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PubMed1994

Materials testing protocol for small joint prostheses.

In this article, a protocol for the evaluation of new materials for small joint prostheses is introduced. The testing methods employed in the protocol were developed by reviewing reported clinical failure modes and conditions found in vivo. The methods developed quantitatively evaluates the fatigue, fatigue crack propagation, and wear resistance properties of materials. For this study, a silicone elastomer similar to Dow Corning Silastic HP100, a radiation stable polypropylene, and a copolymer of polypropylene and ethylene propylene-diene monomer (EPDM) are evaluated. None of the materials tested demonstrated the ideal properties that are sought in a self-hinging joint prostheses. The silicone elastomer had excellent wear properties; however, cracks quickly propagated, causing catastrophic failure when fatigued. Conversely, the copolymer showed excellent fatigue crack propagation resistance and less than favorable wear properties. The polypropylene did not perform well in any evaluation.

Biocompatible Materials↗

PubMed1994

Comparison of tissue factor and prostacyclin production by human umbilical vein endothelial cells on Dacron vascular prostheses and Dacron smooth films.

The functional capacity of human umbilical vein endothelial cells (HUVEC) grown on Dacron (polyethylene terephthalate; PET) vascular prosthetic material was compared with the function of cells on smooth surfaced PET, tissue culture polystyrene (TCPS), and Natrix-coated TCPS. Prosthetic materials include two knitted fabrics (Bionit I and II) and two woven preparations (DeBakey Soft Woven and Extra Low Porosity). Two entities produced by HUVEC that influence blood coagulation were assessed: the procoagulant tissue factor (TF) and the anticoagulant prostacyclin (PGI2). Although TF activity was stimulated on all substrates by endotoxin (LPS), there was no difference among prostheses and no difference among smooth surface materials, but TF was reduced in cells on the prosthetic materials relative to those on smooth surface substrates. The reduced TF production by HUVEC on prosthetic material could be reversed by returning them to TCPS. In contrast, PGI2 production on prostheses was comparable to that on smooth surfaces for both stimulated and unstimulated cells. Stimulation with histamine (1 microM) gave a 2.4-fold increase in PGI2 whereas mellitin (10 micrograms/ml) increased production 12.5-fold. The differential response of HUVEC with regard to these two coagulation factors, one of which is secreted and the other membrane bound, may reflect the distorted shape of cells on fibers of the prosthesis.

Biocompatible Materials↗

PubMed2005

Antibody response to collagen after functional implantation of different polyester vascular prostheses in pigs.

Besides inflammation, specific immune responses are seen also after implantation of biomaterials. The aim was to investigate the humoral response to bovine collagen type I following implantation of various polyester (Dacron) prostheses into pigs. In 24 randomized pigs, the infrarenal aorta was replaced with a segment of collagen-impregnated, woven polyester prosthesis of low, medium, or high porosity. IgG antibodies were detected by immunoassay using native and denatured collagen type I as a target for blood samples taken on day 1 (implantation), 10, 17, 24, 62, and 116. As generally observed, antibodies to native and denatured collagen are of low titer and were significantly correlated with enhanced binding to the denatured form (p < 0.001). The highest overall antibody prevalence to native and denatured collagen was obtained on day 116 with 68% and on day 62 with 59%, respectively. Prostheses with high porosity induced an early immune response on day 10; those with low and medium porosity induced the highest antibody levels later after 2 months. Collagen antibodies neither correlated with serum IgG contents nor with antibodies to the prosthesis polyester matrix. Thus, humoral immune response against implant components may provide a further parameter in describing biocompatibility but also a potential marker that may facilitate monitoring of individual perigraft reaction.

Animals↗

PubMed2006

Influence of the structure of new generation prostheses on shrinkage after implant in the abdominal wall.

When a biomaterial is used to repair an abdominal wall defect, wound contraction can cause the prosthesis to shrink, and the tension generated can provoke recurrence of the defect. This study was designed to determine whether the structure of a prosthesis can directly influence prosthetic shrinkage. Abdominal wall defects (7 x 5 cm) in rabbits were repaired using the laminar prosthesis DualMesh (DM), the composites Sepramesh (Se) and Vypro II (Vy), and the reticular prosthesis Surgipro (PP). The animals were sacrificed 14 and 90 days after surgery, at which time implant specimens were morphologically and immunohistochemically examined to establish the presence of myofibroblasts and macrophages. The size of each prosthesis was measured at the end of the study through image analysis. Morphometric measurements revealed greatest prosthesis shrinkage for Se, PP, and Vy (16.05% +/- 5.08%; 13.75% +/- 4.22%; 16.16% +/- 6.34%), while the DM prostheses only showed a 7.57% +/- 0.62% decrease in size (p < 0.05). In the DM implants, the macrophage response and myofibroblast labeling were reduced. Both biomaterial structure and the macrophage reaction induced at the implant site modulate prosthetic shrinkage, laminar prostheses of the ePTFE type undergoing less shrinkage than reticular meshes. Reduced DM shrinkage was linked to decreased myofibroblast numbers 2 weeks postimplant.

Abdominal Injuries↗

PubMed2007

Strategies for the prevention of microbial biofilm formation on silicone rubber voice prostheses.

Total laryngectomy, a surgical treatment for extensive cancer of larynx, which alters swallowing and respiration in patients, is followed up with a surgical voice restoration procedure comprising tracheoesophageal puncture techniques with insertion of a "voice prosthesis" to improve successful voice rehabilitation. However, microbial colonization is a major drawback of these devices. Antimicrobials are usually used to prevent the colonization of silicone rubber voice prostheses by microorganisms. However, long-term medication induces the development of resistant strains with all associated risks and the development of alternative prophylactic and therapeutic agents, including probiotics and biosurfactants, have been suggested. The inhibition of microbial growth on surfaces can also be achieved by several other techniques involving the modification of physicochemical properties of the biomaterial surface or the covalently binding of antimicrobial agents to the biomaterial surface. An overview of the different approaches investigated to date and future perspectives to reduce the frequent replacements of voice prostheses in laryngectomized patients through microbial biofilm retardation is presented and discussed.

Biocompatible Materials↗

PubMed1975

Echocardiography in evaluation of mitral valve prostheses.

Thirty-three patients with mitral valve prostheses were studied with echocardiography in an effort to determine if this technique could be useful in detecting significant abnormalities. Recordings were obtained in the supine position with the transducer directed to record maximum excursion of the prosthesis. Echoes from the struts, poppet and sewing ring were readily recorded. Amplitude of excursion and opening and closing velocities of the poppet were measured. Fifty echocardiographic recordings were obtained from the 33 patients. Of the 33 patients studied, 22 were thought to have "normal" echo tracings while in 11, the tracings were considered "abnormal." Apparent abnormalities consisted of: 1) abnormal diastolic separation between the poppet and strut, 2) increased echoes near the poppet, strut or sewing ring and 3) a combination of both. There was only one instance of suspected "sticking" of the prosthesis. All patients who had "abnormal" studies except one developed complications associated with their prosthesis (90%) compared to only 36% in patients with "normal" tracings. Five patients in each group died. Autopsy studies are described and correlations with the echocardiographic findings are made. In low profile valves reduction in excursion of the disc may be an indication of malfunction. Echocardiography appears to be of value in the assessment of function of mitral valve prostheses.

Adolescent↗

PubMed2002

Translational and rotational forces on heart valve prostheses subjected ex vivo to a 4.7-T MR system.

PURPOSE: To assess the magnetic field interactions on 60 heart valve prostheses subjected to a 4.7 T MR system. It addresses the question of whether heart valves deemed safe at 1.5 T may pose safety hazards as patients are exposed to increased static magnetic fields. MATERIALS AND METHODS: Ex vivo testing was performed to evaluate translational and rotational forces on 60 heart valves using previously described techniques. RESULTS: Translational forces were detected on 58 heart valves ranging from 0.5 degrees to 7.5 degrees. Seven valves exhibited paramagnetic/weakly ferromagnetic behavior, and 51 valves exhibited diamagnetic behavior. Rotational forces were observed for 46 valves. CONCLUSIONS: Criteria previously used for safety assessment of heart valve prostheses and expressed in terms of magnetic forces suggest the forces observed in this study are compatible with the safe use of these valves in magnetic resonance (MR) systems with static fields up to 4.7 T.

Heart Valve Prosthesis↗

PubMed1992

Migration of porous coated acetabular prostheses fixed with screws: roentgen stereophotogrammetric analysis.

The fixation of screw-fixed, porous-coated acetabular prostheses was studied during 2 years in 21 patients (22 hips) using repeated roentgen stereophotogrammetric measurements. Migration of the center of the prostheses and/or tilting were recorded in five cups after 6 months. Two years after operation, migration was recorded in three, migration and rotation in six, and only rotation in three cups. Bone quality, prosthetic position, and immediate postoperative radiographic appearance of the prosthesis-bone interface did not correlate with the occurrence of migration. Narrow radiolucent zones had developed in half of the patients after 2 years and was associated with proximal migration. Micromovements of screw-fixed, press-fit cups seem to start later compared with previously presented results from cemented acetabular prosthesis.

Acetabulum↗

PubMed1994

Ingrowth reduces implant-to-bone relative displacements in canine acetabular prostheses.

We examined bone-to-implant relative displacement of acetabular prostheses acutely and after ingrowth in a canine model. Uncemented hemispherical acetabular cups with titanium mesh pads comprising approximately 26% of the surface of the cup were inserted in eight adult canine hemipelves ex vivo. The acetabular prostheses were fixed with 13 mm titanium screws. Zero, one, and two-screw configurations were tested, with the order of testing randomly assigned. A load simulating 1,000 cycles of canine gait as applied to the acetabular component, and relative displacements were measured at three locations between implant and bone to determine acute fixation. A repeated measures analysis of variance showed that two screws produced only 42% of the average relative displacement of one screw and 14% that of zero screws. Eight adult mixed-breed dogs then underwent unilateral total hip arthroplasty. All acetabula were biologically fixed with two cancellous screws. The results at 4 months showed significantly less relative displacement between the implant and bone than was measured in ex vivo implantations (p = 0.014). Bone ingrowth filled 20 +/- 6% (mean +/- SD) of the available space. The relative displacements of these implants were small in all cases (12 +/- 13 microns) and did not correlate with the amount of bone ingrowth. These data suggest that acetabular fixation with two screws can lead to bone ingrowth and reduced relative motion of the prosthesis under functional loading.

Acetabulum↗

PubMed1995

High resolution solid-state 29Si NMR spectroscopy of silicone gels used to fill breast prostheses.

We have used 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy to study the chemical structure of the silicone gels in virgin and explanted breast prostheses. Despite evidences of alteration in the morphological appearance of the silicone gel inside the breast prosthesis, our results do not reveal changes in the chemical nature and structure of the silicone gels after implantation. In addition to the main 29Si resonance peak at -22.26 ppm that corresponds to the resonance frequency of the D repeat unit of the polysiloxane chains, the high sensitivity of our NMR technique allows the detection of very low concentrations of silicone compounds. Within our experimental detection limit of 0.2%, no signal between -90 ppm and -150 ppm are observed. This indicates that no silica products are present inside the gel of the prostheses. Furthermore, our 29Si NMR spectra indicate differences in the chemical compositions of the silicone gels from different manufacturers.

Breast Implants↗

PubMed1996

Evaluation of various methods to quantify endothelial cells attached to vascular prostheses: comparison with a new "gold standard" FACS method.

For in vitro evaluation of functional properties of endothelial cells seeded on synthetic vascular prostheses accurate and reproducible quantification of cells is mandatory. Comparison of these properties with those resulting from other studies requires correlation of the functional parameters to reliably counted cell numbers. The accuracy of methods of quantification currently being used is unknown due to the lack of a "gold standard" method to which these methods can be compared. To determine the accuracy and reproducibility of four widely used methods, we have developed a "gold standard" model, using a flow cytometer (FACS). Endothelial cells, attached to collagen-coated Dacron vascular prostheses, were counted by four conventional methods and a new method of quantification after the attached number of cells had been determined with 99% accuracy by FACS. Subsequently, ratios were computed by dividing the cell numbers determined by the methods under investigation by those determined by FACS (x100%). The four conventional methods investigated were (1) removal and subsequent counting of cells from substrata by trypsin (T), (2) digestion of cells by citric acid and counting of crystal violet-stained cell nuclei (CV), (3) light microscopy after hematoxylin staining (LM), and (4) scanning electron microscopy (SEM). The new method consists of the measurement of cell fluorescence after labeling with fluorescein-diacetate (FDA). T and CV had average accuracy ratios of 127 +/- 58% and 96 +/- 48%, respectively (+/- standard deviation). The ratios for LM and SEM were 116 +/- 101% and 44 +/- 10% (respectively). FDA had a ratio of 99 +/- 7%. Reproducibility of cell quantification by T and CV was significantly less than that of quantification by LM, SEM, and FDA, as expressed by data on inter- and intraobserver agreement. Our results indicate that the investigated conventional methods of quantification failed to meet criteria of both high accuracy and reproducibility. Light microscopy and scanning microscopy methods were inaccurate but yielded reproducible countings. We conclude that the FACS method can serve as a "gold standard" to compare the accuracy and reproducibility of cell quantification methods. Moreover, the FDA method results in both accurate and reproducible quantification of endothelial cells attached to vascular prosthetic material.

Blood Vessel Prosthesis↗

PubMed2001

Novel synthetic selectively degradable vascular prostheses: a preliminary implantation study.

BACKGROUND: Vascular grafts perform less well than autologous arterial or vein grafts. The purpose of this study was to evaluate the short-term performance of selectively biodegradable filament-wound vascular prostheses, comprising elastomeric poly(ether urethane) (Lycra) scaffolds and flexible, hydrophilic biodegradable coatings. MATERIALS AND METHODS: Two types of selectively biodegradable vascular grafts were manufactured, comprising a filament-wound Lycra scaffold, subsequently coated with a biodegradable poly(ethylene glycol)/poly(lactic acid) (PELA) block copolymer. The two types of grafts differed in both the overall porosity of the scaffold and the hydrophilicity of the biodegradable constituent. A 60-mm-long and 6-mm-diameter filament-wound and polytetrafluoroethylene (ePTFE) grafts were implanted as interposition prostheses, randomly, at the right- and left-side carotid arteries. RESULTS: Implantation studies proved the grafts to be patent and pulsatile for periods of up to 3 months. Increasing the scaffold porosity and enhancing the hydrophilicity of the biodegradable component improved both the transmural tissue ingrowth process and the vascularization of the prosthesis wall. Also, a well-adhered peripheral tissue and a thin, uniform intima and endothelial lining were obtained. All ePTFE graft controls, although patent, were rather stiff and nonpulsatile. A thick pseudointima, poorly attached to the prosthesis inner surface, was observed. The compliance of the wet grafts was significantly higher than in the dry state, stemming mainly from the water-plasticizing effect on the biodegradable component. The grafts explanted after a period of 6 weeks exhibited compliance only slightly lower than that of the wet grafts. After 12 weeks, however, the hoop compliance was 20% lower than that prior to implantation. At 100 mm Hg, for example, the original compliance of the wet graft was 2.5%/100 mm Hg decreasing to 2.0%/100 mm Hg after a 3-month implantation. The compliance reduction with implantation is attributed to the ingrowth of the perigraft tissue as revealed by the histological study. A compliance of 2.0%/100 mm Hg is slightly better than that of a standard PTFE graft with an original compliance of 1.6%/100 mm Hg. Yet it is still an order of magnitude smaller than that of a canine carotid artery. CONCLUSIONS: The improved mechanical properties and enhanced healing of the highly porous filament-wound Lycra scaffold graft coated with hydrophilic biodegradable PELA has the potential of being a highly effective small caliber prosthetic graft.

Absorbable Implants↗

PubMed1987

Adherence of bacteria to cardiac valve prostheses.

The adherence of bacterial cells to valvular prostheses has been studied. Bacteria were selected on the basis of their surface features (fimbriae, hydrophobicity and specific receptors). It was found that only strains having fimbriae and high cell surface hydrophobicity adhered to bioprostheses, while they did not adhere to metallic prostheses to any significant extent. Adherence to bioprostheses depended on the exposure time and it was affected by the saline concentration of the suspension medium. Furthermore, different bacterial binding capacity was observed for bioprostheses from different companies.

Bacterial Adhesion↗

PubMed1987

The formation of a neo-intima in textile prostheses implanted in the aorta of rats and dogs.

The formation of a neo-intima in textile prostheses implanted in the rat and dog aorta was studied by means of light- and scanning electron microscopy. Two independent cellular layers (the superficial and deep ingrowth layers) developed on the free surface and under the fibrin layer initially deposited on the inner surface of the prostheses. The superficial ingrowth layer invades the prosthesis from both the proximal and distal aortic stumps and extends over the primary fibrin layer, or replaces it. This layer consists mainly of smooth muscle cells of the triangular aortic type covered by endothelial-like cells. The deep ingrowth layer originates from cellular elements of the prosthetic bed. Fibroblasts, myofibroblasts and spindle-shaped smooth muscle cells invade the fibrin layer through the interstices of the fabric structure of the prosthesis. Precursors of endothelial cells, however, are absent from this population. The superficial and the deep ingrowth layers may become joined by progressive replacement of the fibrin layer, but remain distinguishable because of their different cellular components. When a continuous cellular layer is established on the inner surface of the prosthesis, and this is then covered by endothelial-like cells, the neo-intima formed remains stable during long-term studies.

Animals↗

PubMed1986

The effects of extracorporeal shock wave lithotripsy on urological prostheses and endoprostheses.

The combination of ESWL and Endourology (EU) enables a wider range of stones to be treated without open surgery than either modality alone. EU frequently involves the maintenance of a plastic prosthesis in or near the area of maximal shock wave concentration during ESWL. Prostheses subjected to a standard test treatment by ESWL and others removed from patients after ESWL were examined visually, microscopically and biochemically by electron microscopy (SEM) and X-ray emission spectroscopy (XES) to investigate the effects of ESWL on the prosthesis itself. Foley catheter balloons leaked. Previously smooth surfaces were disrupted and possibly toxic additives may be released. Care should be taken in selecting indwelling EU prostheses if ESWL treatment is likely to follow.

Bismuth↗

PubMed1987

[Femoral fractures in subjects with total prostheses of the hip or knee].

Thirty three fractures of the shaft of the femur, which occurred after 28 total hip replacements and 8 total knee replacements, are reviewed. Fracture occurred adjacent to the femoral component of the hip prosthesis in 5 cases, distal to the femoral component in 8, at the tip of the femoral component in 12 hips and 5 knees and between the femoral components of hip and knee replacements in 3 cases. Treatment was by fixation with a plate in 29 cases, revision of a total hip replacement in 2 and traction in the other 2. The mean follow up was 2.5 years. Fractures healed in 3-4 months and function was usually restored. Aseptic loosening of a total arthroplasty after plating of a fracture did not occur. Two prostheses became infected, requiring removal of a hip and revision of a knee. Aetiological factors are stress-raisers in the femoral shaft after revision arthroplasty, defects in the cortex, and modification of shaft elasticity between the stems of hip and knee prostheses. Detection of a cortical defect during revision arthroplasty and bone grafting may help to prevent fracture. Fixation with a plate seems to be the best treatment, but if there is evidence of loosening revision with a long-stemmed component is indicated.

Adult↗

PubMed1980

Technological test-methods for hip prostheses.

Before the implantation of a new type of prostheses it is necessary to perform experimental tests in order to indicate obvious technical and biomechanical inconveniences before the long-time test within the human body will start. Experiments in animals can only give a rough outline of possible results. Appropriate models and simulators, however, can imitate the conditions of movement and so they are able to indicate characteristics of different types of prostheses due to material and design.

Forecasting↗

PubMed1990

Comparison between straight- and curved-stem Müller femoral prostheses. 5- to 10-year results of 545 total hip replacements.

Between 1977 and 1982, 545 cemented femoral prostheses were implanted, in combination with a noncoated cementless polyethylene acetabular component (RM cup). Three hundred and eighty-one straight-stem and 76 curved-stem Müller femoral components were implanted, as well as 88 collared components with a 130-mm stem and a 130 degrees neck-shaft angle, derived from a long-stem steel prosthesis. Survivorship analysis of revisions for aseptic loosening at 10 years revealed 97% straight-stem survival, 91.6% curved-stem survival, and 88.3% 130 degrees stem survival. "Survival" curves were also constructed for radiological loosening, and the survival rates (patients without radiological evidence of loosening) were 69.8%, 78.8%, and 63.1% respectively at 10 years. The 130 degrees collared stem was associated with significantly less acetabular loosening than the other prostheses. This resulted in less calcar resorption, but there was a higher rate of stem loosening. Acetabular loosening and associated wear products appear to be responsible for calcar resorption, and stress shielding of the calcar appears to be of minor importance in the pathogenesis of aseptic stem loosening. Better cementing techniques have improved survivorship of the curved-stem prosthesis, and early fears of high rates of radiological loosening with the straight stem have not been substantiated.

Adult↗