No abstract

Polyglycolic acid (PGA) is commonly used as a scaffold for tissue engineering. Recent studies utilized PGA as a scaffold for vascular tissue engineering using bovine and porcine smooth muscle cells (SMCs). In engineered vessels, the SMCs displayed high rates of mitosis and dedifferentiation in areas where PGA fragments were present. We hypothesized that PGA breakdown products, sequestered within a SMC vessel at the conclusion of culture, led to increased proliferation and dedifferentiation of vascular SMCs. To test this hypothesis, the current study assessed possible means by which PGA breakdown products could lead to changes in SMC phenotype. SMCs grown in high concentrations of PGA breakdown products showed, by Western blotting, decreased expression of calponin, a marker for SMC differentiation. The same was true for SMCs grown in glycolic acid (GA), which also showed decreased expression of proliferating cell nuclear antigen (PCNA), a marker for SMC proliferation. In contrast, cells grown in varying amounts of NaCl or HCl showed little change in differentiation. We conclude that, independent of acidity or osmolality, plausible products of PGA degradation appear to induce dedifferentiation of porcine SMCs in vitro. Because of dedifferentiation and decreased mitosis, commercially available PGA may not represent an optimal scaffold for vascular tissue engineering.

Background and Purpose-During vasospasm after subarachnoid hemorrhage (SAH), cerebral blood vessels show structural changes consistent with the actions of vascular mitogens. We measured platelet-derived vascular growth factors (PDGFs) in the cerebrospinal fluid (CSF) of patients after SAH and tested the effect of these factors on cerebral arteries in vivo and in vitro. Methods-CSF was sampled from 14 patients after SAH, 6 patients not suffering SAH, and 8 normal controls. ELISA was performed for PDGF-AB, transforming growth factor-␤1, and vascular endothelial growth factor. A mouse model was used to compare cerebral vascular cell proliferation and PDGF staining in SAH compared with sham-operated controls.Normal human pial arteries were incubated for 7 days in vitro, 2 groups with human blood clot and 1 with and 1 without PDGF antibodies. Results-PDGF-AB concentrations in CSF from SAH patients were significantly higher than those from non-SAH patients and normal controls, both during the first week after SAH and for all time points measured. Smooth muscle and fibroblast proliferation was observed after SAH in the mouse model, and this cellular replication was observed in conjunction with PDGF protein at the sites of thrombus. In human pial arteries, localized thrombus stimulated vessel wall proliferation, and proliferation was blocked by neutralizing antibodies directed against PDGFs. Conclusions-Vascular

The effect of mechanical stimulation on the development of tissue-engineered blood vessels was examined. In particular, three different rates of radial distension were chosen to produce a nonpulsed environment (0 beats per minute [bpm]), an adult heart rate (90 bpm), and a fetal heart rate (165 bpm). Engineered vessels were cultured for an average of 7 weeks. Vessel walls were then analyzed for collagen content and distribution. In addition, extracellular matrix remodeling was assessed through measurement of active matrix metalloproteinase type 1 (MMP-1) and tissue inhibitor of metalloproteinases type 1 (TIMP-1) levels. Vessels grown at a distension rate of 165 bpm had significantly higher collagen levels than those grown under static conditions. MMP-1 and TIMP-1 levels were also higher under pulsed conditions as compared with nonpulsed conditions. For the 90- and 165-bpm conditions, collagen and MMP-1 levels were not significantly different. TIMP-1 levels were significantly elevated at 165 bpm, indicating an increased cellular response to mechanical stimulation. Mechanical forces and their transduction represent a means to enhance the physical properties of artificial blood vessels, possibly by affecting the rate of extracellular matrix deposition and remodeling.

It has been shown that mechanical stimulation affects the physical properties of multiple types of engineered tissues. However, the optimum regimen for applying cyclic radial stretch to engineered arteries is not well understood. To this end, the effect of mechanical stretch on the development of engineered blood vessels was analyzed in constructs grown from porcine vascular smooth muscle cells. Cyclic radial distension was applied during vessel culture at three rates: 0 beats per minute (bpm), 90 bpm, and 165 bpm. At the end of the 7-week culture period, harvested vessels were analyzed with respect to physical characteristics. Importantly, mechanical stretch at 165 bpm resulted in a significant increase in rupture strength in engineered constructs over nonstretched controls. Stress–strain data and maximal elastic moduli from vessels grown at the three stretch rates indicate enhanced physical properties with increasing pulse rate. In order to investigate the role of collagen cross-linking in the improved mechanical characteristics, collagen cross-link density was quantified by HPLC. Vessels grown with mechanical stretch had somewhat more collagen and higher burst pressures than nonpulsed control vessels. Pulsation did not increase collagen cross-link density. Thus, increased wall thickness and somewhat elevated collagen concentrations, but not collagen cross-link density, appeared to be responsible for increased burst strength.