Function Follows Form: Oriented Substrate Nanotopography Overrides Neurite-Repulsive Schwann Cell-Astrocyte Barrier Formation in an In Vitro Model of Glial Scarring.

Schwann cell (SC) transplantation represents a promising therapeutic approach for traumatic spinal cord injury but is frustrated by barrier formation, preventing cell migration, and axonal regeneration at the interface between grafted SCs and reactive resident astrocytes (ACs). Although regenerating axons successfully extend into SC grafts, only a few cross the SC-AC interface to re-enter lesioned neuropil. To date, research has focused on identifying and modifying the molecular mechanisms underlying such scarring cell-cell interactions, while the influence of substrate topography remains largely unexplored. Using a recently modified cell confrontation assay to model SC-AC barrier formation in vitro, highly oriented poly(ε-caprolactone) nanofibers were observed to reduce AC reactivity, induce extensive oriented intermingling between SCs and ACs, and ultimately enable substantial neurite outgrowth from the SC compartment into the AC territory. It is anticipated that these findings will have important implications for the future design of biomaterial-based scaffolds for nervous tissue repair.

Transformative Materials to Create 3D Functional Human Tissue Models In Vitro in a Reproducible Manner.

Recreating human tissues and organs in the petri dish to establish models as tools in biomedical sciences has gained momentum. These models can provide insight into mechanisms of human physiology, disease onset, and progression, and improve drug target validation, as well as the development of new medical therapeutics. Transformative materials play an important role in this evolution, as they can be programmed to direct cell behavior and fate by controlling the activity of bioactive molecules and material properties. Using nature as an inspiration, scientists are creating materials that incorporate specific biological processes observed during human organogenesis and tissue regeneration. This article presents the reader with state-of-the-art developments in the field of in vitro tissue engineering and the challenges related to the design, production, and translation of these transformative materials. Advances regarding (stem) cell sources, expansion, and differentiation, and how novel responsive materials, automated and large-scale fabrication processes, culture conditions, in situ monitoring systems, and computer simulations are required to create functional human tissue models that are relevant and efficient for drug discovery, are described. This paper illustrates how these different technologies need to converge to generate in vitro life-like human tissue models that provide a platform to answer health-based scientific questions.

A novel in vitro assay for peripheral nerve-related cell migration that preserves both extracellular matrix-derived molecular cues and nanofiber-derived topography.

BACKGROUND: Molecular composition and topography of the extracellular matrix (ECM) influence regenerative cell migration following peripheral nerve injury (PNI). Advanced tissue engineering strategies for the repair of neurotmesis-type PNI include the development of nanofiber-containing implantable scaffolds that mimic features of the ECM to orchestrate regenerative growth. Reliable and quantifiable in vitro assays are required to assess the ability of such substrates to influence migration of the cell types of interest. However, most popular migration assays monitor cell migration into a cell exclusion zone (CEZ) but have dubious abilities to preserve the molecular and topographical cues of the substrate. NEW METHOD: Elastic band spacers (EBS), a simple, economical and standardized technique for the generation of well-defined CEZ based on the use of commercially available elastic bands, are introduced. RESULTS: EBS could sufficiently preserve ECM-derived molecular and poly(ε-caprolactone) (PCL) nanofiber-derived topographical cues. The application of EBS in the absence and presence of nanofiber-derived topographical cues was validated using perineurial cells and Schwann cells, both known to play key roles in peripheral nerve regeneration. COMPARISON WITH EXISTING METHODS: In contrast to EBS, commercial silicone inserts and the popular scratch assay caused substantial ECM substrate disruption, thereby preventing these techniques from being included in further investigations employing deposition of PCL nanofibers and cell migration analysis. CONCLUSIONS: EBS represent a useful addition to the existing repertoire of migration assays offering significant benefits in terms of substrate preservation. The simplicity and economy of the approach make it immediately accessible to research groups at minimal extra expense.

Preparation of spherical calcium phosphate granulates suitable for the biofunctionalization of active brazed titanium alloy coatings.

Titanium-based alloys can be actively brazed onto bio-inert ceramics and potentially be used as biocompatible coatings. To further improve their bioactivity in vivo, introduction of calcium phosphate (CaP)-based granulates onto their surface layer is possible. For this, mechanically stable CaP-based granulates need to be able to withstand the demand of the brazing process. In this study, spherical granulates, made of a calcium phosphate composite composed primarily of ß-tricalcium phosphate and hydroxyapatite, a bioactive glass, and a mixture of the previous two, were manufactured by spray drying. The influence of organic additives (Dolapix CE64, trisodium citrate) and solids content (30-80 wt%) in the slurry on the physical characteristics of granulates was investigated. X-ray diffraction, Brunauer, Emmett, Teller specific surface area standard method, scanning electron microscopy, granulate size analysis, and single granule strength were performed. Our results showed that trisodium citrate permitted the production of granulates with regular morphology, high density, and increased failure stress values. The strong granules also withstood the brazing process. These results show that CaP bioactive agents can be generated and be integrated during the demanding metallurgical processes, allowing for one-step bioactivation of metal brazes.