Studies On PH,Temperature,and Light Triple-Sensitivity Azobenzen-Containing End-Group Polymers And Their Photorenewable Antibacterial Surfaces

In recent years,although the level of healthcare has continuously improved globally,the incidence and mortality rates of bacterial infections remain high.Polymer antibacterial materials have wide applications in the field of antibacterial due to their flexible structure design,recyclability,adjustability,and safety advantages.In this paper,we first synthesized photoresponsive end-functionalized poly（N,N-dimethylacrylamide）（PDMA-AZO）with azobenzene moieties via reversible addition-fragmentation chain transfer（RAFT）polymerization of N,N-dimethylacrylamide（DMA）in the presence of the azo-containing trithiocarbonate chain transfer agent（CTA-AZO）.We then prepared p H-,temperature-,and light-triple-sensitive poly（2-（dimethylamino）ethyl methacrylate）（PDMAEMA）with end-capped azobenzene using CTA-AZO as a RAFT reagent and 2-（dimethylamino）ethyl methacrylate（DMAEMA）as the monomer.The structures of PDMA-AZO and PDMAEMA-AZO were characterized by ultraviolet spectroscopy（UV）,Fourier transform infrared spectroscopy（FT-IR）,proton nuclear magnetic resonance spectroscopy（¹H-NMR）,and gel permeation chromatography（GPC）.The photosensitivity of PDMA-AZO and the photosensitivity,temperature sensitivity,and p H sensitivity of PDMAEMA-AZO were also investigated.The results showed that the relative molecular weight of PDMAEMA-AZO was controllable,and the molecular weight distribution（PDI）was less than 1.78,enabling rapid reversible photo-induced isotropic/anisotropic transition.With the increase of PDMAEMA-AZO concentration,the lower critical solution temperature（LCST）decreased,and the phase transition window became narrower.When the p H exceeds 9.44,the LCST of PDMAEMA-AZO remains unchanged.When the p H decreases from 9.44 to 7.34,the LCST increases,and the polymer no longer exhibits thermo-sensitivity when p H is below 7.34.Under alternating UV and visible light irradiation,the LCST of PDMAEMA-AZO exhibits reversible increase and decrease.These results indicate that PDMAEMA-AZO is a p H and photo-controlled thermo-sensitive polymer with LCST.In addition,the PDMA-AZO polymer can undergo rapid and reversible photoinduced cis-trans isomerization in three types of solvents,water,ethanol,and dichloromethane,reaching photostationary state in 80 s.In addition,a reversible UV-visible light responsive intelligent antimicrobial surface was successfully constructed through self-assembly of quaternized PDMAEMA-AZO（QPDMAEMA-AZO）and aminatedβ-cyclodextrin（NH₂-β-CD）host-guest complexes.Specifically,PDMAEMA-AZO was quaternized with 1-bromohexane to obtain QPDMAEMA-AZO with strong antibacterial activity.Then,by the host-guest recognition between NH₂-β-CD and azobenzene,QPDMAEMA-AZO was assembled onto the NH₂-β-CD modified glass surface（Sub-CD）to obtain the intelligent antibacterial material of Sub@QPDMAEMA,which is highly effective in killing attached bacteria with a killing rate over 90%.Sub@QPDMAEMA can achieve photo-responsive regeneration of the antibacterial surface through reversible photoisomerization.Under UV irradiation,the trans-azobenzene moiety is converted to the cis-structure,leading to the dissociation of the cis-QPDMAEMA-AZO from the surface of Sub@QPDMAEMA and the release of dead bacteria from the surface.After the killing and release cycles,the clean Sub-CD substrate can easily regenerate the Sub@QPDMAEMA on its surface.That is,the new Sub@QPDMAEMA substrate can be regenerated by irradiating with visible light（where the cis structure of QPDMAEMA-AZO undergoes a transition to a trans structure upon visible light irradiation）or reacting with a new QPDMAEMA-AZO containing a trans isomer in NH₂-β-CD on the Sub-CD substrate.The efficient and reversible cycling of this photo-responsive antibacterial surface can provide new ideas and potential low-cost applications for the preparation of new antibacterial materials.