Formulation of liposomes for protective functions for the human dental enamel

Abstract

The present work concerns the development of liposomal formulations that can adsorb to the human dental enamel. The overall aim of this pharmaceutical approach is to physically protect the teeth against detrimental processes, such as tooth wear, acidic challenges and dental caries. Adsorption experiments of different liposomal formulations to hydroxyapatite (HA), a model substance for the dental hard tissue, and the human dental enamel were performed. To find which liposomal formulations are promising for the adsorption to teeth, formulation factors important for the interaction were initially mapped by the use of experimental design and multivariate analysis (Paper I). The type of surface charge became the most significant factor for the adsorption process. Positively charged liposomes adsorbed better than the negatively charged liposomes to HA in phosphate buffer, pH 6.8-7. However, the adsorption of positively charged liposomes to HA in a salivary environment was interfered as they were found to aggregate with components of saliva (Paper II). To overcome problems related to the positively charged liposomes, the surface of the liposomes was modified with the polymer pectin. Three types of pectin were investigated for the surface coating of liposomes: LM-, HM- and amidated pectin (Paper III). Pectin coating of positively charged liposomes was successfully prepared, and a reproducible method was established. Pectin coated liposomes did not seem to interact with salivary components (Paper IV), and were therefore promising for use in the oral cavity. Pectin coated liposomes adsorbed to HA in saliva, and liposomes coated with LMand HM-pectin were selected for further investigation with the dental enamel (Paper IV). Both uncoated negatively charged liposomes and pectin coated liposomes adsorbed onto enamel specimens in a salivary environment (Paper IV), indicating their potential use in the protection of the teeth. The adsorption was examined by exposing a flow on the enamel surfaces for certain time intervals. Pectin coated liposomes seemed to retain better than uncoated negatively charged liposomes at longer time intervals. It was hypothesized that pectin may help to prolong the adhesion of liposomes on the tooth surfaces.