Purpose:
To optimize optical and mechanical properties of collagen vitrigels by varying synthesis parameters, and to correlate these material properties with the nanostructure.
Methods:
Vitrigel preparation entails three main stages: gelation, vitrification, and rehydration. Equal volumes of culture medium (Fetal Bovine Serum, 20 mM HEPES buffer in DMEM (Dulbecco’s Modified Eagle Medium)) and 0.5% acid collagen solution are uniformly mixed. Gelation is initiated via incubation at 37 °C. During vitrification, time, temperature, and humidity are controlled. Following vitrification, the material is rehydrated with Phosphate Buffered Saline. Design of Experiments (DOE) was utilized to systematically vary the synthesis parameters (vitrification temperature (5, 10 and 40 °C), relative humidity (RH) (20, 40 and 60 %), and time (0.5, 1, 2 and 5 weeks)) and understand the relationship with the resulting properties. The characterization includes the transmittance, ultimate tensile strength, denaturing temperatures and the morphology by scanning electron microscopy.
Results:
Varying the synthesis parameters facilitates control of the transparency and mechanical strength of the vitrigel by tailoring the underlying material structure. These structural changes include an increase in the collagen fiber diameter and density as temperature and time increase. Vitrigels with transparency up to 85%, tensile strength up to 12 MPa, and denaturing temperatures that exceed the eye/body temperature have been synthesized at 40°C, 40% RH for one week. This analysis enabled improvements of 140% in tensile strength and 11% in transparency, compared to the previously developed vitrigels, and a 3-week reduction in synthesis time, rendering the vitrigels a more realistic and practical solution.
Conclusions:
The role of synthesis parameters in the vitrigel synthesis were investigated using a systematic DOE approach. As a result, thermal stability of the gels can be controlled, and transparency and ultimate tensile strengths that range from 70 to 87% and 0.7 to 9.8 MPa, respectively. These materials show promise for complex ocular reconstruction due to their biocompatibility, biodegradability, transparency and strength, thermal stability, and drug delivery capability.
Keywords: cornea: basic science • wound healing