663With recent advances in biotechnology, protein and peptide drugs have become a focus on current formulation research. Most of protein pharmaceuticals are mostly administered parenterally, 1) with the limitations included that oscillating blood drug concentrations caused by repeated doses and patient compliance resulted from frequent injections.
2)Oral delivery, which allows for a more varied load to be released, is the most convenient method of administration. However, it still remains a challenge especially since the labile structures of proteins are prone to hydrolization and enzymatic degradation.3) Natural hydrogel systems, especially polysaccharides such as pectin and chitosan, have been researched extensively in the development of protein and peptide drugs delivery systems in recent years. 2,[4][5][6] Pectin is an anionic, soluble heterogeneous polysaccharide containing linear chains of a-(1→4)-D-galacturonic acid residues. 7,8) Low-methoxy pectin with degree of esterification less than 50% can form rigid gels by the action of calcium ions or multivalent cations and cross-link the galacturonic acid chains. The main drawback of calcium pectinate gel (CPG) beads is their macroporous structures, which may cause low entrapment efficiency 4,9) and fast release 9-11) of incorporated drugs, especially for those of low molecular weight and water-solubility. In recent investigation, emulsion-gelation method 12) or a multi-particulate system 13) could also exhibit a high drug entrapment efficiency and a slow release profile. However, to some proteins, this method does not work since the proteins have to be exposed to organic solvent systems which lead to denaturation. Therefore, it is of great importance to develop a method capable to increase drug entrapment efficiencies and stable for protein and peptide drugs loaded.Isoelectric point is of great significance in protein properties because it is the pH at which proteins have minimal solubility and most stable property against denaturation.14-16) We hypothesized that minimization of the protein dissolution and diffusion during their preparation by maintaining the pH of all working solutions at or close to its isoelectric point could enhance the entrapment efficiency of the microbeads. It was of interest to see whether microbeads containing proteins such as insulin could be prepared by this strategy and exhibited better profiles.In this study, the CPG microbeads were prepared by ionotropic gelation technique coupled with working solution pH design for potential use of oral delivery system of protein and peptide drugs. Insulin, one of the most important drugs for diabetes, was chosen as a model amphoteric protein due to its comparative stability and crystallizing under different conditions. In addition, an air compressor was employed to reduce the particle size. This work also focused on the influences of some factors, such as phosphate buffer concentration, pH value of CaCl 2 solution, calcium concentration and pectin concentration, on the CPG microbeads propertie...