Poria cocos (Fuling), also named Wolfiporia extensa, a wood-decaying fungus, is widely used as a traditional Chinese medicinal herb. Linear pachyman from Poria powder can be chemically modified to carboxymethyl pachyman (CMP) which has higher water solubility. Pachyman and CMP may enhance body immunity, and have anti-bacterial, anti-hypoglycaemic and anti-tumour properties.

Aims
The aim of the study was to prepare and study colon targeted microparticulates of different molecular weight pachyman and CMP.

Methods
Pachyman was extracted from Poria cocos dry powder and was chemically modified to CMP. The pachyman and CMP were extracted with hot water and alcohol, degraded by hydrogen peroxide under the ultrasonic wave and then graded through Sephadex G-75. The degradation products with different molecular weights were cross-linked with azobenzene crosslinker to form azo-polymers for colon-specific drug delivery.

Results and discussion
High yields of pachyman, containing low levels of protein and other impurities were obtained. The degradation products of pachyman had MW of 43-56 000 Da. The degraded CMP had MW of around 66 000 Da. Because of the high degree of polymerization in Pachyman and CMP, it was not easy to make the azo cross-linker with colon-specific ability. IR analysis demonstrated that the pachyman degradation products reacted with the azo cross-linker to form colon-specific drug carriers. Degraded pachyman could carry test drugs but CMP products could not. Low molecular weight pachyman degradation products, but not the products from CMP, may be suitable as colon-specific drug carriers.

Conclusion
Keywords: Poria cocos; pachyman; carboxymethyl pachyman; Azo-polymers for Colon-specific Drug Delivery.