Abstract
Bio-based polymeric stimuli-responsive materials have attracted increasing interest, especially in the pharmacological and nutraceutical fields. These materials mainly consist of macromolecules capable of conformational and chemical changes in response to external signals. One active molecule mostly used in bio-related areas is lactoferrin (Lf), which is attracting attention due to its beneficial effects (antimicrobial, anti-inflammatory, and anti-carcinogenic) on the human body. Since pH or temperature in the human body can promote Lf degradation, encapsulation in a suitable system is required. A valid solution is to encapsulate the Lf in a polysaccharidic matrix such as alginate (ALG) thanks to its biocompatibility and easy gelation with bivalent cations. This work aims to encapsulate iron-depleted Lf in alginate gel microspheres for stability improvement by ionic cross-linking with Ca2+ ions. The obtained particles were characterized in terms of structure, thermal stability, and morphology, and their swelling capability was determined. Release studies were carried out on the freeze-dried particles to investigate the effect of neutral pH 7 and acidic pH 5. At last, the optimization of the loaded system was completed by developing a mathematical model able to predict the swelling behavior of the carrier particle and the subsequent Lf kinetic release over time.
1. Introduction
Stimuli-responsive polymeric materials are in high demand in biomedical applications, pharmacology, and tissue engineering. External stimuli from the surrounding physiological environment (e.g., pH, light, temperature) can trigger chemical and/or conformational changes in the material. Subsequently, the release of encapsulated cargoes can be promoted [1,2]. One of the active molecules considered to be of great interest is lactoferrin (Lf) due to its attractive health benefits (i.e., antimicrobial, anti-inflammatory, immunomodulatory, and anti-carcinogenic effects) for humans and animals [3], which are attributed to its highly cationic nature [4]. Lf is a glycoprotein (MW ~ 80 kDa) able to bind to iron with high affinity [5], and for this, it exists in different forms: iron-depleted (apo-), iron-saturated (holo-), or as a mixture of apo- and holo-Lf (native). Lf plays an important role in the first line of the human defense system against microbial infections through two different mechanisms: bacteriostatic and bactericidal effects. In particular, the iron-depleted (apo-) form is considered responsible for the bacteriostatic effect in which bacteria are deprived of the iron necessary for cell growth [6], while the bactericidal effect is a type of membrane-mediated activity of negatively charged Lf that leads to cell death [7].
The use of this protein in industrial applications is limited due to the easy denaturation that would occur under processing conditions, including production, preservation, storage, and transportation [8]. Previous research has shown that even oral administration of Lf leads to reduced effects due to its breakdown under gastric conditions [9]. A valid strategy for optimizing the stability and safe delivery of Lf is encapsulating it into a biocompatible and stable matrix. For this purpose, alginate has been widely used for the encapsulation of Lf [10,11], and more generally, for the encapsulation of active molecules in drug delivery applications. Some existing methods for generating charged microparticles use complex techniques: lithography [12], bioprinting [13], or microfluidics [14]. The use of alginate makes the encapsulation process extremely simple thanks to its unique gelling properties in the presence of bivalent cations (e.g., Ca2+) [15]. This technique is useful for the encapsulation of heat-labile active agents as it does not require high temperatures. Sodium alginate is a natural polysaccharide extracted from brown algae (Phaeophyceae), and it is composed of sequences of β-D-mannuronic acid (M) and α-L-guluronic acid (G) residues of widely varying compositions and sequences. Carboxyl groups endow alginate with a high affinity for divalent and trivalent ions and cationic protein molecules [16]. Since Lf is a protein with positively charged regions, most evidently at the N-terminus, electrostatic interactions occurring with alginate ensure a higher stability of trapped proteins within the alginate gel matrix and minimize loss by diffusion [17,18]. Hence, a prolonged and controlled release of the protein from alginate particles can be allowed [19]. Alginate shows pH-responsive swelling behavior, and particles are used to control release in the oral delivery of drugs and proteins [20,21].
In this work, the release behavior of Lf-loaded alginate microparticles was investigated, exploring the effect of different surrounding pHs. The iron-depleted Lf form was chosen due to its interesting bactericidal effect. Furthermore, ad hoc-formulated mathematical models describing the swelling behavior and release kinetics of active ingredients from loaded systems were used to support the optimization of the release system. The created models will be based on systems of ordinary differential equations and adapted to different sets of experiments [22]. The novelty of this work is the development of a mathematical model that describes and can predict the phenomenon of the release of an active ingredient from charged microparticles in a very accurate and realistic way. The mathematical models currently present in the literature mainly describe phenomena of the adsorption of molecules from liquid or gas, glossing over those of release. These models consider only two phases (solid and liquid) and simple steps of capture (for adsorption) or release. Furthermore, they are empirical models that are based on the Lagergreen pseudo-first-order or pseudo-second-order model (which are all modifications of the model developed by Irving Langmuir for adsorption) [23,24].
Download the full article as PDF here:
Encapsulation of Lactoferrin in Calcium-Alginate Microparticles and Its Release Therefrom Under Neutral and Mild Acidic Conditions Synthesis, Characterization and Mathematical Modeling
or read it here
Paduano, T.; Zuppolini, S.; Vitiello, R.; Zarrelli, M.; Tesser, R.; Borriello, A. Encapsulation of Lactoferrin in Calcium-Alginate Microparticles and Its Release Therefrom Under Neutral and Mild Acidic Conditions: Synthesis, Characterization and Mathematical Modeling. Gels 2025, 11, 116.
https://doi.org/10.3390/gels11020116
