Preparation And Application Of Biodegradablie Coploymers Based On Photoresponsibility

Stimuli-responsive biodegradable copolymers have biocompatible and biodegradable properties and are able to respond to various environmental stimulation.Light is a controllable external environment stimulus,and the photoresponsive process does not produce by-products.Thus the photoresponsive biodegradable copolymer of micelles and hydrogels can be used in tissue engineering,drug delivery and controlled release,which will broaden applications for biomedical materials.In this paper,at the intermediate junctions of the biodegradable polyester copolymers with o-nitrobenzyl groups were designed and synthesized.Among them,the photosensitized polyethylene glycol was used as the hydrophilic segment and the polyester was the hydrophobic segment.The effects of the length of the hydrophobic segment on the light and temperature-sensitive properties of the polymer were studied systematically by 1HNMR,GPC,DLS,UV-VIS,DMA and TEM.Firstly,5-hydroxy-2-nitrobenzyl alcohol have been prepared using 5-hydroxy-2-nitrobenzaldehyde by reduction with sodium borohydride.The p-toluenesulfonate of polyethylene glycol and the sodium salt of 5-hydroxy-2-nitrobenzyl alcohol obtained photo-sensitized polyethylene alcohol by etherification reaction.The experimental results showed that the product had high purity and no fragmentation in the segment,which can meet the requirements of the next experimental reaction.Secondly,PLA-PEG-PLA and PLA-NB-PEG-NB-PLA triblock copolymers were obtained by ring-opening polymerization of D,L-lactide by polyethylene glycol and photo-sensitized polyethylene glycol as macromolecular initiators,respectively.Comparative experiments showed that the initiating activity of the sensitized polyethylene glycol was lower than that of polyethylene glycol.Preparation of photoresponsive copolymer micelles and DOX-loaded micelles by solvent evaporation method.It was found that when the hydrophilic segments were identical,the longer the hydrophobic segment was,the easier it was to form micelles.The shorter the hydrophilic polyethylene glycol in the polymer,the greater the proportion of the light-sensitive onitrobenzyl alcohol in the solution,the longer the photoresponse time.Finally,a series of PCL-PEG-PCL and PCL-NB-PEG-NB-PCL copolymers were obtained by ring-opening polymerization of ?-caprolactone by using polyethylene glycol and photo-sensitized polyethylene glycol as initiators,respectively.With the increase of temperature,self-assembly structure of a series of two copolymers aqueous solution was able to be changed and form hydrogels in the vicinity of human body temperature.Within a temperature range of composite gel,the gel was irradiated with UV for a period of time,and the gel was destroyed and became a flowing liquid.This kind of light and temperature responsive biodegradable composite hydrogel makes full use of the internal temperature response mechanism and the external light response characteristics,to achieve the purpose of internal and external control of biological materials.In summary,a series of ABA-type photoresponsive copolymers were synthesized by using synthetic biodegradable polyesters as the main raw materials.The micelles and hydrogels of photodegradable copolymers were studied,which will provide a reference value for stimuli-responsive and biodegradable of biomedical materials.