Fluidic embedding of additional macroporosity in alginate-gelatin composite structure for biomimetic application.

Biomimetic characteristics of hydrogel scaffold are tuned in this study utilizing the synergy of alginate, gelatin, and microfluidically embedded voids. Superposition of alginate and gelatin polymer networks results in additional rigidity, which can be tuned by introduction of voids, and thereby allowing faster release of pore pressure through movement of aqueous phase through the pore network. More importantly, voids enabled the cells to penetrate from the surface of seeding into the depth of the scaffold and proliferate there, as demonstrated for MDA MB 231 breast cancer cells. The uniform voids, generated by the microfluidic device, self-align creating uniform macroporosity within the gel structure, get readily filled by the media due to hydrophilicity, and extend the characteristics of composite uniformly across the entire scaffold.

Mechanical behaviour of alginate film with embedded voids under compression-decompression cycles.

Voids of 300 µm diameter were embedded uniformly as monolayer in alginate gel film using a fluidic device. Voids of these dimensions in biopolymer gel film are desired for better transport of bioactive species and cell colonization in engineered tissues. In this article, the role of embedded voids in reducing compressive stress, hysteresis, and time scale of reheal vis-a-vis expulsion of pore fluid and its reabsorption upon reversal of load are reviewed. The cyclic loading was conducted with varying amplitude and frequency. The irreversible changes, if any in the gel structure under extreme compression were analyzed. The rate of expulsion of aqueous phase directly relates to the permeability of the gel film that is estimated here using simplified momentum and volumetric balance equations. The decrease in permeability with deformation is analyzed further, and the contribution of voids in this regard is discussed.

Diffusion in and around alginate and chitosan films with embedded sub-millimeter voids.

Hydrogel scaffolds from biopolymers have potential use in the controlled release of drugs, and as 3-D structure for the formation of tissue matrix. This article describes the solute release behavior of alginate and chitosan films with embedded voids of sub-millimeter dimensions. Nitrogen gas was bubbled in a fluidic arrangement to generate bubbles, prior to the crosslinking. The crosslinked gel was dried in a vacuum oven, and subsequently, soaked in Vitamin B-12 solution. The dimensions of the voids immediately after the cross-linking of gel, and also after complete drying were obtained using a digital microscope and scanning electron microscope respectively. The porosity of the gel was measured gravimetrically. The release of Vitamin B-12 in PBS buffer on a shaker was studied. The release experiments were repeated at an elevated temperature of 37°C in the presence of lysozyme. The diffusion coefficient within the gel layer and the mass transfer coefficient at the interface with the bulk-liquid were estimated using a mathematical model. For comparison, the experiment was repeated with a film that does not have any embedded void. The enhancement in diffusion coefficient due to the presence of voids is discussed in this article.