Porous polysulfone coatings for fixation of femoral stems by bony ingrowth

Sixteen porous polysulfone-coated canine femoral stems were inserted into 14 dogs. Coatings were approximately 40% porous, with an average pore size of 125 or 250 microns. Bone was formed within at least about 30% of the surface pores of the implants. The tissue ingrowths filling the pores included marrow and fibrous tissue. Correlated roentgenographic and histologic observations revealed a trabecular "lamina dura" at the coating-bone interface and relatively dense trabeculae distal to the stem tip. These observations support the concept of coating femoral prostheses with porous material for cement-free stabilization.     

Histomorphometric analysis of the repair of a segmental diaphyseal defect with ceramic and titanium fibermetal implants: Effects of bone marrow

We used a rat femoral diaphyseal defect/implant model to quantify the ingrowth of bone, cartilage, and fibrous connective tissue in a comparative study of woven sintered titanium fibermetal and porous hydroxyapatite/tricalcium phosphate ceramic implanted with and without the addition of syngeneic bone marrow cells. The patterns of tissue growth into the implants were analyzed with respect to time, type of implant, and the presence or absence of syngeneic marrow. Significantly more bone was found in ceramic implants than in fibermetal implants, with the addition of syngeneic marrow than without it, and at 4 months than at 2 months. Significantly more bone was found at both time periods in ceramic implants with bone marrow than in any other combination studied. We hypothesize that these findings resulted from interactions between the implanted material and its surroundings, specifically its ability to serve as a substratum for cell attachment, and cells in and around the defect, whether surgically implanted or arising from the soft-tissue bed.     

Repair of bone defects with marrow cells and porous ceramic. Experiments in rats

We studied the role of bone-marrow reconstituted porous ceramics in enhancing healing of a 5-mm femoral diaphyseal defect fixed with a rigid polyethylene plate in rats. Osseous repair was evaluated by histologic scoring. When blocks of porous calcium phosphate ceramics alone were introduced into the defects, most cases showed fibrous tissue interposition at the host bone-ceramic junction 1 month after implantation, and only four of 12 defects developed osseous or osteochondral union at both the proximal and distal junctions 2 months after surgery. However, when the ceramic was combined with syngeneic viable marrow cells, new bone formation occurred in isolated pore regions of the ceramic at 1 month, and extensive bone formation was seen in most pore regions 2 months after implantation. Out of 12 implants, complete bone union was seen in eight, and one showed osseous or osteochondral union at both junctions 2 months after surgery. Our results indicated that composite grafts of porous calcium phosphate ceramics and marrow cells may be clinically applicable to enhance osteogenesis and osteoconduction.     

Porous hydroxyapatite and tricalcium phosphate cylinders with two different pore size ranges implanted in the cancellous bone of rabbits. A comparative histomorphometric and histologic study of bony ingrowth and implant substitution

To investigate the histophysiology of implant degradation, hydroxyapatite and tricalcium phosphate cylinders with a diameter of 3 mm were implanted in the cancellous bone of the distal femur and the proximal tibia of 15 New Zealand White rabbits for up to six months. All implants had a homogeneous pore distribution and a porosity of 60%. Ceramics with a pore size range of 50-100 micron and 200-400 micron were compared. Morphometric analysis showed that up to 85.4% of the originally implanted tricalcium phosphate was degraded after six months, whereas the volume reduction of the hydroxyapatite was only 5.4% after the same period. Within the first months bone and tissue ingrowth and implant resorption occurred at a higher rate in the smaller-pored tricalcium phosphate than in the larger-pored material. Hydroxyapatite cylinders with small pores were totally infiltrated by bone or bone marrow after four months, whereas in the larger-pored hydroxyapatite implants tissue did not penetrate all pores after six months and the amount of bone within the implant was small. Scanning electron microscopy of the material before implantation revealed the existence of numerous pore interconnections with diameters of about 20 micron in the smaller-pored ceramics. Such interconnections were rare in the larger-pored implants. The pore interconnections seem to promote vascular and tissue ingrowth and consequently the initial rate of implant resorption. Implant resorption is an active process and involves two different cell types. Acid phosphatase-positive osteoclast-like cells suggesting active resorption adhere directly to the surface, especially in tricalcium phosphate implants. Clusters of macrophages tightly packed with granular material are found in the pores and along the perimeter of all implant cylinders. They may play an active role in the intracellular degradation of small detached ceramic particles.     

Histological observations on muscle tissue reactions to porous hydroxyapatite sintered bodies in rats

Blocks of porous hydroxyapatite (dimensions, 2 X 3 X 4 mm3; sintering temperature, 1,150 degrees C; macroporosity, 48%; pore diameter, 50-300 microns) were implanted into the intervening space between the tibial periosteum and the tibialis anterior muscle in 36 male Wistar rats at the age of 5 months. Specimens from the lower leg were obtained 1, 2, 3, 5, 8 and 12 weeks after implantation. The implants were found to adhere firmly to the tibialis anterior in the 5 and 12 week-specimens. No inflammatory reactions were seen around the implants and a layer of fibrous tissue was observed between the implanted apatite block and the muscle in all specimens. The fibrous tissue penetrated deeply into pores of the apatite block. The resistance to pulling of the interface (3 X 4 mm2) between porous hydroxyapatite and the tibialis anterior muscle was measured using a universal testing machine. The mean of the resistance to pulling was 24.7 +/- 5.1 gf/mm2 in 4 specimens of 12 weeks implantation.     

Experimental application of calcium phosphate granulate for the substitution of conventional bone transplants (author's transl)]

Autologous spongiosa, a calcium phosphate ceramic and Kiel bone chips were implanted in the tibiae of dogs and compared with respect to tissue compatibility and osteogenetic effect. After the ceramic implants and the autologous spongiosa had been left in the tibial fat marrow for six weeks, bone tissue and bone marrow had formed to the same extent around both materials. Their stimulating effect on osteogenesis was comparable. In contrast to the ceramic material, together with which they had been implanted in active bone marrow, the Kiel bone chips were surrounded by fibrous tissue in addition to bone tissue. All of the three types of implant proved to be tissue compatible. On the whole, the calcium phosphate ceramic was found to be equal to autologous and superior to heterologous spongiosa from a biological point of view. In technical terms the ceramic implant was superior also to the autologous graft.     

种植骨髓基质细胞的骨组织工程学研究

目的 观察骨髓基质细胞在多孔状的人工骨块上三维立体培养后的生长情况及其复合植入体内后的成骨能力。方法 利用组织工程学方法,将骨髓基质细胞种植于羟基磷灰石人工骨块上,立体培养２周,用扫描电镜观察细胞在体外的生长情况;将上述细胞人工骨复合体自体异位植入体内,取材观察其植入体内后的成骨情况。结果 细胞在人工骨块上能立体培养成活,细胞多生长于周边的孔隙表面,尤其以贴近培养瓶底的那一边较多,骨块的中心部位未     

Microtopography and soft tissue response

Implants placed in soft tissue evoke a foreign body reaction. Polymeric implants having smooth surfaces, such as silicone rubber implants, develop a nonadherent fibrogranulous tissue capsule which contracts over time and stiffens. Conventional porous implants, such as those made from textiles, usually have pores larger than 20 microns and they become infiltrated with inflammatory tissue. The in vivo cell reaction to polymeric surfaces having pores smaller than 10 microns has not been investigated systematically. In this study the histocompatibility of materials having mean pore diameters from 0.4 to 10 microns was assessed. A material available with several different defined pore sizes Versapor filter material) was tested in vivo to determine relation between pore size and qualitative tissue response. Silicone-coated samples were also tested to determine the dependence of the observed tissue response on the implant surface chemistry. Results showed nonadherent, contracting capsules around implants having pore diameters smaller than 0.5 microns. Implants with pores ranging from 1.4 to 1.9 microns evoked thin, tightly adherent fibrous capsules without inflammatory cells. Porosities of 3.3 microns and larger became infiltrated with inflammatory tissue. Results indicate that the observed tissue response is predominantly dependent on implant surface topography and that variation in implant material may have little effect. It is concluded that a defined surface topography of 1 to 2 microns appears to allow direct fibroblast attachment to the surface independent of its chemical or electrochemical nature. Attached fibroblasts then produce a minimal connective tissue response to the implant and prevent or diminish the presence of inflammatory cells at the implant/tissue interface.     

Chondroosteogenetic response to crude bone matrix proteins bound to hydroxyapatite

For the development of a new implantable biomaterial that possesses osteogenetic ability, bone matrix morphogenetic proteins were bound to hydroxyapatite (BMP-HAP). A crude protein extract including the bone morphogenetic protein (BMP) fraction was precipitated in the pores of hydroxyapatite (HAP) inside of a dialysis sac. In tissue culture, BMP-HAP or HAP was used as substratum for rat mesenchymal muscle cell explants. The BMP-HAP and HAP controls were also implanted in the muscle pouches of mice. New cartilage and/or new bone formation was observed on the exterior surface of BMP-HAP but not of HAP controls. Implantation of this HAP into bone marrow cavities of rabbit femoral and tibial condyle produced new bone formation. The deposits extended further inside BMP-HAP than HAP pores. The pore diameters of 90-200 microns produced earlier ingrowth than into larger pore sizes. BMP-HAP should be tested for clinical application as osteogenetic biomaterial for augmentation of bone regeneration.     

Porous and porous-compact ceramics in orthopedics

A bioceramic material has been obtained by a group of researchers with the collaboration of bone surgeons and veterinary doctors. This material has the following properties: chemical composition, 97% Al2O3, 2.5% MgO, and 0.5% CaO; mineral composition, alpha-Al2O3 corundum, MgAl2O4 spinel; open porosity, 70-80%; pore diameter, more than 90% of pores between 100 and 800 microns; bending strength, approximately 15 MPa. Experiments performed on rats, rabbits, and sheep demonstrated good biocompatibility with the material implanted in their bone tissue. The outer and the inner pores were filled with the healthy bone tissue adherent to the ceramic material, and a strong biologic bond was created. The material penetrated by this mineralized bone tissue increased its mechanical strength by about 70%. These properties of the material may encourage its application to bone surgery. The porous ceramics were implanted in the bones of more than 200 patients. Observations revealed that the process of bone tissue ingrowth into the pores of material had been accomplished in two to three months. The application of the material included filling the bone cysts, postsurgical or trauma-related bone defects, destroyed vertebra caused by the removal of bone tumors, and in the alloplasty of the hip joint. A modification of the ceramic material described above has been developed: a porous-compact ceramic material that is integrally bonded and has mechanical strength several times greater than the porous one. It also enables the biologic connection with the bone. This type of material has been used for filling the dome of the acetabulum in the "coxa protrusa" and in the alloplasties of the hip joint.     

Bone ingrowth into three different porous ceramics implanted into the tibia of rats and rabbits

Three different porous ceramics--calcium aluminate, calcium hydroxyapatite, and tricalcium phosphate--were implanted into the proximal tibia in rats and rabbits to study the interactions between these ceramics and a bony site that is abundant in bone marrow. New bone was consistently formed within the bone marrow surrounding and adjacent to all three types of ceramics. Calcium hydroxyapatite and tricalcium phosphate ceramics permitted bone ingrowth into their pores. The newly formed bone was found only in the part of the ceramic intruding into the bone, not in the portion protruding in the soft tissues outside the tibia. Partial replacement of the new bone opposite the medullary portion by new hemopoietic marrow occurred with longer implantation times. In contrast, no bone was seen within the pores of any of the calcium aluminate implants.     

Osteogenic capacity of rat and human marrow cells in porous ceramics. Experiments in athymic (nude) mice

Porous hydroxyapatite ceramics, alone and combined with rat marrow cells, were implanted subcutaneously in 22 nude mice. The ceramics alone were invaded by fibrovascular tissue without any bone formation. In contrast, all the ceramics combined with marrow cells had bone formation in the pores 4 to 8 weeks after implantation. The bone formation began on the surface of the ceramic with direct bonding of the bone to the ceramic and proceeded to the center of the pores. The ceramics were also combined with bone marrow cells from 7 humans and implanted in nude mice. In five experiments, bone formation occurred after implantation. In addition, the ceramics were combined with in vitro cultured fibroblastic cells, resulting in bone formation in 2/6 cases. Our results indicate that the osteogenic ability of human marrow cells is sustained by porous hydroxyapatite ceramics.     

Osteogenic capacity of rat and human marrow cells in porous ceramics: Experiments in athymic (nude) mice

Porous hydroxyapatite ceramics, alone and combined with rat marrow cells, were implanted subcutaneously in 22 nude mice. The ceramics alone were invaded by fibrovascular tissue without any bone formation. In contrast, all the ceramics combined with marrow cells had bone formation in the pores 4 to 8 weeks after implantation. The bone formation began on the surface of the ceramic with direct bonding of the bone to the ceramic and proceeded to the center of the pores.

The ceramics were also combined with bone marrow cells from 7 humans and implanted in nude mice. In five experiments, bone formation occurred after implantation. In addition, the ceramics were combined with in vitro cultured fibroblastic cells, resulting in bone formation in 2/6 cases. Our results indicate that the osteogenic ability of human marrow cells is sustained by porous hydroxyapatite ceramics.     

Heterotopic osteogenesis in porous ceramics induced by marrow cells

When untreated porous calcium phosphate ceramics were transplanted into subcutaneous (s.c.) or intramuscular (i.m.) sites, fibrovascular tissue grew in the pore region without evidence of bone formation. However, when these same ceramics were combined with syngeneic marrow cells, osteogenesis was observed inside the pore region of the implanted ceramic. The osteogenesis began on the surface of the pore region at approximately 3 weeks postimplantation by a process of intramembranous bone formation, with the de novo bone tissue observed directly interfacing with the ceramic surface. Infrequently, small isolated areas showed cartilage formation with no noticeable endochondral ossification. At 4 weeks postimplantation of the ceramic with marrow cells, the osteogenesis in the ceramic accompanied an observed increase in compressive strength, rigidity, and energy absorption of the ceramic. These results suggest that a combination of porous ceramics and marrow cells may be useful for clinical problems requiring osseous reconstruction.     

骨髓基质细胞体内外成骨的实验研究

目的：探讨骨髓基质细胞（Bone marrow stromal cell,BMSc)向成骨细胞转化的条件,利用骨髓基质细胞构建组织工程化骨组织。方法：采用地塞米松、β-甘油磷酸钠诱导体外培养的兔骨髓基,上差异显微镜和碱性磷酸酶检测基向成骨细胞转化的能力。将骨髓基质细胞与生物活性玻璃陶瓷（Bioactive glass ceramic,BGC)复合后植入免自体肌袋内,观察成骨过程。结果：在适当诱导条件下,骨髓基质细胞可向成骨细胞分化,在体内外表现出明显的成骨能力,地塞米松、β-甘油磷酸钠起着重要的作用。结论：骨髓基质细胞是骨组织工程的良好细胞来源,利用组织工程化方法可构建新生骨组织。     

Autogeneic cancellous bone grafts in extensive segmental ulnar defects in dogs. Effects of xenogeneic bovine bone morphogenetic protein without and with interposition of soft tissues and interruption of blood supply

Xenogeneic (bovine) bone morphogenetic protein (bBMP) and associated insoluble noncollagenous proteins (NCP) were implanted in inbred adult beagle dogs with 3-4 cm diaphyseal defects in the ulna. Defects were stabilized with internal plate fixation, and the control defects were not stabilized. The defects were implanted with either autogeneic cancellous bone grafts (ACG), bBMP/NCP, or a composite of ACG and bBMP/NCP. Of the plated ulnae, 18 of 19 ACG controls restored bone continuity; six of seven defects healed under the influence of bBMP/NCP plus ACG. Two of four defects with bBMP/NCP plus ACG healed and two were filled with osseous tissue, but fibrous tissue developed at one or both bone ends. Eight of nine defects implanted with bBMP/NCP capsules alone were repaired with fibrous tissue only. Of the nonplated defects, four were implanted with bBMP/NCP plus ACG and only one regenerated; three of four showed hypertrophic bone growth around a pseudarthrosis. Of six nonplated defects implanted with bBMP/NCP without ACG, all developed atrophic bone ends and fibrous tissue repair. Thus, to restore continuity of large segmental defects three times greater than the critical size for spontaneous regeneration, xenogeneic bBMP/NCP failed to induce bone regeneration in dogs. To exclude cell-mediated immune reactions and soft-tissue ingrowth, one defect was bridged with a polytetrafluoroethylene semipermeable tube (pore size 0.45 micron) containing implants of bBMP/NCP. In response to bBMP/NCP, cells from the host bone ends produced ossicles of induced woven bone formation. The observation that bBMP/NCP induced bone formation across the defect inside of semipermeable cylindrical chambers suggests that the experiments on bone defects larger than the critical size for spontaneous repair should be repeated with: (1) allogeneic dog BMP/NCP; (2) semipermeable cylinders to protect against muscle interposition; (3) compartment angiograms to evaluate blood supply; (4) treatment of the recipient with immunosuppressants and immunostaining to observe the concentration gradient of BMP; and (5) histologic observations on the first three days after implantation to evaluate cell-mediated immune barriers to the response of BMP.     

骨髓基质细胞移植修复半月板无血运区损伤的实验研究

目的比较自体与同种异体骨髓基质细胞移植对半月板无血运区损伤修复的影响。方法 40只成年新西兰大白兔随机平均分为 A、 B两组。 A组兔的骨髓基质细胞 (MSC)经体外培养后与纤维蛋白凝胶 (FG)混合,自体移植于其一侧的膝关节半月板缺损区,即 FG＋自体 MSC（自体移植组）;另一侧单纯植入 FG(FG植入组 )。于 B组兔的一侧膝关节半月板缺损区移植 FG＋同种异体 MSC(异体移植组 ),另一侧缺损不予修复 (空白对照组 )。分别于术后第 1、 2、 3个月取材,观察半月板损伤部位的组织形态学变化。结果 (1)自体移植组 :术后 1个月缺损区可见纤维组织,内有大量成纤维细胞;术后 2个月见大量软骨细胞并有胶原纤维形成;术后 3个月损伤区呈纤维软骨愈合。 (2)空白对照组 :术后 1～ 3个月缺损区始终未愈合。 (3)单纯 FG植入组 :术后 1～ 3个月缺损区可见纤维组织,内有少量成纤维细胞,没有软骨细胞生长,呈瘢痕样愈合。 (4)同种异体移植组 :与自体移植组所见大致相同,但有 3侧缺损区可见大量淋巴细胞浸润,胶原纤维少。结论骨髓基质细胞移植可促进半月板无血运区损伤的愈合,同种异体骨髓基质细胞移植修复半月板无血运区损伤发生免疫排斥反应的机率较低。     

Bone tissue engineering using novel interconnected porous hydroxyapatite ceramics combined with marrow mesenchymal cells: quantitative and three-dimensional image analysis

We developed fully opened interconnected porous calcium hydroxyapatite ceramics having two different pore sizes. One has pores with an average size of 150 microm in diameter, an average 40-microm interconnecting pore diameter, and 75% porosity (HA150). The other has pores with an average size of 300 microm in diameter, an average 60-100-microm interconnecting pore diameter, and 75% porosity (HA300). Because of its smaller pore diameter, HA150 has greater mechanical strength than that of HA300. These ceramics were combined with rat marrow mesenchymal cells and cultured for 2 weeks in the presence of dexamethasone. The cultured ceramics were then implanted into subcutaneous sites in syngeneic rats and harvested 2-8 weeks after implantation. All the implants showed bone formation inside the pore areas as evidenced by decalcified histological sections and microcomputed tomography images, which enabled three-dimensional analysis of the newly formed bone and calculation of the bone volume in the implants. The bone volume increased over time. At 8 weeks after implantation, extensive bone volume was detected not only in the surface pore areas but also in the center pore areas of the implants. A high degree of alkaline phosphatase activity with a peak at 2 weeks and a high level of osteocalcin with a gradual increase over time were detected in the implants. The levels of these biochemical parameters were higher in HA150 than in HA300. The results indicate that a combination of HA150 and mesenchymal cells could be used as an excellent bone graft substitute because of its mechanical properties and capability of inducing bone formation.     

The response of mineralizing culture systems to microtextured and polished titanium surfaces

The surface texture of titanium has a predictable effect on peri‐implant tissue formation in vivo. When implanted in an osseous environment, smooth surfaces (R_a < 0.5 mm) are generally apposed by fibrous tissue and textured surfaces (R_a > 1.0 mm) are generally apposed by osseous tissue. Thus in vitro study assessed the mineralization and proliferation response of TF274, MC3T3‐E1, murine femoral stromal cells and canine stromal cells to tissue culture plastic (R_a = 0.001 mm), polished (R_a = 0.01 mm) and irregularly textured (R_a = 3.26 mm) titanium surfaces. Amongst all culture systems, proliferation was significantly decreased on textured vs. smooth surfaces. Midway through the culture of the canine marrow cells, the cell layer detached from the tissue culture plastic and polished titanium surfaces. The TF274, MC3T3‐E1, murine femoral stromal cell systems formed a mineralized matrix on the tissue culture plastic and polished titanium surfaces which was not observed with the canine stromal cell system. Compared to the tissue culture plastic and polished titanium surfaces, matrix mineralization was significantly reduced on the textured titanium surfaces for the TF274, MC3T3‐E1, murine femoral stromal systems, a result which was differed significantly in comparison to the canine stromal system. These results were surprising given the large number of reports concerning the in vivo response to titanium in clinical and pre‐clinical studies. Further work is required to determine if the TF274, MC3T3‐E1 and murine femoral stromal systems are suitable for the in vitro investigation of the effects of titanium surface texture on osteoblast activity. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1347–1354, 2008     

双相磷酸钙组织工程骨块重建股骨头内骨缺损的实验研究

目的 观察在体外构建的具有仿生结构的双相磷酸钙（biphasic calcium phosphate，BCP）组织工程骨块植入犬股骨头缺损内的骨再生情况及预防股骨头塌陷的效果。方法 以犬股骨头的松质骨样本Micro—CT（micro—computed tomography）图像为基础，提取其中的图像信息，利用三维凝胶叠层成形法制备出具有仿骨小梁结构的陶瓷支架。在体外利用诱导分化的自体骨髓间充质细胞与仿生BCP支架复合，构建组织工程骨块，将其植入10只犬的股骨头负重区骨缺损内；另取10只火作为对照组，在股骨头骨缺损区内打球植入自体松质骨粒，对比观察仿生BCP骨块的植入效果。结果 制备出的股骨头仿生BCP支架具有良好的三维空间结构，支架小梁具有一定的方向性，呈板状模型；细胞在支架表面大量生长。植入动物体内30周后，实验组火股骨头外形基本完整，新生骨质包绕支架小梁并沿支架表面生长，而对照组犬股坩头均出现不同程度的塌陷。结论 仿生BCP组织工程骨块具有良好的生物相容性，植入犬股骨头负曩区骨缺损后，能在一定程度上防止股骨头塌陷。