Tissue/biomaterial interface characteristics of four elastomers. A transmission electron microscopical study

The tissue/biomaterial interface reactions of four elastomers--selected as candidates for scaffolding for tympanic membrane tissue in a total alloplastic middle ear prosthesis--were studied at the electron microscopical level after implantation in the rat middle ear. Time-dependent changes in the phagocyte/polymer interface suggested degradation of porous implants made of Estane polyether urethane, polypropylene oxide, and a poly(ethylene oxide hydantoin) and poly(tetramethylene terephthalate) segmented polyether polyester copolymer (HPOE/PBT copolymer), but not of dense Silastic silicone rubber implants. Silastic was always encapsulated in fibrous tissue. Contact between fibrous tissue and HPOE/PBT copolymer or Estane was established in the third month, but fibrous tissue was never seen close to polypropylene oxide. Bone made contact only with Estane and HPOE/PBT copolymer implants. The bone/copolymer interface showed an electron-dense layer morphologically similar to that seen between bone and hydroxyapatite ceramic, suggesting that with respect to bone HPOE/PBT copolymer behaves like a bioactive implant material. The electron-dense layer was absnet at the bone/Estane interface. Estane and especially HPOE/PBT copolymer seem to be suitable as alloplastic tympanic membrane because of their interface behavior with respect to fibrous tissue and bone.     

Ultrastructural comparisons of ceramic and titanium dental implants in vivo: a scanning electron microscopic study

Identically prepared, screw-type ceramic and titanium endosteal dental implants were inserted in the jaws of adult mongrel dogs for periods of up to 6 months. Sixteen of the 32 total implants supported fixed bridgework. The interface of bone and soft connective tissues with the dental implants was examined by routine and innovative scanning electron microscopic (SEM) techniques using both secondary and backscattered electron imaging. Results demonstrated excellent bone adaptation to both titanium and ceramic implants. Direct adaptation of bone to the upper third of both type implants was observed with only minimal amounts of any intervening fibrous connective tissue. A composite of trabecular bone and fibrous connective tissue was observed in the lower two-thirds of the implants examined. Areas of bone alteration suggestive of osteoid were observed at the thread apicis of some loaded implants. From this investigation we concluded that similar longitudinal tissue responses were generated to one-piece, cylindrical screw-type titanium and alpha alumina oxide ceramic dental implants. Possible bone remodeling was observed at the thread apicis of the loaded implants, an area where occlusal forces may be distributed. We further suggest that one-stage endosteal implants are capable of maintaining a proportional bone-to-implant interface at the apical support region, similar to that suggested to two-stage implant systems.     

Small changes in polymer chemistry have a large effect on the bone-implant interface: evaluation of a series of degradable tyrosine-derived polycarbonates in bone defects

In a series of homologous, tyrosine-based polycarbonates, small changes in the chemical structure of the polymer pendent chain were found to affect the bone response in a long-term (1280 d) implantation study. Identically sized pins, prepared from poly(DTE carbonate), poly(DTB carbonate), poly(DTH carbonate), and poly(DTO carbonate) were implanted transcortically in the proximal tibia and the distal femur of skeletally mature New Zealand White Rabbits. The tissue response at the bone-implant interface was characterized in terms of the absence of a fibrous capsule (direct bone apposition, indicative of a bone bonding response) or the presence of a fibrous capsule (referred to as the encapsulation response). The relative frequency of direct bone apposition versus encapsulation was recorded for each polymer throughout the entire period of the study. While all four polymers were tissue compatible, there was a correlation between the chemical structure of the pendent chain and the type of bone response observed, with poly(DTE carbonate) having the highest tendency to elicit direct bone apposition. Based on in vivo degradation data and the ability of model polymers with carboxylate groups at their surface to chelate calcium ions, it is proposed that the ability of poly(DTE carbonate) to bond to bone is caused by the facile hydrolysis of the pendent ethyl ester groups which creates calcium ion chelation sites on the polymer surface. The incorporation of calcium chelation sites into the chemical structure of an implant material appears to be a key requirement if direct bone apposition/bone bonding is desired. This study demonstrates that very subtle changes in the chemical composition of an implant material can have significant effects on the long-term tissue response in a clinically relevant model.     

组织工程骨-假体界面微观结构与元素分析的意义

目的研究假体-组织工程骨界面的微观结构和钙磷元素及构成比动态变化及意义。方法取新西兰大白兔15只,将兔骨髓间充质干细胞培养、扩增及诱导后,与珊瑚羟基磷灰石复合构建组织工程骨;双侧股骨髁分别制作一0.5cm×1.2cm骨缺损,骨缺损中央植入0.2cmx1.0cm钛合金植入体,左侧植入体周围植入组织工程骨,右侧仅植入珊瑚羟基磷灰石为对照,于术后4周、8周和l2周分别行X线检查、扫描电镜及能谱分析观察植入体表面微观结构和钙磷元素百分含量及比值的变化。结果 X线检查示,实验组术后8-12周可见大量模糊的高密度骨痂影,缺损区与周围骨质间分界变模糊。对照组各时间点无明显变化;扫描电镜示,实验组术后8、12周植入体表面孔隙内有大量无定形物质,而对照组未见有无定形物质。能谱分析示,不同时间点实验组较对照组内钙、磷元素百分含量高,有显著性差异（〈0.05）,随着时间的变化实验组和对照组Ca、P百分含量都呈增高的趋势,但12周和8周相比无显著性差异（〉0.05）。实验组内钙磷比值随时间变化有逐渐增大趋势,8周时达峰值,8周后缓慢下降。结论假体-组织工程骨界面钙、磷元素及构成比的动态变化表明骨整合的形成,并随着时间的延长骨改建逐步增加。     

Histological and histomorphometric investigations on bone integration of rapidly resorbable calcium phosphate ceramics

Resorbable ceramics can promote the bony integration of implants. Their rate of degradation should ideally be synchronized with bone regeneration. We report here the results of a histological study of implants with two resorbable calcium phosphate ceramic coatings: Ca(2)KNa(PO(4))(2)-(GB14) and Ca(10)[K/Na](PO(4))(7)-(602020). The results attained with these ceramic-coated implants show the benefits of these materials with regard to bioactive bone-healing stimulation, compared with uncoated implants. The GB14 ceramic coating exhibited greater bone regeneration and differentiation on its surface than the conventional hydroxyapatite coating and helped bone tissue achieve more extensive contact free of connective tissue. Not until the coating disintegrated did the histological features of GB14- and 602020-coated implants converge-both implant types were integrated into bone. Rapid disintegration of the coating material, as with 602020, supports osteoblast proliferation but has negative effects on bone mineralization. Both resorbable ceramics tested, GB14 and 602020, demonstrated bioactivity; even metal surfaces coated with these materials were populated by mature bone tissue without connective tissue after disintegration of their ceramic coating. The less rapidly degrading material, GB14, achieved better results. Degradable calcium phosphate coatings have the potential to stimulate bone regeneration. From the histological viewpoint, the resorbable ceramics examined here can be recommended as coating materials for clinical use.     

Compositional variations in the surface and interface of calcium phosphate ceramic coatings on Ti and Ti-6Al-4V due to sintering and immersion

The compositions of the surface and the interface of calcium phosphate ceramic (CPC) coatings electrophoretically deposited and sintered on titanium or its alloy, were determined by scanning Auger electron spectroscopy before and after 4 wk of immersion in a simulated physiological solution. In the CPC coating-metal interfaces, the phosphorus diffused beyond the titanium oxide layer. The phosphorus concentration in the interface followed a Gaussian distribution for both unalloyed and alloyed titanium. The diffusion depleted P in the ceramic adjacent to the metal. The surface of the ceramic, however, was substantially unchanged. A major change in the compositional depth profiles was induced by immersion: thick and uniform titanium phosphide layers of constant composition were observed on the Ti-based metal substrates.     

Preliminary studies of the histopathological responses to Ti-13% Cu casting alloys

A preliminary study of some of the biological properties of a new dental casting alloy (Ti-13% Cu) was undertaken by employing the skeletal muscle implantation test in rabbits. Routine histopathological and chemical analysis techniques were utilized to study in vivo tissue reactions of skeletal muscle to this alloy. A moderately thick, somewhat cellular fibrous connective tissue capsule surrounded the implants after 2 wk. Remodelling of the fibrous tissue into a thin acellular tissue capsule occurred at 52 wk after implantation. Chemical analyses failed to detect deposition of either Ti or Cu corrosion products at the implant sites or within major organs.     

The interface zone of inorganic implantsIn vivo: Titanium implants in bone

The interface zone between titanium implants and bone is considered at the macroscopic, microscopic, and molecular levels. A high rate of successful dental implants of pure titanium is associated with a very close apposition of the bone to the titanium surface, called osseointegration. At the macroscopic level, osseointegration allows efficient stress transfer from the implant to the bone without abrasion or progressive movement that can take place if a fibrous layer intervenes. At the microscopic level, surface roughness and porosity provide interlocking of the implant and bone tissue which grows into direct contact with titanium. Sections studied in the electron microscope show that calcified tissue can be identified within 50 Å of the implant surface. The interface zone includes a tightly adherent titanium oxide layer on the surface of the implant which may be similar to a ceramic material in relation to tissue response. The five year success rate of 90% in 2895 implants in clinical trials since 1965 is associated with the favorable behavior of bone tissue at the interface zone with pure titanium.     

Osseointegration of 2 different types of calcium phosphate materials: ceramics and ionic cements

Different kinds of calcium phosphate biomaterials can be used as bone substitutes. Ceramics are constituted by HA or TCP grains linked by grain boundaries. Their porosity depends on the powder characteristics and the sintering temperature. It can be very low with a pore size inferior to one micron. The setting of calcium phosphate hydraulic cements results from the precipitation of a calcium phosphate phase different from the one in suspension in the paste. The strength of the cement is given by the entanglement of the growing mineral crystals. Calcium phosphate hydraulic cements and ceramics have very different physico-chemical characteristics. We have studied the histological integration of both kinds of material. The first material was constituted by macroporous ceramics composed of 75% HA and 25% beta-TCP, the cement was made of beta-TCP grains dispersed in a DCPD matrix. The sequence of events which leads to the ceramic integration is always the same: a/ ingrowth of a loose connective tissue; b/ osteoblast differentiation from fibroblast-like cells of the connective tissue in close proximity to the implant surface; c/ osteoid synthesis at the ceramic surface toward the pore center; d/ remodeling of the immature bone and the ceramic itself. The cement is differently integrated. The osteoblasts differentiate at some distance from the implant and there is a trabeculae ingrowth toward the material. CONCLUSIONS: The early stages of both materials osteointegration are different. The integration is centrifugal for ceramics and centripetal for the cement.     

Tensile strength of the interface between hydroxyapatite and bone.

Tensile strength of the interface between hydroxyapatite (HA) and bone was tested. Scanning electron microscopy was used to observe the tensile failure mode and the morphological change of hydroxyapatite ceramic surface in bone. The porosity of hydroxyapatite is 14% and pore size less than 2 microns. After 2 weeks of implantation, the tensile strength of the interface is 0.72 MPa. After 4, 8, and 16 weeks, the average tensile strength stayed at 1.5 MPa. SEM showed that tensile failure occurred at the HA-bone interface at the second week, but after 4 weeks, the failure occurred between HA particles within the bulk, and not at the HA-bone interface. Calcified tissue was directly deposited on the HA ceramic surface and exits also in the micropores. Near the interface, sintered necks among HA ceramic particles were subjected to biodegradation.     

锌修饰硅酸钙陶瓷涂层与骨整合

BACKGROUND: Zinc-modified calcium silicate (CaSiO3) bioceramics coating on the titanium surface prepared in preliminary experiments has good chemical stability and antibacterial property. OBJECTIVE: To observe the effects of zinc-modified CaSiO3 bioceramics coating on osteointegration. METHODS: MC3T3-E1 cells were respectively cultured on the titanium with zinc-modified CaSiO3 bioceramics coating (experiment group), titanium with CaSiO3 bioceramics coating (control group) and pure titanium (blank control group). Then, cell adhesion, proliferation, calcification rate and the expression of type I collagen and osteocalcin were detected. The implant materials mentioned above were respectively inserted into the femurs of New Zealand white rabbits, and after 1.5 months, the osteoproliferation and osteointegration between the implants and the host were tested. RESULTS AND CONCLUSION: In vitro experiment: The number of adhesive cells at 12 hours after co-culture was significantly increased in the experimental group compared with the control group and blank control group (P < 0.05). At 14 days after co-culture, cell proliferation ability and ability of calcium nodule formation in the experiment group were significantly better than those in the other groups (P < 0.05). At 21 days after co-culture, there was no significant difference in the expression of type I collagen, but the expression of osteocalcin in the experiment group was higher than that in the control group and blank control group (P < 0.05). In vivo experiment: In the experiment group, a large amount of bone substances were detected, the coating materials directly contacted with the bone interface, new bone tissues and little fibrous tissues were observed at the interface. In contrast, there was a small amount of bone hyperplasia in the control group and almost no bone hyperplase in the blank control group. Moreover, a small part of the implant directly contacted with the bone interface and the most part was separated from bone trabeculae by fibrous tissues. These findings indicate that zinc-modified CaSiO3 bioceramics coating can enhance the ability of osteointegration between titanium implants and the host.      

Growth of bone marrow cells on porous ceramics in vitro

Following the transplantation of bone marrow cells to extra-osseous sites, bone formation occurs in those sites. This osteogenic potential of bone marrow cells might be utilized for filling defects in bone if they could be transported on porous ceramic materials. Before such an approach becomes feasible, it is important to know what happens to the cells in the presence of the ceramics that might be used. In order to investigate the interaction between bone marrow cells and ceramics, in vitro, a system for culturing bone marrow cells on ceramic materials has been developed. Bone marrow cells adhered well to the surface of calcium hydroxyapatite and tricalcium phosphate ceramics, and this was followed by the formation of fibrous tissue on and within the ceramics. These ceramics were compatible with bone marrow cells even in culture conditions in which there was a large surface area of ceramic interfacing with cells. The results support the proposal that calcium hydroxyapatite and tricalcium phosphate are appropriate as bone replacement materials. In contrast, calcium aluminate had an adverse effect on bone marrow cells when there was a high proportion of ceramic to culture medium. However, this effect was not present if the proportion of ceramic to culture medium was low. Therefore, a large amount of biodegradable porous calcium aluminate ceramic should not be used as an alternative to autogeneous bone grafting.     

Evaluation of ceramics composed of different hydroxyapatite to tricalcium phosphate ratios as carriers for rhBMP-2

We have investigated pellet-shaped implants prepared from biphasic calcium phosphate (BCP) ceramics with five different ratios of hydroxyapatite (HAP) to beta tricalcium phosphate (beta-TCP). The purpose of this study was to evaluate these BCP ceramics as carriers for rhBMP-2. BCP ceramics impregnated with the different doses of recombinant human bone morphogenetic protein 2 (rhBMP-2) (1, 5 and 10g) were used for the experimental purpose and the ceramics without rhBMP-2 were used as control. The pellets were placed into subcutaneous pockets on the dorsum of 4-week-old male Wistar rats. The animals were sacrificed 2 and 4 weeks after implantation. Bone induction was estimated by alkaline phosphatase (ALP) activity measured at 2 weeks after implantation. Pellets were also examined radiologically, histologically and histomorphometrically. The results showed that all experimental pellets exhibited new bone formation whereas the control pellets produced only fibrous connective tissue. Here, 100% HAP ceramic showed most amount of bone formation, whereas 25% HAP to 75% TCP ceramic produced the bone least in amount among different BCP ceramics at the end of 4 weeks. This study indicates that formation of new bone depends on the ceramic content with high HAP-TCP ratio and high dose of rhBMP-2.     

Surface reactions of calcium phosphate ceramics to various solutions

The surface reactions of calcium phosphate ceramics have been thought to play an important role in bonding with living bone. Hydroxyapatite (HA), tricalcium phosphate (TCP), and two kinds of apatite-containing glass ceramics were immersed in three types of solutions with different chemical constituents. The first solution was a physiological saline, the second contained phosphate (PO4), and the third was a balanced salt solution consisting of calcium (Ca), magnesium (Mg), and PO4. After serial incubation periods, changes in the solutions were assessed by measurement of total Ca, Mg, and PO4. The ceramic surfaces were studied using scanning electron spectroscopy, infrared reflection spectroscopy, and thin-film x-ray diffraction. The surface reactions of the ceramics were greatly affected by the chemical compositions of the surrounding media. In the complete solution with both Ca and PO4, a carbonated apatite layer was formed on the surfaces of HA, TCP, and the glass ceramics. In comparison to HA and TCP, the glass ceramics were characterized as Ca-releasing materials, the dissolved Ca creating an apatite layer on the surfaces in a few days, in conjunction with PO4 stock in the surrounding media. The immersion test with various solutions proved to be a simple and effective method of assessing surface conditions of ceramic materials.     

Effect of enamel matrix proteins on the periodontal connective tissue-material interface after wound healing

The periodontal ligament has the potential to regenerate a complete periodontal connective tissue attachment, starting with the deposition of cementum, on pathologically exposed root surfaces as well as several materials including titanium oxide. However, most commonly used dental materials result in a fibrous encapsulation or a chronic inflammatory response after periodontal wound healing rather than the formation of a periodontal connective tissue attachment. Recently, an extract of porcine enamel matrix (Emdogain(R), EMD) has been reported inductive of cementum formation in both in vivo and in vitro studies. The aim of this study was to determine the effect of EMD, when applied to materials previously reported not supportive of periodontal connective tissue formation, on the periodontal connective tissue-material interface obtained with these materials in vivo. Bilateral osteotomies were performed on the mandible of a Yucatan minipig exposing the buccal root surface of four premolars. A series of four preparations were placed in each root surface that were subsequently filled with calcium hydroxide, gutta percha, mineral trioxide aggregate (MTA), or left unfilled. One side, in addition, received an application of EMD prior to surgical closure. A bioabsorbable surgical barrier membrane was placed over the osteotomy sites to exclude gingival connective tissue from the wound-healing environment. The mucoperiosteal flaps were then readapted and sutured in position. The animal was euthanized 10 weeks after the procedure, block sections obtained and prepared for light microscopy. Results demonstrated complete regeneration of alveolar bone and periodontal ligament in all four teeth from the EMD-treated side. Fibers from the periodontal ligament were observed to insert into a mineralized matrix consistent with cementum on all four root preparations. In contrast, massive root resorption without regeneration of alveolar bone was found on all teeth from the side not treated with EMD. The results of this pilot study suggest that the application of EMD to material surfaces that normally do not support periodontal connective tissue attachment formation can alter the type of periodontal connective tissue interface obtained with these materials.     

The biocompatibility of hydroxyapatite ceramic: a study of retrieved human middle ear implants

The biocompatibility of 11 hydroxyapatite auditory canal-wall prostheses and 4 hydroxyapatite incus prostheses implanted for 4 to 40 months was evaluated by light microscopy, scanning electron microscopy, transmission electron microscopy, and R?ntgen microanalysis. These 15 prostheses representing 4% of 375 prostheses, has been removed because of unresolved chronic middle ear infection, residual cholesteatoma, or poor fit. The findings confirmed earlier reports on the biocompatibility of hydroxyapatite in vitro, in animals, and in man. An electron-dense layer was found at the interface with bone and fibrous tissue, and a firm bond between the ceramic and bone at the hydroxyapatite ceramic/bone interface developed. Macropores became filled with bone and fibrous tissue, and the tissue in the individual pores was interconnected. Furthermore the incus prostheses were covered with an epithelium similar to that found in the human middle ear. Findings diverging from those made in other studies were the relatively large amount of exudate in the pores, an apparent increase of degradation during infection, and the accumulation of trace elements in one of the canal-wall prostheses. In all likelihood these three phenomena may be attributed to the unfavorable conditions to which these prostheses were exposed during implantation.     

Bonding osteogenesis in coralline hydroxyapatite combined with bone marrow cells

Coralline hydroxyapatite ceramics alone (control) and the ceramics combined with rat marrow cells were implanted subcutaneously in the backs of syngeneic Fischer rats and harvested at 1,2,3,4,6,8 and 24 wk after surgery. None of the control ceramics (without marrow) showed bone formation. However, ceramics combined with marrow cells showed consistent new bone formation in the pore regions. Histometrical results revealed increased new bone formation over time. Undecalcified sections of the ceramics studied by fluorochrome labelling showed that the osteogenesis began directly on the surface of the ceramic and proceeded centripetally towards the centre of the pores (bonding osteogenesis). SEM-EPMA analysis of the bone-ceramic interface also revealed direct bonding of bone to the ceramic surface.     

Reconstruction of critical size calvarial bone defects in rabbits with glass-fiber-reinforced composite with bioactive glass granule coating

The aim of this study was to evaluate glass-fiber-reinforced composite as a bone reconstruction material in the critical size defects in rabbit calvarial bones. The bone defect healing process and inflammatory reactions were evaluated histologically at 4 and 12 weeks postoperatively. Possible neuropathological effects on brain tissue were evaluated. The release of residual monomers from the fiber-reinforced composite (FRC) was analyzed by high performance liquid chromatograph (HPLC). RESULTS: At 4 weeks postoperatively, fibrous connective tissue ingrowth to implant structures was seen. Healing had started as new bone formation from defect margins, as well as woven bone islets in the middle of the defect. Woven bone was also seen inside the implant. Inflammation reaction was slight. At 12 weeks, part of the new bone had matured to lamellar-type, and inflammation reaction was slight to moderate. Control defects had healed by fibrous connective tissue. Histological examinations of the brain revealed no obvious damage to brain morphology. In HPLC analysis, the release of residual 1,4-butanedioldimethacrylate and methylmethacrylate from polymerized FRC was low. CONCLUSIONS: This FRC-implant was shown to promote the healing process of critical size calvarial bone defect in rabbits. After some modifications to the material properties, this type of implant has the potential to become an alternative for the reconstruction of bone defects in the head and neck area in the future.     

In vitro effects on MG63 osteoblast-like cells following contact with two roughness-differing fluorohydroxyapatite-coated titanium alloys

The chances of integration between an implant and the surrounding bone tissue depend on the surface characteristics of the implant itself. Particularly, chemical composition and surface roughness of the material have emerged as crucial factors in affecting the behaviour of cells in contact with the material. Among various surfaces, calcium phosphate coatings seem to favour a rapid initial integration, but their dissolution by extracellular fluids raises some concern about the long-term stability at the bone-implant interface. Fluorinated apatites are known to be more stable than other ceramic coatings, but, at present, little is known on their effects on human cells. In this study, MG63 osteoblast-like cells were seeded onto two fluorohydroxyapatite (FHA)-coated titanium alloy (Ti6Al4V) materials differing in roughness, respectively, LR-FHA (Ra = 5.6 microm) and HR-FHA (Ra = 21.2 microm). Quantification of the cells in contact with the FHA-coated materials by conventional methods involved some technical difficulties, on which we report. Only the indirect esteem by the measure of total content of proteins and a procedure based on cell count, following a double enzymatic treatment to detach the cells, offered plain results, indicating no significant differences between cellular growth in contact with test materials and with plastic control. Differentiation and functionality of the cells were comparatively evaluated by analysis of alkaline phosphatase activity and osteocalcin production. As far as osteocalcin release is concerned, only slight variations were detected on FHA-coated materials in comparison with the control. Both types of coatings showed a significant increase in alkaline phosphatase activity with respect to the control, the roughest surface exhibiting a more prolonged effect on the time.     

氧化锆陶瓷材料的生物相容性

背景：已有大量研究表明,氧化锆陶瓷具有优良的生物学性能,但作为牙种植基台的研究在国内还鲜见报道,将其应用于种植牙基台上的生物学性能还需要进一步的验证。 目的：评价牙种植基台制作材料氧化锆陶瓷的生物相容性。 方法：将氧化锆陶瓷圆形试件固定在Wistar大鼠左颊黏膜表面,右侧用牙胶试件作为对照,使两组试件与颊黏膜紧密贴合但无压迫,术后2周应用大体观察和组织学方法观察口腔黏膜与氧化锆陶瓷材料的生物学反应;将氧化锆陶瓷棒形试件植入Wistar大鼠背部皮下组织内,于植入后1,2,4,8周应用大体观察和组织学方法动态观察皮肤组织与氧化锆陶瓷材料的生物学反应。 结果与结论：氧化锆陶瓷圆形试件固定后,大鼠颊黏膜局部组织未见异常,与对照组比较差异无显著性意义;氧化锆陶瓷棒形试件植入第1周可见局部组织轻微红肿,组织切片可见少量炎性细胞,2~8周红肿消退,组织切片见纤维包膜形成并逐渐变薄,到8周时包膜形成致密纤维,未见炎性细胞。提示氧化锆陶瓷材料与口腔黏膜、皮肤及皮下组织具有良好的生物相容性。