Robert A. Brown

Surface patterning (micro-moulding) of dense, biomimetic collagen is a simple tool to produce complex tissues using layer-by-layer assembly. The aim here was to channelise three-dimensional constructs for improved perfusion. Firstly, collagen fibril accumulation was measured by comparative image analysis to understand the mechanisms of structure formation in plastically compressed collagen during µ-moulding. This showed that shape (circular or rectangular) and dimensions of the template affected collagen distribution around moulded grooves and consequently their stability. In the second part, this was used for effective fabrication of multi-layered plastically compressed collagen constructs with internal channels by roofing the grooves with a second layer. Using rectangular templates of 25/50/100 µm widths and 75 µm depth, grooves were µ-moulded into the fluid-leaving surface of collagen layers with predictable width/depth fidelities. These grooves were then roofed by addition of a second plastically compressed collagen layer on top to produce µ-channels. Resulting µ-channels retained their dimensions and were stable over time in culture with fibroblasts and could be cell seeded with a lining layer by simple transfer of epithelial cells. The results of this study provide a valuable platform for rapid fabrication of complex collagen-based tissues in particular for provision of perfusing microchannels through the bulk material for improved core nutrient supply.

Venous tumor thrombus occurs in 5-10% of patients with renal cell carcinoma. Surgical excision offers the best chance for survival, but is technically difficult. Risk of pulmonary embolism from venous thrombus or tumor thrombus is high, especially with tumors located higher in the inferior vena cava. Cardiopulmonary bypass may be used when a tumor extends above the diaphragm, but carries significant risk. We present an 86-year-old woman with a 7 cm renal mass extending into the inferior vena cava just below the confluence of the hepatic vessels. Prior to surgery she was found to have increasing pulmonary embolisms despite appropriate anticoagulation. Intraoperatively, the AngioVac aspiration system was utilized to prevent further pulmonary embolism. This is the first reported case of the use of this system during radical nephrectomy.

Pancreatic adenocarcinoma is mostly fatal and generally resistant to conventional treatments, such that effective therapies with tolerable side effects are desperately needed. Ion channels includin...

One of the challenges of tissue engineering is the regulation of vascularization and innervations of the implant by the host. Here, we propose that using soluble phosphate glass (SPG) fibers, incorporated in dense collagen constructs will allow us to control the rate and direction of tissue ingrowth. The idea here was to generate channels with tailored direction using conical phosphate glass fibers. The changing surface area-to-mass ratio of conical fibers will make them to dissolve faster from their narrow ends opening up channels in that direction ahead of any ingrowing cells. In this study, we show that SPG fibers can be manipulated to produce conical shape fibers using graded dissolution. Our result shows that 40 µm fibers of composition ratio 0.5 (P₂O₅):0.25 (CaO):0.25 (Na₂O) and dissolution time of 8–10 h have a mean reduction in fiber diameter of 8.85 ± 2.8 µm over 19.5 mm fiber length, i.e., a mean rate of 0.5 µm/mm ( n = 20) change. These conically shaped fibers can also be manipulated and potentially used to promote uniaxial cell–tissue ingrowth for improved innervations and vascularization of tissue engineered constructs.

Operator control of cell/matrix density of plastically compressed collagen hydrogel scaffolds critically depends on reproducibly limiting the extent of scaffold compaction, as fluid expulsion. A functional model of the compression process is presented, based on the idea that the main fluid‐leaving surface (FLS) behaves as an ultrafiltration membrane, allowing fluid (water) out but retaining collagen fibrils to form a cake. We hypothesize that accumulation of collagen at the FLS produces anisotropic structuring but also increases FLS hydraulic resistance (R_FLS), in turn limiting the flux. Our findings show that while compressive load is the primary determinant of flux at the beginning of compression (load‐dependent phase), increasing FLS collagen density (measured by X‐ray attenuation) and increasing R_FLS become the key determinants of flux as the process proceeds (flow‐dependent phase). The model integrates these two phases and can closely predict fluid loss over time for a range of compressive loads. This model provides a useful tool for engineering cell and matrix density to tissue‐specific levels, as well as generating localized 3D nano micro‐scale structures and zonal heterogeneity within scaffolds. Such structure generation is important for complex tissue engineering and forms the basis for process automation and up‐scaling. Copyright © 2010 John Wiley & Sons, Ltd.

Natural tissues are built of metabolites, soluble proteins and solid extracellular matrix components (largely fibrils) together with cells. These are configured in highly organized hierarchies of structure across length scales from nanometre to millimetre, with alignments that are dominated by anisotropies in their fibrillar matrix. If we are to successfully engineer tissues, these hierarchies need to be mimicked with an understanding of the interaction between them. In particular, the movement of different elements of the tissue (e.g. molecules, cells and bulk fluids) is controlled by matrix structures at distinct scales. We present three novel systems to introduce alignment of collagen fibrils, cells and growth factor gradients within a three-dimensional collagen scaffold using fluid flow, embossing and layering of construct. Importantly, these can be seen as different parts of the same hierarchy of three-dimensional structure, as they are all formed into dense collagen gels. Fluid flow aligns collagen fibrils at the nanoscale, embossed topographical features provide alignment cues at the microscale and introducing layered configuration to three-dimensional collagen scaffolds provides microscale- and mesoscale-aligned pathways for protein factor delivery as well as barriers to confine protein diffusion to specific spatial directions. These seemingly separate methods can be employed to increase complexity of simple extracellular matrix scaffolds, providing insight into new approaches to directly fabricate complex physical and chemical cues at different hierarchical scales, similar to those in natural tissues.

The focus for the rapid progress in the field of tissue engineering has been the clinical potential of the technology to repair, replace, maintain or enhance the function of a particular tissue or organ. However, tissue engineering has much wider applicability in basic research and safety testing, which is often not recognized owing to the clinical focus of tissue engineers. Using examples from a recent National Centre for the Replacement, Refinement and Reduction of Animals in Research/Biotechnology and Biological Sciences Research Council symposium, which brought together tissue engineers and scientists from other research communities, this review highlights the potential of tissue engineering to provide scientifically robust alternatives to animals to address basic research questions and improve drug and chemical development in the pharmaceutical and chemical industries.

Blood vessel engineering requires an understanding of the parameters governing the survival of resident vascular smooth muscle cells. We have developed an in vitro, collagen-based 3D model of vascular media to examine the correlation of cell density, O ₂ requirements, and viability. Dense collagen sheets (100 μxm) seeded with porcine pulmonary artery smooth muscle cells (PASMCs) at low or high (11.6 or 23.2x10 ⁶ cells/mL) densities were spiraled around a mandrel to create tubular constructs and cultured for up to 6 days in vitro, under both static and dynamic perfusion conditions. Real-time in situ monitoring showed that within 24 hours core O ₂ tension dropped from 140 mmHg to 20 mmHg and 80 mmHg for high and low cell density static cultures, respectively, with no significant cell death associated with the lowest O ₂ tension. A significant reduction in core O ₂ tension to 60 mmHg was achieved by increasing the O ₂ diffusion distance of low cell density constructs by 33% (p<0.05). After 6 days of static, high cell density culture, viability significantly decreased in the core (55%), with little effect at the surface (75%), whereas dynamic perfusion in a re-circulating bioreactor (1 ml/min) significantly improved core viability (70%, p<0.05), largely eliminating the problem. This study has identified key parameters dictating vascular smooth muscle cell behavior in 3D engineered tissue culture.