Synthesis of Thermogelling Poly(N-isopropylacrylamide)-graft-chondroitin Sulfate Composites with Alginate Microparticles for Tissue Engineering

Mie scattering theory applied to light scattering of large nonhomogeneous colloidal spheres

Colloidal suspensions made of smart core-shell structures are of current interest in many fields. Their properties come from the possibility of varying the core and shell materials for modifying the composite particles' chemical, biological, and optical properties. These particles are formed with a material with a constant refractive index core and a shell with a refractive index decaying until it matches the solvent refractive index. Poly(N-IsoPropyl AcrylaMide) (PNIPAM) is a typical example of materials forming shells. In this report, we present how to apply Mie scattering theory to predict and understand the static light scattering of large nonhomogeneous colloidal particles with spherical symmetry whose size is comparable with or larger than the light wavelength used for developing scattering experiments, where the Rayleigh-Gans-Debye approximation is not valid. Here, the refractive index decay was approximated by a Gaussian RI profile numerically evaluated through a multilayer sphere. We calculated the form factor functions of suspensions of PNIPAM microgels previously reported and core-shell suspensions made of polystyrene/PNIPAM at 20 and 40 °C synthesized by us. In all the cases, our method succeeded in providing the scattering intensity as a function of the angle. The software for using the numerical method is fairly straightforward and is accessible as an open-source code. The results can not only help predict and understand the photonic properties of microgels with large core-shell structures but also for any particle with a refractive index distribution with spherical symmetry, as in the case of microgels with super chaotropic agents, hollow microgels, or microparticles.

Synthesis of Injectable, Thermally Responsive, Chondroitin Sulfate-Cross-Linked Poly(N-isopropylacrylamide) Hydrogels

In this study, we describe the synthesis and characterization of a biosynthetic hydrogel system that consists of a thermally responsive macromer and biological cross-linkers. By combining a poly(N-isopropylacrylamide)-based thermogelling macromer with epoxy pendant groups and chondroitin sulfate cross-linkers that are modified to contain either hydrazide or N-hydroxysuccinimide pendant groups, we successfully fabricated a system that undergoes gelation when the temperature is raised from room temperature to 37 °C and is further stabilized via covalent links between the macromers. The anionic charge on chondroitin sulfate contributed to a high degree of gel swelling, while the cross-linking reaction between the macromers prevented post-formation syneresis. The rate of degradation of CS-cross-linked hydrogels was dependent on the degree of substitution of hydrazide-modified chondroitin sulfate cross-linkers. A higher molar content of chondroitin sulfate led to a greater osmotic pressure within the hydrogel and thus a higher compressive modulus. On the other hand, excessive amounts of chondroitin sulfate caused time-dependent cytotoxicity, as confirmed by a leachables cytocompatibility study. Overall, the system described in this study provides a versatile platform to synthesize hydrogels with differing combinations of compressive moduli and rates of degradation, which is achievable by varying the degree of substitution of hydrazide groups on CS-based cross-linkers.

Engineering S. equi subsp. zooepidemicus towards concurrent production of hyaluronic acid and chondroitin biopolymers of biomedical interest

Glycosaminoglycans, such as hyaluronic acid and chondroitin sulphate, are not only more and more required as main ingredients in cosmeceutical and nutraceutical preparations, but also as active principles in medical devices and pharmaceutical products. However, while biotechnological production of hyaluronic acid is industrially established through fermentation of Streptococcus spp. and recently Bacillus subtilis, biotechnological chondroitin is not yet on the market. A non-hemolytic and hyaluronidase negative S. equi subsp. zooepidemicus mutant strain was engineered in this work by the addition of two E. coli K4 genes, namely kfoA and kfoC, involved in the biosynthesis of chondroitin-like polysaccharide. Chondroitin is the precursor of chondroitin sulphate, a nutraceutical present on the market as anti-arthritic drug, that is lately being studied for its intrinsic bioactivity. In small scale bioreactor batch experiments the production of about 1.46 ± 0.38 g/L hyaluronic acid and 300 ± 28 mg/L of chondroitin with an average molecular weight of 1750 and 25 kDa, respectively, was demonstrated, providing an approach to the concurrent production of both biopolymers in a single fermentation.