The incorporation and sustained release of bioactive insulin from a bead-formed macroporous hydrogel matrix.

Freeze-thaw photopolymerization of a mixed solution of monomers and bovine insulin around frozen ice crystals has been used to generate a bead-formed macroporous hydrophilic matrix of p-HEMA. The largest proportion of beads was 500-1000 microns in size (distribution < 106-1700 microns) with a mean EBC of 71.7 +/- 0.92%. Insulin release was monitored using RIA and insulin bioactivity determined using the rate of insulin stimulated D-[U14C] glucose oxidation to 14CO2. The cumulative insulin release profile was characterized by an initial lag phase followed by an almost linear increase in insulin release for up to 30 days. Insulin release at 4 degrees C was significantly greater than release at 37 degrees C both in the presence and absence of 2.5% thiomersalate as preservative. The latter served to extend the time period over which significant insulin release could be detected. Increasing the monomer concentration decreased the mean equilibrium buffer content (EBC), the total mean cumulative release of insulin, and the proportion of the incorporated insulin load subsequently released at both 4 degrees C and 37 degrees C in the presence of preservative. Insulin determination using RIA and bioassay confirmed that insulin released from beads was bioactive and that immunoreactivity was a reasonably reliable indicator of bioactivity.

The incorporation and release of glucose oxidase and interleukin 2 from a bead formed macroporous hydrophilic polymer matrix.

Freeze-thaw photopolymerization at low temperature of a mixed solution of 2-hydroxyethyl methacrylate (HEMA), ethylene glycol dimethacrylate (EDM), and either glucose oxidase (GOx) or interleukin 2 (IL-2) around frozen ice crystals has been used to generate a bead-formed macroporous hydrophilic matrix with potential for immobilization and sustained release. The mean equilibrium acetate buffer content (EBC) of unloaded p-HEMA beads at room temperature and controlled humidity was approximately 72%. The incorporation of GOx into beads significantly increased the EBC to approximately 76%. The release of GOx was characterized by a short initial burst release which declined rapidly until by day 14 no further biologically active enzyme release could be detected. Bead size had no significant effect on the total mean cumulative release of GOx at room temperature. Since only approximately 4% of the original therapeutic load of GOx was released over 14 days a substantial proportion of biologically active enzyme had become associated with the hydrogel matrix surface generating a bead formed immobilised enzyme system. Total cumulative release profiles for IL-2 were almost linear and maintained for at least 16 days. In absolute terms, the proportion of the original theoretical incorporated load subsequently released over this period was low. However, such a low level sustained release of IL-2 may lend itself therapeutically to a reduction in unwanted non-specific systemic activity.

Incorporation and release of fluorescein isothiocyanate-linked dextrans from a bead-formed macroporous hydrophilic matrix with potential for sustained release.

Freeze-thaw polymerization has been used to generate a bead-formed (100-3000 microns) macroporous hydrophilic matrix with potential for the sustained release of macromolecules. While the incorporation of FITC-dextrans marginally increased the equilibrium water content, their in vitro release profiles were characterized by an initial burst followed by a low but sustained release lasting > 21 d. The total cumulative release of FD-150 and the percentage of the incorporated FD-150 load subsequently released were reduced compared with FD-20S but for both dextrans these parameters could be enhanced by increasing the bead size and increasing the incubation temperature to 37 degrees C.

Low temperature incorporation of bovine serum albumin into a bead formed macroporous hydrophilic polymer matrix with potential for sustained release.

A process of freeze-thaw polymerization involving the low temperature photopolymerization of a mixed solution of monomers and bovine serum albumin around frozen ice crystals has been used to generate a bead formed macroporous hydrophilic matrix with potential for sustained release. Beads over the size range 100-3000 microns were fabricated with surface and internal pores of between 0.7-2.6 microns whose diameter could be controlled by manipulation of the monomers to solvent ratio. Increasing both the proportion of monomers in the monomer solution and the percentage of BSA incorporated reduced the EWC of beads. The BSA release profile was characterized by an initial burst followed by a lower but sustained release lasting up to 1 month. The total cumulative release of BSA and the proportion of the incorporated BSA load subsequently released were both reduced in physiological saline compared with distilled water but enhanced by freeze drying, mild agitation and incubation at 37 degrees C.