Fabrication Of PU/PNIPAAm Electrospun Fiber And Release Behavior Of Nifedipine

In this paper, electrospun fibers with biocompatible polycaprolactone-based polyurethane (PU) and thermo-sensitive poly(N-isopropylacrylamide)(PNIPAAm) were fabricated by the electrospinning method. The morphology of the electrospun fibers and its composites with nifedipine (NIF) were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The interactions between fibers and NIF were introduced by Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The thermo-sensitivity of electrospun fibers film was characterized by the contact angle (CA) measurements. The release behavior of NIF from electrospun fibers was observed by SEM and demonstrated by UV-vis spectroscopy. The release behavior of NIF from PU, PNIPAAm, P(NIPAAm-co-AAc), PU/PNIPAAm blend and PU-based core-shell electrospun fibers was investigated, respectively.NIF and PCL-based PU composite fibers prepared by blend electrospinning promoted dispersion of NIF in electrospun fibers. NIF dispersed in PU matrix without embedding on the surface of electrospun fibers. NIF was released from fibers upon PU degradation in phosphate buffer solution (PBS). The amount of NIF released from electrospun fiber films was relatively constant. Compared with the coated films, the release amount of NIF was reduced from70%to53%after24h. This demonstrated that electrospun fibers film with large surface area enhanced absorption for NIF and favored controlled release of NIF.The hydrophilicity and hydrophobicity of thermo-sensitive PNIPAAm with NIF electrospun fibers could be controlled by changes of temperature and NIF release also could be controlled. Below the LCST of PNIPAAm, PNIPAAm with NIF electrospun fibers dissolve more easily in PBS and the cumulative release amount of NIF achieved60%after9h. When the temperature exceeded the LCST of PNIPAAm, electrospun fibers did not dissolve in PBS and the cumulative release amount was less than20%. After blended with PU, the wettability of PU/PNIPAAm electrospun fibers could be regulated and the tensile strength of the fibers film increased from1.6MPa to3.0MPa. NIF exhibited a sustained release from PU/PNIPAAm composite electrospun fibers and the release amount reached30%at25℃, but was only10%at42℃after9h, achieved controlled release of drug. The higher temperature favored more stable release of NIF through the introduction of PU and this is basis of the thermo-sensitive effect of PNIPAAm.The LCST of the PNIPAAm could be adjusted from32℃to37℃by copolymerization with the hydrophilic monomer AAc. P(NIPAAm-co-AAc) copolymers with thermo-and pH-sensitivity were synthesized by copolymerization. Due to the presence of AAc component, the hydrophilicity of P(NIPAAm-co-AAc) copolymer electrospun fibers was stronger than that of PNIPAAm homopolymer. When the temperature exceeded37℃, the release amount of NIF from P(NIPAAm-co-AAc) electrospun fibers could be controlled by adjusting the pH values of PBS. At37℃, the release amount of NIF was73%in PBS at (pH7.4) and was only30%at (pH4.2) after9h. This illustrated the lower pH values favored the slow release of NIF. Incorporation of PU decreased the release rate of NIF from P(NIPAAm-co-AAc) electrospun fibers. In the same environment of37℃and pH7.4, the release amount of NIF decreased to32%after9h.Core-shell structured electrospun fibers with PU as the outer component and water-soluble polymer PVP or PNIPAAm as the inner components were fabricated using a home-made coaxial needle. The electrospinning process of PU-based core-shell structure electrospun fibers was investigated. Different morphologies of core-shell fibers could be obtained by changing the flow rate ratio of inner and outer solution. The core-shell fibers with relatively uniform diameter were fabricated with the outer flow rate of0.16mL/h and the inner flow rate of0.08mL/h. PVP/PU and PNIPAAm/PU core-shells with the outer wrapping shell of PU NIF-loaded fibers were obtained. The release behavior of NIF from the PU-based core-shell electrospun fiber was studied. The release rate of NIF from core-shell structural fibers was slower than that from the composite fibers. The cumulative release amount of NIF from core-shell fibers reached43%after8h and them retained unchanged. The cumulative release amount of NIF from composite fibers reached56%after24h. Thus, core-shell structured electrospun fibers with PU shells and NIF cores enabled controlled NIF release of NIF.