Density gradients at hydrogel interfaces for enhanced cell penetration.

We report that stiffness gradients facilitate infiltration of cells through otherwise cell-impermeable hydrogel interfaces. By enabling the separation of hydrogel manufacturing and cell seeding, and by improving cell colonization of additively manufactured hydrogel elements, interfacial density gradients present a promising strategy to progress in the creation of 3D tissue models.

Locally controlling mesenchymal stem cell morphogenesis by 3D PDGF-BB gradients towards the establishment of an in vitro perivascular niche.

The perivascular niche is a complex microenvironment containing mesenchymal stem cells (MSCs), among other perivascular cells, as well as temporally organized biochemical and biophysical gradients. Due to a lack of conclusive phenotypic markers, MSCs' identity, heterogeneity and function within their native niche remain poorly understood. The in vitro reconstruction of an artificial three-dimensional (3D) perivascular niche would offer a powerful alternative to study MSC behavior under more defined conditions. To this end, we here present a poly(ethylene glycol)-based in vitro model that begins to mimic the spatiotemporally controlled presentation of biological cues within the in vivo perivascular niche, namely a stably localized platelet-derived growth factor B (PDGF-BB) gradient. We show that 3D-encapsulated MSCs respond to soluble PDGF-BB by proliferation, spreading, and migration in a dose-dependent manner. In contrast, the exposure of MSCs to 3D matrix-tethered PDGF-BB gradients resulted in locally restricted morphogenetic responses, much as would be expected in a native perivascular niche. Thus, the herein presented artificial perivascular niche model provides an important first step towards modeling the role of MSCs during tissue homeostasis and regeneration.

Tuning electrospinning parameters for production of 3D-fiber-fleeces with increased porosity for soft tissue engineering applications.

Degrapol® and PLGA electrospun fiber fleeces were characterized with regard to fiber diameter, alignment, mechanical properties as well as scaffold porosity. The study showed that electrospinning parameters affect fiber diameter and alignment in an inverse relation: fiber diameter was increased with increased flow rate, with decrease in working distance and collector velocity, whereas fiber alignment increased with the working distance and collector velocity but decreased with increased flow rate. When Degrapol® or PLGA-polymers were co-spun with increasing ratios of a water-soluble polymer that was subsequently removed; fibrous scaffolds with increased porosities were obtained. Mechanical properties correlated with fiber alignment rather than fiber diameter as aligned fiber scaffolds demonstrated strong mechanical anisotropy. For co-spun fibers the Young's modulus correlated inversely with the amount of co-spun polymer. Cell proliferation was independent of the porosity of the scaffold, but different between the two polymers. Furthermore, fibrous scaffolds with different porosities were analyzed for cell infiltration suggesting that cell infiltration was enhanced with increased porosity and increasing time. These experiments indicate that 3D-fiber fleeces can be produced with controlled properties, being prerequisites for successful scaffolds in tissue engineering applications.