pH-Compensation Effect of Lysine on the Acidic Degradation of Electrospun Poly（ lactide-co-glycolide） Fibers in PBS

Electrospun aligned ultrafine fibers of poly（ lactide-coglycolide）（ PLGA） can be used to construct biomimetic scaffolds for engineering those structurally anisotropic and dense tissues（ e. g.,tendon,ligament,etc.）. But the acidic degradation products of the PLGA could result in p H decrease in the vicinity of the scaffolds,which may give rise to biocompatibility concerns. To address the noted problem, this study was designed to evaluate the p Hcompensation capacity of using Lysine（ Lys） —a kind of basic amino acid on the acidic degradation products of PLGA. Ultrafine PLGA（ 50∶ 50） fibers with 0,10%,20%,and 30% by weight of Lys loadings were prepared by a stable jet electrospinning（ SJES）approach. The morphology,structure,and mechanical properties of the electrospun aligned fibrous mats of Lys-incorporated PLGA（ 50∶50） were characterized by scanning electron microscope（ SEM）,Fourier transform infrared spectroscopy（ FTIR）,and tensile testing,respectively. Thereafter,the fibrous PLGA（ 50 ∶50） scaffolds were subjected to degradation by being immersed in phosphate buffered saline（ PBS,p H 6. 86） solution at 37 ℃ for 5weeks. Our results show that the formed Lys / PLGA composite ultrafine fibers have a well-aligned and uniform morphology with a fineness of ca. 1 #m in diameter. Introduction of Lys led to increased mechanical performance; that is,when the Lys loading is less than 30%,tensile strength and Young＇s modulus of the aligned Lys / PLGA fibers reached up to the impressive values of 84. 5 MPa and 2. 4 GPa,respectively. Degradation results show that the p H of the PLGA group fell to 5. 6 in 5 weeks while the p H of the Lys /PLGA groups with 10%,20%, and 30% of Lys loadings was maintained at 6. 3, 6. 5 and 6. 7, respectively. This work demonstrated that incorporation of Lys into electrospun PLGA fibers could be an effective approach in mediating the p H decrease caused by the acidic degradation products of the PLGA.     

Electrospun Nanofibers of Hydroxyapatite/Collagen/Chitosan Promote Osteogenic Differentiation of BMSCs

Bone tissue engineering, aiming at developing bone substitutes for repair and regeneration of bone defects instead of using autologous bone grafts, has attracted wide attention in the field of tissue engineering and regenerative medicine. Developing biomimetic biomaterial scaffolds able to regulate osteogenic differentiation of stem cells could be a promising strategy to improve the therapeutic efficacy. In this study, clectrospun composite nanofibers of hydroxyapatite/collagen/chitosan （ HAp/Col/CTS ） resembling the fibrous nanostructure and constituents of the hierarchically organized natural bone, were prepared to investigate their capacity for promoting bone mesenchymal stem cells （BMSCs） to differentiate into the osteogenic lineage in the absence and presence of the osteogenlc supplementation, respectively. Call morphology, proliferation and quantified specific osteogenic protein expression on the electrospun HAp/Coi/CTS scaffolds were evaluated in comparison with different controls including dectrospun nanofibrous CTS, HAp/CTS and tissue culture plate. Our remits showed that the nanofibrous HAp/Col/CTS scaffolds supported better spreading and proliferation of the BMSCs than other substrates （ P 〈 0.01 ）. Expressions of osteogenesis protein markers, alkaline phosphatase （ALP） and Col, were significantly upregulated on the HAp/Col/CTS than those on the CTS （P 〈0.01） and HAp/ CTS （P 〈 0. 05 ） scaffolds in the absence of the osteogeulc supplementation. Moreover, presence of osteogeulc supplementation also proved to enhance osteogeule differentiation of BMSCs on HAp/ Col/CTS scaffolds, indicative of a synergistic effect. This study highlights the potential of BMSCs/HAp/Col/CTS cell-scaffold system for functional bone repair and regeneration applications.     

胚胎大鼠室下带神经干细胞分离、培养与鉴定

自从1992年Reynolds和Weiss首先报道在成年小鼠纹状体中分离培养出能在体外不断增殖、具有多种分化潜能的细胞群以来,神经干细胞(neural stem cells,NSCs)诱人的应用前景激发了许多科学家的兴趣．近来的研究进一步证实,胚胎和成年哺乳动物的神经组织和人脑中可以分离出神经干细胞,在体外培养时可被生长因子诱导而增殖,并具有分化成神经元和胶质细胞的潜能．本研究采用无血清培养技术,从孕14d胚胎大鼠前脑室下带(SVZ)中成功分离培养出神经干细胞,经增殖获得大量的克隆球团,用nes-     

Fabrication of Dex-Loaded Shape Memory Polymer Based Composite Nanofibers ：for Potential Bone Tissue Engineering

Biodegradable shape memory polymers （SMPs） are a class of intelligent materials with great potential for imparting biomaterial scaffolds multifunetionality in the field of tissue engineering and regenerative medicine. In this study, the biodegradable SMP poly（ D, L-lactide-co-trimethylene carbonate） （PLMC） incorporated with the ,dexamethasone （Dex）, which was a kind of synthetic bone-formation inducing factor, was fabricated into nanofibers via dectrospinning. The morphology, constituent, thermal and mechanical properties of the produced Dex/PLMC composite nanofibers were characterized by scanning electron microscopy （SEM）, Fourier transform ：infrared spectroscopy （ FTIR ）, differential scanning calorimetry （DSC）, and tensile testing, respectively. Then, ultrasound was ,employed as a remote stimulus to regulate the Dex releasing behavior from the composite nanofibers. It was found that the generated Dex/ PLMC composite nanofibers had a uniform and smooth morphology with a diameter of ca. 564 nm. Mechanical testing results showed that incorporation of the Dex gave rise to improved mechanical performance with the tensile strength, Young＇ s modulus and strain- at-break increased by 18.2 %, 20. 0 % and 64.4 %, respectively. DSC data revealed that the glass transition temperature （ Tg ） of the composite nanofibers, i. e., the thermal transition temperature （Ttrans） for activating shape memory effect, was 39. 7 ℃. Moreover, the release kinetics of the encapsulated Dex in the aanofibers could be manipulated by varying the acoustic power and insonation duration. These results suggested that the newly developed Dex/PLMC nanofibers could be a promising drug delivery system for applications in bone tissue engineering （BTE）.