The patent's assignee for patent number 8506972 is
News editors obtained the following quote from the background information supplied by the inventors: "Hydrogels are continuously gaining increased attention as biomaterials for biomedical applications, such as tissue engineering and therapeutics delivery. Furthermore, in situ forming hydrogels or those exhibiting the specific ability of increasing their viscosity with temperature, also called thermosensitive, are preferred over preformed hydrogels, since cells and bioactive compounds, such as drugs, may be easily mixed with the precursor solutions prior to gelation to give homogeneously loaded gels. In addition, in situ gelation facilitates the application and allows for minimally invasive surgery and for adequately fill complex shaped lesion cavities.
"Chitosan is an amino polysaccharide obtained by partial to substantial alkaline N-deacetylation of chitin also named poly(N-acetyl-D-glucosamine), which is a naturally occurring biopolymer found in exoskeleton of crustaceans, such as shrimp, crab and lobster shells. Chitosan contains free amine (--NH.sub.2) groups and may be characterized by the proportion of N-acetyl-D-glucosamine units and D-glucosamine units, which is expressed as the degree of deacetylation (DDA) of the fully acetylated polymer chitin. The properties of chitosan, such as the solubility and the viscosity, are influenced by the degree of deacetylation (DDA), which represents the percentage of deacetylated monomers, and the molecular weight (Mw).
"Chitosan has been proposed in various formulations, alone and with other components, to stimulate repair of dermal, corneal and hard tissues in a number of reports (U.S. Pat. Nos. 4,572,906; 4,956,350; 5,894,070; 5,902,798; 6,124,273; and WO 98/22114). The properties of chitosan that are most commonly cited as beneficial for the wound repair process are its biodegradability, adhesiveness, prevention of dehydration and as a barrier to bacterial invasion. The interesting haemostatic potential of chitosan has also led to its direct application to reduce bleeding at grafts and wound sites (U.S. Pat. No. 4,532,134). Some studies claim that the haemostatic activity of chitosan derives solely from its ability to agglutinate red blood cells while others believe its polycationic amine character can activate platelets to release thrombin and initiate the classical coagulation cascade thus leading to its use as a haemostatic in combination with fibrinogen and purified autologous platelets (U.S. Pat. No. 5,773,033).
"One technical difficulty that chitosan often presents is a low solubility at physiological pH and ionic strength, thereby limiting its use in a solution state. Thus typically, dissolution of chitosan is achieved via the protonation of amine groups in acidic aqueous solutions having a pH ranging from 3.0 to 5.6. Such chitosan solutions remain soluble up to a pH near 6.2 where neutralisation of the amine groups reduces interchain electrostatic repulsion and allows attractive forces of hydrogen bonding, hydrophobic and
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