Material Properties of Various Intraocular Lenses in an Experimental Study

Abstract

Introduction: With the recent introduction of small-incision cataract surgery, requirements for intraocular lens (IOL) flexibility, strength and hydrophilicity have rapidly evolved. The IOL surface, however, remains a critical factor influencing uveal biocompatibility. Purpose: To objectively quantify factors of material properties of various IOLs using contact angle measurements, differential scanning calorimetry, dynamic-mechanical measurements and scanning electron microscopy. Material and Methods: In our study, 17 currently available IOLs were investigated using contact angle measurements to assess hydrophilicity and biocompatibility, as well as differential scanning calorimetry for the estimation of glass transition temperature. Mechanical capacity and flexibility were investigated using dynamic-mechanical measurements. Additional analysis of the IOL surface was performed using scanning electron microscopy. Results: The contact angle measurements of the studied IOLs revealed similar values within each group. The silicone IOLs had values between 106 and 119°. The PMMA IOLs were found to have a narrower range of values, between 73.2 and 75.5°. Lenses made of hydrogel had values between 59.2 and 69.1°. The heparin-modified surface showed the lowest contact angle of 56.5°. The glass transition temperature was determined by dynamic differential scanning calorimetry. The resulting values were between 118.8 and 113.5°C for PMMA IOLs, 15.5 and 14.0°C for acrylic IOLs, and –91.7 and –119.6°C for silicone IOLs. The dynamic-mechanical measurements revealed that PMMA lenses manifested characteristics similar to glass, whereas silicone lenses had characteristics similar to rubber. Acrylic lenses were between rubber and glass. Scanning electron microscopy revealed smooth dispersion of fibrin on hydrophobic IOLs and a relative lack of fibrin adhesion on hydrophilic materials. Conclusion: These results demonstrate that material properties of various IOL materials are consistent within classes of IOL materials. This suggests that the intraoperative and postoperative behavior of an IOL is predictable and related to its composition, thus allowing surgeons to choose IOLs more appropriate for different surgical situations and individual patient characteristics.

Calculation of Intraocular Lens Surface Free Energy and its Components from Contact Angle Measurements

“…Indeed, the hydrophobic character of the biomaterial surfaces studied is not investigated in these works. In fact only few authors have studied the wetting behavior of commercially available IOLs [11,12,13,14,15]. …”

“…Thus, IOLs made of silicone were found to have a water contact angle between 99 and 122° [12,13,14,15], which make them more hydrophobic than hydrophobic acrylic IOLs, which have a water contact angle around 73° (73.3 ± 2.4 for MA60BM) [14]. PMMA is also fairly water repellent, with a water contact angle of 70-75.5° [12,15] compared with hydrophilic acrylic polymers, which have a water contact angle of less than 69° [12]. …”

“…Indeed, contact angle values are insufficient to characterize the wetting behavior of a surface [12]. To obtain the complete parameters of a surface, its surface free energy and its different components such as polar, apolar, electron-donating and electron-accepting properties should be determined.…”

“…Few authors have tried to determine the hydrophobicity parameters of commercially available intraocular lenses [11,12,13,14,15]. To investigate the wetting behavior of IOLs most of them have presented contact angle measurements between IOL surfaces and characterized test liquids: a high value contact angle would indicate a more hydrophobic surface [10].…”

Impact of fibronectin on surface properties of intraocular lenses

“…The measurement of the surface contact angle (SCA) has been proposed to evaluate surface hydrophobicity as one important factor determining the physico-chemical properties of the interface between the IOL and its surrounding tissue [13,14]. This SCA is the angle between a liquid/vapor interface and a solid surface and is specific for any system consisting of a defined surface and a given liquid.…”