The authors evaluated the embolization effects on experimental aneurysm models with a liquid material. This material is a mixture of poly (HEMA-co-MMA), Iopamidol, water and a small amount of ethyl alcohol. We have satisfactorily treated over 30 cases of AVM with this material. Out of four solutions of different viscosity, we used the solution with the highest viscosity to prevent distal migration of the mixture. Glass models of aneurysms of 5 mm in diameter in pulsatile saline flow were embolized with the mixture under various conditions. When an IDC was placed in the aneurysm models, the mixture obliterated them completely and did not migrate out from the aneurysm models. In this experimental study, it is suggested that the liquid material appears to be useful in embolizing cerebral aneurysms safely.

Isolation of islets of Langerhans (islets) has been performed by means of collagenase digestion of the pancreatic tissue combined with density gradient separation of islets from unwanted exocrine tissues. An enormous number of islets are necessary for clinical islet transplantation. The density gradient used for isolation of a large number of islets should satisfy several requirements in addition to those for the conventional density gradients, such as high viscosity for creating fine interfaces with a large area, easy sterilization, and low cost. This study is concerned with the development of a new density gradient made of low-molecular-weight gelatin. We isolated islets from the hamster pancreatic tissue using the gelatin density gradients. The yield and purity of islet and its insulin release function were compared with those of islets isolated using Ficoll and Ficoll-Conray density gradients that have been conventionally used. The new gelatin density gradient can separate islets from the unwanted exocrine tissue as effectively as the Ficoll density gradient and more effectively than the Ficoll-Conray density gradients. The islets collected using the gelatin gradient retain ability of insulin release increase in response to glucose stimulation, similar to those isolated by the Ficoll-Conray gradient and more than those collected by the Ficoll gradient. In addition, the gelatin effectively inhibited enzyme activities, that is, collagenase and proteolytic enzymes released from the exocrine tissue, and thus it can inhibit overdigestion of islets during their density gradient isolation. The gelatin gradient satisfies most of the additional requirements for islet isolation from the pancreatic tissue of large animals mentioned above. Although several factors, such as molecular weight of gelatin, osmolality of the gradient, and centrifugal conditions, still remain to be optimized, our results suggest that the gelatin gradient has potentiality to isolate islets from the pancreatic tissue of a large animal.

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.

The intramedullary cavity is a widely distributed well-vascularized microenvironment capable of sustaining grafts, and is a potential site for islet transplantation. The bone marrow offers sufficient space that may also be suitable for bioartificial pancreas (BAP) implantation.To evaluate the feasibility of bone marrow as an implantation site for BAPs.A calcium phosphate cement chamber satisfies the criteria for immunoisolation. Mouse insulinoma cells were suspended with agarose gel and enclosed in a calcium phosphate cement chamber to create a BAP, which was implanted in the intramuscular space in diabetic swine or the intramedullary cavity in diabetic dogs. Blood glucose and C-peptide concentrations were determined perioperatively.In the swine, the mean ± SD blood glucose concentration decreased from 413 ± 24 mg/dL to 285 ± 47 mg/dL, and was maintained in the range of 285 to 336 mg/dL for 15 days. It increased to 368 to 450 mg/dL after the BAPs were implanted in the intramuscular space. In the dogs, the blood glucose concentration decreased from 422 ± 32 mg/dL to 247 ± 52 mg/dL, and was maintained in the range of 247 to 347 mg/dL after the BAPs were implanted in the intramedullary cavity. The C-peptide concentration increased from 6.1 ± 2.8 pmol/L to 104.7 ± 16.4 pmol/L when the BAPs were implanted in the intramedullary cavity.This study indicates superior effectiveness of BAPs implanted in the intramedullary cavity compared with the intramuscular space. This observation may be attributed to the greater oxygen tension in the bone marrow. The BAPs in direct contact with the circulatory system receive sufficient blood flow for function and survival. This preliminary study demonstrates that the intramedullary cavity may be an implantation site for BAP transplantation.

Interventional radiology is becoming one of the standard treatments of arteriovenous malformation (AVM). Cyanoacrylate derivatives and polymer solutions are widely used to occlude the AVM nidus by their injection through a catheter, but they are far from satisfactory embolic liquids. For instance, cyanoacrylate derivatives sometimes glue the catheter to the artery, resulting in serious complications; in addition, the organic solvents used to dissolve polymers cause damage to the surrounding brain tissue of the AVM. Therefore, we attempted to develop embolic liquids by dissolving poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) in Iopamiron with an addition of a small amount of ethyl alcohol. This new embolic liquid is not cytotoxic and is easily injected into the AVM through a thin, long catheter to effectively occlude the AVM.

Characteristics of a newly developed liquid material for embolization of AVM and its clinical experiments are reported. This liquid is composed of dissolving poly (2-hydroxyethyl methacrylate-co-methyl methacrylate) in Iopamiron with adding a small amount of ethyl alcohol. Thirty-two cases of AVM and 5 cases of spinal AVM were embolized with this liquid with good results. This liquid material is of low viscosity, not adhesive and not cytotoxic, therefore, it can be easily injected through a microcatheter, and can safely and effectively occlude AVM.

In an earlier article we demonstrated that xenogeneic islets of Langerhans in an agarose/poly(styrenesulfonic acid) (PSSa) microcapsule were protected from the host's immune rejection and that diabetic animals maintained a normal glucose level for a long period of time after their transplantation. In this study, we attempted to make clear the immuno-isolative mechanisms of the agarose-PSSa microcapsule from the standpoint of permeability of antibodies and complement proteins through this microcapsule membrane. It was found that the microcapsule was unable to prevent the permeation of IgG for longer than a few days, but protect the encapsulated cells from cytolytic complement attack. This strongly suggests that the cytolytic complement activity was lost during permeation through the microcapsule, probably because of the strong interaction of PSSa in the membrane with complement proteins. Based on these findings we proposed the minimum requirement for the immuno-isolative membrane to be applicable to xenotransplantation.

Immunoisolation, that is, enclosure of cells within a semipermeable membrane to protect them from immunological rejection, may enable the transplantation of cells without use of immunosuppressive drugs. Therefore, in addition to naturally-occurring ionic polymers, several synthetic nonionic polymers which can form dense and strong membranes in water have been studied as materials for immunoisolation. However, such nonionic polymers are required to be soluble in organic solvents which are mostly cytotoxic. In this report we describe enclosure of insulin-releasing cells into water-insoluble poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl methacrylate-co-methyl methacrylate) membranes using X-ray contrast medium as a solvent without use of any special apparatus. The contrast medium employed in our study is iopamidol aqueous solution. Insulin release was observed for 1 month when insulin-releasing cells were encapsulated into these membranes. The permeability of five solutes through the membranes prepared from the iopamidol aqueous solution was also studied to determine their potential immunoisolative efficacy.

This study examines the function of a novel B cell line (MIN6) enclosed in hybrid bioartificial pancreas with mesh-reinforced polyvinyl alcohol hydrogel tube (MRPT) or with improved, three-layer agarose microcapsules. MIN6 was established from insulinomas obtained by targeted expression of the simian virus 40 T-antigen gene in transgenic mice. MIN6 retains the ability to secrete insulin in response to physiological glucose concentrations. The MRPT and the three-layer agarose microcapsules, which were developed to act as an artificial pancreas, were readily permeated by insulin, glucose, and other nutrients. Both can immunoisolate enclosed MIN6 cells from the recipient's humoral and cellular immunosystems, which causes a xenogeneic rejection response. MIN6 cells (5.0 x 10(6) or 1.5 x 10(6)) were enclosed in MRPT or in a hundred three-layer microcapsules and subjected to an in vitro perifusion study or a static incubation study to observe the insulin release from each bioartificial pancreas in response to glucose stimulation. In vitro study revealed that the insulin secretion in response to 16.7 mM glucose stimulation was twice that with 3.3 mM glucose stimulation with both MRPT and the three-layer agarose microcapsules. The present study demonstrates that MIN6 effectively functions as a bioreactor for the hybrid bioartificial pancreas. The application of MIN6 cells to the hybrid bioartificial pancreas may offer a solution to the current serious dearth of organs.

We examined the effectiveness of an improved version of a three-layer agarose microcapsule in islet xenotransplantation. The microcapsule is composed of a mixture of 5% agarose and 5% polystyrene sulfonic acid. The other two outer layers are polybrene and carboxymethyl cellulose. The agarose/polystyrene sulfonic acid membrane is for the purpose of immunoisolation, suppression of complement activity and reinforcement of the microcapsule. The polybrene layer suppresses the polystyrene sulfonic acid leakage by forming a polyionic complex at the surface of the agarose/polystyrene sulfonic acid membrane. The outermost layer, a carboxymethyl cellulose coating, improves the biocompatibility of the microcapsule. In vitro static incubation study showed that the insulin secretion from rat islets in microcapsules in response to 16.7 mM glucose stimulation was more than four times higher than that on 3.3 mM glucose stimulation (n = 8). In an in vivo study, 500 rat islets in microcapsules were xenogenically implanted in the abdominal cavity of mice with streptozotocin-induced diabetes. The graft survival times ranged from 2 to 5 mo, the average being 75 days (n = 5). Our results demonstrate that the improved version of the three-layer agarose microcapsule can effectively prolong the xenograft survival time without employing immunosuppressants, suggesting that this microcapsule could provide a promising biohybrid artificial pancreas for future clinical applications.

Immunoisolation of islets of Langerhans (islets) by their enclosure in a filter to isolate them from the host immune system following implantation is a particularly attractive method for bioartificial pancreas. The filter should have excellent semipermeability so that damaging components of the immune system cannot reach the implanted islets. In addition, oxygen and nutrients should be supplied at a sufficiently high rate to maintain tissue viability. In the present work we conducted in vitro diffusion studies of solutes with various molecular sizes through Nuclepore filters and an XM-50 ultrafilter, which have been preferentially used for immunoisolation. The high permeability of microsolutes was not reduced much by the presence of any filters, implying that oxygen and nutrients could be effectively supplied to living cells by diffusion even if enclosed in a filter. Since the predominant cause of allograft rejection is activation of cellular immunity by T lymphocyte, while humoral immunity including antibodies and complement proteins plays a major role in the rejection of xenografts, requirements for the semipermeability of filters highly depends on the donor of islet tissue. T lymphocytes with a diameter of about 10 microm can permeate through neither Nuclepore nor XM-50 filters because their pore size is less than 2 microm. Therefore all of the filters are anticipated to act as effective immunobarrier for islet allografts. Although the XM-50 ultrafilter and 0.015-microm-diameter Nuclepore filter can sharply fractionate macromolecules in accordance with their size (around 50 kD) in a pressure-driven process such as ultrafiltration, these filters were found to lose the fractionation efficiency of macrosolutes in a concentration-driven process such as diffusion. In other words, neither the Nuclepore filters nor the XM-50 ultrafilter could prevent passage of immunoglobulin G in the diffusion process. This finding suggests that these filters cannot protect xenogeneic islets from the host immune system because biomacromolecules may permeate through these filters by the concentration-driven force.