Toward a bioartificial pancreas: diffusion of insulin and IgG across immunoprotective membranes with controlled hydrophilic channel diameters.

Research continued toward a bioartificial pancreas (BAP). Our BAPs consist of a perforated nitinol scaffold coated with reinforced amphiphilic conetwork membranes and contain live pancreatic islets. The membranes are assemblages of cocontinuous hydrophobic domains and hydrophilic channels whose diameters were varied by the MW of hydrophilic segments between crosslinks (M(c,HI) = 32, 44, and 74 kg x mol(-1)). We studied the diffusion rate of insulin, BSA, and IgG across the membrane of the BAP in the absence of islets. Membranes of M(c,HI) = 74 kg x mol(-1) showed rapid insulin and BSA transport and negligible IgG diffusion. BAPs containing approximately 300 mouse islets showed appropriate response upon glucose challenge in vitro. The BAP implanted into diabetic mice reduced hyperglycemia and maintained islet viability for at least 4 d.

A new bioartificial pancreas utilizing amphiphilic membranes for the immunoisolation of porcine islets: a pilot study in the canine.

We have developed a replaceable bioartificial pancreas to treat diabetes utilizing a unique cocontinous amphiphilic conetwork membrane created for macroencapsulation and immunoisolation of porcine islet cells (PICs). The membrane is assembled from hydrophilic poly(N,N-dimethyl acrylamide) and hydrophobic/oxyphilic polydimethylsiloxane chains cross-linked with hydrophobic/oxyphilic polymethylhydrosiloxane chains. Our hypothesis is that this membrane allows the survival of xenotransplanted PICs in the absence of prevascularization or immunosuppression because of its extraordinarily high-oxygen permeability and small hydrophilic channel dimensions (3-4 nm). The key components are a 5-10 microm thick semipermeable amphiphilic conetwork membrane reinforced with an electrospun nanomat of polydimethylsiloxane-containing polyurethane, and a laser-perforated nitinol scaffold to provide geometric stability. Devices were loaded with PICs and tested for their ability to maintain islet viability without prevascularization, prevent rejection, and reverse hyperglycemia in three pancreatectomized dogs without immunosuppression. Tissue tolerance was good and there was no systemic toxicity. The bioartificial pancreas protected PICs from toxic environments in vitro and in vivo. Islets remained viable for up to 3 weeks without signs of rejection. Neovascularization was observed. Hyperglycemia was not reversed, most likely because of insufficient islet mass. Further studies to determine long-term islet viability and correction of hyperglycemia are warranted.

A novel macroencapsulating immunoisolatory device: the preparation and properties of nanomat-reinforced amphiphilic co-networks deposited on perforated metal scaffold.

This paper describes the design and preparation of the non-biological components (the "hardware") of a conceptually novel bioartificial pancreas (BAP) to correct diabetes. The key components of the hardware are (1) a thin (5-10 microm) semipermeable amphiphilic co-network (APCN) membrane [i.e., a membrane of cocontinuous poly(dimethyl acryl amide) (PDMAAm)/polydimethylsiloxane (PDMS) domains cross-linked by polymethylhydrosiloxane (PMHS)] expressly created for macroencapsulation and immunoisolation of a tissue graft; (2) an electrospun nanomat of PDMS-containing polyurethane to reinforce the water-swollen APCN membrane; and (3) a perforated hollow-ribbon nitinol scaffold to stiffen and provide geometric stability to the construct. The reinforcement of water-swollen hydrogels with an electrospun nanomat is a generally applicable new method for hydrogel reinforcement. Details of device design and preparation are discussed. The advantages and disadvantages of micro- and macro-immunoisolation are analyzed, and the requirements for the ideal immunoisolatory membrane are presented. Burst pressure, and glucose and insulin permeabilities of representative devices have been determined and the effect of device composition and wall thickness on these properties is discussed.

Synthesis and characterization of PCL-b-PEO-b-PCL-based nanostructured and porous hydrogels.

Hydrogels with nanoscale structure were synthesized using amphiphilic poly(epsilon-caprolactone)-poly(ethylene oxide)-poly(epsilon-caprolactone) (PCL-b-PEO-b-PCL) triblock copolymers. Small-angle X-ray scattering (SAXS) studies show that the block copolymers form 30-40 nm structures in aqueous solution and that these patterns are retained, with some increase in length scale, following electron beam cross-linking. Lamellar nanostructures were observed by SAXS and atomic force microscopy (AFM), with SAXS indicating cylindrical structure as the block lengths become more different in length. It is demonstrated through Fourier transform infrared spectroscopy (FTIR), mass loss, and differential scanning calorimetry (DSC) that the PCL can be completely removed by hydrolysis in NaOH(aq) to form porous PEO hydrogels. These hydrogels retain active functional groups following PCL removal that serve as sites for further chemical modification.