Double Crosslinked Research Articles

Double crosslinked chitosan and gelatin submicronic capsules entrapping aminoacid derivatives with potential antitumoral activity

The aim of the article was the synthesis of novel l-phenylalanine derivatives with biological activity and their immobilization into polymeric particles. Thus, new formyl, acetyl and p-methoxy derivatives of l-phenylalanine with antitumor activity were synthesized by reaction with p-nitrobenzoyl chloride, followed by the reduction of nitro group and acylation of the new formed amino group. The chemical structures of the obtained aminoacid derivatives were determined by FT-IR, NMR, MS and elemental analyses. The compounds were encapsulated into chitosan- and gelatin-based submicronic capsules, prepared by double crosslinking (ionic and covalent) in a O/W/O double emulsion. The varying parameter polymer/ionic crosslinker molar ratio was seen to influence particle size, morphology, swelling degree, thermal properties, as well as their capacity to incorporate and release the new active principles. The in vivo acute toxicity and antitumoral effect of aminoacid derivatives in free form or encapsulated were evaluated on rats. Drug encapsulation into polymeric systems was proven to enhance antitumoral activity against implanted Guerin’s carcinoma.

Controlled gelation and degradation rates of injectable hyaluronic acid-based hydrogels through a double crosslinking strategy

Various biodegradable hydrogels have been employed as injectable scaffolds for tissue engineering and drug delivery. We report a double-crosslinking strategy of biocompatible and biodegradable hydrogels derived from aminated and oxidized hyaluronic acid (HA) with genipin (GP), a compound naturally derived from the gardenia fruit. Fast gelation is attributed to the Schiff-base reaction between amino and aldehyde groups of polysaccharide derivatives, and the subsequent crosslinking with GP results in ideal biodegradability and mechanical properties. The gelation time, morphology, equilibrium swelling, compressive modulus and degradation of double-crosslinked hydrogels were examined. The double crosslinked hydrogels were examined in vivo via subcutaneous injection into a mouse model. Histological results indicated favourable biocompatility, as revealed by an absence of neutrophils and macrophages. These studies demonstrate that double-crosslinked HA hydrogels are potentially useful as injectable, biodegradable hydrogels in tissue-engineering applications.

Effects of double cross-linking technique on the enzymatic degradation and calcification of bovine pericardia.

The strength, resorption rates, and biocompatibility of collagenous biomaterials are profoundly influenced by the method of cross-linking. The in vitro and in vivo calcification and enzymatic degradation of bovine pericardia (BP) after a series of surface modifications were studied as a function of exposure time. Collagenase degradations of modified BP were monitored by scanning electron microscopy and tensile strength measurements. Bovine pericardium was modified by a combination of different tissue fixatives such as glutaraldehyde (GA), carbodiimide (EDC), diisocyanate (HMDIC), and polyethylene glycol (PEG). GA-PEG-EDC-PEG and GA-PEG-HMDIC-PEG combination treated BP retained maximum stability in collagenase digestion compared to GATBP. In vitro calcification studies and in vivo rat subcutaneous implantations of modified pericardium have shown substantial reduction in the calcification of double cross-linked BP with PEG modification. Further, the biocompatibility aspects of pericardial tissues were established by platelet adhesion and octane contact angle. It seems that cross-links involving amino and carboxyl residues may provide new ways of controlling biodegradation and calcification.

Stabilities and properties of multilinked hemoglobins.

Crosslinking of both human and dog hemoglobin has been done with a variety of reagents to produce singly, doubly and multiply crosslinked hemoglobins. Succinate and glutarate diaspirins did not crosslink deoxy human hemoglobin in good yield, in contrast to the fumarate analog (DBSF). Deoxy dog Hb did not react well with DBSF, but oxy dog Hb did react, giving crosslinked tetramers as well as dimers on SDS electrophoresis. Crosslinking with a short, rigid reagent (difluorodinitrobenzene) resulted in a similar product for both oxy and deoxy hemoglobin that had high stability and oxygen affinity. The trilinker, tris-chloroethylamine, produced a more stable product than the corresponding crosslinker, bis-chloroethylamine. Double crosslinking oxy Hb with DBSF and dimethylpimelimidate or with DBSF followed by deoxygenation and recrosslinking with DBSF gave products with higher denaturation temperatures. The diaspirin double crosslinked product had high oxygen affinity.