Degree of Carboxymethyl Substitution on Tara Gum Influences the Mucoadhesive and Physicochemical Performance of Gastroretentive Tablets.

The present study investigates the effect of the degree of carboxymethyl substitution in tara gum (TG) on the physicochemical and mucoadhesive properties of gastroretentive tablets. The synthesis of carboxymethyl TG (CMTG) was optimized under various reaction conditions with respect to degree of substitution (DS). The DS varied from 0.47 ± 0.002 to 1.14 ± 0.014 depending on the reaction conditions. The DS significantly influenced the flow properties, swelling behavior, and erosion of the tablets. Ex vivo mucoadhesion studies on goat stomach mucosa revealed that both mucoadhesive strength (MS) and mucoadhesive time (MT) varied with changes in DS. MS and MT progressively increased from 45.51 × 103 ± 2.979 to 111.18 × 103 ± 3.901 dynes/cm2 and from 272.66 ± 2.561 to 517.33 ± 2.516 min, respectively, with increasing DS from 0.47 ± 0.002 to 1.05 ± 0.046, owing to enhanced hydrogen bonding between the -COOH groups of CMTG and functional groups of mucin. However, a further increase in DS to 1.14 ± 0.014 decreased MS and MT to 101.75 × 103 ± 0.297 dynes/cm2 and 504.33 ± 1.041 min, respectively, primarily due to excessive protonation in acidic media, which increased the rigidity of the polymeric networks and reduced interactions between polymeric chains and mucin. The most notable finding of this study was that the MS and MT values of the optimized carboxymethylated derivative (CMTG-4) were superior to those of the commercial mucoadhesives CMC, Carbopol 934, and pectin.