Research

Overview

Our research group develops polymeric materials that possess “smart” properties and functions. We design and synthesize stimuli-responsive polymers for use as biomaterials, sensors, and other applications. Also we prepare a variety of polymer nano-architectures such as nanoparticles, micelles, nanofibers, and nano-porous membranes. Organic and polymer syntheses, characterization, nano-/microfabrications, and chemical, physical, biological, and instrumental evaluations of their functionalities are performed in our lab.

Biofabrication of Implantable, Injectable, and Printable Hydrogels for Tissue Regeneration and Drug Delivery

A key component of regenerative medicine is providing material scaffolds to function as supporting structure as well as delivery of therapeutic molecules or cells. Biofabrication technology has shown rapid progress in a few decades including microelectromechanical systems (MEMS) and 3D/4D bioprinting. However, due to the complex requirements of gel properties, bioprinting is currently limited to a few synthetic and biopolymers. Designing smart polymeric systems for use as bioinks that are versatile, economical, and safe for various tissue regeneration systems is the key for future advancement of biofabrication. Smart bioinks are capable for shape-specific scaffolds through various fabrication methods that meet tissue-specific geometries.

The goals of this project is to develop polymeric bioinks which have capabilities of; (1) stimuli-responsive network formation or shape changes, (2) controlled delivery of therapeutic molecules for tissue regeneration, and (3) degradable support for cell growth and development into specific tissues such as bone, cartilage. These bioinks can be 3D-printed, coated, or injected into specific forms of scaffolds using a variety of stimuli such as light, temperature, pressure, pH, electric fields, etc.

Development of controlled nano-porous membranes and electro-active devices

Our group develops novel proton exchange membrane (PEM) for fuel cell and battery applications. Studying the structure-function relationship of PEM is crucial to develop superior materials. Specifically, we control nanoscale morphologies using block copolymers and different functional groups. Two approaches have been taken; 1) Prepared 8 new monomers and several polyethersulfones (PES) with various functional side groups to compare their performances, for example, hydrocarbon vs. fluorocarbon chains, aromatic vs. aliphatic chains, rigid vs. flexible chains, and short vs. long chains; 2) Prepared nano-phase separated membranes from PES-PLA (polylactide) multi-block copolymers. Degradable block, PLA, was then hydrolyzed to achieve controlled nanoporous membrane template. These membrane templates are ready for further functionalization to create various types of controlled ion channels. Current efforts are the preparation and characterization of membranes from both methods by collaboration with UTK and ORNL.

Temperature-responsive biodegradable hydrogels

The aim of this project is to understand the gelation mechanism of the thermo-responsive hydrogels and to apply for controlled drug/gene delivery systems. We have developed novel 'hybrid' injectable hydrogel systems from micelle blends of enantiomeric polylactide-poly(ethylene glycol) block copolymers, PLLA-block-PEG and PDLA-block-PEG. Unique ABA (A: PLA, B: PEG) type block copolymers exhibit controlled sol-to-gel transition temperature. FromX-ray analysis, the sol-to-gel transition mechanism is suggested as the inter-micelle interaction and stereocomplexation of enantiomeric PLLA and PDLA blocks. To demonstrate this hypothesis, we use a variety of instrumentation such as liquid/solid state NMR, rheometer, atomic force microscopy (AFM), light scattering (DLS/SLS), and synchrotron SANS and SAXS. Current effort is to develop this hydrogel system for gene delivery application using PLA-block-PEI (polyethylene imine) to condense gene in the micelle core.

Stimuli-responsive multilayered micelles and hydrogels for drug and gene delivery

“Three-layered micelles” (3LM) consist of two of low MW triblock copolymers PLLA-PEI-PLLA and PLLA-PEG-PLLA are designed to combine electrostatic interaction and solvent-induced condensation of DNA. The 3LM shows efficient encapsulation of DNA, great stability at neutral pH and efficient DNA release at acidic pH (4.5). A new class of non-viral delivery systems for nucleic acids with superb stability and stealth properties is identified. We have demonstrated the possibility of targeted gene delivery to FR positive macrophages under in vitro and ex vivo conditions with a novel biodegradable and biocompatible targeted delivery system which forms slow degrading hydrogels with enhanced degradation under inflamed conditions and release of 3LM.

Photo-switchable smart polymers

The goal of this project is the development of “smart” polymeric systems for site recognition, sensing, and delivery of organic/inorganic molecules. Incorporation of a photochromic dye into polymers will enable construction of various self-assembly structures for new classes of photo-switching nanomaterials. Spirooxazines are a class of photochromic compounds whose molecular structures are alterable upon exposure to UV/ visible light or changes in temperature. The typical reaction of spirooxazines is the conversion between the closed spiro (Sp) form with the open merocyanine (MC) forms. We have designed functional polymers attached to a newly developed spirooxazine dimer. For example, a palladium catalyst as guest agent was encapsulated by the open-isomer in the micelle core or on the polymer bead. Stable binding affinity towards palladium catalyst indicated potential applications for selective recognition, extraction, and controlled release.

Development of anion exchange membranes (AEM)

Lightning talk (2023):

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