基于CT扫描人体股骨的有限元分析

为了明确人体股骨步态过程的力学特性和股骨固有频率对置换术的影响,通过对采集于国人活体的股骨CT图像数据进行分析处理,提取股骨边界曲线利用逆向工程方法生成实体模型。对该模型进行有限元计算、分析得到其步态运动中不同时刻的力学特性,重点对国人股骨的振动特性进行分析。根据所得数据,对关节置换后假体松动产生的机理提出了新的观点和看法,认为假体的设计不但要考虑材料的生物相容性和假体固定方式,还要考虑假体固有频率的影响,应避免与股骨的频率相近而产生谐振。该文的结论对于指导关节假体的选材和外形设计有一定的借鉴作用。     

Collagen- and gelatine-based films sealing vascular prostheses: evaluation of the degree of crosslinking for optimal blood impermeability

The stiffness as well as the biodegradation rate of collagen and gelatine products can be modulated by performing a number of crosslinking treatments. In many biomedical applications, an optimal degree of crosslinking seems to exist, depending on the mechanical and/or biosynthesis properties of the host site. The aim of this study was to evaluate the optimal degree of crosslinking of collagen and gelatine films, to be used as sealants for vascular prostheses. Various crosslinking treatments, including exposure to aldehydes, dehydrothemal treatment, carbodiimide crosslinking and combinations of them, were performed on collagen and gelatine films, and the resulting increases in stiffness, degree of crosslinking and denaturation temperature were evaluated. Analogue crosslinking treatments were also performed on sealed prostheses, which were then tested for blood leakage. The experimental results showed that a good blood impermeability of both collagen and gelatine films was obtained for crosslinking density of about 1.2–1.3 × 10⁻⁵ mol/cm³, which could be yielded by a dehydrothermal crosslinking treatment (DHT). In particular, dehydrothermally treated gelatine-coated prostheses were found to perform better than analogue collagen-coated ones. The presence of glycerol in crosslinked collagen films was found to have plasticizing effects, which are likely to facilitate blood impermeability, and to increase the thermal stability of collagen.     

Improved mechanical long-term reliability of hip resurfacing prostheses by using silicon nitride

Although ceramic prostheses have been successfully used in conventional total hip arthroplasty (THA) for many decades, ceramic materials have not yet been applied for hip resurfacing (HR) surgeries. The objective of this study is to investigate the mechanical reliability of silicon nitride as a new ceramic material in HR prostheses. A finite element analysis (FEA) was performed to study the effects of two different designs of prostheses on the stress distribution in the femur–neck area. A metallic (cobalt–chromium-alloy) Birmingham hip resurfacing (BHR) prosthesis and our newly designed ceramic (silicon nitride) HR prosthesis were hereby compared. The stresses induced by physiologically loading the femur bone with an implant were calculated and compared with the corresponding stresses for the healthy, intact femur bone. Here, we found stress distributions in the femur bone with the implanted silicon nitride HR prosthesis which were similar to those of healthy, intact femur bone. The lifetime predictions showed that silicon nitride is indeed mechanically reliable and, thus, is ideal for HR prostheses. Moreover, we conclude that the FEA and corresponded post-processing can help us to evaluate a new ceramic material and a specific new implant design with respect to the mechanical reliability before clinical application.     

Dynamic-mechanical properties of a novel composite intervertebral disc prosthesis

Over the past years, a tremendous effort has been made to develop an intervertebral disc (IVD) prosthesis with suitable biological, mechanical and transport properties. However, it has been frequently reported that current prostheses undergo failure mainly due to the mismatch between the mechanical properties of the conventional device and the spine segment to be replaced. The aim of the present work was to develop a poly(2-hydroxyethyl methacrylate)/poly(methyl methacrylate) (PHEMA/PMMA) (80/20 w/w) semi-interpenetrating polymer network (s-IPN) composite hydrogel reinforced with poly(ethylene terephthalate) (PET) fibres, and to investigate the static and dynamic mechanical properties. Filament winding and moulding technologies were employed to obtain the composite IVD prostheses with the unique complex structure that is peculiar to the natural IVD. The compressive properties analysis showed the typical J-shaped stress-strain curve which is displayed by natural IVDs. Compressive modulus varied from 84 to 120 MPa, as a function of the strain rate, and stress was higher than 10 MPa. These values are in the range of those of the natural lumbar IVDs. No failure of the prostheses has occurred during fatigue test performed for ten million cycles in physiological solution. Dynamic mechanical tests have confirmed the composite IVD prostheses exhibited appropriate viscoelastic properties.     

Analysis and prediction of total hip replacement performance

The survival of total hip replacement in patients operated on at the Royal National Orthopaedic Hospital was analysed for two types of Stanmore prostheses: (a) metal-on-metal prostheses of various development designs inserted between 1963–72 (173), and (b) metal-on-plastic prostheses of one design inserted between 1969–72 (248). The survival criterion was taken to be non-removal of the prosthesis and all cases not removed were regarded as survivors. The results indicated that for metal-on-metal prostheses the overall probability of survival was only 53% after 11 years and the average annual probability of removal irrespective of cause was 5.5%. As expected, for metal-on-plastic prostheses the results were considerably better, the figures being 88% after eight years and 1.5% respectively. For both prosthesis types the predominant failure mode was loosening and for this failure mode the annual rate of removal increased as the follow-up time increased, suggesting that loosening is a wearing-out process. Femoral component fracture occurred less frequently, but also appeared to be a wearing-out process. Finally, it is demonstrated how the analysis can be used to predict the probability of survival at some time in the future.     

Visual Prostheses: Technological and Socioeconomic Challenges

Visual prostheses are now entering the clinical marketplace. Such prostheses were originally targeted for patients suff ering from blindness through retinitis pigmentosa(RP). However, in late July of this year, for the first time a patient was given a retinal implant in order to treat dry agerelated macular degeneration. Retinal implants are suitable solutions for diseases that attack photoreceptors but spare most of the remaining retinal neurons. For eye diseases that result in loss of retinal output, implants that interface with more central structures in the visual system are needed. The standard site for central visual prostheses under development is the visual cortex. This perspective discusses the technical and socioeconomic challenges faced by visual prostheses.     

Layered double hydroxides as efficient drug delivery system of ciprofloxacin in the middle ear: an animal study in rabbits

Chronic otitis media is a common disease often accompanied by recurrent bacterial infections. These may lead to the destruction of the middle ear bones such that prostheses have to be implanted to restore sound transmission. Surface coatings with layered double hydroxides (LDHs) are evaluated here as a possibility for drug delivery systems with convenient advantages such as low cytotoxicity and easy synthesis. Male New Zealand White rabbits were implanted with Bioverit^® II middle ear prostheses coated with the LDH Mg₄Al₂(OH)₁₂(SO₄)₂·6H₂O impregnated with ciprofloxacin. 12 (group 1) were directly infected with Pseudomonas aeruginosa and another 12 (group 2) 1 week after the implantation. Clinical outcome, blood counts, histological analyses and microbiological examination showed an excellent antimicrobial activity for group 1, whereas this effect was attenuated in animals where infection was performed 1 week after implantation. This is the first study to demonstrate an efficient drug delivery system with an LDH coating on prostheses in the middle ear.     

Biological behaviour of an endothelial cell line (HPMEC) on vascular prostheses grafted with hydroxypropylgamma-cyclodextrine (HPγ-CD) and hydroxypropylbeta-cyclodextrine (HPβ-CD)

The cytocompatibility of cyclodextrins (CDs) grafting on vascular polyester (PET) prostheses for further loading with biomolecules was investigated in this study. Viability tests demonstrated no toxicity of HP-CDs and PolyHP-CDs at 4,000 mg/l with survival rates of 80 to 96%. Proliferation tests using the human pulmonary microvascular endothelial cell line (HPMEC-ST1) revealed an excellent biocompatibility for Melinex (Film form of PET). For Polythese and Polymaille, a good proliferation rate was observed at 3 days (60-80%) but decreased at 6 days (56-73%). For all CD-grafted samples, low proliferation rates were observed after 6 days (35-38%). Vitality tests revealed excellent functional capacities of HPMEC cells after 3 and 6 days for all samples. Adhesion kinetics tests showed a similar adhesion of HPMEC cells on control and Melinex. A low adhesion was observed on Polythese and especially on Polymaille compared to control. After CD grafting, the cell adhesion was decreased. The woven or knitted architecture and CD grafting were the most likely causes of this weak adhesion. The adhesion kinetic test was confirmed by SEM observations and immunocytochemistry. The low proliferation of HPMEC on virgin prostheses and especially on grafted prostheses was not due to a cytotoxic effect, but to the physical surface characteristics of the prostheses.     

Lipid uptake in ePTFE arterial prostheses implanted in humans

Lipid uptake in 104 ePTFE microporous vascular prostheses implanted in humans was investigated using Fourier transform infrared (FTIR) spectroscopy. The assignment of the infrared features observed in the spectra of explanted ePTFE microporous vascular prostheses shows unambiguously the presence of fatty acids in the structure of the arterial prosthesis wall. In addition, higher lipid concentration is found on the external side of the prostheses before 500 days of implantation, after which this behaviour is reversed. Finally, it seems that a greater amount of lipids are present on the surfaces of prostheses implanted in extra-anatomical sites as compared to those implanted in anatomical sites.     

Ovine anterior cruciate ligament reconstruction using a synthetic prosthesis and a collagen inductor

The evaluation of composite anterior cruciate ligament prostheses, theunion of an inductor of collagen and a synthetic fibre, are described. They wereimplanted in 10 sheep models for six months. None of the ligaments were broken,and the dynamic radiography was stable during this time. After harvesting them,a histologic study was performed on the intra-osseou and intra-articularportion, and on the synovial tissue. Biocompatibility was excellent. An osseousanchorage was found in 50% of cases and a fibrous ingrowth with well orientedfibres in each case. The results of this study show that the matrix has onlypartially played its role, because there was no improvement of fibrous ingrowthcompared with other studies. However this fact corresponds to results at only 6months and it is necessary to identify the type of collagen.     

Finite element modelling—predictor of implant survival?

The cancellous bone stresses surrounding proximal femoral prostheses were investigated using the finite element method and the results correlated with clinical subsidence data for similar implant configurations. The finite element study has shown that press-fit prostheses generate significantly higher cancellous bone stresses than bonded (cemented and HA coated) prostheses. The cancellous bone stresses surrounding press-fit implants are sensitive to the coefficient of friction, with up to a 60% decrease observed when the coefficient of friction was increased from 0 to 0.4. Resecting the femoral neck generally increased the cancellous bone stresses however varying the thickness of the cement mantle had little or no effect. Good correlation was found between the finite element results and the clinically measured subsidence data. Implant configurations generating higher cancellous bone stresses were those which subsided the most. This observation suggests that it may be possible to use the initial cancellous bone stresses to predict the likelihood of migration and hence late aseptic loosening.     

In vitro and in vivo microbial adhesion and growth on argon plasma-treated silicone rubber voice prostheses

Patients who undergo a total laryngectomy usually receive a silicone rubber voice prosthesis for voice rehabilitation. Unfortunately, biofilm formation on the esophageal side of voice prostheses limits their lifetime to 3–4 mon on average. The effects of repeated argon plasma treatment of medical grade, hydrophobic silicone rubber on in vitro adhesion and growth of bacteria and yeasts isolated from voice prostheses, as well as in vivo biofilm formation are presented here. In vitro experiments demonstrated that initial microbial adhesion over a 4 h time span to plasma-treated, hydrophilized, silicone rubber was generally less than on original, hydrophobic silicone rubber, both in the absence and presence of a salivary conditioning film on the biomaterial. Growth studies over a time period of 14 d at 37°C in a modified Robbins device, showed that fewer Candida cells adhered on plasma-treated, hydrophilized silicone rubber as compared to on original, hydrophobic silicone rubber. For the in vivo evaluation of biofilm formation on plasma-treated silicone rubber voice prostheses, seven laryngectomized patients received a partly hydrophilized Groningen Button voice prosthesis for a planned evaluation period of 4 wk. After removal of the voice prostheses, the border between the hydrophilized and the original, hydrophobic side of the prostheses was clearly visible. However, biofilm formation was, unexpectedly, less on the original, hydrophobic sides, although the microbial compositions of the biofilms on both sides were not significantly different. Summarizing, this study demonstrates that in vitro microbial adhesion and growth on silicone rubber can be reduced by plasma treatment, but in vivo biofilm formation on silicone rubber voice prostheses is oppositely enhanced by hydrophilizing the silicone rubber surface. Nevertheless, from the results of this study the important conclusion can be drawn that in vivo biofilm formation on voice prostheses is controlled by the hydrophobicity of the biomaterials surface used. © 1998 Chapman & Hall     

Wear of surface engineered metal-on-metal hip prostheses

The wear of existing metal-on-metal (MOM) hip prostheses (1 mm3/million cycles) is much lower than the more widely used polyethylene-on-metal bearings (30-100 mm3/million cycles). However, there remain some potential concerns about the toxicity of metal wear particles and elevated metal ion levels, both locally and systemically in the human body. The aim of this study was to investigate the wear, wear debris and ion release of fully coated surface engineered MOM bearings for hip prostheses. Using a physiological anatomical hip joint simulator, five different bearing systems involving three thick (8-12 microm) coatings, TiN, CrN and CrCN, and one thin (2 microm) coating diamond like carbon (DLC) were evaluated and compared to a clinically used MOM cobalt chrome alloy bearing couple. The overall wear rates of the surface engineered prostheses were at least 18-fold lower than the traditional MOM prostheses after 2 million cycles and 36-fold lower after 5 million cycles. Consequently, the volume of wear debris and the ion levels in the lubricants were substantially lower. These parameters were also much lower than in half coated (femoral heads only) systems that have been reported previously. The extremely low volume of wear debris and concentration of metal ions released by these surface engineered systems, especially with CrN and CrCN coatings, have considerable potential for the clinical application of this technology.     

Endurance verification of custom-made hip prostheses

Custom-made stems are a particular class of hip prostheses manufactured in a single sample for a specific patient. Experimental fatigue testing according to ISO standards cannot be performed for pre-clinical validation of these devices. However, the implant manufacturers need to assess the endurance properties of custom-made stems. This study investigates a theoretical protocol to predict the maximum stress induced in the stem by the ISO experimental test set-up. Stress was predicted using beam theory and finite element analysis (FEA). Strain measurements were used to assess the accuracy of the theoretical calculation. Fatigue testing was performed to verify the theoretical prediction about the fatigue stem performance. The results showed that FEA is more accurate than beam theory. Beam theory calculation is able to predict the static stresses induced by the ISO 7206/4 loading set-up with a difference always lower than 20% with respect to a prediction of a simplified FEA. Hence beam theory can be used to estimate the maximum stress. FEA becomes useful for a stem stressed at a limit condition. In both cases precise data about the endurance properties of the material are required for corrected predictions. However, endurance verification should be performed by introducing a safety factor to account for the material and manufacturing variations.     

Continuous and discontinuous fatigue crack growth of irradiated ultrahigh molecular mass polyethylene in saline solution at 37°C

To provide data for prosthesis design, the fatigue crack growth resistance of irradiated ultrahigh molecular mass polyethylene (UHMMPE) in saline solution at 37°C was determined from tests performed on compact tension specimens, comparable in size to the components in knee prostheses. The specimens were cyclically loaded by using a sinusoidal wave form at 1 Hz with a minimum-to-maximum load ratio of 0.1. Scanning electron microscopic fractography was used to examine the fracture surfaces. At higher stress levels, the Paris's Law was used to analyse the data, and a striation pattern with each striation corresponding to multi-cycles was observed. At lower stress levels, discontinuous fatigue crack growth was found, a phenomenon which dominated the fatigue life of the material and had not been reported previously in this material. A craze zone ahead of the crack tip was observed, which formed the discontinuous crack growth band with a length relevant to the Dugdale plastic zone length.     

Design and manufacturing of a human standardised hip cup out of titanium

Background: In recent years, the use of hip prostheses has become a routine procedure. Despite this experience and good clinical results different complications arise which have a negative influence on the lifetime of prostheses. Especially the migration or loosening of the hip cup prosthesis due to strain adaptive bone remodelling is still a problem. Patient‐individual prostheses represent a possible solution to this problem. Individual hip cups, however, are just implanted for the treatment of massive deformities or tumours. This study aimed at developing an innovative concept for the production of patient‐specific human hip prostheses made of titanium plates by sheet metal forming. Methods: For the realisation of this innovative concept, a reproducible design method for the generation of standardised human hip cup prosthesis was generated based on 13 original human geometries. By means of this methodology a hip cup was designed. Based on this design a human hip cup was produced by a developed high‐pressure sheet metal forming process. The development of the process was accompanied by a numerical preliminary design. Results: A comparison between the simulation and the fabricated hip cup leads to a standard deviation of 0.404 mm. Furthermore, an implantation of the prosthesis in a synthetic bone model shows a satisfactory fit accuracy at the edge of the prosthesis. Conclusion: The high‐pressure sheet metal forming process is suitable to manufacture the designed standardised hip cup. However, further optimisation is necessary.     

Artifact level produced by different femoral head prostheses in CT imaging: diamond coated silicon nitride as total hip replacement material

Commercial femoral head prostheses (cobalt–chromium alloy, yttria partially stabilized zirconia (Y-PSZ) and alumina) and new silicon nitride ceramic ones (nanocrystalline diamond coated and uncoated) were compared in terms of artifact level production by computed tomography (CT). Pelvis examination by CT allows the correct diagnosis of some pathologies (e.g. prostate and colon cancer) and the evaluation of the prosthesis-bone interface in post-operative joint surgery. Artifact quantification is rarely seen in literature despite having a great potential to grade biomaterials according to their imaging properties. Materials’ characteristics (density and effective atomic number), size and geometry of the prostheses can cause more or less artifact. A quantification procedure based on the calculation of four statistical parameters for the Hounsfield pixel values (mean, standard deviation, mean squared error and worst case error) is presented. CT sequential and helical scanning modes were performed. Results prove the artifact reproducibility and indicate that the cobalt–chromium and Y-PSZ are the most artifact-inducing materials, while alumina and silicon nitride (diamond coated and uncoated) ceramic ones present a low level of artifact. Considering the excellent biocompatibility and biotribological behaviour reported in earlier works, combined with the high medical imaging quality here assessed, diamond coated silicon nitride ceramics are arising as new materials for joint replacement.     

Numerical simulation of the casting process of titanium tooth crowns and bridges

The objectives of this paper were to simulate the casting process of titanium tooth crowns and bridges; to predict and control porosity defect. A casting simulation software, MAGMASOFT, was used. The geometry of the crowns with fine details of the occlusal surface were digitized by means of laser measuring technique, then converted and read in the simulation software. Both mold filling and solidification were simulated, the shrinkage porosity was predicted by a feeding criterion, and the gas pore sensitivity was studied based on the mold filling and solidification simulations. Two types of dental prostheses (a single-crown casting and a three-unit-bridge) with various sprue designs were numerically poured, and only one optimal design for each prosthesis was recommended for real casting trial. With the numerically optimized design, real titanium dental prostheses (five replicas for each) were made on a centrifugal casting machine. All the castings endured radiographic examination, and no porosity was detected in the cast prostheses. It indicates that the numerical simulation is an efficient tool for dental casting design and porosity control. © 2001 Kluwer Academic Publishers     

Influence of a foreign body on the wear of metallic femoral heads and polyethylene acetabular cups of total hip prostheses

Excessive wear of polyethylene in total replacement hip prostheses elicits deleterious biologic reactions and may be thus a limiting factor that compromises the long-term performance of these devices. This study is based on the report of two clinical failures of total hip prostheses with metallic femoral heads and polyethylene acetabular cups. The investigations reveal that foreign bodies (titanium fibermesh pieces) can migrate into the joint space of total hip prostheses and participate in abrasive third-body wear of the polyethylene cups. This excessive wear of polyethylene enhanced by the modification of the metallic counterface roughness is likely to induce the early loosening of the devices.     

Rapid prototyping and rapid manufacturing in medicine and dentistry

The fundamentals and latest developments of Rapid Prototyping (RP) and Rapid Manufacturing (RM) technologies and the application of most common biomaterials such as titanium and titanium alloy (Ti6Al4V) are discussed in this paper. The issues while fabricating pre-surgical models, scaffolds for cell growth and tissue engineering and concerning fabrication of medical implants and dental prostheses are addressed. Major resources related to RP/RM technology, biocompatible materials and RP/RM applications in medicine and dentistry are reviewed. A large number of papers published in leading journals are searched.

Besides the titanium and titanium alloys which were established as bio-compatible materials over five decades ago, other biocompatible materials such as cobalt-chromium and PEEK have also been increasingly used in medical implants and dental prosthesis fabrication. For over a decade RP technologies such as Selective Laser Sintering (SLS) and Selective Laser Melting (SLM) along with the Fused Depositing Modelling (FDM) are predominantly employed in the fabrication of implants, prostheses and scaffolds. Recently Electron Beam Melting (EBM) has been successfully employed for fabrication of medical implants and dental prostheses with complex features. In dentistry crown restoration, the use of thin copings of Ti6Al4V made by the EBM process is an emerging trend. This review is based upon the findings published in highly cited papers during the last two decades. However the major breakthrough in the field of RP/RM for medical implants and dental prostheses took place in the last decade. The fabrication of medical implants and prostheses and biological models have three distinct characteristics: low volume, complex shapes and they are highly customised. These characteristics make them suitable to be made by RM technologies even on a commercial scale. Finally, current status and methodology and their limitations as well as future directions are discussed.