Rheology of Gastric Mucin Exhibits a pH-Dependent Sol-Gel

2

Transition

3 Jonathan P. Celli,^† Bradley S. Turner,^†,‡ Nezam H. Afdhal,^‡ Randy H. Ewoldt,^§ 4 Gareth H. McKinley,^§ Rama Bansil,*^,† and Shyamsunder Erramilli*^,†

5Department of Physics, Boston University, Boston, Massachusetts 02215, Division of Gastroenterology, 6Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, and 7Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering, Massachusetts Institute of 8Technology, Cambridge, Massachusetts 02139

9 Received October 7, 2006; Revised Manuscript Received February 4, 2007

10Gastric mucin, a high molecular weight glycoprotein, is responsible for providing the gel-forming properties and 11protective function of the gastric mucus layer. Bulk rheology measurements in the linear viscoelastic regime 12show that gastric mucin undergoes a pH-dependent sol-gel transition from a viscoelastic solution at neutral pH 13to a soft viscoelastic gel in acidic conditions, with the transition occurring near pH 4. In addition to pH-dependent 14gelation behavior in this system, further rheological studies under nonlinear deformations reveal shear thinning 15and an apparent yield stress in this material which are also highly influenced by pH.