In vitro bioactivity of MOEP grafted ePTFE membranes for craniofacial applications

The bioactivity of three methacryloyloxyethyl phosphate (MOEP) grafted expanded polytetrafluoroethylene (ePTFE) membranes with varying surface coverage as well as unmodified ePTFE was investigated through a series of in vitro tests: calcium phosphate (CaP) growth in simulated body fluid (SBF), serum protein adsorption, and a morphology and attachment study of human osteoblast-like SaOS-2 cells. The graft copolymers were prepared by means of gamma irradiation induced grafting and displayed various surface morphologies and wettabilities depending on the grafting conditions used. Unmodified ePTFE did not induce nucleation of Cal? minerals, whereas all the grafted membranes revealed the growth of Cal? minerals after 7 days immersion in SBF. The sample with lowest surface grafting yield (24% coverage), a smooth graft morphology and relatively high hydrophobicity (theta(adv) = 120 degrees, theta(rec) = 80 degrees) showed carbonated hydroxyapatite growth covering the surface. On the other hand, the samples with high surface grafting yield (76% and 100%), a globular graft morphology and hydrophilic surfaces (theta(adv) = 60 degrees and 80 degrees, theta(rec) = 25 degrees and 15 degrees, respectively) exhibited irregular growth of non-apatitic Cap minerals. Irreversibly adsorbed protein measured after a 1 h immersion in serum solution was quantified by the amount of nitrogen on the surface using XPS, as well as by weight increase. All grafted membranes adsorbed 3-6 times more protein than the unmodified membrane. The sample with the highest surface coverage adsorbed the most protein. Osteoblast-like SaOS-2 cells cultured for 3 h revealed significantly higher levels of cell attachment on all grafted membranes compared to unmodified ePTFE. Although the morphology of the cells was heterogeneous, in general, the higher grafted surfaces showed a much better cell morphology than both the low surface-grafted and the control unmodified sample. The suite of in vitro tests confirms that a judicious choice of grafted monomer such as the phosphate-containing methacrylate monomer (MOEP) significantly improves the bioactivity of ePTFE in vitro. (c) 2005 Elsevier Ltd. All rights reserved.

Vascular remodelling in the internal mammary artery graft and association with elevated endothelin-1 expression

Introduction: The vasoconstricting peptide Endothelin-1 (ET-1) has been associated with atherosclerotic cardiovascular disease, AAA, hypertension and hypercholesterolemia. It is known to stimulate quiescent vascular smooth muscle cells (VSMC) into the growth cycle and has been linked to intimal thickening following endothelial injury and is associated with vessel wall remodelling in salt-sensitive hypertension models. Enhanced ET-1 expression has been reported in the internal mammary artery (IMA) and was markedly higher in patients undergoing cardiac bypass surgery who were diabetic and /or hypercholesterolemic. Aims: To firstly review the histopathology of the IMA and secondly, determine the relationship between ET-1 expression in this vessel and mitogenic activity in the medial VSMC. Methods: Vessel tissue collected at the time of CABG surgery was formalin-fixed and paraffin-embedded for histological investigation. Cross sections of the left distal IMAwere stained with Alcian Blue/Verhoeff’s van Gieson to assess medial degeneration and identify the elastic lamellae and picrosirius red to determine the collagen content (specifically type I and type III). Immunohistochemistry staining was used to assess VSMC growth (PCNA label), tissue ET-1 expression, VSMC (SMCa-actin) area and macrophage/monocyte (anti-CD68) infiltration. Quantitative analysis was performed to measure the VSMC area in relation to ET-1 staining. Results: Fifty-five IMA specimens from the CABG patients (10F; 45M; mean age 65 years) were collected for this study. Fourteen donor IMAspecimens were used as controls (7F; 7M; mean age 45 years). Significant medial hypertrophy, VSMC disorganisation and elastic lamellae destruction was detected in the CABG IMA. The amount of Alcian blue staining in the CABG IMA was almost double that of the control (31.85+/14.52% Vs 17.10+/9.96%, P= .0006). Total collagen and type I collagen content was significantly increased compared with controls (65.8+/18.3% Vs 33.7 + / 13.7%, P= .07), (14.2 + /10.0% Vs 4.8 + /2.8%, P= .01), respectively. Tissue ET-1 and PCNA labelling were also significantly elevated the CABG IMA specimens relative to the controls (69.99 + /18.74%Vs 23.33 + /20.53%, P= .0001, and 37.29 + /12.88% Vs 11.06 + /8.18, P= .0001), respectively. There was mild presence of macrophages and monocytes in both CABG and control tissue. Conclusions: The IMA from CABG patients has elevated levels of type I collagen in the extracellular matrix indicative of fibrosis and was coupled with deleterious structural remodelling. Abnormally high levels of ET-1 were measured in the medial SMC layer and was associated with VSMC growth but not related to any chronic inflammatory response within the vessel wall.