Masahiko Annaka

Biocompatibility of Polyvinylalcohol Gel as a Vitreous Substitute

Polyvinylalcohol (PVA) hydrogel cross-linked by gamma irradiation was assessed as a possible vitreous substitute. From a series of experiments, rise of intraocular pressure and inflammatory changes in the vitreous cavity after operation were observed in some cases. Crab-eating macaques were used for this experiment. PVA gels were injected into vitreous cavity after vitrectomy and followed clinically by opthalmoscopy, tonometry, fundus photography, electroretinogram (ERG), chemotaxis, and flare cell meter. Histopathologic examination by light and electron microscopy was performed after 3 months. As a result, there were no significant changes in ophthalmoscopic findings. No abnormal rising of intraocular pressure (IOP) was recognized. ERG did not show meaningful amplitude weakness. From the photon counting of flare cell meter, significant break of blood-aqueous barrier and blood-retinal barrier was not observed. Histopathologic examination revealed that all layers of the retina were intact and no loss of tissue was evident. However, in PVA gel–injected eyes, some vacuolations of the inner retina were found in some specimens. To conclude, PVA gel was well tolerated in these experiments. The gel with a network similar to the vitreous body showed the best biocompatibility, though it is necessary to investigate the biocompatibility for the long-term. PVA gel is a good candidate for a vitreous substitute.

Thermo-responsive polymer brush-grafted porous polystyrene beads for all-aqueous chromatography

Poly(N-isopropylacrylamide) (PIPAAm) brush-grafted porous polystyrene beads with variable grafted polymer densities were prepared using surface-initiated atom transfer radical polymerization (ATRP) for applications in thermo-responsive chromatography. Utilization of these grafted beads as a stationary phase in aqueous chromatographic analysis of insulin provides a graft density-dependent analyte retention behavior. The separations calibration curve on PIPAAm-grafted polystyrene was obtained using pullulan standards and exhibited inflection points attributed to analyte diffusion into bead pores and partitioning into grafted PIPAAm brush surfaces. Presence of these inflection points supports a separation mechanism where insulin penetrates pores in polystyrene beads and hydrophobically interacts with PIPAAm brushes grafted within the pores. Control of PIPAAm brush graft density on polystyrene facilitates effective aqueous phase separation of peptides based on thermally modulated hydrophobic interactions with grafted PIPAAm within stationary phase pores. These results indicated that PIPAAm brush-grafted porous polystyrene beads prepared by surface-initiated ATRP was effective stationary phase of thermo-responsive chromatography for aqueous phase peptide separations.

Salt-induced volume phase transition of poly(N-isopropylacrylamide) gel

The salt effect on the phase transition of N-isopropylacrylamide (NIPA) gel was studied. The swelling behavior of the NIPA gel strongly depends on the salt concentration and is well described as a function of the chemical potential difference of water molecules in solution from that at the transition. From the analysis of the OH stretching, Raman spectra in water and in various aqueous solutions in terms of collective proton motions reveals that the presence of salts tends to disrupt or distort the water molecules in hydrophobic hydration shell around the NIPA gel. This leads to inducing the growth of the cluster shell around the salts, which leads to gel collapse. The volume phase transitions due to the different types of perturbation (temperature, salt) are induced by the same mechanism, hydrophobic hydration and dehydration, and therefore can be described in a unified manner in terms of the chemical potential and the collective proton motions of water molecules.

Dimensions of a Free Linear Polymer and Polymer Immobilized on Silica Nanoparticles of a Zwitterionic Polymer in Aqueous Solutions with Various Ionic Strengths

The dimensions and intermolecular interactions of a surface-grafted and unbound free polyampholyte, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), were estimated in aqueous solutions with various ionic strengths. Free linear PMPC was synthesized by atom-transfer radical polymerization (ATRP), and static light scattering (SLS) and dynamic light scattering (DLS) were carried out for the PMPC solutions with various concentrations of NaCl, c s. The hydrodynamic radius R H and the second virial coefficient A 2 of PMPC were independent of c s (0-0.5 M), though both R H and A 2 of polyampholytes usually strongly depend on the ionic strength. PMPC-immobilized silica nanoparticles (PMPC-SiNP) were also synthesized by surface-initiated ATRP, and DLS was carried out as for the solutions of linear PMPC to investigate the dependence of the dimensions of PMPC immobilized on a solid surface on the ionic strength. The molecular weight and surface density of PMPC immobilized on SiNP were estimated from the results obtained by GPC, NMR, and thermogravimetric analysis. The independence of R H of PMPC-SiNP was also observed, but its magnitude was larger than that of linear PMPC, although the molecular weight of PMPC immobilized on SiNP was smaller than that of linear PMPC. The larger dimension of PMPC immobilized on SiNP was explained by the excluded volume effect between the immobilized polymer chains.

Thermoresponsive Polymer Brush Surfaces with Hydrophobic Groups for All-Aqueous Chromatography

For developing thermoresponsive chromatographic matrices with a strong hydrophobicity, poly(N-isopropylacrylamide-co-n-butyl methacrylate) (poly(IPAAm-co-BMA)) brush grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) with a CuCl/CuCl(2)/Me(6)TREN catalytic system in 2-propanol at 25 degrees C for 16 h. The prepared beads were characterized by chromatographic analysis. Chromatograms of the benzoic-acid family and phenol as model analytes were obtained with high-resolution peaks because of their strong hydrophobic interactions to the densely grafted hydrophobized copolymers on the beads. Retention times of the analytes increased with the increase in BMA composition ratio. Dehydration of grafted copolymer with large BMA composition was performed at low temperature. These results indicated that the copolymer-brush-grafted surface prepared by ATRP was an effective tool for separating hydrophilic analytes at low temperature through modulating the strong hydrophobic interaction.

Preparation of thermo-responsive polymer brushes on hydrophilic polymeric beads by surface-initiated atom transfer radical polymerization for a highly resolutive separation of peptides

Poly(N-isopropylacrylamide-co-N-tert-butylacrylamide) [P(IPAAm-co-tBAAm)] brushes were prepared on poly(hydroxy methacrylate) (PHMA) [hydrolyzed poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate)] beads having large pores by surface-initiated atom transfer radical polymerization (ATRP) and applied to the stationary phases of thermo-responsive chromatography. Optimized amount of copolymer brushes grafted PHMA beads were able to separate peptides and proteins with narrow peaks and a high resolution. The beads were found to have a specific surface area of 43.0 m(2)/g by nitrogen gas adsorption method. Copolymer brush of P(IPAAm-co-tBAAm) grafted PHMA beads improved the stationary phase of thermo-responsive chromatography for the all-aqueous separation of peptides and proteins.

Liquid crystalline inorganic nanosheets for facile synthesis of polymer hydrogels with anisotropies in structure, optical property, swelling/deswelling, and ion transport/fixation

Macroscopically anisotropic hydrogels were synthesized by hybridization of poly(N-isopropylacrylamide) with liquid crystalline inorganic nanosheets; their anisotropies in the structure and properties are demonstrated.

Preparation of thermoresponsive anionic copolymer brush surfaces for separating basic biomolecules

Poly(N-isopropylacrylamide-co-acrylic acid-co-N-tert-butylacrylamide) (poly(IPAAm-co-AAc-co-tBAAm) brush grafted silica beads were prepared through a surface-initiated atom transfer radical polymerization (ATRP) with CuCl/CuCl(2)/Me(6)TREN catalytic system in 2-propanol at 25 degrees C for 4 h. The prepared beads were characterized by chromatographic analysis. Basic analytes, catecholamine derivatives, and angiotensin peptides could be separated by a short column length containing the beads because of its high densely grafted copolymer structure. Chromatograms for catecholamine derivatives were obtained with high resolution peaks due to their electrostatic and hydrophobic interactions to the densely grafted anionic copolymers on the beads. Effective separation of angiotensin peptides was performed near the lower critical solution temperature of copolymers, because the total electrostatic and hydrophobic interactions between the copolymer and the analytes become strong at the temperature. These results indicated that the copolymer brush grafted surfaces prepared by ATRP was an effective tool for separating basic biomolecules by modulating the electrostatic and hydrophobic interactions.

Effective separation of peptides using highly dense thermo-responsive polymer brush-grafted porous polystyrene beads

For the development of well-defined highly dense thermo-responsive polymer grafted surface as an improved stationary phase for thermo-responsive chromatography, poly(N-isopropylacrylamide) (PIPAAm) brush-grafted porous polystyrene beads were prepared by surface-initiated atom transfer radical polymerization (ATRP). The PIPAAm grafted region of polystyrene beads was adjusted by the addition of isooctane as a poor solvent for polystyrene upon the reaction of ATRP initiator immobilization. Using a thermo-responsive HPLC column containing the prepared beads with PIPAAm brush grafted on the inside pores nearby the outer surfaces, angiotensin subtypes were effectively separated with aqueous mobile phase, because the densely grafted PIPAAm on nearby the outer surface effectively interacted with the peptides hydrophobically. Retention of basic peptide was achieved by the beads with basic mobile phase. These results indicated that the prepared beads with grafted PIPAAm nearby the outer surface became an effective chromatographic stationary phase for retaining basic peptides using wide pH range of mobile phase.

Stereoregulation of Thermoresponsive Polymer Brushes by Surface-Initiated Living Radical Polymerization and the Effect of Tacticity on Surface Wettability

In this study, stereocontrolled poly(N-isopropylacrylamide) (PIPAAm) brushes were grafted from surfaces by atom transfer radical polymerization (ATRP) in the presence of a Lewis acid, and the effect of PIPAAm brush tacticity on the thermoresponsive wettabiliy was investigated. PIPAAm grafted by ATRP in the presence of Y(OTf)(3) showed high isotacticity, while the control brush polymerized in the absence of Y(OTf)(3) was clearly atactic. The isotacticity and molecular weight of PIPAAm brushes were controlled by polymerization conditions. The wettability of isotactic PIPAAm-grafted surfaces decreased slightly below 10 °C, although the phase transition temperature of atactic surface was 30 °C, and the bulk isotactic polymer was water-insoluble between 5 and 45 °C.