Correlation between Fibrin Fibrillation Kinetics and the Resulting Fibrin Network Microstructure.

Fibrin, the prominent extracellular matrix in early wound tissue, is discussed to influence immune cells and healing. The nature of fibrinogen/fibrin to form fibrillary networks is frequently exploited to engineer microenvironments for cellular analysis. This study focuses on revealing the correlation of fibril formation kinetic and the resulting network microstructure of engineered 3D fibrin networks. Different concentrations of fibrinogen (1-3 mg mL-1 ), thrombin (0.01-0.15 U mL-1 ), sodium chloride (40-120 mm), and calcium chloride (1-10 mm) are applied to assess the impact on the fibril growth kinetics by turbidity analysis and on the resulting fibril and pore diameter by laser scanning microscopy. The results highlight a direct influence of the sodium chloride concentration on fibrillation kinetics and reveal a strong correlation between fibrillation kinetics and network microstructure. With the assumption of a first-order growth kinetic, an increase of the growth constant k (0.015-0.04 min-1 ) is found to correlate to a decrease in fibril diameter (1-0.65 µm) and pore diameter (11-5 µm). The new findings enable an easy prediction of 3D fibrin network microstructure by the fibril formation kinetic and contribute to an improved engineering of defined scaffolds for tissue engineering and cell culture applications.

Fibronectin-functionalization of 3D collagen networks supports immune tolerance and inflammation suppression in human monocyte-derived macrophages.

The extracellular matrix (ECM) is dynamically reorganized during wound healing. Concomitantly, recruited monocytes differentiate into macrophages. However, the role of the wound's ECM during this transition remain to be fully understood. Fibronectin is a multifunctional glycoprotein present in early wound ECM with a potential immunomodulatory role during monocyte-to-macrophage differentiation. Hence, to investigate the impact of fibronectin during this differentiation step, 3D fibrillar collagen type I networks with or without fibronectin-functionalization were engineered with defined topology (fibril and pore diameter: 0.8 µm; 7 µm) and amount of adsorbed fibronectin (0.15 µg per µg collagen). Primary, human monocytes were then differentiated into macrophages inside these networks. The immunological imprinting of the resulting macrophages was monitored by means of the expression of FABP4, CLEC4E, SLC2A6, and SOD2 which discriminate naïve and tolerized macrophages, as well pro-inflammatory (M1) and anti-inflammatory (M2) macrophage polarization. The analyses indicate that fibronectin-functionalization of collagen I networks induces macrophage tolerance rather than M1 or M2 macrophage phenotypes. This finding was confirmed by release profiles of pro- and anti-inflammatory cytokines such as IL6, IL8, CXCL10, and IL10. Nevertheless, upon LPS challenge, immune suppression by fibronectin was overridden since these macrophages could then deploy an efficient immune response. Our results therefore provide new perspectives in biomaterial science of wound healing scaffolds and the design of instructive materials for human monocyte-derived cells.