Synthesis of Polyphosphate-Loaded Nanoparticles Using Inverse Miniemulsion Polymerization for Sustained Delivery to the Gastrointestinal Tract

Characterizing the Molecular Architecture of Hydrogels and Crosslinked Polymer Networks beyond Flory-Rehner. II: Experiments

We previously [Borges, F. T. P. Biomacromolecules 2020, 21(12), 5104-5118] introduced a novel methodology for the characterization of the dimensions and architecture of hydrogel networks that provides more detailed information than the classical Flory-Rehner theory [Canal, T.; Peppas, N. A. J. Biomed. Mater. Res. 1989, 23, 1183-1193]. In this article, we illustrate our methodology by applying it to the phototerpolymerization of N-vinyl-2-pyrrolidone (NVP), ethylene glycol methyl ether acrylate (EGA), and poly(ethylene glycol) diacrylate (PEGDA). The experimental design includes 120 formulations using different fractions of the three monomers. Experimental measurements determined the mass swelling ratio and were coupled with theory to compute the internal dimensions of the network. Results demonstrate how the use of a macromeric crosslinker leads to unique network architectures not predicted by classical F-R theory, e.g., the figure shows that the mass between crosslinks predicted by F-R is actually distributed between branches and the backbone. The methodology presented offers a path toward optimizing/customizing hydrogel properties to suit the size and shape of the specific therapeutic targeted for drug delivery.

Nanoemulsions for synthesis of biomedical nanocarriers

Nanoemulsions are kinetically stabilized emulsions with droplet sizes in the nanometer scale. These nanodroplets are able to confine spaces in which reactions of polymerization or precipitation can take place, leading to the formation of particles and capsules that can act as nanocarriers for biomedical applications. This review discusses the different possibilities of using nanoemulsions for preparing biomedical nanocarriers. According to the chemical nature, nanocarriers prepared in nanoemulsions are classified in polymeric, inorganic, or hybrid. The main synthetic strategies for each type are revised, including miniemulsion polymerization, nanoemulsion-solvent evaporation, spontaneous emulsification, sol-gel processes, and combination of different techniques to form multicomponent materials.

Characterizing the Molecular Architecture of Hydrogels and Crosslinked Polymer Networks beyond Flory-Rehner-I. Theory

In the early 1940s, Paul Flory and John Rehner published a series of papers on the properties of swellable polymeric networks. Originally intended for vulcanized rubber, their development has since been extensively used and extended to much more complex systems, such as hydrogels, and used to estimate the mesh size of such networks. In this article, we take a look at the development of the Flory-Rehner equation and highlight several issues that arise when using such a theory for the described hydrogel networks. We then propose a new approach and equations to accurately calculate the backbone molecular weight in-between crosslinks while explicitly accounting for the molecular mass of the crosslinker and branch segments. The approach also provides more applicable mesh dimensions, for complex networks with macromeric crosslinkers and/or a high degree of branching, as is the case of biocompatible hydrogels. The approach is finally illustrated by a case study comparing the values obtained with our proposed approach to those using the state-of-the-art approach.

An in vitro tissue model for screening sustained release of phosphate-based therapeutic attenuation of pathogen-induced proteolytic matrix degradation

Tissue response to intestinal injury or disease releases pro-inflammatory host stress signals triggering microbial shift to pathogenic phenotypes. One such phenotype is increased protease production resulting in collagen degradation and activation of host matrix metalloproteinases contributing to tissue breakdown. We have shown that surgical injury depletes local intestinal phosphate concentration triggering bacterial virulence and that polyphosphate replenishment attenuates virulence and collagenolytic activity. Mechanistic studies of bacterial and host protease expression contributing to tissue breakdown are difficult to achieve in vivo necessitating the development of novel in vitro tissue models. Common techniques for screening in vitro protease activity, including gelatin zymography or fluorogenic protease-sensitive substrate kits, do not readily translate to 3D matrix degradation. Here, we report the application of an in vitro assay in which collagenolytic pathogens are cultured in the presence of a proteolytically degradable poly(ethylene) glycol scaffold and a non-degradable phosphate and/or polyphosphate nanocomposite hydrogel matrix. This in vitro platform enables quantification of pathogen-induced matrix degradation and screening of sustained release of phosphate-based therapeutic efficacy in attenuating protease expression. To evaluate matrix degradation as a function of bacterial enzyme levels secreted, we also present a novel method to quantify hydrogel degradation. This method involves staining protease-sensitive hydrogels with Sirius red dye to correlate absorbance of the degraded gel solution with hydrogel weight. This assay enables continuous monitoring and greater accuracy of hydrogel degradation kinetics compared to gravimetric measurements. Combined, the proposed in vitro platform and the presented degradation assay provide a novel strategy for screening efficacy of therapeutics in attenuating bacterial protease-induced matrix degradation.