The phase transition temperatures, rheological properties and gel-network characteristics for gelation of -carrageenan-salt (NaCl, KCl and CaCl 2 ) solutions and their aged gels were investigated. The effectiveness of increasing gelling and gel-melting temperatures at the salt concentrations examined followed the sequence of K + > Ca 2+ > Na + . This sequence was also true for the gel strength and the melting enthalpy (DH) of the most crosslinked junction zones of aged gels at low salt concentrations. Nonetheless, a different order (Ca ++ > K + and Na + ) was found for increasing storage modulus and gelation rate during early-stage gelation, thermal hysteresis and the DH of aged gels in some salt-carrageenan systems.

An in situ gelling, bioadhesive liquid formulation was developed to enhance the bioavailbility (BA) of a polysaccharide, pentosan polysulfate sodium (PPS). The formulation was tested to determine its bioavailability enhancement in a non-flush/non-ligated rat ileal model. A potent synergistic effect was found with a gelling agent Cremophor and a permeation enhancer sodium salicylate. The absolute bioavailabilities were 1.9%, 4.6%, 6.3% and 46.4%, respectively, for the PPS solution in saline, sodium salicylate/PPS, Cremophor/PPS and Cremophor/sodium salicylate/PPS. Therefore, we successfully demonstrated the approach of utilizing an in situ gelling/bioadhesive liquid carrier to enhancing the bioavailability of a hydrophilic macromolecule at the distal small intestine.