Numerical evaluation of the fields induced by body motion in or near high-field MRI scanners

In modern magnetic resonance imaging, both patients and health care workers are exposed to strong. non-uniform static magnetic fields inside and outside of the scanner. In which body movement may be able to induce electric currents in tissues which could be potentially harmful. This paper presents theoretical investigations into the spatial distribution of induced E-fields in a tissue-equivalent human model when moving at various positions around the magnet. The numerical calculations are based on an efficient. quasi-static, finite-difference scheme. Three-dimensional field profiles from an actively shielded 4 T magnet system are used and the body model projected through the field profile with normalized velocity. The simulation shows that it is possible to induce E-fields/currents near the level of physiological significance under some circumstances and provides insight into the spatial characteristics of the induced fields. The methodology presented herein can be extrapolated to very high field strengths for the evaluation of the effects of motion at a variety of field strengths and velocities. (C) 2004 Elsevier Ltd. All rights reserved.

Advances in vascular tissue engineering

Coronary and peripheral artery bypass grafting is commonly used to relieve the symptoms of vascular deficiencies, but the Supply Of autologous artery or vein may not be sufficient or suitable for multiple bypass or repeat procedures, necessitating the use of other materials. Synthetic materials are suitable for large bore arteries but often thrombose when used in smaller arteries. Suitable replacement grafts must have appropriate characteristics, including resistance to infection, low immunogenicity and good biocompatability and thromboresistance, with appropriate mechanical and physiological properties and cheap and fast manufacture. Current avenues of graft development include coating synthetic grafts with either biological chemicals or cells with anticoagulatory properties. Matrix templates or acellular tubes of extracellular matrix (such as collagen) may be coated or infiltrated with cultured cells. Once placed into the artery, these grafts may become colonised by host cells and gain many of the properties of normal artery. Tissue-engineered blood vessels may also be formed from layers of human vascular cells grown in culture. These engineered vessels have many of the characteristics of arteries formed in vivo. Artificial arteries may be also be derived from peritoneal granulation tissue in body bioreactors by adapting the body's natural wound healing response to produce a hollow tube. (C) 2003 Elsevier Inc. All rights reserved.

Polymeric grafting of acrylic acid onto poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Surface functionalization for tissue engineering applications

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) melt processed disks and solvent cast films were modified by graft co-polyinerization with acrylic acid (AAc) in methanol solution at ambient temperature using gamma irradiation (dose rate of 4.5 kGy/h). To assess the presence of carboxylic acid groups on the surface, reaction with pentafluorophenol was performed prior to X-ray photoelectron spectroscopy analysis. The grafting yield for all samples increased with monomer concentration (2-15%), and for the solvent cast films, it also increased with dose (2-9 kGy). However, the grafting yield of the melt processed disks was largely independent of the radiation dose (2-8 kGy). Toluidine blue was used to stain the modified materials facilitating, visual information about the extent of carboxylic acid functionalization and depth penetration of the grafted copolymer. Covalent linking of glucosamine to the functionalized surface was achieved using carbodimide chemistry verifying that the modified substrates are suitable for biomolecule attachment.

Plasma delipidation process induces rapid regression of atherosclerosis and mobilisation of adipose tissue

Cholesterol is a major component of atherosclerotic plaques. Cholesterol accumulation within the arterial intima and atherosclerotic plaques is determined by the difference of cellular cholesterol synthesis and/or influx from apo B-containing lipoproteins and cholesterol efflux. In humans, apo A-I Milano infusion has led to rapid regression of atherosclerosis in coronary arteries. We hypothesised that a multifunctional plasma delipidation process (PDP) would lead to rapid regression of experimental atherosclerosis and probably impact on adipose tissue lipids. In hyperlipidemic animals, the plasma concentrations of cholesterol, triglyceride and phospholipid were, respectively, 6-, 157-, and 18-fold higher than control animals, which consequently resulted in atherosclerosis. PDP consisted of delipidation of plasma with a mixture of butanol-diisopropyl ether (DIPE). PDP removed considerably more lipid from the hyperlipidemic animals than in normolipidemic animals. PDP treatment of hyperlipidemic animals markedly reduced intensity of lipid staining materials in the arterial wall and led to dramatic reduction of lipid in the adipose tissue. Five PDP treatments increased apolipoprotein A1 concentrations in all animals. Biochemical and hematological parameters were unaffected during PDP treatment. These results show that five PDP treatments led to marked reduction in avian atherosclerosis and removal of lipid from adipose tissue. PDP is a highly effective method for rapid regression of atherosclerosis.

The influence of architecture on degradation and tissue ingrowth into three-dimensional poly(lactic-co-glycolic acid) scaffolds in vitro and in vivo

The in vitro and in vivo degradation properties of poly(lactic-co-glycolic acid) (PLGA) scaffolds produced by two different technologies-therm ally induced phase separation (TIPS), and solvent casting and particulate leaching (SCPL) were compared. Over 6 weeks, in vitro degradation produced changes in SCPL scaffold dimension, mass, internal architecture and mechanical properties. TIPS scaffolds produced far less changes in these parameters providing significant advantages over SCPL. In vivo results were based on a microsurgically created arteriovenous (AV) loop sandwiched between two TIPS scaffolds placed in a polycarbonate chamber under rat groin skin. Histologically, a predominant foreign body giant cell response and reduced vascularity was evident in tissue ingrowth between 2 and 8 weeks in TIPS scaffolds. Tissue death occurred at 8 weeks in the smallest pores. Morphometric comparison of TIPS and SCPL scaffolds indicated slightly better tissue ingrowth but greater loss of scaffold structure in SCPL scaffolds. Although advantageous in vitro, large surface area:volume ratios and varying pore sizes in PLGA TIPS scaffolds mean that effective in vivo (AV loop) utilization will only be achieved if the foreign body response can be significantly reduced so as to allow successful vascularisation, and hence sustained tissue growth, in pores less than 300 mu m. (C) 2005 Elsevier Ltd. All rights reserved.

Systematic selection of solvents for the fabrication of 3D combined macro- and microporous polymeric scaffolds for soft tissue engineering

In this study, we investigate the fabrication of 3D porous poly(lactic-co-glycolic acid) (PLGA) scaffolds using the thermally-induced phase separation technique. The current study focuses on the selection of alternative solvents for this process using a number of criteria, including predicted solubility. toxicity, removability and processability. Solvents were removed via either vacuum freeze-drying or leaching, depending on their physical properties. The residual solvent was tested using gas chromatography-mass spectrometry. A large range of porous, highly interconnected scaffold architectures with tunable pore size and alignment was obtained, including combined macro- and microporous structures and an entirely novel 'porous-fibre' structure. The morphological features of the most promising poly(lactic-co-glycolic acid) scaffolds were analysed via scanning electron microscopy and X-ray micro-computed tomography in both two and three dimensions. The Young's moduli of the scaffolds under conditions of temperature, pH and ionic strength similar to those found in the body were tested and were found to be highly dependent on the architectures.

Adipose tissue engineering based on the controlled release of fibroblast growth factor-2 in a collagen matrix

Adipose tissue forms when basement membrane extract ( Matrigel (TM)) and fibroblast growth factor-2 (FGF-2) are added to our mouse tissue engineering chamber model. A mouse tumor extract, Matrigel is unsuitable for human clinical application, and finding an alternative to Matrigel is essential. In this study we generated adipose tissue in the chamber model without using Matrigel by controlled release of FGF-2 in a type I collagen matrix. FGF-2 was impregnated into biodegradable gelatin microspheres for its slow release. The chambers were filled with these microspheres suspended in 60 mu L collagen gel. Injection of collagen containing free FGF-2 or collagen containing gelatin microspheres with buffer alone served as controls. When chambers were harvested 6 weeks after implantation, the volume and weight of the tissue obtained were higher in the group that received collagen and FGF-2 impregnated microspheres than in controls. Histologic analysis of tissue constructs showed the formation of de novo adipose tissue accompanied by angiogenesis. In contrast, control groups did not show extensive adipose tissue formation. In conclusion, this study has shown that de novo formation of adipose tissue can be achieved through controlled release of FGF-2 in collagen type I in the absence of Matrigel.