Advances in Hydrophilic Drug Delivery: Encapsulation of Biotin in Alginate Microparticles

Abstract

Background: The encapsulation of hydrophilic drugs within microparticles has gained significant interest in drug delivery systems due to their potential to improve stability, bioavailability, and controlled release of therapeutic agents. Biotin, a water-soluble vitamin, presents challenges such as rapid degradation and limited membrane permeability, which constrain its therapeutic effectiveness.

Objectives: This study aims to develop and characterize biotin-loaded microparticles formulated with alginate, Eudragit^® E100, and CaCl₂, and to evaluate their characterization and potential applications.

Methods: The microparticles were produced using the external ionic gelation method, where alginate and CaCl₂ solutions were mixed under probe sonication. Eudragit^® E100 was added as a complexing agent. The optimized formulation was used to encapsulate biotin, and various experimental variables were screened to study their influence on the properties of the microparticles.

Results: Biotin was encapsulated in alginate microparticles (size: 634 nm; polydispersity index: 0.26; zeta potential: −45 mV) with an encapsulation efficiency of 90.5%. In vitro release studies using vertical diffusion Franz cells demonstrated a controlled release profile following the Weibull kinetic model.

Conclusions: Encapsulation techniques offer a promising approach to overcome the limitations of hydrophilic drug delivery. The biotin-loaded microparticles developed in this study have potential applications in both topical and oral formulations, providing controlled release and improved therapeutic efficacy, and illustrate the broader applicability of polymeric encapsulation systems for improving the delivery of labile, hydrophilic bioactives.

Introduction

The development of effective delivery strategies for hydrophilic drugs has emerged as a critical area of pharmaceutical research, driven by the increasing interest in both macromolecular therapeutics—such as nucleic acids, peptides, and proteins—and small hydrophilic molecules for the treatment of cancer, infectious, and inflammatory diseases [1]. Despite their therapeutic potential, hydrophilic drugs frequently suffer from limited membrane permeability, rapid degradation, and short half-lives, which hinder their clinical efficacy and bioavailability [2,3].

Microencapsulation presents a highly effective strategy to overcome these limitations by enhancing the delivery of hydrophilic compounds such as biotin. Microparticles (MPs)—spherical structures typically ranging from 1 to 1000 µm in diameter—can protect sensitive bioactives from adverse environmental conditions (e.g., pH fluctuations, oxidation, temperature), enhance chemical and enzymatic stability, and allow for controlled and targeted release. These polymeric delivery systems can be incorporated into a wide array of pharmaceutical dosage forms, including solids (e.g., tablets, capsules), semisolids (e.g., gels, creams), and liquids (e.g., suspensions), making them highly adaptable to different therapeutic needs [2].

Biotin, also known as vitamin B7 [4], is a water-soluble compound that functions as a cofactor in various metabolic pathways, essential for maintaining healthy skin, hair, and nails, as well as promoting cellular growth and division [5,6]. Chemically identified as cis-hexahydro-2-oxo-1H-thieno [3,4-d] imidazole-4-pentanoic acid, biotin consists of two heterocyclic rings (Figure 1) [7]. With a pKa of 4.5, the vitamin remains stable between pH 4 and 9 and is insoluble in organic solvents, with limited water solubility (20 mg/100 mL) [8]. Since mammals are unable to synthesize biotin endogenously and rely on dietary intake and bacterial biosynthesis in the gut to meet their needs, effective supplementation methods are essential [8,9,10]. The physiological importance of biotin is primarily highlighted by the pathological effects that occur with its deficiency, which can lead to a variety of symptoms affecting the nervous system, skin, and respiratory system [6,10]. However, its hydrophilic nature poses delivery challenges, where precise dosing and controlled release are paramount for maximizing efficacy while minimizing side effects [11,12,13].

This study presents the innovative fabrication of alginate–Eudragit® E100 microparticles for the encapsulation of biotin using the external ionic gelation technique [14]. Alginate, a naturally derived anionic polymer obtained from brown algae consisting of α-L-guluronic acid and β-D-mannuronic acid residues linearly linked by 1,4-glycosidic bonds (Figure 2A), is widely recognized for its biocompatibility, biodegradability, mucoadhesiveness, and non-immunogenicity, making it a suitable candidate for biomedical and pharmaceutical applications [15]. Alginates exhibit significant variability in composition and sequence; the specific alginate used in this study had a molecular weight of 200 kDa [14,16]. Moreover, alginate’s compatibility with other polymers, ease of formulation, and cost-effectiveness make it an ideal material for developing both topical and oral drug delivery systems [17].

A key advantage of alginate is its ability to undergo gelation under mild conditions in the presence of divalent cations—such as calcium (Ca2+)—avoiding the use of harsh solvents or high temperatures, thus preserving the integrity of sensitive bioactives like biotin (Figure 3) [14,15]. In this study, CaCl2 was selected as the cross-linking agent due to its high aqueous solubility and ability to diffuse efficiently into the alginate matrix, promoting the formation of a stable hydrogel network [16].

Alginate-based microparticles have been extensively studied for the encapsulation of hydrophilic drugs due to their protective and release-modulating properties. Previous research has demonstrated their effectiveness in the delivery of compounds such as insulin, vitamin C, and antibiotics, in both oral and topical formulations [18,19,20]. However, the application of alginate-based systems for biotin delivery remains relatively unexplored, and studies evaluating its combination with cationic polymers such as Eudragit® E100 are currently lacking. This highlights the need for novel delivery platforms capable of improving the stability and bioavailability of biotin under physiological conditions.
To enhance the structural and functional properties of the microparticles, Eudragit® E100 was incorporated as a cationic complexing agent. This copolymer—composed of dimethylaminoethyl methacrylate, butyl methacrylate, and methyl methacrylate—is widely recognized for its stability, biocompatibility, and high skin tolerance (Figure 2B). It is used extensively in pharmaceutical formulations, including use as an excipient in solid dosage forms (to mask flavors and odors and provide moisture protection), as a coating agent, and for controlling drug release in various formulations [21]. Its electrostatic interaction with the negatively charged glucuronic acid residues of alginate reinforces the polymeric matrix, leading to the formation of more stable and robust microparticles [22]. This interaction enhances mechanical strength and encapsulation efficiency, introducing a novel strategy beyond conventional alginate–calcium systems, which are more susceptible to ionic exchange and environmental instability. In contrast, the complexation with Eudragit® E100 provides enhanced structural integrity, pH responsiveness, and potential for more precise control over the release profile of the encapsulated agents. Accordingly, microparticles have been identified as an effective strategy for the delivery of hydrophilic substances. In recent years, statistical designs have seen widespread application in the investigation of pharmaceutical processes and formulations, enabling researchers to assess the influence of process parameters or compositional variables on final product characteristics. Typically, factorial or response surface designs serve as initial approaches in experimental design, allowing systematic variation of factors at multiple levels. The goal was to obtain a formulation with the optimal ratio of these polymers (alginate and Eudragit® E100), designed as a versatile platform for the encapsulation of hydrophilic compounds, with biotin selected as a model compound for proof-of-concept studies and system characterization, with the optimization process guided by a design of experiment [23,24,25].

By combining the complementary properties of alginate and Eudragit® E100, the proposed microparticulate system enables efficient biotin encapsulation, offering protection against degradation and supporting controlled release. This novel delivery approach holds promise for improving the therapeutic efficacy of hydrophilic vitamins and can be adapted for a wide range of pharmaceutical and nutraceutical applications.

Although biotin conjugates with alginate have previously been explored for biosensor construction [11], to the best of our knowledge, this is the first report of biotin encapsulation in alginate-based microparticles for controlled drug delivery applications. This work aims to address the need for more stable and bioavailable formulations of biotin, a clinically relevant vitamin involved in metabolic, dermatological, and neurological processes. The development of microparticles for the protection of the model compound biotin, illustrating the capacity of the platform to enhance stability and control the release of hydrophilic molecules, could offer new therapeutic opportunities, particularly for populations with absorption issues or increased vitamin requirements. Beyond biotin, this strategy could serve as a versatile platform for enhancing the delivery of other labile or poorly absorbed hydrophilic compounds, particularly in formulations where stability and targeted release are essential.

Download the full article as PDF here Advances in Hydrophilic Drug Delivery

or read it here

Materials

Sodium alginate (MW (g/mol) > 200,000, Carbo Erba Reagents, Val de Reuil Cedex, France), Basic Butylated Methacrylate Copolymer (Eudragit® E100) (Evonik, Darmstadt, Germany), calcium chloride dihydrate (Scharlab, S.L., Sentmenat, Spain) and purified water (in house) were used to prepare microparticles. Biotin (Kingland Trading Company, Iowa, IA, USA) was the active ingredient used to formulate the MP. Sodium perchloride monohydrate (Scharlab, S.L., Sentmenat, Spain), phosphoric acid (Scharlab, S.L., Sentmenat, Spain), and acetonitrile (Scharlab, S.L., Sentmenat, Spain) were used to perform the different analyses.

Naveira-Souto, I.; Rosell-Vives, E.; Pena-Rodríguez, E.; Fernandez-Campos, F.; Lajarin-Reinares, M. Advances in Hydrophilic Drug Delivery: Encapsulation of Biotin in Alginate Microparticles. Pharmaceutics 2025, 17, 1117. https://doi.org/10.3390/pharmaceutics17091117

Read also our introduction article on Alginates here: