Biomedical subjects
Publications and source records attributed to Larry L Hench.
Whereas second-generation biomaterials were designed to be either resorbable or bioactive, the next generation of biomaterials is combining these two properties, with the aim of developing materials that, once implanted, will help the body heal itself.
Bioactive glasses are known to have the ability to regenerate bone, but their use has been restricted mainly to powder, granules, or small monoliths. This work reports on the development of sol-gel foams with potential applications as bone graft implants or as templates for the in vitro synthesis of bone tissue for transplantation. These bioactive foams exhibit a hierarchical structure with interconnected macropores (10-500 microm) and a mesoporous framework typical of gel-glasses (pores of 2-50 nm). The macroporous matrixes were produced through a novel route that comprises foaming of sol-gel systems. Three glass systems were tested to verify the applicability of this manufacturing route, namely SiO(2), SiO(2)-CaO, and SiO(2)-CaO-P(2)O(5). This new class of material combines large pores to support vascularization and 3-D tissue growth with the ability that bioactive materials have to provide bone-bonding and controlled release of ionic biologic stimuli to promote bone cell proliferation by gene activation.
Although the denaturing of adsorbed proteins on biomaterials surfaces is believed to lead to adverse tissue reactions to implanted materials, very little is currently known of the actual mechanisms involved. These mechanisms must be understood if surfaces are to be proactively designed to control protein adsorption behavior. Concepts widely employed in rational drug design and in protein and RNA folding predictions provide a means to approach this problem. Accordingly, a theoretical analysis has been conducted to estimate the thermodynamic contributions (changes in enthalpy, entropy, and Gibbs free energy) for the adsorption of selected individual mid-chain protein residues to functionalized surfaces. Enthalpic contributions from residue-surface interactions were calculated using semi-empirical quantum mechanical-based computational chemistry methods in a simulated aqueous environment (MOPAC/COSMO), and enthalpic and entropic contributions due to water restructuring effects assumed to occur during adsorption were estimated from experimental data for functional group wetting and calculated changes in solvent accessible surface area as each protein residue approached each surface. When combined with intraprotein residue-residue interactions, the understanding of residue-surface adsorption energy relationships provides a means to begin to predict protein adsorption behavior as a function of biomaterials surface chemistry. It is recognized that several assumptions have been made in this approach that could be challenged, and that truncations necessary due to programming limitations have been applied that may neglect potentially important interactions. Therefore, it must be understood that the modeling predictions may not be directly applicable to biomaterials for surface design under actual physiologic conditions at this stage. However, this attempt at modeling fundamental components of protein adsorption is presented as an initial approach to understanding these complex events.
Bioactive glass has found extensive application as an orthopedic and dental graft material and most recently also as a tissue engineering scaffold. Here we report an initial investigation of the in vitro antibacterial properties of AgBG, a novel bioactive glass composition doped with Ag(2)O. The bacteriostatic and bactericidal properties of this new material and of two other bioactive glass compositions, 45S5 Bioglass and BG, have been studied by using Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus as test microorganisms. Concentrations of AgBG in the range of 0.05 to 0.20 mg of AgBG per ml of culture medium were found to inhibit the growth of these bacteria. Not only was AgBG bacteriostatic, but it also elicited a rapid bactericidal action. A complete bactericidal effect was elicited within the first hours of incubation at AgBG concentrations of 10 mg ml(-1). 45S5 Bioglass and BG had no effect on bacterial growth or viability. The antibacterial action of AgBG is attributed exclusively to the leaching of Ag(+) ions from the glass matrix. Analytical measurements rule out any contribution to AgBG-mediated bacterial killing by changes in pH or ionic strength or the dissolution of other ionic species from the biomaterials. Our observations of the dissolution profiles of Ag(+) from AgBG in the presence and absence of bacteria are consistent with silver accumulation by the bacteria.