Synthesis and Characterization of Hydroxyethyl Chitosan as a Functional Pharmaceutical Excipient

Abstract

This study aims to develop an excellent pharmaceutical excipient based on crosslinked hydroxyethyl chitosan (G-HECTS(GA)), designed to exhibit high intrinsic viscosity and superior moisture absorption and retention properties for wound healing applications. Hydroxyethyl chitosan (HECTS) was synthesized from chitosan through a derivatization reaction with bromoethanol under alkaline conditions, achieving a maximum solubility of 6.8 ± 0.2 g/100 g water. The HECTS was further crosslinked with glutaraldehyde (GA) to produce G-HECTS(GA). Structural characterization of the product was performed using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Key parameters, including crosslinker dosage, reaction time, temperature, and stirring speed, were optimized to evaluate their effects on intrinsic viscosity. The physicochemical properties and wound healing efficacy of G-HECTS(GA) were systematically assessed in a rat wound model. Under optimal conditions (35°C, 25 μL GA, 18 h reaction time), the crosslinked product demonstrated an intrinsic viscosity of 1870 ± 70 mL/g, a moisture retention rate of 39% ± 3%, and a moisture absorption rate of 39.1% ± 0.7%. G-HECTS(GA) rapidly formed a stable film on wound surfaces, effectively absorbing exudates and promoting wound healing. The material exhibited excellent stability, biocompatibility, and antibacterial activity, along with significant anti-inflammatory effects. These properties highlight the potential of G-HECTS(GA) as a high-performance pharmaceutical excipient for hemostatic spray formulations, offering a promising solution for mucosal wound repair and related biomedical applications.

Highlights

Chitosan was hydroxyethylated to improve its water solubility.

Crosslinked derivative exhibited high moisture absorption/retention properties.

Crosslinked derivative showed strong antimicrobial activity and biocompatibility.

Crosslinked derivative promoted wound healing and anti-inflammatory effects.

Introduction

Epistaxis, commonly known as nosebleed, refers to active bleeding from the nasal mucosa and is a common and frequently occurring condition in otorhinolaryngology[1], [2].Although the severity and duration of most cases of epistaxis are limited, its high incidence (with at least 60% of Americans having experienced a nosebleed) and occasional mortality—particularly in patients with coagulopathy where bleeding is uncontrollable—have made epistaxis a research hotspot in hemostasis[3], [4], [5].

Traditional nasal packing materials, exemplified by petroleum gauze, are cost-effective and exhibit good hemostatic effects. However, petroleum gauze is non-biodegradable within the nasal cavity, and its removal after drying can cause significant discomfort to patients. Moreover, petroleum gauze has poor biocompatibility, which may lead to severe mucosal infections and allergic reactions[6]. PVA-based hemostatic sponges[7] (e.g., Mondocel Standard by Mondomed NV), Merocel® (primarily composed of hydroxyethyl polyvinyl acetate), and Rapid Rhino® [8] (cellulose-based) rapidly expand to fill the nasal cavity, absorb blood, and concentrate blood cells to achieve hemostasis. However, since these materials are non-degradable and cannot be absorbed in the nasal cavity, they are difficult to remove in a single procedure, often damaging the mucosa and causing secondary bleeding[9]. Therefore, there is an urgent need for a novel formulation to replace traditional nasal packing materials.

An ideal medicinal dressing should possess several key characteristics: it should effectively adhere to the wound surface to protect the injury, absorb exudates, maintain a moist environment, and promote wound healing, while also exhibiting excellent biocompatibility and antibacterial activity[10].

Chitosan (CS) is a polysaccharide obtained through the deacetylation of chitin, and it is widely found in lower plants, fungi, shrimp, crabs, insects, and the exoskeletons of other crustaceans[11]. Its molecular structure is composed of alternating units of glucosamine and N-acetylglucosamine, linked by β-(1→4) glycosidic bonds[12]. Chitosan is widely used in wound healing[13], [14], [15] and is considered a promising biomolecule due to its excellent adhesiveness[16], good biocompatibility[17], inherent antibacterial activity[18], and abundant availability, making it ideally suited for use in medicinal dressings.

A spray is a product that delivers a liquid formulation to a target area via atomization, offering the advantages of ease of use and rapid application. Because it can rapidly and evenly cover a wound, a spray is particularly suitable for treating irregularly shaped injuries and helps avoid the discomfort associated with direct contact[19]. Based on this characteristic, we plan to use chitosan as an excipient to develop a novel hemostatic spray formulation.
However, due to strong intermolecular hydrogen bonding, chitosan exhibits low solubility under neutral conditions and dissolves only in acidic solutions, which limits its effectiveness in certain applications, particularly in spray formulations[20], [21], [22]. To overcome this limitation, researchers have developed various modification methods. Hydroxyethylation is a commonly used technique that enhances polymer solubility and is widely applied in the modification of cellulose and chitosan[23], [24], [25], [26], [27], [28]. Hydroxyethyl chitosan (HECTS) derivatives exhibit improved water solubility, thereby expanding the application potential of chitosan.

However, despite its improved solubility, hydroxyethyl chitosan solutions have low viscosity and are unable to form a sufficiently robust film on the wound surface. Therefore, increasing the viscosity of hydroxyethyl chitosan solutions is critical to enhancing their efficacy in wound treatment. Increasing the molecular weight can effectively enhance the intrinsic viscosity of chitosan solutions[29], and crosslinking is one of the effective approaches to achieve this. Glutaraldehyde, a commonly used chitosan crosslinker[30], [31], offers advantages such as low cost and high reactivity. It reacts with the amino groups in chitosan molecules to form crosslinked structures[32], thereby significantly increasing the viscosity of hydroxyethyl chitosan.

In summary, this study derivatized chitosan using a hydroxyethylation reagent to obtain hydroxyethyl chitosan (HECTS) with enhanced solubility. Subsequently, these derivatives were crosslinked with glutaraldehyde (GA) to produce a crosslinked hydroxyethyl chitosan product (G-HECTS (GA)). The characteristics of G-HECTS(GA), including intrinsic viscosity, moisture absorption and retention capacity, stability, biocompatibility, and antibacterial properties, were systematically evaluated. The powder product was dissolved in water to prepare a solution, which was then sprayed onto a rat wound model to assess its wound healing and anti-inflammatory effects. The results demonstrated that crosslinked hydroxyethyl chitosan exhibited high intrinsic viscosity and excellent moisture absorption and retention capacity. It formed a thin film on the wound surface, providing a protective barrier and absorbing wound exudates. Moreover, it retained the superior biocompatibility and antibacterial properties of chitosan while significantly promoting wound healing. These characteristics provide a solid foundation for the subsequent development of a hwound healing spray formulation that uses crosslinked hydroxyethyl chitosan as a pharmaceutical excipient.

Materials

Chitosan (MW = 8.0 × 104, degree of deacetylation = 87%) was purchased from Jining Haidebei Biotechnology Co., Ltd. Bromoethanol (≥96%) and isopropanol (≥99.7%) were purchased from Macklin Biochemical Technology Co., Ltd., Shanghai. Acetone (≥99.5%), hydrochloric acid (36-38%), and silver nitrate (≥99.8%) were obtained from Sinopharm Chemical Reagent Co., Ltd. Sodium hydroxide (≥97%) was obtained from Aladdin Biochemical Technology Co., Ltd., Shanghai. Absolute ethanol (95%), polyethylene glycol.

Yu Yi, Qingying Chen, Ye Zhou, Jianfeng Mei, Yanlu Zhang, Bailong Wang, Guoqing Ying, Synthesis and Characterization of Hydroxyethyl Chitosan as a Functional Pharmaceutical Excipient, Carbohydrate Research, 2025, 109479, ISSN 0008-6215, https://doi.org/10.1016/j.carres.2025.109479.