Sprague-Dawley albino male rats (25) were divided into five groups consisting of five rats each. Polymer (polylactic acid) impregnated ALCAP capsules filled with 40 mg DFMO were implanted subcutaneously (SC) or intraperitoneally (IP) in Group I and II rats respectively. Rats in Group III were implanted with empty polymer impregnated ALCAP capsules (ALCAP control). Group IV rats were administered orally 3% DFMO in drinking water. Rats in Group V served as controls. Blood samples were collected every week for nine weeks via the tail artery. The concentration of DFNO in the plasma was determined. Data obtained showed that the levels of DFMO in the serum of rats in groups I, I, and IV were 64.71 ±4.08. 219.18 ± 14.48, 16.71 ± 5.21 ug ml−1, respectively at the end of nine weeks. Body weights of the controls and DFMO treated rats were not significantly different (p<0.05). The diarrhea often noted in rats treated orally with DFHO was not observed in rats implanted with ALCAP or ALCAP capsules filled with DFMO. The results of this study suggest that: (1) polymer impregnated ALCAP ceramic implants can be used to deliver DFMO in vivo in a sustained manner for long durations of time, and (2) a ceramic system can be designed to deliver DFNO and drugs such as DFMO in a sustained manner over long durations of time in humans.

Hydroxyapatite (HAp) fine powders dispersed with zirconia were prepared by hydrothermal techniques at 200°C, under 2 MPa for 10 h. The transmission electron microscopy (TEM) showed the homogeneous mixtures of HAp and zirconia.The HAp powders were stoichiometric fine single crystals of about 90 nm × 25 nm in size and the zirconia powders were also fine single crystals of about 10 nm in size. The reactivity between HAp and zirconia was examined. According to the X-ray diffractometry (XRD), decomposition of HAp to B-tricalcium phosphate (β-TCP) was observed above 800°C then β-TCP was transformed into α-TCP at about 1200°C.

Epoxy resins have physical properties that make them suitable for dental and orthopaedic applications such as adhesives and cements. However, it has been observed that epoxy resins harden too slowly for clinical use when mixed with conventional curing agents, e.g. amines and polyamides. A new epoxy - diepisulfide - polyamide system has been developed which gels in 5 to 20 minutes at room temperature. The system consists of two parts: a polyamide curing agent, and a blend of the diepisulfide analog of diglycidyl ether of bisphenol A [DGEBA] dissolved in a mixture of epoxies of the DGEBA type.

Hyaluronic acid is a high molecular weight, linear polysaccharide composed of repeating subunits of glucuronic acid and N-acetylglucosamine. The structure is shown in figure 1. In vertebrates, the polymer is widely distributed through all connective tissue and has been implicated in cell-cell interaction, cell matrix adhesion, cell mobility and extracellular matrix organization (1,2). NaHA is an important tissue lubricant (3,4) and has been shown to exert a facilitating influence on wound repair (5).

Physio-chemical properties such as coefficients of friction between low energy surfaces (PMMA/PMMA), surface tension, contact angle and viscosity of various water soluble polymer solutions ( 3–62cp) were measured at ambient temperature. The results showed that the surface tension and the contact angle are independent of viscosity of each polymer. The analysis of the data revealed that the system is operating in a region of “Boundary Lubrication”. It is seen, beyond 30 cp viscosity of almost all polymer solutions, the coefficient friction has been found to be independent of viscosity.

Polyvinyl alcohol appears to have better lubricity in the vicinity of 30 cp viscosity or lower values than the cellulose derivatives and dextran. Hydrophobic interaction between PMMA surface and vinyl backbone may be responsible for this observation.

It appears that the coefficient of friction of these polymer solutions depends on the structure, conformation and adsorption characteristics of polymers as well as surface characteristics of sliding surfaces, load, speed and viscosity.

A review of the literature of the past twenty years on the measurements of fracture properties of compact bone, including measurements of critical stress intensity factors, critical strain energy release rates, measurements of “surface free energies” by impact tests, work of fracture tests and other methods, with an emphasis on the relation of fracture measurements to microstructure is presented. Recent results from the author's laboratory on the relation of work of fracture measurements to specimen size and microstructure are presented.

The cells in living bone – osteocytes, osteoblasts and osteoclasts – are embedded in a porous material consisting of an organic-inorganic composite solid containing a distribution of fixed charges, permeated by ionic fluids flowing through a complex network of channels. In the weight-bearing long bones of the body, the largest of these channels are up to a few hundred microns in diameter and contain blood vessels which are connected to the blood supply in the central canal of the long bones. These channels establish fluid connectivity with the cells (osteocytes) responsible for maintenance of the bone tissue through small canals (canaliculi) with diameters ranging down to a tenth of a micron. Outside the blood vessels, perivascular fluid permeates these channels. The solid matrix is itself porous with a high degree of composite material organization beginning at the macromolecular level. The internal connectivity of the pore fraction of the solid, which is not as extensive as the network of channels, and the connectivity of this pore fraction with the fluid channels may affect physiological functions, through its influence on mechanical, electrical and electromechanical properties of the extracellular matrix. It seems apparent that the structure and physical properties of the extracellular material of bone will largely determine the physicochemical environment of the cells. Thus, a materials characterization of the extracellular matrix of living bone has become an essential part of the efforts to advance our knowledge of bone physiology and pathology. This paper is a review of the present state of knowledge of the electrical and electromechanical properties of this material with emphasis on studies that appear to have the most physiological significance.

We have been involved in using several ultrasonic wave propagation techniques to study the relationship between the structure and the elastic properties of bone, both normal and pathological. Pulse through ultrasonic techniques have been used to measure the ultrasonic velocities in human, normal, osteoporotic and osteopetrotic femoral bones in vitro at 5 MHz and room temperature. An ultrasonic right-angle reflector technique has also been used on the same specimens at room temperature and 15 MHz (the third harmonic of a 5 MHz immersion type transducer). In addition, microhardness measurements have been made on the same bones from which the specimens for ultrasonic measurements were obtained.

When an implant is placed into bone, an interface is created. This interface has a critical biomechanical function: it must support the implant in bone. However, failure of implant fixation (i.e., implant “loosening”), continues to be a leading cause of implant failure [1,2]. While there are a number of factors involved in this problem, it is recognized that biomechanical factors play a role, and this paper reviews the more important factors, including relative motion and interfacial stresses and strains. Also, it presents results from a recent in vivo experiment on controlled loading of an interface.

Ultrasonic techniques have been used extensively to measure the anisotropic elastic properties of calcified tissue [1–4]. Yoon and Katz [3] have derived the equations relating the elastic constants to the technical moduli: Young's modulus, shear modulus, and the bulk modulus. In order to make these calculations they assumed that bone was transversely isotropic (hexagonally symmetric). Abendschein and Hyatt [1] demonstrated that there was a good correlation between the longitudinal modulus (E3) of bone experimentally measured with ultrasound and mechanical techniques. Some investigators have even used these techniques to determine the different mechanical properties of pathological bone (osteopetrotic, osteoporotic) [4].

The loss of bone mass and consequently bone strength in persons aged forty and beyond is a continuing problem to the orthopaedic community. This progressive loss has been documented by various means such as radiographs, autopsy materials, CAT scans, and single or dual photon absorptiometrv. Orthopaedic problems arising from osteoporosis include fractures of the lumbar spine, distal radius and the femoral neck. Likewise, this age group represents the fraction of the population that will require prosthetic replacement of a joint. Unfortunately, little information is available concerning the mechanical properties of osteoporotic bones and its interaction with prosthetic devices.

Predicting the stress state in bones is important to the understanding of bone remodeling and the long-term reliability of total joint implants. Beam theory, 2-D and 3-D finite element analysis have been used to calculate stress distributions. These finite element analyses of bone structures are progressing from crude models for which the clinical relevance has been questioned to an important tool which is necessary to understand stress related bone changes.

A recent development in fracture treatment is that of electrical stimulation to enhance healing. Since the fractured limb receiving treatment may have been inmmbilized or fixed with 316L stainless steel (SS) internal fixation devices, there is an interest in docu.menting how the electromagnetic field affects corrosion of this alloy. The stimulator under investigation produces an electrcnagnetic field having a 3.5 ± IMV pulse height delivered at 75 Hz within the treatment coils. Corrosion, as quantified by analyzing test solutions for Ni and Cr levels, was measured for specimens in and out of the stimulator field.

Three-week in vitro corrosion tests were conducted at 37°C in 0.9% NaCl adjusted to pH levels of 7.4 and 4.0. Specimen were 316L SS rods with surfaces finished to 600 grit. 0-rings were added to form crevices in order to accelerate corrosion. Stimulation was continuous for test specimens. An equal number (ten for each pH) of control specimens received no stimulation. A statistical comparison of the data reveals that at a 95% confidence level the stimulator field did not affect corrosion of the 316L SS.

There is a need for new materials which attach to bone. Attachment can occur through bioactive surfaces or porosity. The Replamineform process can be used to produce polymers, metals and ceramics with these properties. In this study, porous implants were manufactured in cobalt-chromemolybdenum (Co-Cr-Mo) vitreous carbon and silicone rubber. The pores were 200 pm in diameter and fully interconnected. The biocompatibility and osteoconduction of these materials was compared to porous hydroxyapatite (Interpore 200 HA). In 10 rabbits, blocks (2mm×3mm×5mm) of each material were implanted subperiosteally onto the femur, or rods (5mm D×10 L) were press-fit into unicortical defects of the proximal tibia. Explants were harvested at 1–6 months, sectioned midsagitally and embedded in plastic for histomorphometry using SEM or bright field microscopy. Bone grew up to and into all implants by two months. However, implants of porous Co-Cr-Mo, vitreous carbon and silicone rubber had less bone than implants of hydroxyapatite. Also, bone formed in direct apposition to hydroxyapatite, but secondly incorporated the other materials. Moreover, implants containing hydroxyapatite in the pores of the Co-Cr-Mo induced more complete and intimate bone ingrowth. This study demonstrates the potential for bone ingrowth and bonding into a range of biocompatible materials with interconnected porosity and the superior osteconduction of porous hydroxyapatite.

The application of metallic porous coatings on hip prostheses stems has increased the need for evaluating the interrelationship of implant design, material properties, and manufacturing process relative to component fatigue resistance.

In testing the PCA®(porous-coated anatomical) hip a three phase approach was followed comparing Vitallium® and Ti-6AI-4V alloys. Material and component fatigue tests were conducted, followed by in vitro stress analysis. The results of these studies are discussed.

The histopathologic characteristics of interface phenomena existing along the surfaces of intraosseous metallic implants has been the subject of much discussion in relating the composition and configuration of implant fixtures to maximal osteointegration. (1,2) The purpose of this study was to evaluate and characterize host bone changes to various types of intraosseous metal implants placed in the femurs of six Papio anubis baboons. We wished to evaluate changes in recipient site bone remodeling which could be related to the specifics of configuration and type of metal implant used.

Fracture of bone cement is considered to be a major factor contributing to total joint replacement failures because of implant loosening. While plane-strain fracture toughness (Klc) provides a parameter for assessing fracture resistance, the standard methods for testing (ASTM E399) require (1) the use of specimens greater than a certain minimum size (for bone cement this minimum size is greater than that found in clinical applications) and (2) fatigue precracking of specimens prior to testing. The short-rod fracture toughness test proposed by Barker offers a method of testing not requiring fatigue precracking and furthermore, it appears that a valid fracture toughness value can be determined using a modified miniature test specimen that we have proposed. Our mini short-rod specimen size approaches the actual dimensions of bone cement as used clinically. In this study mini short-rod fracture toughness test specimens were used to assess fracture toughness for two commercial brands of bone cement (Simplex-P and Zimmer LVC). An elastic-plastic fracture mechanics (EPFM) analysis was used to obtain experimental results with a plasticity correction factor being introduced. The cements were assessed as a function of method of preparation (hand mixed versus centrifuged) and aging conditions (3 days in air versus 7 days in distilled water at 37° C). The results indicated that (1) true fracture toughness values could be obtained only using an EPFM analysis for these specimens, (2) centrifugation did not significantly affect fracture toughness and (3) a significant difference in the plasticity correction factor due to water aging at 37° C was indicated for only the hand-mixed Zimmer LVC cement. There was, however, no significant change in fracture toughness due to water aging.

A brief review of the present consensus of the efficacy of two increasingly used oral biomaterials: castable ceramics and resin bonding agents is presented. The most challenging research problems will be discussed and current progress of the research in the areas reviewed. Some goals for future research will be suggested in light of the current research activity.

Due to the recently indicated causal relationship between the piezoelectric properties of teeth and the formation of root caries, a study was undertaken to further classify the dielectric properties of the actual tooth constituents. The properties considered are the real and imaginary components of the complex dielectric constant, including the electrical conductivity, for human teeth in vitro, both dry and saline solution saturated. The frequency range covered is from 1 Hz to 1.35 GHz. An attempt has been made to present the data for the two most prominent constituents, namely, enamel and dentin. Ways in which the dielectric properties can aid physiological studies and an understanding of the caries process are also described. Some possible explanations for the biological and physiological processes in the dielectric properties of tooth constituents are given. Pathological variations among teeth are noted. Some hypotheses for causal relationships between caries and electrical properties of natural dental constituents are proposed.

The load-bearing ability of dental restorative materials under cyclic high-stress applications depends upon mechanical properties established by the composition and microstructure. The microstructure and the elastic properties of neat resin and two resin-based glass-reinforced composites have been studied. The microstructure of these materials has been examined using x-ray diffractometry (XRD), scanning electron microscopy (SEM) including energy dispersive spectrometry (EDS). The elastic properties, i.e., Young's, shear and bulk moduli and Poisson's ratio were determined from ultrasonic velocities and densities. The ultrasonic velocities were measured using a pulse-through transmission method; density was measured using a buoyant force method. These studies showed that: (1) these materials have amorphous structures; (2) these materials have Young's moduli of the order of 20 GPa, and (3) the silane couplant apparently did not significantly affect the elastic properties of these resin-based composites.