Effect of blending tricalcium phosphate on hydrolytic degradation of a block polyester containing poly(L-lactic acid) segment

The effect of blending tricalcium phosphate (TCP) on hydrolytic degradation of a new type of poly(L-lactic acid)/poly(ethylene;hexamethylene/ sebacate) block polyester (60 : 40 wt%) was studied. 100- and 250-μm film specimens blended with 0, 10, and 30 wt% TCP were immersed in phosphate buffered saline (pH 7.4) at 37°C for up to 80-104 weeks. At appropriate intervals, water absorption, dry and wet tensile strength, molecular weight, and thermal properties of the specimens were measured by weighing, tensile strength testing, size exclusion chromatography, and differential scanning calorimetry, respectively. Some samples were characterized by H NMR spectroscopy. Blending of TCP with the block polyester was effective in retarding degradation. The blended TCP was thought to retard degradation for the most part by neutralizing the lactic acid oligomers produced by hydrolysis of the poly(lactic acid) part during the initial stage of degradation.     

Surface Chemistry of Amphiphilic Polysiloxane/Triethyleneglycol‐Modified Poly(pentafluorostyrene) Block Copolymer Films Before and After Water Immersion

New amphiphilic block copolymers Si‐EFSx composed of a poly(dimethyl siloxane) (Si) block and a poly(4‐(triethyleneglycol monomethyl ether)‐2,3,5,6‐tetrafluorostyrene) (EFS) block are synthesized by atom transfer radical polymerization (ATRP) starting from a bromo‐terminated Si macroinitiator. Similarly, new hydrophobic block copolymers Si‐FSy consisting of an Si block and a poly(pentafluorostyrene) (FS) block are prepared for comparison. X‐ray photoelectron spectroscopy (XPS) analysis on block copolymer films reveals that the Si block is concentrated at the polymer–air interface, while the EFS block is located in the layers underneath. The same polymer films undergo a marked surface reconstruction after immersion in water for 7 d, as probed by XPS. This phenomenon involves the exposure of the hydrophilic oxyethylenic chains to contact water. Such surface reconstruction is even more drastic when an amphiphilic block copolymer is dispersed in a cross‐linked poly(dimethyl siloxane) matrix film.

     

聚乙二醇-柠檬酸共聚物(PEGCA)对聚乳酸的增韧及其机理

通过缩聚反应制备聚乙二醇-柠檬酸共聚物(PEGCA),通过密炼制备了PEGCA与聚乳酸(PLA)的共混物,研究了PEGCA对共混物的形貌结构、热性能和力学性能的影响。结果表明,PEGCA与PLA部分相容,PEGCA呈球状颗粒分散在PLA基体中。PEGCA对PLA有良好的增韧效果,当PEGCA质量分数为15%时,材料的断裂伸长率提高到327.9%,冲击强度提高到63.0 J/m。同时利用空穴化理论解释PEGCA增韧PLA的机理,用临界韧带厚度理论和J积分定量描述增韧的效果。     

Study of the water structure in poly(methyl methacrylate-block-2-hydroxyethyl methacrylate) and its relationship to platelet adhesion on the copolymer surface

The water structure and platelet compatibility of poly(methyl methacrylate (MMA)-block-2-hydroxyethyl methacrylate (HEMA)) were investigated. The molecular weight (Mn) of the polyHEMA segment was kept constant (average: 9600), while the Mn of the polyMMA segment was varied from 1340 to 7390. The equilibrium water content of the copolymers was found to be mainly governed by the HEMA content. The water structure in the copolymers was characterized in terms of the amounts of non-freezing and freezing water (abbreviated as W_nf and W_fz, respectively) using differential scanning calorimetry. It was found that the W_nf for the copolymers were higher than those estimated from the W_nf for the HEMA and MMA homopolymers and that the amount of excess non-freezing water depended on the polyMMA segment length. In addition, X-ray diffraction analysis revealed that some of the copolymers had cold-crystallizable water. These facts suggested that the polyMMA segments were involved in determining the water structures in the copolymers. Furthermore, the platelet compatibility of the copolymers was improved as compared to that of the HEMA homopolymer. It was therefore concluded that the platelet compatibility of the copolymer was related to the amount of excess non-freezing water.     

Fabrication of a live cell-containing multilayered polymer hydrogel membrane with micrometer-scale thickness to evaluate pharmaceutical activity

We propose a spinning-assisted layer-by-layer method for simple fabrication of a multilayered polymer hydrogel membrane that contains living cells. Hydrogel formation occurred based on the spontaneous cross-linking reaction between two polymers in aqueous solution. A water-soluble 2-methacryloyloxyethyl phosphorylcholine polymer bearing phenylboronic acid groups (PMBV) and poly(vinyl alcohol) (PVA) were used as polymers for hydrogel membrane formation. Changing the number of hydrogel membrane layers, polymer concentration, spinning rate, and processing time for diffusion-dependent gelation of PMBV and PVA facilitated the regulation of the multilayered polymer hydrogel membrane thickness and morphology. We concluded that a multilayered polymer hydrogel membrane prepared using 5.0 wt% PMBV and 5.0 wt% PVA at a spinning rate of 2000 rpm was suitable for precise spatial control of cells in single layers. This multilayered polymer hydrogel membrane was used to prepare a single cell-laden layer to minimize barriers to the diffusion of bioactive compounds while preserving the three-dimensional (3-D) context. The pharmaceutical effects of one of the anticancer agents, paclitaxel, on a human cervical cancer line, HeLa cells, were evaluated in vitro, and the usability of this culture model was demonstrated.     

Effects of environmental parameters and composition of poly(2-hydroxyethyl methacrylate)-graft-polyamine copolymers on the retention of rat lymphocyte subpopulations (B- and T-cells)

Retention behavior of rat lymphocyte subpopulations (B- and T-cells) was investigated on poly(2-hydroxyethyl methacrylate)-graft-polyamine (HA) copolymers with various copolymer compositions. Separation mechanism of B- and T-cells was then evaluated by focusing on several parameters, such as pH, temperature, and ionic strength. The interaction of lymphocytes with HA surfaces was mainly through the electrostatic force from their retention profile at varying ionic strengths of the medium. Temperature also has a crucial effect on the response of lymphocytes toward pH-induced phase transition of polyamine grafts at the polymer interface with aqueous milieu. At 4°C, both B- and T-cells showed minimal retention on HA surfaces at pH 8. At this pH, polyamine grafts existed in a compact conformation with a low degree of protonation. However, at pHs below 8, at which polyamine grafts existed in extended conformation, the resolution of B- and T-cells was achieved. In contrast, at 23°C, the phase transition of polyamine grafts significantly influenced T-cell retention, resulting in a decrease in the retention of T-cells on HA with polyamine in a compact conformation. Consequently, preferential retention of B-cells was achieved under this condition. The polyamine content was found to be another important factor affecting the retention behavior of lymphocyte subpopulations. On HA copolymers with low polyamine content (HA7, HA10), conformational transition of polyamine grafts showed a significant influence for B-cell retention, although the influence decreased with increasing polyamine content. From the study estimating the effect of neuraminidase treatment of lymphocytes on their retention to HA surfaces, sialic acid residues on the plasma membrane surface of lymphocytes are suggested as feasible anionic sites showing electrostatic interaction with polyamine grafts.     

The role of protonation and conformational transition of polyamine grafts in platelet retention to polyamine-graft-PHEMA copolymer surfaces

Blood platelet retention on polyamine-graft-poly(2-hydroxyethyl methacrylate) (PHEMA) copolymer (HA) surface was investigated, focusing on pH and ionic strength of the surrounding medium to elucidate the nature of ionic interaction between platelets and HA copolymer surfaces. The conformational transition of polyamine graft chain in response to the protonation degree of amino groups was demonstrated to be an important factor influencing platelet retention on HA surfaces. When the polyamine graft chain exists in an extended conformation, protonated amino groups distribute from the matrix interface into the aqueous interior, resulting in the effective ionic interaction with platelets to increase their retention on HA copolymer surfaces. The number of protonated amino groups in polyamine portions crucially affected platelet retention. Worth noticing is that an introduction of a small but definite amount of cationic sites on the polymer surface led to significantly minimized platelet retention. It is considered that the surface property of PHEMA was drastically changed to a non-adhesive surface by introducing a small amount of protonated amino groups.     

Cell-attachment activities of surface immobilized oligopeptides RGD,RGDS, RGDV,RGDT, and YIGSR toward five cell lines

Tetrapeptides, Arg-Gly-Asp-Ser (RGDS), Arg-Gly-Asp-Val (RGDV), and Arg-Gly-Asp-Thr (RGDT), respectively, appearing in the cell-attachment domains of fibronectin, vitronectin, and collagen, and pentapeptide Tyr-Ile-Gly-Ser-Arg (YIGSR) appearing in B1 chain of laminin, were synthesized by liquid-phase procedure. Bioactivities of RGD, RGDX (X=S, V and T), YIGSR, and YIGSR-NH₂ as cell recognition determinants were investigated by cell-attachment test using these oligopeptides immobilized to ethylene-acrylic acid copolymer (PEA) film. The cell lines used were A431, NRK, CHO-K1, HeLa.S3, and RLC-16 cells. It was found that the residue X in RGDX plays an important role for cell-attachment activity of RGDX, and, regarding YIGSR, introduction of NH₂ residue at the C-terminal of the pentapeptide enhances the cell-attachment activity.     

Polystyrene‐block‐Polyisoprene Diblock‐Copolymer Micelles: Coupled Pressure and Temperature Effects

The structural changes of diblock‐copolymer micelles under pressures from 200 to 16 000 psi are investigated using small‐angle neutron scattering (SANS). Asymmetric polystyrene‐block‐polyisoprene (PS–PI) diblock copolymers are dissolved in decane, a selective solvent for PI, to form spherical micelles with a core of PS and a corona of PI. The micellar solutions are put under pressure at temperatures of 25 to 60 °C. At room temperature, elevating the pressure from 200 to 16 000 psi has no effect on the size of the micelles. While the micellar solutions remain stable, instantaneous association of micelles is detected. In contrast to micelles at atmospheric pressure, increasing the temperature at elevated pressures does not lead to dissociation of micelles; instead, the micelles aggregate and evolve into sheet‐like structures, reminiscent of a macroscopic phase separation. Furthermore, higher pressures lead to a smaller temperature range in which shape transitions take place.

     

Tandem Action of SNS–Cr and CGC–Ti in Preparation of Ethylene–1‐Hexene Copolymers from Ethylene Feedstock

Ethylene–1‐hexene copolymer materials, ranging from semicrystalline linear low‐density poly­ethylene (LLDPE) to completely amorphous polyethylenes (PEs), are prepared from ethylene alone in a single reactor by the tandem polymerization of bis(2‐dodecylsulfanyl‐ethyl)amine–CrCl₃ (SNS–Cr) and (N‐tert‐butylamido) (tetramethylcyclopentadienyl)–titanium dichloride (CGC–Ti) at 75 °C and under atmospheric pressure. The polymerization activities are on the order of 10⁵–10⁶ g (mol Ti)^?1 h^?1. 1‐Hexene incorporation in the resulting copolymers can be adjusted by varying the Cr–Ti molar ratio and/or applying a short period of pre‐trimerization. Copolymers with high 1‐hexene incorporation up to 15 mol% are obtained. Few vinyl and vinylene chain ends are detected by ¹³C NMR, suggesting that 1‐hexene does not act as a chain‐transfer agent. Narrow molecular‐weight distributions with polydispersities from 1.9 to 2.6 are obtained, characteristic of a single‐active‐site nature of the catalyst system.