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ISSN : 1229-6457(Print)
ISSN : 2466-040X(Online)
The Korean Journal of Vision Science Vol.27 No.1 pp.41-51
DOI : https://doi.org/10.17337/JMBI.2025.27.1.41

Fabrication and Ophthalmic Application of Hydrogel Polymer Containing Cerium(IV)-Zirconium(IV) Oxide Nano Particles

Jin-Wook Kim1), A-Young Sung2)
1)Dept. of Optometry and Vision Science, Daegu Catholic University, Student, Daegu
2)Dept. of Optometry and Vision Science, Daegu Catholic University, Professor, Daegu
* Address reprint requests to A-Young Sung (https://orcid.org/0000-0002-9441-919X) Dept. of Optometry & Vision Science, Daegu Catholic University, Daegu TEL: +82-53-850-2554, E-mail: say123sg@hanmail.net
February 20, 2025 March 28, 2025 March 29, 2025

Abstract


Purpose : This study was designed to investigate the potential use of contact lenses made with cerium(IV)-zirconium(IV) oxide nanoparticles as functional ophthalmic lenses by comparing and analyzing the physical properties of the manufactured lenses.



Methods : Nano cerium(IV)-zirconium(IV) oxide was added to 2-hydroxyethyl methacrylate (HEMA) and copolymerized. The physical properties were measured. Then, methacrylic acid (MA), a hydrophilic monomer, was added to further evaluate and compare the physical properties.



Results : The physical properties of lenses manufactured with various ratios of cerium(IV)- zirconium(IV) oxide nanoparticles and methacrylic acid (MA) were evaluated. UV-B transmittance ranged from 40.95% to 66.26%, refractive index from 1.4163 to 1.4357, water content from 37.44% to 47.18%, contact angle from 36.87° to 56.36°, tensile strength from 0.0612 kgf/mm² to 0.561 kgf/mm², and surface roughness from 7.70 nm to 8.72 nm. The addition of nanoparticles and MA improved wettability, tensile strength, and polymerization stability, while decreasing UV-B transmittance and surface roughness. Antibacterial activity against Staphylococcus aureus was also confirmed.



Conclusion : It was verified that the addition of MA to cerium(IV)-zirconium(IV) oxide nanoparticles improved polymerization stability, tensile strength, and wettability. Therefore, these materials may be suitable for use in functional contact lenses for ophthalmic medical applications.


Cerium(IV)-zirconium(IV) oxide , Hydrogel lenses , Nanoparticles , Surface roughness , Wettability

세륨(IV)-지르코늄(IV) 산화물 나노입자를 포함한 친수성 폴리머의 제조 및 안광학적 응용

김진욱1), 성아영2)
1)1대구가톨릭대학교 대학원 안경광학과, 학생, 대구
2)2대구가톨릭대학교 안경광학과, 교수, 대구

    Ⅰ. Introduction

    Contact lenses offer the advantage of a wider field of view compared to glasses and can be conveniently worn in active situations such as sports. Additionally, various designs, such as color and circle lenses for cosmetic purposes, have recently been developed, making them widely used not only for vision correction but also as fashion accessories that express individuality. However, conventional contact lenses have limitations that can cause side effects, including dry eyes, conjunctival congestion, corneal hypoxia, and infections, especially when worn for extended periods.1) These issues arise from various factors, such as the low oxygen permeability of lens materials, protein and foreign substance deposition, and surface friction. Consequently, there is a growing demand for the development of functional ophthalmic lens materials that promote eye health while enhancing comfort.2,3) Nanotechnology enables innovative material research that addresses these needs. By utilizing nanometer-sized particles, nanotechnology can significantly improve the physical and chemical properties of existing materials and has recently been applied across various fields.4,5) In ophthalmic optics, research is actively being conducted to enhance the performance of contact lenses and introduce new functionalities through nanotechnology. Nanoparticles can enhance strength, flexibility, and durability while maintaining lens transparency. Moreover, they can be engineered to offer antibacterial properties, UV blocking, and drug delivery capabilities.6,7) Among various nanoparticles, cerium(IV)-zirconium(IV) oxide nanoparticles show great potential as an ophthalmic lens material.8) This compound, a solid solution of cerium oxide and zirconium oxide, exhibits excellent physical properties by combining the advantages of both oxides. Cerium oxide nanoparticles effectively remove reactive oxygen species, regulate inflammatory responses, and promote wound healing and tissue regeneration.9-11) According to a study by Gojova, Andrea, no significant inflammatory reaction was observed when measuring inflammatory markers in aortic endothelial cells cultured with cerium oxide nanoparticles.12) Zirconium oxide nanoparticles have demonstrated antibacterial, anti-biofilm, and UV-blocking functions, with high biocompatibility and stability. The antibiofilm function of zirconium oxide nanoparticles was confirmed using a colorimetric analysis method with crystal violet staining.13) As nanoparticles, cerium(IV)-zirconium(IV) oxide possesses high oxygen storage capacity, excellent thermal stability, a large surface area, and environmental friendliness due to its low toxicity, durability, and antibacterial properties. As a result, it is widely used in various applications, including catalysts, fuel cells, and oxygen sensors.14-17) Research by Mei, Y. U. E., et al. confirmed the high thermal stability and large surface area of cerium(IV)-zirconium(IV) oxide nanoparticles synthesized using magnesium hydrogen carbonate and ammonia-ammonium hydrogen carbonate.18) Additionally, a study by Pandiyan, et al. established that cerium(IV)- zirconium(IV) oxide nanoparticles exhibited superior antibacterial and antioxidant properties compared to CeO₂ and ZrO₂ nanoparticles. They also demonstrated a biofilm-prevention effect when evaluating the properties of synthesized cerium(IV)- zirconium(IV) oxide nanoparticles measuring 10– 15 nm.19) In this study, hydrogel lenses were manufactured using cerium(IV)-zirconium(IV) oxide nanoparticles, and the durability, antibacterial properties, and stability of the manufactured lenses were evaluated.

    Ⅱ. Materials and Methods

    1. Reagents and Materials

    2-Hydroxyethyl methacrylate (HEMA), the base material for hydrogel soft contact lenses; 2,2'- azobis(2-methylpropionitrile) (AIBN), a thermal initiator; and ethylene glycol dimethacrylate (EGDMA), a crosslinking agent, were used. Cerium(IV)- zirconium(IV) oxide nanoparticles and methacrylic acid (MA) were added as functional components. All reagents were purchased from Sigma-Aldrich (USA).

    2. Methods

    1) Fabrication of Hydrogel Lenses Containing Cerium(IV)-Zirconium(IV) Oxide Nanoparticle

    A reference (Ref) sample was prepared using HEMA, AIBN, and EGDMA as the base composition. Cerium(IV)-zirconium(IV) oxide nanoparticles were added at concentrations of 0.015, 0.03, 0.06, 0.1, and 0.3%, with these groups designated as CZ_1, CZ_2, CZ_3, CZ_4, and CZ_5, respectively. After lens fabrication, their physical properties were evaluated. All lenses were manufactured using the cast molding method. For polymerization, the mixed solution was stirred for 2 hours using a vortex mixer and dispersed for 30 minutes using ultrasonic equipment. The solution was then injected into a contact lens mold and thermally polymerized at 100°C for 1 hour. The fabricated lenses were hydrated in a 0.9% sodium chloride (NaCl) physiological saline solution for 24 hours. Subsequently, their physical properties, including light transmittance, refractive index, water content, and contact angle, were analyzed. The composition ratios for each sample are shown in Table 1.

    2) Fabrication of Cerium(IV)-Zirconium(IV) Oxide Hydrogel Lenses with Added Hydrophilic Monomers

    Reference (Ref) hydrogel lenses were prepared using HEMA, AIBN, and EGDMA as the base combination. Cerium(IV)-zirconium(IV) oxide nanoparticles were added at concentrations of 0.015% and 0.03% (w/w), with these groups labeled as the 15-group and 30-group, respectively. Additionally, MA, a hydrophilic monomer, was incorporated at concentrations ranging from 0% to 10% (w/w). All sample mixtures were stirred and dispersed using the previously described method. The lenses were then fabricated using the cast molding method. After hydration for 24 hours, their physical properties including light transmittance, refractive index, water content, and contact angle were evaluated. The formulation ratios for each sample are detailed in Table 2.

    3) Measurement Instruments and Analysis

    The surface morphology of the fabricated lenses was analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). For SEM analysis, a field-emission scanning electron microscope (JSM-7500F, JEOL Ltd, Japan) was used. AFM measurements were performed using an NX10 system (NX10, Parksystems, Korea). Optical transmittance was measured using a UV-Vis spectrophotometer (Cary 60 UV-Vis, Agilent Technologies, USA), evaluating transmittance in the visible (Vis), near-ultraviolet A (UV-A), and near-ultraviolet B (UV-B) regions. The results were expressed as percentages. Water content was determined gravimetrically using a microwave oven and an analytical balance (Ohaus PAG 214C, USA). The refractive index was measured using an ABBE refractometer (NAR-1T, ATAGO, Japan). The wettability of the fabricated lenses was assessed using the sessile drop method with a DSA30 instrument (DSA30, Kruss GMBH, Germany). Tensile strength was measured using a universal testing machine (AGS-X, Shimadzu, Japan). After removing surface moisture, a force of 0.000 to 1.000 kgf was applied at a speed of 200–300 mm/min for 0–20 seconds. The tensile strength was recorded as the force at which the lens failed. Elution tests were conducted to evaluate absorbance, potassium permanganate consumption, and pH changes. For absorbance measurements, lenses were hydrated in 10 mL of tertiary distilled water for 24 hours. Samples of the extraction solution were collected and analyzed after 1, 3, 5, and 7 days. For potassium permanganate consumption and pH change evaluation, 4 g of fabricated lenses were immersed in 40 mL of tertiary distilled water and heated at 70°C for 24 hours. The extract served as the experimental group, while ultrapure water was used as the control group. Potassium permanganate consumption was considered negligible if the difference between the test and control groups was ≤2 mL. Similarly, pH changes were deemed insignificant if the difference was ≤1.5. Antibacterial activity against Staphylococcus aureus was assessed using 3M Petrifilm™(3M Petrifilm™, 3M, USA). Lenses were hydrated in 0.9% sodium chloride physiological saline for 24 hours along with S. aureus. After hydration, surface moisture was removed, and 1 mL of the physiological saline solution containing both the bacteria and the lens was subjected to shaking. This solution was then applied to the Petrifilm™ and incubated at 36 ± 1°C for 24 hours using a shaking incubator (DS-210SL, Daewon Science, Korea).

    Ⅲ. Results and Discussion

    1. Surface Analysis

    Scanning electron microscopy (SEM) was performed to examine the surface of the fabricated hydrogel lenses and to confirm the presence of nanoparticles. The SEM results verified that nanoparticles were present on the lens surfaces. Surface roughness was measured using atomic force microscopy (AFM), which also confirmed the presence of nanoparticles. The Ref lens exhibited a surface roughness of 33.2 nm, whereas the lenses containing cerium(IV)-zirconium(IV) oxide nanoparticles exhibited reduced roughness, with a minimum value of 7.70 nm. These results are presented in Fig. 1 and Fig. 2.

    2. Spectral Transmittance

    Spectral transmittance measurements of the fabricated lenses showed that UV-B transmittance decreased as the proportion of added cerium(IV)- zirconium(IV) oxide nanoparticles increased. Meanwhile, visible light transmittance decreased with increasing concentration of nano-sized cerium(IV)-zirconium(IV) oxide, but remained above 90%, showing excellent transmittance. This decreasing trend is illustrated in Fig. 3. This result aligns with the findings of MUEEN and RAFID,20) who reported that nano-sized cerium(IV)- zirconium(IV) oxide effectively absorbs UV radiation.

    3. Wettability and Tensile Strength

    Contact angle measurements were conducted to assess wettability. Lenses incorporating cerium(IV)- zirconium(IV) oxide nanoparticles exhibited a decrease in contact angle, ranging from 56.36° to 36.87°, as the nanoparticle concentration increased, indicating improved wettability. A significant enhancement in wettability was observed when the additive concentration increased from 0.03% to 0.06% (Fig. 4). Wettability is influenced by surface roughness,21) and the AFM results indicated that lenses containing cerium(IV)-zirconium(IV) oxide nanoparticles had lower surface roughness than the Ref lens, contributing to improved wettability. Tensile strength measurements assessed the durability of the lenses. The Ref lens exhibited a tensile strength of 0.1512 kgf/mm², whereas the experimental lenses exhibited values ranging from 0.2113 kgf/mm² to 0.5937 kgf/mm², showing an increase with increasing nanoparticle concentration. However, CZ_5, which contained the highest concentration of cerium(IV)-zirconium(IV) oxide nanoparticles, exhibited a slightly lower tensile strength (0.5610 kgf/mm²), likely due to excessive nanoparticle aggregation (Fig. 4). Generally, improved wettability tends to reduce tensile strength, but in this case, the incorporation of cerium(IV)-zirconium(IV) oxide nanoparticles led to simultaneous increases in both wettability and tensile strength.

    4. Refractive Index and Water Content

    The refractive index remained 1.4361±0.0001, showing no significant difference from the Ref lens, regardless of nanoparticle concentration. Similarly, water content remained consistent at 37.18±0.14%, independent of additive concentration (Fig. 5).

    5. Polymerization Stability

    Polymerization stability was evaluated using pH tests, potassium permanganate reduction tests, and absorbance measurements. The pH test results showed a difference of less than 1.5 between the lenses containing cerium(IV)- zirconium(IV) oxide nanoparticles and the Ref lens. In the potassium permanganate reduction test, ultrapure water exhibited a consumption of 22.10 mL, while the Ref lens showed 19.20 mL, a difference exceeding 2 mL. However, the lenses containing cerium(IV)-zirconium(IV) oxide nanoparticles exhibited a difference of less than 2 mL, indicating improved polymerization stability.

    Absorbance values for both the experimental and control groups remained below 0.30, further confirming enhanced polymerization stability in lenses containing cerium(IV)-zirconium(IV) oxide nanoparticles.

    6. Antibacterial Activity

    Antibacterial activity against staphylococcus aureus was evaluated. The Ref lens exhibited no antibacterial effect, whereas lenses containing cerium(IV)-zirconium(IV) oxide nanoparticles inhibited bacterial growth. These antibacterial effects are presented in Fig. 6.

    7. Hydrogel Lenses Containing Hydrophilic Monomers

    While increasing the concentration of cerium(IV)- zirconium(IV) oxide nanoparticles improved wettability, tensile strength, and UV-B blocking, a decrease in visible light transmittance was observed when the concentration exceeded 0.03%. Thus, 0.03% was determined to be the optimal concentration for functional enhancement. To further improve the lens properties, the hydrophilic monomer MA was added, and its effects were evaluated.

    1) UV-B Transmittance

    For cerium(IV)-zirconium(IV) oxide lenses containing the hydrophilic monomer, both the 15-group and 30-group exhibited a decrease in UV-B transmittance as the concentration of MA increased. However, lenses containing only MA showed a UV-B transmittance of approximately 50%, and this did not change with varying concentrations. This result suggests a synergistic UV-B blocking effect when both MA and cerium(IV)-zirconium(IV) oxide nanoparticles are present. These findings are summarized in Fig. 7. Also, Sample S, as a reference for comparison, did not contain cerium(IV)-zirconium(IV) oxide nanoparticles or MA.

    2) Refractive Index and Water Content

    The refractive index of cerium(IV)-zirconium(IV) oxide lenses containing the hydrophilic monomer decreased from 1.4357 to 1.4163 as the concentration of methacrylic acid (MA) increased. This decrease is attributed to the effect of MA. Similarly, the water content increased from 37.44% to 47.18% with higher MA concentrations. The measurement results for each lens are presented graphically in Fig. 8.

    3) Wettability

    Cerium(IV)-zirconium(IV) oxide lenses containing the hydrophilic monomer exhibited a decrease in contact angle as the MA concentration increased, indicating improved wettability. Furthermore, a sharp increase in wettability was observed when the MA addition ratio increased from 6% to 8%. These results are presented in Fig. 9.

    4) Tensile Strength

    For cerium(IV)-zirconium(IV) oxide lenses containing the hydrophilic monomer, tensile strength ranged from 0.2113 kgf/mm² to 0.0612 kgf/mm², showing a decrease as the MA concentration increased. Compared to the Ref lens (without cerium(IV)- zirconium(IV) oxide nanoparticles) and the Pr lens (Ref with only MA added), the addition of MA led to a reduction in tensile strength. However, the incorporation of cerium(IV)-zirconium(IV) oxide nanoparticles mitigated this decrease. These results are presented graphically in Fig. 10. This suggests that cerium(IV)-zirconium(IV) oxide can help counteract the reduction in tensile strength, a common drawback of hydrophilic monomers in lenses.

    Ⅳ. Conclusion

    In this study, hydrogel lenses were synthesized by copolymerizing HEMA with cerium(IV)-zirconium(IV) oxide and MA as functional additives. The optical and physical properties of the fabricated lenses were systematically analyzed. The incorporation of cerium(IV)-zirconium(IV) oxide nanoparticles led to decreased UV-B transmittance, improved wettability, increased tensile strength, antibacterial activity, and reduced surface roughness. These enhancements were more pronounced at higher nanoparticle concentrations. In lenses containing both MA and cerium(IV)-zirconium(IV) oxide, a greater reduction in UV-B transmittance and increased wettability were observed compared to those containing only cerium(IV)-zirconium(IV) oxide. Additionally, all modified lenses exhibited superior polymerization stability compared to the Ref lens. These findings suggest that incorporating cerium(IV)-zirconium(IV) oxide and MA into hydrogel contact lenses holds promise for the development of high-performance ophthalmic lenses with enhanced antibacterial properties, UV-B blocking, and durability.

    Figure

    KJVS-27-1-41_F1.gif

    SEM image of samples (A: Ref, B: cerium(IV)- zirconium(IV) oxide lens).

    KJVS-27-1-41_F2.gif

    AFM images of samples (A: Ref, B: cerium(IV)- zirconium(IV) oxide lens).

    KJVS-27-1-41_F3.gif

    UV-B Spectral transmittance of samples.

    KJVS-27-1-41_F4.gif

    Comparison of contact angle of samples(A), comparison of tensile strength of sample (B).

    KJVS-27-1-41_F5.gif

    Comparison of refractive index and water content of samples.

    KJVS-27-1-41_F6.gif

    Antimicrobial property of samples (A: Ref, B: CZ_5).

    KJVS-27-1-41_F7.gif

    UV-B Spectral transmittance diagrams of samples containing MA.

    KJVS-27-1-41_F8.gif

    Comparison of refractive index and Water content of samples containing MA.

    KJVS-27-1-41_F9.gif

    Comparison of contact angle of samples containing MA.

    KJVS-27-1-41_F10.gif

    Comparison of tensile strength of samples containing MA.

    Table

    Percent compositions of samples (Unit : wt%)

    Percent compositions of samples containing MA (Unit : wt%)

    "-R" is the experimental group with no MA added. "-2" is the experimental group with a 2% concentration of MA. Similarly, the number after "-" indicates the concentration of MA

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