Comparative Study of the Preparation of High-Molecular-Weight Fibroin by Degumming Silk with Several Neutral Proteases.

Removing sericin from the periphery of silk without damage to silk fibroin (SF) to obtain high-molecular-weight SF is a major challenge in the field of SF-based biomaterials. In this study, four neutral proteases, subtilisin, trypsin, bromelain and papain, were used to degum silk, and the degumming efficiency of the proteases and their influence on the molecular weight (MW) of regenerated silk fibroin were studied. The results indicated that all four neutral proteases could remove sericin from silk almost completely, and they caused less damage to SF fibers than Na2CO3 degumming did. The degumming efficiency of trypsin and papain was strong, but they caused relatively high damage to SF, whereas bromelain caused the least damage. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel permeation chromatography and shear viscosity showed that the MWs of regenerated SF derived from neutral protease degumming were significantly higher than that of SF derived from Na2CO3 degumming. The MW of regenerated SF derived from bromelain degumming was the highest, while the MWs of regenerated SF derived from papain and trypsin degumming were relatively low. This study provides an efficient and environmentally friendly biological degumming method for obtaining high-molecular-weight silk fibroin.

A high molecular weight silk fibroin scaffold that resists degradation and promotes cell proliferation.

The regulation of the biodegradation rate of 3D-regenerated silk fibroin scaffolds and the avoidance of premature collapse are important concerns for their effective applications in tissue engineering. In this study, bromelain, which is specific to sericin, was used to remove sericin from silk, and high molecular weight silk fibroin was obtained after the fibroin fibers were dissolved. Afterwards, a 3D scaffold was prepared via freeze-drying. The Sodium dodecyl sulfate-polyacrylamide gel electrophoresis results showed that the average molecular weight of the regenerated silk fibroin prepared by using the bromelain-degumming method was approximately 142.2 kDa, which was significantly higher than that of the control groups prepared by using the urea- and Na2 CO3 -degumming methods. The results of enzyme degradation in vitro showed that the biodegradation rate and internal three-dimensional structure collapse of the bromelain-degumming fibroin scaffolds were significantly slower than those of the two control scaffolds. The proliferation activity of human umbilical vein vascular endothelial cells inoculated in bromelain-degumming fibroin scaffolds was significantly higher than that of the control scaffolds. This study provides a novel preparation method for 3D-regenerated silk fibroin scaffolds that can effectively resist biodegradation, continuously guide cell growth, have good biocompatibility, and have the potential to be used for the regeneration of various connective tissues.

In situ monitoring of carbamazepine-nicotinamide cocrystal intrinsic dissolution behaviour.

Cocrystals have shown huge potential to improve the dissolution rate and absorption of a poorly water soluble drug. However, solution mediated phase transformation of cocrystals could greatly reduce the enhancement of its apparent solubility and dissolution rate. The aim of this study is to gain a deep understanding of the phase transition behaviour of cocrystals during dissolution and to investigate the improvement of dissolution rate. Dissolution and transformation behaviour of carbamazepine-nicotinamide (CBZ-NIC) cocrystal, physical mixture and different forms of carbamazepine: form I (CBZ I), form III (CBZ III) and dihydrate (CBZ DH) were studied by different in situ techniques of UV imaging and Raman spectroscopy. It has been found that compared with CBZ III and I, the rate of intrinsic dissolution rate (IDR) of CBZ-NIC cocrystal decreases slowly during dissolution, indicating the rate of crystallisation of CBZ DH from the solution is slow. In situ solid-state characterisation has shown the evolution of conversion of CBZ-NIC cocrystal and polymorphs to its dihydrate form. The study has shown that in situ UV imaging and Raman spectroscopy with a complementary technique of SEM can provide an in depth understanding during dissolution of cocrystals.