Biocompatibility of total joint replacements: A review

Total joint replacement is one of the most clinically successful, cost-effective surgical procedures. These operations have been shown to improve pain, function and mobility in patients with end-stage arthritis. However, joint replacements that will allow full, unrestricted, high impact activities and last the patient's lifetime have not yet been devised. This is due to biocompatibility issues related to material science, biomechanics, and host responses. In this review, three issues that are highly pertinent to biocompatibility of joint replacements are examined. These topics include how implants initially osseointegrate within bone, potential adverse effects of byproducts of wear that can lead to aseptic loosening and periprosthetic osteolysis, and the potential for new bearing surfaces to extend the lifetime of implants. A clear understanding of these important issues will facilitate the development of novel strategies to improve the longevity and function of implants for joint replacement in the future.     

Nanoindentation of the insertional zones of human meniscal attachments into underlying bone

The fibrocartilagenous knee menisci are situated between the femoral condyles and tibia plateau and are primarily anchored to the tibia by means of four attachments at the anterior and posterior horns. Strong fixation of meniscal attachments to the tibial plateau provide resistance to extruding forces of the meniscal body, allowing the menisci to assist in load transmission from the femur to the tibia. Clinically, tears and ruptures of the meniscal attachments and insertion to bone are rare. While it has been suggested that the success of a meniscal replacement is dependent on several factors, one of which is the secure fixation and firm attachment of the replacement to the tibial plateau, little is known about the material properties of meniscal attachments and the transition in material properties from the meniscus to subchondral bone. The objective of this study was to use nanoindentation to investigate the transition from meniscal attachment into underlying subchondral bone through uncalcified and calcified fibrocartilage. Nanoindentation tests were performed on both the anterior and posterior meniscal insertions to measure the instantaneous elastic modulus and elastic modulus at infinite time. The elastic moduli were found to increase in a bi-linear fashion from the external ligamentous attachment to the subchondral bone. The elastic moduli for the anterior attachments were consistently larger than those for the matching posterior attachments at similar indentation locations. These results show that there is a gradient of stiffness from the superficial zones of the insertion close to the ligamentous attachment into the deeper zones of the bone. This information will be useful in the continued development of successful meniscal replacements and understanding of fixation of the replacements to the tibial plateau.     

Microgrooved silicone subcutaneous implants in guinea pigs

Cell-substratum interactions are of fundamental importance for the reaction of body tissues to surgically implanted foreign materials. In our study we investigated the influence of 2 microm wide microgrooves, with various depths (0.5-6 microm), on capsule formation around subcutaneous silicone implants, in an animal experiment. Silicone sheets with microtexture were glued around silicone tubes. These implants were placed subcutaneously in eight guinea pigs for 10 weeks. The implanted tubes were removed including all surrounding tissues, and processed for light microscopy and subsequent histomorphometrical evaluation. All removed implants were surrounded by a thin fibrous capsule, and it was observed that this capsule was separated from the implants by a thin, single layer of mono- and multinucleated phagocytotic cells. In histomorphometry no significant differences were seen in relation to the reaction towards the various textures. We conclude that microtextures do not have an effect on the morphological characteristics of capsule formation around silicone implants in soft tissue.     

In vivo tissue reactivity of radiation-cured silicone rubber implants.

Silicone rubber implants are clinically used in large numbers and elicit a milk tissue reaction. An occasional patient develops an accentuated reaction, an observation which has stimulated clinicians to try to understand this process more fully. The chemistry of medical silicone implants, including quantitative composition, is reviewed. This in vitro laboratory study show less tissue reaction-cured silicone with SiO2 filler. A proposed system for fabrication and curing of a silicone implant, with the qualities of strength and diminished tissue reactivity, is discussed.     

Wear of medical grade silicone rubber against titanium and ultrahigh molecular weight polyethylene

The replacement of arthritic small joints, such as the fingers and wrist, has typically involved the use of one-piece silicone rubber implants. Newer designs have involved the silicone moving against either a titanium or ultrahigh molecular weight polyethylene (UHMWPE) component. The aim of this study was to investigate the wear of medical grade silicone rubber against titanium and UHMWPE. A pin-on-disc apparatus was used to slide a titanium and UHMWPE pin against a silicone disc, in the presence of either a Ringer's solution or bovine serum lubricant. Testing was undertaken at a sliding speed of 0.079 m/s and was continued for 10 km. Wear factors for titanium against silicone were 40.0 x 10(-6) mm(3)/N m and 66.5 x 10(-6) mm(3)/N m for bovine serum and Ringer's solution, respectively. The wear factors for UHMWPE against silicone were higher with values of 84.4 x 10(-6) mm(3)/N m and 88.3 x 10(-6) mm(3)/N m for bovine serum and Ringer's solution, respectively. The results of this study will be useful in future designs of finger and wrist implants that combine silicone rubber with either titanium or UHMWPE.     

High-density polyethylene facial implants show surface oxidation in SEM and EDX examination: A pilot study

Previous histopathological studies on explanted Medpor high-density polyethylene (HDPE) facial implants indicated signs of material destruction and claimed to observe phagocytized HDPE particles within the tissue samples beside the usual type IV reaction with severe fibrosis. We examined new and explanted Medpor material with scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX). The implant surface of three patient-derived specimens showed significantly higher oxygenation in EDX analysis and morphological changes in SEM compared to the new unused material directly after opening of the package and after 1 year of exposure to air. Our preliminary findings indicate a possible oxidative biocorrosion in HDPE surgical implants. Further studies should confirm these pilot project results.     

Presence of corrosion products and hypersensitivity-associated reactions in periprosthetic tissue after aseptic loosening of total hip replacements with metal bearing surfaces

Aseptic loosening of articular implants is frequently associated with tissue reactions to wear particles. Some patients, who had received metal-on-metal articulations, present early symptoms including persistent pain and implant failure. These symptoms raise the suspicion about the development of an immunological response. Furthermore, the generation of rare corrosion products in association with metallic implants has been observed. Corrosion products are known to enhance third-body wear and contribute to the loss of the implant. The purpose of this study was to investigate periprosthetic tissue containing solid corrosion products after aseptic loosening of second-generation metal-on-metal total hip replacements made of low-carbon cobalt-chromium-molybdenum alloy for the presence of immunologically determined tissue changes. Periprosthetic tissue of 11 cases containing uncommon solid deposits was investigated by light microscopy. In order to confirm the presence of corrosion products, additional methods including scanning electron microscopy (SEM) investigation, energy dispersive X-ray (EDX) and Fourier transform infrared microspectroscopy (FTIR) analysis were used. All investigated cases revealed solid chromium orthophosphate corrosion products as well as metallic wear particles to a various extent. Moreover, various intense tissue reactions characteristic of immune response were observed in all cases. The simultaneous presence of corrosion products and hypersensitivity-associated tissue reaction indicates that a relationship between corrosion development and implant-related hypersensitivity may exist.     

Silicone granulomas: report of three cases and review of the literature

Since silicone is rapidly becoming one of the most commonly used biomaterials in modern medicine, pathologists will be observing increasing numbers of cases of silicone-related disease. Although numerous case reports have established that silicone elicits a characteristic response in tissues, the varying tissue reactions to silicone gels, liquids, and elastomers (rubber) have not been emphasized. Three cases are reported, and the literature is reviewed to illustrate the varying features of tissue reaction to silicone in its different forms. The first case is an example of silicone lymphadenopathy in an inguinal lymph node. This case demonstrates exuberant foreign body granuloma formation in response to particles of silicone elastomer. The second case involves a patient who had facial subcutaneous liquid silicone injections, and the third case is that of a woman in whom breast carcinoma developed 13 years after mammary augmentation with liquid silicone injections. These two cases illustrate the characteristic reaction to silicone liquid, with numerous cystic spaces and vacuoles in the soft tissues but minimal or no foreign body giant cell reaction. Scanning electron microscopy and energy dispersive x-ray analysis were performed in the first two cases, confirming the presence of silicon. Silicone migration and the clinical significance of various silicone-induced lesions are discussed.     

Platinum in silicone breast implants

Silicone elastomers are widely used in implantable devices, including silicone breast implants. These rubbers are generally formed/cured using platinum-catalyzed hydrosilylation. The current scientific literature on the chemistry of platinum is reviewed, as it applies to the use of platinum catalysts for cure of silicone elastomers destined for use in silicone breast implants. These discussions serve as a basis to examine the recent literature describing release of platinum into tissues adjacent to silicone breast implants, the chemical nature of the platinum present in breast implants and the possible association between platinum and clinical outcomes.     

Cystic osteolysis induced by silicone rubber prosthesis

Synovitic symptoms and radiologically documented cystic lesions in several carpal bones and distal radius developed two years after the implantation of silicone rubber scaphoid prosthesis for pseudoarthrosis. Open biopsy revealed granulomatous synovitis and osteitis and foreign material in carpal tissues. Ultrastructurally dense material was found in the cytoplasm of histiocytic, often multinucleated cells. Electron-probe analysis of the material showed a definite peak for silicon, proving the causal relationship of symptoms and signs to the silicone rubber prosthesis.     

Histological patterns of bone and articular tissues after orthopaedic reconstructive surgery (artificial joint implants).

Revision surgery after failures of joint replacements leads to histological studies on joint and bone tissues close to the implanted material. Aspectic loosening is the main complication. The surgical pathologist has to identify wear debris (metal, polyethylene, polymethylmethacrylate, chiefly) which promotes a histiocytic granuloma. Some surgical procedures such as cup or resurfacing arthroplasties create a new articular surface and a bone remodeling or necrosis. Cemented joint prostheses show various membrane structures between bone and the cement mantle while there is an association of bone resorption and formation. Non-cemented, porous-coated joint prostheses induce little bone ingrowth, even in satisfactory clinical results. Mechanical factors are predominant in massive limb prostheses. For silicone elastomer implants or artificial ligaments, wear of material promotes many tissular reactions. Often used bone grafts show little creeping substitution process in case of homografts, even well-incorporated on X-rays. More retrieval specimen studies are necessary to delineate precise topographical histological lesions, including non-loosened joint implants.     

The effect of plasma-induced graft copolymerization of PHEMA on silicone rubber towards improving corneal epithelial cells growth

A PHEMA grafted polymer film was prepared by plasma induced graft copolymerization onto an elastic material, silicone rubber. The control, Ar plasma-treated, and PHEMA-grafted silicone rubber surfaces were characterized by ESCA, FTIR-ATR, and SEM techniques. ESCA verified the respective chemical shift of control and Ar plasma-treated films. The presence of the grafted PHEMA was also verified by ESCA. The amounts of grafted PHEMA did not monotonously increase with the plasma exposure conditions, but decreased after passing a maximum. The introduction of PHEMA onto a hydrophobic support provided an adequate surface for rabbit corneal epithelium cell attachment and growth. Cell attachment and growth onto these surfaces were examined by light microscopy. Cell attachment onto the control and Ar plasma-treated surface was negligible, while improved attachment and growth of rabbit corneal epithelium cells was demonstrated on the PHEMA-grafted polymer surface. The PHEMA-grafted silicone rubber surface demonstrated a confluent cell layer after 72 h.     

硬组织替换用羟基磷灰石复合材料的研究进展

羟基磷灰(HA)石具有与人骨无机质相似的化学成分和晶体结构，被认为是一种很有潜力的人体硬组织替换材料，但脆性太大限制了其在承载部位骨替换中的应用。因而各种羟基磷灰石复合材料受到了极大的关注。本文按照增强体的种类对羟基磷灰石复合材料进行了分类介绍。生物活性陶瓷、生物活性玻璃及玻璃陶瓷、生物惰性陶瓷、聚合物及金属等都被用来制备羟基磷灰石复合材料，但仍没有一种材料能够很好的满足硬组织替换的需要。现有HA复合材料存在的关键问题是生物性能与力学性能之间不能很好地匹配。     

Reconstruction of the canine Achilles and patellar tendons using dacron mesh silicone prosthesis. I. Clinical and biocompatibility evaluation.

Surgical replacement of the Achilles and patellar tendons using Dacron mesh silicone prostheses was performed in 15 mature beagle dogs. This part of the study includes clinical evaluation, gross inspection at autopsy of regrown tendons, and histological determination of biocompatibility of prosthetic implants. Functional continuity and integrity of prosthetic patellar tendons have been established by evaluating the biologic-prosthetic interface and the mechanical properties of regrown tendon tissue around and through the Dacron silicone replacements. Results of prosthetic Achilles tendons were less satisfactory because of difficulties in suturing to a muscle and its fascia. Although the prosthetic tendon did not regrow through the tube, it provided a structure for regrowth around it. The regrown tendons became nearly ten times the normal cross-sectional area after three to four months and decreased to two to three times after 13 months. Histological studies indicate that in the absence of infection, the Dacron mesh silicone tendon was well tolerated for periods up to 13 months. Overall results are encouraging and warrant further investigation although the regenerative capacity of human patellar and Achilles tendons is unknown.     

In vitro and in vivo antimicrobial activity of covalently coupled quaternary ammonium silane coatings on silicone rubber

Biomaterial-centered infection is a dreaded complication associated with the use of biomedical implants. In this paper, the antimicrobial activity of silicone rubber with a covalently coupled 3-(trimethoxysilyl)-propyldimethyloctadecylammonium chloride (QAS) coating was studied in vitro and in vivo. Gram-positive Staphylococcus aureus ATCC 12600, Staphylococcus epidermidis HBH, 102, and Gram-negative Esherichia coli O2K2 and Pseudomonas aeruginos AK1 were seeded on silicone rubber with and without QAS-coating, in the absence or presence of adsorbed human plasma proteins. The viability of the adherent bacteria was determined using a live/dead fluorescent stain and a confocal laser scanning microscope. The coating reduced the viability of adherent staphylococci from 90% to 0%), and of Gram-negative bacteria from 90% to 25% while the presencc of adsorbed plasma proteins had little influence. The biomaterials were also subcutaneously implanted in rats for 3 or 7 days, while pre- or postoperatively seeded with S. aureus ATCC 12600. Preoperative seeding resulted in infection of 7 out of 8 silicone rubber implants against 1 out of 8 QAS-coated silicone rubber implants. Postoperative seeding resulted in similar infection incidences on both implant types, but the numbers of adhering bacteria were 70% lower on QAS-coated silicone rubber. In conclusion, QAS-coated silicone rubber shows antimicrobial properties against adhering bacteria, both in vitro and in vivo.     

The microstructure of ultra-high molecular weight polyethylene used in total joint replacements

The microstructure of ultra-high molecular weight polyethylene (UHMWPE) has been studied using a range of techniques. Both the unprocessed base powder and ram-extruded polymer have been examined using optical microscopy, scanning and transmission electron microscopy and smallangle light scattering. By examining the microstructure of samples compression moulded at a range of temperatures, techniques have been developed to assess the degree of consolidation of the processed polymer. The raw polymer is a powder with a particle size in the range 50–250 μm. These particles are themselves agglomerates of much finer particles typically 0.5–1 μm in size. It has been suggested that these sub-micron particles may be the origin of the sub-micron wear debris found in tissues around total joint replacements. However, examination of the ram-extruded polymer, from which implants are machined, shows a different structure from the powder, with no evidence of retention of the 0.5–1 μm structure seen in the powder in the processed material. It thus appears that the similarity in size between the sub-micron wear debris particles and the fine structure seen in the unprocessed UHMWPE resin is coincidental. Processed UHMWPE does show a ‘memory’ of the grain boundaries between powder particles and the degree of consolidation can be assessed by observing the distinctiveness of these boundaries.     

Liquid- and solid-state high-resolution NMR methods for the investigation of aging processes of silicone breast implants

To investigate aging processes of silicone gel breast implants, which may include migration of free unreacted material from the gel and rubber to local (e.g. connective tissue capsule) or distant sites in the body, chemical alteration of the polymer and infiltration of body compounds, various approaches of multinuclear nuclear magnetic resonance (NMR) experiments (29Si, 13C, 1H) were evaluated. While 29Si, 13C, and 1H solid-state magic angle spinning (MAS) NMR techniques performed on virgin and explanted envelopes of silicone prostheses provided only limited information, high-resolution liquid-state NMR techniques of CDCl(3) extracts were highly sensitive analytical tools for the detection of aging related changes in the materials. Using 2D 1H, 1H correlation spectroscopy (COSY) and 29Si, 1H heteronuclear multiple bond coherence (HMBC) experiments with gradient selection, it was possible to detect lipids (mainly phospholipids) as well as silicone oligomer species in explanted envelopes and gels. Silicone oligomers were also found in connective tissue capsules, indicating that cyclic polysiloxanes can migrate from intact implants to adjacent and distant sites. Furthermore, lipids can permeate the implant and modify its chemical composition.     

Reduced adherence of Candida to silane-treated silicone rubber

Silicone rubber is widely used in the construction of medical devices that can provide an essential role in the treatment of human illness. However, subsequent microbial colonization of silicone rubber can result in clinical infection or device failure. The objective of this study was to determine the effectiveness of a novel silane-treated silicone rubber in inhibiting microbial adherence and material penetration. Test material was prepared by a combination of argon plasma discharge treatment and fluorinated silane coupling. Chemicophysical changes were then confirmed by X-ray photoelectron spectroscopy, contact-angle measurement, and atomic force microscopy. Two separate adherence assays and a material penetration assay assessed the performance of the new material against four strains of Candida species. Results showed a significant reduction (p < 0.01) of Candida albicans GDH 2346 adherence to silane-treated silicone compared with untreated controls. This reduction was still evident after the incorporation of saliva into the assay. Adherence inhibition also occurred with Candida tropicalis MMU and Candida krusei NCYC, although this was assay dependent. Reduced penetration of silane-treated silicone by Candida was evident when compared to untreated controls, plaster-processed silicone, and acrylic-processed silicone. To summarize, a novel silicone rubber material is described that inhibits both candidal adherence and material penetration. The clinical benefit and performance of this material remains to be determined.     

Current developments and future prospects for heart valve replacement therapy

Valve replacement is the most common surgical treatment in patients with advanced valvular heart disease. Mechanical and bio-prostheses have been the traditional heart valve replacements in these patients. However, currently the heart valves for replacement therapy are imperfect and subject patients to one or more ongoing risks, including thrombosis, limited durability, and need for re-operations due to the lack of growth in pediatric populations. Furthermore, they require an open heart surgery, which is risky for elderly and young children who are too weak or ill to undergo major surgery. This article reviews the current state of the art of heart valve replacements in light of their potential clinical applications. In recent years polymeric materials have been widely studied as potential prosthetic heart valve material being designed to overcome the clinical problems associated with both mechanical and bio-prosthetic valves. The review also addresses the advances in polymer materials, tissue engineering approaches, and the development of percutaneous valve replacement technology and discusses the future prospects in these fields.     

Histological changes related to scleral buckling for treatment of retinal detachment

Treatment of retinal detachment frequently uses biocompatible materials to obtain scleral buckling. These materials are not devoid of consequences on surrounding tissues. In 3 eyes enucleated for failure of surgical treatment using scleral buckling materials, the changes prompted by episcleral implants could be observed. The sclera underwent both an inversion of its curvature and a reduction of its thickness under the material, as well as an encapsulation of the material was observed. While a silicone sponge was used in part to encircle one of these eyes, its capsular inner surface was regular and smooth. In contrast, hydrogel implants used in the three eyes showed a peripheral fragmentation prompting in two of them a typical foreign body giant cell granulomatous reaction. Changes in scleral curvature and scleral thinning were observed reflecting the consequences of the buckling procedure. The capsule formation occurred as it does for any nonabsorbable matérial implanted in tissues. Degradation and fragmentation of the hydrogel material suscitated a granuloma in response to fragments. These hydrogel specific changes should be recognized on microscopic examination of slides of either capsule or eyes previously in contact with this implanted material. They attested of the instability of hydrogel after implantation.