Bioactive Electrospun Polycaprolactone Films with Gallic Acid-Loaded Mesoporous Silica Nanoplatelets for Enhanced Seed Germination

Abstract

Enhancing seed germination and promoting early seedling growth are among the primary objectives in advancing agricultural productivity. To address these needs, this study developed electrospun nanofiber films composed of polycaprolactone (PCL) incorporating gallic acid (GA)-loaded, amine-functionalized mesoporous silica nanoplatelets (H-MSN-NH₂@GA). The mesoporous silica nanoplatelets (H-MSNs) with a hexagonal morphology were synthesized by using a sol–gel approach. These nanoplatelets were subsequently functionalized with amine groups using 3-(2-aminoethylamino)­propyltrimethoxysilane (AAPTS) to enable efficient GA loading. The functionalized and nonfunctionalized H-MSNs, both with and without GA, were incorporated into a PCL matrix to produce uniform nanofiber films via electrospinning. A series of films with varying compositions were fabricated to evaluate the effect of the additive content on functionality. All resulting films displayed consistent hydrophobic characteristics and high water vapor transmission rates, exceeding 3000 g/m²/day. This indicated that incorporation of the silica-based additives did not significantly alter the films’ permeability or surface wettability. Tensile tests revealed distinct variations in maximum force and tensile displacement among the five samples, indicating composition-dependent mechanical properties. At 72 h, the 10% H-MSN-NH₂@GA/PCL film achieved 100% germination for corn seeds and a 70% higher germination rate for bean seeds compared to the control group. Root length analysis showed that 10% H-MSN/PCL and 1% H-MSN-NH₂@GA/PCL promoted corn root growth, while 10% H-MSN-NH₂@GA/PCL had an inhibitory effect. For bean seeds, root elongation was enhanced by 10% H-MSN/PCL, 1% H-MSN-NH₂@GA/PCL, and 10% H-MSN-NH₂@GA/PCL. These findings provide valuable insights into the effects of mesoporous silica nanoplatelets with and without GA in electrospun fiber films, offering a sustainable and functional alternative to conventional germination substrates.

Introduction

Bean and corn are globally important staple crops and, along with squash, form the traditional “Three Sisters” agricultural system practiced by Native American communities. Together, they provide essential sources of carbohydrates, protein, vitamins, and other micronutrients vital for the nutrition of both humans and livestock. , In addition to their dietary value, byproducts of these crops have numerous applications, ranging from industrial uses to soil enrichment in agricultural systems. − Due to their wide availability and relatively low cost, beans and corn play a vital role in ensuring global food security and economic sustainability. , Furthermore, the Food and Agriculture Organization of the United Nations estimates that by 2050, global food production will need to increase by 70–100% to accommodate the projected population growth. Seed germination is a critical process in agriculture, directly impacting yield, growth uniformity, and agricultural productivity, especially under challenging environmental conditions or in nutrient-poor soils. − Traditional methods, such as germinating seeds on paper substrates, are used in laboratory settings to evaluate seed viability, germination rates, and early seedling development of certain rare and challenging seeds that are difficult to germinate through conventional sowing methods. These simple paper-based systems provide a controlled environment that ensures consistent moisture and oxygen availability while facilitating the observation of germination progress. However, some of the drawbacks of this approach, including lack of durability, long-term mechanical support, options for additional nutrients, or protection from environmental stressors, ultimately hinder its practical application in large-scale farming.

To overcome these limitations, it would be ideal to develop a more suitable, possibly multifunctional material that not only promotes seed germination but also offers added advantages such as nutrient delivery, mechanical protection, and adaptability to environmental conditions. Polycaprolactone is a biodegradable and biocompatible polymer widely recognized for its mechanical durability, water retention properties, and environmental compatibility, making it an ideal substrate for agricultural applications. , Using electrospinning, polycaprolactone can be fabricated into nanofiber mats with high surface area, tunable porosity, and customizable morphology, offering superior water permeability and nutrient delivery compared to traditional seed germination materials. − Successful seed germination on an electrospun polycaprolactone fiber substrate was recently reported for the germination of mung beans over a 96 h period. The success was attributed to the fibers’ high surface area and exceptional water absorption properties. Building on these findings and leveraging our expertise in advanced functional materials, we aim to enhance the performance of electrospun polycaprolactone substrates by incorporating bioactive components designed to promote seed germination and early plant development. To this end, functionalized mesoporous silica nanoparticles (MSNs), developed by Lai et al., exhibit large surface area, tunable pore size, and excellent loading and release capabilities. , Specific to agricultural applications, a structural alternative to conventional spherical MSNs, the hexagonal MSN (H-MSN) nanoplatelets demonstrated improved foliar adhesion when applied to plants, attributed to its enhanced contact area with plant-accessible surfaces. In seed germination studies, to synergistically support early stage plant growth, we focused on further incorporating phenolic compounds, which are naturally present in plants and known to enhance enzymatic activity, mitigate oxidative stress, and support key metabolic functions. ,

Among these, gallic acid (GA) stands out for its dual role as both a potent antioxidant and plant growth enhancer. , At optimal concentrations, GA has been shown to protect seeds from oxidative damage during germination, while stimulating enzymatic pathways that are critical for radicle emergence and robust seedling development. GA is a low molecular weight compound, which facilitates its diffusion into the seed microenvironment. Furthermore, the silica nanostructure effectively protects the active ingredient from environmental stress. By integrating GA-loaded H-MSNs into polycaprolactone nanofiber substrates, we seek to create a multifunctional material platform that combines mechanical support, controlled bioactive release, and targeted enhancement of seed development. ,

In this study, amine groups were introduced onto the H-MSN-synthesized nanoplatelets, modifying the surface charge to facilitate an effective GA loading. GA exhibits strong affinity for the amino-functionalized mesoporous silica nanoplatelets (H-MSN-NH₂) due to the presence of both a carboxyl group and multiple phenolic hydroxyl groups enabling noncovalent interactions through electrostatic forces and hydrogen bonding with the positively charged amine groups on H-MSN-NH₂, leading to efficient loading and a controlled, sustained release profile. The GA-loaded H-MSN-NH₂ was incorporated into PCL to fabricate the nanofiber films by electrospinning. The electrospinning parameters were optimized to achieve uniform fibers with excellent mechanical properties and porosity. The resulting films were evaluated for their potential as multifunctional substrates for seed germination, providing controlled nutrient delivery and a supportive environment for seedling growth. The synthesis and fabrication process, along with the system design, are illustrated in Figure .

1.

Schematic illustration of precursor materials’ preparation and film fabrication.

Experimental Section

Materials

Hexadecyltrimethylammonium bromide (CTAB, ≥99%) and lithocholic acid (LCA, ≥95%) were acquired from Sigma-Aldrich (Saint Louis, MI). Tetraethyl orthosilicate (TEOS, 99.9%) was purchased from Alfa Aesar (Haverhill, MA). GA was acquired from MP Biomedicals (Solon, OH). PCL CAPA 6800 (molecular weight 80 000 Da) was purchased from Ingevity (North Charleston, SC). 3-(2-Aminoethylamino)­propyltrimethoxysilane (AAPTS, >97%) and 2,2,2-trifluoroethanol (TFE, >99%) were purchased from TCL America (Portland, OR). Ammonium hydroxide solution (NH₄OH, 28% NH₃ basis), hydrochloric acid (HCl, 37%), ethanol (200 proof, 100% by volume), and methanol were purchased from Thermo Fisher Scientific (Waltham, MA). ACS reagent-grade nanopure water was purchased from LabChem (Zelienople, PA). Bean seed and corn seed were purchased from Amazon.com, brand: “Dakota’s Pride”.

Characterization

X-ray diffraction (XRD) measurements were conducted on a Rigaku MiniFlex600 equipped with Cu Kα radiation (λ = 1.5405 Å) operated at 40 mV and 30 mA. Fourier transform infrared spectroscopy measurements were conducted on a Shimadzu/IRTracer-100. Dynamic light scattering (DLS) measurements were conducted on an Anton Paar Litesizer 500 particle analyzer instrument. The thermogravimetric analysis (TGA) measurements were performed on a Hitachi STA200. Scanning electron microscopy (SEM) imaging was conducted on a JEOL/JSM-F100 Schottky field emission scanning electron microscope. Transmission electron microscopy (TEM) imaging and TEM-EDS (energy-dispersive spectroscopy) were conducted on a JEOL JEM-2100Plus instrument equipped with EDS. The specific surface areas of the materials were measured through nitrogen adsorption–desorption isotherms using the Brunauer–Emmett–Teller (BET) method. The pore volume and pore size distribution were assessed by using the density functional theory method. All the analyses were conducted using an Anton Paar Quantachrome/NOVAtouch LX-2 instrument. Ultraviolet–visible (UV–vis) absorption spectroscopy was conducted on a Thermo Scientific/BioMate 160 UV–visible spectrophotometer. The tensile strength testing was performed with the Instron 68TM-50 dual-column table model.

Synthesis of H-MSN

H-MSN was synthesized using a typical templating method. Briefly, 200 mg of CTAB and 18 mg of LCA were dissolved in 100 mL of nanopure water under vigorous magnetic stirring to ensure a homogeneous solution. Subsequently, 5.7 mL of ammonium hydroxide solution and 0.4 mL of methanol were rapidly added to the mixture, followed by stirring for 20 min. Thereafter, 1 mL of TEOS was introduced into the solution, and the reaction was carried out under continuous stirring at 750 rpm and room temperature for 90 min. The resulting white suspension, denoted as H-MSN-CTAB, was isolated by centrifugation and washed three times with nanopure water and twice with ethanol. The product was then dried overnight in a vacuum oven at 60 °C. To remove the surfactant template (CTAB), 1.5 g of H-MSN-CTAB was refluxed for 24 h at 75 °C in a solution containing 160 mL of methanol and 9 mL of hydrochloric acid (37%). The resulting after-wash material denoted H-MSN-AS (as synthesized) was collected by centrifugation at 7000 rpm, followed by washing three times with nanopure water and twice with methanol. The purified material was dried overnight in a vacuum oven, yielding the final H-MSN product.

Preparation of H-MSN-NH₂ by Grafting and H-MSN-NH₂@GA by GA Loading

The synthesized, after-wash H-MSN-AS (1 g) was dispersed in 80 mL of toluene in a round-bottom flask using an ultrasonic bath for 15 min to ensure uniform suspension. Subsequently, 1 mM AAPTS was introduced into the dispersion, and the mixture was refluxed at 70 °C with continuous stirring at 600 rpm for 12 h. Upon reaction completion, the product was washed three times with toluene and methanol to remove unreacted reagents. The washing steps were followed by centrifugation at 7000 rpm for 5 min. Finally, the purified product was dried under vacuum overnight to obtain H-MSN-NH₂.

To load GA in the prepared nanoparticles, 50 mg of H-MSN-NH₂ was placed into a 20 mL vial, and 10 mL of a GA ethanol solution, prepared by dissolving GA in ethanol at a concentration of 40 mg/mL, was added to the vial. The mixture was stirred at 200 rpm for 48 h at room temperature to facilitate effective GA loading. After the loading process, the suspension was centrifuged at 7000 rpm for 5 min. Finally, the nanoparticles were collected and dried under vacuum at room temperature to obtain the GA-loaded nanoparticles named H-MSN-NH₂@GA. The supernatant was collected to determine the loading efficiency of GA from following the eq (eq ), using a calibration curve (Figure S2)­

$$\mathrm{L}\mathrm{o}\mathrm{a}\mathrm{d}\mathrm{i}\mathrm{n}\mathrm{g}\mathrm{e}\mathrm{f}\mathrm{f}\mathrm{i}\mathrm{c}\mathrm{i}\mathrm{e}\mathrm{n}\mathrm{c}\mathrm{y}(\%)=\frac{\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{c}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}-\mathrm{f}\mathrm{i}\mathrm{n}\mathrm{a}\mathrm{l}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{c}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}{\mathrm{i}\mathrm{n}\mathrm{i}\mathrm{t}\mathrm{i}\mathrm{a}\mathrm{l}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{c}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}}\times 100\%$$ 1

Electrospun Film Fabrication

To prepare the precursor solution for electrospinning, 0.4 g of polycaprolactone (PCL, CAPA 6800) was dissolved in 4 g of trifluoroethanol (TFE) under continuous stirring overnight, resulting in a homogeneous PCL solution. Following dissolution, either H-MSN or H-MSN-NH₂@GA nanoparticles were added at concentrations of 1% or 10% (w/w) relative to the PCL content. The mixture was stirred until the nanoparticles appeared uniformly throughout the solution. To further improve dispersion and minimize agglomeration, the stir bar was removed, and the suspension was sonicated for 30 min.

The electrospinning process was carried out using a setup with the following parameters: an 18-gauge needle, a flow rate of 1.0 mL/h, an applied voltage of 15 kV, a working distance of 24 cm, and a collector rotation speed of 550 rpm. After the electrospinning process, the electrospun film was kept in an ambient atmosphere until the solvent (TFE) had completely evaporated. Next, the film was carefully removed from the aluminum foil substrate to obtain the freestanding electrospun film for subsequent analysis or application. The selection of 1% and 10% concentrations for H-MSN/PCL and H-MSN-NH₂@GA/PCL, respectively, was designed to highlight the differences between H-MSN and GA-loaded H-MSN when incorporated into electrospun nanofibers. To evaluate the influence of nanoparticle loading on seed germination and root growth, two concentrations1% (low) and 10% (high) by weightwere selected to represent a broad contrast in material composition. The higher concentration was chosen to approach the upper practical limit for nanoparticle incorporation as exceeding this threshold may compromise the mechanical integrity and uniformity of the electrospun fibers, potentially impairing their structural performance and suitability for agricultural applications.

Contact Angle and Water Vapor Transmission Rate (WVTR) Measurement

The hydrophilicity of the electrospun films was assessed by using an Ossila contact angle goniometer to determine their surface wetting. A 10 μL droplet of water was carefully placed onto the surface of the film, and the contact angle was measured and analyzed using an Ossila contact angle software to evaluate the hydrophobic or hydrophilic nature of the material.

The water vapor transmission rate (WVTR) test was performed to evaluate the films’ permeability. Each film was securely mounted over the opening of a 15 mL centrifuge tube containing 13 mL of nanopure water. The tubes were then placed in a 37 °C incubator and maintained for 24 h to simulate physiological conditions. The weight loss of the tubes was recorded after the incubation period to calculate the WVTR by following eq (eq ):

$$\mathrm{W}\mathrm{V}\mathrm{T}\mathrm{R}=\frac{\mathrm{\Delta }m}{A}\times \frac{24}{\mathrm{\Delta }t}$$ 2

where Δm is the change in the mass of water vapor transmitted (g), A is the surface area of the material (m²), and Δt is the time interval during which the measurement is taken (hour).

Mechanical Tensile Strength Test

To evaluate the mechanical properties of the electrospun film, a test window paper frame was fabricated according to the ASTM D882-10 standard to securely hold the sample during tensile testing. A smaller tab was used to sandwich the electrospun film between the layers, and a double-sided tape was applied to ensure that the film remained firmly attached to the tabs. The assembled test specimen, consisting of the test window frame with the electrospun film, was mounted onto a tensile tester with pneumatic grips clamped onto the tabs holding the film (Figure , left) with a force of 15 psi. Maintaining a low but sufficient grip pressure is critical to minimizing the amount of internal stress that can be introduced to the test specimen before evaluating its mechanical properties. Prior to testing, a portion of the window frame was carefully cut away to expose the film for measurement (Figure , right). The specimen was prepared with dimensions of 40 × 10 mm and a gauge length of 20 mm and subjected to a strain rate of 10 mm/min. A load cell with a capacity of 500 N was used to record the tensile force, enabling precise characterization of the film’s mechanical properties. The specimen was prestretched using a preload program (strain rate: 3 mm/min until a force of 0.1 N was reached) to eliminate slack introduced during mounting. The test was continued until complete failure of the film. All tensile tests were performed at room temperature under a controlled relative humidity of 60%. For each reported value, a minimum of three specimens were tested.

2.

Schematic illustration of the tensile test sample design.

GA Release Profile

The in vitro release profile of GA from H-MSN-NH₂@GA-loaded electrospun films was evaluated by immersing the samples in 5 mL of aqueous solution (pH 7 and pH 5 which are adjusted with HCl) and incubating them on a shaker at room temperature. At predetermined time intervals (5, 10, 15, and 30 min and 1, 2, 3, 4, 5, 6, 9, 12, 16, 24, 36, and 48 h), aliquots of the supernatant were collected and analyzed by UV–vis spectroscopy at wavelengths of 270 and 262 nm to quantify the concentration of released GA using a pre-established calibration curve (Figure S2). After each sampling, an equal volume of fresh aqueous solution at the corresponding pH was added to maintain a consistent concentration gradient and ensure uninterrupted diffusion.

Seed Germination Activity

Seed germination activity was evaluated using corn and bean seeds under the following conditions. For each test group, 10 seeds were placed in a Petri dish with the following treatments: (1) negative control (no film), (2) PCL-only film, (3) 1% H-MSN/PCL composite film, (4) 10% H-MSN/PCL composite film, (5) 1% H-MSN-NH₂@GA/PCL composite film, (6) 10% H-MSN-NH₂@GA/PCL composite film, (7) free GA solution equivalent to the theoretical GA released from 1% H-MSN-NH₂@GA/PCL composite film, and (8) free GA solution equivalent to the theoretical GA released from the 10% H-MSN-NH₂@GA/PCL composite film. The Petri dishes were maintained in the dark at room temperature to simulate the germination conditions. Every 24 h, 3 mL of nanopure water was added to each Petri dish to ensure adequate hydration. Images of the seeds were captured daily to monitor the germination progress. Broken seed coats and deteriorated seeds were promptly removed to ensure the integrity of the experimental samples. Observations were conducted for a total of 144 h. The same procedure was applied to both corn and bean seeds to assess the effect of the films on the germination rates and seedling growth. Data was analyzed using multiple unpaired t tests to assess statistical significance between treatment groups at each time point.

Results and Discussion

Characterizations of MSNs

In this study, H-MSN was synthesized by using the sol–gel method, employing CTAB and LCA as dual templates and TEOS as the silicon source. The SEM (Figure a) images reveal that H-MSN has a hexagonal morphology. The TEM (Figure b) images show the mesoporous structure. The particle diameter is around 310 nm, with a thickness of around 80 nm. The TEM image of H-MSN-NH₂ (Figure c) demonstrates that the mesoporous structure is well-preserved after amine functionalization, with clearly visible pore channels, similar to the pristine H-MSN. After GA loading (Figure d), the surface appears rougher, and the mesoporous channels become less distinct. This noticeable change suggests successful GA loading modification. The high-resolution TEM/EDS (Figure S1) also confirms the morphology and elemental composition. The DLS analysis (Figure d) reveals the hydrodynamic diameters of H-MSN, H-MSN-NH₂, and H-MSN-NH₂@GA to be 360.8, 332.8, and 498.9 nm, respectively, with a normal size distribution. These sizes are slightly larger than those observed in SEM and TEM images, which is expected due to the hydration layer surrounding the particles in the DLS measurements.

3.

Electron microscopy characterization of the nanostructures: (a) H-MSN SEM image; (b) TEM image; (c) TEM images of H-MSN-NH₂ with the inset showing the characteristic mesoporous channels; and (d) H-MSN-NH₂@GA.

4.

Nanoparticle characterization: (a) XRD pattern; (b) FTIR spectra; (c) N₂ adsorption–desorption isothermals; (d) DLS particle size distributions; (e) zeta potential of each material; and (f) TGA curves of the H-MSN, H-MSN-NH₂, and H-MSN-NH₂@GA.

The XRD patterns of the prepared samples are shown in Figure a. The H-MSN sample shows typical peaks consistent with a previous report. In comparison, the (100) peak of two modified samples shifts slightly to a higher angle, indicating a contraction in the lattice spacing due to amine functionalization. Additionally, the (110) and (200) peaks are absent, reflecting a reduction in long-range order caused by surface modification. These changes confirm the successful functionalization of H-MSN. The FTIR spectra of H-MSN and the modified samples (Figure b) display characteristic silica absorption bands at 1126 cm^–1 (Si–O–Si asymmetric stretching), 970 cm^–1 (Si–O stretching), and 800 cm^–1 (Si–O–Si symmetric stretching), confirming the silica structure. In the H-MSN-as-synthesized (H-MSN-AS), additional peaks at 2622 cm^–1 and 2543 cm^–1, corresponding to the –CH₂ groups of CTAB, are observed. These peaks are absent in the modified samples, indicating complete removal of the surfactant template after refluxing with HCl and methanol. Functionalization with AAPTS introduces a weak peak at 1660 cm^–1, corresponding to amide-related vibrations. Following GA loading, the CC stretching vibration at 1545 cm^–1 appears, indicating the successful incorporation of GA.

The N₂ adsorption–desorption isotherms (Figure c) of H-MSN exhibit a classic type IV curve with a hysteresis loop, characteristic of a mesoporous structure. The specific surface area, pore size, and pore volume are summarized in Table S1 (Supporting Information). For H-MSN, the specific surface area is 1431.72 m²/g, the pore volume is 0.99 cc/g, and the average pore size is 3.54 nm, which is suitable for molecular loading. Compared to H-MSN-AS (as synthesized), which had a significantly lower surface area (23.27 m²/g) and pore volume (0.03 cc/g), the substantial increase confirms the successful removal of the CTAB template. Further modifications with amine groups and GA resulted in dramatic reductions in porosity and surface area to 0.28 cc/g and 429.38 m²/g for H-MSN-NH₂ and 0.10 cc/g and 144.42 m²/g for H-MSN-NH₂@GA, respectively, indicating successful functionalization and GA loading.

The surface modification of H-MSN-NH₂ and H-MSN-NH₂@GA was further confirmed by zeta potential measurements (Figure e), conducted in nanopure water with pH 7. The zeta potential of H-MSN of −14.9 mV was attributed to the electronegativity of surface silanol groups (Si–OH) which are partially deprotonated at pH 7. Following functionalization with AAPTS, the zeta potential of H-MSN-NH₂ increased significantly to +30.1 mV, reflecting the introduction of positively charged amino groups, which altered the surface electrical properties. After GA loading, the zeta potential decreased to +16.1 mV, indirectly confirming the successful loading with negatively charged GA molecules, justifying the reduction.

The thermogravimetric (TGA) analysis was conducted under a nitrogen atmosphere. The TG curves of H-MSN, H-MSN-NH₂, H-MSN-NH₂@GA, and H-MSN-AS are shown in Figure f. All samples exhibit a progressive mass decrease. The initial weight loss below 100 °C corresponds to the evaporation of water encapsulated in the nanoparticles or adsorbed onto their surface. For H-MSN-AS, significant degradation occurs between 150 and 320 °C, with a maximum decomposition rate around 300 °C, primarily due to the decomposition of the CTAB template, resulting in a total weight loss of approximately 48%. By 890 °C, the total weight losses of H-MSN, H-MSN-NH₂, and H-MSN-NH₂@GA are 24.8%, 28.3%, and 60.6%, respectively. The difference in weight loss is about 32.3% between H-MSN-NH₂ and H-MSN-NH₂@GA corresponding to the decomposition of loaded GA which is almost matched with loading capacity percentage (Table S3) calculated based on UV. The TGA of GA was also conducted for reference.

Characterization of the Electrospun Films

The microstructure of the electrospun films containing 1% and 10% H-MSN/PCL and 1% and 10% H-MSN-NH₂@GA/PCL is shown in Figure a–d. The SEM images revealed uniform, random oriented fibers across all samples without nonuniformities (e.g., PLA beading). Distinct hexagonal-shaped materials, corresponding to the incorporated nanoparticles, are observed either embedded within or present on the surface of the fibers. For 1% H-MSN/PCL and 10% H-MSN/PCL, the average diameters are 0.4 and 2.1 μm, respectively. The substantial increase in diameter for 10% H-MSN/PCL is attributed to the higher material content, which also leads to isolated fibers due to excessive nanoparticle aggregation, potentially impacting mechanical properties. For 1% H-MSN-NH₂@GA/PCL and 10% H-MSN-NH₂@GA/PCL, the average fiber diameter is approximately 0.35 μm, regardless of material content. The reduced visible material density in the GA-loaded samples, even at the same weight percentage, suggests that the presence of GA affects the dispersion of the nanoparticles within the PCL matrix. Also, observed interconnecting network structures allow for better nutrient and gas exchange.

5.

Incorporation of HMSN in electrospun fibersSEM images of (a) 1% H-MSN/PCL; (b) 1% H-MSN-NH₂@GA/PCL; (c) 10% H-MSN/PCL; and (d) 10% H-MSN-NH₂@GA/PCL.

The XRD patterns (Figure a) of the electrospun films demonstrate characteristic crystalline peaks of PCL, particularly at 2θ = ∼21.3° and ∼23.7°, corresponding to the (110) and (200) planes of PCL. The intensity of these two peaks observed decreases slightly when the concentration of H-MSN-NH₂@GA increases from 1% to 10%. For comparison, the XRD spectra of H-MSN-NH₂@GA and GA are also shown in the same figure. The FTIR spectra confirm the successful incorporation of H-MSN and H-MSN-NH₂@GA into the electrospun films. Figure b depicts the FTIR spectra of the samples. Typical PCL absorption bands, including the CO stretching vibration at 1722 cm^–1 and the C–O–C stretching vibration at 1163 cm^–1, are observed in all samples. Slight decreases of these two peaks are observed with the increase of the material added.

6.

Electrospun film characterization: (a) XRD pattern; (b) FTIR spectra; (c) contact angle data; and (d) WVTR data of different composition electrospinning fibers. (A) PCL; (B) 1% H-MSN/PCL; C: 10% H-MSN/PCL; (D) 1% H-MSN-NH₂@GA/PCL; and (E) 10% H-MSN-NH₂@GA/PCL.

Evaluation of Hydrophilicity and Permeability

The hydrophobicity of the electrospun films was assessed through contact angle measurements, with the results and corresponding water droplet images presented in Figure c. A surface is hydrophobic when it resists water spreading, producing a high contact angle (θ > 90°) and considered hydrophilic with low contact angle (θ < 90°). The pure PCL film exhibits a contact angle of 108.37°, indicative of its hydrophobic nature. For the films containing H-MSN, the contact angle is 101.98° for 1% H-MSN/PCL and slightly higher, 108.06° for 10% H-MSN/PCL, likely due to the higher concentration of nanoparticles and their surface characteristics. In comparison, the incorporation of H-MSN-NH₂@GA results in lower contact angles, with values of 99.67° and 100.84° for 1% H-MSN-NH₂@GA/PCL and 10% H-MSN-NH₂@GA/PCL, respectively. The contact angle measurements of all five electrospun film compositions showed minimal variation, indicating that the incorporation of H-MSN and H-MSN-NH₂@GA did not significantly alter the overall surface wettability of the PCL matrix.

The WVTR values of the electrospun films, displayed in Figure d, were evaluated to assess their permeability. The WVTR for the pure PCL film is measured at 3283.79 g/m²/day, reflecting its baseline performance. The films with 1% and 10% H-MSN/PCL show slightly higher values of 3295.12 and 3419.67 g/m²/day, respectively, suggesting that the incorporation of mesoporous nanoparticles enhances the water vapor permeability. The films containing H-MSN-NH₂@GA demonstrate WVTR values of 3300.78 and 3374.38 g/m²/day for 1% and 10% loading, respectively, which are slightly lower than those of the H-MSN/PCL films. This is probably due to the density difference between the two materials. For the same weight percentage, H-MSN/PCL consists of more nanoparticles compared to H-MSN-NH₂@GA/PCL, as observed in the SEM images. This results in films with H-MSN being more separated and creating additional crevices, which enhance water vapor transmission to create an optimal microenvironment for exchanging water, gas, and nutrients.

Evaluation of Electrospun Film Mechanical Properties

The tensile test is essential for evaluating the mechanical properties of electrospun films as it provides critical insights into their strength, flexibility, and stiffness. Figure and Table S2 show the tensile test and the recorded mechanical properties of each electrospun film, respectively. The pure PCL film exhibited the highest tensile strength (blue curve) and the greatest elongation at the maximum force, indicating a mechanically robust and ductile structure with uniform deformation behavior. Incorporating 1% H-MSN slightly reduces the tensile strength (orange curve) compared with pure PCL but maintains better elongation. This suggests that the low concentration of nanoparticles does not significantly disrupt the polymer matrix and may even enhance the interaction at lower concentrations. Adding 1% H-MSN-NH₂@GA/PCL (olive curve) leads to lower tensile strength compared to the 1% H-MSN/PCL film, but the ductility is relatively preserved. In contrast, 10% H-MSN/PCL (maroon curve) significantly reduced both Young’s modulus and tensile strength due to particle aggregation and fiber isolation, as observed in SEM images (Figure c). The 10% H-MSN-NH₂@GA/PCL film (green curve) exhibited slightly better mechanical performance compared to that of 10% H-MSN/PCL, which may be attributed to reduced particle aggregation.

7.

Electrospun films’ tensile test results.

pH and Time-Dependent GA Release Profile

The in vitro release profile of GA from H-MSN-NH₂@GA/PCL-electrospun films at two different concentrations and under two pH conditions is depicted in Figure (the pH value changes were taken into consideration; Figure S3 in the Supporting Information). All four samples exhibited a characteristic three-phase release pattern: burst release, nonlinear monotonic release, and delayed release. The initial burst release occurred within the first 6 h, attributed to surface-adsorbed GA molecules that readily diffused into the release medium. During that phase, the 10% H-MSN-NH₂@GA/PCL film exhibited the highest release rate, reaching 60.63 ± 1.5%, while the other three groups showed approximately 45% release. This rapid initial release is attributed to the higher surface concentration of H-MSN-NH₂@GA in the 10% loading sample, where more GA-loaded nanoparticles were exposed on the nanofiber surface rather than embedded within the PCL matrix. This behavior may be beneficial for providing an immediate supply of nutrients for seed germination. Following this, the sustained diffusion phase showed a gradual decrease in the release rate, as GA diffused from the mesoporous structure of H-MSN-NH₂ within the nanofibers. Additionally, the lower pH conditions extended the release process, indicating a pH-responsive behavior where acidic environments slowed GA diffusion, potentially influencing nutrient bioavailability under different germination conditions. Finally, the release of GA from all nanofiber samples reached near completion, with the release profile stabilizing into a saturation plateau. These findings confirm this electrospun film system we designed could provide controlled, pH-responsive, and sustained GA release, ensuring both immediate and long-term nutrient availability to support seed germination and early seedling development. In respect to impact on seeds germination, the envisioned mechanism of action based on the three-phase release pattern involves the following. The initial burst release coincides with the imbibition phase, where seeds absorb water and activate their metabolic machinery. , This process leads to the generation of reactive oxygen species (ROS), which in excess can damage membranes and proteins. The early availability of GA helps neutralize ROS, protect cellular integrity, and promote uniform germination. , This burst is further facilitated by GA’s low molecular weight and high water solubility, which allow it to dissolve rapidly in the surrounding moist environment, making it accessible to germinating seeds. The subsequent sustained release phase provides ongoing antioxidant protection during the radicle protrusion and seedling establishment stages, when oxidative stress can still affect root elongation and early growth. Continuous GA delivery during this window supports redox homeostasis, cell division, and root development.

8.

GA release profile for the 1% and 10% H-MSN-NH₂@GA/PCL under pH 5 and 7 at different time intervals (the inset shows adjusted axis of the first 6 h).

Seed Germination

This measurement was conducted to evaluate the role of electrospun fiber substrates in supporting the germination of corn and bean seeds under dark conditions to simulate germinative conditions. Optical images of the complete germination process are presented in Figure S4, while only the 144 h images and seed germination parameters for corn and bean seeds are shown in Figure d. Based on the experimental findings, the germination process of corn and bean seeds began with water absorption between 0 and 48 h. During this period, the seeds absorbed water, which resulted in softening of the seed coat. This effect was particularly pronounced in bean seeds, which exhibited a noticeable increase in size due to swelling of the internal tissues. This suggested that the water uptake triggered metabolic activation within the seeds, initiating the physiological processes required for subsequent stages of development. , Radicle emergence was observed between 48 and 72 h, marking the transition from water absorption to active growth. According to the literature, during this period, enzymes were hydrated and activated, leading to increased metabolic activity to support seedling development. The radicles elongated progressively as continued water uptake and increasing turgor pressure within the cell walls facilitated cellular expansion and growth. By 144 h (Figure d), in the bean group, the plumule had emerged, and the cotyledons began to unfold. The cotyledon color transitioned from pale yellow to green, indicating the initiation of photosynthetic activity and suggesting that the seedlings were ready for transplantation into the soil for exposure to natural light. In the corn group, lateral seminal roots, mesocotyl elongation, and thicker coleoptiles were observed.

9.

Seed germination. (a) Corn and bean seeds on different electrospinning films at 72 h; (b) root length changes of corn seeds on different electrospun films within 96, 120, and 144 h; (c) root length changes of bean seeds on different electrospun films within 96, 120, and 144 h; and (d) optical images of corn and bean seeds, respectively, at 144 h.

The seed germination percentages, summarized in Figure a, showed no significant differences among the different treatments for corn seeds, indicating that all electrospun films provided a similarly supportive environment for germination. However, in the bean seed group, significant differences were observed. Although both low and high concentrations of H-MSN enhanced germination compared to the control, the high-concentration films exhibited reduced germination rates relative to the low-concentration films, suggesting that excessive H-MSN loading may adversely affect bean seed germination, potentially due to changes in film properties that influence water retention or nutrient availability. Meanwhile, films containing H-MSN-NH₂@GA exhibited higher germination rates, highlighting the beneficial effects of functionalization and controlled nutrient release in promoting seed growth.

Figure b shows the root length changes in corn at 96, 120, and 144 h. Error bars and significance indicators are shown. The absence of indicators denotes no statistically significant difference. By comparison of the 10% H-MSN-NH₂@GA/PCL group and the 10% H-MSN/PCL group, the data clearly indicate that a high concentration of GA inhibits corn seed growth. This trend is also supported by Figure S5a, where the free GA solution equivalent to the 10% GA release group significantly suppressed root length compared with the 1% GA equivalent group. In the case of bean seeds (Figure c), only the 10% H-MSN-NH₂@GA/PCL group had roots significantly longer than those of the negative control at 96 h. This may indicate that bean seedsduring their early water uptake phasebenefit from the initial burst release of GA. At later time points, no significant differences among groups were observed, indicating that the nanofiber films are overall nontoxic and ecofriendly.

In addition, Figure S5b shows a similar trend to Figure c. Both Figure S5a and b display more pronounced differences between treatment groups than their film counterparts (Figure b,c), suggesting that a sustained release from electrospun films is more effective than applying the full GA dose at the beginning. Moreover, based on the optical images shown in Figures d, S4, and S5, we observed that treatments with free GA solution led to seed cracking and rotting. This suggests that the PCL-based electrospun film provides a better-regulated water and gas exchange environment, reducing physiological stress and seed damage.

The observed effects of H-MSN/PCL- and H-MSN-NH₂@GA/PCL-electrospun fibers on seed germination and root elongation can be attributed to multiple biochemical mechanisms. Although many studies suggest that phenolic acid compounds can inhibit seed germination, , with some attributing this effect to the suppression of glycolysis and the oxidative pentose phosphate pathway, their role in mitigating biotic and abiotic stresses is also well documented. Under stress conditionssuch as cold, metal ion toxicity, and low temperature, ROS, including H₂O₂ and O₂ ^–, accumulate as toxic byproducts of aerobic metabolism. In such cases, the application of phenolic acids has been shown to alleviate stress-induced damage and promote plant growth. GA’s ability to modulate ROS levels under stress could be a key factor in promoting root development. However, the 10% H-MSN-NH₂@GA/PCL group exhibited a slight inhibitory effect on corn root length, suggesting that corn may be more sensitive to higher concentrations of GA.

Moving forward, this nanofiber-based platform could be further explored for the germination of rare or hard-to-germinate seeds, providing a controlled environment for their early development. Additionally, the targeted design of electrospun films, such as incorporating growth regulators, nutrients, or antimicrobial agents, could further enhance seedling survival and adaptation. Future research could also investigate the application of these nanofiber films for promoting seed germination under various stress conditions, including drought, salinity, and temperature fluctuations, expanding their potential in sustainable agriculture.

Conclusions

Hexagonal MSNs, H-MSNs, were successfully synthesized and incorporated into electrospun PCL fibers for seed germination applications. The nanoplatelets exhibited a hexagonal structure with a transverse diameter of 310 nm and a thickness of 80 nm. Functionalization with amine groups via AAPTS grafting enabled 32.3% GA loading in the pores. Electrospinning of these materials’ suspensions produced uniform, beading-free nanofiber films with high water vapor transmission rates. Seed germination studies showed that 10% H-MSN-NH₂@GA/PCL achieved 100% corn seed germination and a 70% higher germination rate for bean seeds compared to the control. Root length analysis revealed that H-MSN-NH₂@GA/PCL fibers promoted seedling growth, while high concentrations slightly inhibited corn root elongation. The developed H-MSN-NH₂@GA/PCL nanofiber films offer a platform for seed germination enhancement with potential applications for rare or hard-to-germinate seeds. Additionally, the targeted delivery of nutrients, bioactive compounds, or growth regulators through electrospun fibers could further improve seedling establishment under abiotic stress conditions, contributing to sustainable agricultural practices. Our study represents the first report of GA-loaded, amine-functionalized mesoporous silica nanoplatelets incorporated into electrospun PCL films for seed germination enhancement. This novel material system provides a platform for controlled antioxidant release within a biodegradable fiber matrix, demonstrating both biocompatibility and functionality in promoting seedling growth. We selected corn and bean as model species representing monocotyledonous and dicotyledonous plants seeds. These two species are also agronomically and economically important holding great nutritional value. Variability in seed coat morphology, metabolic pathways, and germination behavior across different plants may limit the generalizability of the findings. Future studies will aim to extend this study to a wider range of crops. It is also important to note that this study represents a proof of concept and was conducted entirely under controlled laboratory conditions; therefore, biodegradability of the composite films under real soil conditions will need to be evaluated in future work, as the incorporation of H-MSN-NH₂@GA nanoplatelets in PCL may alter its typical degradation profile. Alongside that, long-term storage stability of these films under variable environmental conditions, such as humidity, temperature fluctuations, various soil types, and microbial conditions, need to be further assessed, to understand the environmental fate of these films. These efforts will help guide the development of scalable, biodegradable, and crop-specific seed-support materials for sustainable agriculture.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsmaterialsau.5c00062.

• TEM/EDS H-MSN-NH₂ and H-MSN-NH₂@GA; N₂ adsorption–desorption data; Young’s modulus of different electrospinning film tensile test; calibration curves of GA; pH value change of nanopure water when different membranes were immersed in water during the 144 h time interval; photographs of corn and bean seed germination; and discussion of GA impact (PDF)

The authors declare no competing financial interest.