Pulsatile perfusion bioreactor system for durability testing and compliance estimation of tissue engineered vascular grafts.

The aim of the study was to design, construct, and test a bioreactor for the conditioning of tissue-engineered vascular grafts under physiological pressure, flow, and environmental conditions and up to supra-physiological pulse frequencies (5 Hz) as the first step towards durability testing. The system also allows the calculation of the compliance of vascular grafts as an indicator of tissue development. The system relies on the combination of a pulse-free pump and a linear magnetic actuator applying pressure pulses with controllable profile and frequency. The compliance estimation is based on the accurate measurement of the vessel's diameter by means of an optical micrometre. Software-based interface enables the control of a magnetic actuator and data acquisition to monitor the conditions of the system. Porcine carotid arteries were tested in the bioreactor for up to 4 weeks at different pulse frequencies. The tissue was analysed by means of histology and immunohistochemistry. Physiological pressures (~80 and 120 mmHg for diastolic and systolic phase, respectively) were generated in the system at frequencies between 1 and 5 Hz. The environmental conditions within the bioreactor were monitored and online determination of the compliance of the arteries was achieved under sterile conditions. Conditioning of the grafts resulted in the abundant production of ECM proteins. In conclusion, we developed a bioreactor for the conditioning of tissue engineered vascular grafts under controlled pressure conditions. The system is suitable to perform durability tests at supra-physiological pulse rates and physiological pressure levels under continuous monitoring of environmental variables (pH, pO2, pCO2, and temperature) and compliance.

Laser printing of three-dimensional multicellular arrays for studies of cell-cell and cell-environment interactions.

Utilization of living cells for therapies in regenerative medicine requires a fundamental understanding of the interactions between different cells and their environment. Moreover, common models based on adherent two-dimensional cultures are not appropriate to simulate the complex interactions that occur in a three-dimensional (3D) cell-microenvironment in vivo. In this study, we present a computer-aided method for the printing of multiple cell types in a 3D array using laser-assisted bioprinting. By printing spots of human adipose-derived stem cells (ASCs) and endothelial colony-forming cells (ECFCs), we demonstrate that (i) these cell spots can be arranged layer-by-layer in a 3D array; (ii) any cell-cell ratio, cell quantity, cell-type combination, and spot spacing can be realized within this array; and (iii) the height of the 3D array is freely scalable. As a proof of concept, we printed separate spots of ASCs and ECFCs within a 3D array and observed cell-cell interactions in vascular endothelial growth factor-free medium. It has been demonstrated that direct cell-cell contacts trigger the development of stable vascular-like networks. This method can be applied to study complex and dynamic relationships between cells and their local environment.

Fabrication of highly porous scaffolds for tissue engineering based on star-shaped functional poly(ε-caprolactone).

The potential of novel functional star-shaped poly(ε-caprolactone)s of controlled molecular weight and low molecular weight distribution bearing acrylate end groups as material for biomedical applications was demonstrated in this study. The polymers were functionalized via Michael-type addition of amino acid esters containing amino or thiol groups showing the potential for immobilization of biomolecules. Furthermore, scaffolds of different geometries were prepared by uniaxial freezing of polymer solutions followed by freeze drying. Different solvents and polymer concentrations were investigated, resulting in scaffolds with porosities between 76 and 96%. Mechanical properties of the scaffolds were investigated and the morphology was determined via scanning electron microscopy. Scaffolds with interconnected channels were prepared using benzene, 1,2-dichloroethane or dioxane as solvent. The tubular longitudinal pores in honeycomb arrangement extend throughout the full extent of the scaffolds (typical pore sizes: 20-100 µm).