A novel approach for UV-patterning with binary polymer brushes.

A mixed self-assembled monolayer (SAM) of an initiator (3-(2-bromo-2-isobutyryloxy)propyl triethoxysilane) for atom transfer radical polymerization (ATRP) and an agent (6-(triethoxysilyl)hexyl 2-(((methylthio)carbonothioyl)thio)-2-phenylacetate) for reversible addition-fragmentation chain transfer (RAFT) polymerization was constructed on the surface of a silicon wafer or glass plate by a silane coupling reaction. When a UV light at 254nm was irradiated at the mixed SAM through a photomask, the surface density of the bromine atom at the end of BPE in the irradiated region was drastically reduced by UV-driven scission of the BrC bond, as observed by X-ray photoelectron spectroscopy. Consequently, the surface-initiated (SI)-ATRP of 2-ethylhexyl methacrylate (EHMA) was used to easily construct the poly(EHMA) (PEHMA) brush domain. Subsequently, SI-RAFT polymerization of a zwitterionic vinyl monomer, carboxymethyl betaine (CMB), was performed. Using the sequential polymerization, the PCMB and PEHMA brush domains on the solid substrate could be very easily patterned. Patterning proteins and cells with the binary polymer brush is expected because the PCMB brush indicated strong suppression of protein adsorption and cell adhesion, and the PEHMA brush had non-polar properties. This technique is very simple and useful for regulating the shape and size of bio-fouling and anti-biofouling domains on solid surfaces.

Titanium alloy modified with anti-biofouling zwitterionic polymer to facilitate formation of bio-mineral layer.

The surface of a titanium (Ti) alloy was modified with a self-assembled monolayer of poly(ethylene glycol) methacrylate phosphate (Phosmer PE). A zwitterionic monomer (carboxymethyl betaine, CMB) could be copolymerized with the surface-bound Phosmer PE due to a flexible linker between the Ti alloy surface and a methacryloyl group of Phosmer PE. The poly(CMB) (PCMB)-modified Ti alloy plate exhibited strong suppression of protein adsorption and cell adhesion, and induced approximately twice the amount of calcium (Ca2+) deposition as compared to the unmodified Ti alloy plate. The zwitterionic polymer-modified surfaces not only showed enhanced mineralization clusters creation and growth, but they were also highly non-responsive to biologically derived materials such as proteins and cells. Therefore, it is possible to easily form highly pure and rigid hydroxyapatite layers on Ti alloy surfaces without the incorporation of organic molecules such as proteins. The present surface modification technique and strategy can be applied to implantable orthopedic materials as a means of encouraging integration with host tissues, such as the thigh bone.

Optimization of the composition of zwitterionic copolymers for the easy-construction of bio-inactive surfaces.

Random copolymers (S-PCMBx) of the zwitterionic monomer carboxymethylbetaine (CMB) and a small percentage of 3-methacryloyloxypropyl trimethoxysilane with various composition ratios were synthesized in ethanol using 2,2'-azobisisobutyronitrile as the initiator. An S-PCMBx layer formed on the glass substrate after soaking in the copolymer solution and had a thickness of 2-3 nm. The S-PCMBx-modified surface was highly hydrophilic and suppressed both the non-specific adsorption of protein (bovine serum albumin) and NIH3T3-fibroblast adhesion. The degree of adsorption suppression increased with increasing copolymer CMB content with a maximum at 90 mol % CMB. In contrast, the modification of the glass substrate with a PCMB homopolymer terminally modified with a trimethoxysilyl group did not effectively suppress protein adsorption and cell adhesion due to the low graft density. The importance of balancing the number of fixation points and the length of the zwitterionic polymer loops to produce bio-inactive metal oxide surfaces is suggested. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2029-2036, 2016.

Carboxymethylbetaine copolymer layer covalently fixed to a glass substrate.

A random copolymer of zwitterionic monomer, carboxymethylbetaine (CMB), and 3-methacryloyloxypropyl trimethoxysilane was prepared in ethanol using 2,2'-azobisisobutyronitrile as initiator. The incubation of ethanol solution of the copolymer with a glass plate gave a layer of the copolymer with a thickness of about 2-3 nm. The copolymer-modified glass substrate became highly hydrophilic upon immersion in water, and showed a resistance against non-specific adsorption of proteins, and the degree of resistance increased with the content of CMB residues in the copolymer and leveled off. The adhesion of various cells to the glass substrate was also strongly suppressed by the surface modification with the copolymer layer. Further introduction of PolyCMB graft chains on the surface of the layer enhanced the suppression of cell adhesion due to the steric hindrance for the cells to approach the layer. The usefulness of the combination of zwitterionic polymer layer and graft chains to afford anti-biofouling properties to a solid surface of metal oxides was shown.