Successes and Failures in Tracheal Bioengineering: Lessons Learned

BACKGROUND

Controversy in tracheal reconstruction using grafts and bioengineered constructs highlights the importance of animal studies before human application. Small animal models help to refine designs but do not adequately model sizes relevant to human anatomy. We have conducted extensive large animal studies and summarize our findings in 26 consecutive transplants.

METHODS

We pooled 26 large animal studies together to investigate common elements related to successes and failures. In general the engineered tracheal graft consisted of a decellularized extracellular matrix surgical patch supported by a 3-dimensional-printed plastic polymer scaffold. Circumferential graft coverage ranged from 50% to 100%, spanning the length of 4 to 6 tracheal rings. Some grafts included embedded stem cells. Control grafts were fabricated without the support scaffold. At death grafts were harvested and examined grossly and through histology.

RESULTS

The support scaffold prevented graft malacia and collapse. Luminal epithelialization was most extensive in grafts with smaller circumferential coverage. Smaller circumferential coverage was also associated with longest animal survival. Chondrogenesis was only observed in grafts with embedded stem cells. Survival time was shortest in 100% circumferential grafts. Granulation tissue was an issue for all graft designs.

CONCLUSIONS

Large animal models capture challenges and complexities relevant to human anatomy. Development of granulation tissue remains a challenge, especially in circumferential grafts. Significant additional research is needed to investigate granulation tissue formation and to provide actionable insight into its management.

Mutational landscape of head and neck squamous cell carcinomas in a South Asian population

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer type globally and contributes significantly to burden of disease in South Asia. In Pakistan, HNSCC is among the most commonly diagnosed cancer in males and females. The increasing regional burden of HNSCC along with a unique set of risk factors merited a deeper investigation of the disease at the genomic level. Whole exome sequencing of HNSCC samples and matched normal genomic DNA analysis (n=7) was performed. Significant somatic single nucleotide variants (SNVs) were identified and pathway analysis performed to determine frequently affected signaling pathways. We identified significant, novel recurrent mutations in ASNS (asparagine synthetase) that may affect substrate binding, and variants in driver genes including TP53, PIK3CA, FGFR2, ARID2, MLL3, MYC and ALK. Using the IntOGen platform, we identified MAP kinase, cell cycle, actin cytoskeleton regulation, PI3K-Akt signaling and other pathways in cancer as affected in the samples. This data is the first of its kind from the Pakistani population. The results of this study can guide a better mechanistic understanding of HNSCC in the population, ultimately contributing new, rational therapeutic targets for the treatment of the disease.

Racial Disparity in Utilization of High-Volume Hospitals for Surgical Treatment of Esophageal Cancer

BACKGROUND

Utilization of high-volume hospitals (HVH) for esophagectomy has been associated with improved perioperative outcomes and reduced mortality. We aimed to test the hypothesis that black-white racial disparities exist in HVH utilization and identify predictors of in-hospital surgical outcomes of esophageal cancer while adjusting for HVH utilization patterns.

METHODS

We queried the New York Statewide Planning and Research Cooperative System database (1995 to 2012) for esophageal cancer patients who underwent surgical resection exclusively. Only records for patients with self-reported white or black race and a valid New York State ZIP code were included (n = 2,895). Analysis was performed to identify factors associated with HVH hospital (≥20 esophagectomies/year) utilization and determine predictors of complications and in-hospital mortality.

RESULTS

Black patients (361 [12.5%]) were significantly different (p < 0.001) than their white counterparts in the proportion of women, Medicaid, income distribution, and privately insured individuals. Although 55% patients overall utilized an HVH, blacks were significantly less likely to utilize an HVH than whites (odds ratio [OR], 0.18; 95% confidence interval [CI], 0.14 to 0.24), even though 74.5% resided within 8.9 miles of one. Operations performed at HVHs were associated with lower in-hospital mortality (OR, 0.48; 95% CI, 0.35 to 0.65); however, mortality remained higher for blacks (OR, 2.04; 95% CI, 1.65 to 3.30; propensity matched OR, 2.45; 95% CI, 1.5 to 4.03).

CONCLUSIONS

Black patients were less likely to undergo esophagectomy at an HVH and experienced higher mortality. Efforts should be made to understand factors influencing patients' decision process and improve referral practices to ensure optimal care is provided across all segments of the population, irrespective of race, insurance, or income status.

Circumferential Three-Dimensional-Printed Tracheal Grafts: Research Model Feasibility and Early Results

BACKGROUND

Methods for tracheal graft research have presented persistent challenges to investigators, and three-dimensional (3D)-printed biosynthetic grafts offer one potential development platform. We aimed to develop an efficient research platform for customizable circumferential 3D-printed tracheal grafts and evaluate feasibility and early structural integrity with a large-animal model.

METHODS

Virtual 3D models of porcine subject tracheas were generated using preoperative computed tomography scans. Two designs were used to test graft customizability and the limits of the construction process. Designs I and II used 270-degree and 360-degree external polycaprolactone scaffolds, respectively, both encompassing a circumferential extracellular matrix collagen layer. The polycaprolactone scaffolds were made in a fused-deposition modeling 3D printer and customized to the recipient's anatomy. Design I was implanted in 3 pigs and design II in 2 pigs, replacing 4-ring tracheal segments. Data collected included details of graft construction, clinical outcomes, bronchoscopy, and gross and histologic examination.

RESULTS

The 3D-printed biosynthetic grafts were produced with high fidelity to the native organ. The fabrication process took 36 hours. Grafts were implanted without immediate complication. Bronchoscopy immediately postoperatively and at 1 week demonstrated patent grafts and appropriate healing. All animals lived beyond a predetermined 1-week survival period. Bronchoscopy at 2 weeks showed significant paraanastomotic granulation tissue, which, along with partial paraanastomotic epithelialization, was confirmed on pathology. Overall survival was 17 to 34 days.

CONCLUSIONS

We propose a rapid, reproducible, resource efficient method to develop various anatomically precise grafts. Further graft refinement and strategies for granulation tissue management are needed to improve outcomes.

Reconstruction of Anterior Tracheal Defects Using a Bioengineered Graft in a Porcine Model

BACKGROUND

Reconstruction of long-segment tracheal defects can be challenging and a suitable tracheal substitute remains lacking. We sought to create a bioengineered tracheal graft to repair such lesions using acellullar bovine dermis extracellular matrix (ECM) and male human mesenchymal stem cells (hMSCs) and implant it in a porcine model.

METHODS

hMSCs were seeded on the ECM and incubated for 1 week with chondrogenic factors. An anterior 4 cm × 3 cm defect was surgically created in the trachea of 4-week-old female Yorkshire pigs. The defect was reconstructed using the bioengineered graft (n = 7) or control (n = 3, ECM only). The study duration was 3 months.

RESULTS

Survival ranged from 7 days (n = 3) to 3 months (n = 7). Early death was due to graft malacia (n = 1, control), graft infection (n = 1, bioengineered), and pneumonia (n = 1, bioengineered). There was substantial animal growth at 3 months (>200% weight). Surveillance bronchoscopy showed patent airway, mild stenosis, and integration of the graft with the native trachea. On histology, luminal epithelialization and neovascularization with scant submucosa were observed in both the bioengineered graft and control groups. Chondrogenesis was seen only in the bioengineered graft. The neocartilage was less mature and organized compared to native cartilage. SRY immunostain was positive in the neocartilage but not control or native trachea.

CONCLUSIONS

We demonstrate the feasibility of the bioengineered graft for reconstruction of long anterior tracheal defects with favorable short-term outcomes. Furthermore, we show its ability to facilitate chondrogenesis, neovascularization, and epithelialization. Importantly, it supported rapid animal growth offering potential solutions for both pediatric and adult applications.

The incidence of trocar-site hernia in minimally invasive bariatric surgery: a comparison of multi versus single-port laparoscopy

INTRODUCTION

Single-port laparoscopy (SPL) employs a 1.5- to 2.5-cm incision at the umbilicus for the placement of a single working port. We hypothesized that the longer incision created by SPL compared with multiport laparoscopy may increase the incidence of trocar-site hernias. We examined our experience with SPL in bariatric operations.

METHODS

There were 734 laparoscopic sleeve gastrectomy and laparoscopic adjustable gastric banding procedures performed at our institution between 2001 and 2011. Fifty-eight patients were lost to follow-up or had a short duration of follow-up (<1 month). Of the remaining 676 cases, 163 were performed via SPL. All laparoscopic wounds created by trocar size greater than 12 mm were closed with absorbable suture.

RESULTS

Patient demographics of the SPL group and the multiport group were similar in terms of age, gender, and comorbidities. The average body mass index (BMI) of the SPL group was lower than the multiport group (43.5 ± 5.3 vs. 45.8 ± 7.7, p < 0.01). The mean follow-up for the SPL group was 11 months versus 24 months for the multiport group. There were three trocar-site hernias out of 513 cases in the multiport compared to one hernia out of 163 cases in the SPL group (0.6 vs. 0.6 %, p = 0.967). All trocar-site hernias occurred at the 15-mm port site. The median time to hernia occurrence for the multiport group was 13 months (range, 1-18). In the SPL group, the hernia occurred at 8 months. On multivariate analysis, age, BMI, SPL, procedure type, and the postoperative weight loss were not associated with the development of trocar-site hernias.

CONCLUSIONS

SPL did not increase the rate of trocar-site hernia in this series. A low rate of trocar-site hernia can be achieved with the use of SPL in bariatric surgery.

The spread of HIV in Pakistan: bridging of the epidemic between populations

In the last two decades, ‘concentrated epidemics’ of human immunodeficiency virus (HIV) have established in several high risk groups in Pakistan, including Injecting Drug Users (IDUs) and among men who have sex with men (MSM). To explore the transmission patterns of HIV infection in these major high-risk groups of Pakistan, 76 HIV samples were analyzed from MSM, their female spouses and children, along with 26 samples from a previously studied cohort of IDUs. Phylogenetic analysis of HIV gag gene sequences obtained from these samples indicated a substantial degree of intermixing between the IDU and MSM populations, suggesting a bridging of HIV infection from IDUs, via MSM, to the MSM spouses and children. HIV epidemic in Pakistan is now spreading to the female spouses and offspring of bisexual MSM. HIV control and awareness programs must be refocused to include IDUs, MSM, as well as bisexual MSM, and their spouses and children.