Photopolymerization of bovine hemoglobin entrapped nanoscale hydrogel particles within liposomal reactors for use as an artificial blood substitute.

Lipogel particles encapsulating bovine hemoglobin (BHb) were synthesized via photopolymerization of poly(N-isopropylacrylamide) (pNIPA) and poly(acrylamide) (pAAm) monomers within liposomal reactors. Nanoscale hydrogel particles (NHPs) encapsulating bovine hemoglobin, which represent a hybrid between acellular and cellular hemoglobin based oxygen carriers, were formed upon solubilization of the lipid bilayer of lipogel particles encapsulating BHb. Lipogels and NHPs encapsulating BHb constitute a new class of blood substitute that prevents both dissociation of hemoglobin (Hb) and in vivo exposure of acellular Hb, while allowing oxygen transport through the polymer matrix. pNIPA and pAAm particles encapsulating BHb displayed oxygen affinities ranging from 9.9 +/- 1.9 to 14.4 +/- 0.1 mmHg for lipogels, methemoglobin levels ranging from 9.3 +/- 3.7% to 26.0 +/- 5.0% for lipogels and NHPs, and encapsulation efficiencies ranging from 34.2 +/- 3.4% to 97.4 +/- 15.8% for lipogels and NHPs. Interestingly, the methemoglobin level of pNIPA particles was reduced 61% by coencapsulating the reducing agent, N-acetylcysteine. Fractionation and light scattering results showed that lipogels and NHPs were spherical and exhibited narrow size distributions. The colloidal osmotic pressure of pNIPA and pAAm lipogels ranged from 3.71 +/- 0.02 to 206.87 +/- 0.42 mmHg, depending on UV-irradiation time, type of buffer, and polymer composition. These results demonstrate that hemoglobin can be encapsulated within hydrogel based particles for use as an artificial blood substitute.