Fabrication of porous bioceramics with porosity gradients similar to the bimodal structure of cortical and cancellous bone

The aim of this study was to fabricate porous implant materials with graded pore structures similar to the bimodal structure of cortical and cancellous bone. Porous hydroxyapatite/tricalcium phosphate (HA/TCP) bioceramics with interconnected porosity and controlled pore sizes required to simulate natural bone tissue morphology were fabricated by a novel technique of vacuum impregnation of reticulated polymeric foams with ceramic slip. Functionally gradient materials (FGMs) with porosity gradients were made by joining different pore per inch (ppi) foams together by either stitching or pressfitting to form templates. Post production, no defects could be seen at the interface between the two different porosity sections. The macropore sizes of the HA/TCP bioceramics were larger than 100 μm which is appropriate for bone ingrowth. A sample with a graded porous structure which is close to the human bone morphology was also developed. The two component structures were conspicuously different but joined together firmly. Four point bend testing of FGM samples showed them to have similar mechanical properties to homogeneous ceramics based on foam templates with uniform pore sizes, with no evidence of interfacial weakness. Many potential biomedical applications could be developed utilising graded porous structures. The ease of processing will make it possible to fabricate a range of complex shapes for different applications.     

Controllable porosity hydroxyapatite ceramics as spine cage: fabrication and properties evaluation

A procedure was designed to prepare porosity-graded hydroxyapatite (HA) ceramics simulating the bimodal structure of natural bone, which could be used to build a cage that would promote the reconstruction of the anterior column after vertebrectomy or corpectomy in tumor and trauma surgery. HA ceramics with controllable pore size distribution and porosity were developed by using chitosan and Poly(vinyl alcohol) (PVA) as the pore-forming agents. HA ceramics with worthwhile properties such as a wide range of volume porosity (10-50%) and pore size (nanometer to 400 microm) can be obtained from this method, which allows the fabrication of HA ceramics with desirable porous characteristics simulating the bimodal natural bone architecture expected to provide advantages for bony fusion in the intervertebral foramina. When coated with chitosan-gelatin network, the bending strength of the porous HA ceramics significantly improved. The polymer network coated porous HA have potential application in the construction of cages for spinal operations.     

基于Micro-CT不同多孔结构陶瓷支架的建模及其贯通性与液流分布分析

贯通性是骨组织工程支架的重要参数, 决定包含蛋白和细胞的体液渗入和组织生长。本研究采用Micro-CT技术对三种不同工艺(球粒堆积、蜡球造孔、纤维堆积)构建的羟基磷灰石多孔支架进行断层扫描, 并从三方面研究支架的贯通性: (1)通过影像重建定量分析支架孔隙的三维贯通结构; (2)统计分析比较三种支架在贯流方向上的孔隙率变化; (3)有限元模拟支架的内部液流分布情况。结果表明, 球粒堆积支架与蜡球造孔支架孔隙率分布较均匀, 而纤维堆积支架孔隙分布较杂乱。液流模拟(流速分布)发现, 球粒堆积支架与蜡球造孔支架中液体流动均匀, 但是蜡球造孔支架孔壁近表面区域存在大量“漩涡流”, 不利于支架内细胞与液流之间的物质交换, 该结果有可能解释球粒堆积支架体内成骨性优于蜡球造孔支架的动物体内实验结果。     

凝胶注模成型法制备多孔羟基磷灰石陶瓷

采用凝胶注模成型工艺制备了多孔羟基磷灰石陶瓷,并通过X射线分析了多孔陶瓷的相成分,采用扫描电镜观测了孔隙结构和形貌.结果表明,所制备的多孔羟基磷灰石陶瓷的孔隙率均大于80%;孔隙尺寸主要分布在350～600μm,孔壁上存在孔径为60～190μm的贯通孔;X射线衍射证明烧结过程未引入异质成分.所制备的多孔羟基磷灰石陶瓷具有适宜的孔隙直径和孔隙率,且孔隙间具有良好的贯通性.     

Artificially controlling of inner structure to porous hydroxyapatite ceramic by using solidified coated fibers

Porous hydroxyapatite (HA) ceramic was fabricated by 3D fiber network. These fibers as channel underprops were treated by surface coating with acidic macromolecule glue. The solidified coated fibers in ceramic block could form run-through channels and also etch stripes on channel walls for cell attachment. The channels formed in sintering process by fibers volatilization may be directed artificially according to beforehand design of structure for ceramic block. The results showed that the pore characteristics and the inner structure of the sample made from this technique have settled for essential requests of porous bioceramic. The channels in sintered scaffold shown in SEM (scanning electron microscopy) micrographs have directional connection, equal distribution, intact configuration and existence of thin stripes on inner walls. All of these characteristics have met requests for tissue cell developing, transplanting and attaching. The samples have appropriate interconnectivity and reasonable structure with equable pore-arranging and uniform size of pore. XRD (X-ray diffraction) patterns of sample indicated no major change of the crystalline structure.     

Porous hydroxyapatite for artificial bone applications

Hydroxyapatite (HA) has been used clinically for many years. It has good biocompatibility in bone contact as its chemical composition is similar to that of bone material. Porous HA ceramics have found enormous use in biomedical applications including bone tissue regeneration, cell proliferation, and drug delivery. In bone tissue engineering it has been applied as filling material for bone defects and augmentation, artificial bone graft material, and prosthesis revision surgery. Its high surface area leads to excellent osteoconductivity and resorbability providing fast bone ingrowth. Porous HA can be produced by a number of methods including conversion of natural bones, ceramic foaming technique, polymeric sponge method, gel casting of foams, starch consolidation, microwave processing, slip casting, and electrophoretic deposition technique. Some of these methods have been combined to fabricate porous HA with improved properties. These combination methods have yielded some promising results. This paper discusses briefly fundamental aspects of porous HA for artificial bone applications as well as various techniques used to prepare porous HA. Some of our recent results on development of porous HA will be presented as well.     

Effect of YSZ fiber addition on microstructure and properties of porous YSZ ceramics

Yttria-stabilized zirconia (YSZ) fiber was introduced as the reinforcement for porous YSZ ceramics fabricated by tert-butyl alcohol-based gel-casting process and pressureless sintering. Effect of YSZ fiber addition on the microstructure and properties of porous YSZ ceramics was studied systematically. Results showed that YSZ fiber obviously obstructed densification during the sintering process and therefore higher porosity could be achieved with the same solid loading of the initial slurry. Mean pore size regularly increased with increasing fiber addition. The reinforcing effect reached its optimum with 10 wt% YSZ fiber addition, yet decreased with increasing porosity. Fiber addition significantly changed the fracture mode of the porous ceramics from brittle to quasi-ductile with increasing fiber additions; fiber pull-out and crack deflection play major roles in the process. Compared with the porous ceramics without fibers, the thermal conductivity decreased a little. With improved mechanical and thermal properties, YSZ fiber-reinforced porous YSZ ceramics are more applicable in thermal insulation materials.     

Porous calcium phosphate ceramics prepared by coating polyurethane foams with calcium phosphate cements

Porous calcium phosphates have important biomedical applications such as bone defect fillers, tissue engineering scaffolds and drug delivery systems. While a number of methods to produce the porous calcium phosphate ceramics have been reported, this study aimed to develop a new fabrication method. The new method involved the use of polyurethane foams to produce highly porous calcium phosphate cements (CPCs). By firing the porous CPCs at 1200 °C, the polyurethane foams were burnt off and the CPCs prepared at room temperature were converted into sintered porous hydroxyapatite (HA)-based calcium phosphate ceramics. The sintered porous calcium phosphate ceramics could then be coated with a layer of the CPC at room temperature, resulting in high porosity, high pore interconnectivity and controlled pore size.     

Osteoblast-like cell ingrowth,adhesion and proliferation on porous Ti-6Al-4V with particulate and fiber scaffolds

This paper presents the results of an experimental study of osteoblast-like cell ingrowth into porous Ti-6Al-4V structures with well-controlled geometries. The effects of pore size and strut geometry are elucidated in in-vitro cell ingrowth experiments on porous Ti-6Al-4V structures with particulate and fiber geometries. The initial stages of cell spreading and proliferation are examined using cell culture experiments. Scanning electron microscope (SEM) and a methylthiazol tetrazolium (MTT) assay are used to reveal the initial stages of cell spreading and attachment. Enzymatic detachment tests are also used to examine cell adhesion after 48 h of cell culture. The results show a strong effect of pore size on the rate of cell bridging over gaps. The extent of cell ingrowth, initial cell adhesion and cell proliferation also increase with decreasing pore size. A lower incidence of cell bridging (over gaps) is observed on the fiber porous structures. However, fiber geometries enable contact guidance during cell spreading along the fiber directions. This enhances the extent of cell ingrowth into the fiber porous structures. No significant differences are observed in cell adhesion and proliferation on porous structures with similar pore sizes.     

Role of interconnections in porous bioceramics on bone recolonization in vitro and in vivo

The interconnections in a porous biomaterial are the pathways between the pores. They conduct cells and vessels between pores. Thus they favour bone ingrowth inside ceramics. The aim of our study was to determine the effect on bone ingrowth of interconnections in two ceramics: hydroxyapatite (HA) and -tricalcium phosphate (-TCP) with the same porosity of about 50% and a mean pores size of 100–300 m and a mean interconnection size of 30–100 m. In vitro, four discs for osteoblast culture were studied after 14 and 28 days of incubation. The results show that human osteoblasts can penetrate interconnections over 20 m in size, and colonize and proliferate inside macropores, but the most favourable size is over 40 m. In vivo, eight cylinders were implanted in the middle shaft of both rabbit femurs for 12 or 24 weeks. The histomorphometric results show that interconnections in porous ceramics favour bone ingrowth inside the macropores. In the HA group the rate of calcification and bone ingrowth do not differ, and chondroid tissue is observed inside pores. But in -TCP, the calcification rate and the bone ingrowth increased significantly. At week 12 significant correlation between new bone ingrowth and the size of the interconnections is observed between new bone ingrowth and the density of pores. In conclusion we notice that in vivo a 20 m interconnection size only allows cell penetration and chondroid tissue formation; however the size of the interconnections must be over 50 m to favour new bone ingrowth inside the pores. We propose the concept of interconnection density which expresses the quantity of links between pores of porous materials. It assures cell proliferation and differentiation with blood circulation and extracellular liquid exchange. In resorbable materials, pore density and interconnection density are more important than their size, contrary to unresorbable materials in which the sizes and the densities are equally important. © 1999 Kluwer Academic Publishers     

Influence of preparation method on hydroxyapatite porous scaffolds

Hydroxyapatite (HA) is extensively used in medical applications as an artificial bone because of its similarity to the natural components of human bones and for its excellent biocompatibility. The porous structure of HA ceramics is more generally used as a scaffold. Many techniques, which are performed under fluid system, have been applied to fabricate HA porous scaffolds. In this work, polymeric sponge technique was employed in the preparation of HA slurry appropriated for porous ceramic fabrication. Effort for strength improvement was made on porous HA ceramic in several aspects. The effect of HA/water, binder/plasticizer ratios and dispersant content on the rheological properties of HA suspension in combination with the addition of SiC and SiO₂ on the compressive strength of porous bodies were investigated and discussed.     

Porous hydroxyapatite ceramics of bi-modal pore size distribution

A route for the fabrication of porous hydroxyapatite ceramics having two populations of open pores is reported. The bodies are prepared by sintering the spherical gelatin/hydroxyapatite granules. As the result, ceramics containing intragranular small-size pores and intergranular large-size interconnecting pores are obtained. The pore size and content are dependent on the route. Ceramics can generally be applied as bone replacement materials where the interconnections in the intergranular pores are the pathway to conduct cells and vessels for the bone ingrowth, whereas the intragranular pores can be filled with a drug, e.g. to eliminate infections.     

Novel production method of porous surface Ti samples for biomedical application

A porous implant material with adequate pore structure and the appropriate mechanical properties for bone ingrowth has long been sought. This article presents details of the development, characterization and in vivo evaluations of powder metallurgy-processed titanium samples exhibiting a dense core with an integrated porous surface for biomedical applications. A space-holder method was applied to investigate the effects of different percentages and particle sizes of the urea on bone neoformation in 30 rabbits. The samples were previously characterized using scanning electron microscopy and mechanical testing. After 8 and 12 weeks of implantation, bone ingrowth was histologically and histometrically analyzed and push-out testing was performed. This study demonstrated that the association of a dense core integrated with the greatest number of interconnected pores of the smallest size is a promising biomaterial for bone tissue engineering. This sample exhibits appropriate mechanical properties combined with increased bone ingrowth, providing enhanced resistance to displacement.     

Structural characterization and strengthening mechanism of forsterite nanostructured scaffolds synthesized by multistep sintering method

In this study, highly porous forsterite scaffolds with interconnected porosities were synthesized using multi-step sintering (MSS) method. The starting powder was nanosized forsterite, which was synthesized from talc and magnesium carbonate powders. The phase composition, average particle size and morphology of the produced forsterite powder were characterized by X-ray diffraction technique (XRD) and transition electron microscopy (TEM). Forsterite scaffolds were produced by foamy method using polymeric sponges. MSS process including three steps was used to efficiently sinter the forsterite nanopowders without destroying the initial porous structure of polymeric sponges. The results showed that MSS technique is an efficient and appropriate procedure to produce highly porous forsterite scaffolds with pore size in the range of 100–300?μm. The compressive strength, compressive modulus and porosity of C12 specimen (sintered at 1650?°C for 1?h with subsequent annealing at 1000?°C for 1000?min) was 1.88?MPa, 29.2?MPa, and 72.4%, respectively, which is very close to that of cancellous bone. The approach studied in this research can be developed for other nanostructure ceramics to produce highly porous scaffolds with interconnected porosities for load bearing applications.     

Preparation and characterization of interpenetrating phased TCP/HA/PLGA composites

The purpose of this study was to fabricate composites consisting of three interpenetrating networks: tricalcium phosphate (TCP), hydroxyapatite (HA), and poly(dl-lactide-co-glycolide) (PLGA). The porous TCP network was first produced by coating a polyurethane (PU) foam with hydrolysable alpha-TCP slurry. The HA network was derived from a calcium phosphate cement (CPC) filled in the porous TCP network. The remaining open pore network in the HA/TCP composite was further infiltrated with a PLGA network. The three sets of spatially continuous networks would have different biodegradation rates and thus bone tissue would grow towards the fastest biodegrading network while the remaining networks still maintaining their geometrical shape and carrying the physiological load for the tissue ingrowth.     

Fabrication and mechanical testing of porous calcium phosphate bioceramic granules

Porous hydroxyapatite/tricalcium phosphate (HA/TCP) granules were fabricated by a novel technique of vacuum impregnation of reticulated polyurethane (PU) foams with ceramic slip. The resultant granules had 5-10% interconnected porosity with controlled pore sizes necessary to allow bone ingrowth combined with good mechanical properties. Using PU foams with a different number of pores per inch (ppi), porous HA/TCP granules in the size range of 2-8 mm were successfully manufactured. Dieplunger tests were used to compare the compression and relaxation properties of the granules with those of a commercially available bone graft product, BoneSave. The results of the die-plunger testing showed that the experimental granules were stiffer than the BoneSave materials and had less of a tendency to crumble to powder after testing. This therefore suggests that these experimental granules would be useful for impaction grafting and space filling applications.     

Tissue-engineered triphasic ceramic coated hydroxyapatite induced bone formation and vascularization at an extraskeletal site in a rat model

Tissue-engineered bone regeneration has attracted much attention because of its high clinical demand for restoration of injured tissues. In the present study, we have evaluated the capability of bare (without cells) and tissue-engineered (with osteogenic-induced rat Mesenchymal Stem Cells (MSCs)) bioactive ceramics such as hydroxyapatite (HA) and triphasic ceramic-coated hydroxyapatite (HASi) to mediate vascularisation and osteoinduction at an extraskeletal site of rat model. The viability, proliferation and osteogenic differentiation of MSCs on the scaffolds were assessed in vitro and thereby established the capability of HASi in providing a better structural habitat than HA. The vascular invasion was relatively low in bare and tissue-engineered HA at 2 and 4 weeks. Interestingly, the implantation site was well vascularised with profuse ingrowth of blood capillaries in HASi groups, with preference for tissue-engineered HASi groups. Similarly, neo-osteogenesis studies were shown only by tissue-engineered HASi groups. The ingrowth of numerous osteoblast-like cells was seen around and within the pores of the material in bare HASi and tissue-engineered HASi groups (very low cellular infiltration in bare HA groups), but there was no osteoid deposition. The positive impact in forming bone in tissue-engineered HASi groups is attributable to the scaffold and to the cells, with the first choice for scaffold because both HA and HASi were engineered simultaneously with the cells from same source and same passage. Thus, highly porous interconnected porous structure and appropriate chemistry provided by HASi in combination with osteogenic-induced MSCs facilitated better vascularisation that lead to neo-osteogenesis.     

静电纺丝制备多孔醋酸纤维素超细纤维

采用静电纺丝法制备了大量尺寸为60 nm～750 nm椭圆形多孔醋酸纤维素(CA)纤维.利用扫描电镜(SEM)表征了纤维及孔的形态和大小,液氮吸附法(BET)测定了纤维的比表面积.探讨了溶刑种类、溶剂配比和溶液浓度对多孔CA纤维的影响.通过调节纺丝溶液性质和纺丝参数,CA纤维表面多孔大小和分布密度是可调控的.成孔机理是...     

Fabrication of novel TiZr alloy foams for biomedical applications

Bone injuries and failures often require the inception of implant biomaterial. Research in this area has received increasing attention recently. In particular, porous metals are attractive due to its unique physical, mechanical, and new bone tissue ingrowth properties. In the present study, TiZr alloy powders were prepared using mechanical alloying. Novel TiZr alloy foams with relative densities of approximately 0.3 were fabricated by a powder metallurgical process. The TiZr alloy foams displayed an interconnected porous structure resembling bone and the pore size ranged from 200 to 500 μm. The compressive plateau stress and the Young’s modulus of the TiZr foam were 78.4 MPa and 15.3 GPa, respectively. Both the porous structure and the mechanical properties of the TiZr foam were very close to those of natural bone.     

多孔PZT95/5铁电陶瓷的机械性能和铁电性能研究

采用添加造孔剂的方法制备多孔锆钛酸铅(PZT95/5)铁电陶瓷, 研究了孔结构包括孔隙率、孔径及孔形状对多孔PZT95/5陶瓷机械性能和电性能的影响及机理, 并揭示多孔PZT95/5陶瓷微观结构、机械性能和铁电性能的内在联系。研究表明: 孔隙率的增加降低了多孔PZT95/5陶瓷的声阻抗, 改善了陶瓷与封装材料的声阻抗匹配. 孔隙率增加, 多孔PZT95/5陶瓷的屈服应力和剩余极化强度降低, 矫顽场强增大。孔结构对多孔PZT95/5陶瓷屈服应力的影响可由应力集中理论解释; 多孔PZT95/5陶瓷剩余极化强度随孔结构的变化可用内应力结合空间电荷理论加以解释。