Fraser W. H. Sutherland

Functional small-diameter neovessels created using endothelial progenitor cells expanded ex vivo

Arterial conduits are increasingly preferred for surgical bypass because of inherent functional properties conferred by arterial endothelial cells, especially nitric oxide production in response to physiologic stimuli. Here we tested whether endothelial progenitor cells (EPCs) can replace arterial endothelial cells and promote patency in tissue-engineered small-diameter blood vessels (4 mm). We isolated EPCs from peripheral blood of sheep, expanded them ex vivo and then seeded them on decellularized porcine iliac vessels. EPC-seeded grafts remained patent for 130 days as a carotid interposition graft in sheep, whereas non-seeded grafts occluded within 15 days. The EPC-explanted grafts exhibited contractile activity and nitric-oxide–mediated vascular relaxation that were similar to native carotid arteries. These results indicate that EPCs can function similarly to arterial endothelial cells and thereby confer longer vascular-graft survival. Due to their unique properties, EPCs might have other general applications for tissue-engineered structures and in treating vascular diseases.

From Stem Cells to Viable Autologous Semilunar Heart Valve

Background—An estimated 275 000 patients undergo heart valve replacement each year. However, existing solutions for valve replacement are complicated by the morbidity associated with lifelong anticoagulation of mechanical valves and the limited durability of bioprostheses. Recent advances in tissue engineering and our understanding of stem cell biology may provide a lifelong solution to these problems. Methods and Results—Mesenchymal stem cells were isolated from ovine bone marrow and characterized by their morphology and antigen expression through immunocytochemistry, flow cytometry, and capacity to differentiate into multiple cell lineages. A biodegradable scaffold was developed and characterized by its tensile strength and stiffness as a function of time in cell-conditioned medium. Autologous semilunar heart valves were then created in vitro using mesenchymal stem cells and the biodegradable scaffold and were implanted into the pulmonary position of sheep on cardiopulmonary bypass. The valves were evaluated by echocardiography at implantation and after 4 months in vivo. Valves were explanted at 4 and 8 months and examined by histology and immunohistochemistry. Valves displayed a maximum instantaneous gradient of 17.2±1.33 mm Hg, a mean gradient of 9.7±1.3 mm Hg, an effective orifice area of 1.35±0.17 cm2, and trivial or mild regurgitation at implantation. Gradients changed little over 4 months of follow-up. Histology showed disposition of extracellular matrix and distribution of cell phenotypes in the engineered valves reminiscent of that in native pulmonary valves. Conclusions—Stem-cell tissue-engineered heart valves can be created from mesenchymal stem cells in combination with a biodegradable scaffold and function satisfactorily in vivo for periods of >4 months. Furthermore, such valves undergo extensive remodeling in vivo to resemble native heart valves.

Dynamic rotational seeding and cell culture system for vascular tube formation.

Optimization of cell seeding and culturing is an important step for the successful tissue engineering of vascular conduits. We evaluated the effectiveness of using a hybridization oven for rotational seeding and culturing of ovine vascular myofibroblasts onto biodegradable polymer scaffolds suitable for replacement of small- and large-diameter blood vessels. Large tubes (12 mm internal diameter and 60 mm length, n = 4) and small tubes (5 mm internal diameter and 20 mm length, n = 4) were made from a combination of polyglycolic acid/poly-4-hydroxybutyrate and coated with collagen solution. Tubes were then placed in culture vessels containing a vascular myofibroblast suspension (10(6) cells/cm(2)) and rotated at 5 rpm in a hybridization oven at 37 degrees C. Light and scanning electron microscopy analyses were performed after 5, 7, and 10 days. Myofibroblasts had formed confluent layers over the outer and inner surfaces of both large and small tubular scaffolds by day 5. Cells had aligned in the direction of flow by day 7. Multiple spindle-shaped cells were observed infiltrating the polymer mesh. Cell density increased between day 5 and day 10. All conduits maintained their tubular shape throughout the experiment. We conclude that dynamic rotational seeding and culturing in a hybridization oven is an easy, effective, and reliable method to deliver and culture vascular myofibroblasts onto tubular polymer scaffolds.

Pneumomediastinum during spontaneous vaginal delivery

We report two rare cases of spontaneous pneumomediastinum that presented shortly after childbirth and resolved without treatment. Spontaneous pneumomediastinum has been described in a wide range of seemingly unrelated but recurrent clinical scenarios. We highlight their common etiologic factors and provide the anatomic and physiologic bases for the radiologic signs that are common in all these conditions.

Ethical and regulatory issues concerning engineered tissues for congenital heart repair

Recent progress in the fields of tissue engineering and xenotransplantation has brought the reality of using engineered tissues for the treatment of congenital heart disease ever closer. However, the introduction of complex scientific advances into the clinic can generate difficult ethical dilemmas for surgeons, patients, and the wider public. Conventional regulatory approaches are not well suited to the introduction of novel cell- and tissue-based therapies. This review presents a short summary of the current state of the art of tissue engineering and xenotransplantation as it relates to congenital heart surgery. The ethical arguments and emerging regulatory framework are then presented, with emphasis on the regulation of tissue-engineered heart valves and the ethics of cardiac xenotransplantation.

A novel bioreactor for the dynamic flexural stimulation of tissue engineered heart valve biomaterials

A novel bioreactor was developed for the purpose of studying the effect of dynamic flexural stimulation on the properties of tissue engineered heart valve (TEHV) scaffolds and constructs. While pulse duplicator and flow loop bioreactors have shown promise in the development of functional tissue engineered cardiovascular constructs, these devices present several drawbacks when applied to the study of fundamental biomechanical phenomena, including: small sample capacity, anatomical sample geometry, and coupled mechanical stimuli. In contrast, our bioreactor was designed to provide a simple, user-controllable mode of mechanical stimulation; cyclic three-point bending; offer a sufficient sample capacity for statistically significant comparisons at multiple time points, and accommodate a simple sample geometry amenable to mechanical testing. The bioreactor has the capacity to dynamically flex twelve rectangular samples (2.5 /spl times/ 0.75 /spl times/ 0.2 cm) under sterile conditions in a humidified cell culture incubator operating at 37/spl deg/C and 5 % CO/sub 2/.

A Novel Bioreactor for the Flexural Stimulation of Tissue Engineered Heart Valve Biomaterials

A novel bioreactor was developed for the purpose of studying the effect of dynamic flexural stimulation on the properties of tissue engineered heart valve (TEHV) scaffolds and constructs. While pulse duplicator and flow loop bioreactors have shown promise in the development of functional tissue engineered cardiovascular constructs [1–3], these devices present several drawbacks when applied to the study of fundamental biomechanical phenomena, including: small sample capacity, anatomical sample geometry, and coupled mechanical stimuli. In contrast, our bioreactor was designed to provide a simple, user-controllable mode of mechanical stimulation; cyclic three-point bending; offer a sufficient sample capacity for statistically significant comparisons at multiple time points, and accommodate a simple sample geometry amenable to mechanical testing. The bioreactor has the capacity to dynamically flex twelve rectangular samples (2.5 × 0.75 × 0.2 cm) under sterile conditions in a humidified cell culture incubator operating at 37 °C and 5% CO2 (Figure 1).Copyright