The wear resistance of N-ion implanted titanium, N-ion implanted Ti-6Al-4V alloy, ion plated Ti-6A1-4V, ion nitrided Ti-6Al-4V and surgical Co-Cr-Mo alloy were studied. All were studied under similar conditions, including dry wear and wear with lubricants of distilled water, saline solution, and human plasma. The results favor use of ion implanted Ti-6Al-4V alloy.

Titanium is generally recognized as one of the most biocompatible metal species, and as such, titanium based alloys are among the top contenders for the material of choice in orthopaedic prostheses. The questionable wear performance of titanium in abrasive and adhesive wearing conditions has been an impediment for a more widespread use of the alloy up to now. The ion implantation process has been shown to be extremely effective, in laboratory experiments, in enhancing the wear performance of the metal and at the same time reducing the wear of ultra high molecular weight polyethylene (UHMWPE) mating surface in contact with the alloy.

The present paper focuses on the increased hardness of the Ti-6Al-4V alloy as a result of ion implantation. It is generally believed that the wear improvements of titanium as a result of ion implantation are directly proportional to increased hardness of the surface. Thus, hardness data can be useful for the screening of ion implantation parameters to identify the optimum processing conditions. The Knoop hardness of ion implanted Ti-6Al-4V samples has been measured for B, C, N, N2, O and Ne ion species.

Nitrogen ion implantation was investigated as a means of improving the wear resistance of Ti-6Al-4V alloy and the performance of the Ti-6Al-4V/ultra high molecular weight polyethylene (UHMWPE) wear couple. Included in the pin-on-disc wear study were cobalt-chromium and stainless steel controls as well as non-ion-implanted Ti-6Al-4V. Ion implanted Ti-6Al-4V and the control alloys exhibited minor scratching whereas non-ion-implanted Ti-6AI-4V exhibited definite wear scars. Gravimetric analysis of the UHMWPE discs revealed no significant difference between those worn against ion implanted Ti-6Al-4V and the control alloys. Discs worn against non-ionimplanted Ti-6Al-4V, however, exhibited significantly more weight loss than the other couples. The results of this testing indicate that nitrogen ion implantation improves the wear resistance of Ti-6Al-4V with an attendant decrease in the amount of polyethylene abrasive wear.

Ion Implantation is emerging as a specialized surface treatment method by which orthopaedic alloys can be doped in order to modify for corrision, fatigue and wear properties.

In this paper alterations in the corrosion and fatigue resistance of 316LVM stainless steel and Ti 6A1-4V ELI titanium alloy are considered. The effect of various variables was investigated; ion species, flux, accelerating voltage.

Changes in corrosion resistance were monitored by performing anodic polarization studies in deaerated 0.1M NaCi solution at 22°C. The most effective species were found to be tantalum and boron for improvements to stainless steel.

Fatigue properties were investigated using a Wohler type rotating bend test. Preliminary results show that nitrogen ion implantation improved the fatigue life for the steel but not the titanium alloy. Indications were found to suggest that time since implantation affect the fatigue properties.

Neural prostheses which are commercially available include cochlear implants for treating certain forms of deafness and urinary bladder evacuation prostheses for individuals with spinal cord disorders. In the future we can anticipate improvements in bioelectrodes and biomaterials which should permit more sophisticated devices such as visual prostheses for the blind and auditory prostheses for the deaf based on microstimulation of the central nervous system.

Decisions concerning patient care, which are routinely made by the attending physician, based on experience and clinical laboratory analyses, will eventually be supplemented or even replaced by real-time, quantified, health assessments from cutaneous and indwelling multisensor probes. These probes will employ a multitude of technologies including optical and solid state techniques for the precise measurement of body analytes such as blood gases, electrolytes, pH, glucose, etc. In addition to clinical monitoring, these sensors will also be used to provide feed-back for closed-loop therapeutic systems.

Currently, there are rapid advances being made in sensor technology and its application for the determination of various analytes. However, a major problem still remains at the device/body interface, especially when chronic implantation is required.

A variety of materials have been evaluated for use as electrodes for neural stimulation. In an effort to maximize the charge density on the electrode surface, faradaic stimulation electrodes have been investigated. Electrodes consisting of thin films of polypyrrole on Pt have been studied in phosphate buffered saline using cyclic voltammetry at 100 mV/s. The electrode capacity diminishes initially but stabilizes after ˜500 cycles. The electrodes were further evaluated in pulsing experiments using constant current, biphasic pulses. In these experiments, significant charge storage was observed only when using pulse widths greater than 5 ms. A modified polypyrrole was prepared using anthraquinone containing electrolyte. This new material is an apparent improvement over the polypyrrole previously studied.

Hydrous manganese dioxide films are being investigated as a new redox material for the active surface of intracortical stimulation electrodes. The films are electrodeposited at room temperature on Pt substrates from a neutral solution of manganese acetate. The electrochemical properties of the films have been evaluated by cyclic voltammetry in neutral saline solutions buffered with bicarbonate. The films undergo a reversible charge injection reaction represented as

The results obtained in electrolytes of different buffer concentrations indicate the film is able to store the most charge in solutions having the lowest buffer capacity. The kinetics of the redox reaction thus favor operation in an acidic or basic environment in agreement with earlier published results. Two different mechanisms are proposed to explain the rate enhancement at the different pH's. In acidic electrolytes the reaction proceeds by dissolution of the film, while in alkaline solutions the rate determining step of proton diffusion in the solid film is increased. For neural stimulation, therefore, electrodes with manganese dioxide films should be pulsed cathodically to insure a neutral or alkaline environment around the electrode and minimize dissolution of the film.

Polyphenylene oxide (PPO) polymer films were electrogenerated on Pt substrates from solutions of o-allylphenol (OAP), 2-allyl-4-methylphenol (2A4MP), and 2-allyl-6-methylphenol (2AGMP). Relatively thick (l–20μm) films of the corresponding PPO films were generated from 50 v/o methanol/water solutions of the monomers or at low phenol:KOH concentration ratios. The film thickness depended on the maximum anodic potential to which the electrode was cycled. Films prepared from these solutions were found to be microporous with respect to ion permeability, allowing the oxidation of Br− and reduction of Fe3+ to take place at the Pt surface. Competing oxidation of methoxide ion was found to be the cause of the film porosity and thickening.

On the other hand, thin (500–1000Å) coherent insulating films which were impervious to Br− and Fe3+ ions could be deposited from aqueous KOH solutions and from methanolic solutions at high phenol:KOH concentration ratios. The thin films were found to decrease the diffusion rates of hydronium and hydrox hydroxide ions to the electrode surface to a significant degree. As a result, the filmed electrodes could be cycled in neutral saline between +1.5 and −0.2 V vs. SCE with no damage to the film.

Multilayered Ir oxide films were prepared on Ti and Pt:Ir electrodes by the thermal decomposition of successive layers of alcohol solutions of IrCl3. The charge capacity of the thermally-formed Ir oxide films (TIROF) and the reversibility of surface oxide-related reactions were evaluated in a physiological saline solution using potential sweep and current pulse techniques. The TIROF-coated electrodes had electrochemical properties similar to an Ir electrode coated with an anodically-formed oxide. The charge injection limits before gassing ranged from 5–10 mC/cm2 for TIROF-Ti and 1–3 mC/cm2 for TIROF-Pt:Ir with biphasic, charge-balanced current pulses of 0.2 ms duration. No Pt dissolution was detected during >100 hr stimulation with TIROF-Pt:Ir electrodes. Small amounts of Ir dissolution were detected which might result from passive leaching of residual chloride complexes of Ir. The TIROF coatings remained firmly attached to the substrate metal during long term pulsing and abrasion tests. The properties of TIROF coatings, e.g., high charge capacity for reversible charge injection and good abrasion and corrosion resistance, are of great advantage for neural prosthesis applications.

The biological repair process tends to cover a vascular prosthesis by normal arterial wall tissue. This process was successfully utilized in rats to form eventually a neo-artery induced by a temporary physiologically functioning prosthetic scaffold. Essential for the regeneration of a normal compliant neo-artery was the initial physiological campliance and the gradual degradation of the prosthetic grafts. Only then the regenerating neo-media was effectively stimulated by the pulsatile flow to produce elastic laminae. Regeneration of the arterial wall could be enhanced by seeding smooth muscle cells. The same concept was successfully applied to replace the trachea and oesophagus in rabbits. These results demonstrate that regeneration of biological organs can be induced by temporary acting artificial organs, which are anatomically correct and superior to permanently implanted artificially organs.

A sustained ultrafiltration during long-dwell peritoneal dialysis exchanges cannot be achieved with rapidly absorbable small molecular weight substances such as commonly used glucose. Uncharged polymeric substances are absorbed slower, but yield insufficient osmotic driving force because osmolality is inversely proportional to the molecular weight.

Charged polymers induce colloid osmotic pressure not only because of the molecules themselves, but also by ions kept in the peritoneal cavity by opposite charges of polymers. In an in vitro model of peritoneal dialysis, a sustained ultrafiltration has been achieved with several synthetic polymers including polyacrylate, dextran sulfate and polyethylenimine. However, these polymers were locally toxic to the peritoneal membrane when tested in rats and rabbits.

Chemically modified gelatin derivatives, such as polygelin, exypolygelatin, and succinylated gelatin are widely used in Europe as plasma substitutes. They are metabolized and have proven to be systemically non-toxic. These gelatin derivative solutions were tested in rat models of peritoneal dialysis. Up to 10% solutions achieved sustained ultrafiltration at the rate proportional to the concentration and no untoward systemic or local effects on the peritoneum were observed. Absorption of gelatin molecules ranged from 40–60% of the infused amounts. The results of the studies indicate that gelatin derivitives have potential for clinical use as osmotic agents in long-dwell peritoneal dialysis exchanges if the absorption rates in humans are markedly lower than in rats.

Spectroscopic ellipsometry has been used to study the dielectric response of indium film evaporated on a glass substrate, as well as that of indium film adsorbed with monolayers of Bovine Serum Albumin (BSA) and Rabbit Antiserum on BSA (RABSA). It is found that the position of the ε2 peak (or the peak of the imaginary part of the complex dielectric function) shifts to longer wavelengths and also increases in height as monolayers of BSA and RABSA are successively adsorbed onto it. The observed peak changes are due to the adsorption of BSA and RABSA on the surface of prolate indium clusters, which in effect increases the effective refractive index of voids between indium islands from 1.0 to 1.075 (BSA) and 1.15 (BSA + RABSA).

Spinal ligaments were obtained from normal and scoliotic individuals. Detailed morphological studies were carried out on the yellow, interspinous and supraspinous ligaments by light and scanning electron microscopy. Normal yellow ligaments are mostly constituted of dense elastin fibers with only a few collagen fibers and sparse blood vessels, while in normal interspinous and supraspinous ligaments, the presence of collagen is highly dominant. In the latter structures, the collagen fascicles are characterized by a regular waviness morphology. The fibrils constituting the fascicles appear either parallel or helical with respect to the fascicle axis. Structural changes are observed in the spinal ligaments of patients with congenital as well as idiopathic scoliosis. For yellow ligaments, only slight differences are found between normal and scoliotic specimens. However, alterations in collagen waviness and architecture are observed mainly in the supraspinous ligaments and to a lesser extent in the interspinous ligaments. In addition, increases in the cellularity, loose connective tissue and vessels are found in both forgoing ligaments. These results indicate that the more pronounced scoliosis-related changes occur in ligaments having the farthest distance from the axis of flexion-rotation.

A collagenous scar capsule forms around biomaterial implants and for deformable implants such as a breast prosthesis, this phenomenon of capsular scar contracture may lead to deformation and hardening of the implant. Relaxin, a peptide hormone of pregnancy which is known to affect collagen rich tissues, was given to mice in an attempt to eliminate or lessen this contracture. A short (8 day) study was performed to observe the effects of relaxin and estrogen on the mechanical properties of Skin and the interpubic ligament. A longer (27 day) study observed the effects of relaxin in estrogen primed mice containing implants. Changes in skin, interpubic ligament, scar capsule and contracture phenomenon were noted. Stress-strain characterization, dynamic mechanical spectroscopy and light microscopy were used to characterize the effects of relaxin and estradiol on the contracture phenomenon. Qualitatively, relaxin given to estrogen primed mice was shown to lessen implant contracture and deformability. Administration of relaxin produced the documented changes in the interpubic ligament, but differences were noted between the 8 and 27 day studies. Differences in the failure stress and strain and modulus for the long implant and short non-implant study were noted for the relaxin treated mice.

Titanium has emerged as one of the most tissue-compatible metallic materials. The high degree of biocompatibility is intimately connected with the oxide that forms on the metal surface. In the present work a broad characterization has been made of titanium samples pretreated both by presently used clinical procedures (mechanical machining, ultrasonic cleaning and autoclaving) and by alternative preparation procedures such as electropolishing and anodic oxidation. The former samples are found to have a surface oxide of TiO2 which is 30–50 Å thick, with some trace element contamination and a relatively large carbon content (30–50 % of a monoatomic layer). The anodically oxidized samples also consist of TiO2 with an oxide thickness range of 50–2000 Å, but the morphology and crystallinity of the anodic oxides are found to depend on thickness and preparation conditions.

The main methods of investigation used in the present study were ESCA, SIMS and transmission electron microscopy.

Among metallic systems, titanium alloys are prime candidate materials for biomedical applications in view of their apparent properties in the body environment. While machined and forged parts of CPTi, or Ti-6Al-4V, are suitable for many applications, they are not economical for one-off objects or artefacts of extreme intricacy. Titanium castings are an obvious solution to the problem but these are extremely difficult to process without contamination. Alloying allows a lowering of the melting point and significantly reduces the risk of contamination but the resultant alloys are normally brittle due to networks of intermetallics forming. This paper describes a process of semi-solid casting using a powder titanium feedstock for making one-off castings of artefacts like those required in dentistry. The process will be described and the mechanical and corrosion properties of several alloys which are compatible with this technique are assessed. The basic process is relatively inexpensive and provides a useful tool for examining a wide range of potential titanium base alloys.

Although mechanical property characterization of materials for loadbearing implant applications is recognized as a necessary prerequisite to their in vivo use, tests are usually restricted to in vitro situations becaus-of specimen size and cost limitation. Thisstid7'Jescribes a fracture toughness test that uses small specimens that can be conveniently placed in intermuscular positions in laboratory rats. The method is illustrated for the evaluation of two orthopaedic biomaterials namely bone cement and a filled composite (hydroxyapatite-filled polyethylene). The results indicated little mechanical degradation of the bone cement after 120 days in vivo but a significant change in the filled polyethylene composite after only 70 days in vivo.

Vertebral body resection in the treatmenL of metastatic neoplasms of the spine is increasingly common for radioresistant tumors. It is also favored for treating progressive neurological disease due to tumor-associated spinal cord compression. Spine stabilization following resection is accomplished by several techniques. Increasing in popularity is the combination of threaded fixation pins and methylmethacrylate filler.

In the two cases reported in this communication, failure of threaded AISI 316 stainless steel pins occured through corrosion fatigue. Corrosion begins at the base of the threads and is exacerbated by galvanic cell formation at the methyl methacrylate-bone interface. Fatigue is experienced because the cervical and vertebral bodies are each a part of a joint that normally experiences 10 – 20 degrees of both antero-posterior and lateral flexion.

We conclude that in active patients, non-threaded cobalt chrome pins are the preferred material for stabilization of the lumbar and cervical spine following vertebral body resections.

Plasma proteins have been recognized as playing a role in the corrosion of metals used as medical implants. In this study, we examined the early events of anodic corrosion of 316L stainless steel in saline/plasma mixtures. Polished, annealed, cleaned and passivated 316L electrodes with a surface area/body fluid volume (SA/BFV) ratio of 23X were driven anodically in a 100 ml acid cleaned cell at 950 and 1150 mV (vs. SCE). Electrolyte solutions of isotonic saline (pH = 7.4) containing 0, 5, 10 and 25 volume percent human plasma were used. Aliquots of solution were taken at intervals and analyzed for Cr, Ni and Fe by atomic absorption spectrophotometry. Corrosion continued until a total charge of 1.0 to 1.5 C was passed. Plots of solution metal concentration versus electrolyte solution composition, calculated at an isocoulombic point (Q = 0.5 C) and adjusted for initial concentration, were prepared to test for effects of the presence of plasma proteins. Increases in elemental release rates of up to 3x (p 0.05) were found, with peak effects in 5 and 10 volume percent plasma solutions. The effects depend upon anodic potential, metal species, plasma protein concentration and possibly plasma composition.