Associate Professor, Department of Chemical and Life Sciences Engineering
Engineering West Hall, Room 406, Richmond, VA, UNITED STATES
Prof. Tang specializes in polymer nanomaterial synthesis/characterization with interest in hybrids with inorganic nanoparticles/biomolecules
NSF Faculty Early Career Development (CAREER) program2017-04-05
Postdoctoral Research Associate
Ph.D., Chemical Engineering
B.Sc., General Engineering
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.
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.
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.
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.
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.
A method to covalently attach radioiodine to the core of pre-fabricated nanocarriers. First, we encapsulated polyvinyl phenol then radiolabeled it with 125I via electrophilic aromatic substitution in high radiochemical yields (>90%). PEGylated [125I]PVPh nanocarriers
exhibited relatively long circulation half-lives (~35 hours) and gradual reticuloendothelial clearance.
A facile, one-step self-assembly of polymer nanoreactors is reported for the fabrication of uniform PEGylated gold nanoparticles. Nanoreactor assembly occurs within milliseconds and gold nanoparticles are produced
within minutes at room temperature.