Fabrication and characterization of a PAM modified PHBV/BG scaffold

In order to improve the bioactivity and mechanical strength of the scaffold used in bone repair simultaneously, a novel porous PAM-poly （β-hydroxybutyrate-co-β-hydroxyvalerate） （PHBV）/bioactive glass （BG） scaffold was prepared by photo-initiated polymerization. PAM was used to improve the hydrophilicity of PHBV matrix while the BG particles were added to increase the bioactivity and strength of the matrix synchronously. The grafted amide group and Si-O moieties from acrylamide and the added BG were confirmed by Fourier Transform Infrared Spectrometry （FTIR）. The micromorphology of the scaffolds before and after grafting was observed by scanning electron microscopy （SEM）. The resulting images demonstrate that the PAM-PHBV/BG scaffold has a well connected pore structure and appropriate pore size which may be convenient for cells to grow and discharge metabolites. The specific gravity method was used to evaluate the pore property of the scaffold and the result shows that the scaffold has an average porosity up to 82.0%. Mercury intrusion porosimetry （MIP） indicated that the pores of PAM-PHBV/BG scaffold were mainly distributed between 75 and 150 μm. The compressive strength test was adopted to evaluate the mechanical property of the scaffold. The result shows that the PAM-PHBV/BG scaffold has a relatively high compressive strength （0.91 MPa） when compared with the pure PHBV scaffold. Besides, the properties of the pure PHBV scaffold, PHBV/BG scaffold were also evaluated. The newly prepared PAM-PHBV/BG scaffold may be worthy of further studying as a bone repair material.     

Melt-Spinning of Nano-Hydroxyapatite/Poly(ε-caprolactone) Composite Fibers for Potential Application in Bone Tissue Engineering

Nano-hydroxyapatite/poly( ε-caprolactone)( n HA/PCL)composite materials are among the best candidates for application in bone tissue engineering. As the main technique to fabricate porous scaffolds, electrospinning produce scaffolds with unsatisfactory mechanical strength and limited pore size for cell infiltration.Micron-sized fiber assembly with higher mechanical strength is qualified to structure hybrid scaffolds. In this study, n HA/PCL monofilament fibers with different mass ratios were fabricated through melt-spinning. Transmission electron microscope( TEM)was used to observe the aggregation between n HA particles. Other characterizations including scanning electron microscopy( SEM),attenuated total reflection Fourier transform infrared spectroscopy( ATR-FTIR) and X-ray diffraction( XRD) were done to discuss the morphology, components and crystallization of the n HA/PCL composite fibers, respectively. The influence of n HA/PCL mass ratio on the tensile properties and water contact angle of composite fibers was also studied. The SEM images show the homogeneous dispersion of nano particles in the polymer matrix. Besides,n HA content increases the tensile strength, initial modulus and hydrophilicity of the composite fibers under the premise of spinnability. This kind of fibers is strong enough to fabricate fiber assembly which may have potential application in bone tissue engineering.     

Distribution of bone marrow stem cells in large porous polyester scaffolds

This work examined the optimal syringing depth during in vitro cell loading in order to even cell distribution after syringing a drop of cell suspension in cylinder poly（lactide-co-glycolide） （PLGA） porous scaffolds. The scaffolds of 10 mm height and 10 mm diameter were fabricated via room-temperature compression molding ＆ particulate leaching technique based on spherical porogens. In vitro tests were employed for such examinations： a global observation of a cell-loaded scaffold stained by the 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyltetrazolium bromide （MTT） technique and a quantitative measurement of spatial distribution of cells after slicing the cell-loaded scaffolds into layers. It was found that an even distribution of cells was soon achieved only if the initial cell suspension was seeded on the layer that was below the top surface but above the middle of scaffolds. The availability of in vitro osteoblastic differentiation of rat bone marrow stem cells in such a kind of spherical-pore PLGA scaffolds was meanwhile confirmed.     

Tussah Silk Fibroin Porous Scaffolds Prepared with a Mild Self-assembly Process for Controlled Drug Release

Besides excellent biodegradability and biocompatibility,a useful tissue engineering scaffold should provide favorable surface properties,outstanding mechanical strength and controlled drug release property. In this paper,a mild process to prepare porous tussah silk fibroin（ TSF） scaffolds from aqueous solution was described. The n-butanol was used to control the self-assembly of tussah silk. The scaffolds with different TSF concentrations and the same volume showed differences in pore size and distribution. The maximum porosity of the poprepared porous scaffolds was 80% in this paper. And the pore size of the prepared porous scaffolds with different concentrations was between 10μm and 230 μm. X-ray diffraction（ XRD） analysis revealed that amorphous TSF was crystallized to β-sheet secondary structure upon gelatin. The TSF scaffolds for controlled drug release was studied and the result showed that the time of drug release was significantly longer. The produced TSF scaffolds with sustained drug release have potential application in tissue engineering.     

In vitro bioactivity and cytocompatibility of porous scaffolds of bioactive borosilicate glasses

The bioactive borosilicate scaffolds （R2O-RO-B2O3-SiO2-P2O5） with four different contents of borate were fabricated by replication technique. The bioactivity, degradability and the cytotoxicity of the scaffolds were studied in this paper. The porosity of the scaffolds was found to be 73%-80%, and the pore size was in the range of 200-300 μm. The porous scaffolds immersed in 0.02 mol.L^-1 K2HPO4 solution were transformed into hydroxyapatite. And it is notable that the D-AIk-2B, D-AIk-3B-scaffolds were covered by hydroxyapatite layers after 7 h-immersion, which proved their high bioactivity. In the cell adhesion test, cells could be seen growing well on the scaffolds, showing stretched morphology and obvious pseudopodia, and only the high cumulative concentration of B ions released from the D-AIk-3B-scaffold samples had an inhibition effect on cell proliferation. But the inhibition effect could be alleviated by diluting the extract solution to a certain concentration （dilution ratio： 1：8）. Therefore, after suitable pretreatment, the porous borosilicate bioactive glass scaffold can be a desirable candidate for bone tissue engineering.     

On Modeling Bio-Scaffolds:Structural and Fluid Transport Characterization Based on 3-D Imaging Data

Bio-scaffolds which are most commonly open celled porous structures are increasingly used for tissue engineering and regenerative medicine. A number of studies have shown that the bulk properties of such irregular structures are poorly modeled using idealized unit cell approaches. The paper therefore uses novel image based meshing techniques to explore both fluid flow and bulk structural properties of a bone scaffold, as accurate modeling of bio-scaffolds with non-uniform cellular structures is very important for the development of optimal scaffolds for tissue engineering application. In this study, a porous hydroxyapatite/tricalcium phosphate (HA/TCP) bone scaffold has been scanned in a Micro-CT scanner, and converted into a volumetric mesh using image processing software developed by the authors. The resulting mesh was then exported to commercial FEA and CFD solvers for analysis. Initial FEA and CFD studies have shown promising results and have highlighted the importance of accurate modeling to understand how microstructures influence the mechanical property of the scaffold, and to analyze flow regimes through the sample. The work highlights the potential use of image based meshing for the ad hoc characterization of scaffolds as well as for assisting in the design of scaffolds with tailored strength, stiffness, and transport properties.     

Mechanical and thermal properties of AA7075/TiO2/Fly ash hybrid composites obtained by hot forging

In the present paper, multiple reinforcements TiO2 and fly ash were utilized for the fabrication of AA7075 matrix based hybrid composites using stir casting technique followed by hot forging. In hybrid composites, the fly ash content was fixed to 3 wt% while that of TiO2 was varied from 2.5 to 10 wt%. Scanning electron microscopy images revealed homogenous dispersion of both the reinforcements in AA7075 matrix.Compression test was conducted to study the mechanical behaviour of hybrid composites. The hybrid composites showed increase in compressive strength with the incorporation of multiple reinforcements and further increased with the increase in the weight fractions of TiO2 particles. The coefficient of thermal expansion was measured between 50 and 250 ℃ with a high precision thermal mechanical analyser. The thermal coefficient of hybrid composites decreased with the addition of TiO2 and fly ash. However a slight decrease in thermal conductivity of hybrid composites was observed when compared to that of AA7075 alloy.     

Comparative study of microstructural remodification to porous β-TCP and HA in rabbits

To assess the remolding ability of repaired bone in hydroxyapatite （HA） and β-calcium phosphate （β-TCP） scaffold, two 75% porosity bioceramics with the same three-dimensional geometry were implanted into femoral condyles of rabbits. Histological and micro-computed tomography （micro-CT） results demonstrated abundant new bone formation in the porous HA scaffold along with indistinctive scaffold degradation. Results also indicated that scaffold resorption in the β-TCP group, which was followed by a replacement with newly formed bone, was significantly higher than that in the HA group. The crosslinking trabeculae remodeled from the mixtures of the newly formed bone and β-TCP scaffold remnants might be helpful to promoting even loading and reducing stress. The bone remodeling pattern resulted from bone formation and scaffold resorption was significantly different for the two bioceramics. The results demonstrated that the 75% porous β-TCP was more suitable for new bone remodification than HA scaffold.     

Preparation and evaluation of biomimetric nano-hydroxyapatite-based composite scaffolds for bone-tissue engineering

In the present study,novel biomimetic composite scaffolds with a composition similar to that of natural bone were prepared,using nano-hydroxyapatite,collagen,and phosphatidylserine.The scaffolds possess an interconnected porous structure with a porosity of 84%.The pore size ranges from several micrometers up to about 400 m.In-vitro studies in simulated body fluids showed that the morphologies of the products derived from mineralization can be regulated by the extracellular matrix components of the scaffolds;this in turn leads to creation of a large number of hydroxyapatite crystals on the scaffold surface.The regulatory properties of collagen and phosphatidylserine also influenced the cell response to the composite scaffolds.MC3T3-E1 cells attached and spread on the surfaces of the materials and interacted with the substrates;this may be the result of charged groups on the composite materials.Radiological analysis suggested that calluses and bone bridges formed in defects within 12 weeks.These composite scaffolds may therefore be a suitable replacement in bone-tissue engineering.     

Effect of Molecular Weight of PCL on the Structure and Mechanical Properties of PCL/PET Composite Vascular Scaffold Prototype

A new scaffold has been developed,which made from poly(ε-caprolactone)( PCL) membrane with porous structure,and reinforcement of PCL scaffold was achieved by embedding polyethylene terephthalate(PET) weft-knit tubular fabric. The aim of this paper is to study the variation tendency of the morphology and the mechanical properties of the sample with the changing of molecular weight. Weighing method was used to analyze the porosity of the sample,and scanning electron microscopy( SEM) images were taken to observe porous structure. The tensile and compressive strengths of the samples were tested by the universal mechanical tester and radial compression apparatus, respectively. And the results showed that the porosity and compressive strength were improved when increasing the molecular weight,and the elastic recovery rate was also improved slightly. However, molecular weight has little impact on the tensile strength properties,because the PET tubular fabric provides most of the strength support rather than PCL membrane.     

Preparation of fiber-microsphere scaffolds for loading bioactive substances in gradient amounts

Gradient scaffolds are needed for interface tissue regeneration. In this study, a technique combining electrospinning and electrospraying was developed for preparing poly(L-lactide-co-glycolide) (PLGA) fiber-microsphere scaffolds for loading bioactive substances in gradient amounts. The gradient fiber-microsphere scaffolds contain two sheets of electrospun membranes and a sheet of microspheres loaded with bioactive substances in gradient amounts between the electrospun membranes. The morphologies of the gradient scaffolds were characterized and bovine serum albumin (BSA) was loaded as a model bioactive substance. The amount of BSA-loaded microspheres decreased gradually along the length of the gradient scaffold. The addition of poly (ethylene glycol) significantly improved the hydrophilicity of the gradient scaffold and the release behavior of BSA with respect to the gradient became apparent, with differences in the release amounts along the length of the gradient scaffold being observed. The biocompatibility of the gradient scaffold was verified using MC3T3-E1 pre-osteoblastic cells. The study demonstrated that the combination of electrospinning and electrospraying was a feasible method for the preparation of gradient scaffolds for potential applications in interface tissue engineering.     

Electrospun composites of PHBV/pearl powder for bone repairing

Electrospun fi ber has highly structural similarity with natural bone extracelluar matrix(ECM). Many researches about fabricating organic–inorganic composite materials have been carried out in order to mimic the natural composition of bone and enhance the biocompatibility of materials. In this work, pearl powder was added to the poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) and the composite nano fi ber scaffold was prepared by electrospinning. Mineralization ability of the composite scaffolds can be evaluated by analyzing hydroxyapatite(HA)formation on the surface of nano fi ber scaffolds. The obtained composite nano fi ber scaffolds showed an enhanced mineralization capacity due to incorporation of pearl powder. The HA formed amount of the composite scaffolds was raised as the increase of pearl powder in composite scaffolds. Therefore, the prepared PHBV/pearl composite nano fi ber scaffolds would be a promising candidate as an osteoconductive composite material for bone repairing.     

Development of a hybrid scaffold and a bioreactor for cartilage regeneration

We developed a hybrid scaffold and a bioreactor for cartilage regeneration. The hybrid scaffold was developed as combination of two components： a biodegradable framework and hydrogel-containing chondrocytes. We performed the MTT cell proliferation assay to compare the proliferation and viability of chondrocytes on three types of scaffolds： an aiginate gel, the hybrid scaffold, and an alginate sponge. Cells were encapsulated in 2% agarose gel. The bioreactor consisted of a circulation system and a compression system. We performed dynamic cell culture on these agarose gels in the bioreactor for 3 days.     

Covalently immobilized gelatin gradients within three-dimensional porous scaffolds

A stable gelatin gradient providing continuous increment of signaling for cell adhesion and proliferation was fabricated within 3D poly（L-lactic acid） （PLLA） scaffolds. The porous PLLA scaffold fabricated by NaCI particle leaching was vertically fixed on a glass vial. 1,6-Hexanediamine/propanol solution was continuously injected into the vial by a micropump to aminolyze the PLLA scaffold. As a result of reaction time difference, the introduced -NH2 groups increased continuously along with the longitude of the PLLA scaffold in the z-direction. After covalent immobilization of gelatin by glutaraldehyde coupling, the gelatin gradient scaffold was thus obtained. In vitro chondrocyte culture showed that the cells had higher viability and more extending morphology in the gelatin gradient scaffold than that in the uniform gelatin control.     

A new bone repair scaffold combined with chitosan/ hydroxyapatite and sustained releasing icariin

Icariin, a plant-derived flavonol glycoside, has been proved as an osteoinductive agent for bone tissue engineering. A new bone repair scaffold was generated by thorough mixing of icariin and chitosan/ hydroxyapatite （icariin-CS/HA） using freeze-drying technigue. Characteristics of morphology, mechanical properties, biocompatibility, drug release behavior and bone repair abilities in vivo were evaluated. The results show that drug loading process of icariin did not affect physical structure of CS/HA composite significantly but decreased mechanical properies of CS/HA composite, which happened with a high dosage; icariin-CS/HA had favorable cell compatibility and promoted osteogenic differentiation of hBMSCs; the controlled release of icariin was satisfactory and the release retained after 90 d in vitro. In addition, icariin-CS/HA scaffolds had favorable osteoconduction and osteoinduction in vivo, and could fill bone defect sites and stimulate newborn bone tissues formation at early stage. On the basis of these data, icariin-CS/HA is believed to be an optical bone repair scaffold for tissue engineering.     

Processing, microstructure and mechanical properties of biomedical magnesium with a specific two-layer structure

A novel magnesium based scaffold with a two-layer structure was synthesized by powder metallurgical process using salt particles as space holder. The outer layer of the scaffold shows an interconnected porous structure and the inner layer presents a compact structure reinforced by the salt particles. Such a specific structure is introduced primarily for the purpose of a better combination of biocompatibility and mechanical compatibility. Experimental results demonstrate that the structural features and mechanical properties of the magnesium based scaffold with a salt content of 30 wt% prepared by the current method are quite compatible with the cancellous bone. Such a novel Mg-based scaffold has the potential to act as degradable implants for bone substitute application.     

Surface Modification of Electrospun Poly(L-lactide)/Poly(ε-caprolactone) Fibrous Membranes by Plasma Treatment and Gelatin Immobilization

Biopolymer fibers have great potential for technical applications in biomaterials. The surface properties of fibers are of importance in these applications. In this study, electrospun poly(L-lactide)(PLLA)/poly(ε-caprolactone)(PCL) membranes were modified by cold plasma treatment and coating gelatin to improve the surface hydrophilic properties. The morphologies of the fibers were observed by scanning electron microscopy(SEM). Atomic force microscopy(AFM) was employed to show the surface characteristics of the fibers. The chemical feature of the fibrous membrane surfaces was examined by X-ray photoelectron spectroscopy(XPS). The surface wettability of the fibrous membrane was also characterized by water contact angle measurements. All these results show that plasma treatment can have profound effects on the surface properties of fibrous membranes by changing their surface physical and chemical features. Gelatin-PLLA/PCL membrane has great potential in applications of tissue engineering scaffolds.     

Disc-Electrospun PCL Nanofiber Formed Micro-patterned Structure Scaffold

Disc-electrospinning using a disc as spinneret and a rotary drum as collector is a novel technology to prepare nanofiber which has been applied in tissue engineering scaffolds. In this study, nanofibrous mats with mlcro-patterned structure were fabricated via disc-electrospinning. Poly （ε-eaprolactone） （PCL） was dissolved in trifluoroethanol （TFE） at various concentrations （ 2 %-7 % ） （w/v） for electrospinning and the applied voltage ranged from 40 to 70 kV. Scanning electron microscopy （SEM） was employed to observe the morphology of the nanofibrous scaffolds. SEM images illustrated that the nanofibers with beads formed micro-patterned structure such as triangles and other polygons. The average diameter of nanofibers presented various size with the concentration increased from 2% to 7%. The beads on the nanofibers constructed the vertexes of the polygons, while nanofibers bridged between adjacent vertexes. The concentration of solution and applied voltage may be two dominant factors to influence the topological structure of the nanofibrons scaffolds. Cells cultured on the micro-patterned scaffold spread along the edges of the polygons. The scaffold with patterned structure may have a promising application in tissue engineering.     

Effect of PLA Knitted Structure on the Mechanical Properties of Composite Vascular Scaffold

A new entire biodegradable scaffold has been developed which does not require precelluiarization before transplantation. This new kind of vascular scaffold prototype made from porous poly- e-caprolactone （PCL） membrane to provide three-dimensional environment for cell growth, and embedded with weft-knitted polylactic acid （PLA） fabric to support mechanics. The aim of this paper is to study the variation tendency of mechanical properties with the fabric spacing changing. The basic geometrical parameters were measured to characterize properties of the samples. The tensile and compressive elastic recovery of the samples were tested by the universal mechanical tester and radial compression apparatus, respectively. Both tensile and compressive properties enhanced when reducing the fabric spacing of the composite vascular scaffold.     

摩擦表面合金化法开发一种 Mg–Zn 表面合金:模拟体液中的体外降解研究

A new variant of friction-assisted process named friction surface alloying (FSA) for developing surface alloys was demonstrated in the present work. In FSA, the dispersed phase is melted and allowed to react with the matrix material to form an alloy at the surface of a metallic substrate. In the present work, magnesium (Mg) sheets and zinc (Zn) powder were selected, and fine grained (~3.5 μm) Mg–Zn surface alloy with improved hardness was produced by FSA. X-ray diffraction studies confirmed the formation of intermetallic phases of Mg and Zn at the surface. From the in vitro degradation studies carried out by immersing in simulated body fluids, a lower corrosion rate was observed for the Mg–Zn surface alloy compared with pure Mg. The surface morphologies after immersion studies indicated large degraded areas on the base Mg compared with Mg–Zn. The results demonstrate the potential of FSA in developing Mg-based surface alloys without melting the substrate to impart better surface properties.