Physical characterization of vascular grafts cultured in a bioreactor

Tubular scaffolds of collagen and elastin (weight ratio 1:1) with interconnected pores were prepared by freeze drying and crosslinked with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) in the presence or absence of a Jeffamine spacer (poly(propylene glycol)-bis-(2-aminopropyl ether), J230). The crosslinked and uncrosslinked matrices had porosities of 90% and average pore sizes of 131–151 μm. Smooth muscle cells (SMC) were cultured in the crosslinked and uncrosslinked tubular scaffolds under pulsatile flow conditions (mean flow rate 9.6 ml/min, 120 beats/min, pressure 80–120 mmHg). All the constructs could withstand cyclic mechanical strain in the absence of any mechanical support without cracking or suffering permanent deformation. After 7 d, SMC were homogeneously distributed throughout the uncrosslinked and EDC/NHS crosslinked constructs, whereas hardly any cell was observed on the luminal side of J230/EDC/NHS crosslinked matrices. Considering the better mechanical performance of EDC/NHS crosslinked matrices compared to non-crosslinked constructs after 7 d of culture, SMC were dynamically cultured in the former scaffolds for 14 d. During this period, the high strain stiffness of the constructs increased more than two-fold to 38±2 kPa, whereas the low strain stiffness doubled to 8±2 kPa. The yield stress and yield strain were 30±10 kPa and 120±20%, respectively. SMC were homogeneously distributed throughout the EDC/NHS crosslinked collagen/elastin constructs and collagen fibres tended to orient in the circumferential direction.