Electrically stimulated drug release using conductive GelMA/k-carrageenan/rGO blended hydrogel for enhanced biomedical applications

Abstract

Background

Hydrogels are hydrophilic polymers with high water content and a porous structure, making them suitable for incorporating water-soluble drugs and functioning as drug delivery systems. Their structural similarity to living tissues renders them valuable for applications in tissue engineering, pharmaceuticals, and medical treatments.

Objective

This study aimed to develop a blended hydrogel with improved mechanical strength and biocompatibility, and to enhance its drug release capabilities through electrical stimulation.

Method

A conductive hydrogel was synthesized by blending gelatin methacrylate (GelMA), kappa carrageenan (k-carrageenan), and reduced graphene oxide (rGO). The hydrogel's physical integrity, biocompatibility, and drug release performance under electrical stimulation were evaluated.

Results

The GelMA/k-carrageenan/rGO hydrogel retained its structural stability, demonstrated excellent biocompatibility, and effectively released drugs in response to electrical stimulation.

Conclusion

The developed conductive hydrogel presents strong potential for advanced drug delivery systems utilizing electrical stimulation, with promising implications across biomedical and pharmaceutical fields.

Keywords

blended hydrogel gelatin methacrylate kappa carrageenan reduced graphene oxide drug delivery system

Introduction

Recent research on drug delivery systems (DDS) using hydrogels has gained significant attention. DDS technology is designed to ensure the efficient delivery of therapeutic drugs to specific body parts, thereby minimizing side effects from excessive drug release and maximizing efficacy.¹ DDS can be categorized based on administration route, purpose, and material² and extensive studies on DDS using medical polymers are underway.^3,4 In such systems, drugs are encapsulated within polymer materials, which may include synthetic polymers, proteins, peptides, and hydrogels.⁵

Hydrogels, hydrophilic polymers capable of holding large amounts of water, form three-dimensional network structures through various physical or chemical cross-linking processes.⁶ They offer flexible properties, excellent biocompatibility, and the ability to expand and contract, facilitating the loading of water-soluble drugs.⁷ These characteristics have led to their use in various medical applications, including skin wound dressings,⁸ DDS,⁹ and soft contact lenses.¹⁰

Hydrogels can be classified into natural and synthetic polymers. Natural polymer-based hydrogels, such as collagen,¹¹ chitosan,¹² and kappa carrageenan (k-carrageenan), derived from natural resources, are valued for their excellent biocompatibility and moisture retention properties. Conversely, synthetic polymer-based hydrogels, such as gelatin methacrylate (GelMA),¹³ polyvinyl alcohol (PVA),¹⁴ polyacrylic acid (PAAc),¹⁵ and polyethylene glycol (PEG),¹⁶ are preferred for their superior mechanical properties.¹⁷

Despite their advantages, hydrogels face limitations in clinical applications due to their low mechanical strength, which makes them unsuitable for high-load applications.⁶ Additionally, their high water content and network structure complicate the control of drug release rates, presenting a challenge for their use.¹⁸ To address these issues, research has focused on blended hydrogels, which combine two types of hydrogels.¹⁹

For example, studies on protein delivery using GelMA and alginate hydrogels have shown that GelMA, a photopolymerizable synthetic polymer, cures upon light exposure. By adjusting the light exposure time, GelMA concentration, and photoinitiator, the mechanical properties of GelMA hydrogels can be tuned. This creates a double network through GelMA cross-linking via photoinitiators and alginate via calcium ions, allowing efficient delivery and release of human platelet lysate. While GelMA offers high mechanical strength, it has relatively lower biocompatibility compared to natural hydrogels. k-carrageenan, a natural hydrophilic polymer from red algae, forms a firm gel and is used in food texture modification.²⁰ Due to its excellent biocompatibility, k-carrageenan can be mixed with GelMA to optimize the composition, thus compensating for the low mechanical properties of traditional hydrogels while retaining superior biocompatibility. This combination creates a blended hydrogel that is both mechanically robust and highly biocompatible.

To impart electrical properties to hydrogels, various studies have incorporated conductive materials. Research using highly conductive silver nanowires has shown enhanced healing efficiency of hydrogels.²¹ This approach not only improves mechanical strength and healing efficiency but also enables real-time monitoring of wound healing via sensors. Reduced graphene oxide (rGO), known for its high conductivity, is primarily composed of carbon and offers exceptional electrical conductivity.²² This property allows for controlled opening and closing of the porous structure of hydrogels with small, harmless electrical stimuli, thereby enabling precise drug release regulation.²³

In this study, I developed a novel drug delivery system by blending GelMA, k-carrageenan, and rGO to overcome the limitations of traditional hydrogels. After synthesizing the synthetic polymer GelMA and the natural polymer k-carrageenan, the mixture was cross-linked using ultraviolet (UV) irradiation and calcium ions. The addition of rGO enabled the hydrogel to expand and contract in response to electrical stimuli, thus controlling the release of the encapsulated drug. This conductive GelMA/k-carrageenan/rGO blended hydrogel demonstrated excellent mechanical properties and high biocompatibility, highlighting its potential as an advanced medical polymer material.

Materials and methods

Fabrication of conductive GelMA/k-carrageenan/rGO blended hydrogel

One gram of k-carrageenan (ES Food, Korea) was dissolved in distilled water at 40 °C using a heated magnetic stirrer (MSH-20a, DAIHAN, Korea). The GelMA solution (3D Materials, Korea) was then mixed with the k-carrageenan solution. Finally, rGO (Graphene Supermarket, USA) was added to impart conductivity. The average granule size of the supplied rGO was approximately 3–10 mm, and it was ultrasonicated to ensure homogeneous dispersion. Photoinitiation was achieved by irradiating the mixture with UV light for 60 s, followed by immersion in a 1% calcium chloride solution for 5 min at room temperature to facilitate ionic cross-linking. To optimize the gelation ratio of k-carrageenan to GelMA, samples were prepared in the following ratios: 8:2, 6:4, 5:5, 4:6, and 2:8.

Analysis of conductive GelMA/k-carrageenan/rGO blended hydrogel

The structural properties of GelMA, k-carrageenan, rGO, and the conductive GelMA/k-carrageenan/rGO blended hydrogels were examined using a scanning electron microscope (JSM-7100f, JEOL, Tokyo, Japan). Elemental analysis was conducted using energy dispersive X-ray spectroscopy (EDS) to confirm the constituent elements. Additionally, the infrared spectra of GO and rGO were measured in the range of 600 to 4000 cm⁻¹ using a Fourier Transform Infrared Spectrometer (FT-IR, Vertex 80, MA, USA). The entire wavelength spectrum was recorded and Fourier-transformed to remove noise and obtain a clear spectrum.

Shape maintenance evaluation of conductive gelMA/k-carrageenan/rGO blended hydrogel

To assess the ability of the conductive GelMA/k-carrageenan/rGO blended hydrogel to maintain its shape over time, samples of GelMA, k-carrageenan, and the blended hydrogel were prepared in patch form, each with a diameter of 4 cm and a thickness of 0.3 cm. These patches were observed for size changes over 24, 48, and 72 h in an incubator set at 37 °C.

Biocompatibility evaluation of conductive GelMA/k-carrageenan/rGO blended hydrogel

To evaluate the biocompatibility of the conductive GelMA/k-carrageenan/rGO blended hydrogel, NIH-3T3 fibroblast cells were cultured in cell culture dishes with Dulbecco's modified Eagle's medium (DMEM, Thermo Fisher Scientific, Waltham, MA, USA). NIH-3T3 fibroblast cells at a concentration of 1 × 10⁶ cells/mL were placed in two six-well plates and incubated for one day. The hydrogel was immersed in one of the six-well plates and incubated for three days. Quantitative cell survival analysis was conducted using live/dead assay kits (Thermo Fisher, Waltham, MA, USA). After removing the hydrogel, the plates were washed with PBS, and a fresh culture medium containing live/dead assay kits was applied and incubated for an additional 30 min. Fluorescence images of live and dead cells were obtained using fluorescence microscopy (Olympus, Tokyo, Japan) and analyzed with ImageJ software (National Institutes of Health, Bethesda, MD, USA).

Evaluation of electrical properties of conductive GelMA/k-carrageenan/rGO blended hydrogel

To assess the electrical properties of the conductive GelMA/k-carrageenan/rGO blended hydrogel, a 1 V voltage was applied for 15, 30, and 60 min using a DC power supply (E36311A, Keysight, USA). Molecular diffusion from the hydrogel was evaluated by incorporating FITC-dextran (Sigma-Aldrich, USA) into the hydrogel, and fluorescence images were captured after 15, 30, and 60 min using a fluorescence microscope.

Results

GelMA hydrogel, which can be gelated by UV light, exhibits varying mechanical strength and swelling ratios depending on the photoinitiator concentration, UV light intensity, and exposure time. These properties can be manipulated to control drug release.²⁴ On the other hand, the gelation and physical properties of k-carrageenan are influenced by the type and concentration of salts such as K⁺, Ca²⁺, and Mg²⁺.²⁵ By blending structurally tunable GelMA with highly biocompatible k-carrageenan, I aimed to develop a novel hydrogel with enhanced mechanical properties and drug release functionality. To impart electrical responsiveness, rGO, known for its high conductivity, was incorporated into the hydrogel.²² The overall design and drug release mechanism of the conductive GelMA/k-carrageenan/rGO blended hydrogel are illustrated in Figure 1.

Figure 1.

A schematic diagram of the conductive GelMA/k-carrageenan/rGO blended hydrogel.

To determine the optimal blend ratio, hydrogels were prepared with different k-carrageenan to GelMA ratios (8:2, 6:4, 5:5, 4:6, and 2:8). Gelation was not observed at the 8:2 ratio, while all other compositions successfully formed stable gels (Figure 2(a), b). Among them, the 6:4 ratio demonstrated superior mechanical and adhesive properties, and was therefore selected as the optimal formulation for further analysis.²⁶

Figure 2.

Gelation analysis of the hydrogel based on the ratio of k-carrageenan to GelMA. (a) Images of gelated hydrogel at varying ratios of k-carrageenan and GelMA. (b) Table depicting the gelation results for different k-carrageenan and GelMA ratios.

In pH 7 or higher alkaline conditions, the keratin protein that makes up the skin's epidermis acquires a negative charge, facilitating water molecule penetration and moisture replenishment in the skin.²⁷ The conductive hydrogel exhibited a slightly alkaline pH of 7.29, which supports moisture retention and promotes skin recovery (Table 1). SEM analysis revealed porous structures in both GelMA and k-carrageenan hydrogels, which can facilitate drug loading and suggest potential applicability in drug delivery system.²⁸

Table 1.

pH values for k-carrageenan, GelMA, and the conductive GelMA/k-carrageenan/rGO blended hydrogel.

Components	pH
k-carrageenan	8.24
GelMA	6.30
GelMA/k-carrageenan	7.31
GelMA/ k-carrageenan/rGO	7.29
CaCl₂	7.68

Based on SEM images (Figure 3(a)), the estimated pore size ranged from approximately 30 to 150 µm, as inferred from the 100 µm scale bars. These pores are suitable for the encapsulation of small drug molecules and support efficient diffusion through the hydrogel matrix. Uniform dispersion of rGO throughout the hydrogel network was also observed, as shown in Figure 3(a). EDS mapping identified C, O, Na, and S elements, indicating compatibility with biological tissues (Figure 3(b)).

Figure 3.

SEM images of the individual components and the blended hydrogel. (a) Surface morphology of k-carrageenan, GelMA, reduced graphene oxide (rGO), and the conductive GelMA/k-carrageenan/rGO hydrogel. White scale bars represent 100 µm for k-carrageenan, GelMA, GelMA/k-carrageenan/rGO hydrogel, and 10 µm for rGO. (b) EDS elemental mapping of the blended hydrogel showing the distribution of C, O, Na, and S, confirming uniform composition and compatibility with biological tissues.

FT-IR analysis confirmed the reduction of GO to rGO by the disappearance of O–H and C–O peaks and recovery of C = C bonds, restoring electrical conductivity (Figure 4).

Figure 4.

FT-IR analysis graph comparing rGO and GO.

The shape retention of the blended GelMA/k-carrageenan/rGO hydrogel was evaluated at 37 °C over 72 h. It retained over 80% of its original shape, demonstrating stable dimensional integrity comparable to κ-carrageenan (Figure 5(a), b). This performance is primarily attributed to the dense crosslinked network formed by GelMA, which limits swelling and enhances mechanical robustness.²⁹ In addition, k-carrageenan contributes structural softness and matrix cohesion, while the incorporation of rGO imparts electroresponsiveness, allowing the hydrogel to respond to external electrical stimulation without compromising its structural integrity.

Figure 5.

Shape maintenance analysis of GelMA, k-carrageenan, and the conductive GelMA/k-carrageenan/rGO hydrogel. (a) Shape maintenance images of GelMA, k-carrageenan, and the conductive GelMA/k-carrageenan/rGO hydrogel on days 1, 2, and 3. (b) Quantitative analysis of the size of GelMA, k-carrageenan, and the GelMA/k-carrageenan/rGO hydrogel on days 1, 2, and 3.

Biocompatibility was assessed by culturing NIH-3T3 fibroblasts with the hydrogel. After three days, live/dead staining showed over 90% cell viability, confirming excellent cytocompatibility (Figure 6(a), b).

Figure 6.

Biocompatibility analysis of the conductive GelMA/k-carrageenan/rGO hydrogel. (a) Live (green) and dead (red) cell fluorescence images after 3 days of culturing NIH-3T3 fibroblast cells with the control and the conductive GelMA/k-carrageenan/rGO hydrogel. Bars represent 100 µm. (b) Quantitative analysis graph corresponding to the fluorescence images.

Electrical responsiveness was evaluated using FITC-dextran-loaded hydrogels. In the absence of electrical stimulation, no dye diffusion was observed. Upon application of 1 V for up to 60 min, significant dye release was detected, indicating expansion and contraction of the hydrogel in response to electrical input (Figure 7).

Figure 7.

Confirmation of drug release capability via electrical stimulation of the conductive GelMA/k-carrageenan/rGO hydrogel. (a) Fluorescent dye diffusion images from the hydrogel without electrical stimulation. (b) Fluorescent dye diffusion images from the hydrogel with applied electrical stimulation.

Discussion

The experimental results demonstrate the successful development of a conductive hydrogel with optimized composition for drug delivery applications. The combination of synthetic GelMA and natural k-carrageenan enabled the fabrication of a blended hydrogel that balances mechanical integrity and biocompatibility. GelMA provided structural robustness and controllable gelation through photoinitiation, while k-carrageenan contributed moisture retention and cytocompatibility, overcoming limitations of individual hydrogel systems. The selected 6:4 composition showed stable gelation and favorable handling properties for skin application. Furthermore, the slightly alkaline pH of the hydrogel supports its use in wound healing environments, where maintaining moisture and facilitating keratinocyte activity is crucial. Uniform rGO dispersion within the hydrogel matrix was critical for achieving electrical responsiveness. rGO is a well-known conductive material that enables the dynamic regulation of hydrogel porosity under mild voltages, offering a non-invasive method for stimulus-responsive drug release.²² FT-IR analysis confirmed the successful reduction of GO to rGO, which is essential for restoring the electrical conductivity necessary for electrical responsiveness. The porous microstructure observed via SEM, along with the elemental uniformity confirmed by EDS, supports the material's potential as a drug reservoir. The superior shape retention over time under physiological conditions further confirms the structural stability necessary for in vivo applications.³⁰ The improved dimensional stability of the conductive hydrogel is indicative of enhanced mechanical strength, which can be attributed to the denser network structure formed by GelMA. Although direct mechanical testing was not performed in this study, the observed dimensional stability and suppressed swelling behavior are widely accepted as indirect indicators of mechanical robustness in hydrogel systems. This interpretation is supported by previous studies, which reported that enhanced shape retention is closely associated with increased network density and improved mechanical integrity, especially in GelMA-based and double-network hydrogels.^29,31 Furthermore, the biocompatibility results showed no cytotoxic effect on NIH-3T3 fibroblasts, validating the suitability of the material for biomedical environments. Figure 6 shows that the conductive GelMA/k-carrageenan/rGO hydrogel supported high cell viability (>90%) after three days, confirming its excellent biocompatibility. This result reflects the combined effects of each component: GelMA promotes cell adhesion through its biomimetic structure, k-carrageenan contributes to moisture retention and mechanical softness, and rGO maintains compatibility when uniformly dispersed within the hydrogel network. The drug release experiment under electrical stimulation clearly demonstrated controlled diffusion behavior, establishing the feasibility of on-demand drug release triggered by external signals. Fluorescence intensity measurements (Figure 7) showed that the hydrogel under electrical stimulation (1 V) exhibited a rapid increase in FITC-dextran release, reaching near-maximum levels within 15 min and remaining stable up to 60 min. In contrast, the non-stimulated group displayed minimal diffusion during the same period. These findings confirm that electrical stimulation effectively promotes and sustains the release of encapsulated molecules. This behavior is attributed to transient structural changes in the hydrogel network under electrical stimulation, which temporarily increase porosity and facilitate the diffusion of encapsulated molecules. To ensure clinical applicability, electrical stimulation can be applied through wearable or implantable devices that deliver low-voltage (∼1 V) signals to the hydrogel. These systems, already used in pain modulation, provide a non-invasive and controllable platform for on-demand drug release, as demonstrated in recent hydrogel-based studies.³² Collectively, these findings indicate that the conductive GelMA/k-carrageenan/rGO hydrogel functions as an intelligent drug delivery platform, capable of electrically controlled release with potential applications in wound dressings, localized therapy, and tissue engineering.

Conclusions

In this study, a conductive GelMA/k-carrageenan/rGO blended hydrogel was prepared and evaluated for drug delivery applications. The optimized 6:4 ratio exhibited excellent gelation ability and shape retention, maintaining over 80% of its original shape after 72 h at 37 °C, which suggests improved mechanical performance. It also exhibited outstanding biocompatibility, with cell viability exceeding 90% after three days. The addition of rGO, known for its excellent conductivity, enabled drug release in response to mild electrical stimulation (1 V), and the system demonstrated repeatable, time-dependent diffusion behavior. Consequently, this conductive GelMA/k-carrageenan/rGO blended hydrogel not only imparts electrical properties but also functions as an actuator for drug delivery. This hydrogel demonstrates significant potential for applications in pharmaceuticals, medical fields, and tissue engineering.

Footnotes

Acknowledgments

This research was supported by the Yeungnam University College Research Grants in 2021. The author would like to thank the members of the Chemical Convergence Technology Laboratory (CCTL) for their technical support and insightful discussions.

ORCID iD

Jong Min Lee

Author contributions

Jong Min Lee performed all tasks related to this research, including study design, data acquisition, data analysis, and writing of the manuscript.

Funding

The author disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported by the Yeungnam University College Research Grants in 2021.

Declaration of conflicting interest

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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