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Biomedical subjects

Y Ikada

Publications and source records attributed to Y Ikada.

At least 55 records · Page 3Linked to original sources
PubMed2000

Transmission electron microscopic study of hepatocytes in bioartificial liver.

A bioartificial liver (BAL) was prepared by simple inoculation of hepatocytes into the inner space of hollow fibers of a hemodialyzer and it was maintained in a closed circuit for in vitro culture. Morphology of hepatocytes in the hollow fibers was studied in detail using transmission electron microscopy (TEM). The hepatocytes formed three-dimensional, rod-shaped aggregates of 200 microm in diameter throughout the whole dimension of the hollow fibers after 1 day of culture. Approximately five hepatocyte layers existed from the surface to the center of the aggregate. The hepatocytes in the aggregate displayed mostly polygonal shapes and were surrounded by five to six cells. Abundant bile canaliculi were formed between the hepatocytes and were sealed by tight junctions. The distance between the adjacent hepatocytes except the bile canaliculus domain was approximately 20 nm, and interdigitation was observed between some hepatocytes. These observations indicate that the hepatocytes formed functionally associated aggregates, that is, organoids. Although the cells facing the inner surface of the hollow fiber lost their polygonal shape and became flattened during the following several-day culture, no drastic change was observed in the morphology of the hepatocytes located inside the aggregate. After 14 days of culture, the number of living cells decreased and most of these had a deformed nucleus, few numbers of organelles, and intermittent lipid droplets.

Animals↗
PubMed2000

Porous polyethylene as a spacer graft in the treatment of lower eyelid retraction.

PURPOSE: An experimental study was performed to: 1) assess the tolerance and incorporation of porous polyethylene (Medpor) in the posterior lamella of the rabbit lower eyelid; 2) analyze the effect of implant thickness on incorporation; 3) investigate the ability of conjunctiva to grow over vascularized Medpor and; 4) determine the effects of Medpor surface modification on biocompatibility and fibrovascularization. METHODS: In phase I, 10 rabbit eyelids were operated on to analyze the effects of implant thickness and to develop the surgical technique used in phase II of the study. In phase II, 20 lower eyelids of 10 rabbits received 0.85-mm-thick Medpor grafts, each rabbit receiving both an uncoated implant and one coated with an immobilized collagen. RESULTS: There were no extrusions in phase II. with a postoperative follow-up from 14 to 17 weeks. Fourteen of 20 eyelids had full-thickness conjunctival incisions or excisions placed over the Medpor implant to determine the growth potential of conjunctiva over a vascularized implant. All but one eyelid showed complete defect coverage, occurring in as little as 3 days. Histopathology indicated complete Medpor fibrovascularization as early as 4 weeks after implantation. Because neither coated nor uncoated implants extruded in phase II, no conclusions can be drawn regarding the efficacy of Medpor surface modification. CONCLUSION: Medpor was well tolerated in this soft tissue application, and it offers advantages over other graft materials.

Animals↗
PubMed2000

Soft tissue adhesive composed of modified gelatin and polysaccharides.

Although fibrin glue has been clinically used as a surgical adhesive, hemostatic agent, and sealant, it has the risk of virus infection because its components, fibrinogen and thrombin, are obtained from human blood. To circumvent this problem, we employed bioabsorbable gelatin and polysaccharides to prepare a safer hemostatic glue. Gelatin was modified with ethylenediamine using water-soluble carbodiimide to introduce additional amino groups into the original gelatin, while dextran and hydroxyethyl-starch were oxidized by sodium periodate to convert 1,2-hydroxyl groups into dialdehyde groups. Upon mixing of the two polymer components in aqueous solution, Schiff base was formed between the amino groups in the modified gelatin and the aldehyde groups in the modified polysaccharides, which thus resulted in intermolecular cross-linking and gel formation. The fastest gel formation took place within 2 s, and its bonding strength to porcine skin was about 225 gf cm(-2) when 20 wt% of an amino-gelatin (55% amino) and 10 wt% of aldehyde-HES (>84% dialdehyde) aqueous solutions were mixed. In contrast, the gelation time and bonding strength of fibrin glue was 5 s and 120 gf cm(-2), respectively.

Adhesives↗
PubMed2000

Influence of gelatin complexation on cell proliferation activity and proteolytic resistance of basic fibroblast growth factor.

The objective of this study is to investigate the influence of gelatin complexation on the biological activity of basic fibroblast growth factor (bFGF) and its resistance to trypsin digestion. When bFGF was mixed at 37 degrees C with acidic gelatin with an isoelectric point (IEP) of 5.0, the activity to promote in vitro proliferation of BHK cells became lower compared with that of free bFGF, in contrast to mixing with the basic gelatin with an IEP of 9.0. A maximum reduction in the bFGF activity was observed for the bFGF-gelatin complex prepared at a mixing molar ratio of 1/1. The bFGF activity of cell proliferation reduced at the initial period after mixing with the acidic gelatin at 37 degrees C, followed by no substantial change. Complexation with the acidic gelatin at 4 degrees C had no influence on the bFGF activity, irrespective of the bFGF/gelatin ratio and complexation time. The biological activity of bFGF was reduced by the trypsin treatment, but the reduced extent was suppressed through gelatin complexation at 37 degrees C. In an electrophoresis study, the protective effect of gelatin complexation on the trypsin digestion was also confirmed in terms of the molecular weight loss. It is possible that the complexing gelatin covers bFGF molecules, resulting in suppression of their interaction with the cell surface receptor as well as protection from their enzymatic attack.

Animals↗
PubMed2000

Bone formation at a rabbit skull defect by autologous bone marrow cells combined with gelatin microspheres containing TGF-beta1.

The objective of the present study is to investigate the addition effect of transforming growth factor (TGF)-beta1 on the bone formation at a rabbit skull defect induced by autologous bone marrow (BM). Following application of gelatin microspheres containing TGF-beta1, with or without BM cells to skull bone defects, bone formation at the defect was assessed by soft X-ray, dual energy X-ray absorptometry (DEXA), and histological examinations. After implantation for 6 weeks, gelatin microspheres containing 0.05 microg of TGF-beta1 plus 10(6) of BM cells induced bone formation at the 6 mm diameter bone defect. The defect was histologically closed by newly formed bone tissue, whilst both gelatin microspheres containing 0.05 microg of TGF-beta1, and 10(6) and 10(7) of BM cells were ineffective. A DEXA experiment revealed that combination of gelatin microspheres containing TGF-beta1 with BM cells enhanced the bone mineral density at the skull defect to a significantly greater extent than other agents. These findings indicate that a combination of gelatin microspheres containing TGF-beta1 enabled BM cells to enhance the osteoinductive ability, resulting in bone formation even at the cell number at which BM cells alone were ineffective.

Animals↗
PubMed2000

Controlled release of vascular endothelial growth factor by use of collagen hydrogels.

In vivo profile of vascular endothelial growth factor (VEGF) release from collagen hydrogels was investigated comparing that of hydrogel degradation while angiogenesis induced by the released VEGF was assessed. Collagen sponges were chemically cross-linked with different amounts of glutaraldehyde for various time periods. When 125I-labeled collagen hydrogels incorporating VEGF were subcutaneously implanted into the back subcutis of mice, the hydrogel radioactivity decreased with time, the decrement profile depending on the cross-linking conditions. The radioactivity was retained for longer time periods as the glutaraldehyde concentration and cross-linking time increased. Implantation study of collagen hydrogels incorporating 125I-labeled VEGF revealed that the remaining VEGF radioactivity decreased with time and the retention period was prolonged with the decreased hydrogel biodegradation. The slower the hydrogel degradation, the longer the period of VEGF retention. The collagen hydrogel incorporating VEGF induced significant angiogenesis around the implanted hydrogel, in marked contrast to VEGF in the solution form and VEGF-free empty hydrogel. The retention period of angiogenesis became longer with a decrease of the in vivo degradation rate of hydrogels. It is possible that the slower degraded hydrogel achieves a longer period of VEGF release, resulting in prolonged angiogenetic effect. We concluded that in our hydrogel system, biologically-active VEGF was released as a result of in vivo degradation of the hydrogel.

Absorbable Implants↗
PubMed2000

Gelatin microspheres as a pulmonary delivery system: evaluation of salmon calcitonin absorption.

The use of negatively and positively charged gelatin microspheres for pulmonary delivery of salmon calcitonin was examined in rats. The microspheres were prepared using acidic gelatin (isoelectric point (IEP):, 5.0) and basic gelatin (IEP, 9.0) for the negatively and positively charged microspheres, respectively. The average diameters of positively charged gelatin microspheres in the dry state were 3.4, 11.2, 22.5 and 71.5 microm, and that of negatively charged gelatin microspheres was 10.9 microm. Neither positively nor negatively charged gelatin microspheres underwent any degradation in pH 7.0 PBS and there was less than 8% degradation in bronchoalveolar lavage fluid (BALF) after 8 h. In in-vitro release studies in pH 7.0 PBS, salmon calcitonin was rapidly released from positively charged gelatin microspheres within 2 h, and its cumulative release was approximately 85%. In addition, the release profiles were not influenced by particle sizes. The release rates of salmon calcitonin from negatively charged gelatin microspheres were lower than that from positively charged gelatin microspheres. The cumulative release was approximately 40% after 2 h, but there was no evidence of any sustained release. The pulmonary absorption of salmon calcitonin from gelatin microspheres was estimated by measuring its hypocalcaemic effect in rats. The pharmacological availability after administration of salmon calcitonin in positively and negatively charged gelatin microspheres was significantly higher than that in pH 7.0 PBS. The pharmacological availability after administration of salmon calcitonin in positively charged gelatin microspheres was significantly higher than that in negatively charged gelatin microspheres. Administration of salmon calcitonin in positively charged gelatin microspheres with smaller particle sizes led to a higher pharmacological availability. The pharmacological availability after pulmonary administration of salmon calcitonin in positively charged gelatin microspheres with particle sizes of 3.4 and 11.2 microm was approximately 50%. In conclusion, the gelatin microspheres have been shown to be a useful vehicle for pulmonary delivery of salmon calcitonin.

Analgesics↗
PubMed2000

Bone regeneration at rabbit skull defects treated with transforming growth factor-beta1 incorporated into hydrogels with different levels of biodegradability.

OBJECT: Skull bone regeneration induced by transforming growth factor-beta1 (TGFbeta1)-containing gelatin hydrogels (TGFbeta1-hydrogels) was investigated using a rabbit skull defect model. Different strengths of TGFbeta1 were examined and compared: different TGFbeta1 doses in gelatin hydrogels with a fixed water content, different water contents in gelatin hydrogels with a fixed TGFbeta1 dose, and TGFbeta1 in solution form. In addition, regenerated skull bone was observed over long time periods after treatment. METHODS: Soft x-ray, dual energy x-ray absorptometry, and histological studies were performed to assess the time course of bone regeneration at a 6-mm-diameter skull defect in rabbits after treatment with TGFbeta1-hydrogels or other agents. The influence of TGFbeta1 dose and hydrogel water content on skull bone regeneration by TGFbeta1-hydrogels was evaluated. Gelatin hydrogels with a water content of 95 wt% that incorporated at least 0.1 microg of TGFbeta1 induced significant bone regeneration at the rabbit skull defect site 6 weeks after treatment, whereas TGFbeta1 in solution form was ineffective, regardless of dose. The in vivo degradability of the hydrogels, which varied according to water content, played an important role in skull bone regeneration induced by TGFbeta1 -hydrogels. In our hydrogel system, TGFbeta1 is released from hydrogels as a result of hydrogel degradation. When the hydrogel degrades too quickly, it does not retain TGFbeta1 or prevent ingrowth of soft tissues at the skull defect site and does not induce bone regeneration at the skull defect. It is likely that hydrogel that degrades too slowly physically impedes formation of new bone at the skull defect. Following treatment with 0.1-microg TGFbeta1-hydrogel (95 wt%), newly formed bone remained at the defect site without being resorbed 6 and 12 months later. The histological structure of the newly formed bone was similar to that of normal skull bone. Overgrowth of regenerated bone and tissue reaction were not observed after treatment with TGFbeta1 -hydrogels. CONCLUSIONS: A TGFbeta1-hydrogel with appropriate biodegradability will function not only as a release matrix for the TGFbeta1, but also as a space provider for bone regeneration. The TGFbeta1-hydrogel is a promising surgical tool for skull defect repair and skull base reconstruction.

Absorptiometry, Photon↗
PubMed2000

Development of an oral drug delivery system targeting immune-regulating cells in experimental inflammatory bowel disease: a new therapeutic strategy.

Several studies have indicated the involvement of macrophages and dendritic cells in active inflammatory bowel disease (IBD). Manipulation of these cells is considered a very important therapeutic strategy for patients with IBD. We evaluated the effect of a new drug delivery system targeting microfold cells and macrophages with poly(DL-lactic acid) microspheres containing dexamethasone (Dx). Colitis was induced in BALB/c mice by 5% dextran sodium sulfate. Dx microspheres (n = 10) and only Dx (n = 10) were orally administered to dextran sodium sulfate-treated mice. Thereafter, serum levels and tissue distributions of Dx were investigated. To estimate the efficacy of this drug delivery system, we measured the histological score, myeloperoxidase activity and nitric oxide production, and gene expressions of tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma in the colonic tissue. Serum Dx levels were not increased after oral administration of Dx microspheres. The tissue distribution of microspheres containing (125)I-labeled Dx in inflamed colon was significantly higher than in other organs. The histological score, myeloperoxidase activity, and nitric oxide production of the group treated with Dx microspheres were significantly lower than of those treated with Dx alone. Gene expressions of tumor necrosis factor-alpha, interleukin-1beta, and interferon-gamma were down-regulated in mice treated with Dx microspheres. Microspheres containing glucocorticoids such as Dx, which target microfold cells and macrophages, can facilitate mucosal repair in experimental colitis and could be an ideal agent for treatment of human IBD.

Administration, Oral↗
PubMed1999

Control of complement activities for immunoisolation.

Immunoisolation of cells by semipermeable membranes is a most promising approach to transplant xenogeneic cells. Although membranes which allow xenotransplantation have been reported, ambiguity remains as to their long term effectiveness. In this review, we would like to reconsider the immuno-isolative effectiveness of membranes reported from the standpoint of permeability and present our strategy to prepare membranes that can realize long-term functioning of xenograft. There are distinct different types of semi-permeable membranes, hydrogel membranes and ultrafiltration membranes. Studies on their permeability indicated that neither of these membranes effectively fractionate solutes on the basis of molecular size under a diffusion-controlled process, nor thus can they immuno-isolate xenograft for a long time. Humoral immunity including antibodies and complement proteins is suspected of playing a major role in the rejection of xenografts. Control of complement cytolytic activities, not antibody permeation, may be a key factor determining the fate of the xenograft enclosed in membranes. We found that the microbead containing poly(styrene sulfonic acid) can consume complement cytolytic activities and thus can effectively protect xenogeneic islets of Langerhans in diabetic mice from the humoral immunity.

Animals↗
PubMed1999

Targeting of tumor necrosis factor to tumor by use of dextran and metal coordination.

Tumor targeting of recombinant human tumor necrosis factor alpha (TNF) and consequently an enhanced anti-tumor effect were achieved through conjugation with dextran having metal chelating, diethylenetriaminepentaacetic acid (DTPA) residues based on metal coordination. A simple mixing with the DTPA-dextran in an aqueous solution containing Cu2+ enabled TNF to coordinately conjugate to dextran. Following intravenous (i.v.) injection into tumor-bearing mice, the TNF-DTPA-dextran conjugate caused a significantly higher tumor accumulation of TNF and the longer retention period than free TNF or its mixture with the DTPA-dextran. Intravenous injection of the TNF-DTPA-dextran conjugate suppressed tumor growth to a significantly greater extent than that of free TNF at a lower injection dose. It is concluded that dextran conjugation based on Cu2+ coordination is a promising way to enhance the anti-tumor effect of TNF as a result of its passive tumor targeting.

Animals↗
PubMed1999

Prevention of fatigue cracks in ultrahigh molecular weight polyethylene joint components by the addition of vitamin E.

Flaking-type wear, so-called delamination, is often observed in polyethylene joint components. This is thought to occur partly due to crack formation and propagation at grain boundaries. This study examined the effect of vitamin E on the crack formation and/or propagation in UHMWPE by using 2-dimensional sliding fatigue testing and micro indenter testing. An in vitro sliding fatigue test was performed under two simplified articulating movements, and the cracks produced were observed by scanning acoustic tomography (SAT). Gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) specimens demonstrated a smaller area of accumulated cracks as compared to virgin specimens, when the loading movement was reciprocated on a single linear locus. However, four out of five gamma-irradiated UHMWPE specimens exhibited severe flaking-like destruction under the complicated sliding condition, suggesting that gamma irradiation accelerated crack propagation under multidirectional loading. All the gamma-irradiated vitamin-E-containing specimens demonstrated no subsurface crack formation and no flaking-like destruction. Results using micro indenter testing showed that the dynamic hardness at grain boundary was higher than that in grain, and was increased by gamma irradiation. This hardening at grain boundary was reduced by adding vitamin E. It is possible that the presence of vitamin E prevents crack propagation partly due to reduced hardness at grain boundaries. The gamma-irradiated vitamin-E-containing UHMWPE is a promising material to prevent flaking-like destruction of polyethylene joint components.

Biocompatible Materials↗
PubMed1999

In vitro and in vivo comparison of bulk and surface hydrolysis in absorbable polymer scaffolds for tissue engineering.

This article describes preliminary in vitro and in vivo studies comparing bulk and surface hydrolysis in absorbable polymer scaffolds proposed for tissue engineering of bone. The two polymers systems used were a bulk hydrolyzing 50:50 poly(DL-lactide-co-glycolide) (PLGA) and a surface hydrolyzing self-catalytic poly(ortho ester) (POE). Polymer scaffolds were exposed to physiological saline at body temperature and changes in polymer mass loss and inherent viscosity were monitored over time. New bone formation and local tissue response were evaluated by implanting scaffold disks of both polymer systems into non-critical-size calvarial defects in rabbits. New bone formation was determined by bone mineral density measurements, and local tissue response was determined by qualitative histology. Preliminary results confirmed that one of the main design characteristics for absorbable polymers in tissue engineering of bone, coordination of controlled polymer mass loss with new tissue formation, appeared to be achieved better using a surface hydrolyzing POE, rather than with a bulk hydrolyzing 50:50 PLGA. Bone mineral density at 6 and 12 weeks was an average 25% higher in the surface hydrolyzing scaffold. Unfortunately, the amount of bone formed was so inconsequential that this observation is of little relevance. Use of a water-soluble signaling factor such as basic fibroblast growth factor (bFGF) failed to increase bone formation. The histological response of these two polymer systems was similar and unaffected by the presence or absence of bFGF. The persistence of structural integrity for self-catalytic POE scaffolds after 6 and 12 weeks implantation, while 50:50 PLGA scaffolds had partially collapsed after 6 weeks, suggests surface hydrolyzing scaffolds may have some advantage over bulk hydrolyzing scaffolds in resisting normal in vivo stresses when used in a calvarial defect.

Animals↗
PubMed1999

Bioadhesion of gelatin films crosslinked with glutaraldehyde.

The present study was carried out in an attempt to make a gelatin film strongly bioadhesive by introducing free dangling aldehyde groups. When gelatin films were treated with 0.5M of glutaraldehyde (GA) solution at 60 degrees C, free aldehyde groups (up to 150 micromol/g) were introduced in the film. The bonding strength of GA-crosslinked gelatin films (GA gelatin films) with biological tissue was assessed using porcine skins. It was found that bonding strength increased with increasing aldehyde content in the film. The GA gelatin films had bonding strength as high as 250 gf/cm2 whereas the native gelatin film (before GA treatment) showed bonding strength of 40 gf/cm2. When the aldehyde groups introduced in the gelatin films were quenched with glycine or reduced by NaBH4, the films no longer demonstrated such high bonding strength. These facts suggest that a Schiff base was formed between the free dangling aldehyde in the GA gelatin films and the amino groups of the natural tissue, which strongly contributed to a marked bioadhesion.

Adhesives↗
PubMed1999

Sealing effect of rapidly curable gelatin-poly (L-glutamic acid) hydrogel glue on lung air leak.

BACKGROUND: Air leak is a problem commonly occurring in lung and thoracic operations. In this study, a rapidly curable hydrogel glue was prepared as the seal for lung air leak. METHODS: Mixing an aqueous solution of gelatin and poly(L-glutamic acid) with a water-soluble carbodiimide produced a hydrogel. The sealing effect on the air leak wound of rat lung was compared with that of conventional fibrin glue. RESULTS: The gelatin-poly(L-glutamic acid) hydrogel glue was solidified as rapidly as the fibrin glue, and was significantly more effective in sealing the lung air leak than the fibrin glue. Approximately 80% of the lungs treated with the hydrogel glue exhibited no air leak at the lung pressure of 50 cm H2O. Urea addition could prevent spontaneous gelatination of the mixed solution at room temperature and did not affect the hydrogel sealing effect. The bonding strength of the hydrogel glue both with and without urea to the lung tissue was significantly higher than that of the fibrin glue. CONCLUSIONS: We concluded that this strong lung adhesion of the gelatin-poly(L-glutamic acid) hydrogel glue resulted in its superior sealing effect.

Animals↗
PubMed1999

Fabrication of porous gelatin scaffolds for tissue engineering.

A novel method which employs water present in swollen hydrogels as a porogen for shape template was suggested for preparing porous materials. Biodegradable hydrogels were prepared through crosslinking of gelatin with glutaraldehyde in aqueous solution, followed by rinsing and washing. After freezing the swollen hydrogels, the ice formed within the hydrogel network was sublimated by freeze-drying. This simple method produced porous hydrogels. Irrespective of any rinsing and washing processes, water was homogeneously distributed into the hydrogel network, allowing the hydrogel network to uniformly enlarge and the ice to act as a porogen during the freezing process. Different porous structures were obtained by varying the freezing temperature. Hydrogels frozen in liquid nitrogen, had a two-dimensionally ordered structure, while the hydrogels prepared at freezing temperatures near -20 degrees C, showed a three-dimensional structure with interconnected pores. As the freezing temperature was lowered, the hydrogel structure gradually became more two-dimensionally ordered. These results suggest that the porosity of dried hydrogels can be controlled by the size of ice crystals formed during freezing. It was concluded that the present freeze-drying procedure is a bio-clean method for formulating biodegradable sponges of different pore structures without use of any additives and organic solvents.

Biocompatible Materials↗