Comparison of Two Photo-polymerizable Gel Oxygen Barrier Formulations for Prevention of Oxidative Damage to the Crystalline Lens

Abstract

 

Purpose

 

To compare the suitability of two biocompatible photo-polymerizable gel formulations in an ex vivo study to seal off the crystalline lens against oxygen diffusion to avoid cataract formation after vitrectomy.

 

Methods

 

Gels were formulated with Hyaluronic Acid (HA) or hydroxypropylmethylcellulose acrylate (HPMCA) combined with polyethylene glycol diacrylate (PEG-DA) at 10:1 or 20:1 ratios, respectively. The antioxidant capacity of the gel formulation was bolstered through addition of sub-micron trehalose particles. A visible light photoinitiator system allowed polymerization with visible light (520 nm). The optical (transmissivity and refractive index) and mechanical (viscosity, osmolarity, swelling and oxygen permeability) properties of both formulations were compared. Each gel was tested in ex vivo porcine lenses for their ability to prevent cataract formation under hypoxic, normoxic, and hyperoxic conditions in a controlled atmosphere incubator. Lens clarity was assessed each day up to 1 week and compared to control lenses with no coating.

 

Results

 

Both gel formulations proved to be effective oxygen barriers. The HA-PEG-DA formulation reduced lens oxygen exposure by 2/3 compared to air or media (Figure 1), with similar results for HPMCA. Both formulations also proved to be biocompatible with porcine lenses in the ex vivo studies and were able to prevent cataract formation in the coated lenses during the time course of the study (Figure 2). Both formulations displayed >95% transmissivity across the visible range and had refractive indices close to that of the lens (1.336) at physiological temperatures. The osmolarity of the gels were both found to be near that of the vitreous (~ 300 mOsm) and both gels displayed similar swelling behavior. The major difference in the formulations was the pre-gel viscosity. The HPMCA formulation viscosity (900 cP) is much lower than the HA formulation (9000 - 10000 cP).

 

Conclusions

 

Both HPMCA and HA gel formulations perform adequately as oxygen barriers and have optical properties suitable for use in lens coating applications. The low viscosity of the HPMCA formulation, however, precludes its use in practical surgical applications.

 

 

Figure 1. Oxygen content of air and media vs. the cortex within the gel-coated crystalline lens.

 

 

Figure 2. Images of un-coated and gel-coated lenses showing the sustained clarity in the coated lens.

 

Keywords: 445 cataract • 762 vitreoretinal surgery • 634 oxidation/oxidative or free radical damage