Colleen Irvin

Zwitterionic hydrogels implanted in mice resist the foreign-body reaction

The performance of implantable biomedical devices is impeded by the foreign-body reaction, which results in formation of a dense collagenous capsule that blocks mass transport and/or electric communication between the implant and the body. No known materials or coatings can completely prevent capsule formation. Here we demonstrate that ultra-low-fouling zwitterionic hydrogels can resist the formation of a capsule for at least 3 months after subcutaneous implantation in mice. Zwitterionic hydrogels also promote angiogenesis in surrounding tissue, perhaps owing to the presence of macrophages exhibiting phenotypes associated with anti-inflammatory, pro-healing functions. Thus, zwitterionic hydrogels may be useful in a broad range of applications, including generation of biocompatible implantable medical devices and tissue scaffolds.

Migration of Arterial Wall Cells Expression of Plasminogen Activators and Inhibitors in Injured Rat Arteries

The expression of plasminogen activators and inhibitors was examined in denuded arteries. Within 5 days, smooth muscle cells (SMCs) on the luminal surface expressed the mRNA for tissue-type plasminogen activator (TPA), urokinase type plasminogen (UPA), the receptor for UPA (UPAR), and plasminogen activator inhibitor type-1 (PAI-1). Similar results were seen after 8 days. Six weeks later, only TPA mRNA was still expressed by SMCs on the luminal surface. En face casein zymograms revealed a net fibrinolytic activity in areas covered with luminal SMCs. Reverse zymography showed no antifibrinolytic activity in these zones. Quiescent endothelial cells did not express TPA, UPA, UPAR, or PAI-1 mRNA. Regenerating endothelium at the wound edge strongly expressed TPA. UPA, and UPAR, as well as PAI-1. UPA and UPAR expression was highly restricted to cells at the wound edge and was not present elsewhere. En face zymography showed no plasmin activity in endothelialized areas, and reverse zymography showed a net fibrinolytic activity in endothelialized zones. These results suggest that plasminogen activator and inhibitor expression correlates with the migration of both SMCs and endothelial cells into an arterial wound.

Smooth Muscle Cell Matrix Metalloproteinase Production Is Stimulated via αvβ3 Integrin

This study tests the hypothesis that alpha(v)beta(3) integrin receptors play a critical role in smooth muscle cell (SMC) migration after arterial injury and facilitate migration through the upregulation of matrix metalloproteinase (MMP) activity. We showed that beta(3) integrin mRNA was upregulated by SMCs in the balloon-injured rat carotid artery in coincidence with MMP-1 expression and early SMC migration. Treatment with the beta(3) integrin-blocking antibody F11 significantly decreased SMC migration into the intima at 4 days after injury, from 110.8+/-30.8 cells/mm(2) in control rats to 10.29+/-7.03 cells/mm(2) in F11-treated rats (P=0.008). By contrast, there was no effect on medial SMC proliferation or on medial SMC number in the carotid artery at 4 days. In vitro, we found that human newborn SMCs produced MMP-1 but that adult SMCs did not. This was possibly due to the fact that newborn SMCs expressed alpha(v)beta(3) integrin receptors, whereas adult SMCs did not. Stimulation of newborn (alpha(v)beta(3)+) SMCs with osteopontin, a matrix ligand for alpha(v)beta(3), increased MMP-1 production from 114.4+/-35.8 ng/mL at 0 nmol/L osteopontin to 232.5+/-57.5 ng/mL at 100 nmol/L osteopontin. Finally, we showed that stimulation of newborn SMCs with platelet-derived growth factor-BB and osteopontin together increased the SMC production of MMP-9. Thus, our results support the hypothesis that SMC alpha(v)beta(3) integrin receptors play an important role in regulating migration by stimulating SMC MMP production.

The effect of lightly crosslinked poly(carboxybetaine) hydrogel coating on the performance of sensors in whole blood

Surface coatings of high packing densities have been routinely used to prevent nonspecific biomolecular and microorganism attachment. Hydrogels are another class of low fouling materials used to create three-dimensional matrixes for the free diffusion of small analytes or drugs and the high-loading of bio-recognition elements. However, biomolecules are subject to being entrapped within hydrogel matrixes or adhered onto hydrogel surfaces, making them questionable for use in whole blood. Here, we demonstrate the feasibility of a lightly crosslinked poly(carboxybetaine) hydrogel for use in whole blood, as opposite to the conventional wisdom of high packing density in surface coatings. Proteins are able to diffuse in and out of the matrix freely without being altered from their native conformations. In order to demonstrate its long-term performance in whole blood, this hydrogel was used as the surface coating of a glucose sensor. This work paves a new way for the development of surface coatings and sensors to achieve long-term stability and high performance in whole blood.

Blood compatibility assessment of polymers used in drug eluting stent coatings.

Differences in thrombosis rates have been observed clinically between different drug eluting stents. Such differences have been attributed to numerous factors, including stent design, injury created by the catheter delivery system, coating application technologies, and the degree of thrombogenicity of the polymer. The relative contributions of these factors are generally unknown. This work focuses on understanding the thrombogenicity of the polymer by examining mechanistic interactions with proteins, human platelets, and human monocytes of a number of polymers used in drug eluting stent coatings, in vitro. The importance for blood interactions of adsorbed albumin and the retention of albumin was suggested by the data. Microscopic imaging and immunostaining enhanced the interpretation of results from the lactate dehydrogenase cell counting assay and provided insight into platelet interactions, total quantification, and morphometry. In particular, highly spread platelets may be surface-passivating, possibly inhibiting ongoing thrombotic events. In many of the assays used here, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) showed a differentiated protein deposition pattern that may contribute to the explanation of the consistently thromboresistant blood-materials interaction for fluororpolymers cited in literature. These results are supportive of one of several possible factors contributing to the good thromboresistant clinical safety performance of PVDF-HFP coated drug eluting stents.

Evaluation of a Sphere-Templated Polymeric Scaffold as a Subcutaneous Implant

OBJECTIVE To evaluate the performance of a sphere-templated poly(2-hydroxyethyl methacrylate) (poly[HEMA]) tissue scaffold as a subcutaneous implant by comparing it with widely used high-density porous polyethylene (HDPPE) implant material. DESIGN We implanted sphere-templated porous poly-(HEMA) and HDPPE disks into the dorsal subcutis of C57BL/6 mice for 4 and 9 weeks. Excisional biopsy specimens of the implants and surrounding tissue were assessed for host inflammatory response, tissue ingrowth, and neovascularization using trichrome, picrosirius red, and anti-endothelial cell antibody staining. RESULTS The poly(HEMA) and HDPPE implants showed resistance to extrusion and elicited a minimal inflammatory response. Both implants supported cellular and collagen ingrowth, but ingrowth within the HDPPE implant was thicker owing to the larger porous structure (>100 μm) of HDPPE, whereas the poly(HEMA) implant had much thinner collagen fibrils within much smaller (40-μm) pores, suggestive of less scar-type reaction. Neovascularization was supported by both implants. Blood vessels were identified within the fibrous ingrowth of the HDPPE and within individual pores of the poly(HEMA). CONCLUSIONS Sphere-templated poly(HEMA) implanted as a subcutaneous tissue scaffold stimulates a minimal inflammatory response and supports cellular infiltration, collagen formation, and neovascularization. Because of its tightly controlled porous structure, poly-(HEMA) appears to induce less scar-type ingrowth compared with HDPPE.