THERMAL-SENSITIVE BETA-CYCLODEXTRIN-CONTAINING POLY(NISOPROPYLACRYLAMIDE)HYDROGELS CROSSLINKED BY Si—O—Si BONDS—SYNTHESIS,CHARACTERIZATION AND PROLONGING IN VITRO RELEASE OF 5-FLUOROURACIL

A series of novel p（N-isopropylacrylamide） （PNIPAM） hydrogels were synthesized by radical copolymerization of N-isopropylacrylamide （NIPAM） and 3-methacryloxypropyltrimethoxysilane （MPTMS）. The copolymers were then crosslinked through hydrolysis of the siloxane in acetic acid/water mixed solvent. Beta-cyclodextrin （Beta-CD） was introduced into the polymeric networks by condensation of 3-glycidoxypropyltrimethoxysilane derived beta-cyclodextrin （KH560-beta-CD） with MPTMS under acidic condition. These gels were heterogeneous, porous and exhibited fast deswelling kinetics when the temperature was elevated to above lower critical solution temperature （LCST）. The swelling ratios of the gels containing beta-CD at room temperature were higher than that of the normal PNIPAM hydrogel, which was caused by the lower crosslinking density in beta-CD contained gels. In comparison to that of the normal PNIPAM gel, the amount of loaded-drug in the hydrogel containing beta-CD was higher, and the release time of 5-fluorouracil （5-Fu） was prolonged, which was attributed to the formation of inclusion compounds between 5-Fu and beta-CD in gel network.

Tribological behavior of thermal- and pH-sensitive microgels under steel/CoCrMo alloy contacts

The tribological behavior of 316L stainless steel/CoCrMo alloy contacts under aqueous lubrication was investigated in this work.Three types of microgels including poly(N-isopropylacrylamide)(PNIPAM),polyacrylic acid(PAA),and poly(N-isopropylacrylamide-co-acrylic acid)(PNIPAM-co-PAA)were prepared and used as lubricant additives in aqueous solutions.Tribological tests were conducted using a ball-on-disk reciprocating tribometer,over a range of temperatures,pH,and concentrations of the microgels.The PNIPAM-co-PAA microgels were proven to have excellent anti-friction and anti-wear properties,depending on the temperature and pH values of the solutions.The maximum friction coefficient coincided with the lower critical solution temperature of the PNIPAM-co-PAA microgels at 32°C.At the same time,the friction coefficient increased with the increase in pH value of the lubricant solution with the PNIPAM-co-PAA microgels.The unique thermal-and pH-sensitive properties of the PNIPAM-co-PAA microgels provided a new strategy for controlling the friction and wear of steel/CoCrMo alloy contacts under aqueous lubrication.

Diethanol Ammonium-borate Based Polybetaine with Tunable UCST Phase Transition

A betaine-type styrene monomer with the quaternary ammonium-borate anion inner-salt pair was synthesized through the quatemization reaction and polymerized to afford the target polybetaine of poly（4-vinylbenzyl methyl-diethanol ammonium borate） （PVMAB）. The chemical structures of the monomer and polymer were well demonstrated with 1H-NMR and llB-NMR spectra analysis. The thermal-sensitive experiment showed that PVMAB in water afforded gradually well- defined sigmoidal transmittance-temperature （T-t） curves along with the increasing polymer concentration. However, the phase transition temperatures at the bottom of the S-shaped curves were always below l0 ~C due to the very weak zwitterionic association of the ammonium-borate inner-salt pairs. The UCST phase transition could also be tuned by changing the ethanol content in the ethanol/water mixture. And the cytotoxicity experiment demonstrated the good biomimetic property of PVMAB. This study enriches the toolbox of polybetaines by introducing the quaternary ammonium- borate anion zwitterionic pair in the repeat units, therefore broadens the scope of synthetic polybetaines.