Enzymatic degradation of poly(L-lactide) and poly (epsilon-caprolactone) electrospun fibers

Poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) ultrafine fibers were prepared by electrospinning. The influence of cationic and anionic surfactants on their enzymatic degradation behavior was investigated by measuring weight loss, molecular weight, crystallinity, and melting temperature of the fibers as a function of degradation time. Under the catalysis of proteinase K, the PLLA fibers containing the anionic surfactant sodium docecyl sulfate (SDS) exhibited a faster degradation rate than those containing cationic surfactant triethylbenzylammonium chloride (TEBAC), indicating that surface electric charge on the fibers is a critical factor for an enzymatic degradation. Similarly, TEBAC-containing PCL fibers exhibited a 47% weight loss within 8.5 h whereas SDS-containing PCL fibers showed little degradation in the presence of lipase PS. By analyzing the charge status of proteinase K and lipase PS under the experimental conditions, the importance of the surface charges of the fibers and their interactions with the charges on the enzymes were revealed. Consequently, a "two-step" degradation mechanism was proposed: (1) the enzyme approaches the fiber surface; (2) the enzyme initiates hydrolysis of the polymer.

Co-electrospun poly(lactide-co-glycolide), gelatin, and elastin blends for tissue engineering scaffolds

In this study, we describe composite scaffolds composed of synthetic and natural materials with physicochemical properties suitable for tissue engineering applications. Fibrous scaffolds were co-electrospun from a blend of a synthetic biodegradable polymer (poly(lactic-co-glycolic acid), PLGA, 10% solution) and two natural proteins, gelatin (denatured collagen, 8% solution) and (x-elastin (20% solution) at ratios of 3:1:2 and 2:2:2 (v/v/v). The resulting PLGA-gelatin-elastin (PGE) fibers were homogeneous in appearance with an average diameter of 380 80 mn, which was considerably smaller than fibers made under identical conditions from the starting materials (PLGA, 780 +/- 200 nm; gelatin, 447 +/- 1.23 nm; elastin, 1060 170 nm). Upon hydration, PGE fibers swelled to an average fiber diameter of 963 +/- 132 nm, but did not disintegrate. Importantly, PGE scaffolds were stable in an aqueous environment without crosslinking, and were more elastic than those made of pure elastin fibers. To investigate the cytocompatibility of PGE, we cultured H9c2 rat cardiac myoblasts and rat bone marrow stromal cells (BMSCs) on fibrous PGE scaffolds. We found that myoblasts grew equally as well or slightly better on the scaffolds than on tissue-culture plastic. Microscopic evaluation confirmed that myoblasts reached confluence on the scaffold surfaces while simultaneously growing into the scaffolds.

Biodegradable electrospun poly(L-lactide) fibers containing antibacterial silver nanoparticles

Biodegradable poly(L-lactide) (PLA) ultrafine fibers containing nanosilver particles were prepared via electrospinning. Morphology of the Ag/PLA fibers and distribution of the silver nanoparticles were characterized. The release of silver ions from the Ag/PLA fibers and their antibacterial activities were investigated. These fibers showed antibacterial activities (microorganism reduction) of 98.5% and 94.2% against Staphylococcus aureus and Escherichia coli, respectively, because of the presence of the silver nanoparticles.

Biodegradable electrospun fibers for drug delivery

The influences of surfactants and medical drugs on the diameter size and uniformity of electrospun poly(L-lactic acid) (PLLA) fibers were examined by adding various surfactants (cationic, anionic, and nonionic) and typical drugs into the PLLA solution. Significant diameter reduction and uniformity improvement were observed. It was shown that the drugs were capsulated inside of the fibers and the drug release in the presence of proteinase K followed nearly zero-order kinetics due to the degradation of the PLLA fibers. Such ultrafine fiber mats containing drugs may find clinical applications in the future.

Ultrafine fibers electrospun from biodegradable polymers

Biodegradable poly(I-lactide) (PLLA) and poly(e-caprolactone) (PCL) were electrospun into ultrafine fibers. The technological parameters influencing the spinning process and morphology of the fibers obtained were examined. These parameters included solvent composition, addition of certain organic salts, molecular weight and concentration of the polymers, capillary diameter, air ventilation, and pressure imposed on the surface of the solution as well as electrostatic field. By properly choosing and adjusting these parameters, submicron PLLA and PCL fibers with a narrow diameter distribution were prepared. Scanning electronic microscopy was used to observe the morphology and diameter size of the fibers.

Photoluminescence of Ag nanoparticle embedded Tb3+/Ce3+ codoped NaYF4/PVP nanofibers prepared by electrospinning

Ag nanoparticle embedded NaYF4:0.05Tb center dot chi Ce/ PVP (PVP stands for poly(vinyl pyrrolidone)) composite nanofibers have been prepared by electrospinning. A field emission scanning electron microscope and x-ray diffraction have been utilized to characterize the size, morphology and structure of the as-prepared electrospun nanofibers. Obvious photoluminescence (PL) of NaYF4:0.05Tb center dot 0.05Ce/PVP electrospun nanofibers due to the efficient energy transfer from Ce3+ to Tb3+ ions is observed. The PL intensity of the electrospun nanofibers decreases gradually with the addition of Ag nanoparticles. No obvious surface plasmon resonance enhanced luminescence is observed. The reasons for the weakening of the emission intensity with the addition of Ag nanoparticles have also been discussed in this work.

可生物降解电纺丝超细纤维

电纺丝技术是一种用来制备超细纤维的方法，成本低廉、简单易行。近十年来，电纺丝技术在理论研究和实验参数研究等方面都取得了不小的进展。由电纺丝技术制备的超细纤维直径至少比传统的纺丝工艺低1-3个数量级，因此，在增强复合材料、过滤系统、防护衣、光学和电学器件及生物医药等方面都显示出巨大的应用潜力。尤其是在生物医药领域，电纺丝超细纤维可广泛用作组织工程支架、药物传输与控制释放的载体及创伤敷料等，这也是国际上的一个研究热点。但由于电纺丝过程的复杂性和实验参数的多样性，制备直径分布范围窄的纤维一直是电纺丝的难点之一，另外，以电纺丝超细纤维作为药物传输与释放的载体也是近两年才刚刚发展起来的，还不十分成熟，经常会存在药物的突释现象。针对以上问题，本论文以可生物降解高分子材料PLA、PLGA（80／20）和PCL进行电纺丝，系统地研究了溶剂体系、表面活性剂、鲜溶液流速、喷丝口直径及环境温度与空气流动速度等因素对电纺丝过程及纤维形貌和直径分布的影响，同时对电纺丝纤维的性质进行了分析。在此基础上，我们研究了PLLA和PCL电纺丝超细纤綷的酶降解行为，并实现了PLLA纤维对抗癌药紫杉醇和1. 以氯仿、氯仿/丙酮、1、2-二氯乙烷及氯仿/1,2-氯乙烷为溶剂体系，制备了PLA、PCL和PLGA（80／20）的电纺丝超细纤维。当氯仿与丙酮的体积比为1：1时为最佳溶剂体系，电纺丝过程和纤维形貌都得到较大的改善。阳离子表面活性剂节基三乙基氯化按（TBBAC）和阴离子表面活性剂十二烷基硫酸钠（SDS）的加入也可以显著改善电纺丝过程和纤维的直径分布，而非离子表面活性剂脂肪醇聚氧乙烯醚（AEO10）的改善程度较小。压力较大或喷丝口直径较粗时，则会由于溶液流量的增大而造成纤维的粘连。空气流速较大时，则纤维会由于空气的对流速度加快而发生缠绕和卷曲。2．PLLA、PCL和PLGA（80／20）超细纤维毡的孔隙率都较大，分别达到89％、68％和80％，因此，PLLA和PCL纤维的力学性能都远远低于膜。3．电纺丝过程会使纤维中的高分子链产生一定的排列和高度的取向，但由于纤维的固化速度很快，高分子链来不及进行规整排列而形成结晶，因此，DSC和WXAD的结果都显示，PCL纤维毡的结晶度要比相应的膜低。对于PLLA纤维毡来说，由于Tg在室温以上，在进行DSC测试的升温过程中，会由于分子链的运动而使结晶度升高。4．蛋白酶K在Tris-HCL缓冲液中略显正电性，因而阴离子表面活性剂对蛋白酶K会有一定的吸附作用，而阳离子表面活性剂对蛋白酶K在纤维表面的吸附则有一定的阻碍作用，因此，含有5wt％SDS的PLLA纤维的酶降解速率比含有swt％TEBAC的PLLA纤维稍快。虽然纤维中PLLA的分子链可能高度取向，但在整个降解过程中，PLLA纤维样品都处在非晶状态，没有明显的结晶行为。5．与PLLA纤维的降解情况恰好相反，由于脂肪酶PS在磷酸盐缓冲液（PBS）缓冲液中显示较强的负电性，因而阳离子表面活性剂TEBAC会对脂肪酶PS有吸附作用，从而含有5wt％TEBAC的PCL纤维降解速度较快，而阴离子表面活性剂SDS会对脂肪酶PS在纤维表面的吸附有阻碍作用，因此，降解反应在含有5wt％SDS的PCL纤维中几乎不能发生。DSC和WAXD的结果均显示，在降解过程中，含有5wt％TEBAC的PCL纤维的结晶度明显升高。这有两个可能原因：一是脂肪酶PS对PCL纤维的降解是优先发生在无定形区：二是因为降解实验是在37℃的条件下进行的，该温度在PCL的Tg之上和TC温度附近，因而，具有高度排列和取向的PCL纤维就会由于分子链的运动而产生结晶，造成结晶度的提局。6，在电纺丝溶液中加入利福平、紫杉醇和阿霉素等药物，同样会改善电纺丝过程，使纤维直径降低，分布变窄。7．SEM照片和药物控制释放实验均显示，药物模型利福平或抗癌药紫杉醇完全被包埋在PLLA纤维内部，同时，利福平一PLLA纤维和紫杉醇－PLLA纤维在含蛋白酶K的Tris-HCl缓冲液中的释放遵循零级动力学，完全没有突释现象。PLLA纤维的降解速度是药物释放的主导因素。这是在国际范围内首次取得这样的结果，从而使电纺丝超细纤维药物剂型的发展取得了本质上的进步。8．药物在溶剂体系中的溶解性及与高分子材料的相容性是影响药物能否被纤维成功包埋的直接因素，一般脂溶性药物易于被脂溶性的高分子纤维包埋。因此，水溶性的盐酸阿霉素难于被包埋在脂溶性的PLLA纤维内部，在纤维外面和表面存在大量盐酸阿霉素的颗粒。相应地，其药物释放行为存在明显的突释现象，这主要是由纤维外面和表面的盐酸阿霉素的溶解、扩散造成的。而经去盐酸化的阿霉素的脂溶性较好，因此，在PLLA纤维中的包埋及释放行为均得到明显的改善，可实现阿霉素的恒速释放，无突释行为。9．SEM照片显示，药物模型利福平被完全包埋在PLGA（80／20）纤维内部，利福平-PLGA（80／20）纤维在PBS中的释放速率是随着纤维中利福平含量的增加而增加的，利福平的含量越大，其释放速率越快。在释放前期，利福平的扩散起主导作用，而在释放后期，其释放行为则是利福平扩散和PLGA（80／20）降解的双重作用结果。适当增加利福平在纤维中的含量（30wt％），则可以获得恒速的释放行为。10．PBS中TEBAC或SDS浓度的增加会在一定程度上使利福平-PLGA（80／20）纤维的释放速率加快，这主要是由于表面活性剂会降低PBS的表面张力，增加水对PLGA（80／20）纤维的浸润能力，从而加快了利福平的扩散速度。