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Article

Microstructured Coatings and Surface Functionalization of Poly(caprolactone-co-lactide) Using Gas-Permeable Mold

by
Mano Ando
1,
Naoto Sugino
2,
Yoshiyuki Yokoyama
3,
Nur Aliana Hidayah Mohamed
4 and
Satoshi Takei
1,*
1
Department of Pharmaceutical Engineering, Toyama Prefectural University, Imizu 939-0398, Toyama, Japan
2
Futuristic Technology Department, Sanko Gosei, Nanto 939-1852, Toyama, Japan
3
Toyama Industrial Technology Research and Development Center, Takaoka 933-0981, Toyama, Japan
4
Faculty of Dentistry, Universiti Teknologi MARA, Sungai Buloh Campus, Jalan Hospital, Sungai Buloh 47000, Selangor, Malaysia
*
Author to whom correspondence should be addressed.
Coatings 2026, 16(1), 10; https://doi.org/10.3390/coatings16010010
Submission received: 27 November 2025 / Revised: 12 December 2025 / Accepted: 18 December 2025 / Published: 20 December 2025
(This article belongs to the Section Functional Polymer Coatings and Films)
Browse Figures
Versions Notes

Abstract

Low-melting bioabsorbable polymers, such as poly(caprolactone-co-lactide) (PCLA), hold significant promise for biomedical applications. However, achieving high-precision micro- and nanotopographical functionalization remains a formidable challenge due to the material’s susceptibility to thermal deformation during conventional thermal molding processes. In this study, functional microstructured PCLA coatings were engineered via low-temperature nanoimprint lithography utilizing a TiO2–SiO2 gas-permeable mold. These molds were synthesized via a sol–gel method utilizing titanium dioxide and silicon precursors. The gas-permeable nature of the mold facilitated the efficient evacuation of trapped air and volatiles during the imprinting process, enabling the high-fidelity replication of microstructures (1.3 μm height, 3 μm pitch) and nanostructured PCLA coatings featuring linewidths as narrow as 600 nm. The resultant microstructured PCLA coatings demonstrated modulated surface wettability, evidenced by an increase in water contact angles from 70.1° to 91.4°, and exhibited enhanced FD4 elution kinetics. These results confirm morphology-driven functionalities, specifically hydrophobicity and controlled release capabilities. Collectively, these findings underscore the efficacy of this microfabrication approach for polycaprolactone-based materials and highlight its potential to catalyze the development of high-value-added biomaterials for advanced medical and life science applications. This study establishes a foundational framework for the practical deployment of next-generation bioabsorbable materials and is anticipated to drive innovation in precision medical manufacturing.

1. Introduction

Polycaprolactone (PCL), an aliphatic polyester, has attracted considerable interest in biomedical research owing to its exceptional biodegradability and biocompatibility [1,2,3,4,5,6]. Distinguished by a relatively slow degradation rate compared to other biodegradable polymers, PCL possesses superior fabrication versatility, leading to its widespread utilization in functional coatings and biomedical devices [7,8,9,10]. Furthermore, PCL has been increasingly adopted as a scaffold material for cell culture, vascular grafts, and osseous tissue regeneration [2,11,12,13,14,15]. Its mechanical strength, elasticity, and degradation kinetics can be precisely modulated through copolymerization or blending strategies [16,17,18,19], facilitating application-specific customization. Consequently, PCL is poised to play a versatile role across a broad spectrum of medical interventions.
Poly(caprolactone-co-lactide) (PCLA), a copolymer synthesized from caprolactone and lactide monomers, has also garnered significant attention due to its enhanced mechanical integrity and biodegradability [20,21]. Upon degradation, PCLA yields non-toxic metabolites, thereby mitigating adverse physiological responses and environmental burden. These attributes position PCLA as a promising candidate not only for implantable devices but also for functional coatings where controlled surface properties, such as wettability and drug release profiles, are requisite.
Despite these advantageous physicochemical properties, the translational utility of PCL and PCLA is constrained by technical challenges, most notably their relatively low melting points. While PCLA exhibits distinct thermal transitions compared to PCL, both materials possess low thermal resistance relative to conventional thermoplastics [22,23]. Although this thermal characteristic ensures mechanical compliance under physiological and ambient conditions, it simultaneously predisposes microcoating structures to deformation at elevated temperatures [24].
In light of these constraints, extant research on PCL and PCLA microfabrication has predominantly employed low-temperature techniques, such as laser processing and photolithography [25,26,27,28]. Conversely, standard high-throughput microfabrication methods, such as hot embossing, typically necessitate high-temperature processing to achieve high-fidelity patterning [29,30]. For heat-sensitive materials like PCL and PCLA, such conditions precipitate excessive softening, loss of structural integrity, and diminished pattern resolution. Consequently, the fabrication of precise microstructures using conventional thermal processes remains a significant engineering hurdle.
To date, there is a paucity of literature regarding high-precision microfabrication technologies for PCLA, particularly within the domain of nanoimprint lithography. The development of a process capable of precise pattern formation while mitigating the risk of thermal deformation represents a critical unmet need. Furthermore, comprehensive investigations into the surface modification of PCLA—specifically those aimed at augmenting functional properties such as hydrophobicity and solubility—remain scarce. The novelty of this study lies in the implementation of a low-temperature nanoimprint process utilizing TiO2–SiO2 gas-permeable molds, which facilitates the high-resolution processing of PCLA coatings. This approach enables high-fidelity patterning and the induction of novel surface functionalities on PCLA substrates.
The objective of the present study is to expand the utility of PCLA in functional coatings by demonstrating a reliable, reproducible, and scalable microfabrication strategy. By integrating low-temperature imprinting with gas-permeable mold technology, we provide a robust foundation for the design of advanced bioabsorbable coatings with tunable surface properties, applicable to both biomedical and broader life-science contexts. Compared to photolithographic or laser-based direct imaging methods, the proposed low-temperature nanoimprint approach offers superior cost-effectiveness, reduced equipment complexity, and operational simplicity [31]. Additionally, the gas-permeable TiO2–SiO2 mold exhibits mechanical durability superior to soft lithographic alternatives, supporting repetitive usage.
In this investigation, we synthesized gas-permeable molds from TiO2–SiO2 and applied them to the low-temperature nanoimprinting of PCLA. Our specific aims included the enhancement of water repellency, degradation kinetics, and biocompatibility through microstructured PCLA coatings, while circumventing the inherent thermal limitations of the polymer matrix. These findings are intended to advance the practical application of next-generation bioabsorbable materials within the medical and life science sectors.

2. Materials and Methodology

2.1. Fabrication of TiO2–SiO2 Gas-Permeable Mold

Figure 1 illustrates the fabrication process of the TiO2–SiO2 gas-permeable mold employed in this study. Following established protocols from previous literature, a gas-permeable porous polymer composed of TiO2–SiO2 was synthesized [32,33,34,35]. A convex master mold (sapphire, Dojin Sangyo, Osaka, Japan) with a height of 1.3 μm and a pitch of 3 μm was used. A release agent (DS-831TH, HARVES, Saitama, Japan) was applied to the surface of the master mold and allowed to dry for 2 h to facilitate subsequent demolding. The TiO2–SiO2 porous polymer was then dispensed onto a glass substrate, onto which the release-treated convex master mold was pressed while applying pressure. Concurrently, ultraviolet (UV) light (LED, AC90V–240V, 365 nm, 72 W) was irradiated for 3 s to cure the polymer. The mold was then detached from the substrate, resulting in a flexible, film-like gas-permeable mold [36,37].

2.2. Fabrication of Non-Gas Permeable Mold

A non-gas-permeable mold was fabricated using a photopolymer blend consisting of 43 wt% isobornyl acrylate, 33 wt% n-butyl acrylate, 20 wt% triethylene glycol diacrylate, and 4 wt% 2-hydroxy-2-methylpropiophenone. The mixture was applied to a glass substrate. A release-treated convex master mold was then pressed onto the coated substrate under pressure, and the assembly was UV-cured for 5 s using an LED light source (AC90V–240V, 365 nm, 72 W). After curing, the master mold was removed, producing a film-type non-gas-permeable mold.
The gas transport behavior of polymeric materials is commonly described by the solution–diffusion model, in which permeability is governed by the solubility and diffusivity of penetrant molecules, both of which are strongly dependent on the free volume and crosslink density of the polymer network [38,39,40]. UV-curable acrylate systems containing multifunctional monomers such as diacrylates are well known to form densely crosslinked networks, resulting in reduced segmental mobility and suppressed gas diffusion [41,42]. The non-gas-permeable mold used in this study was based on a formulation containing n-butyl acrylate together with other commonly used UV-curable monomers, and this composition is considered to be broadly consistent with reported design principles for low-permeability UV-cured networks. Therefore, although direct permeability measurements were not performed, the mold can reasonably be regarded as a non-gas-permeable reference under the present experimental conditions.

2.3. Surface Microfabrication Process

Figure 2 depicts the surface microfabrication procedure utilized in this study. Poly(caprolactone-co-lactide) (PCLA; CL-20, Taki Chemical, Kakogawa, Japan; 20 mol% caprolactone content, elastomeric) was dissolved in a mixture of 22 wt% PCLA and 78 wt% dichloromethane to enhance fluidity. The solvent ratio was selected not only to ensure complete dissolution of the polymer, but also to achieve sufficient flowability while maintaining moderate viscosity to suppress excessive spreading on the substrate. The prepared PCLA/dichloromethane solution exhibited a moderately viscous, thickened fluid-like behavior rather than that of a highly diluted, low-viscosity liquid. The solution underwent ultrasonic agitation at 30 °C using an ultrasonic cleaner (DIGITAL ULTRASONIC CLEANER OZL-2000, Onezili, Guangzhou, China) until complete dissolution was achieved. Polystyrene (PS) was selected as the substrate material owing to its superior interfacial adhesion with PCLA, thereby facilitating the formation of a stable coating layer amenable to subsequent micro- and nanostructuring as a functional coating surface. The PCLA solution was cast onto ethanol-cleaned PS substrates. The gas-permeable mold was positioned onto the coated substrate and pressurized using a fixed weight. The assembly was incubated at low temperature (refrigerated) for 2 h. This step was critical for the gradual volatilization of solvents and the evacuation of entrapped gases and microbubbles, prior to final desiccation. The mold was subsequently detached, yielding a microstructured PCLA coating. A parallel fabrication protocol was executed utilizing the non-gas-permeable mold to serve as a control.

2.4. SEM Analysis of Microcoated PCLA Surfaces

The topographic fidelity of the microstructured PCLA coatings, fabricated via both gas-permeable and non-gas-permeable molds, was characterized using scanning electron microscopy (SEM; Regulus 8100, Hitachi High-Tech, Minato, Tokyo). Observations were conducted without metal coating under the following conditions: acceleration voltage, 3000 V; deceleration voltage, 0 V; magnification, 5000×; working distance, 31.6 mm; and beam current, 9800 nA.

2.5. Fourier Transform Infrared (FT-IR) Spectroscopy

Chemical characterization was performed via Fourier transform infrared (FT-IR) spectroscopy (Spectrum Two, PerkinElmer, Waltham, MA, USA). Spectra were obtained for native PCLA, PCLA processed into surface coatings following dissolution in dichloromethane, and pure dichloromethane.

2.6. Water Contact Angle Measurement

To evaluate the wetting characteristics of both planar and microstructured PCLA surfaces, static water contact angle goniometry was performed using a fully automated contact angle meter (Dropmaster DM500, Kyowa Surface Science, Saitama, Japan). Measurements were carried out using the 0/2 analysis method with a droplet volume of 1.0 μL at an ambient temperature of 25 °C. Contact angles were recorded every second for 9 s post-deposition. Average values were calculated by excluding the measurements at 0 and 9 s. Each sample was evaluated in triplicate.

2.7. Fluorescence Intensity Measurement

To evaluate the influence of microstructured surface on the elution behavior of fluorescent dyes, fluorescence intensity measurements were performed. A solution containing 20 wt% PCLA, 70 wt% dichloromethane, and 10 wt% fluorescein isothiocyanate-dextran (FD4) was prepared. Ultrasonic agitation at 30 °C (DIGITAL ULTRASONIC CLEANER OZL-2000, Onezili) was applied until complete dissolution was achieved. Flat and microstructured PCLA samples containing FD4 were fabricated as described in Section 2.4.
Each sample was immersed in 50 mL of a 20:80 ethanol/phosphate-buffered saline (PBS, pH 7.2) solution under magnetic stirring at 37 °C. At 0, 6, 8, and 23 h, 1.0 mL of the solution was extracted and immediately replaced with an equal volume of fresh buffer. Fluorescence intensity was measured using a microplate reader (Infinite® M Plex, TECAN, Zurich, Switzerland) with monochromator optics. Measurement parameters were as follows: excitation and emission wavelengths of 490 nm and 520 nm, respectively; excitation and emission bandwidths of 9 nm and 20 nm, respectively; integration time, 20 μs; delay time, 9 μs; stabilization time, 0 μs; and 25 flashes per sample.

3. Results and Discussion

3.1. Surface Microfabrication of PCLA

Figure 3 presents scanning electron microscopy (SEM) micrographs of the convex master mold, the gas-permeable mold, and the resultant microstructured PCLA surfaces. The microstructured surfaces exhibited high fidelity to the convex master mold, achieving an approximate 96% correspondence in both structural height and base diameter. From a rheological perspective, the balance between flowability and viscosity of the PCLA/dichloromethane solution is considered critical for achieving stable replication of micro/nanostructures. The moderate viscosity was advantageous in suppressing uncontrolled spreading and enabling reliable filling of microcavities. Although quantitative rheological measurements were not performed in this study, stable and reproducible fabrication was ensured through practical process control. These data demonstrate that the gas-permeable mold facilitates precise pattern transfer, effectively replicating the original microstructure.
Furthermore, these results suggest that the refinement of processing parameters could yield even greater microfabrication precision. Although the long-term cycling of these molds was not the primary objective of this investigation, prior studies have validated the superior thermal stability and reusability of TiO2–SiO2 gas-permeable molds [33]. The robust mechanical durability and resistance to degradation inherent to these molds underscore their suitability for repetitive use in extended manufacturing cycles. The microinjection molding conditions, holding pressure time (10 s) and cooling time (20 s), define the cycle time for each molding process. Scanning probe microscopy observations revealed that nanostructures remained well replicated from the 5th to the 200th injection molding cycles without mold cleaning, and only minor, application-tolerant defects were observed at the 400th cycle. Although direct measurements of gas permeability after repeated cycles were not reported, the preserved structural fidelity suggests that gas transport properties remain largely stable. These results indicate that such gas-permeable molds possess sufficient mechanical robustness and cyclic durability for repeated microfabrication processes. Future investigations will encompass comprehensive mechanical testing and long-term durability assessments to validate their efficacy in scalable production environments. The synergy between the functional gas permeability of the mold and the rheological properties of the polymer holds significant promise for advancing microstructured coating technologies and expanding their applicability across diverse polymeric systems.
Figure 4 delineates the comparative outcomes of microstructured coatings fabricated using a non-gas-permeable mold. In this control group, pronounced patterning anomalies were observed, attributed to the entrapment of air and residual solvent within the polymer matrix and at the mold–polymer interface during pressurization. These trapped volatiles could not be efficiently evacuated—particularly at the apexes of the microstructures—resulting in incomplete pattern transfer and structural deformation. Notably, when the non-gas-permeable mold was utilized in an inverted orientation, the retention of air and solvent was exacerbated, thereby increasing the severity of the structural defects.
Figure 5 illustrates the replication results obtained using a mold featuring a line-patterned geometry with a minimum linewidth of approximately 600 nm. The replicated structures were observed using a digital microscope (VHX-7100, Keyence, Osaka, Japan). When the gas-permeable mold was employed, the replicated lines displayed superior uniformity in both linewidth and pitch, establishing continuous and well-defined patterns across the substrate. Specifically, the acuity of the line edges and periodic consistency were preserved, demonstrating high-fidelity pattern transfer even at the submicron scale. This achievement surpasses the resolution limits reported in our antecedent investigations [32]. Conversely, the use of the non-gas-permeable mold resulted in numerous discontinuities and bulging deformations, suggesting that air and volatile components were not adequately released during the pressurization phase. These defects are attributed primarily to air entrapment and incomplete resin filling within the narrow interstitial regions. Consequently, it is evident that the gas-permeable mold maintains high replication fidelity independent of pattern geometry or scale. These findings corroborate the efficacy of gas-permeable molds for the precise fabrication of functional surfaces featuring fine linear and hierarchical architectures.
As highlighted in Figure 3, the utilization of the gas-permeable mold significantly mitigated patterning errors, a result driven by the efficient evacuation of volatiles and air through the mold’s porous nanostructure. Previous studies have confirmed that TiO2–SiO2 gas-permeable molds exhibit permeability superior to that of conventional PDMS-based flexible molds, a characteristic attributed to their intrinsic molecular architecture [32,35]. This efficient gas evacuation contributes substantially to the augmented fidelity of microstructure transfer, particularly regarding fine structural features such as apexes and edges. These findings underscore the critical importance of process conditions that facilitate effective solvent and gas removal. The implementation of gas-permeable molds offers a robust solution to the limitations encountered with non-permeable systems and represents a promising strategy for achieving high-resolution microstructured coatings. Although this study focused on a singular pattern morphology, the methodology is adaptable to hierarchical or multi-scale patterning in the submicron range through the modulation of PCLA physicochemical properties and process parameters, including pressure, dwell time, and temperature. However, in submicron applications, factors such as mold resolution and polymer filling kinetics may present limiting constraints, warranting further investigation.
While the mechanical strength and stability of microstructured PCLA coatings were not directly evaluated in this study, future work will include systematic assessments of mechanical integrity during handling and potential device integration. These investigations will be critical to further validate the robustness of the microstructured surfaces and to support their practical implementation in biomedical applications.

3.2. FT-IR Spectral Analysis

Figure 6a presents the FT-IR spectra of untreated PCLA and the microstructured PCLA coating. The spectra indicate that the chemical integrity of the PCLA was preserved throughout the microcoating process, evidenced by the congruence of characteristic absorption peaks before and after processing. Figure 6b displays the spectrum of dichloromethane, the solvent employed in the procedure. Notably, the characteristic C–Cl bond peak associated with dichloromethane was absent in the spectrum of the processed PCLA, indicating effective solvent removal during the refrigerated drying phase. This suggests that the optimized drying protocol successfully minimized residual solvent content, thereby preserving the material’s physicochemical stability post-processing. These findings confirm that the dissolution of PCLA in dichloromethane, followed by low-temperature drying, constitutes a reliable methodology for maintaining polymer integrity during microstructured coating. Furthermore, this approach demonstrates versatility, with potential adaptation to other polymer–solvent systems for expanded microstructured coating applications.

3.3. Contact Angle Measurements

Figure 7 presents a comparative analysis of the water contact angles for PCLA with flat versus microstructured surfaces. The microstructured surfaces correspond to the line-patterned geometry depicted in Figure 3. While the flat PCLA surface exhibited a contact angle of 70.1°, the microstructured surface demonstrated a marked increase to 91.4°, indicating enhanced hydrophobicity. This increase suggests that the microstructured coating effectively modulates surface energy distribution [43,44]. Whereas flat surfaces display uniform energy profiles, the introduction of surface roughness induces localized energy variations, impeding the uniform pinning of the triple-phase contact line. Consequently, droplets are compelled to rest on the structural protrusions, resulting in an increased apparent contact angle. Additionally, the surface topography likely obstructs complete wetting (Cassie–Baxter state), further augmenting hydrophobic behavior. These results confirm that surface structuring via microstructured coating is a viable strategy for tailoring surface physicochemical properties. Beyond water repellency, such structural modifications may influence antimicrobial resistance, biofouling resistance, and other functional surface characteristics [45,46].

3.4. Fluorescence Intensity Measurements

Figure 8 depicts the fluorescence intensity profiles representing FD4 elution from PCLA samples with flat and microstructured surfaces. The microstructured surfaces, corresponding to the patterned geometry shown in Figure 3, exhibited markedly higher fluorescence intensity compared to flat surfaces at all measured time points, indicating enhanced FD4 release. The relative fluorescence unit (RFU) values revealed a consistent and reproducible enhancement in elution performance for the microstructured samples, demonstrating the profound influence of surface morphology on molecular diffusion behavior.
The augmented elution observed from the microstructured surfaces can be attributed to multiple synergistic factors [47,48]. To further interpret the enhanced dye release from the microstructured surfaces, a diffusion-based framework was considered. Quantitative diffusion pathways could not be measured, but the introduction of surface microstructures is expected to increase the effective surface area and to modify local interfacial environments compared with flat surfaces. Based on the measured geometrical parameters (pitch: 3 μm, height: 1.3 μm), the effective surface area of the microstructured substrate was estimated using a simplified geometrical model. The calculated surface area (estimated to be approximately 5.2 cm2 to 7.5 cm2 for a 2 × 2 cm2 substrate) was substantially larger than that of the flat surface (4.0 cm2), suggesting that surface area enlargement contributes, at least in part, to the observed enhancement in dye release. In addition, changes in local wettability and interfacial energy at the microstructured surface may influence solvent accessibility and mass transport, thereby facilitating molecular release.
The gradual and continuous increase in fluorescence intensity observed over the 23 h measurement period suggests a sustained and diffusion-controlled release process governed by the structural configuration of the microstructured surfaces. These results indicate that deliberate surface design enables modulation of elution behavior and holds significant potential for controlled drug delivery systems, where tuning surface geometry can precisely regulate the release rate and profile of incorporated molecules.

4. Conclusions

A low-temperature nanoimprint lithography technique employing a TiO2–SiO2 gas-permeable mold was successfully implemented to address the processing limitations associated with the low melting points of polycaprolactone (PCL) and poly(caprolactone-co-lactide) (PCLA), thereby broadening their utility in medical and life science sectors. This methodology enables the fabrication of microstructures on polymer surfaces without necessitating high-temperature processing, demonstrating significant potential for a spectrum of biomedical applications.
The nanoimprinting protocol developed herein obviates the need for capital-intensive or complex instrumentation, supports cost-effective low-temperature patterning, and permits the repeated utilization of durable, gas-permeable molds. While this approach offers distinct advantages regarding sustainability and versatility, challenges persist, particularly concerning high-resolution patterning in the submicron regime and throughput optimization relative to conventional techniques such as photolithography. Consequently, further investigation is warranted to refine the process for specific high-precision applications.
The gas-permeable mold exhibited high molding fidelity, superior microstructure transfer capabilities, and stable performance under low-temperature conditions. Surface microstructured coatings of PCLA fabricated via this technique demonstrated enhanced hydrophobicity, evidenced by a significant increase in contact angles compared to untreated, planar surfaces. Furthermore, fluorescence intensity assays revealed elevated elution from microstructured samples, indicating that surface architecture can be strategically manipulated to modulate drug release kinetics.
FT-IR spectroscopy confirmed the preservation of PCLA’s chemical structure post-processing, with no detectable absorption peaks corresponding to the volatile solvent dichloromethane. These findings validate the chemical and physical stability of the polymer following microstructured coating and underscore the high processing accuracy and reliability of the gas-permeable mold system.
Given that PCLA is a bioabsorbable polymer that undergoes gradual in vivo degradation, the introduction of surface microstructures is expected to influence cellular adhesion, migration, and local biological responses at the material–tissue interface. In this context, the microstructured PCLA surfaces developed in this study demonstrate high compatibility with biomedical devices that require surface functionalization, including drug-eluting coatings for implantable devices, bioactive wound dressings, anti-biofouling catheter surfaces, and temporary tissue-contacting implants.
Furthermore, previous studies have established that surface patterning and microstructural dimensions play critical roles in regulating cellular morphology, alignment, and differentiation [49,50,51]. Accordingly, the structures engineered in this work may provide a biologically favorable surface environment that supports functional tissue integration while maintaining the inherent biodegradability of PCLA.
The present study was primarily focused on establishing a robust fabrication platform for microstructured biodegradable polymer coatings, and direct in vitro cytotoxicity and cell adhesion assays were not performed. Nevertheless, the well-established biocompatibility of PCLA and the absence of detectable residual solvent in the processed materials support the potential safe application of the proposed coatings, and this limitation is recognized as an important step toward practical biomedical implementation. In future studies, systematic investigations of cell–material interactions and immune responses will be required to establish robust evidence of biocompatibility and to define rational design principles for next-generation biomedical devices.
In summary, these results suggest that the integration of gas-permeable molds with low-temperature nanoimprint lithography will expand the processing envelope for PCL and PCLA, enhancing their potential for applications within the medical and life sciences. This research provides critical foundational technologies for the development of drug delivery systems, tissue engineering scaffolds, and next-generation medical devices. Furthermore, these findings highlight the efficacy of machining methods utilizing gas-permeable molds for achieving high-precision coatings on low-melting-point materials, suggesting their potential to drive innovation in precision manufacturing and industrial coating processes.

Author Contributions

Conceptualization, M.A. and S.T.; data curation, M.A. and S.T.; formal analysis, N.S. and Y.Y.; funding acquisition, S.T.; investigation, M.A., N.A.H.M. and S.T.; methodology, M.A., N.S., Y.Y. and S.T.; project administration, S.T.; resources, S.T.; supervision, S.T.; validation, M.A. and S.T.; writing—original draft preparation, M.A. and S.T.; writing—review and editing, M.A., N.A.H.M. and S.T. All authors have read and agreed to the published version of the manuscript.

Funding

The authors wish to acknowledge the funding received from Nakato Scholarship Foundation 2024–2025, Japan Science and Technology Tech Startup HOKURIKU Program No. TeSH2024-17, Japan Society for the Promotion of Science Bilateral Joint Research Projects No. 120259947, Die and Mould Technology Promotion Foundation 2025, Fuji Seal Foundation 2025, Toyama Prefecture Grant 2025, Amada Foundation 2025, Ame Hisaharu Foundation 2025, and Fujikura Foundation 2025.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The datasets generated and/or analyzed during the current study are not publicly available because they belong to ongoing research but are available from the corresponding author upon reasonable request.

Acknowledgments

The authors would like to express their sincere gratitude to Rio Yamagishi, Sayaka Miura, Yuna Hachikubo, Misaki Oshima, Mayu Morita, and Hiryu Hayashi of the Takei Laboratory at Toyama Prefectural University for their invaluable support, fruitful discussions, and assistance with the experiments. We also sincerely thank the staff of Taki Chemical Co., Ltd. for their generous support.

Conflicts of Interest

Author Naoto Sugino was employed by the company Sanko Gosei. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Coatings 16 00010 g001
Figure 1. Fabrication of TiO2–SiO2 gas permeable mold.
Figure 1. Fabrication of TiO2–SiO2 gas permeable mold.
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Figure 2. Microstructured PCLA coating process.
Figure 2. Microstructured PCLA coating process.
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Figure 3. Scanning electron microscopy observations of convex master mold, gas-permeable mold, and microstructured PCLA coating surfaces with a structure height of 1.3 μm and a pitch of 3 μm.
Figure 3. Scanning electron microscopy observations of convex master mold, gas-permeable mold, and microstructured PCLA coating surfaces with a structure height of 1.3 μm and a pitch of 3 μm.
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Figure 4. Comparison of microstructured surfaces results of PCLA using non-gas permeable mold.
Figure 4. Comparison of microstructured surfaces results of PCLA using non-gas permeable mold.
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Figure 5. Line pattern transfer results using gas-permeable and non-gas-permeable molds with a minimum linewidth of approximately 600 nm.
Figure 5. Line pattern transfer results using gas-permeable and non-gas-permeable molds with a minimum linewidth of approximately 600 nm.
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Figure 6. (a) Comparison of FT-IR spectra in untreated and surface-fine-treated lactone polymers; (b) FT-IR results for dichloromethane confirm solvent removal.
Figure 6. (a) Comparison of FT-IR spectra in untreated and surface-fine-treated lactone polymers; (b) FT-IR results for dichloromethane confirm solvent removal.
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Figure 7. Contact angle measurements on flat and microstructured PCLA surfaces.
Figure 7. Contact angle measurements on flat and microstructured PCLA surfaces.
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Figure 8. Fluorescence intensity measurements of PCLA with flat surfaces and PCLA with microstructured surfaces.
Figure 8. Fluorescence intensity measurements of PCLA with flat surfaces and PCLA with microstructured surfaces.
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MDPI and ACS Style

Ando, M.; Sugino, N.; Yokoyama, Y.; Mohamed, N.A.H.; Takei, S. Microstructured Coatings and Surface Functionalization of Poly(caprolactone-co-lactide) Using Gas-Permeable Mold. Coatings 2026, 16, 10. https://doi.org/10.3390/coatings16010010

AMA Style

Ando M, Sugino N, Yokoyama Y, Mohamed NAH, Takei S. Microstructured Coatings and Surface Functionalization of Poly(caprolactone-co-lactide) Using Gas-Permeable Mold. Coatings. 2026; 16(1):10. https://doi.org/10.3390/coatings16010010

Chicago/Turabian Style

Ando, Mano, Naoto Sugino, Yoshiyuki Yokoyama, Nur Aliana Hidayah Mohamed, and Satoshi Takei. 2026. "Microstructured Coatings and Surface Functionalization of Poly(caprolactone-co-lactide) Using Gas-Permeable Mold" Coatings 16, no. 1: 10. https://doi.org/10.3390/coatings16010010

APA Style

Ando, M., Sugino, N., Yokoyama, Y., Mohamed, N. A. H., & Takei, S. (2026). Microstructured Coatings and Surface Functionalization of Poly(caprolactone-co-lactide) Using Gas-Permeable Mold. Coatings, 16(1), 10. https://doi.org/10.3390/coatings16010010

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