Cả hai lớp phủ polymer của các liposome có chứa tropicamide không làm tăng đáng kể khả dụng sinh học của thuốc bọt liên quan đến các túi không tráng (63). Tuy nhiên, trái ngược với công việc trước đây (53), kích thước và đo lường tiềm năng zeta của liposome tropicamide không tráng và liposome phủ trong cả hai giải pháp polymer đã chứng minh mối liên quan | 426 Johnston et al. tropicamide liposomes 63 . Both polymer coatings of tropicamide-contain-ing liposomes failed to significantly increase the bioavailability of the entrapped drug relative to uncoated vesicles 63 . However in contrast to previous work 53 size and zeta potential measurements of uncoated tro-picamide liposomes and liposomes coated in both polymer solutions demonstrated an association between the Carbopols and the vesicles at both pH and pH 5 as evidenced by an increase in size and a decrease in the corresponding zeta potential. It was suggested that the prolongation in precorneal residence for Carbopol 1342-coated tropicamide liposomes was due to the formation of a three-dimensional microgel structure which interacted with the phospholipid vesicles and subsequently increased their retention via a mechanism of adhesion to the mucin network 63 . Microsphere formulations have been evaluated for their capacity to retain 111In as indium chloride in the preocular precorneal area of the rabbit eye 64 . Clearance of the radiolabeled compound was monitored using gamma scintigraphy and the influence of pH and prehydration of the microspheres on precorneal retention was assessed. These authors prepared microspheres of poly acrylic acid Carbopol 907 cross-linked with maltose by a water-in-oil w o emulsification process. Precorneal clearance of the microspheres at pH 5 and were compared to an 111In aqueous suspension 64 . Clearance of the microspheres demonstrated a biphasic a rapid initial phase and p slower phase profile and microspheres buffered at pH 5 exhibited a significantly slower p phase than microspheres buffered at pH . Presumably the neutralized Carbopol formulation pH did not possess the same degree of mucoadhesive strength as the microsphere preparation formulated at pH 5. In vitro tests of mucoadhesive strength verified that the force of detachment of the microspheres formulated at pH 5 from mucus glycoprotein was significantly .
