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Biomedical subjects

L L Hench

Publications and source records attributed to L L Hench.

At least 19 recordsLinked to original sources
PubMed1995

Structural evaluation of human and sheep bone and comparison with synthetic hydroxyapatite by FT-Raman spectroscopy.

The composition of whole human and sheep cortical bone tissue, and of a synthetic hydroxyapatite (P120), were compared using Fourier transform Raman (FT-Raman) spectroscopy. Deproteination procedures to remove the bulk of the collagen present in bone tissue allowed isolation of the mineral phase. A comparison of the spectra obtained from both whole and deproteinated bone with those of synthetic hydroxyapatite showed direct correlation only in the region of 952 cm-1 (symmetric P-O mode). In contrast, human and sheep bone were very closely matched in both, the organic and inorganic structures. The results demonstrate that deproteination of bone is not a necessary precursor to obtain spectral information.

Animals↗
PubMed1994

AM-1 molecular orbital calculations of silica-alanine-nitrogen interaction.

Chemical binding of proteins with bioactive surfaces is modeled using a semi-empirical molecular orbital theory (AM-1). The model calculates the optimized molecular structures of an amino acid (L-alanine) interacting with a cyclotetrasiloxane silica cluster (a four-membered hydrated silica ring). The calculated heats of formation for various orientations of alanine show +5 kcal/mol difference for binding via the -NH2 group following a condensation reaction with a pentacoordinate Si intermediate. Hydrogen bonding of the alanine via the -COOH group occurs with +13 to +15 kcal/mole differences in heats of formation and imposes a highly specific geometric orientation on the amino acid. Association of a diatomic N2 molecule with the silica cluster before interaction with alanine inhibits formation of an intermolecular bond, as is observed experimentally in studies of silica-alanine epitaxy.

Alanine↗
PubMed1994

Calcium phosphate formation on sol-gel-derived bioactive glasses in vitro.

When soluble salts are used in the sol-gel processing of bioactive glasses, the resulting materials are not homogeneous. To produce homogeneous gel-glasses, a sol-gel method using all alkoxide precursors was developed. In this work the in vitro bioactivity of the new all-alkoxide gel-glasses is investigated. Three compositions in the system, CaO-P2O5-SiO2, were studied. Solid samples were soaked in Tris buffer and simulated body fluid (SBF), and the rate of formation of hydroxy carbonate apatite (HCA) on the surface of the glasses was measured by Fourier transform infrared spectroscopy. The solutions were analyzed before and after reaction by inductively coupled plasma. All compositions studied formed a hydroxy carbonate apatite (HCA) layer within 8 h in both test solutions. The HCA layer grew rapidly when SBF was used.

Apatites↗
PubMed1994

Analysis of surface layers on bioactive glasses.

FT-Raman spectroscopy proves to be a powerful technique to study surface reactions on bioactive glasses and it eliminates the fluorescence of the organic phase of whole bone, thereby making it possible to compare the reaction layers formed on bioactive glasses with the mineral phase of bone. The spectrum of hydroxycarbonate apatite (HCA) developed on the bioactive glasses is closer to that of bone than synthetic hydroxyapatite (HA) and closely matches that of bone mineral obtained by deproteination of whole human femoral cortical bone.

Apatites↗
PubMed1993

Solution effects on the surface reactions of a bioactive glass.

The in vitro surface reactions of a 45S5 bioactive glass in three simulated body fluids (SBF) are analyzed using Fourier transform infrared (FTIR) spectroscopy. Five reaction stages are observed. Calcium and phosphate ions in SBF accelerate to a small extent the repolymerization of silica (Stage 3) and formation of an amorphous calcium-phosphate (a-CP) layer (Stage 4) on the glass surface. The a-CaP layer is crystallized to form hydroxy-carbonate apatite (HCAp) (Stage 5) more rapidly in the Ca- and P-containing SBF solutions (in 90 min rather than 120 min). However, Mg ions in SBF slow down formation of the a-CaP layer and greatly retard crystallization of HCAp on the glass surface.

Biocompatible Materials↗
PubMed1993

Solution effects on the surface reactions of three bioactive glass compositions.

The in vitro five-stage surface reactions of two bioactive glass compositions, 45S5 and 52S4.6, and one bioinert glass, 60S3.8, exposed to three simulated body fluids (SBF) were analyzed using Fourier Transform infrared Spectroscopy (FTIR). There was little effect of SBF composition on ion exchange, silica hydrolysis, and silica polymerization (stages 1-3) of glass with silica content up to 52 wt%. However, calcium and phosphate ions in SBF accelerated the formation of an amorphous calcium-phosphate (a-CP) layer (stage 4), and crystallization (stage 5) of the hydroxycarbonate apatite (HCAp) layer. The magnesium ions had a retardation effect on the kinetics of stages 4 and 5, but little effect on stages 1-3. In SBF solutions which contained calcium and phosphate ions an amorphous calcium-phosphate (a-CaP) layer formed on even a 60S3.8 glass which was not bioactive in vivo. However, the a-CaP layer did not crystallize to form HCAp. Thus, there is a significant contribution from the ions present in the SBF solutions to the HCAP formation and crystallization of HCAp on bioactive glasses. Also, silanol repolymerization is necessary for rapid crystallization of HCAp.

Apatites↗
PubMed1993

Tissue response to Bioglass endosseous ridge maintenance implants.

Conical devices placed in the alveolar ridge after tooth extraction have been used clinically for several years to maintain the ridge morphology. In this way, the bone atrophy which occurs after extractions is minimized, and denture fit and function are enhanced. A system using such cones made from Bioglass (registered trademark of the University of Florida) and matching burs has been developed and tested clinically. Average four-year data show a retention rate of over 90%, which compares favorably with other systems using other materials (see Hench et al., 1991). Stanley et al. (to be published), in a review of the four-year clinical data, point out that a few of the cones, although firmly positioned within the alveolar ridge, have a radiolucent zone around the implant. In a clinical study, it is not possible to determine whether this radiolucent zone represents areas of fibrous capsule which are not attached to the implant and therefore compromise its long-term stability, or whether the soft tissue is adherent to the implant and thus contributes to its long-term stability. In a recent study, conical implants identical to those in the clinical trial were placed in the alveolar ridges of dogs and evaluated for up to two years. The adhesion of bone and soft tissue was measured and the development and stabilization of the reactive gel layer monitored. The findings in this animal study support the clinical observations and contribute to an explanation of the success of the Bioglass system in patients.

Alveolar Bone Loss↗
PubMed1992

Compositional dependence of calcium phosphate layer formation in fluoride Bioglasses.

Bioglasses form a double layer composed of apatite and a silica-rich layer when placed in a simulated physiological solution as well as in living tissue [A.E. Clark, C.G. Pantano, and L. L. Hench, "Auger spectroscopic analysis of bioglass corrosion films," J. Am. Ceram. Soc., 59(1-2), 37-39 (1976).]. In the present work, the mechanisms of the calcium phosphate layer and the silica-rich layer formation of fluoride Bioglasses in Tris-buffer solution are studied as a function of the SiO2 content. Fourier Transform Infrared Reflection Spectroscopy (FTIRS) is used to investigate the mechanism of formation of calcium phosphate and silica-rich layers on the glass surface. Ion concentration in reacted solution and elemental depth profiles are obtained by Induced Coupled Plasma Atomic Emission Spectrometry (ICP) and Auger Electron Spectroscopy (AES), respectively. Si--O bonds with one nonbridging oxygen and Si--O--Si bonds form at the early stage of reaction. Strong phosphorus ion uptake occurs when an amorphous calcium phosphate layer crystallizes. Glasses with high silica content (conventional glass) form the silica-rich layer first followed by a calcium phosphate layer on top. However, glasses with low silica content (invert glass) form both layers simultaneously. The rate of apatite formation decreases with increasing SiO2 content, especially in the region of conventional glass compositions. Ion release rates decreases as SiO2 content increases, with a significant change occurring at the compositional boundary between invert and conventional glasses.

Biocompatible Materials↗
PubMed1989

Bioceramics and the origin of life.

Creation of life involves establishing an organism that is capable of self-maintenance, self-reproduction, and adjustment to a changing environment. A Bioactive Substrate Theory of the origin of life is proposed, where the function of the bioactive substrates was to achieve the irreversible ordering of macromolecules into replicative structures. The ordering was a result of six precytic ordering factors which provide the mechanisms for simultaneous formation of primitive codonic-bases, anabolic processes and energy-producing, catabolic processes on bioactive inorganic glassy crystalline assemblages. Time dependent changes in the isoelectric point of the inorganic assemblages enabled the anabolic and catabolic processes to be isolated within the same bilipid membrane. The enormous diversity of inorganic glass-crystal assemblages associated with volcanic activity resulted in many alternative evolutionary pathways for the precytic structures, eventually producing the major genetic pathways for life observed today. The evidence for bioactive ordering factors is examined including selective adsorption of optically active amino acids on optically active mineral substrates and specific cellular responses to bioactive implant materials. The implications of this theory on the biochemical design of implants, and prevention of disease states in modern man are discussed.

Biocompatible Materials↗
PubMed1989

An investigation of Bioglass powders: quality assurance test procedure and test criteria.

Bioglass, in bulk form, has been used to bond to the body's hard and soft tissues in many surgical and dental applications over the past 18 years. There is also a large potential use of Bioglass, in powder or paste from, to fill irregular-shaped bony defects caused by local or systemic disease, congenital malformations, or trauma in the fields of otolaryngology and dental sciences. A quality assurance test procedure to analyze powdered Bioglass to guarantee that the bioactivity of the glass has been maintained during manufacturing was developed. Herein states the quality assurance test procedure, test variables, and test criteria to assure the bioactivity of Bioglass powders made from known bioactive bulk Bioglass samples. Also described herein is the path taken to develop the test procedure and test criteria and experiments performed to study the test variables.

Bone Cements↗
PubMed1986

Biocompatibility of silicates for medical use.

Implantation of commercial silicate glasses in soft or hard tissue will produce a thick non-adherent capsule consisting of scar tissue. However, special compositions of bioactive silicate glasses and crystallized glass-ceramics bond to bone and soft tissue without such a capsule. Bonding is via ion exchange and formation of active surface layers which incorporate collagen and bone mineral. These bioactive silicates have been studied in vivo and in vitro and the cellular response appears to depend on total cell surface nectin concentrations as well as on specific nectins and cellular proteins which may be silicon-sensitive. Simple amino acids polymerize and adhere strongly and randomly to binding sites on the bioactive surfaces, in contrast to their epitaxial behaviour on crystalline quartz. Toxicity tests in vivo and in vitro on powders and on solid forms show no adverse effects associated with bioactive silicates, in contrast with the marked toxicity of crystalline quartz. The bioactivity of the bioactive silicates may be destroyed by addition of small quantities of multivalent ions. The bioactive materials are currently in clinical use and being tested preclinically for a variety of surgical and dental applications.

Animals↗
PubMed1986

The bonding of Bioglass to a cobalt-chromium surgical implant alloy.

A biocompatible composite implant system was developed by coating Bioglass onto cobalt-chromium alloy substrates. Strong bonding between glass and metal was obtained by immersion of preoxidized implants into molten Bioglass under controlled conditions. The thin, adherent Bioglass coating provides the capability of bonding directly to bone, while the underlying metal substrate gives the composite implants sufficient strength to be used in load bearing applications.

Biocompatible Materials↗
PubMed1984

Surface-active biomaterials.

Since the discovery in 1969 of a man-made surface-active material that would bond to bone, a range of materials with the same ability has been developed. These include glass, glass-ceramic, and ceramic materials which have a range of reaction rates and from which it should be possible to select a surface-active material for a specific application. The available materials and their similarities, differences, and current clinical applications are reviewed.

Animals↗
PubMed1983

Bioglass composites: a potential material for dental application.

Bioglass, a promising material for dental applications, can be reinforced with ductile stainless steel fibres. Three aspects of the fibre-reinforced bioglass composites are discussed. They are the interface between the glass and the metal fibres, the mechanical properties of the composites and their in vivo bonding behaviour. The importance of a good interfacial bond between the glass and the metal fibres is outlined. The improvement in strength and toughness, due to the fibres, is explained. The in vivo bonding behaviour of the bioglass composite is checked under statically loaded conditions.

Animals↗
PubMed1982

Effect of fibronectin on the adhesion of an established cell line to a surface reactive biomaterial.

We have demonstrated that an established hamster cell line (NIL 8 M-2) will adhere to the bioceramic bioglass. The rate at which the NIL 8 M-2 cells assume a spread morphology on bioglass is density dependent and the morphology displayed by NIL 8 M-2 cells attached to bioglass is much more elongated than that displayed by NIL 8 M-2 cells attached to nonreactive glass. Precoating the bioglass with the plasma form of human fibronectin significantly reduces the density dependent nature of cell spreading. Coating the bioglass with fibronectin also reduces the time required for cell spreading and changes the morphology of the attached cells from an elongated to an extremely flattened shape. Our work raises the possibility that bone-implant adhesion might be improved by introducing molecules relevant to cell-substrate attachment into the biomaterial prior to implantation.

Animals↗