Christina Tang Ph.D.

Nanofibrous Membranes for Single-Step Immobilization of Hyperthermophilic Enzymes

Journal of Membrane Science

2014

A single-step method to immobilize hyperthermophilic enzymes within chemically crosslinked polyvinyl alcohol (PVA) nanofibrous membranes. The polymer crosslinking that entraps the enzyme within the fiber. Upon immobilization, the enzyme retains 20% of its catalytic activity as well as its hyperthermophilicity, as the maximum activity occurs at ~90 °C, and that activity at 90 °C is an order of magnitude higher than at 37 °C. Furthermore, thermostability of the enzyme is enhanced upon immobilization as indicated by the 2-fold increase in half-life at 90 °C. The apparent activity using the single-step method is significantly higher than alternative two-step methods.

Cross-linked Polymer Nanofibers for Hyperthermophilic Enzyme Immobilization: Approaches to Improve Enzyme Performance

ACS Applied Material Interfaces

2014

We report an enzyme immobilization method effective at elevated temperatures (up to 105 °C) and sufficiently robust for hyperthermophilic enzymes. Upon immobilization, the enzyme retains its hyperthermophilic nature and shows improved thermal stability indicated by a 5.5-fold increase in apparent half-life at 90 °C, but with a significant decrease in apparent activity. The loss in apparent activity is attributed to enzyme deactivation and mass transfer limitations. Minimizing the mat thickness to reduce interfiber diffusion was a simple and effective method to improve apparent immobilized enzyme activity.

Effect of pH on Protein Distribution in Electrospun PVA/BSA Composite Nanofibers

Biomacromolecules

2012

We examine the protein distribution within an electrospun polymer nanofiber using polyvinyl alcohol and bovine serum albumin as a model system. We hypothesize that the location of the protein within the nanofiber can be controlled by carefully selecting the pH and the applied polarity of the electric field as the pH affects the net charge on the proteins. Using fluorescently labeled BSA and surface analysis, we observe that the distribution of BSA is affected by the pH of the electrospinning solution. Therefore, we further probe the relevant forces on the protein in solution during electrospinning. The role of hydrodynamic friction was assessed using glutaraldehyde and HCl as a tool to modify the viscosity of the solution during electrospinning. By varying the pH and the polarity of the applied electric field, we evaluated the effects of electrostatic forces and dielectrophoresis on the protein during fiber formation. We surmise that electrostatic forces and hydrodynamic friction are insignificant relative to dielectrophoretic forces; therefore, it is possible to separate species in a blend using polarizability contrast. A coaxial distribution of protein in the core can be obtained by electrospinning at the isoelectric point of the protein, whereas surface enrichment can be obtained when the protein carries a net charge.

In Situ Cross-linking of Electrospun PVA Nanofibers

Macromolecules

2010

A single step reactive electrospinning of poly(vinyl alcohol) (PVA) and a chemical cross-linking agent, glutaraldehyde (GA) to cross-link during the electrospinning process, thereby eliminating the need for post-treatment. Significant changes in the rheological properties occur during in situ cross-linking correlate with electrospinnability. Dynamic rheology is used to define an “electrospinning window” to produce uniform fibers.

Polymer Directed Self-Assembly of pH-Responsive Antioxidant Nanoparticles

Langmuir

We have developed pH-responsive, multifunctional
nanoparticles based on encapsulation of an antioxidant,
tannic acid (TA) through polymer directed self assembly of insoluble coordination complexes of tannic acid and iron. In vitro, the nanoparticles have low cytotoxicity and show antioxidant activity.