pioneering work on preparation of monodisperse micro-Poly(acrylamide-co-acrylic acid) hydrogel microspheres of four spheres using SPG membrane (Sirasu porous glass memdifferent average sizes were prepared using a membrane emulsifibrane) by Nakashima (4), various kinds of monodisperse cation technique. These four kinds of microspheres had average microspheres with a narrow size distribution have been dediameters of 1.35, 2.33, 3.09, and 7.43 mm in distilled water and veloped (5-8).
were all fairly monodisperse. Their surface properties were studied
In addition to the microsphere size, the electrical surface by measuring the electrophoretic mobility of the microspheres.
properties of microspheres as a drug device are also im-
The mobility values were negative at pH 7.4 with the ionic strengths between 0.005 and 0.154 at 25ЊC. More negative mobility portant, because the device interacts with the surfaces of values were obtained with smaller microspheres than the larger various biological cells after they are administered to biologones. By analyzing the data with an electrokinetic theory for ''soft'' ical systems (9). Further, drug releasing devices should be surfaces, it was found that smaller microspheres have higher surbiocompatible, so that many attentions have been focused face charge density than the larger ones, although all kinds of on hydrogel as a device material (10).
microspheres were prepared from monomer solutions with the Recently, we have reported that the surfaces of biological same monomer composition. The observed size dependence of the cells such as erythrocytes, leukocytes, and endothelial cells electrophoretic mobility suggests that copolymerization of acrylare in general negatively charged and ''soft'' by analyzing amide monomers and acrylic acid monomers does not proceed homogeneously within a microsphere. That is, charged acrylic acid the electrokinetic data (11-13) with an electrokinetic theory monomers have a tendency to be localized in the microsphere core for ''soft '' particles (14). Also, we have shown that a negaregion, whereby the surface region of microspheres becomes poor tively charged poly(N-isopropylacrylamide) hydrogel plate in charges, reducing the mobility of larger microspheres. This is and poly(N-isopropylacrylamide)-coated-poly(styrene) lanot the case for smaller microspheres, so that their mobility betex particle have ''soft '' surfaces (15, 16).
comes more negative. ᭧ 1998 Academic Press
In the present work, in order to obtain an effective drug Key Words: poly(acrylamide-co-acrylic acid) hydrogel; memdevice, we have prepared four kinds of monodisperse poly brane emulsification technique; monodisperse; polymerization in (acrylamide-co-acrylic acid) microspheres with different small systems.
average diameters, whose surfaces are all negatively charged. To control the microsphere size, we have prepared microspheres from w/o emulsions by using SPG membrane.
''softness'' of poly(acrylamide-co-acrylic acid) monodis-377