In Vitro Characterizations of PLLA/β-TCP Porous Matrix Materials and RMSC-PLLA-β-TCP Composite Scaffolds

To develop a novel degradable poly (L-lactic acid)/β-tricalcium phosphate (PLLA/β-TCP) bioactive materials for bone tissue engineering, β-TCP powder was produced by a new wet process. Porous scaffolds were prepared by three steps, I.e. Solvent casting, compression molding and leaching stage. Factors influencing the compressive strength and the degradation behavior of the porous scaffold, e.g. Weight fraction of pore forming agent-sodium chloride (NaCl), weight ratio of PLLA: β-TCP, the particle size ofβ-TCP and the porosity, were discussed in details. Rat marrow stromal cells (RMSC) were incorporated into the composite by tissue engineering approach. Biological and osteogenesis potential of the composite scaffold were determined with MTT assay, alkaline phosphatase (ALP) activity and bone osteocalcin (OCN) content evaluation. Results show that PLLA/β-TCP bioactive porous scaffold has good mechanical and pore structure with adjustable compressive strength needed for surgery. RMSCs seeding on porous PLLA/β-TCP composite behaves good seeding efficacy, biocompatibility and osteoinductive potential. Osteoprogenitor cells could well penetrate into the material matrix and begin cell proliferation and osteogenic differentiation. Osseous matrix could be formed on the surface of the composite after culturing in vitro. It is expected that the PLLA/β-TCP porous composites are promising scaffolds for bone tissue engineering in prosthesis surgery.     

Osteogenesis and Degradation Behavior of rhBMP-2/β-Tricalcium Phosphate Porous Composite Materials

Ultrafine β-tricalcium phosphate (β-TCP) powders with good crystalline structure were produced by a new wet process. Through bone tissue engineering approach, porous β-TCP ceramic was combined with recombined human bone morphogenetic proteins-2 (rhBMP-2) to develop a novel composite material. Osteogenesis capacity of the composite was investigated intramuscularly in rat with histological analyses and SEM examination. Pure β-TCP porous ceramic was investigated as the control. Results show that the composite materials possess good biocompatibility, biodegradation and strong osteogenesis capacity through inductive process after implantation. Material degradation began from 2 weeks post-implantation accompanying with the changing of pore structure, with the enwrapping and separation of materials by hyperplatic mesenchymal cells and fibroblast, and with the phagocytose reaction of multinucleated giant cells. Early in 72 h, immature cartilage could be found within novel composite; mature lamellar bone was induced to generate after 3 weeks. With strong osteoinduction capacity and controllable biodegradation, the novel rhBMP-2/β-TCP porous ceramic is expected to be a promising bone grafting substitute for bone tissue engineering.     

Hierarchical Micropore/Nanorod Apatite Hybrids In-Situ Grown from 3-D Printed Macroporous Ti6Al4V Implants with Improved Bioactivity and Osseointegration

The advent of three-dimensional(3-D) printed technique provides great possibility in the fabrication of customized porous titanium(Ti) implant. However, the bioinert property of the printed Ti poses an outstanding problem. Hybrid micro-arc oxidation and hydrothermal(MAO–HT) treatment on porous metals is able to produce multi-scaled hierarchical orthopedic implant, showing great potential for surface modification of 3-D printed implant. In this study, cylindrical porous Ti6Al4V(Ti64) scaffolds with pore size of 640 μm, porosity of 73% were 3-D printed by electron beam melting process, and their surfaces were left untreated or treated by a combined MAO–HT procedure. In vitro bioactivity was tested by immersion in simulated body fluid for different time points. Then, 12 scaffolds in each group were implanted into the femoral condyles of New Zealand rabbit for 8 weeks. Osseointegration was evaluated by qualitative and quantitative histological analysis, and the bone ingrowth features were probed by sequential fluorescent labeling at 3 and 6 weeks post-surgery. Following the MAO–HT treatment, the porous Ti64 scaffold was endowed with multi-scaled micro/nano-topographies and high amounts of Ca P on its surface.The treated scaffold exhibited drastically enhanced apatite forming ability compared with the untreated one. In vivo test revealed significantly that a higher amount of bone ingrowth and bone implant contact at the treated scaffold. The 2 types of scaffolds had different patterns of bone ingrowth: the treated scaffold exhibited a pattern of contact osteogenesis, by which bone formed directly on the treated implant surface, whereas bone formed distal to the implant surface of the untreated scaffold. MAO–HT treatment can significantly enhance the in vitro apatite-inducing ability and in vivo osseointegration capacity of 3-D porous Ti64 scaffold and may provide as a viable approach for the fabrication of bioactive 3-D printed porous implant for orthopedic applications.     

Ultrastructural Analysis on the Osteogenesis and Transformation of Calcium Phosphate Ceramics in Vivo

To study the osteogenesis and transformation process of calcium phosphate bioceramic in vivo, biodegradable porous β-tricalcium phosphate ceramics (β-TCP, φ5×8 mm) were implanted in the tibia of rabbits. β-TCP ceramics with surrounding bone tissue were retrieved and observed by SEM, TEM and EPMA every month after implantation.The results showed that osteogenesis was active and β-TCP ceramics bonded to bones directly. The new bones were forming and maturing as materials were continuously degrading, and materials were finally replaced by new bone. Parts of the materials were degraded, absorbed and recrystallized, while the rest were dispersed to the spongy bone and the Haversian lamella in an irregular arrangement, becoming incorporated into bone formation directly by remodeling the structure. Some β-TCP crystals cleaved along its (001) rhombohedral plane and formed lath-like crystals in vivo.     

Preparation and application of highly porous aerogel-based bioactive materials in dentistry

In this study, the possibility of preparation and application of highly porous silica aerogel-based bioactive materials are presented. The aerogel was combined with hydroxyapatite and p.tricalcium phosphate as bioactive and osteoinductive agents. The porosity of aerogels was in themesoporous region with a maximum pore diameter of 7,4 and 12.7 nm for the composite materials. The newly developed bioactive materials were characterized by scant electron microscopy. The in vitro biological effect of these modified surfaces was also tested on SAOS-2 osteogenic sarcoma cells by confocal laser scanning microscopy.     

EPMA Study of the Interface of β-Tricalcium Phosphate Ceramies in Vivo

Electron probe and X-ray energy spectrum were used to investigate the chemical composition of the interface between material and new bone after porous tricalcium phosphate ceramie implanted in tibia of rabbits. The element changes of the interface, the materials transformation and the situation of new bone formation at different implantation period were observed. The results showed that the carbon element content decreased gradually in new bone tissue, and the content of calcium and phosphor element increased by degrees with the implantation time. At the same time, calcium-phosphor ratio in the new bone kept a higher Ievel. New bone grew into the materials interior, material dispersed and degraded simultaneously. Both composition of materials and new bone tended to be consentient. Finally, the materials were substituted by new bone. After implantation, not only the materials itself dissolved and degraded partially, but also new bone formed on the outer and pore surface of β-TCP porous bioceramics, which     

EPMA Study of the Interface of β-Tricalcium Phosphate Ceramics in Vivo

Electron probe and X-ray energy spectrum were used to investigate the chemical composition of the interface between material and new bone after porous tricalcium phosphate ceramic implanted in tibia of rabbits. The element changes of the interface, the materials transformation and the situation of new bone formation at different implantation period were observed. The results showed that the carbon element content decreased gradually in new bone tissue, and the content of calcium and phosphor element increased by degrees with the implantation time. At the same time, calcium-phosphor ratio in the new bone kept a higher level. New bone grew into the materials interior, material dispersed and degraded simultaneously. Both composition of materials and new bone tended to be consentient. Finally, the materials were substituted by new bone. After implantation, not only the materials itself dissolved and degraded partially, but also new bone formed on the outer and pore surface of β-TCP porous bioceramics, which showed that the degradation products of lifeless calcium phosphate inorganic materials took part in constituting of new bone tissue.     

Improvement on compressive properties of lotus-type porous copper by a nickel coating on pore walls

The aim of this work is to understand the effect of a thin coating on the compressive properties of the porous metal. In our work, the uniaxial compressive behavior and the energy absorption properties of the lotus-type porous copper deposited with Ni coatings with thickness from 3.9 to 4.8 μm on pore walls were investigated. It is found that the Ni coating on pore walls shows a clear enhancement effect on compressive properties of the lotus-type porous copper, in which the specific yield strength and the energy absorption per unit mass at densification strain increase from 5.27 to 7.31 MPa cm~3 g~(-1) and from 11.50 to 18.21 J g~(-1) with the Ni coating, respectively. Furthermore, the enhancement appears to be insensitive to the coating thickness. It is considered that the resistance of the interface between the nickel coating and the pore walls to the dislocation slip plays an important role in the improvement on compressive properties of the lotus-type porous copper.     

Plasmid DNA-loaded asymmetrically porous membrane for guided bone regeneration

Although bone defects can be restored spontaneously,bone reconstruction with sufficient strength and volume continues to be a challenge in clinical practices.In recent years,the use of a variety of biomaterials with bioactivity has been attempted to compensate for this limitation.Herein,we fabricated a pDNA(encoding for BMP-2)-loaded asymmetrically porous polycaprolactone(PCL)/Pluronic F127 membrane as a bioactive guided bone regeneration(GBR)membrane,using a modified immersion-precipitation method.It was observed that the GBR membrane allows continuous release of pDNA for more than20 weeks.The pDNA was sufficiently transfected into human bone marrow stem cells(h BMSCs)without significant cytotoxicity and the gene-transfected cells showed prolonged synthesis of BMP-2.From in vitro osteogenic differentiation and in vivo animal studies,the effective induction of osteogenic differentiation of h BMSCs and enhanced bone regeneration by the pDNA-loaded asymmetrically porous PCL/Pluronic F127 membrane was observed,suggesting that the pDNA-loaded membrane as a bioactive GBR membrane can be an alternative therapeutic technique for effective bone regeneration.     

Anisotropic Porous Ti6Al4V Alloys Fabricated by Diffusion Bonding:Adaption of Compressive Behavior to Cortical Bone Implant Applications

In this work, porous Ti6Al4V alloys with 30%–70% porosity for biomedical applications were fabricated by diffusion bonding of alloy meshes. Pore structure was characterized by Micro-CT and SEM. Compressive behavior in the out-of-plane direction and biocompatibility with cortical bone were studied. The results reveal that the fabricated porous Ti6Al4V alloys possess anisotropic structure with square pores in the in-plane direction and elongated pores in the out-of-plane direction. The average pore size of porous Ti6Al4V alloys with 30%–70% porosity is in the range of 240–360 μm. By tailoring diffusion bonding temperature, aspect ratio of alloy meshes and porosity, porous Ti6Al4V alloys with different compressive properties can be obtained, for instance, Young's modulus and yield stress in the ranges of 4–40 GPa and70–500 MPa, respectively. Yield stress of porous Ti6Al4V alloys fabricated by diffusion bonding is close to that of alloys fabricated by rapid prototyping, but higher than that of fabricated by powder sintering and space-holder method. Diffusion bonding temperature has some effects on the yield stress of porous Ti6Al4V alloys, but has a minor effect on the Young's modulus. The relationship between compressive properties and relative density conforms well to the Gibson–Ashby model. The Young's modulus is linear with the aspect ratio, while the yield stress is linear with the square of aspect ratio of alloy meshes. Porous Ti6Al4V alloys with 60%–70% porosity have potential for cortical bone implant applications.     

Diamond/β-SiC film as adhesion-enhanced interlayer for top diamond coatings on cemented tungsten carbide substrate

In present work, diamond/β-SiC composite interlayers were deposited on cemented tungsten carbide(WC-6%Co) substrates by microwave plasma enhanced chemical vapor deposition(MPCVD) using H_2,CH_4 and tetramethylsilane(TMS) gas mixtures. The microstructure, chemical bonding, element distribution and crystalline quality of the composite interlayers were systematically characterized by means of field-emission scanning electron microscopy(FE-SEM), X-ray diffraction(XRD), X-ray photoelectron spectrometer(XPS), electron probe microanalysis(EPMA), Raman spectroscopy and transmission electron microscropy(TEM). The influences of varying TMS flow rates on the diamond/β-SiC composite interlayers were investigated. Through changing the TMS flow rates in the reaction gas, the volume fraction of β-SiC in the composite interlayers were tunable in the range of 12.0%–68.1%. XPS and EPMA analysis reveal that the composite interlayers are composed of C, Si element with little cobalt distribution. The better crystallinity of the diamond in the composite is characterized based on the Raman spectroscopy, which are helpful to deposit top diamond coatings with high quality. Then, the adhesion of top diamond coatings were estimated using Rockwell C indentation analysis, revealing that the adhesion of top diamond coatings on the WC-6%Co substrates can be improved by the interlayers with the diamond/β-SiC composite structures. Comprehensive TEM interfacial analysis exhibits that the cobalt diffusion is weak from WC-6%Co substrate to the composite interlayer. The homogeneous microcrystalline diamond coatings with the most excellent adhesion can be fabricated on the substrates with the composite interlayer with the β-SiC/diamond ratio of about 45%. The composite structures are appropriate for the application in high-efficiency mechanical tool as a buffer layer for the deposition of the diamond coating.     

Evaluating and Modeling the Mechanical Properties of the Prepared PLGA/nano-BCP Composite Scaffolds for Bone Tissue Engineering

In this paper, preparation of nano-biphasic calcium phosphate (nBCP), mechanical behavior and load-bearing of poly (lactide-co-glycolide) (PLGA) and PLGA/nBCP are presented. The nBCP with composition of 63/37 (w/w) HA/β-TCP (hydroxyapatite/β-tricalcium phosphate) was produced by heating of bovine bone at 700℃. Composite scaffolds were made by using PLGA matrix and 10-50 wt% nBCP powders as reinforcement material. All scaffolds were prepared by thermally induced solid-liquid phase separation (TIPS) at -60℃ under 4 Pa (0.04 mbar) vacuum. The results of elastic modulus testing were adjusted with Ishai-Cohen and Narkis models for rigid polymeric matrix and compared to each other. PLGA/nBCP scaffolds with 30 wt% nBCP showed the highest value of yield strength among the scaffolds. In addition, it was found that by increasing the nBCP in scaffolds to 50 wt%, the modulus of elasticity was highly enhanced. However, the optimum value of yield strength was obtained at 30 wt% nBCP, and the agglomeration of reinforcing particles at higher percentages caused a reduction in yield strength. It is clear that the elastic modulus of matrix has the significant role in elastic modulus of scaffolds, as also the size of the filler particles in the matrix.     

Synergistic effects of Mg-substitution and particle size of chicken eggshells on hydrothermal synthesis of biphasic calcium phosphate nanocrystals

Magnesium(Mg^2+))ion plays important roles in biomineralization of bone,teeth and calcium carbonate skeletons.Herein,chicken eggshells mainly comprising of Mg-calcite nanocrystals(Mg/(Mg+Ca)2.0 mol.%)were used to fabricate biphasic calcium phosphate(BCP),a mixture of hydroxyapatite(HA)and p-tricalcium phosphate(p-TCP)nanocrystals,through hydrothermal reactions at 200℃for 24 h.Our results indicated thatβ-TCP nanocrystals formed through the ion-exchange reactions of Mg-calcite,while HA nanocrystals were mainly produced by dissolution-reprecipitation reactions on the surfaces of eggshell samples in the hydrothermal system.Mg substitution in calcite resulted in formation ofβ-TCP nanocrystals instead of HA crystals through ion-exchange reactions.BCP samples with different compositions(28.6-77.8 wt.%β-TCP)were produced by controlling particle sizes of eggshells for hydrothermal reactions.The larger particles lead to the larger proportion ofβ-TCP in the BCP composition.Therefore,Mg substitution and particle size had synergetic effects on the hydrothermal synthesis of BCP using chicken eggshells through balance of ion-exchange and dissolution-reprecipitation reactions.Cell culture results showed that the BCP products were non-cytotoxic to MC3 T3-E1 cells,which may be used for bone substitute materials in future.     

Osteogenesis and Degradation Behavior of rhBMP-27/β-Tricalcium Phosphate Porous Composite Materials

Ultrafine-tricalcium phosphate(β-TCP)Powders with good crystalline structure were produced by a new wet process Throough bone tissue engineering approach     

A Green Biocompatible Fabrication of Highly Porous Functional Ceramics with High Strength and Controllable Pore Structures

A green biocompatible foaming method utilizing natural coconut oil and cornstarch was developed to fabricate highly porous functional ceramics with controllable strengths and pore structures. The porosity of Al2O3 ceramics prepared via this method reached 79.6%–86.9% while these ceramics maintained high compressive strengths of 2.2–5.5 MPa. More importantly, porous Al2O3 ceramic with a pore size gradient was also readily fabricated by casting serial layers of foams that were set for different time periods.The potential applications of porous Al2O3 and HA ceramics fabricated by this green foaming method including scaffolds for oil cleaning and cell culture, respectively, were also demonstrated.     

Heat Dissipation Performance of Porous Copper with Elongated Cylindrical Pores

The purpose of this paper is to investigate heat dissipation performance of porous copper with long cylindrical pores fabricated by a unidirectional solidification method. Three samples with porosity of 29.87%, 34.47% and 50.98% were chosen and cut into size of 60 mm （length） × 26 mm （width） × 2 mm （thickness） along the vertical direction of pore axis. Their heat dissipation performance was evaluated by a nonsteady method in air and compared to those of not only bulk copper but also bored coppers with porosity of 30.61% and 32.20%. It is found that the porous copper dissipated heat faster by a forced air convection than that by natural convection from 80 ℃ to room temperature and both porosity and pore size play an important role in the performance for the porous copper. Furthermore, the heat dissipation rate is higher when the forced air was circulated along the specimens than that perpendicular to the specimens for the porous copper. It is revealed that porous copper with bigger porosity and a proper pore size possesses a higher heat dissipation rate. It is concluded that the porous copper with elongated cylindrical pores has larger heat dissipation performance than both the bulk copper and the bored copper, which is attributed to its higher specific surface area. Application of the porous copper for heat dissipation is promising.     

Synthesis of Non-oxide Porous Ceramics Using Random Copolymers as Precursors

In this paper,we reported a novel method for synthesis of non-oxide porous ceramics by using random copolymers as precursors.A silazane oligomer and styrene monomer were used as starting materials,which were copolymerized at 120 ℃ to form random polysilazane-polystyrene copolymers.The copolymers were then pyrolyzed at 500 ℃ to obtain porous ceramics by completely decomposing polystyrene(PS) and converting polysilazane(PSZ) into non-oxide Si-C-N ceramics.The obtained material contained a bi-model pore-structure consisting of both micro-sized and nano-sized pores with very high surface area of more than500 m~2/g.We also demonstrated that the pore structure and surface area of the materials can be tailored by changing the ratio of the two blocks.Current results suggest a promising simple method for making multiscaled porous non-oxide materials.     

Destructive Interactions between Pore Forming Agents and Matrix Phase during the Fabrication Process of Porous BiFeO_3 Ceramics

Porous bismuth ferrite ceramics were synthesized by sacrificial pore former method.A mixture of BiFeC3and 20 wt%of various pore formers including high density polyethylene,polyethylene glycol,polyvinyl alcohol,urea and graphite was intensively milled for 10 h in a planetary ball mill,uniaxially cold pressed and then subjected to the multi-stage heat treatment.The results revealed that urea and polyvinyl alcohol are appropriate candidates for maintaining the strength of the final porous structure.Density and porosity measurements showed that by employing 20 wt%of high density polyethylene and graphite,a porous sample with a maximum porosity of nearly 40%could be obtained.Mercury porosimetry results showed that using urea as a pore former gives porous bismuth ferrite with a mean pore diameter of 7 μm,uniform pore distribution as well as interconnected pores.Moreover,reactions between BiFeO_3 matrix phase and thermal decomposition products of pore formers can lead to degradation of the BiFeO_3 phase in the final porous samples.Analysis of X-ray diffraction patterns illustrated that in the samples processed with graphite,high density polyethylene and polyvinyl alcohol as pore former,BiFeO_3 matrix phase partially or completely decomposed to intermediate phases of Bi_2Fe_4O_9 and Bi_(25)FeO_(40).Using of urea did not damage the matrix phase and porous BiFeO_3 within the original perovskite structure could be prepared.Furthermore,thermodynamic investigation was carried out for prediction of possible interactions between matrix phase and pore former at elevated temperatures.     

Fabrication of Titanium/Fluorapatite Composites and In Vitro Behavior in Simulated Body Fluid

Titanium/fluorapatite（Ti/FA） composites with various FA additions were fabricated by powder metallurgy.The decomposition of FA during sintering was accelerated by the presence of Ti.The main reaction products of FA and Ti were identified as CaO,Ti phosphides,and CaTiO₃.The addition of FA significantly inhibited the densification of Ti.The in vitro bioactivity of the composites was evaluated in a simulated body fluid（SBF）. After immersion into the SBF,all the Ti/FA composites induced nucleation and growth of bone-like carbonated apatite on the surface.Co-precipitation of CaCO₃ and Mg（OH）₂ was also detected on the surface of the composite with high FA addition at an early stage of immersion.Furthermore,the release of fluorine ions from the composite was confirmed,which could promote bone regeneration and retard the formation of caries in the biological environment.The in vitro behavior was attributed to multiple factors,including the surface conditions and the constituents of the composite.The results demonstrated that the Ti/FA composites were bioactive in nature even with a low FA addition and they could introduce the benefit of fluorine ions in the service.     

A Facile Synthesis of Hierarchically Porous TiO_2 Microspheres with Carbonaceous Species for Visible-light Photocatalysis

Hierarchically porous anatase TiO_2 microspheres composited with carbonaceous species(TCS) have been successfully fabricated by a one-step template-free solvothermal method,combined with subsequent low temperature dried process.In this configuration,the TCS microspheres are constructed by the interconnected porous nanosheets,which are further assembled with abundant nanoparticles and carbonaceous species.Such composite microspheres possess a large specific surface area of 337 m~2g~(–1),uniform mesopores of 3.37 nm and high total pore volumes of 0.275 cm3g–1.The materials exhibit the enhanced photocatalytic properties and stability for degradation of rhodamine B(Rh B) under visible-light irradiation.The enhanced photocatalytic degradation performance may be ascribed to their abundant porous structure,large specific surface area and the unique assist-function of the carbonaceous species.