Carboxymethylation of polysaccharides has been widely studied because it is a simple chemical modification achieved by the acid-catalyzed reaction of polymers with chloroacetic acid. In the case of cellulose, carboxymethylation modifies the hydroxyl groups on the glucose backbone, attaching a CH2-COOH group, as shown in Figure 12.4. The exact nature of CMC depends on the degree of substitution and the molecular weight of the resulting polymer. CMC was first prepared in 1918 and was first produced on a commercial scale in Germany in the 1920s (Balser et al., 1986). The sodium salt of CMC is water-soluble, and this variant is most commonly used in medical applications; however, treatment with mineral acids forms the insoluble free carboxylic acid form of the polymer.
CMC forms a highly viscous clear solution and has been used in many fields, including as "artificial tear" eye drops. This is primarily because CMC have been found to be non-irritating and bind to corneal epithelial cells to improve ocular lubrication and stimulate wound repair (Garrett et al., 2007, 2008). CMC is also used in the form of an aqueous gel to prevent the formation of postoperative adhesions (Murphy, 2002). This study demonstrated that intraperitoneal administration of 1% CMC solution reduced the occurrence of adhesions and had no negative effects on wound healing, intra-abdominal defenses, or patient health. chloroacetic acid
Other forms of CMC include wound dressings for the treatment of chronic wounds, manufactured by Convatec Ltd and marketed under the name Aquacel®. This dressing is 100% CMC and is applied dry to the wound to absorb wound exudate and create a moist wound healing environment. A trial of 44 patients found that wounds treated with Aquacel had fewer dressing changes compared to alginate dressings, but no improvement in wound closure was observed. Aquacel has also been shown to have antioxidant properties in in vitro studies, which may be beneficial in the treatment of chronic wounds (Moseley et al., 2002).
CMC has also been shown to be a suitable drug delivery vehicle; drugs can be incorporated into viscous solutions such as Regranex® (discussed in Section 12.6.1), or ionic nutrients can be formed through the interaction of CMC with polyvalent metal cations gel. Sunger, (1999) studied the use of ionophilic gel spheres as a controlled release carrier for erythromycin.
In summary, CMC is a renewable resource polymer that is biodegradable, biocompatible, and in a high-purity form, making it a suitable candidate for a range of medical applications.