Development of hydrogel-based composite scaffolds containing eggshell particles for bone regeneration applications.

This study describes the development and characterization of novel composite scaffolds, made of an alginate-chitosan hydrogel matrix containing eggshell (ES) particles, for bone tissue engineering applications. Scaffolds with ES particles, either untreated or treated with phosphoric acid to create a nanotextured particle surface, were compared to scaffolds without particles. Results indicate that the nanotexturing process exposed occluded ES proteins orthologous to those in human bone extracellular matrix. Scaffolds with ES or nanotextured ES (NTES) particles had a higher porosity (81 ± 4% and 89 ± 5%, respectively) than scaffolds without particles (59 ± 5%) (p = .002 and p < .001, respectively). Scaffolds with NTES particles had a larger median pore size (113 µm [interquartile range [IQ]: 88-140 µm]) than scaffolds with ES particles (94 µm [IQ: 75-112 µm]) and scaffolds without particles (99 µm [IQ: 74-135 µm]) (p < .001 and p = .011, respectively). The compressive modulus of the scaffolds with ES or NTES particles remained low (3.69 ± 0.70 and 3.14 ± 0.62 kPa, respectively), but these scaffolds were more resistant to deformation following maximum compression than those without particles. Finally, scaffolds with ES or NTES particles allowed better retention of human mesenchymal stem cells during seeding (53 ± 12% and 57 ± 8%, respectively, vs. 17 ± 5% for scaffolds without particles; p < .001 in both cases), as well as higher cell viability up to 21 days of culture (67 ± 17% and 61 ± 11%, respectively, vs. 15 ± 7% for scaffolds without particles; p < .001 in both cases). In addition, alkaline phosphatase (ALP) activity increased up to 558 ± 164% on day 21 in the scaffolds with ES particles, and up to 567 ± 217% on day 14 in the scaffolds with NTES particles (p = .006 and p = .002, respectively, relative to day 0). Overall, this study shows that the physicochemical properties of the alginate-chitosan hydrogel scaffolds with ES or NTES particles are similar to those of cancellous bone. In addition, scaffolds with particles supported early osteogenic differentiation and therefore represent a promising new bone substitute, especially for non-load bearing applications.

Systems biology based metabolic engineering for non-natural chemicals.

Production of chemicals in microorganisms is no longer restricted to products arising from native metabolic potential. In this review, we highlight the evolution of metabolic engineering studies, from the production of natural chemicals fermented from biomass hydrolysates, to the engineering of microorganisms for the production of non-natural chemicals. Advances in synthetic biology are accelerating the successful development of microbial cell factories to directly produce value-added chemicals. Here we outline the emergence of novel computational tools for the creation of synthetic pathways, for designing artificial enzymes for non-natural reactions and for re-wiring host metabolism to increase the metabolic flux to products. We also highlight exciting opportunities for applying directed evolution of enzymes, dynamic control of growth and production, growth-coupling strategies as well as decoupled strategies based on orthogonal pathways in the context of non-natural chemicals.