Fabrication Of Biocompatible Multilayer Microcapsules And Their Drug Delivery Properties

The Layer-by-Layer (LbL) self-assembly based on electrostatic interaction was initially introduced by Decher and co-workers in 1991. Later on, the technique was applied onto decomposable colloidal particles by Mohwald, Caruso, Donath and co-workers, followed by core removal to produce hollow microcapsules. We applied this novel strategy to incorporate and release anti-cancer drugs of daunorubicin (DNR) and doxorubicin (DOX) in preformed microcapsules. Oppositely charged poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) were assembled onto PSS doped-CaCO₃ colloidal particles in a LbL manner to yield core-shell particles. After removal of the carbonate cores by disodium ethylenediaminetetraacetic acid (EDTA), hollow microcapsules with entrapped PSS were fabricated, which showed spontaneous loading ability of positively charged DNR and DOX. The drug loading was confirmed qualitatively by observations under confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM) and scanning force microscopy (SEM). Quantification of the drug loading was performed under different conditions, revealing that a larger amount of drugs could be incorporated at higher drug feeding concentrations and higher salt concentrations. The DNR and DOX concentration in the microcapsule interiors can reach to 29.6mg/mL and 32.0 mg/mL, respectively, with a drug feeding concentration of 1mg/mL. However, putting additional polyelectrolyte layers on the microcapsules after core removal resulted in weaker drug loading efficiency due to the loss of PSS during assembly. The drug release behaviors from the microcapsules with different layer numbers were studied too, revealing a diffusion controlled release mechanism at the initial stage (4h).Biocompatible multilayer microcapsules were fabricated by LbL self-assembly of natural polysaccharides onto CaCO₃ particles, following with core removal. The micron-sized CaCO₃ particles were synthesized by reaction between Ca(NO₃)₂ and Na₂CO₃ solutions in the existence of carboxylmethyl cellulose (CMC). The incorporated amount of CMC in the CaCO₃ particles was found to be 5.3wt% by thermogravimetric analysis. Two biocompatible polysaccharides, chitosan and sodium alginate were alternately deposited onto the CaCO₃(CMC) templates to obtain hollow microcapsules. Regular oscillation of surface charge as detected by zeta potential demonstrated that the assembly proceeded surely in an LbL manner. The stability of the microcapsules was effectively improved by crosslinking of chitosan withglutaraldehyde. The chemical reaction was verified by infrared spectroscopy. The microcapsules thus fabricated could be spontaneously filled with positively charged low molecular weight substances such as rhodamine 6G and showed good biocompatibility as detected by in vitro cell culture. DNR and DOX can be effectively encapsulated into the fabricated (CMC)/(chitosan/alginate)₅ microcapsules. The drug concentration can be as high as 83.7 mg/mL and 88.6mg/mL for DNR and DOX, respectively, with the drug feeding concentration of 1mg/mL. The entrapped drugs can be released again in a diffusion controlled manner in the initial stage (～2h).The DOX loaded microcapsules were further used to treat tumor by in vitro cell culture and in vivo animal experiments. The microcapsules composed of totally polysaccharides were fabricated by deposition of oppositely charged chitosan and alginate onto CMC doped CaCO₃ colloidal particles in an LbL fashion, followed by crosslinking with glutaraldehyde and decomposition of the cores by EDTA. The as-prepared microcapsules contain negatively charged CMC, which may either in a free state or most possibly coupled with the excess chitosan of the first layer. They showed strong ability to accumulate the positively charged DOX with a factor of tens to hundreds, i.e. the drug concentration within the microcapsules was hundreds times higher than the feeding concentration. CLSM and TEM observed homogeneous distribution of the drug. In vitro experiment showed that the encapsulated drug can effectively induce the apoptosis of HepG2 tumor cells, as evidenced by various microscopy techniques after acridine orange, Hoechst 33342 and osmium tetraoxide staining, respectively. By seeding the HepG2 hepatoma cells into BALB/c/nu mice, tumors were created for the experimental studies. The results showed that the encapsulated DOX had better efficacy than that of the free drug in terms of tumor inhibition in a 4 week in vivo culture period.For the purpose of targeted delivery of microcapsules onto cancer cells, folic acids (FA) were immobilized onto polyelectrolyte microcapsules through the linkage of diamino terminated poly(ethylene glycol) (PEG). The FA modified microcapsules can selectively adsorb onto SMMC-7721 liver cancer cells via folate receptor mediated specific recognition. DOX loaded FA modified microcapsules had better inhibition efficacy to HepG2 cells than that of the free drug in the same culture period.