Abstract
Purpose:
To develop a biocompatible photopolymerizable gel to seal off the crystalline lens against oxygen diffusion to avoid cataract formation after vitrectomy.
Methods:
A composite gel was formulated to accommodate 13 preset criteria: (1) Viscoelasticity, for intraoperative injectability through a 26-gauge cannula, (2) Spreadability, (3) Smoothness, (4) Ability to polymerize in situ, (5) Optical clearance, (6) Cohesiveness, to remain adherent to the lens capsule, (7) Iso-osmolarity, (8) Biocompatibility, (9) Oxygen impermeability, (10) Refractive index close to lens (n=1.336), (11) Surface energy of >40 dyne/cm, to avoid protein and cell adhesion, (12) Elastic modulus >40 N/m2 to preserve the accommodative ability of the lens, and (13) Biodurability. For this purpose, polyethylene glycol diacrylate (PEG-DA, MW: 3350-6000 kDa) base material was enriched with various concentrations of hyaluronic acid (10-12 mg/mL, HA) or hydroxypropylmethyl cellulose (30-100 mg/mL, HPMC) prepared in different solvents (PBS, HEPES, or dI H2O). After adding ascorbic acid (1 mg/mL) or trehalose to the composite material, it was polymerized using different photo-initiators (acetophenone, eosin Y system and Irgacure 2959). Resultant biogels were assessed in their compliance to the preset criteria.
Results:
Ninety different permutations of the ingredients were tested for their conformity to the required criteria. The best match was attained by mixing 100 mg/mL PEG (6000 Da) with 10 mg/mL of HA (viscosity 5200 mP.sec) and photoinitiating under a green LED source with Irgacure 2959 that was dissolved at 0.1 g/mL in 70% EtOH and added to PEG-polymer solutions to complex with the acrylate groups on the PEG molecules in a 1.2/1 ratio. The resultant clear (265-800 nm) gels have perfect spreadability, leveling, coverage, durability and cohesiveness with a thermally stable (25-37 ‘C) refractive index of 1.33, surface energy of 66 dyne/cm, and elastic modulus of 41.4 N/m2. These iso-osmolar gels resist protein and cell adhesion, and can reduce oxygen diffusion 34 times.
Conclusions:
Formulated biogels can limit oxygen diffusion to crystalline lens. This technology can eliminate tedious head-down positioning and cataract formation after vitrectomy surgery.
Keywords: 445 cataract •
635 oxygen •
608 nanomedicine