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Biomedical subjects

Y Ikada

Publications and source records attributed to Y Ikada.

At least 91 records · Page 5Linked to original sources
PubMed1998

Occlusive effects of lactic acid-glycolic acid copolymer membrane on gingival fibroblasts in vitro.

The cell occlusive effects on human gingival fibroblasts of degradable lactic acid-glycolic acid copolymer membranes (noncoated membranes) and membranes coated with a sucrose ester of fatty acid (coated membranes) were studied and compared with those of expanded polytetrafluoroethylene (e-PTFE) membranes. The membranes were immersed in a culture medium periodically for 21 days and interposed into a chemotaxis chamber, and the fibroblasts then were cultured in the chamber for another 7 days. The passage rate of cells through the membranes was calculated and the change in surface structure of each membrane after immersion for 28 days was observed by an environmental scanning electron microscope. The passage rate of coated membranes (3.4+/-2.2%) was significantly lower than that of noncoated (25.7+/-5.1%) at the 28th day whereas the passage rate of e-PTFE membranes was 0.8-1.5%. Many pores were observed on the noncoated membranes before immersion while the coating material covered most of the pores on the coated membranes. The average pore size of the noncoated membranes was larger than that of the coated membranes at day 28. The structure of the e-PTFE membranes underwent no change. The passage rate of the coated membranes was not different from the e-PTFE membranes, suggesting an effect that might be useful for a guided tissue regeneration procedure.

Fibroblasts↗
PubMed1998

Synthesis of monomeric and polymeric conjugates carrying a thrombin inhibitor through an ester bond.

Four kinds of monomers carrying a thrombin inhibitor, (2R,4R)-4-methyl-1-[N2-[(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl)sulfon yl]-L-arginyl]-2-piperidinecarboxylic acid (argatroban), were synthesized. These monomers were copolymerized with acrylamide to yield water-soluble polymeric conjugates possessing the argatroban moiety in the side chain. Their antithrombogenic activities were determined from the inhibitory effect on thrombin action and the prolongation effect on blood clotting time. The monomeric conjugates of 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate (HEMA), and 4-hydroxybutyl acrylate (HBA) linked with argatroban through an ester bond were potent inhibitors of thrombin, prolonging the blood-clotting time, whereas a conjugate of amino methyl styrene (AMS) and argatroban through an amide bond was a less potent inhibitor than argatroban. None of the copolymers could prolong blood clotting when assessed just after preparation of their aqueous solutions, but the antithrombogenic activity of the aqueous solutions increased after incubation for 7 days at 37 degrees C for the polymeric conjugates through an ester bond. Free argatroban was detected in the aqueous solutions of polymeric conjugates after incubation, suggesting that argatroban was released by hydrolysis of the ester bond during incubation.

Antithrombins↗
PubMed1998

Tumor accumulation of poly(vinyl alcohol) of different sizes after intravenous injection.

The body distribution and tumor accumulation of polymers were evaluated using poly(vinyl alcohol) (PVA) which has the simplest chemical structure among water-soluble polymers, similar to poly(ethylene glycol). To study the effect of polymer size on the tumor accumulation, we used not only water-soluble PVA with different molecular weights but also PVA microgels prepared through gamma-irradiation of aqueous PVA solutions. The PVA specimens in the aqueous solution were intravenously injected to mice carrying a tumor mass at their footpad. Both types of PVA (water-soluble and microgel) of larger size were retained in the blood circulation for longer time periods and excreted more slowly from the kidney than those of smaller size. The plasma half-life period of PVA became longer with increasing size both for the water-soluble and microgel PVA, indicating that the body fate of PVA is governed only by the size. Both the water-soluble PVA and PVA microgels were accumulated in tumor tissue to a significantly greater extent than in normal tissue. The size dependence of the plasma half-life period and tumor accumulation was similar between the water-soluble PVA and the PVA microgels and the tumor accumulation became maximum around the size of 60 nm both for water-soluble and microgel PVA. A pharmacokinetical study demonstrated that the tumor uptake rate index of PVA decreased with the increase in PVA size. On the other hand, the greater the size, the larger the value of the area under the blood concentration-time curve (AUC). In addition, the PVA around 60 nm in diameter showed the smallest liver clearance. It was concluded that the balance between the uptake rate and the AUC as well as the liver clearance resulted in the maximum accumulation of PVA with the size of 60 nm.

Animals↗
PubMed1998

Entrapment of islets into reversible disulfide hydrogels.

Currently, there are three types of devices for a bioartificial pancreas; microencapsulation, an extravascular diffusion chamber, and an intravascular diffusion chamber. The purpose of the present study was to provide a new extracellular matrix hydrogel for the devices of extra- and intravascular diffusion chamber types. As the sol-gel transition of this hydrogel is reversible, refilling of islets in vivo will be possible without a severe traumatic procedure. The hydrogel was produced from a polyacrylamide derivative carrying thiol groups synthesized by radical copolymerization of acrylamide and N,N'-bis-acrylcystamine, followed by reduction of the disulfide bonds in the copolymer. This water-soluble copolymer was used to entrap hamster islets by re-formation of disulfide bonds on the copolymer to produce a hydrogel. The formed hydrogel was easily reliquefied by reduction of the disulfide crosslinks to thiols. Insulin release from the islet-entrapped hydrogel continued for more than 1 month when examined in vitro. A static glucose stimulation test for the entrapped islets exhibited an increased insulin release.

Animals↗
PubMed1998

Detection of cracks in polyethylene components of retrieved knee joint prostheses.

Subsurface cracks that had formed in polyethylene artificial knee components were observed nondestructively with a new method, scanning acoustic tomography (SAT). Standardization of the SAT observation was done by in-vitro rolling fatigue testing on an unimplanted ultra high molecular weight polyethylene (UHMWPE) knee component. Retrieved knee components were of two types; KOM (Kyocera, Kyoto, Japan) sterilized with ethylene oxide gas, and MG (Zimmer, IN, USA) sterilized with gamma-irradiation. The SAT images revealed cracks in all the retrieved components, and these existed mainly 0. 3-1.0 mm from the surface. Comparison of crack formation in each portion of the contact area of the polyethylene components showed that the middle portion of the MG type had the highest concentration of cracks. When the distribution of compressive stress on the polyethylene components was assessed by mechanical testing, the strongest compressive stress was seen in the middle portion of MG type components.

Acoustics↗
PubMed1998

In vitro sorption and desorption of basic fibroblast growth factor from biodegradable hydrogels.

In vitro interaction of basic fibroblast growth factor (bFGF) with biodegradable gelatin hydrogels was investigated, focusing on its sorption into the hydrogels and desorption from them. Basic bFGF was sorbed to the hydrogel of acidic gelatin with an isoelectric point (IEP) of 5.0 over time at 4 degrees C, in contrast to that of basic gelatin with an IEP of 9.0 and type I collagen. The bFGF sorption was almost independent of the sorption temperature except for 4 degrees C and the hydrogel water content. Fluorescent microscopic observation revealed that bFGF was sorbed into the interior of the acidic gelatin hydrogel. The binding molar ratio of bFGF to the acidic gelatin was around 1.0. The bFGF sorption to the acidic gelatin hydrogel increased when gelatin was further carboxylated. bFGF was sorbed into the acidic gelatin hydrogel more slowly than into the poly(acrylic acid) (PAAc) hydrogel, probably because of the lower density of negative charge of gelatin. The bFGF sorption decreased with an increase in solution ionic strength, indicating that an electrostatic interaction was the main driving force for bFGF sorption to the acidic gelatin hydrogel. However, even at higher ionic strengths of solution, the sorbed bFGF was not desorbed from the acidic gelatin hydrogel, in contrast to the PAAc hydrogel.

Acrylic Resins↗
PubMed1998

A novel surgical glue composed of gelatin and N-hydroxysuccinimide activated poly(L-glutamic acid): Part 1. Synthesis of activated poly(L-glutamic acid) and its gelation with gelatin.

Although fibrin glue has been widely used as a surgical adhesive, its components, fibrinogen and thrombin, obtained from human blood are not completely free from the risk of virus infection due to acquired immune deficiency and hepatitis. Recently, we have reported that a polymer pair composed of gelatin and poly(L-glutamic acid) (PLGA) promptly forms a gel and can firmly bond to soft tissues when crosslinked with the aid of water-soluble carbodiimide (WSC). The present study was undertaken to design a new PLGA-gelatin glue without using WSC. Two kinds of PLGA with molecular weights of 71 and 22 kDa were employed to prepare N-hydroxysuccinimide (NHS) activated derivatives. The NHS-activated PLGA could be synthesized at high yields and was found to be stable for an extended time without losing the ability to crosslink with gelatin when stored under a dry-cold condition. This NHS-activated PLGA could spontaneously form a gel with gelatin in an aqueous solution within a short time, comparable to a commercial fibrin glue, when gelation was allowed to proceed at pH 8.3. The NHS-activated PLGA prepared from PLGA with the molecular weight of 22 kDa could be readily dissolved at high concentrations and its ability to form a gel was maintained for more than 10 min when an acidic 8% NHS-activated PLGA solution was used. The bonding strength of PLGA gelatin glues with natural tissue was higher than that of fibrin glue. These findings strongly suggest that this combination of gelatin and NHS-PLGA is very promising as a surgical adhesive and may possibly replace fibrin glues prepared from human blood components.

Animals↗
PubMed1998

Hemostatic capability of rapidly curable glues from gelatin, poly(L-glutamic acid), and carbodiimide.

The hemostatic capability of rapidly curable glues composed of gelatin and poly(L-glutamic acid) (PLGA) was compared with that of the conventional fibrin glue. The hydrogels produced from mixed gelatin and PLGA aqueous solution within several seconds by addition of water-soluble carbodiimide (WSC) was applied to the dog spleen injured by needle pricking. The WSC-catalyzed gelatin-PLGA glues exhibited higher hemostatic capability than the fibrin glue. The total amount of bleeding from the injured spleen until hemostasis when the gelatin-PLGA hydrogel glues were applied was significantly smaller than that of the fibrin glue application. The gelatin-PLGA glue application enhanced the success rate of complete hemostasis to a significantly greater extent than the fibrin glue, while the frequency of glue applications until achieving complete hemostasis decreased. The gelatin PLGA hydrogels strongly adhered to the surface of dog spleen, whereas the fibrin hydrogel was easily detached from the spleen surface. It was concluded that this strong adhesion mechanically suppressed the bleeding, leading to enhanced hemostasis by the rapidly curable gelatin-PLGA glues.

Animals↗
PubMed1998

Effect of additives on gelation and tissue adhesion of gelatin-poly(L-glutamic acid) mixture.

Gelation and tissue adhesion of mixtures of gelatin and poly (L-glutamic acid) (PLGA) aqueous solution were investigated in the presence of additives following the addition of a water-soluble carbodiimide (WSC) that induced chemical cross linking between gelatin and PLGA. To prevent spontaneous gelation of the mixed solution through physical cross linking between gelatin molecules at room temperature, additives were added to the mixed solution. Among the additives studied, starch and urea were effective in preventing the spontaneous physical gelation. The mixed gelatin and PLGA solution set to a cross-linked hydrogel within scores of second by WSC addition, irrespective of the presence of urea, whereas the viscosity of the solution with added starch was too high to measure the gelation time. The cross-linked gelatin-PLGA hydrogels with and without urea showed higher bonding strength to soft tissues than fibrin glue. This was in marked contrast to gelatin-PLGA hydrogels with soluble starch. Irrespective of the presence of urea, the gelatin-PLGA hydrogels gradually biodegraded in the back subcutis of mice over 3 months and no severe inflammatory response to the hydrogels was observed. These findings indicate that urea is promising as an additive to prevent spontaneous physical gelation of the mixed gelatin and PLGA aqueous solution without changing the characteristics of WSC-induced cross linking and tissue adhesion of the formed hydrogel.

Animals↗
PubMed1998

Assessment of heat and storage conditions on gamma-ray and electron beam irradiated UHMWPE by electron spin resonance.

Electron spin resonance (ESR) spectroscopic study was undertaken to explore the nature of any remaining radicals in ultra-high molecular weight polyethylene (UHMWPE) after irradiation with gamma-rays and electron beams to a dose of 25 KGy in air or N2 environment. The decay of radicals was studied by observing the ESR intensity change as a function of time. The following post-irradiation conditions were employed: (1) storage in air or N2 at 25 degrees C, and (2) heat treatment in air or N2 at 80, 100, and 120 degrees C for time intervals up to 8 h. The study suggests that radicals remaining trapped in the matrix of UHMWPE could be dramatically scavenged by heat treatment, independently of the atmosphere during irradiation and the heating process. The melting temperature and mechanical properties of irradiated UHMWPE under the experimental conditions employed were shown not to alter significantly by heat treatment, except in the presence of air.

Biocompatible Materials↗
PubMed1998

Effects of static magnetic field on bone formation of rat femurs.

Effects of static magnetic fields (SMF) on bone formation of rat femurs, were evaluated using tapered rods made of magnetized and unmagnetized samarium cobalt of the same size. They were implanted transcortically into the middle diaphysis of rat femurs under press-fit loading. The bone mineral density (BMD) and bone calcium content were measured 12 weeks after implantation by dual-energy X-ray absorptiometry and chemical analysis with o-cresolphthalein complexon, respectively. The result revealed that the femurs adjacent to magnetized specimens had significantly higher BMD and calcium content than those adjacent to the unmagnetized specimen (p < 0.01). However, the value of BMD and calcium content of rats with magnetized specimens was similar to that of non-operated rats. No specific change was found in the body weight, serum Ca, activity of alkaline phosphatase, hemogram, and BMD of the tibia and humerus among the magnetized and unmagnetized. These results suggest that the long-term local SMF stimulation on the bone has a local effect to prevent the decrease in BMD caused by surgical invasion or implantation.

Absorptiometry, Photon↗
PubMed1998

Histologic findings in polyacrylamide-coated polytetrafluoroethylene (PTFE) arterial grafts in the rat abdominal aorta.

To improve cell attachment without inducing thrombogenesis, the authors coated the inner surface of polytetrafluoroethylene (PTFE) prostheses (I.D.: 1 mm; length: 10 mm; wall thickness: 0.5 mm; fibril length: 30 microm) with polyacrylamide (PAA), known to have a strong antithrombotic effect (PAA-PTFE). They implanted the prostheses into the abdominal aorta of rats, and retrieved them at intervals of up to 9 months. Graft healing was observed under light and scanning electron microscopy. All the inner surfaces of the grafts examined were barely covered with fibrin or platelets. The PAA-coated fibers had many projections, in contrast to the original PTFE prostheses. Neo-endothelium was observed to be directly attached to these structural fibers of the PAA-PTFE grafts. Restoration of the neointima was also observed in these vascular prostheses.

Acrylic Resins↗