Synthesis and characterization of porous κ-carrageenan/calcium phosphate nanocomposite scaffolds

The polysaccharide κ-carrageenan was used in the production of macroporous composites containing nanosized hydroxyapatite, with potential application in bone tissue engineering. Biodegradable composite scaffolds were prepared combining in situ co-precipitation of calcium phosphates with a freeze-drying technique. The effect of the Ca/P molar ratio and total ceramic content on the chemical composition, microstructure and mechanical performance of the scaffolds were investigated by thermal analysis, X-ray diffraction, FTIR, transmission electron microscopy, scanning electron microscopy, He porosimetry and compressive tests. A mixture of amorphous calcium phosphates and/or nanosized calcium-deficient hydroxyapatite was obtained in most of the composites. The formation of hydroxyapatite was induced by higher Ca/P ratios, probably due to competing reticulation of the biopolymer with calcium cations. The composite scaffolds presented interconnected pores (50–400 μm) and porosity around 97% and calcium phosphates were uniformly dispersed in the κ-carrageenan matrix. Both microstructure and compressive mechanical properties of the scaffolds were affected by the ceramic content and, for a Ca/P molar ratio of 1.67, maximum compressive strength was achieved for a ceramic content of ca. 25 wt%. Above this value the structural integrity of the composite was damaged and a dramatic decrease in mechanical strength was verified. Compressive mechanical properties of the composites were improved by increasing Ca/P atom ratio.     

In vitro biocompatibility study of calcium phosphate glass ceramic scaffolds with different trace element doping

Porous calcium phosphate based glass ceramics (CaO-P₂O₅-Na₂O) containing different trace elements (2.0 mol% Mg, Sr and Zn respectively) were prepared by coating polyurethane foams with sol-gel derived glass slurry. After heat treatment at suitable temperatures, main phase catena hexaphosphate (Ca₄P₆O₁₉) and minor phase calcium pyrophosphate (β-Ca₂P₂O₇) crystallized from the glass matrix. These scaffolds were soaked in simulated body fluid (SBF) to determine the solubility and apatite formation, and mouse MC3T3-E1 cells were used to investigate the bioactivity and biocompatibility. The Sr doped scaffold showed a higher degradability than those samples containing Zn or Mg, inducing the formation of an apatite layer with a high (Sr + Ca)/P molar ratio of 1.64, whereas only some discontinuous CaP layers and spare apatite agglomerates were found on the scaffolds doped with Mg ((Mg + Ca)/P = 1.12) and Zn ((Zn + Ca)/P = 1.55) respectively. In vitro cell culture, a high degree of cell adhesion and spreading was achieved on the samples containing Sr or Zn, while only a few cells adhered to the Mg doped sample. These results implied that the bioactivity and biocompatibility of the scaffolds were not only strongly associated with the apatite forming ability, but also related with the Ca/P molar ratios of the deposits.     

Porous polymer/hydroxyapatite scaffolds: characterization and biocompatibility investigations

Poly-lactic-glycolic acid (PLGA) has been widely used as a scaffold material for bone tissue engineering applications. 3D sponge-like porous scaffolds have previously been generated through a solvent casting and salt leaching technique. In this study, polymer–ceramic composite scaffolds were created by immersing PLGA scaffolds in simulated body fluid, leading to the formation of a hydroxyapatite (HAP) coating. The presence of a HAP layer was confirmed using scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy in attenuated total reflection mode. HAP-coated PLGA scaffolds were tested for their biocompatibility in vitro using human osteoblast cell cultures. Biocompatibility was assessed by standard tests for cell proliferation (MTT, WST), as well as fluorescence microscopy after standard cell vitality staining procedures. It was shown that PLGA–HAP composites support osteoblast growth and vitality, paving the way for applications as bone tissue engineering scaffolds.     

Fabrication of mesoporous calcium silicate/calcium phosphate cement scaffolds with high mechanical strength by freeform fabrication system with micro-droplet jetting

In this study, we explored the feasibility of fabrication bioactive mesoporous calcium silicate/calcium phosphate cements (MCS/CPC) scaffolds with high mechanical strength by Freeform Fabrication System with Micro-Droplet Jetting. After preparation of ordered mesoporous calcium silicate (MCS) powder, ready-to-use MCS/CPC paste was formed by mixing calcium phosphate cement (CPC) powder and MCS powder with the binder polyvinyl alcohol (PVA) aqueous solution at a certain ratio of powder to liquid. MCS/CPC scaffolds with various architectures, pore sizes, and interconnectivity were then directly printed at room temperature using MCS/CPC paste. The mechanical strength, apatite formation, degradation rate, and cytocompatibility of the composite scaffolds were systematically investigated. The results showed that MCS/CPC paste exhibited outstanding printability to form MCS/CPC scaffolds. The hybrid MCS/CPC scaffolds with predefined pore size of 350 μm showed fast degradation rate, high mechanical strength, and good cytocompatibility. It was indicated that the hybrid MCS/CPC scaffolds might be a promising candidate for critical bone defect repair.     

Growth,characterization and biocompatibility of bone-like calcium phosphate layers biomimetically deposited on metallic substrata

Much research has been devoted to the coating of orthopedic and dental implants with porous ceramics, such as hydroxyapatite to increase hard tissue integration in vivo. Chemical immersion in simulated body fluids and supersaturated calcium-phosphate solutions (SCPS) have been shown to elicit apatite coatings on the order of 10–100 μm of thickness, which are very homogenous and would be more favorable to biological interaction than plasma-sprayed coatings.This study focuses on the growth, characterization and biocompatibility of bone-like apatite layers on metallic biomaterials produced through diminished time duration chemical immersion. The method presented here includes a pre-calcification step, in which samples were immersed in a boiling Ca(OH)₂ solution to initiate and increase favorable ion exchange prior to immersion. Subsequent immersion in SCPS produced homogenous coatings of calcium phosphate with a thickness of 20–30 μm, 100% coverage and crystal sizes of 1–2 μm in 3 days. Coated samples were favored biologically over non-coated samples by osteoblast cells as indicated by alkaline phosphatase activity. This study suggests that an industrially viable method of chemical immersion in a SCPS, coupled with simple pre-treatments can produce calcium phosphate coatings that favor positive biological interactions, conducive to osseointegration.     

Alginate/calcium phosphate scaffolds with oriented,tube‐like pores

Porous and mineralised scaffolds are required for various applications in hard tissue engineering. Scaffolds with oriented tube‐like pores facilitate homogenous cell seeding, a sufficient nutrient supply during cell culture (even in big constructs) and a fast vascularisation after implantation. The phenomenon of ionotropic gelation has been known since more than 30 years which describes that alginate forms gels with capillary‐like pores when covered with solutions of di‐ or trivalent cations [1]. This technique has been used here to develop scaffolds with tube‐like and regular pores from alginate/calcium phosphate composites and to stabilise them by mineralisation with hydroxyapatite from solution.     

Processing and characterization of porous alumina scaffolds

Bioceramic materials are used for the reconstruction or replacement of the damaged parts of the human body. In this study an improved procedure is described for producing ceramic scaffolds with controlled porosity. Bioinert alumina ceramic was used to make porous scaffolds by using indirect fused deposition modeling (FDM), a commercially available rapid prototyping (RP) technique. Porous alumina samples were coated with hydroxyapatite (HAp) to increase the biocompatibility of the scaffolds. Initial biological responses of the porous alumina scaffolds were assessed in vitro using rat pituitary tumor cells (PR1). Both porous alumina and HAp coated alumina ceramics provided favorable sites for cell attachments in a physiological solution at 37 °C, which suggests that these materials would promote good bonding while used as bone implants in vivo. Based on these preliminary studies, similar tests were performed with human osteosarcoma cells. Cell proliferation studies show that both the ceramic materials can potentially provide a non-toxic surface for bone bonding when implanted in vivo.     

Preparation and characterization of macroporous chitosan/wollastonite composite scaffolds for tissue engineering

Chitosan/wollastonite composite scaffolds were prepared by a thermally induced phase separation method. The microstructure, mechanical performance and in vitro bioactivity of the composite scaffolds were investigated. The composite scaffolds were macroporous and wollastonite particles were dispersed uniformly on the surface of the pore walls. Scanning electron microscope images of the composite scaffolds demonstrated that the scaffolds had interconnected pores with diameters from 60 to 200 microm. Both the pore size and structure were affected by freezing temperature. The mechanical performance of the composite scaffolds was improved compared to that of pure chitosan scaffolds. The in vitro bioactivity of the scaffolds was evaluated by soaking samples in simulated body fluid and the apatite layer was observed on the surface of the pore walls of the composite scaffolds. Our results suggest that the incorporation of wollastonite into chitosan could enhance both the mechanical strength and the in vitro bioactivity of the resultant composite. The macroporous chitosan/wollastonite scaffolds may be a potential candidate for application in tissue engineering.     

Preparation and mechanical properties of calcium phosphate/copoly-L-lactide composites

New artificial bone materials were prepared using calcium phosphates, hydroxyapatite and -tricalicum phosphate, and copoly-L-lactide, CPLA. Calcium phosphate powder and CPLA were mixed at 453 K for 10 min with various mixing ratios. Scanning electron microscope observations indicated that the composites of -tricalicum phosphate and CPLA were homogeneously dispersed and highly adhesive. Youngs modulus of the composites was the same as bone, and bending strength was over half that of bone. The improvement of Youngs modulus compared to the original two materials was due to a composite effect. The composites are expected to be usable as artificial bone materials.     

PVA复合磷酸钙骨水泥的制备和性能研究

将含有不同质量分数聚乙烯醇(PVA)的PVA-KH2PO4-Na2HPO4体系缓冲溶液作为骨水泥的调和液,将其与磷酸钙骨水泥粉末混合后成型。将试样在接近生理条件(相对湿度100%,温度(37±1)℃)下养护24h,发现PVA掺入量为1%时的抗压强度达到31.71MPa,比未掺入的提高了将近70%。     

Fabrication and characterization of porous calcium polyphosphate scaffolds

Porous calcium polyphosphate (CPP) scaffolds with different polymerization degree and crystalline phases were prepared, and then analyzed by scanning electron microscopy (SEM), Thermmogravimetry (TG) and X-ray diffraction (XRD). Number average polymerization degree was calculated by analyzing the calcining process of raw material Ca(H₂PO₄)₂, as a polycondensation reaction. Amorphous CPP were prepared by the quenching from the melt of Ca(H₂PO₄)₂ after calcining, and CPP with different polymerization degree was prepared by controlling the calcining time. Meanwhile, CPP with the same polymerization degree was prepared to amorphous or different crystalline phases CPP which was made from crystallization of amorphous CPP. In vitro degradation studies using 0.1 M of tris-buffered solution were performed to assess the effect of polymerization degree or crystalline phases on mechanical properties and weight loss of the samples. With the increase of polymerization degree, the weight loss during the degradation decreased, contrarily the strength of CPP increased. The degradation velocity of amorphous CPP, α-CPP, β-CPP and γ-CPP with the same polymerization degree decreased in turn at the same period. The full weight loss period of CPP can be controlled between 17 days and more than 1 year. The results of this study suggest that CPP ceramics have potential applications for bone tissue engineering.     

Improving the strength and biocompatibility of porous titanium scaffolds by creating elongated pores coated with a bioactive, nanoporous TiO2 layer

This paper reports a novel way of improving the mechanical properties and biocompatibility of porous Ti scaffolds using a combination of the modified sponge replication method and anodization process. The use of a stretched polymeric sponge as a novel template allowed the creation of elongated pores in a porous Ti scaffold, which, accordingly, led to a high compressive strength of 24.2 ± 2.08 MPa at a porosity of approximately 70 vol%. Furthermore, the surfaces of the Ti walls were coated successfully with a bioactive nanoporous TiO₂ layer using the anodization process, which enhanced the biocompatibility remarkably, as assessed by the attachment of MC3T3-E1 cells.     

磷酸钙涂覆炭织物体外细胞毒性的评价

医用植人体的成功与否常常取决于器件植入后细胞与材料表面间的相互作用.采用生物体外测试法考察了声电化学法制备的磷酸钙涂层对炭织物的骨细胞附着、增殖能力的影响.借助MTS检测技术、扫描电子显微镜,选择人类成骨细胞(MG63)作为细胞模型,通过测定细胞与炭织物、磷酸钙涂覆炭织物、以及其各自的提取液作用后的存活能力,研究了细胞/材料的相互作用,并对基底材料的细胞毒性进行了评价.结果表明,炭织物、磷酸钙涂覆炭织物均不具有细胞毒性,且磷酸钙涂层可提高成骨细胞的附着和增殖.SEM图像显示,细胞形貌正常,与对照组相比较生长增殖情况相似.     

Cell growth and function on calcium phosphate reinforced chitosan scaffolds

Macroporous chitosan scaffolds reinforced by calcium phosphate powders such as hydroxyapatite (HA) or calcium phosphate invert glass were fabricated using a thermally induced phase separation technique. Human osteoblast-like MG63 cells were cultured on the composite scaffolds for up to 11 days, and the cell growth and function were analyzed. The cell growth is much faster on the chitosan/HA scaffolds incorporated with the glass (CHG) than on the chitosan/HA scaffold without the glass (CH). The total protein content of cells were quantified and increased over time on both composites (CH, CHG) but was significantly higher on CHG after 7 days of culture. The cells on CHG also expressed significantly higher amount of alkaline phosphatase at days 7 and 11 and osteocalcin at day 7 than those on CH. The results suggested that the addition of glass in chitosan/hydroxyapatite composite scaffolds might enhance the proliferation and osteoblastic phenotype expression of MG63 cells. However, the chitosan-matrix scaffolds did not show higher phenotype expression of MG63 cells, in comparison with the TCPS plate, probably due to the degradation of chitosan and release of acidic byproducts. Larger amount of soluble calcium phosphate invert glasses should be added into the scaffolds to prevent chitosan from fast degradation that may affect the differentiation of osteoblast cells.     

Morphological, rheological and mechanical characterization of polypropylene nanocomposite blends

In the present work, the effectiveness of styrene/ethylene-butylene/styrene rubbers grafted with maleic anhydride (MA) and a metallocene polyethylene (mPE) as toughening materials in binary and ternary blends with polypropylene and its nanocomposite as continuous phases was evaluated in terms of transmission electron microscopy (TEM), scanning electron microscopy (SEM), oscillatory shear flow and dynamic mechanical thermal analysis (DMA). The flexural modulus and heat distortion temperature values were determined as well. A metallocene polyethylene and a polyamide-6 were used as dispersed phases in these binary and ternary blends produced via melt blending in a corotating twin-screw extruder. Results showed that the compatibilized blends prepared without clay are tougher than those prepared with the nanocomposite of PP as the matrix phase and no significant changes in shear viscosity, melt elasticity, flexural or storage moduli and heat distortion temperature values were observed between them. However, the binary blend with a nanocomposite of PP as matrix and metallocene polyethylene phase exhibited better toughness, lower shear viscosity, flexural modulus, and heat distortion temperature values than that prepared with polyamide-6 as dispersed phase. These results are related to the degree of clay dispersion in the PP and to the type of morphology developed in the different blends.     

Feasibility of three-dimensional macroporous scaffold using calcium phosphate glass and polyurethane sponge

Tissue engineering presents an alternative approach to the repair of a damaged tissue by avoiding the need for a permanent implant made of an engineered artificial material. A suitable temporary scaffold material that exhibits adequate mechanical and biological properties is required to enable tissue regeneration by exploiting the body’s inherent repair mechanism, i.e. a regenerative allograft. Synthetic bioresorbable polymers have been attracting attention as tissue engineering scaffolds. However, a number of problems have been encountered such as inflammatory responses and lack of bioactivity. Another good candidate for a tissue engineering scaffold is the calcium phosphates because of their good biocompatibility and osteointegrative properties. Their slow biodegradation is still remains problem, especially for the filling of large bony defects. In this study, we investigated the fabrication method of a three-dimensional reticulated scaffold with interconnected pores of several hundred micrometers using calcium phosphate glass in the system of CaO-CaF₂-P₂O₅-MgO-ZnO and a polyurethane sponge as a template. Calcium phosphate glass slurry was homogenously thick coated when the weight percentage of the calcium phosphate glass powder was 40% with 8 wt% of polyvinyl alcohol as a binder. Addition of 10 wt% dimethyl formamide as a drying control chemical additive into a slurry almost prevented the crack formation during drying. Sintering of the dried porous block at 850°C exhibited the densest microstructure as well as the entire elimination of the organic additives. Repeating the process significantly increased compressive strength of sintered porous body due to the thickening of the struts. To summarize, macroporous calcium phosphate glass can be fabricated with 500∼800 μm of pore size and a three-dimensionally interconnected open pore system. It is thought that this kind of biodegradable glass scaffold combined with osteogenic cells has potential to be studied further as a tissue-engineered bone substitute.     

Physicochemical properties and cytotoxicities of Sr-containing biphasic calcium phosphate bone scaffolds

This study demonstrates a new biomaterial system composed of Sr-containing hydroxyapatite (Sr-HA) and Sr-containing tricalcium phosphate (Sr-TCP), termed herein Sr-containing biphasic calcium phosphate (Sr-BCP). Furthermore, a series of new Sr-BCP porous scaffolds with tunable structure and properties has also been developed. These Sr-BCP scaffolds were obtained by in situ sintering of a series of composites formed by casting various Sr-containing calcium phosphate cement (Sr-CPC) into different rapid prototyping (RP) porous phenol formaldehyde resins, which acted as the negative moulds for controlling pore structures of the final scaffolds. Results show that the porous Sr-BCP scaffolds are composed of Sr-HA and Sr-TCP. The phase composition and the macro-structure of the Sr-BCP scaffold could be adjusted by controlling the processing parameters of the Sr-CPC pastes and the structure parameters of the RP negative mould, respectively. It is also found that both the compressive strength (CS) and the dissolving rate of the Sr-BCP scaffold significantly vary with their phase composition and macropore percentage. In particular, the compressive strength achieves a maximum CS level of 9.20 ± 1.30 MPa for the Sr-BCP scaffold with a Sr-HA/Sr-TCP weight ratio of 78:22, a macropore percentage of 30% (400–550 μm in size) and a total-porosity of 63.70%, significantly higher than that of the Sr-free BCP scaffold with similar porosity. All the extracts of the Sr-BCP scaffold exhibit no cytotoxicity. The current study shows that the incorporation of Sr plays an important role in positively improving the physicochemical properties of the BCP scaffold without introducing obvious cytotoxicity. It also reveals a potential clinical application for this material system as bone tissue engineering (BTE) scaffold.     

静电纺丝聚乳酸/磷酸钙复合纳米纤维的力学性能

运用静电纺丝技术制备了聚乳酸纳米纤维和聚乳酸/磷酸钙复合纳米纤维.对两种电纺纳米纤维的表面形态进行了扫描电子显微镜(SEM)的表征及单轴拉力测试表征.讨论了聚乳酸纳米纤维和聚乳酸/磷酸钙复合纳米纤维的力学性能.结果表明掺加了磷酸钙的聚乳酸纳米纤维的力学性能得到明显提高.     

Compressive strength and processing of camphene-based freeze cast calcium phosphate scaffolds with aligned pores

Porous calcium phosphate (CaP) scaffolds with aligned pores were fabricated by unidirectionally freezing a CaP/camphene slurry at 32 °C for various times (1, 2, 3 days). During this process, camphene dendrites grew preferentially from the bottom to the top of the cast body. The frozen samples were then freeze-dried to remove the solid camphene and sintered at 1200 °C for 3 h to densify the CaP walls. All of the fabricated samples showed a highly aligned pore structure with a porosity of 62-65 vol.%, regardless of the freezing time. As the freezing time was increased from 1 to 3 days, the pore size increased from 122 to 166 μm due to the continual overgrowth of camphene dendrites, while the compressive strength decreased from 9.3 ± 1.6 to 6.2 ± 1.3 MPa due to the increase in pore size. However, it should be noted that the compressive strength of the sample tested parallel to the freezing direction was much higher than that of the sample tested normal to the direction of freezing, indicating the utility of the aligned pores.     

Preparation and characterization of calcium phosphate biomaterials

Calcium phosphate cement (CPC) samples have been prepared with a mixture of monocalciumphosphate monohydrate (MCPM) and calcium carbonate (CC) powders, in stechiometric moles ratio 1:2.5 to obtain a Ca/P ratio of about 1.67 typical of hydroxyapatite (HAp), with or without addition of HAp. All specimens are incubated at 30 °C in a steam saturated air environment for 3, 6 and 15 days respectively, afterwards dried and stored under nitrogen. The calcium phosphate samples have been characterized by X-ray diffraction (XRD), Vickers hardness test (HV), diametral compression (d.c.), strength compression, and porosity evaluation. MCPM/CC mixture has a 30% HAp final concentration and is characterized by higher porosity (amount 78%) and mechanical properties useful as filler in bone segments without high mechanical stress.