@article{burke_park_srinivasarao_khan_2005, title={A novel enzymatic technique for limiting drug mobility in a hydrogel matrix}, volume={104}, ISSN={["1873-4995"]}, DOI={10.1016/j.jconrel.2005.01.017}, abstractNote={An oral colon specific drug delivery platform has been developed to facilitate targetted release of therapeutic proteins as well as small molecule drugs. A simple enzymatic procedure is used to modify the molecular architecture of a lightly chemically crosslinked galactomannan hydrogel as well as a model drug-galactomannan oligomer conjugate, fluoroisocynate (FITC) tagged guar oligomer, to entrap the model drug. The enzyme-modified hydrogel retains the drug until it reaches the colonic environment where bacteria secrete enzymes (namely beta-mannanase) to degrade the gel and release the drug molecule. Laser scanning confocal microscopy combined with fluorescence recovery after photobleaching is used to quantify the diffusion of the drug conjugate. The diffusion coefficient of solutes in the lightly crosslinked galactomannan hydrogel is approximately equal to the diffusion coefficient in the guar solution for simple diffusional drug loading. After drug loading, alpha-galactosidase treatment generates additional physical crosslinks in the hydrogel matrix as well as between the drug-oligomer conjugate and the hydrogel, which reduces diffusion of the drug-oligomer conjugate significantly. Degradation of the hydrogel by beta-mannanase results in a slow and controlled rate of FITC-guar oligomer diffusion, which generates an extended release profile for the model drug.}, number={1}, journal={JOURNAL OF CONTROLLED RELEASE}, author={Burke, MD and Park, JO and Srinivasarao, M and Khan, SA}, year={2005}, month={May}, pages={141–153} }
 @article{burke_ha_pysz_khan_2002, title={Rheology of protein gels synthesized through a combined enzymatic and heat treatment method}, volume={31}, ISSN={["0141-8130"]}, DOI={10.1016/S0141-8130(02)00043-0}, abstractNote={Whey protein gels prepared under acidic conditions (pH<4.6) remain largely unutilized because of their weak and brittle nature in contrast to the favorable elastic gels produced at neutral or basic conditions. However, such usage is important, as low pH food products are desirable due to their shelf stability and less stringent sterilization processes. In this study, we use a two-step process involving enzyme followed by heat treatment to produce whey protein gels at low pH (4.0). Dynamic rheological measurements reveal that the gel elastic modulus and yield stress increase substantially when heat treatment is supplemented with enzyme treatment. Both the elastic modulus and yield stress increase with increasing enzyme concentration or treatment time. In contrast, the dynamic yield strain decreases with enzyme concentration but increases with time of enzyme treatment. These results are explained in terms of the enzyme treatment time affecting the diffusion of the enzyme within the gel. This in turn leads to two types of gel microstructure at short and long enzyme treatment times, with the extent of enzyme diffusion modulating the structure at intermediate times.}, number={1-3}, journal={INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES}, author={Burke, MD and Ha, SY and Pysz, MA and Khan, SA}, year={2002}, month={Dec}, pages={37–44} }
 @article{burke_park_srinivasarao_khan_2000, title={Diffusion of macromolecules in polymer solutions and gels: A laser scanning confocal microscopy study}, volume={33}, ISSN={["1520-5835"]}, DOI={10.1021/ma000786l}, abstractNote={Laser scanning confocal microscopy combined with fluorescence recovery after photobleaching is an effective tool to measure the diffusion coefficients of macromolecules in cross-linked hydrogels and polymer solutions. In this study, the effects of enzyme treatment on the diffusion of macromolecules (FITC-dextran) in guar solutions and titanium-guar hydrogels are examined. Enzyme treatment with β-mannanase, a polymer backbone cleaving enzyme, quickly increases the diffusion coefficient of the probe molecules in both solutions and hydrogels to that in water. Enzyme treatment of guar solutions and hydrogels with α-galactosidase, a side chain cleaving enzyme, displays a unique behavior due to changes in the fine structure of guar. The removal of galactose branches from the mannan backbone of guar creates additional hyperentanglements (i.e., cross-links), which reduce the water holding capacity of guar and induce syneresis. If the depth at which the diffusion coefficient is measured remains constant, a minimum...}, number={20}, journal={MACROMOLECULES}, author={Burke, MD and Park, JO and Srinivasarao, M and Khan, SA}, year={2000}, month={Oct}, pages={7500–7507} }
 @article{burke_khan_2000, title={Triggered enzymatic degradation of a water-soluble polymer solution using a novel inhibitor}, volume={1}, ISSN={["1526-4602"]}, DOI={10.1021/bm000051o}, abstractNote={Controlled enzymatic degradation of solutions of guar galactomannan, a naturally occurring polysaccharide, offers a powerful tool to enhance its usage in a variety of applications. In this study, we use viscometry to investigate the use of tris(hydroxymethyl)aminomethane (Tris) as a reversible, pH-dependent inhibitor to control the degradation of guar galactomannan by Aspergillus niger beta-mannanase. Viscosity measurements of pH 9 guar solutions containing 25 mM Tris show no reduction in the viscosity when treated with beta-mannanase. In contrast, samples containing no Tris show significant reduction in viscosity within an hour. Samples maintained at a pH of 9 in the presence of Tris for several hours show no change in viscosity; however, reduction of the pH of the sample to 4 initiates enzymatic degradation of the guar solution resulting in a rapid reduction in solution viscosity. This reversible, pH-dependent inhibition is possibly a result of the protonation state of Tris as well as key amino acids in the active site.}, number={4}, journal={BIOMACROMOLECULES}, author={Burke, MD and Khan, SA}, year={2000}, pages={688–695} }