Prolonged transendothelial migration of human haematopoietic stem and progenitor cells (HSPCs) towards hydrogel-released SDF1.

The therapeutic success of haematopoetic stem and progenitor cell (HSPC) transplantation is critically dependent on HSPC engraftment in the bone marrow. Gradients of stromal cell-derived factor 1 (SDF1) direct HSPC homing, both in vitro and in vivo. Potentially, regulating the delivery levels of exogenous SDF1 applied to the bone marrow could augment HSPC engraftment. Thus, the aim of the present study was to revise the ability of biocompatible hydrogels to direct HSPC migration in vitro. The delivery system of choice is based on heparin cross-linked with collagen1. We confirm that hydrogel is capable of trapping and releasing SDF1 and using it to generate a protein gradient in transendothelial migration experiments. The use of SDF1-functionalised hydrogel to produce a chemokine gradient revealed, sustained and increased HSPC migration when compared to diffusible SDF1 controls. In conclusion, regulating SDF1 gradients with heparin-containing hydrogels may offer valuable options to direct site-specific migration of HSPC.

Thermo-responsive poly(NiPAAm-co-DEGMA) substrates for gentle harvest of human corneal endothelial cell sheets.

Gentle harvesting of corneal endothelial cell sheets grown in culture is of interest for the development of cornea replacement strategies. Thin films of a fast responding copolymer of N-isopropylacrylamide (NiPAAm) and diethyleneglycol methacrylate (DEGMA) with a phase transition temperature of 32 degrees C were prepared and evaluated for that purpose. The polymer layers were immobilized onto fluorocarbon substrates using low pressure argon plasma treatment. Cell culture and detachment experiments were performed with L929 mouse fibroblasts and human corneal endothelial cells (HCEC) at standard conditions. The hydrogel-coated supports were found to permit adhesion, spreading, and proliferation of both cell types. Harvesting of cell sheets was achieved upon lowering the temperature to about 30 degrees C. The formation of a closed monolayer as a crucial prerequisite for maintaining ionic pump function in HCEC was proven by ZO-1 immunostainung. Labeling of fibronectin indicated that the vast majority of the extracellular matrix is detached from the hydrogel coatings together with the cell layer. Inspired by this result, the reuse of the hydrogel-coated culture carriers was investigated confirming the suitability of the substrates for repeated cell harvesting. Altogether, the introduced thermoresponsive coating was found advantageous for the efficient generation of HCEC sheets and will be further utilized in transplantation strategies.

Biomaterials trigger endothelial cell activation when co-incubated with human whole blood.

Endothelial cell activation resulting from biomaterial contact or biomaterial-induced blood activation may in turn also affect hemostasis and inflammatory processes in the blood. Current in vitro hemocompatibility assays typically ignore these modulating effects of the endothelium. This study describes a co-incubation system of human whole blood, biomaterial and endothelial cells (ECs) that was developed to overcome this limitation. First, human endothelial cells were characterized in terms of their expression of coagulation- and inflammation-relevant markers in response to various activators. Subsequently, their capacity to regulate hemostasis as well as complement and granulocyte activation was monitored in a hemocompatibility assay. After blood contact, quiescent ECs exhibited anticoagulant and anti-inflammatory properties. When they were co-incubated with surfaces exhibiting pro-coagulant or pro-inflammatory characteristics, the ECs down-regulated coagulation but not complement or leukocyte activation. Analysis of intracellular levels of the endothelial activation markers E-selectin and tissue factor showed that co-incubation with model surfaces and blood significantly increased the activation state of ECs. Finally, the coagulation- and inflammation-modulating properties of the ECs were tested after blood/biomaterial exposure. Pre-activation of ECs by biomaterials in the blood induced a pro-coagulant and pro-inflammatory state of the ECs, wherein the pro-coagulant response was higher for biomaterial/blood pre-activated ECs than for TNF-α-pre-activated cells. This work provides evidence that biomaterials, even without directly contacting the endothelium, affect the endothelial activation state with and have consequences for plasmatic and cellular reactions in the blood.