Optically active polymers having chiral 2-aminomethylpyrrolidine side chains have been newly synthesized by a radical homopolymerization of the corresponding protected acrylamide monomer and copolymerization with N-isopropylacrylamide followed by deprotection. The resulting polymers were found to be thermoresponsive showing lower critical solution temperatures (LCSTs) at 27-65 C in their aqueous solutions. The pyrrolidine side chains of the resulting thermoresponsive polymer promoted aldol reaction between cyclohexanone and p-nitrobenzaldehyde in water, and the reaction proceeded most smoothly at its LCST. Moreover, the diastereomeric ratio (syn : anti) of the aldol adducts obtained at the reaction at 40 C was 22 : 78, whereas the diastereomeric ratio (syn : anti) was 55 : 45 at 20 C. These results indicate that the pyrrolidine side chains catalyze the aldol reactions in the relatively hydrophobic field generated by the thermoresponsive polymer at its LCST.
Thermoresponsive polymers having 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties were fixed on the graphite surface by using the reversible addition-fragmentation chain transfer (RAFT) graft polymerization technique. The surface of graphite has been anodically oxidized by using our original electrochemical method, and then modified with 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoyloxy groups (RAFT reagents) by esterification with the corresponding acid chlorides. From the resulting RAFT reagent-modified graphite, 2,2,6,6-tetramethyl-4-piperidyl methacrylate (TEMPMA) and N-isopropylacrylamide (NIPAAm) monomers were copolymerized stepwise under RAFT polymerization conditions to afford the thermoresponsive block-copolymer-grafted graphite, poly(TEMPMA)-block-PNIPAAm-grafted graphite. N-Oxylation of tetramethylpiperidyl groups on the resulting graphite successfully afforded the corresponding TEMPO-containing thermoresponsive polymer-grafted graphite. Redox behavior of the resulting graphites was observed by cyclic voltammetry. The potential and intensity of the cathodic current peaks were discontinuously changed below and above the lower critical solution temperature (LCST) of the grafted thermoresponsive polymers. These results indicate that the phase transition of the thermoresponsive polymer on the graphite influences the electron transfer between the TEMPO moieties and the graphite surface.
Thermoresponsive and redox-active block copolymers having 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties have been synthesized by using the reversible addition-fragmentation chain transfer (RAFT) polymerization technique.N-Isopropylacrylamide (NIPAAm) and 2,2,6,6-tetramethylpiperidyl methacrylate (TEMPMA) monomers were copolymerized stepwise under RAFT polymerization conditions to afford the thermoresponsive block copolymers, PNIPAAm-block-PTEMPMA and PNIPAAm-block-PTEMPMA-block-PNIPAAm. Oxidation of tetramethylpiperidine groups in the copolymers successfully afforded the corresponding TEMPO-containing block copolymers. The resulting triblock copolymer was found to be thermoresponsive showing lower critical solution temperature (LCST) at 34∘C in its aqueous solution. Redox behavior of the resulting copolymer was observed by cyclic voltammetry. The potential of anodic current peak changed below and above the LCST of the block copolymer. These results indicate that the phase transition of thermoresponsive polymer influences the redox potential of TEMPO moieties.
Partitioning of organic substrates by thermoresponsive polymer having N-acryloylaminoalcohol moieties in aqueous phase has been studied. Thermoresponsive polymers, such as poly(N-isopropylacrylamide) (PNIPAAm) and poly(NIPAAm-co-N-acryloyl-(6)-alaninol) (poly(NIPAAm-co-HIPAAm)), were found to concentrate several organic substrates into the hydrophobic field generated during their phase transition. The amount of the substrates recoverd from the polymer phase mainly depended on the hydrophobicity of the substrates.
Electron beam melting (EBM) has been used to fabricate three-dimensional (3D) porous Ti-6Al-4V surfaces for acetabular cups in total hip arthroplasty. However, there are radiographic concerns regarding poor implant fixation and bone ingrowth around electron beam melted (EBMed) 3D porous cups. We hypothesize that nano-hydroxyapatite (nHA) coating can promote bone ingrowth and thus decrease the occurrence of radiolucent lines around EBMed 3D porous cups. This study aimed to investigate the effect of a novel nHA coating on the biological performance of EBMed 3D porous implants in a beagle transcortical model. Low-porosity (control) and high-porosity 3D porous Ti-6Al-4V implants were manufactured using EBM. Half of the high-porosity implants were coated with nHA without clogging the 3D pores. Implants were inserted into the femoral diaphysis of the beagles. The beagles were euthanized at 4, 8, and 12 weeks postoperatively, and push-out testing was performed. Bone ingrowth was evaluated by histological analysis. Although the increase in porosity alone had no effect on biological behavior, the addition of nHA to high-porosity 3D implants significantly improved early bone fixation and bone ingrowth into the deep region of porous structures compared to low-porosity implants. This is the first report of a novel nHA coating that improved bone ingrowth into the deeper regions of 3D porous implants, which can prevent the occurrence of radiolucent lines around EBMed 3D porous cups.
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