It is becoming increasingly evident that recombinant DNA technology, physical-chemistry and selected biological processes can be coupled leading to the development of new “synthetic” biomaterials. This summary and prospectus will highlight selected features related to dental enamel biomineralization towards the development of human dental enamel as a restorative biomaterial.

Bone, teeth and shells are complex composite ceramics which are fabricated at low temperature by living organisms. The detailed understanding of this fabrication process is required if we are to attempt to mimic this low temperature assembly process. The guiding principles and major components are outlined with the intent of establishing non-vital fabrication schemes to form a complex composite ceramic consisting of an organix matrix inorganic crystalline phase.

Artificial lipid vesicles (liposomes) provide an in vitro approach for microencapsulating calcium phosphate precipitation reactions in a manner similar to that which occurs in matrix vesicles, the initial loci for extracellular mineralization in many skeletal tissues. Apatitic precipitates readily form within the aqueous interiors of liposomes prepared from phosphatidylcholine, dicetylphosphate, and cholesterol when the liposomal membranes enclosing pH 7.4 buffered PO4 solutions are made permeable to external Ca2+ with ionophores. If the external Ca solution is rendered metastable with PO4, the apatitic precipitates rapidly expand to outside the liposomes as well. The present paper describes the basic features of liposomal mineralization and presents some specific examples on how compositional alterations in the liposomal membrane and external Ca solution can affect the progress of this mineralization.

This paper discusses the principal features of biomineralization in relation to the controlled crystallization of inorganic materials, and the modelling of these concepts in vitro. The biological strategies adopted in the regulation of nucleation and growth are; (a) the use of constrained reaction environments, (b) the synthesis of chemically and structurally specific organic macromolecules, and (c) the secretion of tailor-made additives of low and high molecular weight. Underlying these strategies is the concept of molecular recognition at interfaces comprising organic and inorganic surfaces. The structural, electrostatic and stereochemical aspects of these interfacial interactions in systems involving supramolecular asemblies, Langmuir monomolecular films and tailored additives will be described.

The effects of varying the particle sizes of particulate reactants which form hydroxyapatite by a dissolution-precipitation reaction is considered. The effect of Mg2+ ion, known to inhibit hydroxyapatite formation in vivo. on the reaction to form hydroxyapatite is discussed.

Peptides have been synthesized by solid phase methods with structures which are in part based on experimentally-determined features of a major class of organic matrix phosphoproteins isolated from the calcium carbonate shell of the oyster. The matrix structures mimicked in the synthetic peptides included runs of aspartic acid (Asp), which were contrasted with peptides having other deployments of Asp with serine (Ser) and glycine (Gly). In addition, peptide-Ser was phosphorylated (PSer) and the hydrophobic carboxyterminus of natural matrix was mimicked using polyalanine tails. The interaction of the various peptides with CaCO3 as well as calcium phosphates was determined using a variety of crystallization assays and studies of adsorption of radio-labelled peptides to crystal surfaces.

In general, peptides that include runs of Asp regulate crystal nucleation and growth more effectively than those which contain (Asp-X)n or (Asp-X-Y)n sequences with X and Y being either Gly or Ser. Further, CaCO3 crystals have a much higher binding capacity for polyAsp than for peptides with other deployments of Asp. Phosphorylation increases the regulatory activity and the crystal capacities of Asp/Ser - containing peptides. PolyAsp peptides having terminal PSer's are especially effective as regulators of CaCO3 nucleation and the conversion of amorphous calcium phosphate to apatite. The activity of Asp15 molecules in CaCO3 nucleation assays is markedly increased by the addition of polyalanine tails.

Mineralization processes used by bioorganisms have been adapted for the nucleation and growth of ceramic oxide thin films onto surfaces from aqueous solutions. These strategies include the use of surfaces derivatized with specific functional groups that control the nucleation and growth and properties of materials deposited. Iron oxide materials were deposited onto functionalized polystyrene surfaces, resulting in the formation of thin films composed of densely packed, nanometer-sized crystallites. Evidence for the formation of oriented crystallites was found. This process may have advantages over conventional thin film processing methods due to the ability to systematically control properties of materials deposited.

The aim of this work is to produce dense, fired thin sheets of barium titanate less than 30μm thick via flexible green bodies produced by in situ precipitation of BaTiO3 in polymer films, with burnout of the polymer followed by sintering of the mixed oxide powder film.

Polyethylene and oxide substrates were derivatized with functional groups commonly associated with biomineralization substrates. These groups include carboxylate, phosphate, hydroxy, sulfonate, thiol, and amine. FTIR, XPS, and contact angle wetting were used to identify and characterize the products at each step. The efficacy of these groups toward inducing mineralization will be compared with naturally occurring substrates.

The adsorption and crystal growth effects of salivary cystatin SA-II and non-glycosylated amylase on hydroxyapatite have been compared to the effects of the salivary cystatins SA-I and SA-III. Amylase was the least active HAP crystal growth inhibitor and adsorbed weakly to HAP. Although the three cystatins were active inhibitors of hydroxyapatite crystal growth in supersaturated solution, their affinities showed marked differences.

The adsorption of citrate and phosphocitrate on calcium oxalate monohydrate (COM) surfaces has been measured in saturated solutions of calcium oxalate monohydrate at 37°C. In separate adsorption experiments, the uptake of phosphocitrate was markedly greater than that of citrate. When both additives were present, the adsorption of phosphocitrate was further increased. In constant composition studies of the crystallization of CON from supersaturated solution, phosphocitrate was more effective as an inhibitor than was citrate.

The Air Force has been supporting a number of research and development programs directed at exploring the possibility of utilizing biological processes for the preparation and modification of materials with aerospace applications. Areas addressed by these programs include biosynthesis of key chemical intermediates, biological removal of materials such as paint or sealants, biodegradation for environmentally safe destruction of wastes, and biological leaching and accumulation of strategic metals, utilization of naturally occurring materials with electrooptical properties, and modeling the design of natural structures with synthetic materials.

The paper presents the detailed study of the structural features of the biomineralized bivalvia shells. The Cristaria plicata(Leach), Anodonta woodianal(Lea) and Lamprotula Leai(Gray) are selected as the prototype in the present study. Scanning electron microscope (SEM), X-ray diffraction, laser Raman spectroscope and electron spectroscopy for chemical analysis (ESCA) are employed to study the structures of the shells. It is found that three different layers of the shells possess distinct morphologies and structures with a clear boundary between every two layers. The prismatic layer can be further divided into two sub–layers. The preferential growth orientation of the biominerahzed phases were different from the natural ones. The Raman spectra present the detailed vibrational states of these biomineralized phases, while ESCA reveals that the chemical environments of the atoms in pearl layer are less varied than those in the other two layers.

The microstructure and mechanical properties of abalone shell were studied. It was found that fracture strength, αf, is 180 MPa, and fracture toughness, KIC, is 7 ± 3 MPa-m1/2; these values are comparable with or better than most “high technology” ceramic materials. The microarchitecture of the nacre section of the red abalone shell is similar to a “brick and mortar” structure, where CaCO3 is the brick and organic matter is the mortar, constituting 95% and 5% of the microstructure by volume, respectively. This impressive combination of af and KIc values is attributed to the laminated structure of the shell with hard and thick (0.25±0.5 μm) CaCO3 and superplastic and thin (20–30 nm) organic components. Although there are several toughening mechanisms operating in the shell, fractographic studies identified sliding of CaCO3 layers and bridging by the organic layers to be the most effective ones. These phases also have a strong interface. The results of our experiments are discussed in the context of using abalone shell as a model for the design of synthetic laminates such as cermet (ceramic-metal) and cerpoly (ceramic-polymer) composites.

A scanning and transmission electron microscopy study is presented of the microstructure of the Strombus gigas shell. The heirarchical nature of this crossed-lamellar structure and the defect content of the mineral component are described. This mineral component consists of small single crystal grains of aragonite, the metastable orthorhombic polymorph of CaCO3. The habit and morphology of the grains discussed here have not been determined previously. The observed habit and defect structure suggest that the organic matrix exerts a high degree of control over the crystal growth of the mineral phase and is responsible for the long range order in the microarchitecture. Electron beam heating of the mineral component leads to certain phase changes and these are discussed.

An investigation of the relationship between structure and mechanical behavior is reported for mollusk shells employing foliated, nacreous, and crossed-lamellar structures by microindentation in the Knoop and Vickers geometries. Indentation damage zones develop crack systems that reflect the micro-architecture. For the crossed-lamellar structure, the system of cracks about the indentation normally developed in a brittle material is suppressed. Previous reports that shells are harder than the corresponding minerals, calcite and aragonite, are confirmed, but it is found that this effect can be strongly dependent on orientation. This anomalous hardness is not an artifact of the identation test technique, since scratch tests confirm the relative hardness of shell over the mineral. It is suggested that microstructural organization is of central importance in producing this hardness, as opposed to intrinsic properties of the mineral or matrix phases.

The crystalline lens of the eye is a unique optical structure that continues to develop within the eye throughout life. This process of development results in the formation of a lens with a gradient refractive index that has important optical consequences, particularly in the control of spherical aberration. The optical characteristics of the vertebrate crystalline lens are reviewed in terms of environmental concerns and spherical aberration. Lens shape and relative size are determined by such factors as whether the eye is to be used in air or water and whether it is to be used under scotopic or photopic conditions. The continued growth of the lens through life can be related to whether the lens exhibits positive or negative spherical aberration. In general, spherical aberration, as measured using a split laser beam method with excised lenses, is minimized in species with life histories indicating superior resolution ability. In addition, lens optical quality, as indicated by zonular differences in focal length, deteriorates with lens age. While the embryonic and post-embryonic lens undergoes significant change in size, shape and refractive index distribution, it appears that focal constancy is maintained, at least in certain species. This finding may indicate a means of simplifying the process of emmetropization.

The intervertebral disc is a complex hierarchical structure composed of the annulus fibrosus and nucleus pulposus which are anchored to the vertebral bodies by cartilaginous endplates. The hierarchical structure of the collagenous components of the intervertebral disc is characterized using optical microscope techniques. In the lamellae of the annulus, collagen fibers exhibit a planar crimped morphology similar to that seen in other collagenous tissues. A model of the intervertebral disc has been developed that incorporates the structure of the collagen fibers on the macro- and microscopic scales.

Mechanical testing in load-deflection, stress relaxation, and creep modes reveals the response at each level of organization to compression. These mechanical data are analyzed with models that reflect the hierarchical composite structure.

Parallel nanometer molecular lithography has recently been demonstrated to be a parallel fabrication process for structures with features defined by single molecules [1]. In this process two dimensional (2d) monolayer protein crystals are used as patterning elements in the parallel fabrication of structures on the 10nm length scale (nanostructures). The parallelism of this technique is in contrast to such serial fabrication methods as x-ray and electron-beam lithography.

Neutron small-angle scattering measurements of several different chlorophylls hydrated in deuterated octane-toluene mixtures show that long, hollow cylinders of aggregated chlorophyll are formed. Clear secondary maxima are present in the scattering, and the cylinder diameters are well determined, but depend on the type of chlorophyll. Chlorophyll-a and Bacteriochlorophyll-a were particularly studied, and several samples of each have been measured. Other chlorophylls have also been studied. The results provide strong evidence that chlorophyll cylinders are only certain sizes, with diameters very nearly in the ratio of small integers. Thus, the cylinder diameters appear to be quantized. Neutron scattering results that further test this quantization property are presented here, together with a proposal for the stereochemical features of chlorophyll aggregation which account for the diameter quantization.