Synthesis of Pigmented Parylene Coatings and Control of the Chromatism Based on Chemical Vapor Deposition Copolymerization

Coloring and identification procedures for medical devices are important to reduce the risks of defective medical devices or incorrect operations and implantations. The study herein reports a novel platform of color pigment‐modified Parylene coatings to fulfill the needs of medical coatings, providing a surface modification route to alter the important property of color for an underlying material and/or device from its original color. Modification with a naphthalimide derivative is employed for the Parylene precursor. The synthesis of the final color Parylene coating is performed based on a vapor‐phase deposition polymerization process, and the coating is conformally coated on a variety of materials regardless of the shape or dimension. Furthermore, control of the color to create a series of color‐changing Parylene coatings is enabled by vapor deposition copolymerization with a second Parylene derivative source, and predictable color tuning from a primary to a secondary and/or tertiary color is achievable in the experiments and shows accordance with color theory. The reported coating platform represents a colored coating tool and is biocompatible for biotechnological applications.


Introduction
With the development of biomedical technology/biomaterials, prospective biomaterials are being designed with functions that mimic natural biological activities. [1]In nature, color plays a vital role in conveying information, [2] for example, bright colors often represent warnings and toxicity, and red colors often represent danger. [3,4]Color identification is a fundamental element and is deeply influencing in daily life, ranging from inside out, from mood swings to decision-making and emergency alerts. [2,4]For instance, specific identification colors can speed up instinctive recognition and control activities, enhancing the communication/connection between users and devices and reducing the burden of medical operations when applied to medical devices. [5,6]n many cases, a purposeful coloring procedure during the manufacturing of medical devices is performed and is clinically used for early detection and identification by the naked eye [7] and to reduce the risks of defective/damaged medical devices or incorrect operations and implantations. [6]However, color is mostly presented by pigments and dyes, which are limited for various reasons, such as dispersibility, [8,9] durability, [8] stability, [10] desired color performance, [8] and the presence inorganic pigments containing heavy metals that are toxic to humans. [11]For structural color, the mechanism of color presentation is based on a diffraction strategy resulting from particle stacking; therefore, the surface morphology/architecture needs to be carefully constructed, thereby reducing the defects. [12]Currently, common biomedical coating materials, such as polyamide, [13] poly(methyl methacrylate), [14] polyurethane, [15] and silicone, [16] are fabricated and constructed on the surface based on an irritative solvent system, which causes negative effects on the environment.Additionally, due to the fabrication approaches, the formation of pinholes in the coating that yield hermetic seals on the surface of the medical device cannot be avoided. [14,17]n the present study, we report on a series of pigment-modified poly-p-xylylene coatings (commercially named Parylene, US military regulations MIL-I-46058C, IPC-CC-830 certification and nontoxic test certificates, SGS nontoxic test certification, UL94V-0 combustion test certification, and the United States Pharmacopoeia (USP) XXII, VI level of biocompatibility), and the accordant chromatism control of various colored Parylene coating products that is achievable based on vapor deposition copolymerization.The native properties of Parylene are acknowledged to be advantageous: i) no solvents, catalysts, initiators, or other additives are needed, and a high polymerization yield with no byproducts is achieved during the vapor-phase deposition polymerization process; [18] ii) the Parylene coatings are deposited at ≈20 °C or a lower temperature, [18,19] which avoids the possibility of heat damage for delicate and precision medical devices; iii) The vaporphase polymerization process results in a uniform and conformal coating film on substrates, irrespective of their material or geometry,20 with the exception of specific conditions such as selective deposition [21] ; and iv) a variety of modified functionalities can be installed on the backbone of poly-p-xylylene. [22]We therefore hypothesize the synthesis of a color pigment-modified Parylene coating through modification with a naphthalimide derivative [23] containing a chromophore/functional group based on a donoracceptor system, and the resultant modified Parylene can represent a color-functionalized coating platform for any of the mentioned materials and applications, providing new color identification specifications and functions.The proposed color Parylene coating technique with coating thickness in the range from tens to hundreds of nanometer is applicable rendering a layered configuration with existing thick coatings such as Parylene C, Parylene N, or Parylene HT, to achieved an industrial coating product.Additionally, control and modification of chromatic properties are achieved based on vapor-phase copolymerization with a second Parylene derivative source during the synthesis process to produce a state-of-the-art series of color-changing Parylene coatings.The copolymerization ratio exhibits a predictable relation with the resultant color-display property and performance, which is in accordance with color theory in forming primary, secondary, and/or tertiary colors.Furthermore, the biocompatibility and stability of the color-modified Parylene platform were examined, showing suppressed cytotoxicity and excellent biocompatibility, which is consistent with existing Parylene derivatives.The present study establishes a unique interface coating platform that provides an important color identification capability that fulfills the shortage in meeting the current needs in biotechnological applications.

Vapor Deposition and Polymerization of Pigment-Modified Parylene
To give a color-display property, naphthalimide derivatives were used to modify [2,2]paracyclophane.The detailed synthesis approach is shown in Figure S1, Supporting Information.In brief, pigment-modified Parylene was synthesized from the pigmented Parylene coating precursor 4-morpholine-1,8-naphthalimido-[2,2]paracyclophane (4), which resulted from modification of the commercial product [2,2]paracyclophane by grafting a wavelength-absorbing chromophore, that is, a derivative of 4-morpholine-1,8-naphthalimido (MPNA), based on donor-acceptor theory. [23]The combination of chemical and structure analysis, including 1 H nuclear magnetic resonance ( 1 H NMR), 13 C NMR, electrospray ionization mass spectrometry (ESI-MS), ultraviolet-visible (UV-vis) spectroscopy and Fourier transform infrared spectroscopy (FTIR), have verified the chemical structure and the chromatizing property.These data are included in Figure S2a-e, Supporting Information.As illustrated in Figure 1a, the preparation of pigment-modified Parylene coatings started by sublimating the above-synthesized precursor at 393 K (120 °C), and the vaporized precursors were then pyrolyzed into the intermediate radicals MPNA-p-quinodimethane and pquinodimethane at 873 K (600 °C).Finally, the highly reactive radicals polymerized upon deposition on a cooled substrate at 298 K (25 °C) with the formation of color pigment-modified Parylene coatings (5).During vapor deposition polymerization, the entire process was performed under a pressure of 0.67 mbar, and the vapor compositions of the system were monitored in real-time by a mass spectrometer.As shown in Figure 1b, the characteristic signals of 100 and 210 amu representative of the fragments of MPNA-p-quinodimethane and the signal of 104 amu representative of p-quinodimethane indicate the presence of the vaporized chromophore precursors in the processing system.To further confirm the chemical composition and structure of the resultant coating products and the chromophore functional group, X-ray photoelectron spectroscopy (XPS) was used to examine the coatings.The XPS results are shown in Figure 1d and they revealed the existence of key elements, including N, C, and O, in the survey spectrum, and the high-resolution C 1s spectrum deconvoluted peaks, comprised of C─C/H (285.0 eV), N─C═O (288.2 eV), C─C─N (286.3 eV), C─C─O (286.7 eV) and ─* (291.0 eV), are shown in Figure 1e.The corresponding ratios of the peaks were 74.13%, 7.12%, 11.95%, 6.8%, and 3.68%, which compared well with the expected theoretical values and confirmed the successful vapor deposition and synthesis of the proposed pigmentmodified Parylene.Additional data of the resultant modified coatings analyzed by Fourier transform infrared spectroscopy (FTIR) also unambiguously confirmed the formation of the coating, and the results are included in Figure S3, Supporting Information.The vapor deposition polymerization was performed based on a refined Gorham process, [24] and are similar to other functionalized Parylene systems. [25]The characterizations based on FTIR and XPS also confirmed no side products for the deposition polymerization nor on resultant coatings.The adhesion test of the coating was also tested with a multiblade scratch tester and a Scotch tape, [26] and the results were evaluated following the crosscut scale of ASTM D3359 [27] showing a 5B classification of adhesion strength.The tested data are also included in Figure S4, Supporting Information.
The important chromatizing performance was further examined.The UV-vis spectroscopy analysis in Figure 1c indicated that the coating exhibited a high level of UV-vis absorption in the wavelength range of 200-300 nm, effectively blocking light within this range.Moving to the right, the UV-vis absorbance peak in the visible domain was observed at 430 nm, and the absorbance band ended at a wavelength of ≈500 nm.As a result, light wavelengths corresponding to the cool color region of the visible spectrum were absorbed, leading to the perceived warm color of the coating. [28]Similarly, transparency also holds a significant factor in further applications.According to the UV-vis transmittance analysis presented in Figure 1c, the transmittance of the pigmented Parylene coatings significantly decreased at 430 nm, corresponding to the absorbance result.In more detail, the degree of decrease in transmittance was enhanced with increasing film thickness, showing that the film transparency was dependent on the thickness.However, the transmittance in the wavelength range of 570-700 nm, belonging to the warm color region, [28] was only slightly affected by thickness.

Stability and Cell Compatibility
The minimum requirements of stability and biocompatibility were also examined for the proposed color coatings.To verify the coating stability, selected solvents, including ethanol, ethyl acetate (EA) and toluene, were applied to the coating samples for 24 h, and the FTIR spectra were recorded before and after the solvent test for comparison.The FTIR results show comparable spectra for the solvents tested on the coatings with no significant wavenumber shifts for characteristic peaks and no reduction of peak intensity.The data are included in Figure S6, Supporting Information.For biocompatibility, a cell viability test was performed via acute toxicity studies based on a direct contact approach and an extract approach, [29] using 3T3 cell culture analysis.As revealed in Figure 2a, no significant differences in terms of cell numbers and cell shapes were observed in the fluorescence images of the samples on Day 1 and Day 3 among the sample groups of pigment-modified Parylene coatings and the control groups where the 3T3 cells were cultured on tissue-culture polystyrene (TCPS).Statistically, in Figure 2b, similar analytical results had no significant differences in the cell viability after 3 days of the cell culture tests, thereby unambiguously verifying the compatibility of the colored synthesized Parylene coatings.

Control of Chromatism
The rationale of the color coating technology was extended, creating a series of color gradient platforms based on the abovedescribed warm color, and this platform was enabled by a vapor deposition copolymerization process, as illustrated in Figure 3a.
During the process, we introduced a second precursor, dichloro-[2,2]paracyclophane (6) (forming colorless and transparent Parylene), [30] to the deposition system, and copolymerization occurred between the two precursors, forming a copolymer (7) that comprised both chemical and physical properties from the two precursor parties, [31]' that is, a synergistic effect from colorless/transparent compartment and a warm color compartment.
The important control was performed by determining the precursor ratio during the vapor deposition copolymerization, which was realized to be a dual-sourced vapor deposition system comprised of two independent precursor inlet installations connected to the same deposition chamber.Because the sublimation rates of the [2,2]paracyclophane precursors are temper-ature dependent [31] and controlling the sublimation temperature in each of the precursor inlets can produce mixed vapors of [2,2]paracyclophane precursors with a determined composition ratio, we hypothesized that the final copolymer composition ratio (colorless Parylene compartment/warm-colored Parylene) was produced accordingly.In the experiment, a combination of characterizations of the vaporized partial pressure and the composition analysis by XPS on selected precursor samples were compared and plotted in Figure 3b, and the results show a linear relation of the natural logarithm of pressure (P), that is, the pressure obtained based on the relation of the mass loss and system temperature derived by Langmuir and others, [32] and the inverse sublimation temperature (1/T), which could be described by the Clausius-Clapeyron equation, [33] as shown in the following equation: where P, R, ΔH sub , and T are the vapor pressure, universal gas constant, latent heat of sublimation and system temperature, respectively.Therefore, the inlet compositions could be well manipulated by this temperature-control system, thereby providing predictable and controllable initial conditions for the proposed color coating platform.
To demonstrate chromatism control of the coating system, under heating conditions of 317, 322, and 331 K for the colorless Parylene precursor, the resultant products of various colored Parylene coatings covered on SiO 2 transparent substrates were analyzed by XPS, as shown in Figure 3c.The element ratios of A, indicative of chlorine (Cl) from the colorless Parylene precursor, and B, indicative of nitrogen (N) from the pigmented Parylene precursor, were 3/1, 8/1, and 16/1 for the sublimation conditions of 317, 322, and 331 K for the colorless Parylene precursor, respectively.Furthermore, a linear relation existed between the sublimation temperature and the composition of the coatings, which implies a predictable and controllable colored coating system.The resultant optical images of color-changing Parylene coatings deposited on SiO 2 transparent substrates are shown in Figure 3d.From left to right, the proportions of elements, A/B, contained in each sample were as follows: 1/0, 16/1, 8/1, 3/1, and 0/1, corresponding to each sample in the optical images below.Through naked-eye observation, the color performance/chromatism was enhanced due to the increment of the N content from the pigmented Parylene precursor in the color-changing coating, resulting from operating conditions with a lower colorless Parylene coating sublimation temperature.For advanced and quantified analyses based on UV-vis spectroscopy, the optical performance was characterized via the UV-vis absorbance spectrum shown in Figure 3d.The absorbance spectra from top to bottom correspond to the order of the top images from left to right.For the coating with a 1/0 A/B ratio, the spectrum of the colorless Parylene coating, poly(2-chloro-para-xylylene), revealed a significant signal at 200 to 300 nm, and no absorbance signal was found in the region beyond 200 to 300 nm.As no visible light was absorbed, the coating remained colorless, relating to the left coating in the top image.In contrast, for the pure pigmented Parylene coating, 0/1 A/B, as previously mentioned, there was a significant characteristic peak at ≈430 nm.With an increasing proportion of B, the peaks at 430 nm resulting from the pigmented Parylene coatings were gradually intensified.As more cool light was absorbed, the color of the coatings gradually darkened from left to right.Additional analyses of the transmittance data for the produced coatings are also included in Figure S7, Supporting Information, where the transmittance at 430 nm decreased as B increased.The intensity of the UV-vis absorption peak at 430 nm (transmittance signal) had a positive (negative) correlation with the trend of the color chromatism and the proportional ratio of B from XPS.Moreover, the optical transmittance of each color-changing Parylene coating reached above 70% at 570 to 700 nm in the warm color region.

Control of the Hue of the Substrates
Aside from presenting the color nature of the synthesized coatings, the reported coating technology can also provide a mixing of primary and/or secondary color on a given substrate color space.For instance, color regulation is commonly applied in dental applications for mimicking natural teeth. [34]Various colorful substrates are used in medical devices, such as white tooth implants, red hip bone implants, green ureteral stents, blue condylar buttress plates, and colored contact lenses. [35]Finally, white, blue, red, and green substrates were used to demonstrate color manipulation with the color Parylene coating platform.Based on subtractive color theory, a secondary color results from the mixture of primary colors; for instance, a mixture of blue and yellow would be green, and a mixture of red and yellow will be orange.A tertiary color could be obtained by mixing primary and secondary colors, such as yellow-green resulting from the combination of yellow belonging to the primary colors and green belonging to the secondary colors. [36]Therefore, to verify the feasibility of chromatism/color blending based on this colored coating tool, pigmented Parylene coatings were deposited on various colored substrates.The optical images of the resultant products after vapor deposition/polymerization with an inlet composition of 100% pigmented Parylene precursor are displayed in Figure 4a.The resultant substrates presented colors of yellow, green, orange, and yellow-green, which correspond to the substrates with original colors of white, blue, red and green, respectively.We hypothesized that subtractive color theory can be applied via the proposed color coatings supported by a layer-by-layer approach due to the transparent and warm color properties of the pigment-modified Parylene coatings.As shown in Figure 4a, the proposed color coating platform enabled color hues, and chromatic gradients were established on each color substrate by the aforementioned color-gradient copolymers via deposition copolymerization and by the same mechanism of controlling the ratios of A content from the colorless Parylene precursors and B content from warm-colored Parylene precursors.In addition, a 3D color space method of the CIELAB color space model, [37] was exploited for the analysis of the color coatings on substrates.As illustrated in Figure 4b, the CIELAB color space is composed of three components/parameters, L, a and b, which individually represent different colors, including red (+a), yellow (+b), green (−a), and blue (−b), and lightness, including black (L = 0) and white (L = 100). [38]Furthermore, the color difference, ΔE*, used to measure the perceptibility between two images/objects, can be defined by the following equation: which is composed of ΔL*(L* sample −L* standard ), Δa*(a* sample −a * standard ), and Δb* (b* sample −b* standard ). [39]The larger the value of ΔE* is, the larger the difference in the object colors, and the higher the visual perceptibility with the naked human eye; [40] according to previous studies, ΔE* equal to/exceeding a value of 1 means that the color difference is visually perceptible. [39,41]o express the color more objectively, each sample of colorchanging Parylene coatings on various colored substrates was analyzed and plotted in the 3D CIELAB color space, as shown in Figure 4c.The four streamlines/groups represent the four color systems: white, blue, red, and green, and each color system contains five spots, which correspond to the samples in Figure 4a.The analyzed results show a similar shift direction in the coordinate system with increasing B content of the colored Parylene precursor.Additional quantitative data based on the chromaticity/color difference, ΔE*, were also measured based on the above equation in comparison to the original substrate; these data are included in Figure S8, Supporting Information.Briefly, the larger the ΔE* value is, the greater the chromaticity/color difference from the original substrate.The resultant analyses in Figure S8, Supporting Information, show that the ΔE* values became larger as the amounts of B from the pigmented Parylene precursor increased, corresponding to the results from nakedeye and the 3D CIELAB color space observations; moreover, the chromatic degrees on each different substrate had mostly similar differences under the same operating conditions, thereby expressing the superior capability for chromatism control of this color-functionalized coating platform.To focus on the impact of chromatism/color based on this colored coating tool by excluding the influence of light-dark contrast (L-axis), the resultant samples of color-changing Parylene coatings coated on the white substrate were quantified and plotted on the 2D chromatic coordinate space composed of the a-and b-axes based on the CIELAB color chart (L = 50), as shown in Figure 4d.The original whitecolored substrate was initially close to the center; however, the sample spot gradually shifted to higher b values, approaching the yellow region (higher chromatism), when the inlet amounts of the pigmented Parylene precursor gradually increased, which corresponded to expectations (the copolymerization condition)  (c) and (d) were created using on MATLAB packages. [43]d naked-eye observations.Furthermore, based on these coordinates, it was easier to observe that in addition to the b value, the a value would also be positively enlarged and drive the sample spot toward the red region with increasing color Parylene precursor content (B content) due to the polarity-enhancement consequence. [42]

Conclusions
For the Parylene coating family, historical records of environmentally friendly processing conditions, solvent-and moisturefree fabrication procedures for sensitive materials and devices, and, most importantly, agreed-upon biocompatibility have been shown, and these coatings have been market-approved in many biotechnological products.The present study introduces and synthesizes a series of colored Parylene coatings that were introduced into the family, providing a solution to the urgent need for biocompatible coatings for biomaterials and biomedical devices.Predictable control of the color among primary, secondary, and/or tertiary colors for the coated materials and devices from their original colors is also shown for the colored Parylene coatings.With the existing chemically functionalized Parylene materials already on the shelf and the feasibility of vapor deposition copolymerization with various combinations of Parylene precursors to produce controlled ratios of multifunctional Parylene copolymers that have been demonstrated, we foresee the possibility of a new chromatism modification capability for Parylene coatings and unlimited applications for prospective biomaterials and biomedical devices.

Experimental Section
Synthesis of Product (4), a Pigmented Parylene Derivative Precursor: First, for the synthesis of product (2), a mixed solution comprising sulfuric acid (4.4 mL, 76.8 mmol) and nitric acid (2.7 mL, 38.4 mmol) was slowly added dropwise to [2,2]paracyclophane (1) (4.0 g dissolved in 370 mL of dichloromethane, 19.2 mmol) over an hour in an ice bath.After 4 h, most of the organic solvent was first removed by a rotary concentrator and then extracted three times with 150 mL of ethyl acetate.During the final extraction, anhydrous magnesium sulfate was added to remove the residual water.Then, the mixture with the resultant product (2) could be collected after rotary evaporation.Subsequently, the desired product (2) (2.94 g) was obtained by column chromatography (eluent: n-hexane/ethyl acetate = 19/1) with a yield of 60%.Rf = 0.5 (with silica gel 60; n-hexane/ethyl acetate = 19/1); 1H-NMR (300 MHz, CDCl ).Finally, for the synthesis of product (4), the above product (3) (50 mg, 0.224 mmol), 4-chloro-1,8-naphthalic anhydride (65 mg, 0.279 mmol) and morpholine (0.03 mL, 0.336 mmol) were added to 0.25 mL of dimethyl sulfoxide and then synthesized by a microwave method in the instrument with a power of 150 W and a temperature of 150 °C.After reacting for 2 h, the mixture containing product (4) was filtered with water; simultaneously, the filter cake was soaked in a water solution during the removal process.After the process, the filter cake was dissolved in dichloromethane; then, anhydrous magnesium sulfate was subsequently added to remove the residual water.The mixture with the resultant desired product (4) could be obtained after rotary evaporation.Finally, the mixture with the resultant desired product (4) was purified by column chromatography (eluent: nhexane/ethyl acetate = 3/1) to obtain a yellow powder, that is, pigmented Parylene precursor (4) ( The characterization of infrared spectroscopy for the synthesized precursor was performed by dissolving precursor power with chloroform and then with a solvent evaporation procedure on Au-coated silicon waters.The infrared spectroscopy (Figure S2e, Supporting Information) was then recorded by using infrared reflection absorption spectroscopy (IRRAS) technique.
Vapor Deposition Polymerization and Copolymerization: Color pigmentmodified Parylene coatings (5) were fabricated by polymerization of pigmented Parylene precursor (4), a colored dimeric derivative.In the vaporphase deposition polymerization, the precursor of pigmented Parylene coatings was sublimated at a temperature of ≈393 K (120 °C), and the sublimating material was carried by argon into the pyrolysis region for transformation into radicals, quinodimethanes, at 873 K (600 °C).After the formation of radicals based on pyrolysis, polymerization occurred in the deposition chamber and formed color pigment-modified Parylene coatings on the template maintained at 298 K (25 °C).The thickness of pigmented Parylene was monitored via a QCM (quartz crystal microbalance) installed within the deposition chamber, and the thickness was reconfirmed by AFM (an example was shown in Figure S5, Supporting Information) after retrieving the samples from the deposition chamber.The combination of QCM and AFM was used as a standard in the study to estimate the thickness of the polymer coating.Approximately, a 150 nm pigmented Parylene coatings could be obtained in 30 min with 30 sccm of argon as the carrier gas.For the color-changing Parylene coatings (7) based on vapor deposition copolymerization, the sublimation ratio of the colorless Parylene precursor (6) and the pigmented Parylene precursor was controlled by the different sublimation temperatures.Under the fixed temperature of 393 K (120 °C) for the pigmented Parylene precursor, the temperatures of the colorless Parylene precursor were controlled at 317, 322, and 331 K (44, 49, and 58 °C), corresponding to 3/1, 8/1, and 16/1 for each group of modulated visually identifiable colored coatings, respectively.After sublimation, various radicals formed at 600 °C and copolymerized on the template, whose temperature was held at 298 K (25 °C), to produce various color-changing Parylene coatings from various inlet ratios of the colorless Parylene precursor/pigmented Parylene precursor.Statistical analysis was based on three independent batch of vapor deposition polymerization and experiments, and the error bar represents the mean value and the standard deviation (±SD).
Characterizations: From the vapor composition during vapor-phase deposition polymerization, masses from 45 to 400 amu were detected by a real-time mass spectrometer (RGA, Hiden Analytical, UK) operated at 10 −7 mbar with an electron ionization energy of 70 eV and an emission current of 20 μA.The mass spectra were established by Hiden Analytical software (MASsoft7 professional).The X-ray photoelectron spectroscopy (XPS) spectra were obtained by a theta probe X-ray photoelectron spectrometer (Thermal Scientific, UK) with an X-ray source of monochromatized Al K.For the XPS analysis, polymers were coated on a silicon wafer.The survey, containing the C1s, N1s, and Cl2p spectra, were collected with an X-ray power of 150 eV and a pass energy of 200 eV (for the survey spectra) or 20.0 eV (for the individual elemental spectra).Each elemental spectrum was fitted by Xpspeak41 software.A U-3010 UV-vis spectrometer (Hitachi, Japan) with a mercury and deuterium lamp was used to collect the absorbance and transmittance spectra of the coating on SiO 2 transparent substrates between 200 and 800 nm.Fourier transform infrared spectroscopy (FTIR) spectra were used to analyze the compositions of the materials.The Parylene coating was prepared onto Au-coated silicon wafers and a similar IRRAS technique was used for recording the infrared spectroscopy.The spectra over a scanning range of 600 to 4000 cm −1 were collected by a Spectrum 100 FTIR Spectrometer (PerkinElmer, USA) equipped with a liquid nitrogen-cooled mercury cadmium telluride (MCT) detector and Spectrum software (Version 6.3.5.0176).The parameters L, a and b of each colored coating sample were quantified by Adobe Photoshop CC 2017.The 2D and 3D CIELAB charts were graphed based on MATLAB packages via MATLAB R2022b. [43]The mechanical stability of modification layers was characterized by using a commercial multiblade scratch tester by Zehntner (Switzerland).The scratch tester was used to create multiple scratches on polymer-coated silicon substrates.Subsequently, a Scotch tape (3 m, USA) was adhered to the scratched samples, and then the tape was pulled steadily and rapidly with a direction of ≈60 degree angle to remove the tape.
Biocompatibility Test: Two methods, the direct contact method and the extract method, were used to confirm the cell survival situation on the newly developed coating.The color pigment-modified Parylene-coated SiO 2 transparent substrates, as tested substrates, were first cleaned with alcohol and distilled water.For the direct contact method, 3T3 fibroblasts directly contacted the tested substrates for the culture for the cytotoxicity tests.In contrast, for the extract method, 3T3 fibroblasts were cultured in medium that had been exposed to color pigment-modified Parylene coatings for 3 days.For the control group, 3T3 fibroblasts were cultured in tissue-culture polystyrene (TCPS) for further comparison. [44]ach group was incubated with 3T3 fibroblasts at a cell density of 105 cells cm −2 On Day 1 and Day 3, the live or dead cells in each group were characterized by a fluorescence-based LIVE/ DEAD kit (Thermo Fisher Scientific, USA) and observed by a fluorescence microscope (Leica Microsystems, Germany).Moreover, the cell viability of each group was confirmed by a commercial MTT assay kit (Sigma-Aldrich, USA).MTT signals were obtained by an ELX800 microplate reader (BioTek Instruments, USA) based on the absorbance wavelength of 570 nm, and the MTT signal percentage was determined using TCPS as a control group.

Figure 1 .
Figure 1.a) Polymerization mechanism of color pigment-modified Parylene coatings based on vapor-phase deposition polymerization.b) Real-time mass analysis of color pigment-modified Parylene coating formation during vapor-phase deposition polymerization.c) UV-vis absorbance spectrum of color pigment-modified Parylene coatings with a thickness of 150 nm and transmittance spectrum of color pigment-modified Parylene coatings with thicknesses of 30, 50, and 150 nm.d) Survey spectrum from XPS analysis of the color pigment-modified Parylene coatings based on vapor-phase deposition polymerization.e) C1s spectrum of the color pigment-modified Parylene coatings comprising various peaks from different bonds with different binding energies.The percentage of the peaks except for ─* applied to all the other kinds of experimental data.The ─* value was additionally calculated based on the overall experimental value.

Figure 2 .
Figure 2. Cytotoxicity tests based on the direct contact method and the extraction method on the pigment-modified Parylene coatings on Day 1 and Day 3. The results of a) recorded fluorescence images and b) statistical analysis were compared on the 3T3 cell culture on the coating samples and the tissue-culture polystyrene (TCPS) plates.

Figure 3 .
Figure 3. Color-changing Parylene coatings (7) obtained through vapor-phase deposition copolymerization: a) Mechanism of color-changing Parylene coatings based on vapor deposition copolymerization.b) Plot of the copolymerization conditions: sublimation temperature of the colorless Parylene precursor versus ln Pc. c) Plot of the element composition from copolymerization based on XPS analysis: sublimation temperature of the colorless Parylene precursor versus element ratio of the surface composition (A/B, A is representative of chlorine from the colorless Parylene precursor; B is representative of nitrogen from the pigmented Parylene precursor).d) Optical images of color-changing Parylene coatings fabricated under various copolymerization conditions on SiO 2 transparent substrates (top) with optical transmittance of over 70% at 570 to 700 nm, and UV-vis absorbance analysis of the coatings fabricated under various copolymerization conditions (bottom).