Implementation of the Seeded Growth Method in Fabricating 3D‐Printed Nanocomposite Contact Lenses for Selective Transmission

Gold nanoparticles (GNPs) are useful materials that may be used in a variety of applications such as colorblindness management, drug delivery, and bacteria reduction. When incorporated with optical lenses, GNPs cause an absorption dip in the transmission spectra of the lenses. Out of the aforementioned medical applications, colorblindness management is the most benefited from such spectra absorption as it can potentially block problematic wavelengths that patients suffer from and hence manage their colorblindness, where color vision deficiency (CVD), also known as colorblindness, is a congenital ocular disorder that has no current cure, and patients suffering from it rely on wearable aids that enhance their color perception by filtering out the certain wavelengths. Herein, customized gold nanocomposite contact lenses are fabricated via additive manufacturing to filter selective transmission wavelengths in the range of 540 and 560 nm. To allow selective filtering, seed‐mediated synthesis of GNPs through nine growth steps is utilized to vary the GNPs’ size and plasmonic filtering properties. Thereafter, three contact lenses are fabricated with different GNPs concentrations and particle sizes. In the results of the study, it is indicated that the fabricated lenses can block certain wavelengths selectively while acquiring properties similar to commercially available eyewear.


Introduction
The phenomenon of localized surface plasmon resonance (LSPR) has been discovered exclusively for nanoparticles (NPs). [1]A plasmon describes a kind of conducting electron oscillation caused by light interaction. [1]When the vibration occurs at the metal's outermost (surface) layer, this is often called surface plasmon (SP). [1]However, if the SP occurs on a particle with a diameter similar to the light wavelength, it is commonly referred to as localized surface plasmon (LSP). [1]An interesting consequence of LSP is that NPs have a transmittance minimum associated with the LSPR frequency, which corresponds to an absorbance peak that can be seen using UV-visible spectroscopy. [1]Out of the various uses of gold NPs (GNPs), this transmittance minimum is most beneficial in the case of incorporation in contact lenses to potentially selectively block certain wavelengths that are problematic to red-green colorblindness patients.
Color perception in the eye is achieved by the three types of photoreceptor cones in the retina, namely short-(S-), medium-(M-), and long-(L-) wavelength-sensitive cones. [2]The S, M, and L photoreceptor cones are primarily activated at 440, 540, and 560 nm, respectively. [2]Colorblindness or color vision deficiency (CVD) occurs when any of the three cones are absent or malfunctioning. [3]CVD is a disorder that affects nearly 200 million people around the world. [4]he disability of people observing certain colors considerably affects their private and professional lives. [4]The difficulties sufferers endure daily range from driving and observing traffic lights to cooking and reading colored graphs. [5]CVDs can either be inherited or acquired from old age, trauma, or chronic illness. [3]he most prevalent form of CVD is anomalous trichromacy, in which one or more cones are not functioning as intended (Figure 1a). [3]Figure 1a illustrates the two main groups of anomalous trichromacy: a red-green deficiency and a blue-yellow deficiency.Red-green CVD is further divided into two categories: protanomaly and deuteranomaly, in which sufferers have malfunctioning red cones (L cones) and green cones (M cones), respectively. [3]Likewise, blue-yellow CVD, also known as tritanomaly, is where S cones are not functioning as intended.Another group of CVDs is monochromacy (achromatopsia), in which all cones are nonfunctional; hence, vision depends solely on the photoreceptor rods. [6]Monochromats do not perceive colors of any wavelength; they only see white and black. [3]The last group of CVDs is dichromacy, in which one of the cones is missing. [7]ichromacy is further divided into protanopia, deuteranopia, and tritanopia. [7]Where protanopia, deuteranopia, and tritanopia patients are missing the red (L cone), green (M cone), and blue (S cone) cone, respectively, [7] further, 95% of patients suffer from red-green CVD. [8]Figure 1b demonstrates the red-green crossover region, which occurs at 520-580 nm, whereas the intersection is prominent at 560 nm. [8]The crossover mentioned earlier occurs because the red and green cones are activated at similar percentages at the same wavelengths, making the individual unable to distinguish between the shades of the two colors. [8]ebeck suggested that filtering out light wavelengths at the crossover range will help individuals differentiate between the two colors.Yet, it will not allow them to observe the actual red or green colors. [9]horough research on the management of CVD in nonhuman primates using gene therapy has yielded encouraging findings in recent years; however, the latter has yet to be tested on human beings. [10,11]As a result, most CVD patients depend on wearables to help them cope with the challenges they face on a daily basis.A tinted glass/lens is the most prevalent type of wearable that CVD patients use. [7,9]Furthermore, CVD corrective glasses have been demonstrated to improve color contrast and perception in patients during experiments conducted by EnChroma, the leading firm in producing tinted glasses, and other companies.Based on the patient's CVD, these glasses are designed to filter out a spectrum of problematic wavelengths where an overlap of cone sensitivities occurs.In terms of lenses, organizations such as Chromagen have created red contact lenses to help CVD patients; however, their success has been reported to vary among subjects. [7,12]Organic Atto dyes have lately been utilized to alter the color of contact lenses, but their high cost limits their practicality.Smart glasses created by firms such as Google have also recently been included in CVD research. [13,14]Researchers employed image processing techniques to filter and recolor the patients' vision dynamically.The disadvantage of such glasses is their bulky size, making them unsuitable for daily usage.More recently, Salih et al. have utilized GNPs and silver NPs in contact lenses to enhance color distinction in patients with red-green and blue-yellow CVD, respectively. [8,15]imilarly, Roostaei et al. utilized plasmonic NPs, particularly GNPs, to enable patients with red-green CVD to enhance their perception of certain colors and view colors more vividly. [16,17]esearchers have lately utilized the LSPR of GNPs to filter out red-green CVD's problematic wavelengths.The peak of the LSPR, its intensity, and its full width at half maximum (FWHM) rely primarily on the morphology of the NPs, their composition, and the medium in which they exist. [18,19]In Salih's work, commercial GNPs were utilized, which were relatively polydispersed due to their synthesis technique.The polydispersity in the largely sized GNPs (>40 nm) utilized by Salih et al. diminished their optical absorption efficacy due to significant increases in their FWHM, causing unproblematic wavelengths to be filtered out.Hence, nanocomposite contact lenses based on the aforementioned GNPs cannot effectively aid patients with M-L crossovers beyond 550 nm.
The issues previously mentioned are adequately addressed through the seeded growth method. [20]This method involves inhibiting new particles' nucleation and growing the already existing seeds in multiple steps. [21]This enables the control of spherical GNPs' diameter and hence the control over the LSPR position with minimum FWHM. [21]The seeded growth method involves a seeding stage at the beginning of the synthesis process.This stage is done once, and afterward, the growth steps are repeated until the desired GNP diameter is obtained. [20]ccording to Mie's theory, increasing the GNP diameter at a particular solution medium redshifts (increases) the LSPR position.Moreover, the desired optical characteristics from the gold nanocomposite lenses are as follows: 1) 560 nm LSPR, for it is the most prominent crossover wavelength, and 2) 60 nm FWHM, analogous to commercial CVD glasses and lenses. [8][24][25] These processes include spin casting and molding, as they provide simplicity and cost efficiency, but they require post-processing because of an issue related to adherence. [24,26]Additive manufacturing is known to be used in the biomedical field, owing to its relatively high accuracy, low machine cost, and suitability for rapid prototyping/manufacturing. [27,28] Several additive manufacturing processes have been used for biomedical purposes, yet for contact lenses, vat photopolymerization processes that are laser based are the most promising, as they use thermosetting polymers and are suitable for printing nanocomposites. [29,30]These processes include stereolithography (SLA), digital light processing (DLP), and liquid crystal display (LCD) vat photopolymerization. [29,30] In addition to the fact that these three processes use thermosets, they are fast and cost efficient, making them suitable for experimental purposes on optical devices. [30]n this work, gold nanocomposite contact lenses are fabricated utilizing a seed-mediated synthesis of GNPs and 3D printing of customized contact lenses.
Here, GNPs were integrated into the 3D-printed contact lenses to filter out specific wavelengths through selective transmittance, for example, the wavelengths that cause CVD patients to suffer in distinguishing between specific colors.The transmission electron microscope (TEM) and scanning electron microscope (SEM) were utilized to study morphology and the distribution of GNPs, respectively.While UV/vis spectrophotometer was used to obtain the optical transmission of the GNPs.Also, the hydration contact angle and water content of the fabricated contact lenses were studied.In this study, gold (III) chloride hydrate and sodium citrate dihydrate will be used to synthesize the GNPs, while 2-hydroxyethyl methacrylate (HEMA), polyethylene (glycol) diacrylate (PEGDA), and diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide (TPO) will be used to fabricate the resin.

Results/Discussion
The process of synthesizing GNPs using the seeded growth method is summarized in Figure 2a, where G0, G1, and G2 are the seeds, stage one, and stage two solutions, respectively. [20]he GNPs solutions obtained from the seeded growth method at each stage are shown in Figure 2b, whereas their optical absorption and transmission spectra are shown in Figure 2c,f.The GNP solution of the first stage of seeded growth (G1) shows an absorption peak at about 523 nm, which is far from the targeted wavelength.Evidently, the position of LSPR redshifts with stage incrementation until it reaches 547 nm for G9.
The phenomenon of LSPR shift can be explained by using the Mie's theory, where the increase in diameter of the GNPs in the same medium increases the LSPR.The rate of increase of the LSPR position starts slowly, where there is only a 1.96% rise from G1 to G6, yet beyond the sixth growth step, a 3.11% increase can be noticed.The LSPR for the ninth growth step was at 547 nm for G9, indicating that the range of LSPR position shift was %25 nm (Figure 2d).The increase in the LSPR is consistent with the work of Bastus et al.In their study, they performed fourteen growth stages.Similarly, the rate of increase of the LSPR position starts slowly, where there is only a 2.41% rise from G1 to G5, yet beyond the fifth growth step, a significantly higher rate of increase of the LSPR position is observed. [20]he transmission spectra of all the GNP solutions were recorded and are shown in Figure 2e.It is noticed that the transmission dip can hardly be identified due to the low transmission of the solutions.However, as there is a log relationship between absorption and transmission, it can be deduced that the dips in the transmission curves will be at the same position as the absorption peaks.Moreover, Figure 2f shows how the FWHM of the solutions is altered with each stage.This is vital as the FWHM determines the filtering selectivity of the contact lens (i.e., lower FWHM indicates better selectivity).The FWHM decreased initially after the first growth step but was generally constant over the following six growth steps, indicating uniform GNPs' growth.Overall, the FWHM's range of change was less than 10 nm, and the differences between the first and last growth steps were less than 2 nm, which shows that the bandwidth of the transmission was not significantly altered because of the seeding process.The process was halted at G9 to avoid overly increased FWHM values.
The recommended commercial GNPs from Sigma Aldrich used in a study indicated LSPRs of 522 and 528 nm. [8]ompared to the GNPs fabricated using the seeded growth method in this study, the fabricated GNPs reached a significantly higher LSPR of 549 nm, which is considerably closer to the intended LSPR of 560 nm.This indicates that using the seeded growth method is highly efficient and effective in this case of altering the transmission of contact lenses selectively.
The GNPs distribution was determined using TEM. Figure 3 illustrates the results of the TEM that was performed on G1, G3, G5, G7, and G9 solutions.With increasing growth stage (Figure 3a(i)-e(i)), the NPs are observed to be well dispersed.Also, it is observed that no aggregation occurred in the solutions during the growth stages and NP synthesis.Also, when observing the zoomed view (50 nm), with increasing growth stages, the NPs merged, forming larger-sized NPs.This formation of larger NPs confirms that the seeded growth method's use in synthesizing GNPs was successful as the NPs' diameter increased instead of having second nucleation and forming new NPs.Also, the mean diameters and the standard deviations of the GNPs of each solution are illustrated in Figure 3a(ii)-e(ii).Where the mean diameter increased by 10.9, 15.2, 12.3, and 19.5 nm when going gradually through all the solutions G1, G3, G5, G7, and G9, this behavior of the mean diameter shows no specific pattern, as sometimes the diameter increase is relatively high between two consequent stages.At the same time, it decreases between the other two consequent stages.The standard deviation for all solutions remained within the 2.37-3.50nm range.This range is about 4.4-12% of the mean diameters.Since these percentages are low, this is an indicator that the NPs in each solution are uniform in size.These are near the findings of a similar study, [20] where the results they obtained indicated that the mean diameter increased by 13.5, 11.1, 22.6, and 15.3 nm when going gradually through all the solutions G1, G3, G5, G7, and G9. [20]Again, the same mean diameter behavior is observed.The standard deviation for the solutions from G1 to G9 remained within the range of 1-5.4 nm. [20]This range is about 5.2-11.9% of the mean diameters, which is also consistent with the obtained percentages.
To fabricate the lenses, a 3D model was first built, as shown in Figure 4a.The model was extracted to the Kudo3D Print Job software to orient the lenses vertically with supports, as shown in Figure 4b. Figure 4c shows one of the fabricated contact lenses being placed on an artificial eye as a demonstration of the lens usage.
Three of the fabricated lenses were doped in GNP solutions of growth stage stages five (G5), seven (G7), and nine (G9).The lenses were doped for different periods ranging from 30 min to 2 h.This is to observe and analyze the alternation that will occur in different characteristics.The resulting optical properties, including transmission, light blockage, and LSPR position, are illustrated in Figure 4.
Figure 4d illustrates the transmission of the lens doped in the G5 solution with time.The overall transmission decreases with an increase relative to the transparent case.Also, the LSPR position is observed to remain constant.Moreover, a picture of the lens doped in the G5 solution for 2 h is presented in Figure 4d.That is to show the final shape and color of the fabricated contact lens after the doping process is complete.Similarly, for lenses doped in G7 and G9 solutions (Figure 4e,f ), the overall transmission of the lenses decreased with time, the LSPR position remained constant for each one of them, and pictures of the final contact lenses post-doping are presented.It should be noted that the FWHM of all three doped lenses is initially wide and gets narrower with increasing doping time.This indicates that the NPs in the contact lenses are becoming monodispersed, which means they have uniform sizes and shapes.
The light blockage at LSPR was variant based on the doping period for all three lenses (Figure 4g).The lens doped in the G5 solution had a light blockage of 6%, 32%, 41%, and 48% at the LSPR with increasing time of doping, while the lens doped with G7 NP solution had a light blockage of around 10%, 26%, 38%, and 46% at the LSPR with increasing time of doping.Similarly, the lens doped in the G9 solution had a light blockage of 10%, 20%, 28%, and 37% at the LSPR with increasing time of doping.This means that the blockage of the transmitted light at LSPR lenses doped in G5, G7, and G9 varied by 42%, 36%, and 27% after 2 h of doping, respectively.It is important to note that the transmission blockage is measured while taking each transparent lens as a reference.
Moreover, the LSPR position of the lenses was invariant as a result of doping time; the lenses doped in solutions G5, G7, and G9 had an LSPR position of 539, 552, and 563 nm, respectively.For all the doped lenses, the FWHM increased with doping time.The FWHM reached 61 nm with the 2 h doped contact lens in the G9 solution.This FWHM is very close to the desired 60 nm FHWM.Reaching such FWHM indicates that the seeded growth method was successful in synthesizing NPs that are well dispersed and evenly distributed on the surface of the lens, with no evident aggregation.
Surface SEM images of the 3D-printed lenses doped with G5, G7, and G9 solutions are shown in Figure 5.The pictures in Figure 5 show the NPs at the surface of the lenses and not in a cross section.The surface of the lens doped in G5, as shown in Figure 5a, has big clusters of GNPs, unlike the other lenses doped with G7 and G9 solutions, shown in Figure 5b,c.The clusters forming at the surface of the G5 lens could be attributed to the utilization of smaller-sized NPs yielding low surface energy. [31]Figure 5 shows that the diameters of the GNPs at the surface of the G5, G7, and G9 lenses were 45.2, 61.3, and 72.7 nm, respectively.These diameters fall in the standard deviation of the GNPs sizes that were shown in the TEM micrographs in Figure 3.In addition, the GNPs also retained their intrinsic spherical morphology.Thus, excess it can be concluded that there were no signs of aggregation happening at the surface of all the lenses.
Unlike their distribution with the solution (Figure 3), the GNPs' distribution within the lenses was nonuniform due to the random introduction of GNPs at the surface of the lenses.Although the lens doped in G5 had a cluster of GNPs at its surface, it did not have any effect on the FWHM of the transmission dip (Figure 4), as it had similar FWHM to G7 and G9 lenses.
Furthermore, the sessile drop method was used to measure the static contact angle and assess the surface wettability of the 3D-printed lenses.Figure 6a-d shows the contact angle measurements of non-doped, 1 h doped, and 2 h doped lenses.The trend was analogous for all three gold nanocomposite lenses with varying GNPs sizes: the increase in doping time enhanced the surface wettability of the contact lenses; yet initial doping of the lenses caused the most prominent reduction in contact angle (Figure 6d).Furthermore, size differences among the utilized GNP solutions had minimal effect on the contact angle of the lens, as the range of variance for the 2 h doped lenses was less than 2°.The obtained contact angle values herein fall within the range of commercial contact lenses. [32]The decrease of contact angle with the addition of NPs is expected as the NPs increase the hydrophilicity of the surface. [33]The latter could also be due to the increase of surface roughness with the introduction of GNPs at the surface.Moreover, Figure 6e illustrates the transient water uptake by the doped lenses.The water content increased when the transparent lenses were doped.However, this increase did not have a specific trend, as the 2 h doped lenses had less water content than that of 1 h doped lenses, where the water content of the non-doped, 1 h doped, and 2 h doped lenses stabilized at about 18%, 33.62%, and 25.71%, respectively.The highest water content was achieved by the 1 h doped lens.The water content values of the fabricated lenses fall within the range of commercial contact lenses. [34]n addition, tensile tests were used to deduce tensile strength, modulus of elasticity, and elongation of dry and wet hydrogel samples (Figure 6f ).The wet samples were kept in water for 24 h prior to testing, allowing them to swell and increase their length slightly.Wet samples were used to simulate the performance of the resin under realistic scenarios of the actual conditions in that the lens will operate where lenses are usually exposed to moisture and other fluids while being used, while the usage of dry samples will provide the performance of uninfluenced resin, allowing a comparison between both types of samples.Stress-strain curves were extracted from the obtained load-displacement data.The dry samples' tensile strength, modulus of elasticity, and elongation were 14.299, 0.211 MPa, and 28.293%, respectively, as for the wet samples were 4.047, 0.415 MPa, and 20.461%, respectively.The decrease in the strength could be because the introduction of water into the resin weakens the chemical bonds between the molecules of the resin.The increase in the tensile modulus could be because of hydrogen bonds (from water exposure) being filled up between the polymer chains in the resin.Also, the decrease in the elongation could be due to a disruption of the resin polymers, which caused the resin to become brittle.A summary of the results is presented in Figure 6g.It should be noted that the mechanical properties were similar to what was found in the literature, which validates the obtained results. [35]urthermore, the effectiveness of the doped gold nanocomposite contact lenses was evaluated through two approaches: 1) assessing their optical properties relative to the problematic wavelengths of red-green CVD patients and 2) comparing their transmission spectra to those of commercial colorblind products.The aforementioned comparison is crucial as it assesses the rate of success that the fabricated contact lens achieves in filtering out a spectrum of problematic wavelengths selectively.For such comparison, lenses doped in ideal NP solutions were used, that is, G5, G7, and G9.As shown in Figure 7a, the spectra of redgreen CVD patients have been plotted along with the spectra of the doped lenses to evaluate their efficacies.At the intersection of the M-L cones (circled in purple), both photoreceptor cone cells have the closest activation percentages; hence, typical red-green CVD wearable aids should target to filter out this overlap, found to be at around 560 nm.The dip of G5-, G7-, and G9-doped lenses occurred at 539, 552, and 563 nm, respectively.The percentages of transmitted light through the lenses were generally more than 60% prior to 500 nm and after 600 nm.Blocked percentages at the dip could evidently vary based on the doping time without compromising the FWHM, as is shown in Figure 4. Therefore, the contact lens doped with G9 NP solution was the closest in terms of blocking light at the crossover between M-L cones.The second evaluation of the doped lenses was done by comparing their transmission spectra to those of commercial CVD wearable aids like EnChroma and VINO glasses, in addition to Atto 565-dyed lenses. [36]The lenses of EnChroma glasses, commercial CVD wearables, are known to be made of Trivex material which is stronger and lighter than broadly used materials of glasses. [7]A multi-notch filter is utilized in such glasses to block/filter the problematic wavelengths where red and green cones overlap.EnChroma uses Seebeck's color-filtering concept in its tinting process.The tinting of glasses is done by integrating certain dyes into the lenses of the glasses.The dye is diffused into the lens of the glasses at a temperature of less than 60 °C or less than the temperature at which the solvent that contains the dye boils.The lenses are forced to swell by the solvent and hence the dye diffuses into the material.Finally, the lenses deswell and gain their original shapes while the dye remains inside the lens material. [7]The Atto 565-dyed lens operates using a similar principle which is filtering/blocking problematic wavelengths (where red and green cones overlap).The dye was integrated into the contact lenses using two methods and they are dipping the lens in dye solution for a specific interval of time so that the Atto 565 dye diffuses into the lens and the drop method, which is basically casting one drop of the Atto 565 dye on the surface of the lens.They tried using different concentrations of the Atto 565 dye and studied the resulting effect. [36]EnChroma, VINO, and Atto-dyed lens have transmission dips at 595, 527-585, and 565 nm, respectively.The dip of lens G5 (539 nm) is far from the dips of the EnChroma and Atto-dyed lens.Moreover, the dip of lens G7 (552 nm) was also far from the dip of EnChroma but with a difference of 13 nm from Atto-dyed len's dip.Moreover, the dip of lens G9 (563 nm) was far from the dip of EnChroma but very near to the dip of the Atto-dyed lens with a difference of 2 nm.The three doped lenses filtered light around the same wavelengths blocked by VINO glasses.Hence, based on the commercial evaluation, the lenses doped with G7 and G9 solutions are the most adequate for utilization.The FWHM of the Attodyed lens is analogous to that of lenses G7 and G9.Since lenses G7 and G9 had very similar dips to the Atto-dyed lens (<13 nm difference) and FWHM (<13 nm difference), they can potentially be deployed as selective transmittance optical wearable aids.Salih et al. used commercial NPs and contact lenses, and the recommended final lenses had an LSPR of 540 and 550 nm, which is at a difference of 25 nm from the LSPR of Atto-dyed lens. [8]lso, the FWHM with about 20 nm difference from that of Atto-dyed lens. [8]When comparing the recommended Atto-dyed lens to the ones in this study, the lenses in this study have significantly closer LSPR and FWHM to the Atto-dyed lens. [8]This indicates that the seeded growth method and the 3D printing of contact lenses significantly impacted the optical properties of the fabricated lenses, where they successfully produced contact lenses that are more reliable and efficient in terms of altering the transmittance selectively.In addition, unlike the seeded growth method, the LSPR of NPs used in such similar studies cannot be altered significantly and is restricted into specific changes.

Conclusion
In this work, contact lenses that are 3D printed for selective transmission alteration were successfully fabricated.The desired NPs of different sizes and LSPR were synthesized, the resin and the printing process were optimized, and the 3D-printed contact lenses were fabricated using the Bean 3D printer.For each of the synthesized NPs, their transmission spectrum and size (diameter) were measured.The effect of adding GNPs concentration was studied using the transmission spectrum of each stage solution.It was found that as the GNPs increase, the LSPR shifts toward the desired wavelength (about 560 nm).The FWHM decreases to a certain limit and then starts increasing again with increasing the concentration.Three out of the nine NP solutions (stages five [G5], seven [G7], and nine [G9]) were chosen to be used for doping the 3D fabricated contact lenses.The results of the study showed that the fabricated lenses doped in solutions G5, G7, and G9 have an LSPR of 539, 552, and 563 nm, respectively.The LSPR of lens G7 and lens G9 are very close to the targeted wavelength (560 nm).
Moreover, the effectiveness of lenses G5, G7, and G9 as a potential wearable aid for CVD patients was studied.The study results showed that the transmission spectra of lenses G7 and G9 are analogous in terms of wavelength blockage and transmission bandwidth to those of widely used commercial CVD wearable aids.Furthermore, the mechanical material, optical, water content, and wettability properties of the fabricated nanocomposites were obtained and studied.The results of the study showed that their properties are also comparable to those of commercially used contact lenses.Hence, it was concluded that the fabricated contact lenses having selective transmission could potentially be utilized commercially as a potential red-green CVD managing wearable aids.Also, since the size and LSPR of the NPs can be altered selectively using the seeded growth method; then this work can be used with some modifications to fabricate a potential wearable aid for other CVDs.
Finally, the synthesis approach of the GNPs and the 3D fabrication of contact lenses showed a successful selective alteration in the transmission and promising results in being utilized by different individuals commercially.The GNPs in the fabricated lenses can be functionalized for glucose and protein sensing. [37]he utilization of 3D printing technology will enable the production of CVD management wearables at a low cost and in a short time.Also, using 3D printing instead of traditional commercial lenses has benefits, such as the ability of optical diagnostics using integrated optical sensors and making customized optic devices. [37]

Experimental Section
Gold NPs Fabrication: The seeded growth method was utilized to synthesize the GNPs. [20]The process is as follows: a) sodium citrate dihydrate (2.2 mM) was placed in deionized (DI) water (150 mL) to form a solution; b) the solution was stirred and heated until boiling; c) gold (III) chloride hydrate (1 mL of 25 mM) was injected into the solution; and d) the solution was stirred for 10 min, and a soft pink color was observed.Second, the growth steps: a) the seeds solution was cooled down to 90 °C; b) gold (III) chloride hydrate (1 mL of 25 mM) was injected into the solution; c) the solution was stirred for 15 min; d) gold (III) chloride hydrate (1 mL of 25 mM) was injected into the solution; e) the solution was stirred for 15 min; f ) 55 mL of the solution was extracted; g) sodium citrate dihydrate (2 mL of 60 mM) and DI water (53 mL) were added to the remaining solution; and h) for further growth steps, growth steps (a) through (g) were repeated.
Resin Fabrication: The resin used in this study was fabricated using TPO, HEMA, and PEGDA.HEMA and PEGDA were thoroughly mixed with a 1:1 ratio, and then TPO (5 w v À1 %) was added to the mixture solution.The solution was mixed continuously until the added TPO was completely dissolved.This HEMA to PEGDA ratio and TPO percentage were chosen to provide the best balance of properties.
Additive Manufacturing: The 3D-printed lenses were printed using the Bean 3D printer by Kudo3D.A 3D model of the lens was created using Creo Parametric, a 3D modeling software.The utilized dimensions of the contact lens model were obtained from the literature.The 3D model was converted into a format that is readable by the printer, that is, stereolithography (STL) format.The model was then sliced and oriented, using the Kudo3D Print Job software.In addition, printing supports were added to the model.Optimization of the printing parameters was then carried out.The layer height and exposure time were set to 405 nm and 80 s, respectively.
Gold NPs and Nanocomposites Characterization: USB 4000 þ UV-vis spectrophotometer was used to obtain the NPs' and the nanocomposites' transmission spectra.The spectrophotometer could detect wavelengths in the range of 200-1100 nm.The size distribution and the morphology of the NPs were characterized using Tecnai TEM 200 kV.The TEM had a 0.24 nm resolution, and its voltage could vary from 20 to 200 kV.The NPs' distribution within the nanocomposite lens was examined using the field electron and ion (FEI) Nova NanoSEM 650.The electron beam resolution of the FEI Nova NanoSEM 650 was 0.8 nm.
Mechanical Characterization: The Zwick Roell Z005 universal testing machine was used to perform the tensile testing.The load cell capacity of the machine was 2.5 kN.The tests were done at temperature and crosshead speed of 24 °C and 50 mm min À1 , respectively.A total of four tests were done, where two wet samples and two dry samples were tested.The results of the two tests per sample were averaged and reported.The resulting loadÀdisplacement curves were used to obtain the stress-strain curves.The stress-strain curves were then used to determine the tensile strength, modulus of elasticity, and elongation.

Figure 1 .
Figure 1.Color vision deficiency (CVD) types, insight, and cone sensitivities.a) Types of CVDs.b) Cone sensitivities of normal human vision.c) Cone sensitivities of protanomaly deficiency.d) Cone sensitivities of deuteranomaly deficiency.e) Colored objects and how they are perceived normally and with different deficiencies.

Figure 2 .
Figure 2. Synthesis of gold nanoparticles (GNPs): a) seeded growth steps (seeding stage þ first growth stage).b) Nanoparticle (NP) solutions in cuvettes.c) Absorption spectra of the synthesized NPs.d) Localized surface plasmon resonance (LSPR) position with increasing stages.e) Transmission spectra of the synthesized NPs.f ) Full width at half maximum (FWHM) with increasing stages.

Figure 3 .
Figure 3. NP solutions transmission electron microscope (TEM) results: a) size of G1 NPs.b) Size of G3 NPs.c) Size of G5 NPs.d) Size of G7 NPs.e) Size of G9 NPs.i) The size of the NPs with zoomed views from left to right; ii) the standard deviation of the NPs.

Figure 4 .
Figure 4. Model and orientation of the lenses: a) 3D model of the lens; b) vertical orientation of the lenses with supports; and c) fabricated lens placed on an artificial eye.Doping of fabricated contact lenses G5, G7, and G9 from left to right: d) transmission spectrum of lens G5; e) transmission spectrum of lens G7; and f ) transmission spectrum of lens G9. g) Fabricated doped lens transmission blockage.h) LSPR position with increasing stages.i) FWHM with increasing stages.

Figure 5 .
Figure 5. Scanning electron microscope (SEM) results with increasing focus from left to right: a) G5 NPs solution distribution; b) G7 NP solution distribution; and c) G9 NPs solution distribution.

Figure 6 .
Figure 6.Contact angle of the fabricated lenses and material mechanical characterization: a) contact angles of lenses G5, G7, and G9 prior to the doping process.b) Contact angles of lenses G5, G7, and G9 after 1 h and c) 2 h of doping.d) Average contact angle with increasing time.e) Water content with increasing time.f ) Mechanical characterization setup (tensile test) and dog bone fracture.g) Summary of the mechanical characterization results.

Figure 7 .
Figure 7. Evaluating the performance of the fabricated lenses by comparing the transmission spectra of lenses G5, G7, and G9 to a) the spectral sensitivity of photoreceptor cones in protans and deutans.b) The spectra of EnChroma, VINO, and the Atto 565 lens.