stones supported crystallization of CaOx and crystals formed in association with the membranes. Lipids of the stone matrix appeared better nucleators than whole matrix. Urine spends only minutes within the kidneys thus any nucleation which can lead to stone formation has to occur rapidly. In studies described here, we demonstrate that under specific circumstances relevant to conditions in the kidney, membrane vesicle- supported CaOx crystallization can occur within seconds, demonstrating the possibility of such events happening in the kidneys. We also studied CaOx monohydrate (COM) precipitation at Langmuir monolayers of dipalmitoylphosphatidylglecerol (DPPG), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylserine (DPPS) showed precipitation to be heterogeneous and selective with a majority of crystals orienting with the 101 face of COM facing the monolayer. Our results show that membrane lipids can initiate nucleation of calcium oxalate crystals in solutions similar to those present in the kidneys. In addition these crystals form within the time urine spends inside the renal tubules demonstrating for the first time the likelihood of occurrence of such a phenomenon in the kidneys during stone formation.

The present study compares the fatigue propagation behavior of a fluorinated and nonfluorinated polyurethane-calcium salt blends. The calcium salts used in this study are calcium chloride and hydroxyapatite (HAP). The fatigue crack propagation (FCP) behavior of the polyurethanes exhibited a dependence on the chemical composition of the polymer and calcium salt. The pure non-fluorinated PTMG2000 did no undergo crack propagation. While the fluorinated PTMG2003F exhibit a crack propagation rate of 7.8 × 10-6 m/cycle at constant strain amplitude and tearing energy range. The incorporation of calcium chloride into PTMG2000 did not promote any changes in the FCP behavior; while the addition of HAP produced cracks with a growth rate of 3.33 × 10-6 m/cycle. In the case of PTMG2003F, the addition of calcium chloride did not lead to formation of cracks; while HAP produced a material in which cracks propagated at a rate of 10.0 × 10-6 m/cycle. The difference in the response the non-fluorinated and fluorinated polyurethane-calcium salt blends to cyclic loading can be attributed to molecular level variations such as domains disruption and changes in chain orientation at the crack tip.

Non-esterified geminal bisphosphonate groups (0.06–0.12 mmol/g) were covalently attached to elastomeric polyurethanes (PU) based on 4,4′-methylenebis(phenyl isocyanate) (MDI) and represented by a polyether-urethane (PEU), a polyurethane-urea (PUU), and a polycarbonate-urethane (PCU). Auxiliary 6-bromohexyl or carboxylic groups were attached to PU via base-induced N-alkylation of urethane NH sites either with 1,6-dibromohexane or with lithium salts of ω-bromocarboxylic acids. An alternative method to introduce carboxylic groups into the polymers via reactions of bromoalkylated PU with thiol-containing carboxylic acids was found to be more suitable than the direct carboxyalkylation. The subsequent reactions either of thiol-containing bisphosphonates with the attached 6-bromohexyl groups or of 3-amino-Ihydroxypropylidene-1,1-bisphosphonate (pamidronate) with N-hydroxysuccinimide-activated carboxylic groups of PU led to the bisphosphonate-modified PU. The polymers do not undergo a significant degradation in the course of the modification reactions, their mechanical properties and elasticity remain mostly unaffected. Water uptake of the bisphosphonate-modified PU increased up to 26% depending on the extent of modification. Bisphosphonate-modified PUU showed a significantly lower in vivo calcification compared to the non-modified polymer.

A critical target for the development of new antimalarial treatments is the detoxification pathway of free heme released during the catabolism of host hemoglobin in the digestive vacuole of the malaria parasite Plasmodium falciparum. We have synthesized and examined two peptide dendrimers (BNT I and II) based on the tandem repeat motif of HRP II from P. falciparum for their abilities to both bind heme substrates and to form the critical detoxification polymer hemozoin. Each substrate was capable of binding significant amounts of the natural substrate Fe(III)PPIX along with other substrates such as Zn(II)PPIX and the metal free PPIX. Further, it was shown that the dendrimeric BNT I and II were capable of supporting the aggregation of hemozoin and that this process could be inhibited by the known antimalarial drug, chloroquine.

In this work, the adsorption isotherm and kinetics of bovine submaxillary gland mucin (BSM) onto a hydrophobic polystyrene surface were studied by the solution depletion method, in which mucin surface concentrations were analyzed by amino acid analysis. Using a Langmuir adsorption model and non-linear curve fitting, kinetics parameters, kon and koff were determined. The coating was found to be very stable with very limited desorption (less than 2%) from a long term observation. By measuring the water contact angles, the changes in surface hydrophobicity due to mucin coating were monitored on four polymer materials, namely polymethylmethacrylate (PMMA), polyurethane (PU), polystyrene (PS), and silicone. After coating, all the hydrophobic surfaces turned into very hydrophilic. A strict correlation between mucin surface concentration and surface wettability has been found.

Advances in the understanding of biomineralization processes in a variety of organisms have revealed the critical role of three-dimensional scaffolding architectures to create a highly functionalized surface. These complex matrices function on a variety of length scales ranging from the macromolecular (10–100 nm) to the cellular (1–10mm) and larger. One dominant structural motif found in many of these architectures is macromolecules containing antiparallel β-pleated sheets. These “hints” from Nature have lead to the iterative design and development of a novel multipurpose platform technology based on a self-assembled periodic peptide architecture for use in bone-tissue engineering. Combining molecular modeling, structural biochemistry and synthetic techniques, we have produced a β-sheet hollow tube peptide nanoassembly. Such a synthetic approach allows for the template's designed parameters of electrostatic, geometric and stereochemical complimentarily to match those of the desired biomineral. Consequently, these templates readily nucleate calcite. Future studies will investigate the in vitro osteoconductive and osteogenic properties of these templates.