骨诱导无机材料BAM 修复牙种植体周围骨缺损的实验研究

目的:评价骨诱导磷酸钙生物陶瓷(BAMOICPC)与可吸收胶原膜(BME-10X医用胶原膜)在牙种植体周围骨缺损中的修复能力。方法:在兔股骨上植入羟基磷灰石涂层BLB种植体,然后在其侧壁制造高4 mm、宽3 mm、深2 mm的骨缺损。对照组为单纯侧壁骨缺损,实验A组骨缺损区仅覆盖BME-10X膜,B组骨缺损区植入BAMOICPC,C组骨缺损区植入BAMOICPC并加盖BME-10X膜。于术后6个月取带种植体的骨段,通过HE染色和扫描电镜(SEM)分析。结果:对照组骨缺损区种植体表面见纤维包裹,实验A组骨缺损边界区少许骨质移行覆盖,实验B组下半部分缺损区新生骨覆盖。C组新生骨完全覆盖骨缺损区,且较B组硬度高,扫描电镜见与种植体结合更紧密。组织学观察B、C两实验组新生骨均可见比较成熟的哈弗氏管系统。结论:骨诱导磷酸钙生物陶瓷BAMOICPC是一种较理想的骨替代材料,联合运用胶原膜修复种植体周骨缺损效果佳。     

The induction of bone by an osteogenic protein and the conduction of bone by porous hydroxyapatite: a laboratory study in the rabbit.

The influence of the addition of an osteoinductive protein, capable of inducing extraskeletal ossification, on bone ingrowth into coralline porous hydroxyapatite was evaluated in the rabbit using a calvarium onlay model. Twenty-three rabbits received hydroxyapatite implants (10 x 10 x 2 mm) prepared with and without osteoinductive protein. These were implanted on the frontal bone and secured by wire fixation after 0.25 mm of the cortical surface was abraded. The implants were harvested at 3 and 4 months and analyzed for percentage of bone ingrowth by histologic examination of decalcified H&E sections and by scanning electron microscope backscatter image analysis. The osteoinductive protein-treated implants demonstrated significantly greater amounts of bone ingrowth at both 3 (52.0 versus 10.3 percent; p less than 0.001) and 4 months (66.1 versus 39.2 percent; p less than 0.005) than the untreated implants. The type of bone found in all osteoinductive protein-treated implants was predominantly lamellar. Untreated implants contained mostly woven bone at 3 months, with increasing amounts of lamellar bone appearing at 4 months. These results suggest that the combination of a bone-inducing protein and a suitable osteoconductive matrix may provide an alternative to bone grafting.     

应用3D适形打印制备网状复合体对兔颅骨缺损的修复作用及安全性研究

目的:探讨采用3D适形打印技术制备的羟基磷灰石/聚乳酸网状复合体在兔颅骨缺损中的修复作用及安全性。方法:以24只新西兰兔为研究对象,以羟基磷灰石/聚乳酸为材料,采用3D适形打印技术制备网状复合体,于兔颅骨顶部制成两个颅骨全层缺损,分别为孔A(左)和孔B(右),孔A(阳性对照组)以自体颅骨为修复材料,孔B(实验组)以复合体为修复材料,观察缺损修复区域的形态学、影像学(X线及CT扫描)及组织学检查结果。结果:植入后24周时,形态学显示:阳性对照组可见致密的骨组织修复,与缺损边缘界限不清,实验组中支架孔隙内纤维组织由新生骨质取代,且新生骨成熟度较提高,材料表面有部分吸收。CT扫描观察显示:冠状面上,阳性对照组缺损修复区域与周围正常骨组织融合为一体,实验组修复材料与缺损边缘融合紧密,与周围正常骨组织结合良好,部分边缘结合不连贯。组织学观察显示:实验组材料部分降解,材料间隔可见新生骨小梁。研究中无实验动物死亡,皮肤切口处缝合良好,无皮下积液,无移植物脱出、红肿感染等情况出现。结论:以3D适形打印技术制备的羟基磷灰石/聚乳酸复合体对兔颅骨缺损有较好的修复作用,能促进缺损区域新骨的形成和生长,且安全性较高。     

Evaluation of new porous β-tri-calcium phosphate ceramic as bone substitute in goat model

The present study was carried out to evaluate the porous β-tri-calcium phosphate (TCP) (prepared by aqueous solution combustion technique) as bone substitute and compared with normal healing in 12 adult Black Bengal goats on the basis of clinical and radiographic findings, histological studies, oxytetracycline labeling, angiography studies (on day 90). Bone defects created in the diaphysis of radius were left unfilled in control animals (group I); while in treated (group II) animals the defects were filled with porous TCP blocks. The three months study showed no marked acute inflammatory reactions in all animals, wound healing was uneventful and the implants were clinically stable in the bone. Radiological studies showed presence of unabsorbed implants which acted as a scaffold for new bone growth across the defect whereas in control animals the defect was more or less same except that the newly formed bony tissue was less organized. Histological section showed moderately differentiated lamellar bone in the cortical part with presence of woven bone at peripheral cortex whereas control animals showed moderate fibro-collagenisation and good amount of marrow material, fat cells and blood vessels. Oxytetracycline labeling study showed crossing over of new bony trabeculae along with presence of resorption cavities within the new osteoid tissues whereas in group I, the process of new bone formation was active from both the ends; the defect site appeared as a homogenous non-fluorescent area. Angiogram of the animals in control showed uniform angiogenesis in the defect site with establishment of trans transplant angiogenesis, whereas in group II there was complete trans transplant shunting of blood vessels communication. The results of this study pointed out that the porous TCP promoted extensive bone formation over the entire extension of the defect in comparison to control group, thus conforming their biological osteoconductive property.     

Validation of Bone Conversion in Osteoconductive and Osteoinductive Bone Substitutes

Bone reconstruction can be performed with an autogeneic graft from various donor regions. Osteoconductive and osteoinductive bone substitutes originate from substances of diverse chemical and morphological types and can have a synthetic or a biological derivation. Alongside autogeneic bone transplants and allogenic and xenogeneic bone implants, alloplastic bone replacements of synthetic or semi-synthetic origin are being used for defect reconstruction. In an animal model in rabbits five bone substitutes and one autogeneic graft were surgically incorporated into identical bone defects (10times 10 mm in size) in six anatomically defined regions of the skull. With scintigraphic and histological methods, the metabolic dynamics of the bone is examined as it reacts to the transplantation of autogeneic bone or to implanted bone replacement material. The different autogeneic, xenogeneic and alloplastic bone replacement materials can be differentiated according to the functional quality of the new tissue and the dynamics of the bone conversion thus induced. In the comparison of mineralized, osteoconductive bone subsitutes (TCP, HA, calcium carbonate ceramics) with demineralized, osteoinductive implants (DBM new, DBM old) and autogeneic bone grafts, the bone inducing matrices show the largest quantity of new bone formation, making possible a volume-constant reconstruction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Experimental hydroxyapatite cement cranioplasty.

Hydroxyapatite cement is a calcium phosphate-based material that when mixed with water forms a dense paste that sets within 15 minutes and isothermically converts in vivo to a microporous hydroxyapatite implant. This cement was used to reconstruct bilateral 2.5-cm-diameter full-thickness critical-sized parietal skull defects in six cats. One side was reconstructed with 100 percent hydroxyapatite cement, and the other with a mixture of 50 percent hydroxyapatite cement and 50 percent ground autogenous bone by weight. These animals were sacrificed at 6 and 12 months after implantation. Positive and negative controls also were prepared. The anatomic contour of the soft tissue overlying all hydroxyapatite cement implants was well maintained, there were no wound infections or structural failures, and the implants were well tolerated histologically. None of the negative (unreconstructed) control defects was completely filled with repair bone, and all positive (methyl methacrylate) controls demonstrated foreign-body giant-cell formation and fibrous encapsulation of the implants. Examination of decalcified and undecalcified sections revealed progressive but variable replacement of the cement by new bone and soft tissue without a change in the shape or volume of the hydroxyapatite cement-reconstructed areas. New bone comprised 77.3 and 64.7 percent of the tissue replacing the hydroxyapatite cement and hydroxyapatite cement-bone implants, respectively. Replacement of the hydroxyapatite cement implants by new bone is postulated to occur by a combination of osteoconduction and implant resorption. These results indicate that further experimental research leading to the possible application of hydroxyapatite cement for full-thickness calvarial defect reconstruction in humans is warranted.     

Biomimetic tubular nanofiber mesh and platelet rich plasma-mediated delivery of BMP-7 for large bone defect regeneration

There is a growing need for successful bone tissue engineering strategies and advanced biomaterials that mimic the structure and function of native tissues carry great promise. Successful bone repair approaches may include an osteoconductive scaffold, osteoinductive growth factors, cells with an osteogenic potential and capacity for graft vascularisation. To increase osteoinductivity of biomaterials, the local combination and delivery of growth factors has been developed. In the present study we investigated the osteogenic effects of calcium phosphate (CaP)-coated nanofiber mesh tube-mediated delivery of BMP-7 from a PRP matrix for the regeneration of critical sized segmental bone defects in a small animal model. Bilateral full-thickness diaphyseal segmental defects were created in twelve male Lewis rats and nanofiber mesh tubes were placed around the defect. Defects received either treatment with a CaP-coated nanofiber mesh tube (n?=?6), an un-coated nanofiber mesh tube (n=6) a CaP-coated nanofiber mesh tube with PRP (n=6) or a CaP-coated nanofiber mesh tube in combination with 5?μg?BMP-7 and PRP (n?=?6). After 12?weeks, bone volume and biomechanical properties were evaluated using radiography, microCT, biomechanical testing and histology. The results demonstrated significantly higher biomechanical properties and bone volume for the BMP group compared to the control groups. These results were supported by the histological evaluations, where BMP group showed the highest rate of bone regeneration within the defect. In conclusion, BMP-7 delivery via PRP enhanced functional bone defect regeneration, and together these data support the use of BMP-7 in the treatment of critical sized defects.     

Segmental bone defects: from cellular and molecular pathways to the development of novel biological treatments

Several conditions in clinical orthopaedic practice can lead to the development of a diaphyseal segmental bone defect, which cannot heal without intervention. Segmental bone defects have been traditionally treated with bone grafting and/or distraction osteogenesis, methods that have many advantages, but also major drawbacks, such as limited availability, risk of disease transmission and prolonged treatment. In order to overcome such limitations, biological treatments have been developed based on specific pathways of bone physiology and healing. Bone tissue engineering is a dynamic field of research, combining osteogenic cells, osteoinductive factors, such as bone morphogenetic proteins, and scaffolds with osteoconductive and osteoinductive attributes, to produce constructs that could be used as bone graft substitutes for the treatment of segmental bone defects. Scaffolds are usually made of ceramic or polymeric biomaterials, or combinations of both in composite materials. The purpose of the present review is to discuss in detail the molecular and cellular basis for the development of bone tissue engineering constructs.     

Osteogenesis in calvarial defects: contribution of the dura,the pericranium,and the surrounding bone in adult versus infant animals

Guided bone regeneration is a promising means for reconstructing bone defects in the cranium. The present study was performed to better define those factors that affect osteogenesis in the cranium. The authors studied a single animal model, investigating the contribution of the dura, the pericranium, and the adjacent calvarial bone in the process of calvarial regeneration in both mature and immature animals. Bilateral, 100-mm2, parietal calvariectomies were performed in immature (n = 16) and mature (n = 16) rabbits. Parietal defects were randomized to one of four groups depending on the differential blockade of the dura and/or the pericranium by expanded polytetrafluoroethylene membranes. Animals were humanely killed after 12 weeks, and histometric analysis was performed to quantitate the area of the original bone defect, new bone formation, and new bone density. Bone formation was quantified separately both at the periphery and in the center of the defects. Extrasite bone formation was also quantified both on the dural and on the pericranial sides of the barriers. Bone regeneration was incomplete in all groups over the 12-week study period, indicating that complete bone healing was not observed in any group. The dura was more osteogenic than the pericranium in mature and immature animals, as there was significantly more extrasite bone formed on the dural side in the double expanded polytetrafluoroethylene barrier groups. In both the dural and the double expanded polytetrafluoroethylene barrier groups, dural bone production was significantly greater in immature compared with mature animals. The dura appeared to be the source of central new bone, because dural blockade in the dural and double expanded polytetrafluoroethylene groups resulted in a significant decrease in central bone density in both mature and immature animals. Paradoxically, isolation of the pericranium in mature animals resulted in a significant reduction in total new bone area, whereas pericranial contact appeared to enhance peripheral new bone formation, with the control group having the greatest total new bone area. The present study establishes a model to quantitatively study the process of bone regeneration in calvarial defects and highlights differences in the contribution of the dura and pericranium to calvarial bone regeneration between infant and adult animals. On the basis of these findings, the authors propose that subsequent studies in which permeability of the expanded polytetrafluoroethylene membranes is altered to permit migration of osteoinductive proteins into the defect while blocking prolapse of adjacent soft tissues may help to make guided bone regeneration a realistic alternative for the repair of cranial defects.     

Combination of Bioactive Polymeric Membranes and Stem Cells for Periodontal Regeneration: In Vitro and In Vivo Analyses

Regeneration of periodontal tissues requires a concerted effort to obtain consistent and predictable results in vivo. The aim of the present study was to test a new family of bioactive polymeric membranes in combination with stem cell therapy for periodontal regeneration. In particular, the novel polyester poly(isosorbide succinate-co-L-lactide) (PisPLLA) was compared with poly(L-lactide) (PLLA). Both polymers were combined with collagen (COL), hydroxyapatite (HA) and the growth factor bone morphogenetic protein-7 (BMP7), and their osteoinductive capacity was evaluated via in vitro and in vivo experiments. Membranes composed of PLLA/COL/HA or PisPLLA/COL/HA were able to promote periodontal regeneration and new bone formation in fenestration defects in rat jaws. According to quantitative real-time polymerase chain reaction (qRT-PCR) and Alizarin Red assays, better osteoconductive capacity and increased extracellular mineralization were observed for PLLA/COL/HA, whereas better osteoinductive properties were associated with PisPLLA/COL/HA. We concluded that membranes composed of either PisPLLA/COL/HA or PLLA/COL/HA present promising results in vitro as well as in vivo and that these materials could be potentially applied in periodontal regeneration.     

Effect of dolomite on the repair of bone defects in rats: histological study

The aim of the present study was to evaluate histologically and radiographically the tissue response to dolomite [CaMg(CO3)2] and its osteogenic potential in the repair of bone cavities in the calvaria of rats. A bone defect 10 mm in diameter and 1 mm deep was made in the calvaria of male Wistar rats. The defects were filled with dolomite, inorganic bovine bone (positive control), or coagulum (negative control). The animals were euthanized 7, 15, 30, and 60 days after surgery, and specimens were collected for radiographic and microscopic analyses. The bone defects were processed for paraffin embedding and H&E staining. The histological study revealed that dolomite stimulated a moderate inflammatory response, with programmed cell death in the first 15 days, compared to bovine bone which showed a moderate to intense acute response. In the chronic phase, the inflammatory response was characterized by the occurrence of macrophages organized as epithelioid cells in the dolomite group, and giant cells in the bovine-bone group. Fibrosis developed in all three groups; however, encapsulation of the fragments, reabsorption, and osteoconductive activity occurred only in the defects filled with bovine bone. The radiographic analysis showed that the bovine bone was most efficient in the repair of the defects, followed by the dolomite and the coagulum. This study demonstrated that the dolomite stimulated a moderate acute inflammatory response with programmed cell death, and a chronic inflammatory response by means of the phagocytic mononuclear system. Although osteo-conductive activity was not shown, the dolomite favored the repair process, compared to the coagulum group.     

The effects of gelatin,fibrin-platelet glue and their combination on healing of the experimental critical bone defect in a rat model: radiological,histological, scanning ultrastructural and biomechanical evaluation

Fibrin-platelet glue (FPG) is a blood derivative, in which platelets and fibrinogen are concentrated in a small plasma volume, by differential centrifugation and precipitation. It can form a three-dimensional and biocompatible fibrin scaffold with a myriad of growth factors and proteins that are released progressively to the local environment and contribute to the accelerated postoperative bone healing. Gelatin (Gel) is a derivative of collagen and can promote cell adhesion and proliferation due to its unique sequence of amino acids, so it is suitable for bone tissue applications. This study examined the effects of Gel, FPG and their combinations as bone scaffold on the healing of surgically created critical-size defects in rat radius. Fifty critical size defects of 5 mm long were bilaterally created in the radial diaphysis of 25 rats. The animals were randomly divided into five equal groups as empty defect, autograft, Gel, FPG and Gel–FPG groups (n = 10 in each group). Radiographs of each forelimb were taken postoperatively on the 1st day and then at the 28th and 56th days post injury to evaluate bone formation, union and remodeling of the defect. After 56 days, the rats were euthanized and their harvested healing bone samples were evaluated by histopathology, scanning electron microscopy (SEM) and biomechanical testing. The results of present study showed that the Gel alone did not significantly affect bone healing and regeneration; however, the Gel treated defects promoted healing more than those that were left untreated (negative control). Furthermore, the FPG-enhanced grafts provided a good scaffold containing numerous growth factors for proliferation of osteoinduction and was effective in improving the structural and functional properties of the newly formed bone more than that of the untreated and also the Gel treated groups. Incorporation of Gel into the FPG scaffold improved healing potential of the FPG scaffold; however, it was still inferior to the autograft (positive control). Although the Gel–FPG scaffolds had best effectiveness during bone regeneration, it still needs to be further enhanced by incorporation of the ceramic and osteoinductive biomaterials.     

利用聚己内酯/羟基磷灰石复合支架修复犬胸骨缺损

目的：探讨利用生物可降解支架修复动物胸骨缺损,为临床手术治疗提供新的可行性方法。方法：对于12只比格犬进行手术切除部分胸骨,并利用聚己内酯/羟基磷灰石（PCL/HA）复合支架,并制备出与临床相似的胸骨缺损模型。实验动物分成2组,分别是：空白对照组和PCL/HA支架组。分别于术后第4、12周进行胸部CT扫描,并对胸廓进行三维重建,观察胸骨缺损部位的修复情况,并在第12周取胸骨缺损部位组织进行硬组织切片,苦味酸-品红染色,观察缺损部位的骨组织修复情况,并利用软件进行骨组织比率分析,评估修复情况。结果：通过检查发现空白对照组的胸骨缺损部位未见明显骨连接,胸廓的骨性结构有明显畸形,PCL/HA支架组能很好地维持胸廓的完整性,组织学检查发现PCL/HA支架组的缺损部位有明显新生骨形成,通过软件分析可发现支架组的骨组织比率较空白组的高（P〈0.05）。结论：这些结果表明采用PCL/HA复合材料支架能很好地修复胸骨缺损。     

Bone‐Inspired Tube Filling Decellularized Matrix of Toad Cartilage Provided an Osteoinductive Microenvironment for Mesenchymal Stem Cells to Facilitate the Radius Defect Repair of Rabbit

Toad bone not only contains the rich cartilage‐like matrix but also presents low immunogenicity. It is inferred that decellularized toad bone matrix (dBECM) may provide the more profitable osteoinductive microenvironment for mesenchymal stem cells (MSCs) to promote the repair of bone defects. Herein, a hollow bone‐inspired tube is first made from hydroxyapatite (HA) and poly (γ‐glutamic acid) (PGA), and then MSCs/dBECM hydrogel is uniformly filled to its central cavity, constructing a biomimetic bone (dBECM + MSCs ? PGA + HA). In vitro scratch and transwell experiments show that dBECM hydrogel not only effectively promotes migration and proliferation of MSCs but also induces their osteogenic differentiation. Moreover, the less inflammatory macrophages infiltrate at rat skin after subcutaneously injecting dBECM hydrogel, indicating its low potential for inflammatory attack. After implanting dBECM + MSCs ? PGA + HA to critical radius defect of rabbit, X‐ray and CT imaging shows that the cortex is effectively regenerated and the medullary cavity recanalization is completed at 20 weeks. Moreover, the expression of Collagen‐II and OCN are obviously increased in the defect after implanting dBECM + MSCs ? PGA + HA. The therapeutic mechanism of dBECM + MSCs ? PGA + HA scaffold are highly associated with the enhanced angiogenesis. Collectively, the biomimetic dBECM + MSCs ? PGA + HA scaffold may be a promising strategy to improve radius defect healing efficiency.     

A 1-year study of osteoinduction in hydroxyapatite-derived biomaterials in an adult sheep model: part II. Bioengineering implants to optimize bone replacement in reconstruction of cranial defects

The present study investigated hydroxyapatite biomaterials implanted in critical-size defects in the calvaria of adult sheep to determine the optimal bioengineering of hydroxyapatite composites to facilitate bone ingrowth into these materials. Five calvarial defects measuring 16.8 mm in diameter were made in each of 10 adult sheep. Three defects were filled with cement paste composites of hydroxyapatite and beta-tricalcium phosphate as follows: (1) 100 percent hydroxyapatite-cement paste, (2) 60 percent hydroxyapatite-cement paste, and (3) 20 percent hydroxyapatite-cement paste. One defect was filled with a ceramic composite containing 60 percent hydroxyapatite-ceramic, and the fifth defect remained unfilled. One year after implantation, the volume of all biomaterials was determined by computed tomography, and porosity and bone replacement were determined using backscatter electron microscopy. Computed tomography-based volumetric assessment 1 year after implantation demonstrated that none of the unfilled cranial defects closed over the 1-year period, confirming that these were critical-size defects. There was a significant increase in volume in both the cement paste and ceramic implants containing 60 percent hydroxyapatite (p < 0.01). There was no significant change in volume of the remaining cement paste biomaterials. Analysis of specimens by backscatter electron microscopy demonstrated mean bone replacement of 4.8 +/- 1.4 percent (mean +/- SEM) in 100 percent hydroxyapatite-cement paste, 11.2 +/- 2.3 percent in 60 percent hydroxyapatite-cement paste, and 28.5 +/- 4.5 percent in 20 percent hydroxyapatite-cement paste. There was an inverse correlation between the concentration of hydroxyapatite and the amount of bone replacement in the cement paste for each composite tested (p < 0.01). Bone replacement in 60 percent hydroxyapatite-ceramic composite (13.6 +/- 2.0 percent) was not significantly different from that in 60 percent hydroxyapatite-cement paste. Of note is that the ceramic composite contained macropores (200 to 300 microm) that did not change in size over the 1-year period. All cement paste composites initially contained micropores (3 to 5 nm), which remained unchanged in 100 percent hydroxyapatite-cement paste. Cement paste implants containing increased tricalcium phosphate demonstrated a corresponding increase in macropores following resorption of the tricalcium phosphate component. Bone replacement occurred within the macropores of these implants. In conclusion, there was no significant bone ingrowth into pure hydroxyapatite-cement paste (Bone Source, Stryker-Leibinger Inc., Dallas, Texas) in the present study. The introduction of macropores in a biomaterial can optimize bone ingrowth for reconstruction of critical-size defects in calvaria. This was demonstrated in both the ceramic composite of hydroxyapatite tested and the cement paste composites of hydroxyapatite by increasing the composition of a rapidly resorbing component such as beta-tricalcium phosphate.     

Assessment of the effects on growth of porous hydroxyapatite granule cranioplasty in the immature guinea pig craniofacial skeleton

The immature guinea pig was used to study the effects on growth of porous granular hydroxyapatite used as an onlay cranioplasty and inlay cranioplasty to reconstruct full-thickness cranial defects in a growing craniofacial skeleton. Forty Hartley guinea pigs, 20 immature animals and 20 mature animals, were divided into four groups each containing five mature and five immature animals. The mature animals served as controls. Group I underwent elevation and replacement of the parietal periosteum. Group II underwent placement of hydroxyapatite between periosteum and parietal bone. Group III underwent elevation and replacement of autogenous bone flap after the formation of a 1 x 1-cm craniectomy defect in the parietal skull. Group IV underwent elevation of a 1 x 1-cm parietal craniectomy and reconstruction of the defect with hydroxyapatite granules placed between the dura and periosteum. Immature animals were killed at maturity at 3.5 months and mature animals were killed 2.5 months postoperatively. Macroscopic examination of the operative field, transverse and longitudinal cephalometric measurements, and histological sections encompassing the operative sites were compared. Macroscopically, all reconstructed operative sites were fully incorporated into the cranium. Histological staining of the sectioned operative site revealed no hydroxyapatite migration through the cranial bone or dura. No inflammatory or foreign body reaction was evident in the subcutaneous tissue, periosteum, or dura. No statistically significant cephalometric intergroup or intragroup differences were found at the conclusion of the study. The results of this study indicate that a granular porous form of hydroxyapatite may be used as an onlay or inlay cranioplasty in the immature guinea pig craniofacial skeleton without evidence of dural inflammation, granule migration, or growth restriction or retardation.     

Immunologic and Osteogeneic Properties of Xenogeneic and Allogeneic Demineralized Bone Transplants

Xenografting is increasingly being developed as a response to the shortage of human tissues. However, antigenic components of bone material eliciting immune responses – particularly of cellular nature – are blamed for the reduction of the osteoinductive properties of bone and bone-derived implants. The aim of our study was to compare the immunologic response and osteogenesis induced by antigen-depleted allogeneic and xenogeneic bone-derived implants to that induced by partially antigen-depleted material heterotopically placed (muscular pouch) in rats. Wistar rats received bone-derived implants of different antigeneic condition, from both xenogeneic (rabbit) and allogeneic (rat) origin. After sacrifice, animals were evaluated for osteogenesis and immune response. New bone formation was observed around all bone-derived implants, whether fully or partially antigen-extracted, and from both xenogeneic and allogeneic origin. No significant humoral response resulted following bone implantation. Cellular response showed a similar pattern in partial and fully antigen-extracted bone of both allogeneic and xenogeneic origin. Xenogeneic antigen-extracted bone from safe donor sources could be a suitable solution to human tissue shortage in a near future.     

Treatment of large complex cranial bone defects by using hydroxyapatite ceramic implants

Hydroxyapatite ceramic implants were used in the reconstruction of very large and complex-form cranial bone defects in nine patients. The bone defects were the result of craniectomy after infections and other complications such as severe brain edema, after neurosurgery, and as a result of trauma, subdural hemorrhage, and surgery for brain tumor. The size, shape, and curvature of the hydroxyapatite ceramic implants were determined based on high-precision, full-scale models fabricated through a laser lithographic molding method by using computed tomographic data. The use of this method allowed the fabrication of hydroxyapatite ceramic implants of shapes that accurately matched the area of bone defect, allowing for a minimum of adjustment during the operation even with a complex-form implantation. Not only were good cranial contour reconstructed and aesthetically satisfactory results obtained in the cases treated by incorporating this series of techniques, but neurologic conditions present in some cases were also improved to some extent. The postoperative course has been steady for all nine patients, with no blood transfusions required during or after the operations and no implants requiring removal because of infection or other postoperative complications. The average length of postoperative hospitalization for the nine cases was 11.7 days, remarkably short considering the clinical conditions.     

Osteogenin, a bone morphogenetic protein, adsorbed on porous hydroxyapatite substrata, induces rapid bone differentiation in calvarial defects of adult primates.

Osteogenin, a bone morphogenetic protein, in conjunction with insoluble collagenous bone matrix initiates local endochondral bone differentiation by induction in vivo. This study, by exploiting the affinity of native osteogenin for hydroxyapatite, was designed to construct a delivery system for the expression of the biologic activity of osteogenin in nonhealing calvarial defects of adult primates. After exposure of the calvaria, 64 cranial defects, 25 mm in diameter, were prepared in 16 adult male baboons (Papio ursinus). Defects were implanted with disks of porous nonresorbable and resorbable hydroxyapatite substrata obtained after hydrothermal conversion of calcium carbonate exoskeletons of corals. In each animal, one disk of each hydroxyapatite preparation was treated with osteogenin isolated and purified from baboon bone matrix after sequential chromatography on heparin-Sepharose, hydroxyapatite, and Sephacryl S-200 gel filtration columns. The remaining two defects were implanted with one disk of each hydroxyapatite preparation without osteogenin as control. Histomorphometry on decalcified sections prepared on days 30 and 90 showed superior osteogenesis in osteogenin-treated nonresorbable hydroxyapatite specimens as compared with controls. On day 90, substantial bone formation also had occurred in control nonresorbable hydroxyapatite specimens. On day 90, but not on day 30, significantly greater amounts of bone had formed in osteogenin-treated resorbable specimens as compared with resorbable controls. Overall, resorbable substrata performed poorly when compared with nonresorbable substrata, perhaps due to a premature dissolution of the implants. These results provide evidence that the biologic activity of osteogenin can be restored and delivered by a substratum other than the organic collagenous matrix, inducing rapid bone differentiation in calvarial defects of adult nonhuman primates. The adsorption strategy of osteogenin on porous inorganic nonimmunogenic substrata may help to design appropriate osteogenic delivery systems for craniofacial and orthopedic applications in humans.     

A 1-year study of osteoinduction in hydroxyapatite-derived biomaterials in an adult sheep model: part I

The study presented here investigated hydroxyapatite biomaterials implanted in soft-tissue sites in adult sheep to determine whether these materials are osteoinductive and whether the rate of osteoinduction can be increased by manipulating the composition and porosity of the implants. For the study, 16.8-mm x 5-mm discs were prepared from mixtures of hydroxyapatite and beta-tricalcium phosphate. Five mixtures of hydroxyapatite-ceramic and hydroxyapatite-cement paste forms were studied: 100 percent hydroxyapatite-ceramic (Interpore), 60 percent hydroxyapatite-ceramic, 100 percent hydroxyapatite-cement paste, 60 percent hydroxyapatite-cement paste, and 20 percent hydroxyapatite-cement paste. Biomaterials were implanted in subcutaneous and intramuscular soft-tissue pockets in 10 adult sheep. Cranial bone grafts of equal dimension were implanted as controls. One year after implantation, the volume of all biomaterials and bone grafts was determined from a computed tomographic scan, and porosity and bone formation were determined using backscatter electron microscopy. Cranial bone and the 20 percent hydroxyapatite-cement paste implants demonstrated significant volume reduction in all sites after 1 year (p < 0.001). No significant difference in volume of the remaining four biomaterials was found. There was no significant change in pore size in the ceramic implants (range, 200 to 300 micro) and in the cement-paste implants containing 60 percent hydroxyapatite or more (range, 3 to 5 nm). Pore size in the cement-paste implants containing 20 percent hydroxyapatite increased significantly with resorption of the tricalcium-phosphate component, reaching a maximum of 200 to 300 micro in the periphery, where the greatest tricalcium-phosphate resorption had occurred. Both ceramic biomaterials demonstrated lamellar bone deposition within well-formed haversian systems through the entire depth of the implants, ranging from a mean of 6.6 percent to 11.7 percent. There was minimal bone formation in the cement-paste implants containing 60 percent hydroxyapatite or more. In contrast, cement-paste implants containing 20 percent hydroxyapatite demonstrated up to 10 percent bone replacement, which was greatest in the periphery of the implants where the greatest tricalcium-phosphate resorption had occurred. This study confirms the occurrence of true osteoinduction within hydroxyapatite-derived biomaterials, when examined using backscatter techniques. In this study, the rate of osteoinduction was greatest when a porous architecture was maintained, which was best achieved in ceramic rather than cement-paste forms of hydroxyapatite. Porosity and resultant bone formation in cement-paste implants can be improved by combining hydroxyapatite with a rapidly resorbing component, such as tricalcium phosphate.