Flexible, Suturable, and Leak-free Scaffolds for Vascular Tissue Engineering Using Melt Spinning.

Coronary artery disease affects millions worldwide. Bypass surgery remains the gold standard; however, autologous tissue is not always available. Hence, the need for an off-the-shelf graft to treat these patients remains extremely high. Using melt spinning, we describe here the fabrication of tubular scaffolds composed of microfibers aligned in the circumferential orientation mimicking the organized extracellular matrix in the tunica media of arteries. By variation of the translational extruder speed, the angle between fibers ranged from 0 to ∼30°. Scaffolds with the highest angle showed the best performance in a three-point bending test. These constructs could be bent up to 160% strain without kinking or breakage. Furthermore, when liquid was passed through the scaffolds, no leakage was observed. Suturing of native arteries was successful. Mesenchymal stromal cells were seeded on the scaffolds and differentiated into vascular smooth muscle-like cells (vSMCs) by reduction of serum and addition of transforming growth factor beta 1 and ascorbic acid. The scaffolds with a higher angle between fibers showed increased expression of vSMC markers alpha smooth muscle actin, calponin, and smooth muscle protein 22-alpha, whereas a decrease in collagen 1 expression was observed, indicating a positive contractile phenotype. Endothelial cells were seeded on the repopulated scaffolds and formed a tightly packed monolayer on the luminal side. Our study shows a one-step fabrication for ECM-mimicking scaffolds with good handleability, leak-free property, and suturability; the excellent biocompatibility allowed the growth of a bilayered construct. Future work will explore the possibility of using these scaffolds as vascular conduits in in vivo settings.

Scaffold-free and label-free biofabrication technology using levitational assembly in a high magnetic field.

The feasibility of magnetic levitational bioassembly of tissue-engineered constructs from living tissue spheroids in the presence of paramagnetic ions (i.e. Gd3+) was recently demonstrated. However, Gd3+ is relatively toxic at concentrations above 50 mM normally used to enable magnetic levitation with NdFeB-permanent magnets. Using a high magnetic field (a 50 mm-bore, 31 T Bitter magnet) at the High Field Magnet Laboratory at Radboud University in Nijmegen, The Netherlands, we performed magnetic levitational assembly of tissue constructs from living spheroids prepared from the SW1353 chondrosarcoma cell line at 0.8 mM Gd3+ containing salt gadobutrol at 19 T magnetic field. The parameters of the levitation process were determined on the basis of polystyrene beads with a 170 µm-diameter. To predict the theoretical possibility of assembly, a zone of stable levitation in the horizontal and vertical areas of cross sections was previously calculated. The construct from tissue spheroids partially fused after 3 h in levitation. The analysis of viability after prolonged exposure (1 h) to strong magnetic fields (up to 30 T) showed the absence of significant cytotoxicity or morphology changes in the tissue spheroids. A high magnetic field works as a temporal and removal support or so-called 'scaffield'. Thus, formative biofabrication of tissue-engineered constructs from tissue spheroids in the high magnetic field is a promising research direction.

Tubular collagen scaffolds with radial elasticity for hollow organ regeneration.

Tubular collagen scaffolds have been used for the repair of damaged hollow organs in regenerative medicine, but they generally lack the ability to reversibly expand in radial direction, a physiological characteristic seen in many native tubular organs. In this study, tubular collagen scaffolds were prepared that display a shape recovery effect and therefore exhibit radial elasticity. Scaffolds were constructed by compression of fibrillar collagen around a star-shaped mandrel, mimicking folds in a lumen, a typical characteristic of empty tubular hollow organs, such as ureter or urethra. Shape recovery effect was introduced by in situ fixation using a star-shaped mandrel, 3D-printed clamps and cytocompatible carbodiimide crosslinking. Prepared scaffolds expanded upon increase of luminal pressure and closed to the star-shaped conformation after removal of pressure. In this study, we applied this method to construct a scaffold mimicking the dynamics of human urethra. Radial expansion and closure of the scaffold could be iteratively performed for at least 1000 cycles, burst pressure being 132±22mmHg. Scaffolds were seeded with human epithelial cells and cultured in a bioreactor under dynamic conditions mimicking urination (pulse flow of 21s every 2h). Cells adhered and formed a closed luminal layer that resisted flow conditions. In conclusion, a new type of a tubular collagen scaffold has been constructed with radial elastic-like characteristics based on the shape of the scaffold, and enabling the scaffold to reversibly expand upon increase in luminal pressure. These scaffolds may be useful for regenerative medicine of tubular organs. STATEMENT OF SIGNIFICANCE: In this paper, a new type I collagen-based tubular scaffold is presented that possesses intrinsic radial elasticity. This characteristic is key to the functioning of a number of tubular organs including blood vessels and organs of the gastrointestinal and urogenital tract. The scaffold was given a star-shaped lumen by physical compression and chemical crosslinking, mimicking the folding pattern observed in many tubular organs. In rest, the lumen is closed but it opens upon increase of luminal pressure, e.g. when fluids pass. Human epithelial cells seeded on the luminal side adhered well and were compatible with voiding dynamics in a bioreactor. Collagen scaffolds with radial elasticity may be useful in the regeneration of dynamic tubular organs.