Study On Preparation Of PLCL And DEX/PLCL Ultrafine Core/shell Fibers

Although endowed with good biocompatibility and biodegradability, poly(L-lactic acid) (PLLA) is a highly hydrophobic and brittle polymer that is not suitable to use as drug or growth factor carriers. When hydrophilic poly(ethylene glycol) (PEG) and flexible poly(ε-caprolactone) (PCL) are introduced in PLLA macromolecular chains, the obtained poly(L-lactide-co-ε-caprolactone) copolymers (PLCL) present better hydrophilicity and flexibility. Besides, by changing the fraction of PLLA, PEG and PCL, the hydrophilicity/hydrophobicity and mechanical properties of PLCL copolymers can be adjusted, so that they exhibit a good of potential applications in controlled drug delivery, tissue engineering and so on. In this study, a series of PLCL copolymers with different molar ratios of L-lactide (L-LA) andε-caprolactone (CL) were synthesized by the ring-opening polymerization (ROP), and then one of them was chosen as the shell polymer, and dextran (DEX) was used as the core one in coaxial electrospinning. After that, core/shell fiberous membranes of DEX/PLCL with platelet derived growth factor-bb (PDGF-bb) encapsulated in the core were produced, and controlled release behaviours and cell compatibility of these electrospun membranes were studied.Four kinds of PLCL were produced by ROP of L-LA and CL, with Sn(Oct)2 as the catalyst and PEG2000 as the reaction initiator. The structures were investigated by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the relative molecular mass and molecular mass distribution were detected by gel permeation chromatography. The contact angle test indicated that with the introduction of PEG component, the hydrophilicities of the copolymers were greatly improved. Results of the differential scanning calorimetry indicated that when L-LA and CL were of the same feed ratio, the higher the PEG content was,and the lower the values of Tg of PLCL appeared, and when PEG content was fixed, Tg decreased with the growing of CL content.Fibrous core/shell membranes of DEX/PLCL were produced by coaxial electrospinning. The morphology and structure of ultrafine fibers were investigated by scanning electron microscope, transmission electron microscope and laser scanning confocal microscopy. Due to the introduction of the DEX component, the DEX/PLCL electrospun membranes showed relatively larger water absorption in phosphate buffer solution (PBS) than that of PLCL electrospun membrane, but worse tensile properties in dry states. With increasing the DEX contents, DEX/PLCL membranes gained better elongation but worse tensile stress in wet state than in dry state.Three fibrous DEX/PLCL membranes containing PDGF-bb [DEX(PDGF-bb)/PLCL] were produced by coaxial electrospinning via changing the flow rate of the core solution. The loading efficiency of PDGF-bb in DEX(PDGF-bb)/PLCL-1 with 0.1 mL/h flow rate of the core solution was much lower than the rest two, and didn't show obvious burst release, in two days only 14.4% of PDGF-bb was released. With the increasing flow rate of the core solution, the loading efficiency of PDGF-bb rose significantly, but the burst releases of DEX(PDGF-bb)/PLCL-2 and DEX(PDGF-bb)/PLCL-3 in the first 2 days were also obvious. After that, the release behaviors of all the three membranes were much smoother and steadier. The three DEX(PDGF-bb)/PLCL membranes all could keep fibrous morphologies during the whole release process.Studies on cell adhesion, proliferation and morphology on the fibrous membranes of PLCL, DEX/PLCL-2 and three DEX(PDGF-bb)/PLCL showed that all the five membranes could mimic the structure of ECMs and positively promote cell-cell and cell-matrix interactions because hydrophilicity and charge balance.