Novel pH-sensitive microgels prepared using salt bridge

Thermo-sensitive self-assembly of poly(ethylene imine)/(phenylthio) acetic acid ion pair in surfactant solutions

Poly(ethylene imine)/(phenylthio) acetic acid (PEI/PTA) ion pairs exhibited an upper critical solution temperature (UCST) behavior in an aqueous solution and the UCST was higher as the PTA content was more. The UCST of the ion pair decreased with increasing Brij S100 (BS 100, a nonionic surfactant) concentration but increased with increasing cetylpridinium chloride (CPC, a cationic surfactant) and sodium lauroylsarcosinate (SLS, an anionic surfactant) concentration. TEM microscopy demonstrated BS 100 markedly reduced the size of PEI/PTA ion pair self-assembly (IPSAM) whereas CPC and SLS had little effect on the size and the integrity of IPSAM. ¹H NMR spectroscopy showed the hydrophobic interaction among the phenyl groups of PEI/PTA ion pairs took place. It also demonstrated the hydrophobic interaction between BS 100 and PTA and the electrostatic interaction between CPC and PTA and between SLS and PEI occurred. X-ray photoelectron spectroscopy disclosed the PTA of PEI/PTA IPSAM could be readily oxidized by H₂O₂ even at a low concentration (e.g. 0.005%). IPSAM released its payload (i.e. nile red) in a temperature and oxidation-responsive manner. The surfactants (i.e. BS 100, CPC, and SLS) suppressed the thermally triggered release in a different way. The effectiveness of the surfactant to suppress the release was in the order of BS 100 > CPC > SLS. IPSAM released its content more extensively as H₂O₂ (an oxidizing agent) concentration was higher. The ionic surfactants (i.e. CPS and SLS) had little effect on the oxidation-induced release degree but the nonionic surfactant (BS 100) markedly suppressed the release degree.

Droplet-Assisted Microfluidic Fabrication and Characterization of Multifunctional Polysaccharide Microgels Formed by Multicomponent Reactions

Polysaccharide-based microgels have broad applications in multi-parametric cell cultures, cell-free biotechnology, and drug delivery. Multicomponent reactions like the Passerini three-component and the Ugi four-component reaction are shown in here to be versatile platforms for fabricating these polysaccharide microgels by droplet microfluidics with a narrow size distribution. While conventional microgel formation requires pre-modification of hydrogel building blocks to introduce certain functionality, in multicomponent reactions one building block can be simply exchanged by another to introduce and extend functionality in a library-like fashion. Beyond synthesizing a range of polysaccharide-based microgels utilizing hyaluronic acid, alginate and chitosan, exemplary in-depth analysis of hyaluronic acid-based Ugi four-component gels is conducted by colloidal probe atomic force microscopy, confocal Brillouin microscopy, quantitative phase imaging, and fluorescence correlation spectroscopy to elucidate the capability of microfluidic multicomponent reactions for forming defined polysaccharide microgel networks. Particularly, the impact of crosslinker amount and length is studied. A higher network density leads to higher Young's moduli accompanied by smaller pore sizes with lower diffusion coefficients of tracer molecules in the highly homogeneous network, and vice versa. Moreover, tailored building blocks allow for crosslinking the microgels and incorporating functional groups at the same time as demonstrated for biotin-functionalized, chitosan-based microgels formed by Ugi four-component reaction. To these microgels, streptavidin-labeled enzymes are easily conjugated as shown for horseradish peroxidase (HRP), which retains its activity inside the microgels.

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

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.

Crosslinked ionic polysaccharides for stimuli-sensitive drug delivery

Polysaccharides are gaining increasing attention as components of stimuli-responsive drug delivery systems, particularly since they can be obtained in a well characterized and reproducible way from the natural sources. Ionic polysaccharides can be readily crosslinked to render hydrogel networks sensitive to a variety of internal and external variables, and thus suitable for switching drug release on-off through diverse mechanisms. Hybrids, composites and grafted polymers can reinforce the responsiveness and widen the range of stimuli to which polysaccharide-based systems can respond. This review analyzes the state of the art of crosslinked ionic polysaccharides as components of delivery systems that can regulate drug release as a function of changes in pH, ion nature and concentration, electric and magnetic field intensity, light wavelength, temperature, redox potential, and certain molecules (enzymes, illness markers, and so on). Examples of specific applications are provided. The information compiled demonstrates that crosslinked networks of ionic polysaccharides are suitable building blocks for developing advanced externally activated and feed-back modulated drug delivery systems.