Michael Cho

Designing a gas foamed scaffold for keratoprosthesis

Artificial corneas or keratoprostheses are intended to replace diseased or damaged cornea in the event that vision cannot be restored using donor cornea tissue. A new class of artificial cornea comprising a combination of poly (2-hydroxyethyl methacrylate) and poly (methyl methacrylate) was developed which was fabricated using a gas foaming technique. Referred to as the gas-foamed KPro, it was designed to permit clear vision and secure host biointegration to facilitate long-term stability of the device. In vitro assessments show cell growth into the body of the porous edge or skirt of the gas-foamed KPro. The optically transparent center (i.e., core) of the device demonstrates 85 - 90% of light transmittance in the 500 - 700 nm wavelength range. Mechanical tensile data indicates that the gas-foamed KPro is mechanically stable enough to maintain its structure in the ocular environment and also during implantation. The gas-foamed KPro may provide an alternate option for cornea replacement that minimizes post implantation tissue melting, thereby achieving long-term stability in the ocular environment.

Characterization of pore structure in biologically functional poly(2-hydroxyethyl methacrylate)-poly(ethylene glycol) diacrylate (PHEMA-PEGDA).

A copolymer composed of poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(ethylene glycol) diacrylate (PEGDA) (PHEMA-PEGDA) is structurally versatile. Its structure can be adjusted using the following porogens: water, sucrose, and benzyl alcohol. Using phase separation technique, a variety of surface architectures and pore morphologies were developed by adjusting porogen volume and type. The water and sucrose porogens were effective in creating porous and cytocompatible PHEMA-PEGDA scaffolds. When coated with collagen, the PHEMA-PEGDA scaffolds accommodated cell migration. The PHEMA-PEGDA scaffolds are easy to produce, non-toxic, and mechanically stable enough to resist fracture during routine handling. The PHEMA-PEGDA structures presented in this study may expedite the current research effort to engineer tissue scaffolds that provide both structural stability and biological activity.

Engineering copolymeric artificial cornea with salt porogen

Artificial corneas or keratoprostheses (KPros) are designed to replace diseased or damaged cornea. Although many synthetic KPros have been developed, current products are often inappropriate or inadequate for long term use due to ineffective host integration. This study presents an alternative approach of engineering a KPro that comprises a combination of poly (2-hydroxyethyl methacrylate) (PHEMA), poly (methyl methacrylate) (PMMA), and sodium chloride (NaCl) as porogen. Based on the core-skirt model for KPro, the porous outer portion of artificial cornea (skirt) was engineered by combining NaCl with HEMA and MMA monomers to promote tissue ingrowth from the host. The central optic (core) was designed to provide >85% light transmission in the visible wavelength range and securely attached to the skirt. Mechanical tensile data indicated that our KPro (referred to as salt porogen KPro) is mechanically stable to maintain its structure in the ocular environment and during implantation. Using human corneal fibroblasts (HCFs), we demonstrate that the cells grew into the pores of the skirt and proliferated, suggesting biointegration is adequately achieved. This novel PHEMA-PMMA copolymeric salt porogen KPro may offer a cornea replacement option that leads to minimal risk of corneal melting by permitting sufficient tissue ingrowth and mass transport.

Engineering a light-attenuating artificial iris

Purpose Discomfort from light exposure leads to photophobia, glare, and poor vision in patients with congenital or trauma-induced iris damage. Commercial artificial iris lenses are static in nature to provide aesthetics without restoring the natural iriss dynamic response to light. A new photo-responsive artificial iris was therefore developed using a photochromic material with self-adaptive light transmission properties and encased in a transparent biocompatible polymer matrix. Methods The implantable artificial iris was designed and engineered using Photopia, a class of photo-responsive materials (termed naphthopyrans) embedded in polyethylene. Photopia was reshaped into annular disks that were spin-coated with polydimethylsiloxane (PDMS) to form our artificial iris lens of controlled thickness. Results Activated by UV and blue light in approximately 5 seconds with complete reversal in less than 1 minute, the artificial iris demonstrates graded attenuation of up to 40% of visible and 60% of UV light. There optical characteristics are suitable to reversibly regulate the incident light intensity. In vitro cell culture experiments showed up to 60% cell death within 10 days of exposure to Photopia, but no significant cell death observed when cultured with the artificial iris with protective encapsulation. Nuclear magnetic resonance spectroscopy confirmed these results as there was no apparent leakage of potentially toxic photochromic material from the ophthalmic device. Conclusions Our artificial iris lens mimics the functionality of the natural iris by attenuating light intensity entering the eye with its rapid reversible change in opacity and thus potentially providing an improved treatment option for patients with iris damage.