Electrical stimulation of bone growth into porous A12O3.

Porous, cylindrical, high alumina, ceramic structures were fabricated for implantation in the superior third of canine femoral medullary canals. Implant durations of one, two, four, and eight weeks using three animals per time period were studied. A constant current (10 muA) power supply was used to attempt to stimulate bone growth into the porous ceramic structures. Osseous tissue in-growth was evaluated using a mechanical push-out test, microadiography, and histological thin sectioning. The interfacial shear strength and tissue micro-structure was studied as a function of implant residence site and implant residence site and implant residence time. The results indicate that initially the proximal implants have a higher interfacial shear strength, however, after eight weeks of implantation the distal implants have a shear strength about twice that of the proximal implants. This trend is observed for both the electrically stimulated and nonstimulated specimens. The 10 muA current level used in this investigation was found to have a small but significant effect on shear strength increasing it at implantation times of less than eight weeks.     

Investigation as to the osteoinductivity of macroporous calcium phosphate cement in goats

For bone formation in critical-sized or poor healing defects, osteoinductive behavior of synthetic bone grafts is crucial. Although the osteoconductive behavior of calcium phosphate (CaP) cement is generally accepted, its osteoinductive potential is less reported. In this study, osteoinduction of porous CaP cement was investigated. Four goats received each six subcutaneous placed prehardened porous CaP cement implants. Implantation time was 3 and 6 months. After explantation, histological evaluation and scoring with a histological grading scale for soft-tissue implants were performed. The histological sections revealed that the implants degraded for more than 50% over time. The implants had lost their macroporous structure from 3 months on. A medium-thick fibrous capsule with a few inflammatory cells surrounded the implants after 3 months. This capsule significantly decreased in thickness after 6 months. Throughout the implant ingrowth of fibrous tissue was seen with scattered foci of inflammatory cells. Cement particles were surrounded by a layer of inflammatory cells. The massive inflammatory response in the interstice was seen after 3 months, which disappeared after 6 months implantation. No bone formation was detected in any of the specimens. The fast degradation and thereby collapsing of the porous structure of our CaP cement implant might have prevented osteoinduction.     

The effects of PRGF on bone regeneration and on titanium implant osseointegration in goats: a histologic and histomorphometric study

The effect of local application of scaffold-like preparation rich in growth factors (PRGF) on bone regeneration in artificial defects and the potential effect of humidifying titanium dental implants with liquid PRGF on their osseointegration were investigated. The PRGF formulations were obtained from venous blood of three goats and applied either as a 3D fibrin scaffold (scaffold-like PRGF) in the regeneration of artificial defects or as liquid PRGF via humidifying the implants before their insertion. Initially, 12 defects were filled with scaffold-like PRGF and another 12 were used as controls. The histological analysis at 8 weeks revealed mature bone trabeculae when PRGF was used, whereas the control samples showed mainly connective tissue with incipient signs of bone formation. For the second set of experiments, 26 implants (13 humidified with liquid PRGF) were placed in the tibiae of goats. Histological and histomorphometric results demonstrated that application of liquid PRGF increased the percentage of bone-implant contact in 84.7%. The whole surface of the PRGF-treated implants was covered by newly formed bone, whereas only the upper half was surrounded in control implants. In summary, PRGF can accelerate bone regeneration in artificial defects and improve the osseointegration of titanium dental implants.     

An optical and electron microscopy study of materials implanted in the rat middle ear. I Carbon

Glassy carbon implants in the middle ear of the rat model appear well tolerated over periods of 6 months. The implants are rapidly covered with a fibrous capsule resulting in some bonding to the surrounding tissue. At a later stage (12 wk), further development of this bond takes place through growth of bone onto the implant surface from adjoining bone lamellae. No adverse tissue reactions were found in the histological sections produced.     

Development of a pre-vascularized 3D scaffold-hydrogel composite graft using an arterio-venous loop for tissue engineering applications

Hyaluronic acid (HA) and fibrin glue (FG) are effective hydrogels for tissue engineering applications as they support tissue in-growth, retain growth factors, and release them slowly with time. The scaffolds, in combination with a hydrogel, effectuate a successful graft. However, the survival of a graft entirely depends upon a functional vascular supply. Therefore, hydrogels must support the in-growing vasculature. To study and compare the vascular patterns, HA and FG hydrogel-containing PLDLLA-TCP-PCL scaffolds were implanted in the groin of male Lewis rats and supplied with a micro-surgically prepared arterio-venous (A-V) loop. The rats were perfused with a vascular contrast media after 4 and 8 weeks and sacrificed for further analysis. The specimens were scanned with micro-CT to find the vascular growth patterns. Corrosion casting of blood vessels followed by SEM demonstrated a high vascular density near the parent blood vessels. Histologically, HA and FG implanted animal groups showed significant angiogenetic activity, especially within the pores of the scaffold. However, formation of new blood vessels was more conspicuously observed at 4 weeks in FG than HA implants. Furthermore, by 8 weeks, the number and pattern of blood vessels were comparable between them. At this time, HA was still present indicating its slow degradation. The finding was confirmed by histomorphometric analysis. This experimental study demonstrates that HA containing composite scaffold systems permit stabile in-growth of blood vessels due to sustained degradation over 8 weeks. HA is a potential matrix for a tissue engineered composite graft.     

Resorbable defect analog PLGA scaffolds using CO2 as solvent: structural characterization

After tooth extraction, the immediate wound treatment by implanting an exact copy of the root could prevent alveolar bone atrophy. The implant should have an interconnected porosity in order to promote tissue in-growth. This communication reports a novel method to realize such net-shaped porous scaffolds fabricated within a few minutes. Porosity and micro-architecture are evaluated by Hg-porosimetry and by image analysis of electron and light microscopy as well as by computed micro-tomography. The total porosity of the scaffold corresponds to (63 +/- 3)%, mainly related to open interconnected porosity. Micro-tomography, as a noninvasive 3D method, is best suited to uncover pores of about 100 microm, a diameter especially important for tissue in-growth. The differentiation between open and closed porosity, however, depends on the method chosen. This effect is attributed to the spherical pores with an orifice only detected in the 3D analysis. Consequently, the closed porosity is overestimated by 8% evaluating 2D images. Finally, the mean pore diameter is found to be 106 and 100 microm for 2D and 3D analysis, respectively. Although the porosity of the scaffold needs to be further optimized for clinical applications, the procedure proposed is a promising route in manufacturing open porous implants without the use of any organic solvent.     

Soft-tissue response to injectable calcium phosphate cements

In this study, the soft tissue reaction to two newly developed injectable calcium phosphate bone cements (cement D and W) was evaluated after implantation in the back of goats. For one of the cements (cement D) the tissue reaction was also investigated after varying the concentration of accelerator Na(2)HPO(4) in the cement liquid (resulting in cement D1 and D2). Eight healthy mature female Saanen goats were used. The cement was applied 10min after mixing while it was still moldable and plastic. The material was given a standardized cylindrical shape. Thirty-two implants of each cement formulation were inserted and left in place for 1, 2, 4, and 8weeks. At the end of the study, eight specimens of each material and healing period were available for further analysis. Two specimens were used for X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) and six specimens were used for light microscopical evaluation. XRD and FTIR showed that the cements did set as microcrystalline carbonate apatite with the disappearance of monetite from the cements during implantation. Histological analysis showed that after 8weeks of implantation around all materials a thin soft-tissue capsule was formed (thickness ranging from 5 to 15 cell layers) with almost complete absence of inflammatory cells. Only in some specimens a slightly higher inflammatory reaction was observed. This was due to cement surface defects and a zone of dispersed particles near the cement-soft tissue interface. There was almost no resorption of the material after 8 weeks of implantation. In a few 4 and 8weeks samples, small areas of calcification were found in the fibrous capsule surrounding the implants. On the basis of our observations, we conclude that the tested cements were biocompatible and can be used next to soft tissue.     

Enhancement of bony in-growth to metal implants by combining controlled hydroxyapatite coating and heat treatment

The rate of bony in-growth to heat-treated and controlled hydroxyapatite metal implants made of either titanium alloy (Ti-6Al-4V) or stainless steel (SS) 316L inserted to the medullar canal of the femur in rats was investigated. It was found that while partial coverage of hydroxyapatite (HA) did not cause a significant elevation of their bonding strength when compared with nonheated implants, HA, and heat treatment caused a significant (p < 0.01) elevation of 3.1-fold in the bonding strength of the implants to the host bone. A similar phenomenon to that found for the titanium alloy implants was found to be true for the SS implants as well. It is concluded that the novel approach presented in this article, that is, to heat treat implants as well as controlled partial coating of them by HA, prior to their insertion to host bone, produce an enhancement of bone growth to metal implants greater than utilization of each method alone. Our findings may be used to further enhance bony in-growth to metal implants in several clinical settings, producing avid implants with superior integration capabilities.     

Wound healing around bone-anchored percutaneous devices in experimental diabetes mellitus

The objective of this investigation was to study the influence of impaired wound healing on the tissue response to bone-anchored percutaneous devices. For this reason, diabetes mellitus was induced in rabbits with alloxan. Untreated rabbits were used as controls. Skin-penetrating titanium implants were inserted in the tibial bone of diabetic and healthy animals. The enossal part of half of the implants was provided with a thin magnetron-sputtered calcium-phosphate coating. The soft-tissue and bone response was evaluated clinically, histologically, and histomorphometrically. We did not observe more infectious complications in diabetic animals. Furthermore, histological analysis revealed no differences in soft-tissue response between diabetic and healthy animals. A close bone-implant contact was observed for all implants. Nevertheless, the density of cortical bone around the implants was clearly lower in diabetic animals compared with control animals. In control rabbits, but not diabetic animals, coated implants showed more downgrowth of bone into the marrow cavity than uncoated ones. In general, diabetes mellitus was shown to have no adverse effect on the clinical performance of the percutaneous devices. We think that this is due to the good fixation of the implants in diabetic as well as control animals. Therefore, we conclude that the presence of impaired healing in chronic health disorders like diabetes is no contra-indication for the anchorage of percutaneous implants in cortical bone.     

Osteoconductive properties of poly(96L/4D-lactide)/beta-tricalcium phosphate in long term animal model

The objective of this study was to determine the effect of calcium phosphate mineral content on the bone in-growth at the expense of composite of co-polylactide polymer charged with 2 different ratios of β-TCP granules (10 and 24 w-% of β-TCP). The evaluation was realized in a long term rabbit bone model. After 24, 48 and 76 weeks, the implants were examined by micro CT, scanning electron microscopy (SEM) using backscattered electron (BSE) and light microscopy (polarized and blue light microscopy). No foreign body reaction was detected during the 76 weeks follow-up in any of the test samples. Polymer hydrolysis began at approximately 24 weeks, by 76 weeks, the pure polymer implant had begun to release P(96L/4D)LA particles and show signs of peripheral localized bone resorption. A decrease in the amount of CaP was noticed between 24 and 76 weeks in both 10?wt-% and 24?wt-% β-TCP/P(96L/4D)LA composites. The study showed that the highest bone in-growth was with 24 wt-% β-TCP/P(96L/4D)LA composite. Bone in-growth and mineralization were evident for the composites associated with specific peripheral bone architecture. Fluorescent labelling demonstrated high bone in-growth and remodeling at the interface, while for pure co-polymer no bone remodeling or bone activity was maintained after 48 weeks. The study demonstrated the positive effect of calcium phosphate content into P(96L/4D)LA. This kind of composite is a suitable resorbable osteoconductive matrix, which provides long term stability required for ligament fixation device.     

Mechanical verification of soft-tissue attachment on bioactive glasses and titanium implants

Soft-tissue attachment is a desired feature of many clinical biomaterials. The aim of the current study was to design a suitable experimental method for tensile testing of implant incorporation with soft-tissues. Conical implants were made of three compositions of bioactive glass (SiO(2)-P(2)O(5)-B(2)O(3)-Na(2)O-K(2)O-CaO-MgO) or titanium fiber mesh (porosity 84.7%). The implants were surgically inserted into the dorsal subcutaneous soft-tissue or back muscles in the rat. Soft-tissue attachment was evaluated by pull-out testing using a custom-made jig 8 weeks after implantation. Titanium fiber mesh implants had developed a relatively high pull-out force in subcutaneous tissue (12.33+/-5.29 N, mean+/-SD) and also measurable attachment with muscle tissue (2.46+/-1.33 N). The bioactive glass implants failed to show mechanically relevant soft-tissue bonding. The experimental set-up of mechanical testing seems to be feasible for verification studies of soft-tissue attachment. The inexpensive small animal model is beneficial for large-scale in vivo screening of new biomaterials.     

Tissue response around silicon nitride implants in rabbits

The chemical and dimensional stability associated with suitable fracture toughness and propitious tribological characteristics make silicon nitride-based ceramics potential candidates for biomedical applications, mainly as orthopedic implants. Considering this combination of properties, silicon nitride components were investigated in relation to their biocompatibility. For this study, two cylindrical implants were installed in each tibia of five rabbits and were kept in the animals for 8 weeks. During the healing time, tissue tracers were administrated in the animals so as to evaluate the bone growth around the implants. Eight weeks after the surgery, the animals were euthanized and histological analyses were performed. No adverse reactions were observed close to the implant. The osteogenesis process occurred during the entire period defined by the tracers. However, this process occurred more intensely 4 weeks after the surgery. In addition, the histological analyses showed that bone growth occurred preferentially in the cortical areas. Different kinds of tissue were identified on the implant surface, characterized by lamellar bone tissue containing osteocytes and osteons, by a noncalcified matrix containing osteoblasts, or by the presence of collagen III, which may change to collagen I or remain as a fibrous tissue. The results demonstrated that silicon nitride obtained according to the procedure proposed in this research is a biocompatible material.     

The influence of carbon fibres on the resorption time and mechanical properties of the lactide-glycolide co-polymer

In this study the influence of short carbon fibres (CF) on mechanical properties and degradation time of the lactide-glycolide co-polymer (PGLA) and on the mechanism of bone ingrowth into the implants was determined. Mechanical properties and push-out tests were measured. The pH of solutions and the implants' weights were tested after incubation in Ringer fluid. Analysis was based upon FT-IR and SEM with EDS studies. Pathological examinations were also performed. The in vitro examination revealed that carbon fibres accelerated polymer degradation process and increased the mechanical strength of polymer. In the case of PGLA + CF under in vivo conditions, initially, the superficial polymer degradation with new tissue in-growth was observed. Next, the degradation process included also the inner part of the implant, while the bone began to grow on exposed carbon fibres. In the case of pure PGLA the growth of soft tissue can be observed at the bone-implant interface and in the implant area. Our research indicates that PGLA + CF composite can be used in bone surgery as a short-term multifunctional load-bearing implant, which initially provides a mechanical support. During the time of controlled resorption of PGLA, carbon fibres act as a scaffold for the bone growth.     

Histological changes associated with an artificial anterior cruciate ligament.

AIMS--To investigate the histopathological features of the synovial lining of the knee following implantation of an artificial cruciate ligament. METHODS--Eighty two patients underwent anterior cruciate ligament reconstruction for chronic, symptomatic instability of the knee. The cruciate ligament was reconstructed with a scaffold type prosthetic ligament. All patients underwent arthroscopy at the time of cruciate reconstruction and also as a "second look" procedure at a mean 26.5 months later, at which time synovial biopsy specimens were obtained in all cases. RESULTS--The most frequent histological finding was granulomatous synovitis in 48% (39/82) of patients. Particulate polyester debris produced a greater response than carbon fibres. In 24% (20/82), nonspecific inflammation was present and in 28% (23/82) the synovium was considered normal. When the prosthetic ligament was fully covered by soft tissue in-growth, a granulomatous reaction was present in 42% (24/57), irrespective of whether the ligament was partially or totally uncovered. Stabilisation of the joint did not prevent subsequent deterioration in the articular cartilage; other factors such as increasing patient age, interval between injury and reconstruction and altered knee kinematics after reconstruction are probably important. Granulomatous synovitis was not associated with progressive chondral changes. CONCLUSIONS--Although present in 48% of cases, granulomatous synovitis was not shown to have adverse effects on either chondral surface or the prosthetic material of the ligament. Rupture of the implant is caused by mechanical factors and granulomatous synovitis is not responsible for implant failure.     

Regenerative dental medicine: stem cells and tissue engineering in dentistry.

The dawn of this century is brightened by the growing understanding and experimentation with stem cells as primary tools in the expanding regenerative medicine and tissue engineering revolution. The tradition of using prosthetic artificial implants to restore lost or damaged dental tissue will gradually be supplanted by more natural alternatives, including biological tooth replacement or induction. The practice of dentistry is likely to be revolutionized by biological therapies based on growth and differentiation factors that accelerate and/or induce a natural biological regeneration. This prospect has flourished from the gained knowledge provided by the molecular biological characterization of the genetic makeup of human cells and from a growing understanding of the effect of environmental factors. Prevention of dental diseases will also gain new ground as more insight is gained into the genetic makeup of microbial pathogens, their interactions with the host, and the host repair mechanisms. This review summarizes current knowledge, barriers, and challenges in the clinical use of stem cells with an emphasis on applications in dentistry.     

The influence of carbon fibres on the resorption time and mechanical properties of the lactide–glycolide co-polymer

In this study the influence of short carbon fibres (CF) on mechanical properties and degradation time of the lactide–glycolide co-polymer (PGLA) and on the mechanism of bone ingrowth into the implants was determined. Mechanical properties and push-out tests were measured. The pH of solutions and the implants' weights were tested after incubation in Ringer fluid. Analysis was based upon FT-IR and SEM with EDS studies. Pathological examinations were also performed. The in vitro examination revealed that carbon fibres accelerated polymer degradation process and increased the mechanical strength of polymer. In the case of PGLA + CF under in vivo conditions, initially, the superficial polymer degradation with new tissue in-growth was observed. Next, the degradation process included also the inner part of the implant, while the bone began to grow on exposed carbon fibres. In the case of pure PGLA the growth of soft tissue can be observed at the bone–implant interface and in the implant area. Our research indicates that PGLA + CF composite can be used in bone surgery as a short-term multifunctional load-bearing implant, which initially provides a mechanical support. During the time of controlled resorption of PGLA, carbon fibres act as a scaffold for the bone growth.     

Optimal kvp selection for dual-energy imaging of the chest: evaluation by task-specific observer preference tests

Human observer performance tests were conducted to identify optimal imaging techniques in dual-energy (DE) imaging of the chest with respect to a variety of visualization tasks for soft and bony tissue. Specifically, the effect of kVp selection in low- and high-energy projection pairs was investigated. DE images of an anthropomorphic chest phantom formed the basis for observer studies, decomposed from low-energy and high-energy projections in the range 60-90 kVp and 120-150 kVp, respectively, with total dose for the DE image equivalent to that of a single chest radiograph. Five expert radiologists participated in observer preference tests to evaluate differences in image quality among the DE images. For visualization of soft-tissue structures in the lung, the [60/130] kVp pair provided optimal image quality, whereas [60/140] kVp proved optimal for delineation of the descending aorta in the retrocardiac region. Such soft-tissue detectability tasks exhibited a strong dependence on the low-kVp selection (with 60 kVp providing maximum soft-tissue conspicuity) and a weaker dependence on the high-kVp selection (typically highest at 130-140 kVp). Qualitative examination of DE bone-only images suggests optimal bony visualization at a similar technique, viz., [60/140] kVp. Observer preference was largely consistent with quantitative analysis of contrast, noise, and contrast-to-noise ratio, with subtle differences likely related to the imaging task and spatial-frequency characteristics of the noise. Observer preference tests offered practical, semiquantitative identification of optimal, task-specific imaging techniques and will provide useful guidance toward clinical implementation of high-performance DE imaging systems.     

Bone induction by demineralized bone particles: long-term observations of the implant-connective tissue interface.

Allogeneic demineralized bone (DB) powder was applied to subcutaneous pockets and cranial defects of rats and histological, histomorphometrical, and radiological evaluation was performed one to 52 weeks after implantation. In both type of implants cartilage formation was observed after 1 week between DB particles and in former vascular channels and cervices within the particles. Foci of bone formation were observed after 2 weeks in the center of the implant. Remineralization of DB particles only occurred in close contact with the new bone tissue by which they became incorporated, indicating that remineralization of DB is a continuation of a process which has started in live bone. At all times, the interface between implant and connective tissue of the host consisted of a layer of non-remineralized DB particles embedded in fibrous connective tissue. This rim was thinner at the dura-mater-side in the cranial implants, compared with the skin-side of the same implants as well as all sides of the subcutaneous implants. The rim became thinner with time but never disappeared completely. The outer contour of the mineralized implant sometimes ran right through a DB particle. A critical concentration of bone-inducing agent leaking from DB particles seems to be necessary for bone induction. We suggest that at the interface of the implant and loose connective tissue this concentration is never reached, which results in maintenance of the rim.     

重组人骨形态发生蛋白2修饰的组织工程化骨修复眼眶骨折的实验研究

目的 探讨组织工程化骨修复眼眶骨折缺损的治疗效果.方法 体外构建以自体骨髓基质干细胞(BMSC)为种子细胞、可降解吸收的生物材料聚乳酸羟基乙酸聚合物(PLGA)为载体、重组人骨形态发生蛋白2(rhBMP-2)为生长因子的组织工程化骨,将实验动物分为对照组(植入PLGA/rhBMP-2复合物)和实验组(植入组织工程化骨),观察术后1个月、3个月和6个月伤口愈合情况、并发症及眼眶外观、CT影像学和组织学变化.结果 术后所有动物伤口愈合良好,无并发症和眼球凹陷.CT三维成像显示术后3个月实验组的缺损范围[(25.1±6.8) mm2]小于对照组[(55.3±7.7)mm2];术后6个月,实验组的眼眶骨折缺损消失,而对照组仍存在.组织学结果显示,术后1个月即可观察到实验组植入区边缘植入物开始缓慢吸收,少量成骨细胞沿支架长人材料内,而对照组未观察到;术后3个月可见实验组形成条带状新生骨长入将其分割包绕呈交叉排列,材料降解吸收明显高于对照组;术后6个月实验组植人材料完全被降解吸收,同时被新生骨组织取代,植入物与自身骨组织紧密结合,融为一体.而对照组仅部分降解吸收.结论 重组人骨形态发生蛋白2修饰的组织工程化骨具有较强的传导成骨和诱导成骨活性,生物相容性好,材料可完全降解,为骨组织取代,对眼眶骨折缺损具有较好的修复效果.     

Behavior of dense and porous hydroxyapatite implants and tissue response in rat femoral defects

Porous and dense hydroxyapatite cylinders (PHA and DHA) were implanted into cavities produced in rat femora and the sites of implantation were examined at different times over a period of 24 weeks by microradiologic and histological techniques. Microradiographs showed the presence of a layer of trabecular bone around the implants, which became more radiopaque and thinner along the experimental time. The microradiologic methodology used was suitable for the evaluation of the interface between hydroxyapatite and newly formed bone in nondecalcified materials. Microscopic observations showed that young bone grew over the surface of both types of implants after 1 and 2 weeks of surgery and that bone also grew inside PHA implants. Progressive bone absorption was observed in both types of implants after the fourth week. A layer of fibrous tissue was formed in the interface between new bone and DHA. Mature bone with haversian systems surrounded DHA implants and filled the pores of PHA implants throughout the experimental period. The pores of PHA implants were smaller than those commonly reported, which should have been a disadvantage, although it was observed that the extra cellular fluid induced disintegration of the ceramic granules, allowing the gradual growth of bone tissue into the spaces among them, without the interposition of fibrous tissue.