Study On The Synthesis, Electrospinning And Drug Release Properties Of Glyceryl Polylactic Acid

Polylactic acid（PLA）has been reported and applied in a lot of research and long-term testing in the field of biomedicine.It has many excellent properties,such as low toxicity,endogenous metabolites,and strong thermoplasticity.It is widely used in drug carriers,clinical surgical repair materials,tissue substitutes and bio-3D printing.In recent years,electrospinning and its assistant technology have been developed rapidly.As a scaffold of tissue engineering,electrospinning has the characteristics of controllable morphology,a large specific surface area and high porosity.The mats formed by electrospinning fiber can effectively simulate the cell’s supporting tissue and provide a good environment for cell growth and reproduction.It can form a good auxiliary for tissue culture,healing and growing in vivo and in vitro.The application of PLA in electrospinning technology has broadened its prospects for its application as the drug-loaded tissue engineering scaffolds or drug delivery carriers.However,the development and application of PLA electrospinning are limited due to the poor hydrophilicity,weak drug loading capacity,unclear controlled release performance and high difficulty in fiber precision control.Three-arm polylactic acid（3-arm PLA）and glycerol phosphate polylactic acid（GP-PLA）were designed and prepared in this paper.The electrospinning of the two kinds of PLA with different morphologies were prepared.The morphology control conditions of the electrospinning of3-arm PLA and GP-PLA were studied.The drug loading capacity,the release performance and the bacteriostasis of the model drugs loaded with different kinds of PLA were studied.The specific contents and achievements included:（1）Two copolymers of 3-arm PLA and GP-PLA were prepared by one-pot method with glycerol and sodium glycerophosphate as branching agents.The effects of a catalyst,the reactant ratio and the reaction time on the copolymerization reaction were studied in detail.The copolymerization process conditions with different molecular weights and molecular weight distributions were explored.The thermodynamic properties,the crystallinity,the dielectric properties and the surface properties of 3-arm PLA and GP-PLA were characterized.By controlling the reaction conditions,the mass average molecular weight（Mw）of 3-arm PLA could reach 1000 kDa,the average molecular weight dispersion index（PDI）was below 1.7,the Mw of GP-PLA could reach 800kDa,and the average PDI was below 1.8.The effects of the catalyst,the reactant ratio and the reaction time on the different products were monitored by molecular gel chromatography（GPC）.It was found that the reaction time had a great influence on the molecular weight and PDI of the copolymer.The Sn（Oct）₂ of the catalyst had an average shear effect on the“molecular arm”.The reaction time has a significant effect on the average molecular weight of the catalyst.The 3-arm PLA and GP-PLA have different properties from the linear PLA.The surface roughness of the materials is like Linear PLA>GP-PLA>3-arm PLA.The static water contact angle of GP-PLA and 3-arm PLA can reach 80°.The crystallinity of the materials is like Linear PLA>GP-PLA>3-arm PLA.The glass transition temperature（Tg）of the material is like Linear PLA>GP-PLA>3-arm PLA.The apparent dielectric constant is 3-arm PLA>GP-PLA>Linear PLA.The mechanical properties linear is PLA>GP-PLA>3-arm PLA.（2）The suitable solvents for Linear PLA,3-arm PLA and GP-PLA have been selected.The steady-state jet conditions suitable for PLA were determined by screening the viscosity of the spinning solution,the voltage of an electrostatic field,the injection speed of the spinning solution,the distance between the electric fields and the temperature.The model drugs of diclofenac potassium,avermectins and ivermectin were used as model drugs in the framework fibers and microspheres of Linear PLA,3-arm PLA and GP-PLA,respectively.The drug loading capacity and releasing characteristics of PLA was discussed in detail.The release model of the drug loaded skeleton fibers and microspheres were explored.Scanning electron microscopy（SEM）characterization and in vitro dissolution test showed that the model drug was more dispersed in 3-arm PLA electrospun skeleton fibers than in Linear PLA and GP-PLA,and the sustained release ability of 3-arm PLA skeleton was stronger in vitro release.The release rates of 3-arm PLA microspheres Linear PLA microspheres were lower than Linear PLA microspheres.The release of 3-arm PLA avermectin drug loaded microspheres was less than that of its fiber.GP-PLA loaded avermectin microspheres exhibited greater release in vitro.Weibull model was used to fit the release rate data of electrospun fibers and microspheres.Higuchi model was used to fit the cumulative dissolution curves in vitro.Experiments and fitting equations showed that the release of drug loaded fibers and microspheres consisted of the rapid release of adsorbed drugs and the sustained release of skeletal drugs.3-arm PLA has the stronger sustained-release property and its sudden release effect is lower during the release.The release characteristics of Linear PLA and GP-PLA are close to the normal rapid release,and the sudden release phenomenon is obvious during the release process.Both 3-arm PLA and GP-PLA have the photoprotective ability of ivermectin.Microspheres can effectively prevent the degradation of ivermectin.（3）By controlling the electrospinning conditions,the porous fibers and microspheres of Linear PLA,3-arm PLA and GP-PLA were successfully prepared to form the fiber mat with second-level pores.In accordance with the Breath figure effect in thermo-induced phase separation,the effects of different solvent systems and environmental humidity on the formation of porous fibers and microspheres were studied in detail.The stability of electrospinning process was explained by the diameter statistics of fibers and microspheres.Ag⁺as a model drug.Linear PLA,3-arm PLA and GP-PLA Ag⁺porous fibers and microspheres were prepared by adsorption.It was found that the change of ambient humidity and the hydrophilicity of PLA materials had some effects on the phase separation of PLA induced by the Breath figure effect.Linear PLA,3-arm PLA and GP-PLA porous fibers prepared under a certain humidity have obvious differences in morphology.By adjusting the ratio of the humidity and the solvent,the morphology and the number of porous fibers can be controlled.Adding N,N-dimethylformamide（DMF）and dimethylsulfoxide（DMSO）to the solvent can enhance the phase separation and prepare the porous fibers with deep pores.The valence of Ag⁺was characterized by an X-ray photoelectron spectroscopy（XPS）and the loading degree was qualitatively characterized.It was found that the reduction of Ag⁺was not caused by the loading process of Linear PLA,3-arm PLA and GP-PLA fibers.The Ag⁺load was corresponding to the diameter of the fiber,and the corresponding relationship with the porous fiber was weak.Porous microspheres with high dispersity could be prepared by3-arm PLA in an ethanol-chloroform solvent.The microspheres prepared by Linear PLA,3-arm PLA and GP-PLA also had the ability to support Ag⁺and the degree of adsorption of Ag⁺on the microspheres was higher than that of porous fibers.Escherichia coli and Staphylococcus aureus were used as indicator bacteria to test the antimicrobial activity.The results show that the Ag⁺porous fibers and microspheres of Linear PLA,3-arm PLA and GP-PLA have broad-spectrum antibacterial activities,and the Ag⁺porous fibers and microspheres of 3-arm PLA and GP-PLA have higher antibacterial activities than that of Linear PLA.（4）The mechanism of ultrafine fibers prepared by bead-jet method was discussed,and the process of bead-jet method was explored.Combining with the thermal properties and crystallinity analysis of Linear PLA,3-arm PLA and GP-PLA,the preparation conditions of 3-arm PLA and GP-PLA for the ultrafine fiber mats were screened.The bead-like nodes in the fiber mat was eliminated by optimizing the solvent system and the environmental humidity.The bead-like nodes of the 3-arm PLA ultrafine fiber mat were controlled in the range of 1³micron,and finally the 3-arm PLA ultrafine fiber with a diameter of 40¹00 nm and GP-PLA with a diameter of 200⁵00 nm were obtained.The mechanical properties show that the breaking elongation of the fiber mat can be effectively improved by preparing the ultrafine fibers.The suspension of Acetobacter xylinum was filtered by the ordinary fibers and the ultrafine fibers,and then cultured again with the mats.It was found that Acetobacter xylinum could enter the primary pore of the ordinary fiber mat and produce bacterial cellulose,but it could not enter the primary pore of the ultrafine fiber mat to form and grow.Through the study of this subject,the mechanism formed the high molecular weight 3-arm PLA and GP-PLA and their structure had the effects on the surface hydrophilicity.The loading and releasing properties of the skeleton electrospinning drug carrier,the influencing factors of porous morphology spinning mat and the adsorption drug loading were revealed.And a new ultrafine fiber preparation scheme was formed.These innovations provided a new preparation scheme and ideas for the formation of high molecular weight hydrophilic PLA materials,drug-loaded tissue engineering scaffolds,drug-loaded microspheres,Ag⁺antibacterial dressings,bacterial isolation dressings or new packaging.