Thermal Regulating And Controlled Releasing Properties Of Poly (Lactic Acid) Matrix Electrospun Fiber Membranes With Multilevel Structure

Conventional dressings suffer from the deficiencies of not being able to deliver medication on time and having a single function,making it difficult to meet the growing market demand for wound care.Electrostatic spinning technology is an efficient method for preparing micro and nanofibers with flexibility in spinning substrate selection and structural tunability.Micro and nanofiber membranes with multi-stage structure can be prepared by coaxial electrostatic spinning method to load drugs in fibers and achieve controlled release of drugs through structural regulation to obtain functional medical dressings.Firstly,in this study,porous skin-core structure PLA/PEG fiber membranes were obtained by coaxial electrostatic spinning technique with polyethylene glycol（PEG）as the core layer and poly（lactic acid）（PLA）as the skin layer,using solvent dichloromethane（DCM）and non-solvent N,N-dimethylformamide（DMF）through phase separation.The effects of core layer advancement speed and skin layer advancement speed on the morphology,phase change temperature regulation performance,thermal stability performance,drug release control performance and hydrophilicity of PLA/PEG fiber membranes were investigated.The results showed that PLA/PEG fiber membranes with a pore size of 325.9 nm and a fiber diameter of9.8μm were obtained at a core advancement speed of 0.6 mm·min^-1 and a skin advancement speed of 1.4 mm·min^-1.The results showed that the PLA/PEG fiber membranes had an obvious heat absorption peak on the heating curve with phase change enthalpies ranging from 76.0 J·g^-1 to 138.0 J·g^-1,which increased with the increase of the core layer advancement speed and decreased with the increase of the skin layer advancement speed.It was also observed that the PLA/PEG fiber membrane can absorb latent heat energy and reduce the temperature in the phase change temperature range,which has a thermoregulatory effect.The drug release behavior of PLA/PEG fiber membranes was investigated by adding the reactive red dye X-3B as a simulated drug to the core PEG layer.The results showed that the porous skin-core structure PLA/PEG fiber membranes had a temperature-controlled drug release effect by increasing the release efficiency of reactive red dye X-3B by 9%～25%in the phase change temperature range of PEG.Secondly,TD/PLA fiber membranes were prepared by uniaxial electrostatic spinning technique using co-blended tetradecanol/poly（lactic acid）（TD/PLA）as the spinning solution.The effects of TD concentration on the morphology,thermoregulation performance,thermal stability performance and mechanical properties of TD/PLA fiber membranes were investigated.The results showed that TD/PLA fiber membranes with a fiber diameter of 4.4μm were obtained at a TD concentration of 3%.By releasing TD from the 3%TD/PLA fiber membrane,it was observed that the surface of the treated fiber membrane was rough and showed microporous structure.The results showed that the PLA/PEG fiber membranes had a clear heat absorption peak on the warming curve with phase change enthalpies ranging from 35 J·g^-1 to102 J·g^-1,which increased with the increase of TD.Meanwhile,it is observed that the PLA/PEG fiber membrane’s can absorb latent heat energy and lower the temperature in the phase change temperature range,which has a thermoregulation effect.Based on the above findings,this thesis used coaxial electrostatic spinning method to obtain skin-core structure TD/PLA/PVA fiber membrane with polyvinyl alcohol（PVA）as the core layer and co-blended TD/PLA solution as the skin layer.The effects of core layer advancement speed on fiber morphology,temperature regulation performance,thermal stability performance and controlled drug release performance were investigated.The results showed that TD/PLA/PVA fiber membranes with microporous structure and fiber diameter of 3.2μm were obtained at the core layer advancement speed of 0.12 mm·min^-1.The results show that the TD/PLA/PVA fiber film has a clear heat absorption peak on the heating curve with the phase change enthalpy ranging from 27 J·g^-1 to 50 J·g^-1,which decreases with the increase of the core layer advancement speed.Meanwhile,it was observed that the TD/PLA/PVA fiber film could absorb latent heat energy and reduce the temperature in the phase change temperature range,which has a thermoregulatory effect.Active red X-3B was added to the core layer PVA to study the drug release behavior of TD/PLA/PVA fiber film.The results showed that TD/PLA/PVA fiber membranes had a temperature-controlled drug release effect by increasing the release concentration of active red dye X-3B in the phase change temperature range of TD from 0.4mg·m L^-1 to 0.5 mg·m L^-1.Secondly,the morphology of TD/PLA/PVA fiber membranes after the release of X-3B was observed,and the results showed that the TD/PLA/PVA fiber membranes had a microporous structure.The results showed that TD dissolved in the phase change temperature range and the reactive red dye X-3B in the core layer was released through the porous structure.In summary,poly（lactic acid）-based fiber membranes with both phase change modulation and controlled drug release properties and multi-level structure were prepared by electrostatic spinning technology in this study,which have broad application prospects in functional medical dressings.