Jeroen Visjager

Living, autologous pulmonary artery conduits tissue engineered from human umbilical cord cells

BACKGROUND Tissue engineering represents a promising approach to in vitro creation of living, autologous replacements with the potential to grow, repair, and remodel. Particularly in a congenital operation, there is a substantial need for such implantation materials. We previously demonstrated fabrication of completely autologous, functional heart valves on the basis of peripheral vascular cells. Presently the feasibility of creating pulmonary artery conduits from human umbilical cord cells was investigated. METHODS Human umbilical cord cells were harvested and expanded in culture. Pulmonary conduits fabricated from rapidly bioabsorbable polymers were seeded with human umbilical cord cells and grown in vitro in a pulse duplicator bioreactor. Morphologic characterization of the generated neo-tissues included histology, transmission, and scanning electron microscopy. Characterization of extracellular matrix was comprised of immunohistochemistry. Extracellular matrix protein content and cell proliferation were quantified by biochemical assays. Biomechanical testing was performed using stress-strain and burst-stress tests. RESULTS Histology of the conduits revealed viable, layered tissue and extracellular matrix formation with glycosaminoglycans and collagens I and III. Cells stained positive for vimentin and alpha-smooth muscle actin. Scanning electron microscopy showed confluent, homogenous tissue surfaces. Transmission electron microscopy demonstrated elements typical of viable myofibroblasts, such as collagen, fibrils, and elastin. Extracellular matrix proteins were significantly lower compared with native tissue; the cell content was increased. The mechanical strength of the pulsed constructs was comparable with native tissue; the static controls were significantly weaker. CONCLUSIONS In vitro fabrication of tissue-engineered human pulmonary conduits was feasible utilizing human umbilical cord cells and a biomimetic culture environment. Morphologic and mechanical features approximated human pulmonary artery. Human umbilical cord cells demonstrated excellent growth properties representing a new, readily available cell source for tissue engineering without necessitating the sacrifice of intact vascular donor structures.

Optimized growth conditions for tissue engineering of human cardiovascular structures.

Optimized in vitro formation of strong tissue is a prerequisite for tissue engineering of cardiovascular structures, such as heart valves and blood vessels. This study evaluates different growth media additives as to cell proliferation, extracellular matrix formation, and mechanical characteristics. Biodegradable polymers were seeded with human vascular myofibroblasts. Group A was cultured with standard medium, groups B, C, and D were in addition supplemented with ascorbate, fibroblast growth factor (bFGF), and both respectively. Analysis included histology, electron microsocopy, mechanical testing, and biochemical assays for cell proliferation (DNA) and extracellular matrix (collagen). DNA content increased in all groups, showing significantly more cells in group C and D after 14d. Collagen increased in all groups, except for C. Morphology showed viable, layered cellular tissue, with collagen fibrils after 2w, most pronounced in B and D. Mechanical properties decreased initially, stabilizing after 2w. In conclusion, standard nutrient media were efficient for seeded human vascular cells cultured on biodegradable meshes. Supplementation with bFGF+ascorbate resulted in enhanced early cell proliferation and structurally more mature tissue formation.

Melt-processable poly(tetrafluoroethylene)—compounding, fillers and dyes

Abstract Recently, a window of molar mass has been identified where poly(tetrafluoroethylene) (PTFE) homopolymer can be processed from the melt, but at the same time has good mechanical properties in the solid state, so called HD-PTFE ® . This research evaluates the use of conventional melt-compounding with a co-rotating twin-screw to introduce a variety of fillers in this material. It was found that melt-compounding is indeed an efficient way to achieve a filler distribution of excellent homogeneity in HD-PTFE ® .

Synthesis and properties of liquid crystalline aromatic copolyesters with lactide moieties

High molecular weight liquid crystalline copolyesters were obtained by copolycondensation of aromatic diols and diacyl chlorides with oligolactides. The molecular structure of these copolyesters was verified by NMR studies. The copolyesters form nematic melts, which can be frozen in into a nematic glass. Unexpectedly, a fibrillar structure was observed exclusively on the surface of solution cast films. In spite of a significant content of lactide moieties of the copolyesters their films and fibers are characterized by exceptional mechanical properties. Initial experiments indicated excellent biocompatibility based on cell seeding experiments and microscopic evidence.

Solid-solution formation and phase segregation in binary systems of homologous extended-chain perfluorinated alkanes

Using differential scanning calorimetry (DSC) and X-ray analysis it is shown that binary systems of perfluorinated alkanes form solid solutions or exhibit eutectic phase behaviour, depending on their difference in chain length. A simple model, which successfully correlated experimental results for this aspect of phase behaviour of binary n-alkane systems, is demonstrated to quantitatively describe the behaviour of perfluorinated alkanes as well. From the model parameters and experimental observations, it appears that, at equal number of carbon atoms, binary perfluorinated alkane systems allow for a larger chain difference than their hydrogenated analogues, before eutectic phase behaviour sets in.