Biomedical subjects

A L Sieminski

Publications and source records attributed to A L Sieminski.

7 recordsLinked to original sources

PubMed2004

The relative magnitudes of endothelial force generation and matrix stiffness modulate capillary morphogenesis in vitro.

When suspended in collagen gels, endothelial cells elongate and form capillary-like networks containing lumens. Human blood outgrowth endothelial cells (HBOEC) suspended in relatively rigid 3 mg/ml floating collagen gels, formed in vivo-like, thin, branched multi-cellular structures with small, thick-walled lumens, while human umbilical vein endothelial cells (HUVEC) formed fewer multi-cellular structures, had a spread appearance, and had larger lumens. HBOEC exert more traction on collagen gels than HUVEC as evidenced by greater contraction of floating gels. When the stiffness of floating gels was decreased by decreasing the collagen concentration from 3 to 1.5 mg/ml, HUVEC contracted gels more and formed thin, multi-cellular structures with small lumens, similar in appearance to HBOEC in floating 3 mg/ml gels. In contrast to floating gels, traction forces exerted by cells in mechanically constrained gels encounter considerable resistance. In constrained collagen gels (3 mg/ml), both cell types appeared spread, formed structures with fewer cells, had larger, thinner-walled lumens than in floating gels, and showed prominent actin stress fibers, not seen in floating gels. These results suggest that the relative magnitudes of cellular force generation and apparent matrix stiffness modulate capillary morphogenesis in vitro and that this balance may play a role in regulating angiogenesis in vivo.

Actins↗

PubMed2003

Bone morphogenetic protein 9: a potent modulator of cartilage development in vitro.

Few publications describe the activity of bone morphogenetic protein-9 (BMP-9), but the consensus of these largely in vivo studies is that while BMP-9 can induce ectopic bone formation at relatively large concentrations, it is primarily active in non-skeletal locations--including the liver, nervous system and marrow. To study the effects of BMP-9 on chondrogenesis in a well-defined environment, calf articular chondrocytes were seeded onto biodegradable PGA scaffolds. The resulting cell-polymer constructs were cultured in either control medium or medium supplemented with 1, 10, 50 or 100 ng/ml of BMP-9. After 4 weeks of in vitro culture, all concentrations of BMP-9 increased the total mass of the constructs, and the amounts of collagen, glycosaminoglycans (GAG) and cells per construct. On a mass percentage basis, BMP-9 tended to increase GAG, to decrease the relative amount of collagen and had little effect on the relative amount of cells. BMP-9 elicited qualitatively similar responses as BMP-2, -12 and -13. However, in contrast to BMP-12 and -13, BMP-9 (at concentrations > or = 10 ng/ml) induced hypertrophic chondrocyte formation and was the only BMP tested to induce mineralization. Taken together, these data suggest that BMP-9 is a potent modulator of cartilage development in vitro.

Alkaline Phosphatase↗

PubMed2002

Systemic delivery of human growth hormone using genetically modified tissue-engineered microvascular networks: prolonged delivery and endothelial survival with inclusion of nonendothelial cells.

Endothelial cells have the potential to provide efficient long-term delivery of therapeutic proteins to the circulation if a sufficient number of genetically modified endothelial cells can be incorporated into the host vasculature and if these cells persist for an adequate period of time. Here we describe the ability of nonendothelial cells to modulate the survival of implanted endothelial cells and their incorporation into host vasculature. Bovine aortic endothelial cells (BAECs) suspended in Matrigel and cultured in vitro remained spherical and decreased in number over time. Subcutaneous implantation of gels containing BAECs secreting human growth hormone (hGH) in mice initially resulted in detectable plasma hGH levels, which were undetectable after 2 weeks. When mixed with fibroblasts and suspended in Matrigel, hGH-secreting BAECs formed microvascular networks in vitro. Implantation of these gels resulted in plasma hGH levels that decreased slightly over 2 weeks and then remained stable for at least 6 weeks. BAECs incorporated into blood vessels within both the implant and fibrous capsule that surrounded and invaded implants. Within implants containing BAECs and fibroblasts, viable BAECs were present for at least 6 weeks at a higher density than in implants containing BAECs alone at 3 weeks. These results indicate that implanted BAECs can incorporate into host blood vessels and that inclusion of fibroblasts in this system prolongs BAEC survival and hGH delivery.

Animals↗

PubMed2002

Bone morphogenetic proteins-2, -12, and -13 modulate in vitro development of engineered cartilage.

Bovine calf articular chondrocytes were seeded onto biodegradable polyglycolic acid (PGA) scaffolds and cultured in either control medium or medium supplemented with 1, 10, or 100 ng/mL of bone morphogenetic proteins (BMPs) BMP-2, BMP-12, or BMP-13. Under all conditions investigated, cell-polymer constructs cultivated for 4 weeks in vitro macroscopically and histologically resembled native cartilage. Addition of 100 ng/mL of BMP-2, BMP-12, or BMP-13 increased the total mass of the constructs relative to the controls by 121%, 80%, and 62%, respectively, which was accompanied by increases in the absolute amounts of collagen, glycosaminoglycans (GAG), and cells. The addition of 100 ng/mL of BMP-2, BMP-12, or BMP-13 increased the weight percentage of GAG in the constructs by 27%, 18%, and 15%, and decreased the weight percent of total collagen to 63%, 89%, and 83% of controls, respectively. BMP-2, but not BMP-12 or BMP-13 promoted chondrocyte hypertrophy. Taken together, these data suggest that BMP-2, BMP-12, and BMP-13 increase growth rate and modulate the composition of engineered cartilage and that 100 ng/mL of BMP-2 has the greatest effect. In addition, in vitro engineered cartilage provides a system for studying the effects of BMPs on chondrogenesis in a well-defined environment.

Animals↗

PubMed2001

IGF-I and mechanical environment interact to modulate engineered cartilage development.

Bovine calf articular chondrocytes were seeded onto biodegradable polyglycolic acid scaffolds and cultured for four weeks using in vitro systems providing different mechanical environments (static and mixed Petri dishes, static and mixed flasks, and rotating vessels) and different biochemical environments (medium with and without supplemental insulin-like growth factor I, IGF-I). Under all conditions, the resulting engineered tissue histologically resembled cartilage and contained its major constituents: glycosaminoglycans, collagen, and cells. The mechanical environment and supplemental IGF-I (a) independently modulated tissue morphology, growth, biochemical composition, and mechanical properties (equilibrium modulus) of engineered cartilage as previously reported; (b) interacted additively or in some cases nonadditively producing results not suggested by the independent responses, and (c) in combination produced tissue superior to that obtained by modifying these factors individually.

Animals↗

PubMed2000

Biomaterial-microvasculature interactions.

The utility of implanted sensors, drug-delivery systems, immunoisolation devices, engineered cells, and engineered tissues can be limited by inadequate transport to and from the circulation. As the primary function of the microvasculature is to facilitate transport between the circulation and the surrounding tissue, interactions between biomaterials and the microvasculature have been explored to understand the mechanisms controlling transport to implanted objects and ultimately improve it. This review surveys work on biomaterial-microvasculature interactions with a focus on the use of biomaterials to regulate the structure and function of the microvasculature. Several applications in which biomaterial-microvasculature interactions play a crucial role are briefly presented. These applications provide motivation and framework for a more in-depth discussion of general principles that appear to govern biomaterial-microvasculature interactions (i.e., the microarchitecture and physio-chemical properties of a biomaterial as well as the local biochemical environment).

Animals↗

PubMedDate not supplied

Improved microvascular network in vitro by human blood outgrowth endothelial cells relative to vessel-derived endothelial cells.

Evidence suggests that bone marrow-derived cells circulating in adult blood, sometimes called endothelial progenitor cells, contribute to neovascularization in vivo and give rise to cells expressing endothelial markers in culture. To explore the utility of blood-derived cells expressing an endothelial phenotype for creating tissue-engineered microvascular networks, we employed a three-dimensional in vitro angiogenesis model to compare microvascular network formation by human blood outgrowth endothelial cells (HBOECs) with three human vessel-derived endothelial cell (EC) types: human umbilical vein ECs (HUVECs), and adult and neonatal human microvascular ECs. Under every condition investigated, HBOECs within collagen gels elongated significantly more than any other cell type. Under all conditions investigated, gel contraction and cell elongation were correlated, with HBOECs demonstrating the largest generation of force. HBOECs did not exhibit a survival advantage, nor did they enhance elongation of HUVECs when the two cell types were cocultured. Network formation of both HBOECs and HUVECs was inhibited by blocking antibodies to alpha2beta1, but not alpha(v)beta3, integrins. Taken together, these data suggest that superior network exhibited by HBOECs relative to vessel-derived endothelial cells is not due to a survival advantage, use of different integrins, or secretion of an autocrine/paracrine factor, but may be related to increased force generation.

Adult↗