Abstract
Intraocular lenses (IOL), used to treat cataracts, successfully replace the cloudy crystalline lens of the eye to restore vision. However, no clinically available lens can effectively mimic the accommodative ability of the natural lens, responding to reflexive ciliary muscle movements to allow changes in optical focus. An optoelectronic approach could be used, incorporating smart sensor biomaterials which respond to optical stimulus by lens accommodation. However, materials with a suitable combination of optoelectronic and biological properties are limited. The two dimensional transition metal carbides and/or nitrides, MXenes, are a family of nanomaterials with physical properties including high electronic conductivity, optical transparency, flexibility, biocompatibility, and hydrophilicity suggesting their suitability for use within an accommodating lens design. The aim of this work was therefore to investigate the suitability of Ti3C2Tx (MXene) for use as a transparent conductive electrode within an accommodating lens design.Ti3C2Tx was synthesised through liquid exfoliation of the MAX phase precursor with lithium fluoride and hydrochloric acid. X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy and dynamic light scattering (DLS) size analysis was performed on the synthesised Ti3C2Tx colloidal solution. The solution was spin-coated onto hydrophobic acrylate IOLs, and optical measurements of lens power and modulation transfer function were made. Optoelectronic performance was evaluated through spectral transmittance and conductivity using UV Vis spectroscopy and a four-point probe technique. Biocompatibility was assessed using a human lens epithelial B-3 cell line with the CellTiter 96® AQueous One Solution Cell Proliferation Assay (MTS) and the CytoTox96 non-radioactive cytotoxicity assay (LDH). A monocytic THP-1 cell line was used to evaluate oxidative stress using the dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay and stimulation of inflammation by enzyme-linked immunosorbent assay (ELISA) for inflammatory markers interleukin (IL)-6, IL-8, and TNF-α. A nematic liquid crystal (LC), 4’-Pentyl-4-cyanobiphenyl, 5CB, was used in the fabrication of a Ti3C2Tx test cell to explore an electronically stimulated adjustable focus proof-of-concept design. The electric field-induced refractive index modulation of the LC was measured using iii a purpose-built refractometer. Ti3C2Tx/LC lens design was explored in a glass-based model and optical methods were used to evaluate focusing performance and spatial frequency. In the development of an accommodative IOL prototype, a polymer-based Ti3C2Tx/LC design was investigated, as a more appropriate IOL base material.
Ti3C2Tx physical characterisation studies produced an optimised synthesis route for spin-coating onto hydrophobic acrylate IOLs. The coatings optoelectronic evaluation found sheet resistance to range from 0.2 – 1.0 kΩ sq-1 with transmittance in the visible region ranging from 50 – 80 %. In vitro biological studies investigating the interaction of Ti3C2Tx coated IOLs with human lens epithelial cells indicated that the Ti3C2Tx coatings were non-cytotoxic with cell numbers of 3.5x104 ± 5.1x103 for the cell only and 3.8x104 ± 5.4x103 and 4.1x104 ± 5.4x103 for the Ti3C2Tx coated IOLs and uncoated IOL. A monocytic cell was used to evaluate inflammatory pathways, that demonstrated no significant upregulation of pro-inflammatory markers exposed to the coating (p < 0.05). The proof-of-concept adjustable focus test cell was constructed with a layer of LC sandwiched between Ti3C2Tx coatings on glass substrates. The LC layer experienced molecular reorientation with an applied electric field that resulted in optical changes to the point of focus. The fabrication of a Ti3C2Tx/LC lens was optimised in a glass model which demonstrated adjustable focus through electrical stimulation.
In conclusion, the synthesis, physical, and biological characterisation of the Ti3C2Tx nanomaterial, spin-coated onto hydrophobic IOLs for use within an ophthalmic IOL has been demonstrated for the first time. Moreover, the proof-of-concept test cell and adjustable focus lens indicated the feasible use of Ti3C2Tx as a transparent conductive electrode within a smart lens device capable of inducing changes in optical power on the application of an external force.
| Date of Award | 2022 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Susan Sandeman (Supervisor), Marcus Dymond (Supervisor), Cyril Crua (Supervisor), Joseph Lacey (Supervisor) & Yury Gogotsi (Supervisor) |