Tamar L. Mirensky

Tissue-engineered vascular grafts transform into mature blood vessels via an inflammation-mediated process of vascular remodeling

Biodegradable scaffolds seeded with bone marrow mononuclear cells (BMCs) are the earliest tissue-engineered vascular grafts (TEVGs) to be used clinically. These TEVGs transform into living blood vessels in vivo, with an endothelial cell (EC) lining invested by smooth muscle cells (SMCs); however, the process by which this occurs is unclear. To test if the seeded BMCs differentiate into the mature vascular cells of the neovessel, we implanted an immunodeficient mouse recipient with human BMC (hBMC)-seeded scaffolds. As in humans, TEVGs implanted in a mouse host as venous interposition grafts gradually transformed into living blood vessels over a 6-month time course. Seeded hBMCs, however, were no longer detectable within a few days of implantation. Instead, scaffolds were initially repopulated by mouse monocytes and subsequently repopulated by mouse SMCs and ECs. Seeded BMCs secreted significant amounts of monocyte chemoattractant protein-1 and increased early monocyte recruitment. These findings suggest TEVGs transform into functional neovessels via an inflammatory process of vascular remodeling.

Small-diameter biodegradable scaffolds for functional vascular tissue engineering in the mouse model.

The development of neotissue in tissue engineered vascular grafts remains poorly understood. Advances in mouse genetic models have been highly informative in the study of vascular biology, but have been inaccessible to vascular tissue engineers due to technical limitations on the use of mouse recipients. To this end, we have developed a method for constructing sub-1mm internal diameter (ID) biodegradable scaffolds utilizing a dual cylinder chamber molding system and a hybrid polyester sealant scaled for use in a mouse model. Scaffolds constructed from either polyglycolic acid or poly-l-lactic acid nonwoven felts demonstrated sufficient porosity, biomechanical profile, and biocompatibility to function as vascular grafts. The scaffolds implanted as either inferior vena cava or aortic interposition grafts in SCID/bg mice demonstrated excellent patency without evidence of thromboembolic complications or aneurysm formation. A foreign body immune response was observed with marked macrophage infiltration and giant cell formation by post-operative week 3. Organized vascular neotissue, consisting of endothelialization, medial generation, and collagen deposition, was evident within the internal lumen of the scaffolds by post-operative week 6. These results present the ability to create sub-1mm ID biodegradable tubular scaffolds that are functional as vascular grafts, and provide an experimental approach for the study of vascular tissue engineering using mouse models.

Tissue-engineered vascular grafts: does cell seeding matter?

PURPOSE Use of tissue-engineered vascular grafts (TEVGs) in the repair of congenital heart defects provides growth and remodeling potential. Little is known about the mechanisms involved in neovessel formation. We sought to define the role of seeded monocytes derived from bone marrow mononuclear cells (BM-MNCs) on neovessel formation. METHODS Small diameter biodegradable tubular scaffolds were constructed. Scaffolds were seeded with the entire population of BM-MNC (n = 15), BM-MNC excluding monocytes (n = 15), or only monocytes (n = 15) and implanted as infrarenal inferior vena cava (IVC) interposition grafts into severe combined immunodeficiency/bg mice. Grafts were evaluated at 1 week, 10 weeks, or 6 months via ultrasonography and microcomputed tomography, as well as by histologic and immunohistochemical techniques. RESULTS All grafts remained patent without stenosis or aneurysm formation. Neovessels contained a luminal endothelial lining surrounded by concentric smooth muscle cell layer and collagen similar to that seen in the native mouse IVC. Graft diameters differed significantly between those scaffolds seeded with only monocytes (1.022 +/- 0.155 mm) and those seeded without monocytes (0.771 +/- 0.121 mm; P = .021) at 6 months. CONCLUSIONS Monocytes may play a role in maintaining graft patency. Incorporation of such findings into the development of second-generation TEVGs will promote graft patency and success.

Tissue-engineered arterial grafts: long-term results after implantation in a small animal model

BACKGROUND Use of prosthetic vascular grafts in pediatric vascular surgical applications is limited because of risk of infection, poor durability, potential for thromboembolic complications, and lack of growth potential. Construction of an autologous neovessel using tissue engineering technology offers the potential to create an improved vascular conduit for use in pediatric vascular applications. METHODS Tissue-engineered vascular grafts were assembled from biodegradable tubular scaffolds fabricated from poly-L-lactic acid mesh coated with epsilon-caprolactone and L-lactide copolymer. Thirteen scaffolds were seeded with human aortic endothelial and smooth muscle cells and implanted as infrarenal aortic interposition grafts in SCID/bg mice. Grafts were analyzed at time-points ranging from 4 days to 1 year after implantation. RESULTS All grafts remained patent without evidence of thromboembolic complications, graft stenosis, or graft rupture as documented by serial ultrasound and computed tomographic angiogram, and confirmed histologically. All grafts demonstrated extensive remodeling leading to the development of well-circumscribed neovessels with an endothelial inner lining, neomedia containing smooth muscle cells and elastin, and a collagen-rich extracellular matrix. CONCLUSIONS The development of second-generation tissue-engineered vascular grafts shows marked improvement over previous grafts and confirms feasibility of using tissue engineering technology to create an improved arterial conduit for use in pediatric vascular surgical applications.

Pure transvaginal appendectomy versus traditional laparoscopic appendectomy for acute appendicitis: a prospective cohort study.

Objective: This report describes the first cohort study comparing pure transvaginal appendectomies (TVAs) to traditional 3-port laparoscopic appendectomies (LAs). Methods: Between August 2008 and August 2010, 42 patients were offered a pure TVA. Patients who did not wish to undergo a TVA underwent a LA and served as the control group. Demographic data, operative time, length of stay, patient controlled analgesia (PCA) 12-hour-morphine utilization, complications, return to normal activity, and return to work were recorded. Results: Eighteen of 40 enrolled patients underwent a pure TVA. Two patients refused to participate in this study. Mean age (TVA: 31.3 ± 2.5 years vs. LA: 28.2 ± 2.3 years, P = 0.36), mean body mass index (TVA: 23.7 ± 1.2 kg/m2 vs. LA: 23.6 ± 0.7 kg/m2, P = 0.96) mean operative time (TVA: 44.4 ± 4.5 minutes vs. LA: 39.8 ± 2.6 minutes, P = 0.38), and mean length of hospital stay (TVA: 1.1 ± 0.1 days vs. LA: 1.2 ± 0.1 days, P = 0.53) were not statistically significant. However, mean postoperative morphine-use (TVA: 8.7 ± 2.0 mg vs. LA: 23.0 ± 3.4 mg, P < 0.01), return to normal activity (TVA: 3.3 ± 0.4 days vs. LA: 9.7 ± 1.6 days, P < 0.01), and return to work (TVA: 5.4 ± 1.1 days vs. LA: 10.7 ± 1.5 days, P = 0.01) were statistically significant. One conversion in the TVA group to a LA was necessary because of inability to maintain adequate pneumoperitoneum. Four complications were observed: 1 intraabdominal abscess and 1 case of urinary retention in the TVA group; 1 early postoperative bowel obstruction and 1 case of urinary retention in the LA group. Conclusions: Pure TVA is a safe and well-tolerated procedure with significantly less pain and faster recovery compared to traditional LA. This study is registered with www.clinicaltrials.gov as NCT00806429.

The Development of Tissue-Engineered Grafts for Reconstructive Cardiothoracic Surgical Applications

Surgical correction of congenital heart defects often requires the use of valves, patches, or conduits to establish anatomic continuity. Homografts, xenografts, or mechanical prosthetic devices are frequently implanted during these surgical procedures. These grafts however lack growth potential, are associated with increased risk of thrombosis and infection and have limited durability, thus increasing the morbidity and mortality of their application in pediatric cardiac surgery. These limitations are being addressed through the development of living, biologic tissue-engineered valves, patches, and conduits. Pilot studies and phase 1 clinical trials are currently underway to evaluate their feasibility, safety, and efficacy. The optimal scaffold, cell source, and conditioning parameters, however, still remain to be determined and are areas of active research.

Functional Small-Diameter Human Tissue–Engineered Arterial Grafts in an Immunodeficient Mouse Model: Preliminary Findings

HYPOTHESIS The immunodeficient (severe combined immunodeficiency beige [SCID/bg]) mouse model provides a useful model for investigating vascular neotissue formation in human tissue-engineered arterial conduits (TEAC). DESIGN Human aortic smooth muscle cells and endothelial cells were statically seeded on porous biodegradable polymeric scaffolds for vascular tissue engineering. These 2-cell tissue-engineered vascular conduits were implanted into immunodeficient female mice as aortic interposition grafts. Grafts were evaluated over a 30-week course to investigate their patency and structure. SETTING In vivo animal study. PATIENTS Thirteen female C.B-17 SCID/bg mice. INTERVENTION The TEACs implanted as infrarenal abdominal aortic interposition grafts. MAIN OUTCOME MEASURES Selective microcomputed tomography with intra-arterial contrast revealed graft patency and structure. Histological and immunohistochemical evaluations revealed cellularity and extracellular matrix composition. Species-specific immunohistochemical evaluation determined the source of cells within TEACs. RESULTS All TEACs were patent without evidence of thrombosis or rupture over the 30-week course. Histological and immunohistochemical evaluation revealed a von Willebrand factor-positive luminal monolayer surrounded by concentric collagen-rich layers of alpha-smooth muscle actin-positive cells. CONCLUSIONS The SCID/bg mouse is a useful model for investigating vascular neotissue formation in human TEACs. We see evidence that these grafts remain patent while developing into vascular neotissue histologically similar to native aorta. This chimeric animal model also enables determination of seeded cell retention, providing insight into cellular mechanisms underlying neotissue formation.

Outcomes of small bowel obstruction in patients with previous gynecologic malignancies

BACKGROUND Features predictive of malignant small bowel obstructions among patients with previous gynecologic malignancies remain undetermined. METHODS Predictors of malignancy and mortality among patients with gynecologic malignancies and bowel obstructions were identified through a retrospective review of records. RESULTS Malignancy was noted among 69.8% of 189 patients included in the analysis. Advanced-stage cancer (P = .006, odds ratio [OR] = 6.62), ovarian malignancy (P = .001, OR = 25.64), and early-onset obstruction (P = .014) predicted malignant etiology, whereas chemotherapy (P < .001, OR = .02) or radiation therapy (P = .027, OR = .09) predicted benign obstruction. The average survival was 9 months versus 49 months for malignant and benign obstructions, respectively. Ovarian cancer (P = .009, hazard ratio [HR] = 4.45), anemia (P = .001, HR = 1.11), and renal dysfunction (P < .001, HR 1.81) impaired survival. CONCLUSIONS Palliative care should be considered for patients with advanced-stage cancer, ovarian malignancy, and a shorter time interval between cancer diagnosis and bowel obstruction, especially in the setting of anemia and renal dysfunction.