Biomedical subjects

P A DiMilla

Publications and source records attributed to P A DiMilla.

8 recordsLinked to original sources

PubMed2000

Characterization of osteoblast-like behavior of cultured bone marrow stromal cells on various polymer surfaces.

The creation of novel bone substitutes requires a detailed understanding of the interaction between cells and materials. This study was designed to test certain polymers, specifically poly(caprolactone) (PCL), poly(D,L-lactic-CO-glycolic acid) (PLGA), and combinations of these polymers for their ability to support bone marrow stromal cell proliferation and differentiation. Bone marrow stromal cells were cultured from New Zealand White rabbits and were seeded onto glass slides coated with a thin layer of PCL, PLGA, and combinations of these two polymers in both a 40:60 and a 10:90 ratio. Growth curves were compared. At the end of 2 weeks, the cells were stained for both matrix mineralization and alkaline phosphatase activity. There was no statistically significant difference in growth rate of the cells on any polymer or polymer combination. However, there was a striking difference in Von Kossa staining and alkaline phosphatase staining. Cells on PCL did not show Von Kossa staining or alkaline phosphatase staining. However, in the 40:60 and 10:90 blends, there was both positive Von Kossa and alkaline phosphatase staining. These data indicate that PCL alone may not be a satisfactory material for the creation of a bone substitute. However, it may be used in combination with PLGA for the creation of a bone substitute material.

Animals↗

PubMed2000

Spreading and motility of human glioblastoma cells on sheets of silicone rubber depend on substratum compliance.

Although there is a substantial quantity of experimental data examining the effects of adhesion on the morphology and migration of tissue cells, little attention has been focused on how changes in substratum mechanical properties affect these cellular behaviours. To determine whether the ability of a substratum mechanically to support traction influences cell morphology and motility, measurements are taken of the spreading, the fraction of a population with pseudopodia, the number of pseudopodia and the translocation of human SNB-19 glioblastoma cells cultured on films of poly(methylphenyl)siloxane possessing a range of mechanical compliances. Cells cultured on these films generate deformations (i.e. 'wrinkles') that are used as a basis to estimate effective substratum compliances. The average projected cell area decreases by over 60%, with a two-orders-of-magnitude increase in compliance. Time-lapse videomicroscopy reveals that cell migration also decreases with increasing compliance: the average cell speed decreases from approximately 8 microns h-1 on the most rigid substrata to 1.2 microns h-1 on the most compliant substrata examined. Changes in compliance do not alter mean directional persistence time. These results are interpreted in terms of the predictions of mathematical models for the effects of substratum compliance on motility.

Cell Adhesion↗

PubMed1999

In vitro analysis of biodegradable polymer blend/hydroxyapatite composites for bone tissue engineering.

Blends of biodegradable polymers, poly(caprolactone) and poly(D, L-lactic-co-glycolic acid), have been examined as scaffolds for applications in bone tissue engineering. Hydroxyapatite granules have been incorporated into the blends and porous discs were prepared. Mechanical properties and degradation rates in vitro of the composites were determined. The discs were seeded with rabbit bone marrow or cultured bone marrow stromal cells and incubated under physiological conditions. Polymer/ceramic scaffolds supported cell growth throughout the scaffold for 8 weeks. Scanning and transmission electron microscopy, and histological analyses were used to characterize the seeded composites. This study suggests the feasibility of using novel polymer/ceramic composites as scaffold in bone tissue engineering applications.

Animals↗

PubMed1999

Control of attachment, morphology, and proliferation of skeletal myoblasts on silanized glass.

Generating skeletal muscle in vitro is an attractive approach to overcome problems associated with autologous transfer of muscle and donor site morbidity during plastic surgery. Such tissue engineering requires application of biomaterials that selectively control the attachment, morphology, and proliferation of muscle progenitor ("satellite") cells. This study examined the initial attachment, morphological characteristics, and proliferative behavior of murine C2C12 myoblasts on glass substrata derivatized with self-assembled monolayers (SAMs) of the organosiloxanes N-(2-aminoethyl)(3-aminopropyl)trimethoxysilane (EDA) and tridecafluoro-1,1,2,2-tetrahydrooctyl-1-dimethylchlorosil ane (13F). The fraction of myoblasts resisting detachment upon rinsing was greater on EDA than on 13F. Application of a quantitative moments-based analysis of cell morphology demonstrated that projected area and two size-invariant metrics of shape (extension and dispersion) for these cells were greater for EDA than for 13F. Myoblasts also proliferated faster on EDA than on 13F. These data indicate that EDA-derivatized glass provides a superior substratum for myoblast culture compared to 13F-derivatized glass. Understanding myoblast behavior on these biomaterials that promotes contrasting cellular responses is the first step toward using patterned SAMs to control myotube alignment for tissue engineering skeletal muscle.

Alkanes↗

PubMed1999

Muscle tissue engineering.

Only recently have scientists come to appreciate that many tissues and cell populations that were formerly considered to be in a terminally differentiated state are capable of division and or dedifferentiation. It is the goal of the tissue engineer to understand and redirect this potential. Muscle tissue-engineering efforts will be directed toward building in vitro replacements for in vivo problems. Tissue-engineering advances will be interdependent with advances in gene therapy techniques to restore function at a cellular level.

Animals↗

PubMed1993

Maximal migration of human smooth muscle cells on fibronectin and type IV collagen occurs at an intermediate attachment strength.

Although a biphasic dependence of cell migration speed on cell-substratum adhesiveness has been predicted theoretically, experimental data directly demonstrating a relationship between these two phenomena have been lacking. To determine whether an optimal strength of cell-substratum adhesive interactions exists for cell migration, we measured quantitatively both the initial attachment strength and migration speed of human smooth muscle cells (HSMCs) on a range of surface concentrations of fibronectin (Fn) and type IV collagen (CnIV). Initial attachment strength was measured in order to characterize short time-scale cell-substratum interactions, which may be representative of dynamic interactions involved in cell migration. The critical fluid shear stress for cell detachment, determined in a radial-flow detachment assay, increased linearly with the surface concentrations of adsorbed Fn and CnIV. The detachment stress required for cells on Fn, 3.6 +/- 0.2 x 10(-3) mu dynes/absorbed molecule, was much greater than that on CnIV, 5.0 +/- 1.4 x 10(-5) mu dynes/absorbed molecule. Time-lapse videomicroscopy of individual cell movement paths showed that the migration behavior of HSMCs on these substrates varied with the absorbed concentration of each matrix protein, exhibiting biphasic dependence. Cell speed reached a maximum at intermediate concentrations of both proteins, with optimal concentrations for migration at 1 x 10(3) molecules/micron2 and 1 x 10(4) molecules/micron2 on Fn and CnIV, respectively. These optimal protein concentrations represent optimal initial attachment strengths corresponding to detachment shear stresses of 3.8 mu dyne/micron2 on Fn and 1.5 mu dyne/micron2 on CnIV. Thus, while the optimal absorbed protein concentrations for migration on Fn and CnIV differed by an order of magnitude, the optimal initial attachment strengths for migration on these two proteins were very similar. Further, the same minimum strength of initial attachment, corresponding to a detachment shear stress of approximately 1 mu dyne/micron2, was required for movement on either protein. These results suggest that initial cell-substratum attachment strength is a central variable governing cell migration speed, able to correlate observations of motility on substrata differing in adhesiveness. They also demonstrate that migration speed depends in biphasic manner on attachment strength, with maximal migration at an intermediate level of cell-substratum adhesiveness.

Cell Adhesion↗

PubMed1991

Mathematical model for the effects of adhesion and mechanics on cell migration speed.

Migration of mammalian blood and tissue cells over adhesive surfaces is apparently mediated by specific reversible reactions between cell membrane adhesion receptors and complementary ligands attached to the substratum. Although in a number of systems these receptors and ligand molecules have been isolated and identified, a theory capable of predicting the effects of their properties on cell migration behavior currently does not exist. We present a simple mathematical model for elucidating the dependence of cell speed on adhesion-receptor/ligand binding and cell mechanical properties. Our model can be applied to propose answers to questions such as: does an optimal adhesiveness exist for cell movement? How might changes in receptor and ligand density and/or affinity affect the rate of migration? Can cell rheological properties influence movement speed? This model incorporates cytoskeletal force generation, cell polarization, and dynamic adhesion as requirements for persistent cell movement. A critical feature is the proposed existence of an asymmetry in some cell adhesion-receptor property, correlated with cell polarity. We consider two major alternative mechanisms underlying this asymmetry: (a) a spatial distribution of adhesion-receptor number due to polarized endocytic trafficking and (b) a spatial variation in adhesion-receptor/ligand bond strength. Applying a viscoelastic-solid model for cell mechanics allows us to represent one-dimensional locomotion with a system of differential equations describing cell deformation and displacement along with adhesion-receptor dynamics. In this paper, we solve these equations under the simplifying assumption that receptor dynamics are at a quasi-steady state relative to cell locomotion. Thus, our results are strictly valid for sufficiently slow cell movement, as typically observed for tissue cells such as fibroblasts. Numerical examples relevant to experimental systems are provided. Our results predict how cell speed might vary with intracellular contractile force, cell rheology, receptor/ligand kinetics, and receptor/ligand number densities. A biphasic dependence is shown to be possible with respect to some of the system parameters, with position of the maxima essentially governed by a balance between transmitted contractile force and adhesiveness. We demonstrate that predictions for the two alternative asymmetry mechanisms can be distinguished and could be experimentally tested using cell populations possessing different adhesion-receptor numbers.

Animals↗

PubMedDate not supplied

Effect of cell-cell interactions on the observable strength of adhesion of sheets of cells.

Previous research in cellular adhesion has focused primarily on studying isolated cells under conditions where cells do not interact with each other. However, in vivo cells form sheets where both cell-substratum and cell-cell interactions contribute to the overall adhesive behavior. Our understanding of how cell-cell and cell-substratum interactions affect the overall process of cell adhesion in these situations is limited. To address this problem, we developed a systematic approach to evaluate how cell-cell and cell-substratum interactions affect the critical shear stress for detachment for semi-confluent and confluent sheets of cells. Our studies were based on subjecting cultures of adherent cells to a defined hydrodynamic flow in a radial-flow chamber with a gap height of 140 microm. Using phase-contrast microscope imaging and analysis we measured shear-dependent patterns of detachment as a function of the extent of cell confluency. Our results show that the critical shear stress for detachment is maximum at intermediate extents of confluency of 10%-40%. These results have important implications for sodding vascular grafts and tissue engineering.

Animals↗