In vivo response of ionomeric cements: effect of glass composition,increasing soda or calcium fluoride content

The in vivo response of two defined groups of set ionomeric cements (ICs), were evaluated following implantation in the midshaft of three week old Wistar rat femora for four weeks. New bone formation was associated with all the IC implants, the amount of new bone increasing with increasing sodium or calcium fluoride content of the basic glass component. Previous work has shown that there is a link between glass composition and ion release, fluoride ion release increasing as the sodium or fluoride content of the glass increases. It thus appears that in the series studied improved bone formation associated with the ICs was mediated by increased fluoride ion release.     

The effects of implanted ionomeric and acrylic bone cements on peripheral nerve function

The effects of two experimental ionomeric and one commercial acrylic bone cement and set ionomeric microimplant bone substitute (lonogran®) on peripheral nerve conduction, 1 and 3 weeks after implantation, have been compared. In 44 experiments the rat saphenous nerve was exposed midway between the ankle and thigh and bone cement placed into a pocket created in the connective tissue adjacent to the nerve. In terminal experiments, 1 and 3 weeks later, stimulating electrodes were placed on the saphenous nerve at the ankle, and the amplitude and conduction velocity of the compound action potential (CAP) evoked was recorded through another pair of electrodes positioned on the nerve proximal to the implant, in the thigh. One week after placing an ionomeric bone cement (HVA or V-4), no neural activity could be recorded. Three weeks, after HVA implantation apparently normal CAPs were recorded indicating a recovery from a temporary nerve conduction block, but 3 weeks after V-4 implantation only small CAPs were recorded and these could be attributed to axonal regeneration. After implantation of acrylic bone cement, small CAPs were recorded after 1 week, and within 3 weeks nerve conduction appeared to have completely recovered. Three weeks after placing set ionomeric microimplant particles the amplitude and conduction velocity of the CAP was similar to the controls.     

Assesment of the Biological Activity of Chemically Immobilized rhBMP‐2 on Titanium surfaces in vivo

Previously it has been shown that recombinant human bone morphogenetic protein (rhBMP‐2) can be chemically immobilized by “anchor molecules” on titanium surfaces for serving as a drug delivery device. This opened the question of whether the insoluble immobilized rhBMP‐2 retained its activity in comparison to the same amount of soluble rhBMP‐2 included with the implant samples. Electropolished titanium miniplates (10 × 6 × 0.8 mm) were “surface‐enhanced” by a novel treatment with chromosulfuric acid and then coated with a total amount of 150–200 ng rhBMP‐2 prepared by recombinant technology. Periosteal flaps (7 × 20 mm) were detached and isolated from the anterior surface of the tibiae of adult rabbits and wrapped around the titanium sample plates which were then implanted in the M. gastrocnemius. In the first experimental group various controls without rhBMP‐2 were combined (n = 12). In the second experimental group implants with chemically immobilized rhBMP‐2 (n = 8) were compared with implants to which non‐immobilized soluble rhBMP‐2 was added (n = 8). Animals were sacrificed after 28 days and a quantitative evaluation was carried out by means of serial sections. Untreated control plates showed bone formation in 2/12 implants, rhBMP‐2 coated implants in 6/8 and implants with free rhBMP‐2 administered subperiostally in 8/8 cases. In the case of rhBMP‐2 coated implants the induced bone had direct contact to the implant in all cases while in the group with free administered rhBMP‐2 the bone had no contact to the implant in two cases, but was separated by a fibrous capsule. Bone volume, bone surface area, and trabecular number displayed no difference between the two rhBMP‐2‐groups. However, in the biocoated group a tendency to an increase in the bone‐implant contact area was evident. No differences in osteoid area, osteoid perimeter and eroded perimeter were detected. We conclude that in the case of non‐immobilized rhBMP‐2 there is the danger for formation of fibrous tissue between the implant and the newly formed bone and in addition the generation of ectopic bone at inappropriate places. In contrast chemically immobilized rhBMP‐2 does not have these drawbacks and at the same time displays a biological activity on surfaces similar to that of soluble rhBMP‐2 demonstrating that biomaterial surfaces can be tailored for a selective and specific interaction with the target tissue.     

A novel method for local administration of strontium from implant surfaces

This study proves that a film of Strontianite (SrCO₃) successfully can be formed on a bioactive surface of sodium titanate when exposed to a strontium acetate solution. This Strontianite film is believed to enable local release of strontium ions from implant surfaces and thus stimulate bone formation in vivo. Depending on the method, different types of films were achieved with different release rates of strontium ions, and the results points at the possibility to tailor the rate and amount of strontium that is to be released from the surface. Strontium has earlier been shown to be highly involved in the formation of new bone as it stimulates the replication of osteoblasts and decreases the activity of osteoclasts. The benefit of strontium has for example been proved in studies where the number of vertebral compression fractures in osteoporotic persons was drastically reduced in patients receiving therapeutical doses of strontium. Therefore, it is here suggested that the bone healing process around an implant may be improved if strontium is administered locally at the site of the implant. The films described in this paper were produced by a simple immersion process where alkali treated titanium was exposed to an aqueous solution containing strontium acetate. By heating the samples at different times during the process, different release rates of strontium ions were achieved when the samples were exposed to simulated body fluid. The strontium containing films also promoted precipitation of bone like apatite when exposed to a simulated body fluid.     

A histomorphometric study on osteoconduction and osseointegration of titanium alloy with and without plasma-sprayed hydroxyapatite coating using back-scattered electron images

A quantitative evaluation, at the scanning electron microscopic (SEM) level, was made of the osteoconduction and osseointegration of Ti-6AI-4V implants with and without plasma-sprayed hydroxyapatite coatings (HACs). By employing the Chinese Coin implant model in the lateral femora cortices of canines, different biological properties between HA-coated and uncoated Ti-6AI-4V implants could be compared in one specimen. After 4, 6 and 12 weeks, the implants with surrounding bone were removed and assessed histologically in undecalcified sections under SEM. The osteoconductivity and the ability of osseointegration of implants were histomorphometrically analysed from back-scattered electron images (BEIs) and represented in terms of the new bone healing index (NBHI) and apposition index (AI), respectively. Throughout all implant periods, the HA-coated Ti-6AI-4V implants revealed higher NBHI than the uncoated ones, it appearing that the HA-coated Ti-6AI-4V implants revealed more osteoconductive than the Ti-6AI-4V was. For HA-coated implant, the evidence of direct bone-to-HAC contact was observed. However, at the bone/Ti-6AI-4V interface, there intervened a fibrous membrane without calcium content, indicating that the Ti-6AI-4V implant was not osseointegrated in the SEM field of view. The maximum value of AI was reached 6 weeks after implantation for HA-coated implant, implying that the HAC had a stimulating influence on bone apposition within 6 weeks of healing. The signs of partial dissolution of HACs within the remodelling canals were evident at the HAC-bone interface 12 weeks after implantation, accounting for the slight decrease in NBHI and the obvious decrease in AI for HAC implant.     

Effect of CaCl2 hydrothermal treatment on the bone bond strength and osteoconductivity of Ti–0.5Pt and Ti–6Al–4V–0.5Pt alloy implants

To achieve osteoconductivity, Ti–0.5Pt and Ti–6Al–4V–0.5Pt alloys were hydrothermally treated at 200°C in 10 mmol/l CaCl₂ aqueous solution for 24 h (HT-treatment). We conducted histological investigations of the HT-treated materials by using Wistar strain rats (SD rats) to evaluate the usefulness of the treatment. To measure the bone bond strength, the specimens were implanted in the tibia of SD rats, and a pull-out test was conducted. From the early postoperative stages, direct bone contact was obtained for the HT-treated implants. Within 1–4 weeks of implantation, the bone contact ratios and bone bond strengths of the HT-treated implants were higher than those of the non-treated implants. The Ti–0.5Pt and Ti–6Al–4V–0.5Pt alloys with HT-treatment showed the potential to develop a new implant with a high bone bond strength and rapid osteoconduction.     

Quantitative analysis of the bone-hydroxyapatite coating interface

The bone implant interface in stainless steel pins coated with hydroxyapatite, used in a monoaxial fracture external fixation system was examined. The pins were transversally inserted into sheep tibial diaphyses where a defect was created, and they were loaded for 6 weeks. Uncoated pins were implanted as control. The microscopic relation between bone and implant was quantified through image analysis: the residual thickness of the hydroxyapatite coating, pin-bone contact surface and bone ingrowth value in between the threads were measured. The bone tissue at the interface appeared regularly mineralized and viable both in the implants of coated pins and in the control uncoated ones. The ceramic coating showed a slight and not statistically significant increase in thickness. The ceramic coated pins presented contact with bone higher than the uncoated pins (75.6±20.0 versus 47.5±19.4); they also induced a higher bone ingrowth (86.6±22.4 versus 78.7±13.5). Both differences are not statistically significant, but suggestive of a trend. The authors concluded that the hydroxyapatite coating of the pins might improve the performance of external fixators, by favouring bone apposition and reducing rate of loosening.     

Micro-CT Analysis of Implanted Poly-Ether-Ether-Ketone Scaffolds: Plasma Immersion Ion Implantation Increases Osteoconduction

Poly-ether-ether-ketone (PEEK) is a biocompatible, high-strength polymer with biomechanical properties similar to soft bone that has been proposed as an alternative to titanium for orthopedic implants. Herein, micro-CT imaging of a 3D printed PEEK scaffold treated with plasma immersion ion implantation (PIII) to assess the degree of osteoconduction relative to an identical untreated structure, by implantation in the scapula of sheep, is performed. To overcome the lack of contrast between soft tissue and PEEK, a customized apparatus and alignment technique is designed and constructed. Principal component analysis is used to accurately locate the boundaries of the implant in the 3D dataset, with respect to reference coordinates. It is found that, within the interior volume of the scaffold, the PIII treated PEEK contains bone that is both more dense and in higher amounts than for untreated PEEK. The untreated PEEK shows more bone immediately outside the boundaries of the scaffold, indicating a lower affinity of the untreated scaffold for in-diffusion of osteocytes and associated mineralization. The greater osteoconduction of the PIII treated scaffold is attributed to the improvement in hydrophilicity and the provision of protein covalent binding.     

In vitro and in vivo evaluation of bone morphogenetic protein-2 (BMP-2) immobilized collagen-coated polyetheretherketone (PEEK)

Polyetheretherketone (PEEK) is regarded as one of the most potential candidates of biomaterials in spinal implant applications. However, as a bioinert material, PEEK plays a limited role in osteoconduction and osseointegration. In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) was immobilized onto the surface of collagen-coated PEEK in order to prepare a multi-functional material. After adsorbed onto the PEEK surface by hydrophobic interaction, collagen was cross-linked with N-(3-dimethylaminopropyl)-N'-ethyl carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). EDC/NHS system also contributed to the immobilization of rhBMP-2. Water contact angle tests, XPS and SEM clearly demonstrated the surface changes. ELISA tests quantified the amount of rhBMP-2 immobilized and the release over a period of 30 d. In vitro evaluation proved that the osteogenesis differentiation rate was higher when cells were cultured on modified PEEK discs than on regular ones. In vivo tests were conducted and positive changes of major parameters were presented. This report demonstrates that the rhBMP-2 immobilized method for PEEK modification increase bioactivity in vitro and in vivo, suggesting its practicability in orthopedic and spinal clinical applications.     

Early tissue response to titanium implants inserted in rabbit cortical bone

The tissue response to screw-shaped implants of commercially pure titanium was studied by light microscopy 3–180 days after insertion in the rabbit tibia. The implant site in the tibial metaphysis consisted mainly of cortical bone. Three days after implantation, osteoblasts, producing osteoid, were observed at the endosteal surface and elongated mesenchymal cells were present in the injury area. Some macrophages but rather few other inflammatory cells were identified. Multinuclear giant cells were in direct contact with the implant and formed an almost continuous layer along the surface from the 7th day. The number of giant cells decreased with time and with increased bone-titanium contact. Bone formation was never seen direct on the implant surface but was first observed at day 7 as a woven trabecular bone formed at the endosteal surface and extending towards the implant and as a solitary formation of woven bone close to the implant. The solitary bone matrix served as a base for surface osteoblasts which produced osteoid in a lamellar arrangement. With time the two types of newly formed bone fused and more bone filled the threads and became remodelled by bone remodelling units. Light microscopic morphometry in ground sections demonstrated that the bone/titanium contact and bone area in the threads increased with time up to 6 months after implantation     

可注射磷酸钙骨水泥的研究进展

可注射磷酸钙骨水泥以其良好的生物相容性、骨传导性和可降解性等优点被广泛应用于临床的骨替换和修复等领域。综述了磷酸钙骨水泥(CPC)注射性能的评价指标,提出了评价CPC注射性能的有效方法,讨论了骨水泥的注射体系、制备方法和组成等对CPC注射性能的改进措施,并在此基础上探讨了CPC存在的问题及对策。     

Bone response to surface modified titanium implants – studies on the tissue response after 1 year to machined and electropolished implants with different oxide thicknesses

The bone formation around titanium implants with varied surface properties was investigated after 1 year in rabbits. Machined and electropolished samples with and without thick, anodically formed surface oxides were prepared, surface characterized and inserted in the cortical bone of rabbits. Scanning electron microscopy, scanning Auger electron spectroscopy and atomic force microscopy revealed marked differences in oxide thickness, surface topography and roughness, but no significant differences in surface chemical composition between the different groups of implants. Light microscopic morphology and morphometry showed that all implants were in contact with bone and had a large proportion of bone within the threads. There were no significant differences between the differently prepared implant groups. Our study shows that a high degree of bone contact and bone formation is achieved after 1 year with titanium implants which are modified with respect to oxide thickness and surface topography. There is no indication that a reduction of surface roughness, which in the initial phase decreases the rate of bone formation, had any influence on the amount of bone after 1 year in rabbit cortical bone.     

<Emphasis Type="Italic">In vitro</Emphasis> and <Emphasis Type="Italic">in vivo</Emphasis> evaluation of bone morphogenetic protein-2 (BMP-2) immobilized collagen-coated polyetheretherketone (PEEK)

Polyetheretherketone (PEEK) is regarded as one of the most potential candidates of biomaterials in spinal implant applications. However, as a bioinert material, PEEK plays a limited role in osteoconduction and osseointegration. In this study, recombinant human bone morphogenetic protein-2 (rhBMP-2) was immobilized onto the surface of collagen-coated PEEK in order to prepare a multi-functional material. After adsorbed onto the PEEK surface by hydrophobic interaction, collagen was cross-linked with N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). EDC/NHS system also contributed to the immobilization of rhBMP-2. Water contact angle tests, XPS and SEM clearly demonstrated the surface changes. ELISA tests quantified the amount of rhBMP-2 immobilized and the release over a period of 30 d. In vitro evaluation proved that the osteogenesis differentiation rate was higher when cells were cultured on modified PEEK discs than on regular ones. In vivo tests were conducted and positive changes of major parameters were presented. This report demonstrates that the rhBMP-2 immobilized method for PEEK modification increase bioactivity in vitro and in vivo, suggesting its practicability in orthopedic and spinal clinical applications.     

Bioactive glass granules and polytetrafluoroethylene membrane in the repair of bone defects adjacent to titanium and bioactive glass implants

An experimental animal model was used to investigate the effect of bioactive glass (BG) granules and nonresorbable polytetrafluoroethylene (PTFE) membrane on the repair of cortical bone defects adjacent to titanium and BG implants. Thirty-two Astra® (diameter 3.5 mm) dental implants were inserted bicortically and 42 conical BG implants (diameter 2.5–3.0 mm) monocortically, into fitted holes of rabbit tibia. Before implantation, a standardized bone defect was created by drilling an extra hole (diameter 3.0 mm) adjacent to each implant site. Twenty-eight defects were filled with BG granules (diameter 630–800 m) (BG group) and 28 defects were left empty but covered with PTFE membrane (PTFE group). No material was used in 18 control defects (control group). Morphometrical evaluation with a digital image analysis system was used to measure bone repair as percentages of the defect area on scanning electron microscopy (SEM) and light microscopy pictures. Bone–implant contact was measured as percentages of the thickness of the cortical bone. At 6 and 12 wk, bone repair in defects in connection with titanium implants was 23.2% and 36.6% in the BG group, 23.2% and 32.4% in the PTFE group, and 47.2% and 46.2% in control defects. Corresponding figures for BG implants were 33.2% and 40.1% in the BG group, 16.6% and 33.5% in the PTFE group, and 25.7% and 54.9% in control defects, BG granules and new bone together filled 82.7% and 68.5% of the defect area adjacent to titanium implants, and 75.9% and 74.4% of the defect adjacent to BG implants at 6 and 12 wk, respectively. Better bone–implant contact was achieved at the defect side with BG than titanium implants (77.0% versus 45.0% at 12 wk). The results indicate that BG granules are useful in treatment of bone defects adjacent to dental implants. BG coating of the implant seems to improve osseointegration in the defect area.     

Studies of the healing of bone grafts, and the incorporation of titanium implants in grafted bone: an experimental animal model

An insufficient quality and amount of bone often necessitate the clinical use of implants together with bone transplants. The present study describes an experimental animal model for the study of implants in bone grafts. Circular defects were made bilaterally in the tibia of 36 rabbits. The defects received either autologous cortical bone (control), demineralized bone matrix (DBM), plasma-augmented DBM or were left empty (without bone graft). In all defects a titanium implant was centrally placed and anchored in the opposite cortex. Evaluation with light microscopic morphometry showed that the insertion of a threaded titanium implant centrally in a cortical defect was followed by a spontaneous healing of the defect after 6 mon. After 6 wk, all implants in cortical grafts were well integrated with a significantly higher bone-to-implant contact than in the DBM and plasma-augmented groups. After 6 mon, all experimental groups had a mean bone area within the threads ranging between 69% and 80% and a mean bone-to-implant contact between 31% and 42%. The results from the present study indicate that the model allows comparative studies on the early formation, resorption and remodelling of bone around implants after modification of implant, graft and host properties.     

明胶/硫酸钙复合生物材料

将具有传骨性的生物可吸收无机材料硫酸钙与具有诱骨性的明胶组合起来,构制新型可吸收复合生物材料。该材料可避免硫酸钙颗粒的脱落,可以作为骨填充物或支架材料。明胶的加入减缓了半水硫酸钙向二水硫酸钙的转化,形成了CSH/CSD/CLG e l复合材料。在该复合材料表面培养了人成骨细胞,细胞在支架表面粘附良好,可见该支架和细胞有较好的生物相容性。硫酸钙吸收后形成一可供细胞生长的多孔支架,所以明胶/硫酸钙(CLG e l/CS)复合材料实为原位成孔支架材料,解决了多孔支架材料初期强度低的致命弱点。     

Evaluation of trabecular bone formation in a canine model surrounding a dental implant fixture immobilized with an antimicrobial peptide derived from histatin

JH8194 induces osteoblast differentiation, although it was originally designed to improve antifungal activity. This suggests that JH8194 is useful for implant treatment. Therefore, the aim of this study was to evaluate the osseointegration capacity of JH8194-modified titanium dental implant fixtures (JH8194-Fi). The implants were randomly implanted into the edentulous ridge of dog mandibles. Healing abutments were inserted immediately after implant placement. Three weeks later, peri-implant bone levels, the first bone-to-implant contact points, and trabecular bone formation surrounding the implants were assessed by histological and digital image analyses based on microcomputed tomography (microCT). The histological analysis revealed an enhancement of mature trabecular bone around the JH8194-Fi compared with untreated fixtures (control-Fi). Similarly, microCT combined with analysis by Zed View? also showed increased trabecular bone formation surrounding the JH8194-Fi compared with the control-Fi (Student's t-test, P < 0.05). JH8194 may offer an alternative biological modification of titanium surfaces to enhance trabecular bone formation around dental implants, which may contribute to the transient acquirement of osseointegration and the long-term success of implant therapy.     

Bone tissue reactions to biomimetic ion-substituted apatite surfaces on titanium implants

The aim of this study was to evaluate the bone tissue response to strontium- and silicon-substituted apatite (Sr-HA and Si-HA) modified titanium (Ti) implants. Sr-HA, Si-HA and HA were grown on thermally oxidized Ti implants by a biomimetic process. Oxidized implants were used as controls. Surface properties, i.e. chemical composition, surface thickness, morphology/pore characteristics, crystal structure and roughness, were characterized with various analytical techniques. The implants were inserted in rat tibiae and block biopsies were prepared for histology, histomorphometry and scanning electron microscopy analysis. Histologically, new bone formed on all implant surfaces. The bone was deposited directly onto the Sr-HA and Si-HA implants without any intervening soft tissue. The statistical analysis showed significant higher amount of bone–implant contact (BIC) for the Si-doped HA modification (P = 0.030), whereas significant higher bone area (BA) for the Sr-doped HA modification (P = 0.034), when compared with the non-doped HA modification. The differences were most pronounced at the early time point. The healing time had a significant impact for both BA and BIC (P < 0.001). The present results show that biomimetically prepared Si-HA and Sr-HA on Ti implants provided bioactivity and promoted early bone formation.     

Laser stereolithography and supercritical fluid processing for custom-designed implant fabrication

This paper describes the laser photopolymerization of a liquid mixture of polyfunctional acrylic monomers, photoinitiator and hydroxyapatite (HA). Pure polymeric and composite materials of specific shape and structure were fabricated by laser stereolithography based on images derived from three-dimensional (3D) computer modeling. The polymeric objects then were treated with supercritical carbon dioxide to remove potentially toxic residues (monomers, low molecular weight oligomers, etc.) and to provide interconnective microporosity. Finally, samples were implanted into white rats (diastolic epiphysis of femoral bone) to study living tissue response and processes of osteointegration and osteoinduction. It was shown that incorporation of HA into the composite implant structure encouraged periosteal as well as endosteal osteogenesis and improved their osteointegrative characteristics in particular. Supercritical carbon dioxide treatment significantly enhanced the biocompatibility of the materials, increasing the area of direct contact of the implant surface with regenerated bone tissue.     

In vitro evaluation of bioactive strontium-based ceramic with rabbit adipose-derived stem cells for bone tissue regeneration

The development of bone replacement materials is an important objective in the field of orthopaedic surgery. Due to the drawbacks of treating bone defects with autografts, synthetic bone graft materials have become optional. So in this work, a bone tissue engineering approach with radiopaque bioactive strontium incorporated calcium phosphate was proposed for the preliminary cytocompatibility studies for bone substitutes. Accumulating evidence indicates that strontium containing biomaterials promote enhanced bone repair and radiopacity for easy imaging. Hence, strontium calcium phosphate (SrCaPO₄) and hydroxyapatite scaffolds have been investigated for its ability to support and sustain the growth of rabbit adipose-derived mesenchymal stem cells (RADMSCs) in vitro. They were characterized via Micro-CT for pore size distribution. Cells used were isolated from New Zealand White rabbit adipose tissue, characterized by FACS and via differentiation into the osteogenic lineage by alkaline phosphatase, Masson’s trichome, Alizarin Red and von Kossa staining on day 28. Material-cell interaction was observed by SEM imaging of cell morphology on contact with material. Live–Dead analysis was done by confocal laser scanning microscopy and cell cluster analysis via μCT. The in vitro biodegradation, elution and nucleation of apatite formation of the material was evaluated using simulated body fluid and phosphate buffered saline in static regime up to 28 days at 37 °C. These results demonstrated that SrCaPO₄ is a good candidate for bone tissue engineering applications and with osteogenically-induced RADMSCs, they may serve as potential implants for the repair of critical-sized bone defects.