Bioceramics ― Yesterday,Today, Tomorrow

Developments and applications of bioceramics are reviewed. Used initially as alternatives to metallic materials in order to increase the biocompatibility of implants, bioceramics have become a diverse class of biomaterials presently including three basic types: bioinert high-strength ceramics; bioactive ceramics which form direct chemical bonds with bone or even with the soft tissue of a living organism; various bioresorbable ceramics which are actively included in the metabolic processes of an organism with predictable results. Certain members of the different types of bioceramics are the most bioinert and biocompatible of all known biomaterials. A review of the composition, physicochemical properties, and biological behavior of the principal types of bioceramic materials is given, based on the literature and some of our own data. The materials include, in addition to classical sintered ceramics, bioglass-ceramics and bioglasses which are similar in composition, properties, and applications. Special attention is given to structure as the main physical parameter determining not only the properties of the ceramic materials, but also their reaction with the biomedium. The present status of research and development in bioceramics is characterized as a first step in the solution of complex problems at the confluence of materials science, biology, and medicine by the synthesis of smart materials.     

Albumin adhesion on ceramics and correlation with their Z-potential

An investigation into albumin adhesion on ceramics was carried out, providing useful information on the relationship between the Z-potential of ceramic materials and the amount of closely adhered albumin. The chemical nature of the substance constituting the ceramic is mainly responsible for the adhesion, but additional influencing factors are also considered. A differentiation in the amount of adhesion (which is a consequence of the forces of attraction between the ceramic surface and the molecules of albumin) is found and concerns the biological quality of the materials, particularly the bioactive and bioinert ceramics.     

Biodegradable interlocking nails for fracture fixation

Serious problems such as stress shielding, allergic reactions, and corrosion are associated with the use of metallic fracture fixation devices in fractured long bones. Metal implants often are removed during a second retrieval operation after fracture healing has completed. A biocompatible implant that degrades slowly during implantation would obviate the need for a second operation and save the patient from considerable physical, psychologic, and financial discomfort. The biodegradable implant must provide the fractured limb sufficient support for a certain time, allowing early loading. A gradual transfer of load from the biodegradable implant to the bone would result in a better product of bone healing and avoid stress shielding. In an animal model using adult sheep, two types of biodegradable polymer interlocking nails were tested in comparison with a stainless steel interlocking nail. Fracture healing, mechanical properties of the bones, degradation behavior in vivo and in vitro, and tissue response were monitored during a 2 1/2-year followup study. To detect shifts in acid base relations caused by the release of acid compounds, pH measurements were performed. Fracture healing was unimpaired, and the mechanical test results of all three groups were excellent. Histologic analysis showed a mild inflammatory response, but no pH shifts were observed. The results of this study justify additional research on these promising materials.     

Effect of acetaldehyde generated from ethanol by ADH-transfected CHO cells on their membrane fatty acid profiles

Unloaded cylindrical grit-blasted titanium (Ti-6A-4V) implants (6 x 10 mm) coated with hydroxyapatite ceramic were inserted into the proximal part of the humerus of 20 skeletally mature Labrador dogs. The implants were initially surrounded by a 2 mm gap. In 10 dogs, HA-coated implants without growth factor were inserted in one humerus and implants with 0.3 microgram rhTGF-beta 1 adsorbed onto the HA coating were inserted in the contralateral humerus. In another group of 10 dogs, a dose of 3.0 micrograms rhTGF-beta 1 was tested in a similar design. All dogs were killed at 6 weeks after treatment. Results were evaluated by histomorphometry and mechanical push-out testing. Bone ongrowth was increased by one third, using the 0.3 mg rhTGF-beta 1 stimulation. Bone volume in the gap and mechanical testing showed no statistically significant differences between control and rhTGF-beta 1 stimulated implants. RhTGF-beta 1 only moderately enhanced bone ongrowth to hydroxyapatite-coated implants.     

Resorption of hydroxyapatite and fluorapatite coatings in man. An experimental study in trabecular bone

The clinical use of hydroxyapatite (HA) coating is controversial especially in regard to the long-term performance of the coating and the effects of resorption. In each of 15 consenting patients we inserted two implants, coated with either HA or fluorapatite (FA) into the iliac crest. They were harvested at a mean of 13.6 +/- 0.6 months after surgery. Histological examination showed that bone ongrowth on the HA-coated implants was significantly greater (29%) than that on the FA-coated implants. When bone was present on the coating surface the HA coating was significantly thicker than the FA coating. When bone marrow was present, the HA coating was significantly thinner than the FA coating. The reduction in coating thickness when covered by bone or bone marrow was 23.1 +/- 9.7 microm for HA and 5.1 +/- 1.7 microm for FA (p < 0.01) suggesting that FA is more stable than HA against resorption by bone marrow. The findings suggest that in man the osteoconductive properties of HA coating are superior to those of FA. Resorption rates for both coatings were approximately 20% of the coating thickness per year. Bone ongrowth appears to protect against resorption whereas bone marrow seems to accelerate resorption. No adverse reaction was seen in the surrounding bone.     

Tissues and bone adhesives--historical aspects

Glues and adhesives attach to a surface principally involving molecular attraction, whereas cements mostly work through mechanical interlocking. The adhesive and its degradation products must be biocompatible: chemical, clinical, legal, physical aspects are considered; the toxicity of even minor components must be extremely reduced. The idea of bone bonding using biological materials has been proposed by Gluck, in Berlin, more than a century ago. Cements and adhesives have been used for the fixation of fractures, the repair of defects and the fixation of prostheses. The cements are initially liquid or plastic and conform with the irregularities in the substratum, producing better bonding on rough surfaces. Developed during the early 1950s, cyanocrylate adhesives attracted the medical community by their bonding strength and ability to bond in wet environments but reports of displacement of the fracture ends were followed by reports of high infection rates, nonunion, and severe local reactions. Polymethylmethacrylate does not form a chemical bond with bone but a mechanical bond, a weak bone-polymer joint. Charnley used self-curing acrylic cement to bond a femoral head prosthesis into a femur. When adhesives are used to bond tissues, the polymer acts as a barrier between the growing edges and delay healing; the adhesive tends to be rapidly isolated from the bone by a fibrotic, non-adhesive capsule. No proof exists concerning the osteogenic potential of fibrin sealing (FS); its beneficial effect on bone formation has been questioned even if there is some evidence that FS should influence the early phases of bone repair and may help to solve the problem of reattachment of small osteocartilagenous fragments following joint trauma.     

纳米技术在电触头材料中的应用

自80年代纳米技术在材料领域通过纳米粒子以及各种超微细的结构模块，导致产生出许多新的具有优异性能和新的应用可能的纳米复合材料。纳米材料由于组成晶粒超细，大量原子位于晶界上，因而在机械性能、物理性能和化学性能等方面都优于普通的粗晶材料。最近几年这一技术在电触头材料的研究和制备过程中已经有了初步的应用，并取得了良好的效果。综述了近几年来纳米技术在电触头材料中的应用概况，介绍了已经制备出并见于报道的和正在研究的纳米晶触头材料的具体制备工艺及其性能的改善情况，展望了纳米技术在该类材料中的应用前景。     

Biomaterials: a forecast for the future

The survivability half-life of prostheses made with current bio-inert materials is approximately 15 years, depending upon clinical applications. Bioactive materials improve device lifetime but have mechanical limitations. This paper proposes that biomaterials research needs to focus on regeneration of tissues instead of replacement. Alternatives are: use hierarchical bioactive scaffolds to engineer in vitro living cellular constructs for transplantation, or use resorbable bioactive particulates or porous networks to activate in vivo the mechanisms of tissue regeneration.     

Ceramic/metal interfacial crack growth: Toughening by controlled microcracks and interfacial geometries

Toughening of ceramic/metal interfaces through the use of controlled interfacial geometries and non-coplanar microcrack-like pores is examined with respect to both critical and subcritical crack growth. Patterned uniform arrays of inclined interfacial steps and of “microcracks/voids” (with width 22 μm and spacing 10 μm), out-of-plane to the main interfacial crack, were produced for glass/copper interfaces by photo-lithographic techniques combined with evaporation and diffusion bonding processes. Significant toughening and improved stress corrosion crack-growth resistance is achieved through the promotion of crack-tip shielding primarily from crack bridging. Specifically, plastic void growth within the copper is seen to generate bridged ligaments of metal film between the glass substrates; the resulting mechanical crack bridging leads to plastic stretching of the film and provides the dominant toughening mechanism, with a smaller contribution from crack deflection. Correspondingly, subcritical (pre-instability) crack-growth rates with the patterned arrays in “wet” and “dry” gaseous atmospheres are retarded by orders of magnitude compared to rates for plain interfaces. The toughness with the various patterned interfaces exhibits marked resistance-curve (R-curve) behavior with fracture toughness values increased by factors of 4–9 compared to intrinsic fracture toughness, G₀, values of ∼2 J/m² for these plain glass/copper interfaces. Surface roughness of the glass substrate is reasoned to be a controlling parameter for the shape and magnitude of such crack-resistance curves.     

Collagen/apatite coating on 3-dimensional carbon/carbon composite

A three-dimensional carbon/carbon composite (3D C/C) was studied as potential bone-repairing material; its major mechanical properties were found to be closer to those of human bone than other common bone-repairing materials available. In vitro calcification tests revealed that as-received 3D C/C is almost bioinert in simulated body fluid (SBF) over an immersion period of 4 weeks. To improve the bioactivity of 3D C/C, surface modification was accomplished through two practical routes: (1) grafting with polyethylene glycol (PEG) and (2) phosphorylation and precalcification. After grafting with alpha, omega di(aminopropyl) polyethylene glycol 800 (NH2-PEG-NH2), a continuous layer of calcium phosphate was formed on the surface of 3D C/C in SBF after 4 weeks. Phosphorylated 3D C/C samples have the ability to induce apatite precipitation after precalcification in a saturated Ca(OH)2 solution for 1 week. To speed up the coating process, a calcification solution with collagen was developed in which a collagen/apatite coating layer can be formed on 3D C/C in 9 h in ambient conditions.     

Making Calcium Phosphate Biomaterials

Processes are considered for making materials for medical purposes (filling bone cavities). Methods are surveyed for making materials for osteoplastic treatment such as bioactive glasses, glass ceramics, biological or synthetic hydroxyapatite, and composites based on them.     

Atomic structure of heterophase interfaces

High-resolution electron microscopy (HREM) has been used to study internal interfaces between dissimilar materials, notably ceramic-metal interfaces. Structures observed for systems with small and large misfits are compared in metal-metal, metal-ceramic, and ceramic-ceramic boundaries. The interfaces were prepared by a variety of techniques, including internal reduduction, internal oxidation, and epitaxial growth by MOCVD and special thin-film techniques. While interfaces produced by internal oxidation and reduction in f.c.c. systems typically form boundaries on (111) planes, non-equilibrium boundaries have also been generated using special thin film techniques. All boundaries can be characterized by their tendency to form coherent structures. While it appears that the amount of misfit and the bond strength primarily determine the degree of coherency, kinetic factors and substrate defects also seem to play an important role in determining the local defect structure at the boundary and the type of misfit localization.     

Application of computational thermodynamics to Fe/Ni,Fe-3%Si/Ni and 316L/Ni systems produced by powder metallurgy

The commercial simulation software packages, Thermo-Calc and DICTRA, are widely used to predict phase formation and diffusion in materials prepared by traditional metallurgical processes. The goal of this work was to clarify whether the software can also be applied to materials produced by powder metallurgy techniques. For this purpose, diffusion couples of the material combinations Fe/Ni, Fe-3%Si/Ni and 316L/Ni were prepared by two techniques: co-pressing of powders followed by co-sintering and joining of two sintered parts followed by annealing. Thermo-Calc and DICTRA were used to predict interface formation and phase transformations during heat treatments. Scanning electron micrography and energy-dispersive X-ray spectrometry showed the formation of interdiffusion interfaces. The diffusion rate was higher in co-sintered couples, resulting in broader interdiffusion zones than those predicted by simulations, but the annealed couples exhibited interdiffusion profiles similar to those predicted by DICTRA simulations. In general, simulations and experimental results showed the same tendencies.     

Bone bonding ability of bioactive bone cements

The bone bonding ability of three types of bioactive bone cement A, B, and C consisting of glass or glass ceramic powder and bisphenol-alpha-glycidyl methacrylate resin was evaluated. Type A contained MgO-CaO-SiO2-P2O5-CaF2 glass powder; Type B, MgO-CaO-SiO2-P2O5-CaF2 glass ceramic powder; and Type C, MgO free CaO-SiO2-P2O5-CaF2 glass powder. Rectangular plates (2 x 10 x 15 mm) of Types A, B, C, and polymethylmethacrylate cements were implanted into the tibial metaphyses of male rabbits and the failure load measured by mechanical failure testing (detaching test) 10 and 25 weeks after implantation. The failure loads of Types A, B, C, and polymethylmethacrylate cements were respectively, 29.52, 41.48, 28.22, and 0.29 N at 10 weeks and 33.42, 41.27, 33.64, and 0.20 N at 25 weeks. Examination of the bone cement interface revealed that all the bioactive bone cements achieved direct bone contact with the bone. These results showed that all three types of bioactive bone cement have the ability to bond to bone, and the cement containing glass ceramic powder revealed higher bonding strength than did those containing glass powder.     

Endotherapy for chronic pancreatitis

This is a review of salient studies of sterilization, toxicity, biocompatibility, clinical applications and current work in the field of orthopaedics, using implants made of polylactic acid (PLA), polyglycolic acid (PGA) and their copolymers. The intrinsic nature of these biomaterials renders them suitable for applications where temporally slow releases of bioactive agents in situ may be required. They are also desirable as fixation devices of bone, because they can virtually eliminate osteopenia associated with stress shielding or additional surgery. The majority of currently available sterilization techniques are not suitable for these thermoplastic materials and it may be desirable to develop new sterilization standards, which can account for the special character of PLA-PGA materials. Biocompatibility and toxicity studies suggest that, overall, PLA-PGA biomaterials may be suitable for orthopaedic applications, although certain problems, especially pertaining to reduction in cell proliferation, have been reported. Clinical applications are also promising, albeit not without problems usually associated with transient tissue inflammation. The future of these materials appears bright, especially in soft tissues. They may be used to address the exceedingly complex problem of osteochondral repair, but also as a means to enhance fixation and repair processes in tendons and ligaments.     

A method for shape optimization of a hip prosthesis to maximize the fatigue life of the cement

The long term success of total joint replacement can be limited by fatigue failure of the acrylic cement and the resulting disruption of the bone-cement interface. The incidence of such problems may be diminished by reduction of the fatigue notch factor in the cement, so that stress concentrations are avoided and the fatigue crack initiation time maximized. This study describes a method for numerical shape optimization whereby the finite element method is used to determine an optimal shape for the femoral stem of a hip prosthesis in order to minimize the fatigue notch factor in the cement layer and at interfaces with the bone and stem. A two-dimensional model of the proximal end of a femur fitted with a total hip prosthesis was used which was equivalent to a simplified three-dimensional axisymmetric model. Software was developed to calculate the fatigue notch factor in the cement along the cement/stem and cement/bone interfaces and in the proximal bone. The fatigue notch factor in the cement at the cement/stem interface was then minimized using the ANSYS finite element program while constraining the fatigue notch factor at the cement/bone interface at or below its initial level and maintaining levels of stress in the proximal bone to prevent stress shielding. The results were compared with those from other optimization studies.     

A review of the recent advances in magnetic resonance imaging in the assessment of osteoporosis

Osteoporosis is a common metabolic disorder with considerable associated morbidity and mortality. The loss of bone mineral integrity and the resultant occurrence of atraumatic fractures are typically symptomatic of the disease. Currently skeletal status is commonly assessed using non-invasive conventional radiography and scintigraphy as well as densitometric techniques such as quantitative computed tomography and dual-energy X-ray absorptiometry. But, apart from gross bone mineral density, the fine structure of trabecular bone also plays an important role in defining the biomechanical competence of the skeleton. Recently attention has been focused on deriving measures that provide information about not only trabecular bone density but also microstructure. Magnetic resonance imaging (MRI) is one such new technique which potentially may provide information pertaining to bone density and structure as well as to occult fracture detection. Cortical bone produces a signal void in MR images, due to the fact that it contains very few mobile protons that give rise to a signal in MRI; also the MR relaxation time T2 of these protons is very short which produces a very fast decay of the MR signal during image acquisition. However, the trabecular bone network affects the MR properties of bone marrow. The difference in the magnetic properties of trabecular bone and bone marrow generates local imperfections in the magnetic field. The MR signal from bone marrow is modified due to these imperfections and the MR relaxation time T2 of marrow is shortened. The extent of relaxation time shortening and hence loss of signal intensity is proportional to the density of trabecular bone and marrow interfaces and their spatial architecture. Recent investigation in this area include studies aimed at quantifying marrow relaxation times and establishing their relationship to trabecular bone density and structure. In addition, with advances in imaging software and hardware, MR images at in-plane resolutions of 78-200 microns may be obtained. The trabecular bone structure is clearly revealed in such images and studies aimed at the development of high-resolution MRI techniques combined with quantitative image analysis techniques are currently under way. These potentially useful techniques for assessing osteoporosis and predicting fracture risk are reviewed in this paper.     

临床外科手术中骨切削技术的研究现状及进展

对骨切削研究中的骨切削数值仿真本构模型、骨切削手术工艺及机理等方面进行了综述, 着重介绍了切削参数对骨切削的影响、骨切削刀具设计等, 并对医学领域新兴的超声骨切削技术进行了介绍和分析.最后得出应从以下方面完善骨切削研究: (1)骨切削数值仿真的本构模型有待开发; (2)构建系统的骨材料切削理论以解释骨材料切屑形态的切削机理; (3)骨材料切削刀具的开发需要进一步深化; (4)超声骨切削由于安全性高、损伤小、愈合快的特点将成为未来临床骨切割操作的发展方向和趋势.      

Clinical use of a bioactive glass particulate in the treatment of human osseous defects

The dental practitioner has a wide choice of materials available for use in bone grafting procedures. A bioactive glass particulate possesses many favorable qualities not often found in other materials, including the ability to remain where placed even with adjacent suctioning; hemostasis; and incorporation into the host bone without the fibrous encapsulation encountered with most other synthetic materials. It is also quick and easy to prepare. This article reviews clinical experiences with PerioGlas in the setting of private practice periodontics, in which this material was used as the grafting material for periodontal defects, apicoectomies, cysts, and ridge augmentation and maintenance procedures, as well as for implant repairs. Several cases detail the advantages of this grafting material.