Ph.D. Institution: University of Tennessee
Princeton Postdoctoral Research:
(1) A New Approach to Eye Surgery Using Femtosecond Lasers
Femtosecond (fsec) laser technology offers the potential to totally or partially remove crystalline lens without any thermal or mechanical collateral damage to the eyes, combined with easy delivery of fsec laser pulse to different sections of eye via flexible optical fibers. This procedure will find applications in eye surgeries such as non-invasive, partial or total cataract removal and optically reshaping the crystalline lens for correction of refractive errors. After the laser surgery, an artificial substitute will fill the capsule as a prosthetic lens. Our task is to formulate a stable, optically clear, poly(ethylene glycol)-based (PEG) hydrogel to act as this kind of prosthetic lens, which has a Young’s modulus similar to the human lens (several kPa) and also the same refractive index as natural lens (n » 1.42). Currently, we are employing the condensation polymerization technique via Michael-type addition reaction between acrylate (or acrylamide) terminated PEG and di- or polyfunctional thiols (or cysteine oligomers or peptides having two or more cysteine residues) to make this hydrogel. Those precursors (multi-acrylates and multi-thiols) can be pre-mixed to form a low-viscosity fluid and then injected through the surgical aperture (200 m m) created for lens removal and then cross-linked in-situ. This type of addition reaction has many advantages over photopolymerization of PEG-acrylates, which requires the introduction of photoinitiators and delivery of strong UV light to the eye: 1) mild character and high yield in physiological conditions, 2) fewer side reactions, 3) no toxic by-products, 4) negligible leaching when cross-linkable materials are produced, 5) gels within a surgically relevant time scale (5 to 10 minutes).
(2) Organic Memory Materials (Write Once Read Many times memory (WORM))
Poly(3,4-ethylenedioxythiophene) (PEDOT) is the first commercially available successful intrinsically conducting polymer (ICP). It combines optical transparency in the visible spectrum, good electrical conductivity and stability with conductivity up to 102 S/cm. Its dispersion form in aqueous solution by using poly(styrene sulfonic acid) (PSSH) as dispersant and dopant has been used as antistatic layer in photographic films, hole-injection layer in prototype organic light emitting diode (OLED) displays. Recently, it is found when there is a large current passed through the two component polymer system (PEDOT/PSSH), it will undergo an irreversible reduction in conductivity (Nature 2003, 426, 166). An active matrix array of cross-points can be formed with PEDOT/PSSH acting as an organic fuse if placed in series with a nonlinear electrical element, which is called write-once-read-many times (WORM) memory device. In collaboration with Prof. Stephen Forrest in the department of electrical engineering, we are currently exploring the mechanism to fully understand the reaction that PEDOT undergoes in its extreme and permanent conductivity change with hole and electron injection. Whether this is a surface (i.e. contact) or bulk phenomenon is a key focus of developing a full understanding of the process. At the same time, we will synthesize new PEDOT-based complexes by using other polyelectrolytes to achieve greater control of the process and larger read-write contrast ratio.