a new gel - like composition of matter containing a complex carbohydrate with a high degree of carboxyl substitution cross - linked by an organic cross - linker has been developed . the cross - linkers have complex ring structures , e . g ., polynuclear or heterocyclic compounds , which permit development of two distinct partial positive charges under conditions where a carbohydrate is negatively charged . antibiotics are the preferred cross - linking agents and a method of sustained release of the antibodies is also disclosed .