Yasuhide Nakayama

Biomaterial adherent macrophage apoptosis is increased by hydrophilic and anionic substrates in vivo

An in vivo rat cage implant system was used to identify potential surface chemistries that prevent failure of implanted biomedical devices and prostheses by limiting monocyte adhesion and macrophage fusion into foreign-body giant cells while inducing adherent-macrophage apoptosis. Hydrophobic, hydrophilic, anionic, and cationic surfaces were used for implantation. Analysis of the exudate surrounding the materials revealed no differences between surfaces in the types or levels of cells present. Conversely, the proportion of adherent cells undergoing apoptosis was increased significantly on anionic and hydrophilic surfaces (46 ± 3.7 and 57 ± 5.0%, respectively) when compared with the polyethylene terephthalate base surface. Additionally, hydrophilic and anionic substrates provided decreased rates of monocyte/macrophage adhesion and fusion. These studies demonstrate that biomaterial-adherent cells undergo material-dependent apoptosis in vivo, rendering potentially harmful macrophages nonfunctional while the surrounding environment of the implant remains unaffected.

Design concept and construction of a hybrid lamellar keratoprosthesis.

A novel hybrid lamellar keratoprosthesis composed of epithelium and stroma was developed. Artificial extracellular matrices were constituted of photocrosslinkable copolymers of N,N-dimethylacrylamide and 2-(7-coumaroxy)ethyl methacrylate; a copolymer with a high content of coumarin (A) was used as a basement membrane (BM) for the epithelium, and a copolymer with a low content (B) was used for entrapment of keratocytes. The lamellar keratoprosthesis was constructed as follows: First, a viscous buffer solution containing water-soluble copolymer (B), collagen, and keratocytes derived from rabbit was prepared. Then, a cast film of copolymer (A) was tightly placed onto the mixed solution. Ultraviolet light irradiation leading to intermolecular dimerization of coumarin groups resulted in the formation of a transparent keratocyte-entrapped hydrogel that was layered with an artificial BM. Epithelial cells were seeded on the BM. Further culturing produced the lamellar keratoprosthesis, within which both kinds of cells proliferated well. The preliminary study on two week implantation of the lamellar keratoprosthesis in rabbits provided quite promising results; adverse tissue reactions, such as corneal opacity and neovascularization, were not observed.

Photo induced surface heparin immobilization.

This paper describes a novel method providing durable layering of heparin immobilized hydrogels on fabricated devices. The preparation method is based on photochemistry of a dithiocarbamate group that is dissociated into a highly reactive radical pair upon ultraviolet (UV) irradiation. By taking advantage of characteristics of the photo generated radicals, hydrogel formation and its fixation onto a substrate surface were attained. The immobilization of heparin onto poly(ethylene terephtalate) was demonstrated. First, a mixed aqueous solution containing a photoreactive water soluble poly(N,N-dimethylacrylamide-covinylbenzyl N,N-diethyldithiocarbamate) and heparin was coated on the substrate. Subsequent UV irradiation resulted in the simultaneous formation of a heparin immobilized hydrogel and its chemical fixation onto the substrate. No delamination was found after vigorous washing with water. Significant inhibition of platelet adhesion and markedly prolonged blood coagulation times were observed, which are apparently derived from the surface hydrogel, and from released and chemically fixed surface heparin. Thus, it is expected that the photochemical method developed here provides potent antithrombogenicity to artificial organs.

Excimer laser‐induced surface fixation of polymer and its patterning

When ArF excimer laser pulses irradiated an UV‐absorbing polymer film, such as poly(N,N‐dimethylacrylamide) or polystyrene, in close contact with an optically transparent substrate, such as polyethylene or poly(vinyl alcohol), the target was selectively photolyzed, resulting in the formation of a crosslinked polymer which was covalently bonded onto the substrate surface. The formed polymer exhibited IR spectral features very similar to those of the target. Fine surface patterning of the formed polymer layer was attained by pulsed irradiation through a projection mask.

Surface Fixation of Lumbrokinase via Photochemical Reaction of Azidophenyl Group

A new method for the immobilization of lumbrokinase (LK) on polymer was developed. The method is based on the photochemical reaction of the azidophenyl group, which produces a highly reactive phenylnitrene upon ultraviolet (UV) light irradiation. First, an aminated polymer, partially derivatized with a photoreactive phenyl azido group in its side chains, was coated onto a polyurethane (PU) surface. Subsequently, the surface was exposed to UV light. To induce the carboxyl group on the UV-light-treated surface, poly(methyl vinyl ether-co-maleic acid) (MAcMEC) was reacted. LK was immobilized on the PU surface using l-ethyl-3-(3-dimethylaminopropyl)carbo-diimide (EDC) in aqueous solvent. Electron spectroscopy for chemical analysis (ESCA) and water contact angle measurement before and after sequential surface reactions revealed that LK was immobilized successfully. The LK immobilized on the PU surface had fibrinolytic activity. In conclusion, LK immobilization via this photochemical reaction will be useful in improving the blood compatibility of blood-contacting polymer.

Transfer and Surface Fixation of Gels by an Excimer Laser Ablation

This paper presents a new method to provide a durable layering of gels on a polymer film by an excimer laser ablation. The procedure is as follows. At first, three-layered (A-B-A type) polymer films were prepared, where A is polyethylene or poly(vinyl alcohol), both of which have extremely small absorption coefficients at the laser wavelength (193nm) and B is poly(N, N-dimethyl acrylamide) or polystyrene, both of which have large ones. The layered film was subjected to irradiation of ArF excimer laser pulses. The irradiated surface portion of A film exhibited a gel-like nature. No delamination occurred even upon vigorous washing with water or organic solvents. XPS and FT-IR spectral analyses showed that the A surface was completely layered with a polymer resembled to B. The thickness of the fixed gel increased with an increase in fluence and the number of pulses. Significant inhibition of platelets adhesion on hydrogelated surface was observed in vitro. When heparin was mixed with the polymer B, heparin was immobilized in a hydrogelated surface.