STRUCTURE AND STABILITY OF HUMAN HEMOGLOBIN MICROPARTICLES PREPARED WITH A DOUBLE EMULSION TECHNIQUE

Hemoglobin solutions can be used as blood substitutes but they present some disadvantages often due to their rapid removal from the bloodstr eam after injection. A possible way of overcoming this problem is to t rap hemoglobin inside particles. This study deals with the preparation , structure and stability of poly(lactic acid) and ethylcellulose micr oparticles containing human hemoglobin obtained with a double emulsion technique. We investigated the manufacturing process of these particl es in order to increase the encapsulation ratio of hemoglobin. For thi s purpose, some parameters involved in the procedure were optimized, s uch as hemoglobin concentration and duration of stirring hemoglobin lo ading increases with its concentration in the preparation and well-def ined stirring time avoids a leakage of hemoglobin. Hemoglobin concentr ation, surfactant concentration i.e. poly(vinylic alcohol), amounts of polymer and solvent (methylene chloride), duration and speed of stirr ing. The microparticles were prepared with satisfactory yields (60 to 73%). They were spherical and their mean size was lower than 200 mu m. The functional properties of entrapped hemoglobin were studied. The e ncapsulation did not alter hemoglobin and the oxygen affinity of the h emoglobin remained unmodified (P-50 about 13.9 mm Hg in a Bis-Tris buf fer pH 7.4 at 37 degrees C). Moreover, only low levels of methemoglobi n could be detected (less than 3%). Besides, about 90% of encapsulated hemoglobin could be released from microparticles, with a speed relate d to the internal structure of the particles. The prepared micropartic les were stored during one month at +4 degrees C. No degradation of th e particle structure occurred and the functional properties of hemoglo bin were preserved. These particles could provide a potential source o f oxygen in the field of biotechnologies but any application for a tra nsfusional purpose would first require a drastic reduction in particle size.