WO2024220762A1

WO2024220762A1 - Optical devices based on nanostructured surfaces in hydrogels using nonlinear absorption

Info

Publication number: WO2024220762A1
Application number: PCT/US2024/025345
Authority: WO
Inventors: Wayne H. Knox
Original assignee: University of Rochester
Current assignee: University of Rochester
Priority date: 2023-04-21
Filing date: 2024-04-19
Publication date: 2024-10-24
Anticipated expiration: 2025-10-21

Abstract

A method of forming surface features in a hydrogel includes providing a hydrogel material having at least one surface; irradiating the hydrogel material with laser pulses of light from a femtosecond laser, wherein the laser pulses are focused into a focal volume in the hydrogel material at the surface of the hydrogel material and are of sufficient energy such that an intensity of light within the focal volume will cause a nonlinear absorption of photons and result in depolymerization of the material within the focal volume, while the material just outside of the focal volume will be minimally affected by the laser light; and removing depolymerized material at the surface of the hydrogel material to form surface features in the hydrogel material. The method enables writing structures of sub-wavelength size that appear on the surface of a hydrogel device, so that large refractive index discontinuities of e.g., >0.50 can be obtained. These structures can be written with a wide range of depth and lateral profiles, using multi-photon induced absorption to cause localized bond breaking that results in localized depolymerization. Devices such as diffraction gratings, mirrors, lenses etc. can be produced with this methodology.

Description

OPTICAL DEVICES BASED ON NANOSTRUCTURED SURFACES IN HYDROGELS USING NONLINEAR ABSORPTION

RELATED FIELDS

[0001] The present disclosure relates to optical devices made from hydrogel-based materials and having nanostructured surfaces formed by nonlinear absorption of femtosecond laser exposures.

BACKGROUND

[0002] There are many kinds of ophthalmic materials of interest in vision science and human vision correction applications. One particular class of materials, known as hydrogels, have remarkable properties owing to their great affinity for water, and ability to transport fluids and gases easily in cases where direct on-eye contact is required, such as the case of contact lenses. Furthermore, hydrogels are of interest for intra-ocular lens applications, where they are directly implanted into the eye and left for many years. Nonlinear absorption of tightly focused femtosecond laser beams has been shown to result in localized depolymerization of the hydrogel matrix, allowing water or other solvents to enter nano-voids that are created in the process of writing 3D localized refractive index changes, as shown, e.g., in [1] “Inventing a New Way to See Clearly: Non-invasive Vision Correction with Femtosecond Lasers,” Wayne H. Knox, Technology & Innovation, Volume 20, Number 4, August 2019, pp. 385-398; [2] “Advances in Deterministic Femtosecond Laser Writing of Vision Correction Devices in Ophthalmic Hydrogels,” Gustavo Gandara-Montano PhD Thesis, University of Rochester (2019) (ProQuest Number 13856499); and [3] “Femtosecond laser micromachining in ophthalmic hydrogels: spectroscopic study of materials effects,” Dan Yu, Ruiting Huang and Wayne H. Knox, Optical Materials Express Vol. 9, No. 8 (2019), the disclosures of which are incorporated herein by reference in their entirety. By varying the system laser writing parameters such as pulsewidth, wavelength, numerical aperture, writing speed, etc. 3D localized refractive optical structures have been written with, e.g., refractive index change as large as 0.06. [0003] It would be desirable to provide new ways of writing structures of sub-wavelength size and higher relative refractive index changes in hydrogel materials, and in particular which would allow for new kinds of customization of hydrogel lens properties.

SUMMARY

[0004] In the present case, a method of writing structures of sub-wavelength size that appear on the surface of a hydrogel device is described, so that larger refractive index discontinuities of e.g., >0.50 can be obtained. These structures can be written with a wide range of depth and lateral profiles, using multiphoton induced absorption to cause localized bond breaking that results in localized depolymerization. Devices such as diffraction gratings, mirrors, lenses etc. can be produced with this methodology.

[0005] In one embodiment of the disclosure, a method of forming surface features in a hydrogel is described, where the method comprises: providing a hydrogel material having at least one surface; irradiating the hydrogel material with laser pulses of light from a femtosecond laser, wherein the laser pulses are focused into a focal volume in the hydrogel material at the surface of the hydrogel material and are of sufficient energy such that an intensity of light within the focal volume will cause a nonlinear absorption of photons and result in depolymerization of the material within the focal volume, while the material just outside of the focal volume will be minimally affected by the laser light; and removing depolymerized material at the surface of the hydrogel material to form surface features in the hydrogel material.

BRIEF DESCRIPTION OF THE FIGURES

[0006] Figure 1 is an illustration showing areas of localized multiphoton excitation inside the bulk of a polymer or at the surface, using focused femtosecond laser beams in the transparency range of the material, and the corresponding localized refractive index changed regions that result after the sample is processed.

[0007] Figure 2 depicts electron microscope images of surface features written on a Contamac 58 HEMA hydrogel. [0008] Figure 3 is an illustration of localized multiphoton excitation at the surface of a polymer sample using focused femtosecond laser beams in the transparency range of the material similar to Figure 1, and writing features on the surface in combination with a second writing just below the surface, producing controllable depth surface features.

[0009] Figure 4 is a graph illustrating relationship of the diffraction-limited beam size as a function of excitation wavelength and numerical aperture of the writing system.

DETAILED DESCRIPTION

[0010] Figure 1, part (a) shows a case where a laser beam 11 is focused inside a transparent material 10 such as a hydrogel. The material is transparent to the laser radiation wavelength, therefore there is no absorption outside of the focus region. But in the focus region, as shown by the area 12, the intensity is high enough to cause nonlinear (intensity-dependent) absorption. The localized energy absorption that happens in this case is enough to change the polymer structure in the region of the focus, due to localized bond breaking. In particular, the laser may be a femtosecond laser (e.g., pulsewidth 50-200 fs) with visible or near-IR wavelength (e.g., 1030 nm, 800-900 nm, 517 nm, or 405 nm). The laser repetition rate may generally be in the range of 1 Hz - 100 MHz, more often in the range of 1 - 100 MHz (e.g., 50- 100 MHz, or 1-10 MHz), but even in the range 1-5000 Hz in certain cases. After the localized depolymerization takes place as shown in Figure 1, part (a), then the material is processed by placing in one or more of several solvents and temperature/pressure cycling treatments (e.g. autoclaving) and then the monomer and n-mer fragments that were left in the focus region are flushed out. Those regions are re-filled with the solvent that the material is placed in, and by diffusive transport, the fluids re-fill the nano-pores created by the laser irradiation. What is left is some regions 13 of changed refractive index, as shown in Figure 1, part (b). In the case of strongly hydrophilic polymers including water content up to 58% or more in hydrated state, the polymer, having an index of refraction of (e.g.) 1.41 can achieve a significantly lower index of refraction if water re-fills the nano-voids. Since the water has an index of refraction near 1.33, the refractive can drop by as much as 0.08 after the water rushes in to fill the voids.

[0011] To get larger index of refraction changes, in accordance with the present disclosure such structures using nonlinear absorption are written in a similar manner, but instead of writing in the bulk where the refractive index changes are limited due to the physics of water, they are now written on the surface of the material 10. As shown in Figure 1, part (a), previously disclosed systems typically write with a laser beam focused inside the bulk of a transparent hydrogel. After the material is processed, the change in refractive index appears in regions where the laser intensity was highest (Figure 1, part (b)). In Figure 1, part (c), a different configuration is now proposed wherein the laser is focused on or near the surface of the material 10. The polymer is then depolymerized locally near the surface of the hydrogel, as shown in Figure 1, part (c). In that case, after the material is processed, the depolymerized materials that resulted from exposure to the femtosecond laser are removed to the solution, and the result is surface features 14 as shown in Figure 1, part (d). The depth of the features may be comparable to half of the Rayleigh range of the focused laser, which may be controlled in accordance with the laser system operating parameters. This particular feature stands in great contrast to previously demonstrated methods of making surface features on polymers using one-photon absorption and ablation of material, such as with ultraviolet lasers. In the case of one-photon ordinary absorption, the light penetration is rigorously limited by the Beer's length absorption depth as determined by the material and the wavelength, and it cannot be changed.

[0012] Figure 2 shows an actual demonstration of this concept as illustrated in Figure 1, using a femtosecond laser system similar to that as described in detail in "Femtosecond laser micromachining in ophthalmic hydrogels: spectroscopic study of materials effects," Dan Yu, Ruiting Huang and Wayne H. Knox, Optical Materials Express Vol. 9, No. 8 (2019), but with the following specific laser parameters. A flat sample of Contamac (Acofilcon A) Hydrogel was hydrated normally, and femtosecond laser exposure lines were written with a 150 fs laser at 80 MHz repetition rate, 400 nm wavelength and focused on the surface of the hydrogel. In such step, the laser power and scan rate are selected and controlled for maintaining an energy profile in the hydrogel material within the focus spot above a nonlinear absorption threshold of the hydrogel material, but preferably below an material damage breakdown threshold of the hydrogel material which would result in ablation or otherwise observed burning (scorching) or carbonization of the hydrogel material. Such material damage can be caused, e.g., by excitation intensities exceeding a critical free-electron density. Then the sample was dehydrated and placed in vacuum and coated with a thin film of platinum for study in the electron microscope. The thin metal film is needed to avoid surface charging effects that reduce the imaging performance of the electron microscope. Figure 2, part (a) shows resulting surface grating lines 25, 26 written with 10 micron spacings at 10 mm/sec speed (lower) and 5 mm/sec (upper), while Figure 2, part (b) shows a 10 micron grating lines 27 written at a slower speed (1 mm/sec). The surface features cause by the localized depolymerization are clearly seen. Furthermore, deeper, more pronounced end sections 28 resulting from the longer dwell times caused by the slow turnaround motion of the piezoelectric translator are clearly shown indicating that the depth of the features can be controlled by the exposure/speed combination.

[0013] Since the absorption is nonlinear, it would be possible to write deeper features by doing multiple writing exposures as shown in Figure 3. Figure 3, parts (a) and (b) shows surface feature writing with laser beam 31, focus region area 32, and resulting surface feature 34 similar as in Figure 1, parts (a) and (b), but Figure 3, part (c) shows a second exposure 32' at a slightly deeper position, and in doing so the resulting surface grating feature 34' shown in Figure 3, part (d) is deeper. This offers far greater control than the use of single-photon excitation with a fixed absorption depth. The lateral size of the written features is ultimately limited by the diffraction-limited wavelength, and by using higher numerical apertures (e.g. NA greater than about 0.5, or greater than about 1.0, including in some embodiments from about 0.5 to 1.0, from about 1.0 to about 1.3, and more particularly around 1.3), it should be possible to write sub-micron dimensioned surface features into the range of, e.g., approximately 100-200 nm, as shown in Figure 4.

[0014] Useful devices that could benefit from this advance could include diffraction gratings, Fresnel and other kinds of lenses, reflectors, wavelength-dependent reflectors, etc. Materials could include hydrogels in the HEMA class, or Silicone-based class or Acrylic class, and they could be initially written in "never-hydrated", "hydrated" or "hydrated-then dehydrated" states (with subsequent hydration and/or solvent flushing when required to remove depolymerized materials from the laser exposed surface regions). The surface features formed in the hydrogel (in hydrated or dehydrated form) in such devices may be coated with a metal, dielectric, or polymer layer for added function or protection of the surface features.

[0015] In particular embodiments, the surface features may be formed in a hydrogel material by irradiating the hydrogel material with very short laser pulses of light as described in U.S. Publication Nos. 2008/0001320, 2009/0287306, 2012/0310340 and 2012/0310223, but where such short laser pulses are focused at the surface of the hydrogel material and are of sufficient energy such that the intensity of light within the focal volume will cause a nonlinear absorption of photons (typically multi-photon absorption) and lead to depolymerization of the material within the focal volume, while the material just outside of the focal volume will be minimally affected by the laser light. The femtosecond laser pulse sequence pertaining to an illustrative embodiment, e.g., operates at a high repetition-rate, e.g., 80 MHz , and consequently the thermal diffusion time (>0.1ps) is much longer than the time interval between adjacent laser pulses (~11 ns). Under such conditions, absorbed laser energy can accumulate within the focal volume and increase the local temperature.

[0016] According to one specific embodiment, surface features are formed by providing a hydrogel material having a surface, and forming at least one laser-modified region at the surface of the hydrogel material with light pulses from a laser by focusing and scanning the light pulses along surface regions of the hydrogel material to cause non-linear absorption of the laser light and depolymerization of the hydrogel polymer within the focus regions.

[0017] Femtosecond laser pulse writing methods may be more advantageously carried out if the hydrogel material further includes a photosensitizer, as more particularly taught in U.S. Publication Nos. 2009/0287306 and 2012/0310340. The presence of the photosensitizer permits one to set a scan rate to a value that is at least fifty times greater, or at least 100 times greater, than a scan rate without a photosensitizer present in the material, and yet provide similar amount of non-linear absorption in the focal volume. Alternatively, the use of a photosensitizer may permit one to set an average laser power to a value that is at least two times less, more particularly up to four times less, than an average laser power without a photosensitizer in the material, yet provide similar results. A photosensitizer having a chromophore with a relatively large multi-photon absorption cross section is believed to capture the light radiation (photons) with greater efficiency and then transfer that energy to the material within the focal volume. The photosensitizer may include, e.g., a chromophore having a two-photon, absorption cross-section of at least 10 GM between a laser wavelength range of 750 nm to 1100 nm. In the case of a non-polymerizable photosensitizer, solutions containing a photosensitizer may be prepared and the hydrogel polymeric materials may be allowed to come in contact with such solutions to allow up-take of the photosensitizer into the polymeric matrix of the polymer. In the case of a polymerizable photosensitizer, monomers containing a chromophore, e.g., a fluorescein-based monomer, may be used in the monomer mixture used to form the polymeric material such that the chromophore becomes part of the polymeric matrix. Further, one could use a solution containing a non-polymerizable photosensitizer to dope a polymeric material that had been prepared with a polymerizable photosensitizer. Also, it is to be understood that the chromophoric entities could be the same or different in each respective photosensitizer.

[0018] The concentration of a polymerizable, monomeric photosensitizer having a two-photon, chromophore in a hydrogel material can be as low as 0.05 wt.% and as high as 10 wt.%. Exemplary concentration ranges of polymerizable monomer having a two-photon, chromophore in a hydrogel material is from 0.1 wt.% to 6 wt.%, 0.1 wt.% to 4 wt.%, and 0.2 wt.% to 3 wt.%. In various aspects, the concentration range of polymerizable monomer photosensitizer having a two-photon, chromophore in a hydrogel material is from 0.4 wt.% to 2.5 wt.%.

[0019] Due to the repetition rate pulse sequence used in the irradiation process, the accumulated focal temperature increase can be much larger than the temperature increase induced by a single laser pulse. The accumulated temperature increases until the absorbed power and the dissipated power are in dynamic balance. For hydrogel polymers, thermal-induced depolymerization can produce a change in the refractive index as the local temperature exceeds a transition temperature. If the temperature increase exceeds a second threshold, a somewhat higher temperature than the transition temperature, the polymer is pyrolytically degraded and carbonized residue and water bubbles are observed. In other words, the material exhibits visible optical damage (scorching). Each of the following experimental parameters such as laser repetition rate, laser wavelength and pulse energy, TPA coefficient, and water concentration of the materials should be considered so that a desired change can be induced in the hydrogel polymers without optical damage.

[0020] The pulse energy and the average power of the laser, and the rate at which the irradiated regions are scanned, will in-part depend on the type of polymeric material that is being irradiated, how much energy absorption is required to create surface features in the material. The selected pulse energy will also depend upon the scan rate and the average power of the laser at which the surface features are written into the polymer material. Typically, greater pulse energies will be needed for greater scan rates and lower laser power. For example, some materials will call for a pulse energy from 0.05 nJ to 100 nJ or from 0.2 nJ to 10 nJ.

[0021] In one embodiment, the average pulse energy may be from 0.2 nJ to 10 nJ and the average laser power may be from 40 mW to 220 mW. The laser may also operate within the visible or near-IR wavelengths. Within the stated laser operating powers, the hydrogel polymeric material may be irradiated at a scan rate, e.g., of from 0.4 mm/s to 4 mm/s. With higher laser powers, significantly faster scan speeds may be employed.

[0022] A photosensitizer will include a chromophore in which there is little or no intrinsic linear absorption in the spectral range of 600-1000 nm. The photosensitizer is present in the hydrogel polymeric material to enhance the photoefficiency of the two-photon absorption required for the formation of the described surface features.

[0023] The laser may generate light with a wavelength in the range from violet to near-infrared. In various aspects, the wavelength of the laser may be in the range from 400 nm to 1500 nm, from 400 nm to 1200 nm, or from 650 nm to 950 nm.

[0024] The laser may have a peak intensity at focus of greater than 10¹³ W/cm². At times, it may be advantageous to provide a laser with a peak intensity at focus of greater than IO¹⁴ W/cm², or greater than 10¹⁵ W/cm².

[0025]

[0026] The following include various specific enumerated embodiments of the present disclosure.

[0027] Embodiment 1. A method of forming surface features in a hydrogel comprising: providing a hydrogel material having at least one surface; irradiating the hydrogel material with laser pulses of light from a femtosecond laser, wherein the laser pulses are focused into a focal volume in the hydrogel material at the surface of the hydrogel material and are of sufficient energy such that an intensity of light within the focal volume will cause a nonlinear absorption of photons and result in depolymerization of the material within the focal volume, while the material just outside of the focal volume will be minimally affected by the laser light; and removing depolymerized material at the surface of the hydrogel material to form surface features in the hydrogel material.

[0028] Embodiment 2. The method of Embodiment 1, further comprising controlling a laser power and scan rate for maintaining an energy profile in the hydrogel material within the focus volume above a nonlinear absorption threshold of the hydrogel material, and below a material damage breakdown threshold of the hydrogel material which would result in ablation or observable burning or carbonization of the hydrogel material.

[0029] Embodiment 3. The method of Embodiment 1 or 2, wherein the laser is focused with an objective having a numerical aperture selected to provide a focal volume having a submicron dimension and forming submicron dimensioned surface features in the hydrogel material.

[0030] Embodiment 4. The method of Embodiment 3, wherein the objective has a numerical aperture of greater than 1.0.

[0031] Embodiment 5. The method of Embodiment 3, wherein the objective has a numerical aperture of about 1.3.

[0032] Embodiment 6. The method of any one of Embodiments 1-5, wherein the surface features have a width of less than 1.0 micrometers.

[0033] Embodiment 7. The method of Embodiment 6, wherein the surface features have a width of from about 100 to about 200 nanometers.

[0034] Embodiment 8. The method of any one of Embodiments 1-7, further comprising re-irradiating the hydrogel material with additional laser pulses of light from a femtosecond laser, wherein the additional laser pulses are focused into a focal volume in the hydrogel material directly below focal volume at the surface of the hydrogel material to provide an extended combined focal volume relative to the surface, and removing depolymerized material from the extended focal volume to form surface features in the hydrogel material having an extended depth from the surface of the hydrogel material. [0035] Embodiment 9. The method of any one of Embodiments 1-8, wherein the surface features form a diffraction grating.

[0036] Embodiment 10. The method of any one of Embodiments 1-8, wherein the surface features form a lens.

[0037] Embodiment 11. The method of any one of Embodiments 1-8, wherein the surface features form a Fresnel lens.

[0038] Embodiment 12. The method of any one of Embodiments 1-8, wherein the surface features form a reflector.

[0039] Embodiment 13. The method of any one of Embodiments 1-8, wherein the surface features form a wavelength-dependent reflector.

[0040] Embodiment 14. The method of any one of Embodiments 1-13, wherein the hydrogel material is irradiated with the laser pulses of light from the femtosecond laser while in a hydrated state.

[0041] Embodiment 15. The method of Embodiment 14, wherein depolymerized material at the surface of the hydrogel material is removed from irradiated regions of the hydrogel material by diffusion into hydrated hydrogel material adjacent to the irradiated regions.

[0042] Embodiment 16. The method of any one of Embodiments 1-13, wherein the hydrogel material is irradiated with the laser pulses of light from the femtosecond laser hydrated while in a never-hydrated or dehydrated state.

[0043] Embodiment 17. The method of Embodiment 16, wherein depolymerized material at the surface of the hydrogel material is removed from irradiated regions of the hydrogel material by subsequently hydrating the hydrogel material and diffusion of the depolymerized material into hydrated hydrogel material adjacent to the irradiated regions.

[0044] The specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of embodiments of the invention. However, other embodiments of the invention may be directed to specific embodiments relating to each individual aspect, or specific combinations of these individual aspects.

[0045] The above description of example embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above.

[0046] Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Additionally, details of any specific embodiment may not always be present in variations of that embodiment or may be added to other embodiments. It should be noted that, unless otherwise explicitly noted or required by context, the word "or" is used in this disclosure in a non-exclusive sense.

[0047] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

[0048] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a method" includes a plurality of such methods and reference to "the device" includes reference to one or more devices and equivalents thereof known to those skilled in the art, and so forth. The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practice within the scope of the appended claims.

[0049] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes. None is admitted to be prior art.

Claims

Claims:

1. A method of forming surface features in a hydrogel material, comprising: providing a hydrogel material having at least one surface; irradiating the hydrogel material with laser pulses of light from a femtosecond laser, wherein the laser pulses are focused into a focal volume in the hydrogel material at the surface of the hydrogel material and are of sufficient energy such that an intensity of light within the focal volume will cause a nonlinear absorption of photons and result in depolymerization of the material within the focal volume, while the material just outside of the focal volume will be minimally affected by the laser light; and removing depolymerized material at the surface of the hydrogel material to form surface features in the hydrogel material.

2. The method of claim 1, further comprising controlling a laser power and scan rate for maintaining an energy profile in the hydrogel material within the focus volume above a nonlinear absorption threshold of the hydrogel material, and below a material damage breakdown threshold of the hydrogel material which would result in ablation or observable burning or carbonization of the hydrogel material.

3. The method of claim 1 or 2, wherein the laser is focused with an objective having a numerical aperture selected to provide a focal volume having a submicron dimension and forming submicron dimensioned surface features in the hydrogel material.

4. The method of claim 3, wherein the objective has a numerical aperture of greater than 1.0.

5. The method of claim 3, wherein the objective has a numerical aperture of about 1.3.

6. The method of any one of claims 1-5, wherein the surface features have a width of less than 1.0 micrometers.

7. The method of claim 6, wherein the surface features have a width of from about 100 to about 200 nanometers.

8. The method of any one of claims 1-7, further comprising re-irradiating the hydrogel material with additional laser pulses of light from a femtosecond laser, wherein the additional laser pulses are focused into a focal volume in the hydrogel material directly below focal volume at the surface of the hydrogel material to provide an extended combined focal volume relative to the surface, and removing depolymerized material from the extended focal volume to form surface features in the hydrogel material having an extended depth from the surface of the hydrogel material.

9. The method of any one of claims 1-8, wherein the surface features form a diffraction grating.

10. The method of any one of claims 1-8, wherein the surface features form a lens.

11. The method of any one of claims 1-8, wherein the surface features form a Fresnel lens.

12. The method of any one of claims 1-8, wherein the surface features form a reflector.

13. The method of any one of claims 1-8, wherein the surface features form a wavelength-dependent reflector.

14. The method of any one of claims 1-13, wherein the hydrogel material is irradiated with the laser pulses of light from the femtosecond laser while in a hydrated state.

15. The method of claim 14, wherein depolymerized material at the surface of the hydrogel material is removed from irradiated regions of the hydrogel material by diffusion into hydrated hydrogel material adjacent to the irradiated regions.

16. The method of any one of claims 1-13, wherein the hydrogel material is irradiated with the laser pulses of light from the femtosecond laser hydrated while in a never-hydrated or dehydrated state.

17. The method of claim 16, wherein depolymerized material at the surface of the hydrogel material is removed from irradiated regions of the hydrogel material by subsequently hydrating the hydrogel material and diffusion of the depolymerized material into hydrated hydrogel material adjacent to the irradiated regions.