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Biomedical subjects

L L Hench

Publications and source records attributed to L L Hench.

15 recordsLinked to original sources
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↗
PubMed1979

Use of fracture mechanics theory in lifetime predictions for alumina and bioglass-coated alumina.

The fatigue behavior of alumina and bioglass-coated alumina was determined in air and biological test environments by the dynamic fatigue test technique in which strength is measured as a function of stressing rate. The good correlation found between the test data and fracture mechanics theory indicates that fatigue failure is controlled by the slow crack growth of preexisting flaws and that fracture mechanics theory can be used in making failure predictions for alumina and bioglass-coated alumina in biological environments. Thus, it is believed that lifetime predictions can be made for ceramic implants on the basis of short-term test data utilizing fracture mechanics principles.

Aluminum↗
PubMed1979

Short term bonding behaviour of bioglass coatings on metal substrate.

Bioglass specimens were implanted in 11 dogs for periods ranging between two and twelve weeks in order to study the short term bonding behaviour of bioglass coated on metal. Metal fibre porous coated specimens without bone growth inducive microlayer were implanted as controls. The conclusions reached pertain to the validity of push out test results, bioglass short term bonding and the effect of the dipping procedure to coat bioglass on metal: 1. It is impossible to compare the bonding effectiveness of bonding materials tested under slightly differing circumstances, and a fortiori at different laboratories, 2. there is no sufficient evidence to establish a difference in bone bonding strength with regard to trabecular bone of bioglass and metal fibre porous coated specimens at 2 and 4 weeks; at 12 weeks, however, a higher interfacial failure shear strength is obtained with the control porous specimens, 3. bone bonding may be hampered by compositional differences arising as a result of the processing of a bioglass on metal coating. Technologically it is, however, possible to exclude this problem.

Animals↗
PubMed1979

Future developments and applications of biomaterials: an overview.

It is recommended that the emphasis of biomaterials research and development for the future should be to achieve improved reliability. Use of increasing numbers of implants per year coupled with decreasing long term (greater than 5 years) success rates are resulting in progressively larger numbers of reparative implant operations. This trend can be altered by emphasizing three areas of R&D: 1) Studies of composite biomaterial systems offering unique combinations of biological surface behavior and substrate mechanical performance; 2) Investigate mechanisms of interfacial reactions so that long term responses of the host-implant can be predicted; 3) Develop long term predictive relationships for biomaterials reliability based upon interfacial reactions, biomechanics, fracture mechanics, fatigue testing, and retrieval analysis. Brief examples of efforts to develop undrestanding in these three areas are described using bioglass coated metal and bioglass coated alumina implants.

Alloys↗
PubMed1977

Analysis of bioglass fixation of hip prostheses.

The analysis of the bonding interface between hip prostheses and bone after functional use in animals was carried out. Scanning electron microscopy (SEM) with energy dispersive analysis (EDX), and Auger electron spectroscopy were used to evaluate the bonding interface. Various methods of postsacrifice sample preparation were used to evaluate the effect of such different methods on the analysis of the bonding interface. Comparison of the results with several rat tibia implant experiments is also presented.

Aluminum↗
PubMed1977

An in vitro and in vivo analysis of anodized tantalum capacitive electrodes: corrosion response, physiology, and histology.

Oxidation-reduction reactions which can destroy high current-density metal-stimulating electrodes are avoided when using capacitive electrodes. The results of in vitro and in vivo testing of anodized, high surface area, sintered tantalum electrodes are presented. The corrosion response of the electrodes is excellent; there is no evidence of dissolution of the electrode. A deposit forms on the surface of the electrodes, but has little effect on the voltage response to constant current stimulation. The physiological and histopathological results indicate the capacitive tantalum electrode to be the safest yet tested.

Animals↗
PubMed1977

An in vitro analysis of metal electrodes for use in the neural environment.

The results of evaluation of the corrosion response of Pt, Au, Rh, Ir, Pt-10% Ir and Pt-10% Rh electrodes subjected to bipolar current pulses of 0.1 and 1.0 A/geom. cm2 in a simulated neural environment are reported. The criteria for evaluation include the extent and morphology of material removal and corrosion product formation. The chemical changes on the electrode surface and in the test electrolyte are also evaluated. Modified potentiographic methods were developed which monitor interface conditions of the electrodes during chronic, long-term biphasic current passage. Under the test conditions established by the neural model, evaluation of the corrosion response of the candidate electrode materials shows that Rh was moderately damaged at 1.0 A/geom. cm2, while the remaining test electrodes were severely damaged at this current density. While Rh, Ir and Au exhibit corrosion resistance at 0.1 A/geom. cm2, damage to all of the test materials preclude their use in any long-term chronic neural prosthetic implant under the simulated stimulation parameters of the tests. The relative corrosion resistance of the test electrode materials is related to the adherence and coherence of the corrosion product produced on the electrode surface during the first few hundred hours of stimulation. Analysis of the voltage response of the electrodes to current passage provides a means of monitoring the nucleation and growth of the corrosion product.

Corrosion↗
PubMed1977

Cortical histopathology following stimulation with metallic and carbon electrodes.

Stimulation of the cat striate cortex with polished 1 mm2 gold, platinum, rhodium or carbon electrodes for 40h, at 50 Hz, and 0.5 msec duration, results in tissue damage at current densities of 0.6 A/cm2. At 0.1 A/cm2 rhodium and carbon were toxic to brain. In vitro gold and platinum corroded after 1,500-2,300 h of testing in simulated cerebrospinal fluid. The materials utilized are not suitable for long-term chronic electrodes for neural prosthetics.

Animals↗
PubMed1976

The influence of surface chemistry on implant interface histology: a theoretical basis for implant materials selection.

A theory is proposed stating that an ideal implant material must have a dynamic surface chemistry that induces histological changes at the implant interface which would normally occur if the implant were not present. Evidence for the validity of this theory is provided with a series of bone-implant studies which result in stable interfacial osteogenesis under specific implant surface chemistry conditions. Insufficient or excess surface ion concentrations produce negative osteogenesis and fixation results. Implantation of osteogenic implants in soft tissues also produces undesirable histological responses as proposed in the theory. A variety of surface chemical analyses of the implant are reviewed which provide a scientific basis for the implant surface theory.

Animals↗
PubMed1976

Chemical and mechanical behavior of bioglass-coated alumina.

This work has shown that it is possible to produce a bioglass-coated, high-strength, fully dense alumina implant system with a variable surface reactivity. Furthermore, it has been demonstrated that this system will bond with bone. These two factors, plus the inherent strength of the dense alumina, make this system an attractive candidate as a new prosthetic material.

Aluminum↗
PubMed1976

Evaluation of a bioglass-coated Al2O3 total hip prosthesis in sheep.

A bioglass-coated fully dense alumina total hip was evaluated in sheep without using polymer bone "cement." After 3 months following surgery, both the acetabular cup and femoral stem component were firmly attached to bone. Histologic and radiographic analysis of the bone-implant interface showed regions of woven and even lamellar bone formation where high load transmission occurred. In regions of low loading or poor fit, a pseudosynovial fibrous lining was present.

Acetabulum↗
PubMed1976

An in vitro model for evaluating neural stimulating electrodes.

A model for in vitro evaluation of materials for use as neural stimulation electrodes is developed. Critical areas of concern in developing an in vitro test model discussed include: selection of environment, choice of material, design of stimulating equipment, and analytical procedures used to evaluate materials response. A method of providing quantitative analysis of materials response to stimulation conditions is presented. Evaluation techniques involve the use of scanning electron microscopy, x-ray spectroscopy, atomic absorption spectrometry, and potentiographic and dielectric analysis of the test electrodes. A diagnostics matrix is presented which assigns a scale factor to quantify the relative corrosion response of the candidate materials. The corrosion response of Pt electrodes is evaluated in terms of scale factors assigned through use of the diagnostics matrix.

Corrosion↗
PubMed1975

Mechanical studies of the bone bioglass interfacial bond.

A series of squirrel monkeys received segmental femoral replacements in a study of the strength of the interface developed between the implant and bone. Implants were either made completely of bioglass-ceramic, or 316L stainless steel with a flame-sprayed coating of bioglass. Fracture torque, energy at fracture, and shear stress at failure were compared to values obtained from a control group of pairs of tibias. Femurs containing bulk bioglass-ceramic implants showed about a 25% difference in strength compared to the opposite bone, while femurs containing flame-sprayed implants exhibited extremely low structural strength. While the strength of the metal-glass bond was very low (less than 500 kgf/cm2), the bone-bioglass bond was found to be at least as strong as the bioglass-ceramic, and at least 3/4 as strong as the host bone.

Animals↗