Cast silk membranes exhibit useful properties. However, there is limited control over the molecular architecture in these structures. The Langmuir-Blodgett technique can enhance the control of the membrane structure and allow improved control over membrane properties. We have formed natural silk monolayers using the Langmuir technique. Silk fibroin, regenerated from Bombvx mori cocoons, formed stable monolayers evident from pressure/area isotherms. Multilayers of the silk fibroin monolayers were deposited on a number of substrates and characterized. Transmission Electron Microscopy (TEM) and ellipsometry data provide basic information about the physical characteristics of the monolayer. Preliminary analysis of electron diffraction data of the monolayer indicate polycrystalline structure, consistent with the known structure of silk. Infrared spectrometric analysis of the monolayer using Attenuated Total Reflectance (ATR) gave wavenumbers for Amide I, II, III and V bands which compare with the silk II conformation reported for cast silk membranes.

Phycobiliproteins form highly efficient light absorbing systems in certain algae. We have investigated the charge-transport phenomena in these proteins by analyzing the dark current-voltage and photocurrent characteristics obtained across Au-phycobiliprotein-Au samples. A photovoltaic effect was observed for Au-phycoerythrin-Au sample. At low intensity levels, the photocurrent closely follows Onsager's law of geminate recombination in three dimensions.

Molecular simulations that predict the molecular mechanical response of alpha-helical biopolymers with a reinforcing intra-molecular hydrogen bonding network, viz,, a ‘spring-like’ behavior, are presented in this study. Mechanical properties of extended biopolymer strands based on naturally occurring amino acids, namely poly(L-A1a) and for comparison poly(LGlu), versus synthetic PPTA containing an amide bond, are compared to those assuming alpha-helical structures. Thus, the pivotal role of such motifs in biological systems utilizing superior compressive mechanical properties can be inferred.

We have expressed in E. coli a series of periodic polypeptides represented by sequence 1. Our objective has been an understanding of the role of chemical sequence in determining the chain folding behavior of periodic macromolecules. Molecular organization has been examined by infrared spectroscopy and 1H and 13C NMR methods and a preliminary model of the folded structure has been developed.

A variety of natural silk secretions (from spiders, silkworms and aquatic insect larvae), and also reconstituted silk solutions, are able to form a nematic liquid crystalline phase. The anisotropic structures that self-assemble in this phase are formed from the isotropic phase by aggregation of molecules, rather than by individual molecules undergoing a conformational change to a rod-like form. This enables the molecules to retain their solubility in water while, simultaneously, the viscosity of the solution is reduced. The liquid crystalline phase is stable under a wide range of equilibrium conditions, but its ability to form is sensitive to the rate at which the initially isotropic solution is allowed to dry. The kinetics of phase transitions exhibited by solutions of silk proteins must be taken into account if solutions of silk fibroin are to be successfully processed in vitro.

Avian eggshells are one of the most rapidly calcifying systems known. Although the entire shell contains ∼ 97 weight % CaCO3, etching in EDTA reveals great spatial variability in etching rate. A correlation between the etching rate of various regions and the relative positions of the different parts in the calcium reserve assembly (CRA) has been made; the CRA is the source of calcium during natural decalcification by chick embryos.

We studied the microstructures of hydroxyapatite (HA) ceramics which were sintered under three different conditions. It was found that all the ceramics were of sub-micrometer structure. The synthetic HA ceramics were also compared with human enamel. It is concluded that human enamel has higher strength because of its unique microstructure.

Crazing and shear-deformation phenomena are found in thin gelatin films. The gelatin crystallinity and relative humidity affect these deformation mechanisms significantly. A deformation map of gelatin films at low strain rate is established.

Thin films of organic molecules, such as Langmuir monolayers and freely suspended smectic films, can exhibit a spontaneous breaking of chiral symmetry. This chiral symmetry breaking can occur through at least three possible mechanisms: (1) the relation between tilt order and bond-orientational order in a tilted hexatic phase, (2) a special packing of non-chiral molecules on a two-dimensional surface, and (3) phase separation of a racemic mixture. Because the chiral order parameter is coupled to variations in the direction of molecular tilt, chiral symmetry breaking leads to the formation of patterns in the tilt direction with one-dimensional or two-dimensional order. Using a Landau theory, we investigate these patterns and predict the critical behavior near the chiral symmetry breaking transition.

α-Hemolysin (αHL) is secreted by the bacterium Staphylococcus aureus as a watersoluble polypeptide of 293 amino acid residues. When presented with lipid bilayers or the detergent deoxycholate (DOC), aHL assembles into hexameric cylindrical pores that each contain one channel ∼ 1 to 2 nm in Internal diameter. A long-term goal of this laboratory is to use wild-type or re-engineered αHL pores as components of nanoscale materials: for example, to confer novel permeability properties upon thin films. The implementation of this concept would be facilitated by a better understanding of the mechanism by which the pore assembles. Reviewed here are findings that have given us insight Into the assembly mechanism, including the results of recent mutagenesis experiments. A critical summary is given of knowledge about the conformation of the monomer In solution, the hexamerIc pore and two proposed intermediates in assembly (a membrane-bound monomer and an oligomeric pore precursor). Future directions are outlined Including the prospects of obtaining three-dimensional structural data on the αHL pore or its precursors, methods for obtaining better monolayer sheets and new experiments on the topography of the pore and its precursors. The role of membrane receptors in facilitating the assembly of αHL is also discussed. Finally, it is demonstrated that despite our rather rudimentary knowledge of the assembly process, the Information gained so far still allows the design of mutant (αHL polypeptides with useful properties. For example, αHL mutants whose pore-forming ability is activated by proteases have been made.

The origins, syntheses, variable composition and physical properties of bioelastic materials are discussed. The latter includes their capacity to undergo inverse temperature transitions to increased order on raising the temperature and to be designable to interconvert free energies involving the intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential and light.

Bioelastic materials include analogues and other chemical variations of the viscoelastic polypeptide, poly(Val-Pro-Gly-Val-Gly), and cross-linked elastomeric matrices thereof. This parent material has been shown to be remarkably biocompatible; it can be minimally modified to vary the rate of hydrolytic breakdown; it can contain enzymatically reactive sites; and it can have cell attachment sites included which promote excellent cell adhesion, spreading and growth to confluence.

One specific application is in the prevention of postoperative adhesion. There are some 30,000,000 per year surgical procedures in this country and a large portion of these would benefit if a suitable material were available for preventing adhesions. Bioelastic materials have been tested in a contaminated peritoneal model, and promising preliminary studies have been carried out in the rabbit eye model for strabismus surgery. In the peritoneal model, 90% of the 29 control animals exhibited significant adhesions; whereas, only 20% of the 29 animals using gas sterilized matrices had significant adhesions. On the basis of this data, it appears that cross-linked poly(VPGVG) is an effective physical barrier to adhesion formation in a trauma model with resulting hemorrhage and contamination.

The potential use of bioelastic materials as a pericardial substitute following the more than 400,000 open heart surgeries per year in the U.S. is under development beginning with the use of bioelastic matrices to prevent adhesions to the total artificial heart being used as a bridge to heart transplantation such that the site will be less compromised when receiving the donor heart.

We have evaluated the physical properties and animal efficacy of a hyaluronic acid (HA) based bioresorbable membrane for the prevention of post-surgical adhesions. Test methods were developed to measure the dry and wet tensile properties and ia Xilm tissue adhesiveness of the membranes. The thin membranes were found to have sufficient strength and flexibility in the dry state for surgical handling. When hydrated in buffered saline, the membranes became weaker and more elastic. The membranes exhibited a high degree of tissue adhesiveness and significantly reduced adhesion formation in a rat cecal abrasion model.

A new type of composite biomaterial was developed and is described in this paper. The composite is based on a high strength Al2O3 ceramic substrate, sintered with a layer of hydroxyapatite. The layer was examined by x-ray diffraction and infrared spectroscopy. Animal experiment showed that the composite has good biocompatibility, and can form tight osteointegration with bone in 12 weeks. It is a bioactive material with a high strength.

Polyanionic proteins isolated from biominerals serve as models for the development of biodegradable surface-reactive commercial polymers. A simple model for the natural polyanions is polyaspartic acid. This polymer may be made on a large scale using thermal polymerization of dry aspartic acid. The immediate result of the reaction is polysuccinimide which is hydrolyzed with base to form the polypeptide. The overall process yields up to 99% conversion of aspartic acid to polyaspartate. The thermal polyaspartate (TPA) is a copolymer having 70% of the amide bonds formed from β-carboxyl groups and 30% from α-carboxyl groups. TPA is as effective as the commercial polyanion polyacrylate in mineral dispersion and growth inhibition assays. Biodegradation of the TPA has been established using standard BOD and CO2 evolution assays. In contrast, polyacrylates appear to be non-degradable. Modifications of the TPA have been made by reacting the succinimide with nucleophiles. Crosslinking of the polymer has been achieved, a process which results in absorbent gels. Because TPA can be produced in large scale, has similar activity to polyacrylate and is biodegradable, it seems a likely candidate for use in numerous applications in which non-degradable polyanions are employed. These applications include use as detergent additives, water treatment chemicals, dispersants for the paint and paper industry and as superabsorbents in health and sanitary products.