Evaluation of a new CPC-to-gauge bonding technique with the use of in vitro fluid flow

Strain gauging enables the measurement of bone deformation during physical activity, leading to a better understanding of the physiological effects of loading on bone growth and remodeling. Development of a technology that will withstand long-term in vivo exposure and bond securely to bone is imperative for accurate, consistent measurement collection. Polysulfone is currently used to attach calcium-phosphate ceramic (CPC) particles, which promote bone-to-gauge bonding, to polyimide-backed strain gauges. This study evaluated the use of an implant-grade epoxy as an alternative CPC-polyimide adhesive. Polyimide-epoxy-CPC interfaces were loaded to failure and shear strengths calculated. In vitro studies providing a constant flow of medium over test specimens were designed, and long-term in vitro fluid exposure studies of the epoxy's shear strength were conducted. Average shear strength of polysulfone-polyimide interfaces were reported to be 7 MPa. The average shear strength of the epoxy-polyimide interface before long-term in vitro exposure was 17 MPa, which is stronger than the shear strength of the bone-CPC interface. The strength of the epoxy-polyimide interface decreased to 6.8 MPa after 24 weeks in vitro and 3 MPa after 24 weeks in vivo.     

HA-40vo1％Ti复合材料与动物骨组织相容性体内研究

采用热压烧结法制备HA-40vol％Ti复合材料，并通过体内植入试验，研究了该复合材料的生物相容性。结果表明，HA-40vol.％Ti复合材料具有良好的生物相容性和骨引导性，可以与骨发生骨整合，早期骨整合和骨引导性优于纯Ti。在整个植入时间段内，HA-40vol．％Ti复合材料与周围骨组织的结合强度均比纯钛的高，且增长的快。植入3月后，复合材料与新骨的结合强度已达到4．73MPa。     

电沉积HA-Ti/HA复合涂层及其生物学性能

为了提高HA涂层的结合强度，采用两步电沉积法制备HA—Ti／HA复合涂层，对涂层的组分结构、表面形貌和结合强度进行了研究，并对涂层进行模拟体液和体外细胞实验，以考察涂层的生物学性能。实验结果表明：HA—Ti／HA复合涂层的结合强度明显高于HA涂层，当涂层中Ti的质量分数为51．2wt％时，涂层与基体的结合强度达到21．2MPa，约为纯HA涂层的3倍。涂层经模拟体液浸泡后，表面覆盖一层碳磷灰石（Carbonate—apatite），表明涂层具有良好的生物活性。体外细胞实验表明，骨髓基质细胞能在涂层表面黏附繁殖生长，表明涂层具有良好的生物相容性。     

Mechanical and histological evaluations of hydroxyapatite-coated and noncoated Ti6Al4V implants in tibia bone

This paper evaluates the behavior of hydroxyapatite (HAP) coated and noncoated Ti6Al4V implants in dog tibia after 3 and 5 months implantation. HPA-coated implants were obtained by plasma spraying. XRD, SEM, and EPMA were employed to estimate the coating characteristics and their behavior in vivo. Investigation of material characteristics showed that the as-received coatings consisted mainly of amorphism and HAP phase. Other phases such as TCP and CaO were identified due to thermal changes of HAP particles in plasma flame. SEM micrographs showed a typical microstructure of plasma-sprayed coating. The as-received coating was formed by well-melted pancake-like splats that lead to a dense coating with a rough surface. Lamellar structure, micropores, and microcracks, observed inside the coating, are characteristic of plasma spraying. Push-out tests revealed that HAP coating had a significant promotion of interfacial shear strength. The shear strength between bone and HAP-coated implants was much higher than that between bone and noncoated implants due to the different bone-implant interfaces formed after implantation. SEM observation revealed a direct attachment between HAP coating and newly formed bone. However, noncoated implants were separated from newly formed bone by fibrous tissues. Ti ions were found to be released into the surrounding environment after long time immersion in body fluid, and thus caused low shear strength. Prolongation of implantation time had different effects on shear strength. It improved the shear strength between HAP-coated implant and newly formed bone. However, it had little effect on that between noncoated implant and surrounding tissues.     

Correlations between the in vitro and in vivo bioactivity of the Ti/HA composites fabricated by a powder metallurgy method

Ti/HA composites were successfully prepared by a powder metallurgy method and the effect of phase composition on the in vitro and in vivo bioactivity of the Ti/HA composites was investigated in the present study. The correlations between the in vitro and in vivo biological behaviors were highlighted. The results showed that the in vitro and in vivo bioactivity of the Ti/HA composites was dependent on their phase composition. The in vitro bioactivity of the Ti/HA composites was evaluated in simulated body fluid with ion concentrations similar to those of human plasma. After immersion in the simulated body fluid for a certain time, apatite precipitations formed on the surface of the composites with an initial titanium content of 50 and 70 wt.%, and no apatite was found on the surface of the composite with 30% titanium. Ti(2)O was responsible for the apatite formation on the surfaces of the composites. For in vivo analysis, Ti/HA cylinders were implanted in the metaphases of the rabbit femur. At the early stage of implantation, the new bone formed on the surface of the composite with 30% titanium was much less than that on the surfaces of the composites with 50% and 70% titanium. All the Ti/HA composites formed a chemical bone-bonding interface with the host bone by 6 months after implantation. The Ti/HA composites formed the bone-bonding interface with the surrounding bone through an apatite layer. The results in the present study suggested that the in vivo results agreed well with the in vitro results.     

Bone bonding strength of calcium phosphate ceramic coated strain gauges

Although strain transfer from bone to gauge has been used as an indication of the extent of bone bonding to calcium phosphate ceramic (CPC) coated strain gauges, interface strength measurements have not been reported. In order to develop bone-bonded gauges that remain attached to bone surfaces for long periods, the strength of the CPC-bone interface must be optimized. A shear test to assess the interface strength of the CPC-bone interface was developed using the femora of 120-day-old male rats. The mean interface strength of a blended CPC coating bonded to the femora of the rats for 6 weeks in vivo was 4.8+/-2.4 MPa, and one specimen achieved a strength of nearly 10 MPa. This mean strength value is higher then the CPC-gauge interface strength reported in early studies, but it is lower than recently developed heat treated CPC-gauge interfaces that have average strengths of approximately 7.0+/-2.0 MPa.     

Bone bonding behavior of the hydroxyapatite containing glass-titanium composite prepared by the Cullet method.

Bioactive composites composed of hydroxyapatite containing glass (HA-G) as a coating and titanium (Ti) or titanium alloy implants as a substrate were prepared by the Cullet method. This method results in the HA-G coating layer on the substrate with a compositional gradient in HA concentration. The results of in vitro and in vivo experiments investigating the characteristics of the composite materials are reported and discussed in this article. In vitro evaluations confirmed that the Cullet method was suitable for the preparation of the functionally gradient composite implants with higher reliable quality. In vivo experiments permitted evaluation of bonding strength of these composite implants to living bone tissue. Mechanical pull-out tests indicated that the implants bonded to living bone at least as firmly as those by the conventional method, and that the adhesion between the HA-G coating layer and metal substrate was well integrated and strongly maintained in vivo. SEM observations with EDX and a histological study of the interface between the HA-G-Ti composite implants and bone tissue revealed not only that the implants bonded to bone directly without any intervening tissue but that bone ingrowth into the HA-G layer occurred. The HA-G-Ti composite implants demonstrate both biocompatible and osteoconductive characteristics, and may be expected to obtain good and lasting results when applied clinically.     

Bond strength of plasma-sprayed hydroxyapatite/Ti composite coatings

One of the most important clinical applications of hydroxyapatite (HA) is as a coating on metal implants, especially plasma-sprayed HA coating applied on Ti alloy substrate. However, the poor bonding strength between HA and Ti alloy has been of concern to orthopedists. In this paper, an attempt has been made to enhance the bonding strength of HA coating by forming a composite coating with Ti. The bioactivity of the coating has also been studied. HA/Ti composite coatings were prepared via atmospheric plasma spraying on Ti-6Al-4V alloy substrates. The bond strength evaluation of HA/Ti composite coatings was performed according to ASTM C-633 test method. X-ray diffractometer and scanning electron microscopy were applied to identify the phases and the morphologies of the coatings. The bioactivity of HA/Ti composite coating was qualified by immersion of coating in simulated body fluid (SBF). The obtained results revealed that the addition of Ti to HA improved the bonding strength of coating significantly. In the SBF test, the coating surface was covered by carbonate-apatite, which was testified by X-ray photoelectron spectroscope, indicating good bioactivity for HA/Ti composite coating. The bioactivity of the coating has not been reduced by the addition of Ti.     

Comparison of plasma-sprayed hydroxyapatite coatings and zirconia-reinforced hydroxyapatite composite coatings: in vivo study

The clinical use of plasma-sprayed hydroxyapatite (HA) coatings on metal implants has been widely adopted because the HA coating can achieve the firmly and directly biological fixation with the surrounding bone tissue. However, the long-term mechanical properties of HA coatings has been concern for the long-term clinical application. Previous research showed that the concept of adding ZrO2 as second phase to HA significantly increased the bonding strength of plasma-sprayed composite material. The present work aimed to explore the biological properties, including the histological responses and shear strength, between the plasma-sprayed HA and HA/ZrO2 coating, using the transcortical implant model in the femora of canines. After 6 and 12 weeks of implantation, the HA coating revealed the direct bone-to-coating contact by the backscattered electron images (BEIs) of scanning electron microscope (SEM), but the osseointegration was not observed at the surface of HA/ZrO2 coating. For new bone healing index (NBHI) and apposition index (AI), the values for HA implants were significantly higher than that for HA/ZrO2 coatings throughout all implant periods. After push-out test, the shear strength of HA-coated implants were statistically higher than HA/ZrO2 coated implants at 6- and 12-week implantation, and the failure mode of HA/ZrO2 coating was observed at the coating-bone interface by SEM. The results indicate that the firm fixation between bone and HA/ZrO2 has not been achieved even after 12-week implantation. Consequently, the addition of ZrO2 could improve the mechanical properties of coatings, while the biocompatibility was influenced by the different material characteristics of HA/ZrO2 coating compared to HA coatings.     

A 12 month in vivo study on the response of bone to a hydroxyapatite-polymethylmethacrylate cranioplasty composite

We investigated the osteoconductivity and biocompatibility in vivo of a new hydroxyapatite-polymethylmethacrylate (HA-PMMA) composite developed for use as an implant material for cranioplasty, which is expected to have the good osteoconductivity of HA together with the strength and ease of handling of PMMA. The HA-PMMA composites were implanted in eight full-grown beagles and then 6, 12, 24 weeks and 1 year after implantation, the animals were sacrificed and the implanted materials removed along with the surrounding tissues. Extirpated specimens were studied using an optical microscope and micro-computed tomography (micro-CT). Fibrous connective tissue was prominent in the interface of the composite at 6 weeks. New bone formation was seen around the implant, 12 and 24 weeks after operation. At 1 year, new bone filled in the interface of the HA-PMMA composite and adhered to the surrounding autogenous bone. Mixing HA and PMMA did not interfere with the osteoconductivity of the HA component. In micro-CT findings, the new bone growing on the HA-PMMA composite could be seen attaching preferentially to HA particles exposed at the composite surface, rather than the PMMA. This study demonstrated that this HA-PMMA composite is a good candidate for cranial bone implants due to its good osteoconductivity and biocompatibility.     

一种碳/碳复合材料表面制备高结合强度羟基磷灰石涂层的新方法

背景：目前在碳/碳表面制备羟基磷灰石涂层的方法有很多种,但所制涂层与基体的结合强度不高。 目的：提出一种在碳/碳复合材料表面制备高结合强度羟基磷灰石涂层的新方法。 方法：首先利用感应加热法在基体表面制备出无水磷酸氢钙涂层,而后对其进行水热处理,转变为羟基磷灰石相。扫描电镜观察涂层的形貌,划痕法测试涂层的临界载荷,顶出法测试剪切强度。 结果与结论：感应热沉积法可以在碳/碳复合材料表面制备出致密的块状晶粒结构的无水磷酸氢钙涂层;通过水热处理可以将其转变成结晶完好致密的羟基磷灰石涂层。涂层的临界载荷为13.31 N,剪切强度约为47 MPa。     

Effect of sintered silicate-substituted hydroxyapatite on remodelling processes at the bone-implant interface

Phase pure, sintered granules of hydroxyapatite (HA) and silicon-substituted hydroxyapatite (Si-HA) were implanted for 6 and 12 weeks in an ovine model. Samples containing the bone-implant interface were prepared for ultramicrotomy and transmission electron microscopy (TEM) using an anhydrous sample preparation procedure. The results demonstrate that the morphology of apatite deposits and the sequence of events at the interfaces of bone with pure HA and with Si-HA implants, were different. Organised collagen fibrils were first found at the bone/Si-HA interface after 6 weeks, whereas they were found only after 12 weeks around the pure HA implant. Many more nodular aggregates comprised of plate-like apatite crystallites were observed in the vicinity of Si-HA than around the pure HA after 12 weeks in vivo. These findings suggest that the incorporation of silicate ions into HA promotes processes of bone remodelling at the bone/HA interface. TEM observations suggested that the trabecular bone weaves over the Si-HA and that the collagen fibrils form a mechanical interlock with the Si-HA ceramic implants. High-resolution lattice imaging illustrated apatite crystallites contiguous with the Si-HA ceramic and revealed a direct relationship between the bone mineral and the Si-HA ceramic.     

Structure and strength at the bonding interface of a titanium-segmented polyurethane composite through 3-(trimethoxysilyl) propyl methacrylate for artificial organs

The objective of this study was to investigate the structure and strength at the bonding interface of a titanium (Ti)-segmented polyurethane (SPU) composite through (3-trimethoxysilyl) propyl methacrylate (gamma-MPS) for artificial organs. The effects of the thickness of the gamma-MPS layer on the shear bonding strength between Ti and SPU were investigated. Ti disks were immersed in various concentrations of gamma-MPS solutions for several immersion times. The depth profiles of elements and the thickness of the gamma-MPS layer were determined by glow discharge optical emission spectroscopy and ellipsometry, respectively. The bonding stress at the Ti/gamma-MPS/SPU interface was evaluated with a shear bonding test. Furthermore, the fractured surface of a Ti-SPU composite was observed by optical microscopy and characterized using X-ray photoelectron spectroscopy. Consequently, the thickness of the gamma-MPS layer was controlled by the concentration of the gamma-MPS solution and immersion time. The shear bonding stress at the interface increased with the increase of the thickness of the gamma-MPS layer. Therefore, the control of the thickness of the gamma-MPS layer is significant to increase the shear bonding stress at the Ti/gamma-MPS/SPU interface. These results are significant to create composites for artificial organs consisting of other metals and polymers.     

Integration of dense HA rods into cortical bone

HA ceramics are daily used in human surgery for bone healing partly due to their ability to integrate into bone. They are generally used under a macroporous form. The behaviour of dense HA after implantation is not so well known. We implanted within cortical sheep femurs dense pure HA-ceramics cylinders for periods from 2 weeks to 18 months. The samples were then sectioned and examined using back-scattered and secondary SEM and the interface was analysed using EDS. Histomorphometry measurement was also performed using an image analysis device coupled to a light microscope. It appeared that the cylinders were in direct contact with immature bone after three weeks. The bone maturated within three months. The implant surface showed moderate signs of resorption and some grains were released from the surface. The resorption zone was only a few microm thick after 18 months. The bulk ceramic contained default zones of increased porosity. They can constitute fragile zone when located close to the surface in which the resorption rate is increased. We conclude that dense pure HA is poorly degraded when implanted in cortical bone. Degradation depends on the defaults found on the ceramic structure and the remodelling of bone surrounding the material.     

Characterization of the interface in the plasma-sprayed HA coating/Ti-6Al-4V implant system.

The successful use of plasma-sprayed hydroxyapatite (HA) coatings on Ti-alloy implants for implant-to-bone fixation requires strong adherence of the ceramic coating to the underlying metal substrate. In this study, the metal-ceramic interface was evaluated using mechanical, chemical, and structural characterization methods. Evaluations of an HA-coated Ti-6Al-4V implant system using a modified short bar technique for interfacial fracture toughness determination revealed relatively low fracture toughness values. Additionally, conventional tensile bond strength testing indicated much lower values than previously reported. Using high resolution electron spectroscopic imaging, evidence of chemical bonding was revealed at the plasma-sprayed HA/Ti-6Al-4V interface, though bonding was primarily due to mechanical interlock at the interface. This study illustrates the benefits of, and the need for, a multilevel approach to evaluate and improve these plasma-sprayed ceramic-metal substrate interfaces.     

Micro-observation and characterization of bonding between bone and HA-glass-titanium functionally gradient composite

Bioactive composite implants consisting of hydroxyapatite (HA)-glass (G) ceramic layer and Ti-6AI-4V alloy, so-called HA-G-Ti functionally gradient implant, were provided for investigating the bonding behaviour of bone to the implant in vivo. The HA-G-Ti composites were implanted in femur and tibia of dog for various periods (1-12 month). Microstructural appearance of the interface between bone and the HA-G coating layer as well as the transverse sections of the HA-G coating layer and further apposition of bone to the implant have been studied in detail with SEM. The ingress of collagen fibres into the HA-G coating layer and the deposit of apatite on the collagen fibres and HA crystal grains being containing within the HA-G coating layer have been observed. Radiographical experiments indicate that the reparative process in the bone tissue surrounding the implants is markedly ahead even at one month after implantation. FT-IR measurement and X-ray diffraction were carried out for studying the characterization of the calcified bone matrix around the implants and the new bone proliferated along the HA-G-coated face (surface).     

High-resolution transmission electron microscopy investigations of a highly adhesive hydroxyapatite coating/titanium interface fabricated by ion-beam-assisted deposition

An atomic intermixing layer, 25 nm in width, has been identified by high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS) analysis at the ceramic/metal interface of a hydroxyapatite (HA) coating/titanium implant prepared by an ion-beam-assisted deposition (IBAD) technique and post-heat-treatment process. The detailed interfacial microstructure revealed a gradient evolution of both the structure and composition of the interfacial phases from the titanium substrate to HA coatings. An enhancement of the tensile bond strength was found and was attributed to the possible chemical bonding at the ceramic/metal interface.     

Mechanism and strength of bonding between two bioactive ceramics in vivo.

A study was conducted to examine the mechanism and strength of bonding between two bioactive ceramic plates in vivo. Rectangular plates (15 mm X 10 mm X 2 mm) of Bioglass, apatite-wollastonite-containing glass ceramic (designated A-W.GC), and two types of hydroxyapatite sintered at 900 degrees C and 1200 degrees C (designated HA900 and HA1200) were prepared. Two plates of the same materials tied together with silk thread were implanted subcutaneously into rats. The force required to detach the mutually bonded bioactive ceramic plates was measured 4, 8, 12, and 24 weeks after implantation. The interface between the two bonded plates was examined by SEM-EPMA and thin-film x-ray diffraction analysis. At 24 weeks after implantation, the mutual bonding of Bioglass and A-W.GC was stronger than that of the two HA types. SEM-EPMA and thin-film x-ray diffraction analysis of the bonded area of Bioglass and A-W.GC plates showed bonding zones with apatite in the margins, and a bonding zone with calcite in the center. The greater strength of bonding of Bioglass and A-W.GC plates compared with the two types of HA plate 24 weeks after implantation is explained by the wider bonding zone provided by the calcite layer formed in the center of the plates, which is considered to have been perfused with PO4-poor body fluids resulting from PO4 consumption for apatite formation in the margins.     

A comparison of in vitro and in vivo degradation of two CPC strain gauge coatings

Calcium phosphate ceramic (CPC) coated strain gauges have been used to measure bone strain in animal models for up to 16 weeks and are being developed to collect measurements in patients for periods of 1 year or more. A published surface roughening and heat treating procedure produced improved dry strength and in vivo stability of CPC-gauge interfaces after 16 weeks. The long term bond strength of two CPC-gauge interfaces prepared using the roughening and heat treating process were evaluated after up to 1 year in vitro and in vivo using a lap shear test. The feasibility of using an in vitro test to predict long term in vivo interface changes was established. A blended tricalcium phosphate + hydroxyapatite had a CPC-gauge interface strength which decreased from 6.07 +/- 2.64 MPa at 16 weeks to 4.71 +/- 1.840 MPa after 1 year in Hanks Balanced Salts (HBS). The same coating had a strength that decreased from 8.51 +/- 2.63 MPa at 16 weeks to 5.35 +/- 1 MPa after 1 year in vivo. A soluble calcium enhanced hydroxyapatite had an interface strength of 4.83 +/- 1.106 MPa after 16 weeks and 4.51+/- 1.100 MPa after 1 year in HBS. The same coating had an interface strength of 8.34 +/- 2.40 MPa after 16 weeks and 5.20 +/- 2.00 MPa after 1 year in vivo. Although interface strengths decreased slightly with time in vivo, after 1 year they were in the same strength range as published CPC-bone interface strengths of 4.8 +/- 2.4 MPa. Comparison of in vitro with in vivo results indicated that in vitro results were a good predictor of strength change in the blended CPC coating, but a poorer predictor of strength changes in the soluble calcium-enhanced coating.     

An evaluation of BMP-2 delivery from scaffolds with miniaturized dental implants in a novel rat mandible model

The purpose of this study was three-fold: (a) to develop a new small animal model to evaluate dental implant systems that recapitulates aspects of the challenging intraoral environment, (b) screen several scaffolds for in vivo bone forming efficacy when used to deliver non-glycosylated bone morphogenetic protein-2 (BMP-2) together with a miniaturized titanium (Ti) dental implant, and (c) identify correlations between in vitro BMP-2 release rates and in vivo results. The scaffolds tested were: (1) collagen-hydroxyapatite composite (Col/HA), (2) polyethylene glycol hydrogel (PEG-hydrogel), and (3) Col/HA infused with PEG-hydrogel (Col/HA/PEG-hydrogel). BMP-2 delivery directly from the Ti implants rather than from the scaffolds was also tested. MicroCT analyses at 4 weeks showed that the maximum volume and height of new bone occurred when BMP-2 (10 μg) was delivered from the Col/HA/PEG-hydrogel scaffolds. BMP-2 delivery from the Ti implant was not as effective as from the scaffolds. While in vitro BMP-2 release was highest for the PEG-hydrogel, the scaffold most successful in vivo was the Col/HA/PEG-hydrogel scaffold because it had the necessary mechanical strength to perform well in the mandibular bone environment. The in vitro release studies suggested a threshold dose of 5 μg which was borne out by the in vivo dose response studies.