Monica T. Hinds

Phase-sensitive optical coherence elastography for mapping tissue microstrains in real time

The authors present a phase-sensitive optical coherence elastography (PSOCE) approach to image instantaneous tissue deformations, strain rates, and strains of soft tissue in real time with sensitivity at the nanometer scale. This method exploits the phase information available in the complex optical coherence tomography images and measures the phase changes between the successive B scans to resolve the instantaneous tissue deformations. The PSOCE system described is capable of producing localized microstrain rate and strain maps of tissue subjected to a dynamic compression in real time. They show that this approach is capable of resolving deformations as small as 0.26nm.

Mechanical Property Characterization of Electrospun Recombinant Human Tropoelastin for Vascular Graft Biomaterials

The development of vascular grafts has focused on finding a biomaterial that is non-thrombogenic, minimizes intimal hyperplasia, matches the mechanical properties of native vessels and allows for regeneration of arterial tissue. In this study, the structural and mechanical properties and the vascular cell compatibility of electrospun recombinant human tropoelastin (rTE) were evaluated as a potential vascular graft support matrix. Disuccinimidyl suberate (DSS) was used to cross-link electrospun rTE fibers to produce a polymeric recombinant tropoelastin (prTE) matrix that is stable in aqueous environments. Tubular 1cm diameter prTE samples were constructed for uniaxial tensile testing and 4mm small-diameter prTE tubular scaffolds were produced for burst pressure and cell compatibility evaluations from 15 wt.% rTE solutions. Uniaxial tensile tests demonstrated an average ultimate tensile strength (UTS) of 0.36±0.05 MPa and elastic moduli of 0.15±0.04 and 0.91±0.16 MPa, which were comparable to extracted native elastin. Burst pressures of 485±25 mm Hg were obtained from 4mm internal diameter scaffolds with 453±74 μm average wall thickness. prTE supported endothelial cell growth with typical endothelial cell cobblestone morphology after 48 h in culture. Cross-linked electrospun rTE has promising properties for utilization as a vascular graft biomaterial with customizable dimensions, a compliant matrix and vascular cell compatibility.

Endothelial cell cytoskeletal alignment independent of fluid shear stress on micropatterned surfaces

Endothelial cells (ECs) in athero-protective regions are elongated with actin and microtubule fibers aligned parallel to the direction of blood flow. Fluid shear stress (FSS) affects EC shape and functions, but little is known about shape-dependent EC properties that are independent of FSS. To evaluate these properties, ECs were elongated on micropatterned (MP) 25mum wide collagen-coated lanes (MPECs) and characterized by cell shape index, actin and microtubule alignment, and polarization of the microtubule-organizing center (MTOC). ECs on non-patterned surfaces were also exposed to FSS. MPEC elongation was microtubule-dependent (and actin-independent); shape indices and cytoskeletal alignment were comparable to FSS-elongated ECs. Cytoskeletal alignment was lost when MPECs were exposed to perpendicular FSS, but not parallel FSS. MTOC polarization was FSS-dependent. Thus, by isolating EC elongation and cytoskeletal alignment from FSS, micropatterning creates a platform for studying EC shape-related cellular functions that are independent of FSS.

Capture of flowing endothelial cells using surface-immobilized anti-kinase insert domain receptor antibody.

In humans, self-endothelialization of synthetic grafts is severely limited, but a recent interesting idea is to attract endothelial progenitor cells (EPCs) from peripheral blood onto grafts via antibodies directed at proposed EPC markers. Results with anti-CD34 antibodies have shown some promise, but it is unclear whether CD34 is the best marker for cells with re-endothelializing potential. Much evidence points to kinase insert domain receptor (KDR) as an important indicator of endothelial potential if not a definitive marker. Because KDR is not an adhesion molecule (like CD34), we first demonstrated the ability to use adsorbed and protein G-oriented antibody to this receptor to capture flowing cells onto a solid surface. Using endothelial cells and smooth muscle cells, we show in a model system under low shear rates the ability to selectively capture cells by this receptor. Furthermore, our results indicate that concomitant flow of cells lacking the receptor does not affect the efficiency of capture of KDR(+) cells but that orienting the antibody significantly increases the efficiency of capture.

Percutaneous management of chronic deep venous reflux: review of experimental work and early clinical experience with bioprosthetic valve

Abstract Lower extremity chronic deep venous insufficiency (CDVI) is common and remains a major health problem worldwide. Selected patients benefited from direct deep vein valve surgical repair or valve transplantation. A major limitation of this approach is that most of the patients are not candidates for these procedures due to obstructions or residual thrombus throughout the vein. The past 15 years have witnessed experimental efforts at catheter-based management of CDVI. This review describes the initial designs and experimental evolution of a mechanical and bioprosthetic venous valve that can be implanted by using a transcatheter technique. These valves consisted of single, double, or triple cusp leaflets made of synthetic or biological materials attached to a carrier or frame. All described devices for percutaneous transcatheter valve placement rely on some form of a vascular stent for valve attachment.

Endothelial cell micropatterning: Methods, effects, and applications

The effects of flow on endothelial cells (ECs) have been widely examined for the ability of fluid shear stress to alter cell morphology and function; however, the effects of EC morphology without flow have only recently been observed. An increase in lithographic techniques in cell culture spurred a corresponding increase in research aiming to confine cell morphology. These studies lead to a better understanding of how morphology and cytoskeletal configuration affect the structure and function of the cells. This review examines EC micropatterning research by exploring both the many alternative methods used to alter EC morphology and the resulting changes in cellular shape and phenotype. Micropatterning induced changes in EC proliferation, apoptosis, cytoskeletal organization, mechanical properties, and cell functionality. Finally, the ways these cellular manipulation techniques have been applied to biomedical engineering research, including angiogenesis, cell migration, and tissue engineering, are discussed.

Successful Repair of Esophageal Injury Using an Elastin Based Biomaterial Patch

An esophageal injury with significant tissue loss is very difficult to repair. We conducted an in vivo study to test our elastin based acellular biomaterial patch to repair such defect. The patch was made from porcine aorta, by decellularization and sterilization. Collagen fibers were preserved to retain mechanical strength and enhance cellular in-growth. Ten domestic pigs underwent right thoracotomy. A 2 cm circular defect was made on the distal esophagus, excising half its circumference, and was repaired using the biomaterial patch and sutures. Soon after the procedure, the animals resumed oral feeding. They were followed for clinical status, weight gain, barium studies, and endoscopic studies, and were killed after 6 weeks to 4 months. All ten animals survived long term, with a procedure success rate of 100% (10 of 10). With the exception of one pneumothorax, no complications occurred, and all animals resumed oral feeding and gained weight. Endoscopic studies showed mucosal coverage by 6 weeks, with minimal stricture at the repair site. Excised specimens showed complete mucosal coverage with regeneration of all three layers. Our biomaterial patch can be used safely and reliably for repair of esophageal injury with significant tissue loss when repaired immediately as in our experiment.

Cytoskeletal structure regulates endothelial cell immunogenicity independent of fluid shear stress

The cardiovascular disease atherosclerosis is directly linked to the functions of endothelial cells (ECs), which are affected by fluid shear stress (FSS). High, unidirectional FSS causes EC elongation with aligned cytoskeletal components and nonimmunogenic EC functions that protect against atherosclerosis. In contrast, low, oscillatory FSS is associated with cobblestone-shaped ECs with randomly oriented cytoskeletons and proinflammatory EC functions that promote atherosclerosis. Whether EC shape plays a role in EC immunogenic functions, independent of FSS, has not been previously determined. The goal of this study was to determine the effect of EC elongation and cytoskeletal alignment on the expression of inflammatory genes and functions. With the use of micropatterned lanes, EC elongation and cytoskeletal alignment were achieved in the absence of FSS. EC gene expression of key inflammation markers determined that the elongation and cytoskeletal alignment of micropattern-elongated ECs (MPECs) alone significantly downregulated VCAM-1 while having no effect on E-selectin and ICAM-1. The positive control of FSS-elongated ECs promoted E-selectin and VCAM-1 downregulation and upregulation of ICAM-1. Functionally, monocytic U937 cells formed weaker interactions on the surface of MPECs compared with cobblestone ECs. Interestingly, MPEC expression of the known FSS-dependent transcription factor krüppel-like factor 2 (KLF2), which promotes a nonimmunogenic EC phenotype, was significantly upregulated in MPECs compared with cobblestone ECs. Cytoskeletal regulation of KLF2 expression was shown to be dependent on microtubules. Therefore, the cellular elongation and cytoskeletal alignment of MPECs regulated immunogenic gene expression and functions and may act synergistically with FSS to create an EC surface with reduced inflammatory capability.

Distinct extracellular matrix microenvironments of progenitor and carotid endothelial cells.

Endothelial cells (ECs) produce and maintain the local extracellular matrix (ECM), a critical function that contributes to EC and blood vessel health. This function is also crucial to vascular tissue engineering, where endothelialization of vascular constructs require a cell source that readily produces and maintains ECM. In this study, baboon endothelial progenitor cell (EPC) deposition of ECM (laminin, collagen IV, and fibronectin) was characterized and compared to mature carotid ECs, evaluated in both elongated and cobblestone morphologies typically found in vivo. Microfluidic micropatterning was used to create 15-microm wide adhesive lanes with 45-microm spacing to reproduce the elongated EC morphology without the influence of external forces. Both EPCs and ECs elongated on micropatterned lanes had aligned actin cytoskeleton and readily deposited ECM. EPCs deposited and remodeled the ECM to a greater extent than ECs. Since a readily produced ECM can improve graft patency, EPCs are an advantageous cell source for endothelializing vascular constructs. Furthermore, EC deposition of ECM was dependent on cell morphology, where elongated ECs deposited more collagen IV and less fibronectin compared to matched cobblestone controls. Thus micropatterned surfaces controlled EC shape and ECM deposition, which ultimately has implications for the design of tissue-engineered vascular constructs.

Hyperglycemia Slows Embryonic Growth and Suppresses Cell Cycle via Cyclin D1 and p21

In pregnant women, the diabetic condition results in a three- to fivefold increased risk for fetal cardiac malformations as a result of elevated glucose concentrations and the resultant osmotic stress in the developing embryo and fetus. Heart development before septation in the chick embryo was studied under two hyperglycemic conditions. Pulsed hyperglycemia induced by daily administration of glucose during 3 days of development caused daily spikes in plasma glucose concentration. In a second model, sustained hyperglycemia was induced with a single injection of glucose into the yolk on day 0. The sustained model raised the average plasma glucose concentration from 70 mg/dL to 180 mg/dL and led to decreased gene expression of glucose transporter GLUT1. Both models of hyperglycemia reduced embryo size, increased mortality, and delayed development. Within the heart outflow tract, reduced proliferation of myocardial and endocardial cells resulted from the sustained hyperglycemia and hyperosmolarity. The cell cycle inhibitor p21 was significantly increased, whereas cyclin D1, a cell cycle promoter, decreased in sustained hyperglycemia compared with controls. The evidence suggests that hyperglycemia-induced developmental delays are associated with slowed cell cycle progression, leading to reduced cellular proliferation. The suppression of critical developmental steps may underlie the cardiac defects observed during late gestation under hyperglycemic conditions.