Femtosecond laser micromachining in ophthalmic hydrogels: spectroscopic study of materials effects

Yu, Dakuan; Huang, Ruiting; Knox, Wayne H.

doi:10.1364/ome.9.003292

Cited by 8 publications

(2 citation statements)

References 79 publications

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“…Raman spectroscopy has been utilized for the compositional analysis of hydrogels . In addition, the Raman spectra of hydrogels have also been utilized to characterize the structure of hydrogels. , For example, the sharpness of peaks in the Raman spectra as characterized by the full width at half maximum (FWHM) has been associated with the extent of network structure heterogeneity. As shown in Figure a, we found that the amplitude of the peak at 1409 cm –1 associated with CC bonds differed among the various controllers, suggesting that more CC bonds were consumed from the rate-based bang-bang controlled photopolymerization process ( K D ), which exhibited the lowest curing rate among the closed-loop controlled processes.…”

Section: Resultsmentioning

confidence: 99%

Closed-Loop Controlled Photopolymerization of Hydrogels

Singh

Zhang

Bethel

et al. 2021

ACS Appl. Mater. Interfaces

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Here, we present a closed-loop controlled photopolymerization process for fabrication of hydrogels with controlled storage moduli. Hydrogel crosslinking was associated with a significant change in the phase angle of a piezoelectric cantilever sensor and established the timescale of the photopolymerization process. The composition, structure, and mechanical properties of the fabricated hydrogels were characterized using Raman spectroscopy, scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA). We found that the storage moduli of photocured poly(ethylene glycol) dimethacrylate (PEGDMA) and poly(Nisopropylacrylamide) (PNIPAm) hydrogels could be controlled using bang-bang and fuzzy logic controllers. Bang-bang controlled photopolymerization resulted in constant overshoot of the storage modulus setpoint for PEGDMA hydrogels, which was mitigated by setpoint correction and fuzzy logic control. SEM and DMA studies showed that the network structure and storage modulus of PEGDMA hydrogels were dependent on the cure time and temporal profile of UV exposure during photopolymerization. This work provides an advance in pulsed and continuous photopolymerization processes for hydrogel engineering based on closed-loop control that enables reproducible fabrication of hydrogels with controlled mechanical properties.

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Section: Resultsmentioning

confidence: 99%

Closed-Loop Controlled Photopolymerization of Hydrogels

Singh

Zhang

Bethel

et al. 2021

ACS Appl. Mater. Interfaces

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“…Moreover, understanding the role of water in the LIRIC writing process itself is fundamental as water will only enter the picture after laser treatment has taken place. Increased (O-H) peak at ~3400 cm -1 in confocal Raman spectroscopy 9 post LIRIC writing indicate that water is necessary to create regions of lower refractive index once bonds have been broken 10 but may not be directly involved in the bond breaking process. Given this finding, it is conceivable that LIRIC techniques could be applied to dry contact lens materials by rehydrating the hydrogel after the writing process, which parallels the hydration in the contact lens production process shown in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Laser induced refractive index change writing in dehydrated ophthalmic materials: feasibility study

Islam,

Knox

2023

ODS 2023: Industrial Optical Devices and Systems

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Laser Induced Refractive Index Change (LIRIC) uses femtosecond laser pulses to locally modify a material’s refractive index below material damage thresholds. This technique has been successfully applied to create refractive correctors in wet ophthalmic materials such as hydrated contact lenses. However, applying LIRIC in wet contact lens materials to mass produce refractive correctors would require drastic changes to the current manufacturing infrastructure. To integrate LIRIC in the production line in a cost-effective manner, applying this technique in a dry contact lens is necessary. Therefore, this study seeks to understand how the absence of water affects LIRIC writing mechanisms. Our experiments have shown that LIRIC writing using 400nm laser light produced rough, non-uniform regions of index change in dehydrated Hydroxyethyl Methyl Acrylate based hydrogels. However, in dehydrated silicone hydrogels, LIRIC successfully induced greater index changes than when the materials are in hydrated state.

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Directional phase-unwrapping algorithm and phase shift technique on hydrogel

Knox

2021

Appl. Opt.

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Refractive index microstructures, which can be written by multiphoton absorption with femtosecond lasers, have many applications. Here we present a directional phase-unwrapping algorithm with phase-shifting technique and apply it to the metrology of hydrogel microstructures. A staircase phase-unwrapping algorithm is demonstrated. This fast quality-guided path phase-unwrapping applies well to situations that are geometrically well defined and is quite tolerant of phase noise. To achieve precise very small phase shifts, we also present a slant angle technique on a DC servo stage along with phase shift measurement, allowing us to achieve 6.5 nm step sizes.

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Femtosecond laser micromachining in ophthalmic hydrogels: spectroscopic study of materials effects

Cited by 8 publications

References 79 publications

Closed-Loop Controlled Photopolymerization of Hydrogels

Closed-Loop Controlled Photopolymerization of Hydrogels

Laser induced refractive index change writing in dehydrated ophthalmic materials: feasibility study

Directional phase-unwrapping algorithm and phase shift technique on hydrogel

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