Designing biopolymer microgels to encapsulate, protect and deliver bioactive components: Physicochemical aspects

Abstract

Biopolymer microgels have considerable potential for their ability to encapsulate, protect, and release bioactive components. Biopolymer microgels are small particles (typically 100nm to 1000μm) whose interior consists of a three-dimensional network of cross-linked biopolymer molecules that traps a considerable amount of solvent. This type of particle is also sometimes referred to as a nanogel, hydrogel bead, biopolymer particles, or microsphere. Biopolymer microgels are typically prepared using a two-step process involving particle formation and particle gelation. This article reviews the major constituents and fabrication methods that can be used to prepare microgels, highlighting their advantages and disadvantages. It then provides an overview of the most important characteristics of microgel particles (such as size, shape, structure, composition, and electrical properties), and describes how these parameters can be manipulated to control the physicochemical properties and functional attributes of microgel suspensions (such as appearance, stability, rheology, and release profiles). Finally, recent examples of the utilization of biopolymer microgels to encapsulate, protect, or release bioactive agents, such as pharmaceuticals, nutraceuticals, enzymes, flavors, and probiotics is given.

Biopolymer Microparticles Prepared by Microfluidics for Biomedical Applications

“…Many of these macromolecules are composed of repeat units that enable inter/intramolecular interactions, leading to the formation of higher order structures . Typically, an aqueous phase of biopolymer solution containing biomolecules or cells is emulsified into an oil phase, and then the biopolymer emulsion droplets are ultimately crosslinked upon the change of environmental conditions (e.g., temperature) or the addition of crosslinking agent (e.g., multivalent ions and chemical crosslinker) . In particular, the high content of functional groups in biopolymers, such as amine groups in chitosan and carboxylic acid groups in alginate, can be used for crosslinking of biopolymer to fabricate functional MPs with tunable mechanical properties .…”

“…The functional performance of biopolymer MPs depends on the composition, concentration, and bulk properties of biopolymers. [32] To obtain the desired functional attributes from microfluidically prepared biopolymer MPs, the physicochemical properties of biopolymers in droplets, such as their solubility and charge, as well as the specific properties necessary the resulting biopolymer MPs, such as their size, structure, stability, and Small 2020, 16,1903736 stimuli-responsive property, should be considered. The physicochemical properties and structural characteristics of biopolymers are discussed in more detail in Sections 3, 4, 5.…”

“…Several crosslinking approaches have been developed for different biopolymers to produce hydrogel MPs from emulsion droplets (Figure 5), [44] since biopolymers possess insufficient mechanical properties and stability in physiological Small 2020, 16,1903736 Figure 2. Drop generation in a microfluidic device.…”

“…Similarly, the tail-shaped ampicillin-loaded Ca-alginate MPs exhibited a higher drug release rate than the spherical MPs. [62] Small 2020, 16,1903736 Alginate MPs composed of d-mannuronic acid and l-guluronic acid residues with the pKa values of 3.6 and 3.7, respectively, can be used for pH-responsive drug delivery. [63] At a pH value higher than the pKa values of the residues, the carboxylic acid groups of alginate become ionized, leading to the swelling of alginate MPs due to increased osmotic pressure within the MPs.…”

Reactive Precursor Particles as Synthetic Platform for the Generation of Functional Nanoparticles, Nanogels, and Microgels

“…Nanoparticles are a cornerstone of modern nanotechnology. Especially crosslinked polymer nanoparticles (e.g., nanogels, microgels, and crosslinked micelles) offer high structural stability and dynamic functionalities that enable advanced applications such as delivery of drugs and bioactive agents, chemical sensing, and catalysis . A key requirement in tailoring the colloidal properties to such desired macroscopic functions is the adjustment of the particles' internal functionality, i.e., the introduction of functional groups into the polymer chains that build the 3D network.…”