A series of well-defined poly(D,L-lactide) and poly(ε-caprolactone) macromonomers (M n of ∼ 600 and ∼1200 Da) bearing a (meth)acrylate group at one side of the chain and either a hydrophobic nonpolar butyl group or a hydrophilic polar hydroxyl group at the other side of the chain were synthesized via 1,8-diazabicyclo[5.4.0]undec-7-ene-catalyzed ring-opening polymerization (ROP) of D,L-lactide and methanesulfonic acidcatalyzed ROP of ε-caprolactone, respectively. Then, a series of well-defined random copolymers (M n of ∼ 30 000 Da, Đ < 1.25) were prepared via reversible addition−fragmentation chain transfer (RAFT)-mediated copolymerization of N-isopropylacrylamide with these macromonomers. It was found that the cloud point temperature of the graft copolymers almost linearly decreased from 32.1 to ∼14 °C, with increasing the content of the polyester macromonomer with a hydrophobic butyl end group in a copolymer chain from 0 to 17 wt %. A much smaller shift in the transition temperature (from 32.1 to ∼ 23 °C) was observed for the graft copolymers of N-isopropylacrylamide with polyesters bearing a polar hydroxyl group at the chain end. The thermoresponsive behavior dependence on the copolymer composition of the synthesized graft copolymers or their binary mixtures with poly(N-isopropylacrylamide) (PNIPAM) was also demonstrated in this study. Finally, it was proved that the obtained graft copolymers showed no cytotoxicity, and films prepared from these copolymers displayed better cell adhesion as compared to those prepared from neat PNIPAM.
Superior polymers represent a promising alternative to mechanical and biological materials commonly used for manufacturing artificial heart valves. The study is aimed at assessing poly(styrene-block-isobutylene-block-styrene) (SIBS) properties and comparing them with polytetrafluoroethylene (Gore-texTM, a reference sample). Surface topography of both materials was evaluated with scanning electron microscopy and atomic force microscopy. The mechanical properties were measured under uniaxial tension. The water contact angle was estimated to evaluate hydrophilicity/hydrophobicity of the study samples. Materials’ hemocompatibility was evaluated using cell lines (Ea.hy 926), donor blood, and in vivo. SIBS possess a regular surface relief. It is hydrophobic and has lower strength as compared to Gore-texTM (3.51 MPa vs. 13.2/23.8 MPa). SIBS and Gore-texTM have similar hemocompatibility (hemolysis, adhesion, and platelet aggregation). The subcutaneous rat implantation reports that SIBS has a lower tendency towards calcification (0.39 mg/g) compared with Gore-texTM (1.29 mg/g). SIBS is a highly hemocompatible material with a promising potential for manufacturing heart valve leaflets, but its mechanical properties require further improvements. The possible options include the reinforcement with nanofillers and introductions of new chains in its structure.
We introduce new oxygen-and moisture-proof polymer matrices based on polyisobutylene (PIB) and its block copolymer with styrene PIB-b-PSt for encapsulation of colloidal semiconductor nanocrystals. In order to prepare transparent and processable composites, we developed a special procedure of the nanocrystal surface engineering including ligand exchange of parental organic ligands to inorganic species followed by attachment of specially designed shortchain PIB functionalized with amino-group (PIB-NH2). The latter provides excellent compatibility of the particles with the polymer matrices. As colloidal nanocrystals we chose CdSe nanoplatelets (NPLs), since they possess a large surface and thus are very sensitive to the environment, in particular in terms of their limited photostability. The encapsulation strategy is quite general and can be applied Final edited form was published in "ACS Applied Nano Materials". 2019, 2 (2), S. 956 -963.
Nanocomposites based on poly(styrene-block-isobutylene-block-styrene) (SIBS) and single-walled carbon nanotubes (CNTs) were prepared and characterized in terms of tensile strength as well as bio- and hemocompatibility. It was shown that modification of CNTs using dodecylamine (DDA), featured by a long non-polar alkane chain, provided much better dispersion of nanotubes in SIBS as compared to unmodified CNTs. As a result of such modification, the tensile strength of the nanocomposite based on SIBS with low molecular weight (Mn = 40,000 g mol–1) containing 4% of functionalized CNTs was increased up to 5.51 ± 0.50 MPa in comparison with composites with unmodified CNTs (3.81 ± 0.11 MPa). However, the addition of CNTs had no significant effect on SIBS with high molecular weight (Mn~70,000 g mol−1) with ultimate tensile stress of pure polymer of 11.62 MPa and 14.45 MPa in case of its modification with 1 wt% of CNT-DDA. Enhanced biocompatibility of nanocomposites as compared to neat SIBS has been demonstrated in experiment with EA.hy 926 cells. However, the platelet aggregation observed at high CNT concentrations can cause thrombosis. Therefore, SIBS with higher molecular weight (Mn~70,000 g mol−1) reinforced by 1–2 wt% of CNTs is the most promising material for the development of cardiovascular implants such as heart valve prostheses.
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