Tissue engineered vascular grafts (TEVGs) have the potential to overcome the issues faced by existing small diameter prosthetic grafts by providing a biodegradable scaffold where the patient's own ...cells can engraft and form functional neotissue. However, applying classical approaches to create arterial TEVGs using slow degrading materials with supraphysiological mechanical properties, typically results in limited host cell infiltration, poor remodeling, stenosis, and calcification. The purpose of this study is to evaluate the feasibility of novel small diameter arterial TEVGs created using fast degrading material. A 1.0mm and 5.0mm diameter TEVGs were fabricated with electrospun polycaprolactone (PCL) and chitosan (CS) blend nanofibers. The 1.0mm TEVGs were implanted in mice (n = 3) as an unseeded infrarenal abdominal aorta interposition conduit., The 5.0mm TEVGs were implanted in sheep (n = 6) as an unseeded carotid artery (CA) interposition conduit. Mice were followed with ultrasound and sacrificed at 6 months. All 1.0mm TEVGs remained patent without evidence of thrombosis or aneurysm formation. Based on small animal outcomes, sheep were followed with ultrasound and sacrificed at 6 months for histological and mechanical analysis. There was no aneurysm formation or calcification in the TEVGs. 4 out of 6 grafts (67%) were patent. After 6 months in vivo, 9.1 ± 5.4% remained of the original scaffold. Histological analysis of patent grafts demonstrated deposition of extracellular matrix constituents including elastin and collagen production, as well as endothelialization and organized contractile smooth muscle cells, similar to that of native CA. The mechanical properties of TEVGs were comparable to native CA. There was a significant positive correlation between TEVG wall thickness and CD68+ macrophage infiltration into the scaffold (R2 = 0.95, p = 0.001). The fast degradation of CS in our novel TEVG promoted excellent cellular infiltration and neotissue formation without calcification or aneurysm. Modulating host macrophage infiltration into the scaffold is a key to reducing excessive neotissue formation and stenosis.
Abstract Background Tissue-engineered vascular grafts (TEVGs) offer potential to overcome limitations of current approaches for reconstruction in congenital heart disease by providing biodegradable ...scaffolds on which autologous cells proliferate and provide physiologic functionality. However, current TEVGs do not address the diverse anatomic requirements of individual patients. This study explores the feasibility of creating patient-specific TEVGs by combining 3-dimensional (3D) printing and electrospinning technology. Methods An electrospinning mandrel was 3D-printed after computer-aided design based on preoperative imaging of the ovine thoracic inferior vena cava (IVC). TEVG scaffolds were then electrospun around the 3D-printed mandrel. Six patient-specific TEVGs were implanted as cell-free IVC interposition conduits in a sheep model and explanted after 6 months for histologic, biochemical, and biomechanical evaluation. Results All sheep survived without complications, and all grafts were patent without aneurysm formation or ectopic calcification. Serial angiography revealed significant decreases in TEVG pressure gradients between 3 and 6 months as the grafts remodeled. At explant, the nanofiber scaffold was nearly completely resorbed and the TEVG showed similar mechanical properties to that of native IVC. Histological analysis demonstrated an organized smooth muscle cell layer, extracellular matrix deposition, and endothelialization. No significant difference in elastin and collagen content between the TEVG and native IVC was identified. There was a significant positive correlation between wall thickness and CD68+ macrophage infiltration into the TEVG. Conclusions Creation of patient-specific nanofiber TEVGs by combining electrospinning and 3D printing is a feasible technology as future clinical option. Further preclinical studies involving more complex anatomical shapes are warranted.
Fibrocytes are hematopoietic-derived cells that directly contribute to tissue fibrosis by producing collagen following injury, during disease, and with aging. The lack of a fibrocyte-specific marker ...has led to the use of multiple strategies for identifying these cells
. This review will detail how past studies were performed, report their findings, and discuss their strengths and limitations. The motivation is to identify opportunities for further investigation and promote the adoption of best practices during future study design.
For over 25 years, our group has used regenerative medicine strategies to develop improved biomaterials for use in congenital heart surgery. Among other applications, we developed a tissue-engineered ...vascular graft (TEVG) by seeding tubular biodegradable polymeric scaffolds with autologous bone marrow-derived mononuclear cells. Results of our first-in-human study demonstrated feasibility as the TEVG transformed into a living vascular graft having an ability to grow, making it the first engineered graft with growth potential. Yet, outcomes of this first Food and Drug Administration-approved clinical trial evaluating safety revealed a prohibitively high incidence of early TEVG stenosis, preventing the widespread use of this promising technology. Mechanistic studies in mouse models provided important insight into the development of stenosis and enabled advanced computational models. Computational simulations suggested both a novel inflammation-driven, mechano-mediated process of in vivo TEVG development and an unexpected natural history, including spontaneous reversal of the stenosis. Based on these in vivo and in silico discoveries, we have been able to rationally design strategies for inhibiting TEVG stenosis that have been validated in preclinical large animal studies and translated to the clinic via a new Food and Drug Administration-approved clinical trial. This progress would not have been possible without the multidisciplinary approach, ranging from small to large animal models and computational simulations. This same process is expected to lead to further advances in scaffold design, and thus next generation TEVGs.
The International Society for Stem Cell Research (ISSCR) presents its 2016 Guidelines for Stem Cell Research and Clinical Translation (ISSCR, 2016). The 2016 guidelines reflect the revision and ...extension of two past sets of guidelines (ISSCR, 2006; ISSCR, 2008) to address new and emerging areas of stem cell discovery and application and evolving ethical, social, and policy challenges. These guidelines provide an integrated set of principles and best practices to drive progress in basic, translational, and clinical research. The guidelines demand rigor, oversight, and transparency in all aspects of practice, providing confidence to practitioners and public alike that stem cell science can proceed efficiently and remain responsive to public and patient interests. Here, we highlight key elements and recommendations in the guidelines and summarize the recommendations and deliberations behind them.
•The ISSCR presents its new Guidelines for Stem Cell Research and Clinical Translation•The guidelines outline core principles and best practices for the field•Recommendations drive rigor and transparency in all aspects of stem cell research•The guidelines build widespread confidence in the integrity of the research enterprise
The International Society for Stem Cell Research (ISSCR) presents its 2016 Guidelines for Stem Cell Research and Clinical Translation (ISSCR, 2016). The 2016 guidelines reflect the revision and extension of two past sets of guidelines (ISSCR, 2006; ISSCR, 2008) to address new and emerging areas of stem cell discovery and application and evolving ethical, social, and policy challenges. These guidelines provide an integrated set of principles and best practices to drive progress in basic, translational, and clinical research. The guidelines demand rigor, oversight, and transparency in all aspects of practice, providing confidence to practitioners and public alike that stem cell science can proceed efficiently and remain responsive to public and patient interests. Here, we highlight key elements and recommendations in the guidelines and summarize the recommendations and deliberations behind them.
Objective
Composite tracheal grafts (CTG) combining decellularized scaffolds with external biomaterial support have been shown to support host‐derived neotissue formation. In this study, we examine ...the biocompatibility, graft epithelialization, vascularization, and patency of three prototype CTG using a mouse microsurgical model.
Study Design
Tracheal replacement, regenerative medicine, biocompatible airway splints, animal model.
Method
CTG electrospun splints made by combining partially decellularized tracheal grafts (PDTG) with polyglycolic acid (PGA), poly(lactide‐co‐ε‐caprolactone) (PLCL), or PLCL/PGA were orthotopically implanted in mice (N = 10/group). Tracheas were explanted two weeks post‐implantation. Micro‐Computed Tomography was conducted to assess for graft patency, and histological analysis was used to assess for epithelialization and neovascularization.
Result
Most animals (greater than 80%) survived until the planned endpoint and did not exhibit respiratory symptoms. MicroCT confirmed the preservation of graft patency. Grossly, the PDTG component of CTG remained intact. Examining the electrospun component of CTG, PGA degraded significantly, while PLCL+PDTG and PLCL/PGA + PDTG maintained their structure. Microvasculature was observed across the surface of CTG and infiltrating the pores. There were no signs of excessive cellular infiltration or encapsulation. Graft microvasculature and epithelium appear similar in all groups, suggesting that CTG did not hinder endothelialization and epithelialization.
Conclusion
We found that all electrospun nanofiber CTGs are biocompatible and did not affect graft patency, endothelialization and epithelialization. Future directions will explore methods to accelerate graft regeneration of CTG.
Level of Evidence
N/A Laryngoscope, 134:1155–1162, 2024
Composite tracheal grafts (CTG) combining decellularized scaffolds with external biomaterial support have been shown to support host‐derived neotissue formation. In this study, we examine the biocompatibility, graft epithelialization, vascularization, and patency of three prototype CTG using a mouse microsurgical model.
Objective:
To provide a state-of-the-art review discussing recent achievements in tissue engineered tracheal reconstruction.
Data Sources and Review Methods:
A structured PubMed search of the current ...literature up to and including October 2015. Representative articles that discuss the translation of tissue engineered tracheal grafts (TETG) were reviewed.
Conclusions:
The integration of a biologically compatible support with autologous cells has resulted in successful regeneration of respiratory epithelium, cartilage, and vascularization with graft patency, although the optimal construct composition has yet to be defined. Segmental TETG constructs are more commonly complicated by stenosis and delayed epithelialization when compared to patch tracheoplasty.
Implications for Practice:
The recent history of human TETG recipients represents revolutionary proof of principle studies in regenerative medicine. Application of TETG remains limited to a compassionate use basis; however, defining the mechanisms of cartilage formation, epithelialization, and refinement of in vivo regeneration will advance the translation of TETG from the bench to the bedside.
Tissue engineering holds great promise for the advancement of cardiovascular surgery as well as other medical fields. Tissue-engineered vascular grafts have the ability to grow and remodel and could ...therefore make great advances for pediatric cardiovascular surgery. In 2001, we began a human clinical trial evaluating these grafts in patients with a univentricular physiology. Herein, we report the long-term results of patients who underwent implantation of tissue-engineered vascular grafts as extracardiac total cavopulmonary conduits. Tissue-engineered vascular grafts seeded with autologous bone marrow mononuclear cells were implanted in 25 patients with univentricular physiology. The graft is composed of a woven fabric of poly-l-lactide acid or polyglycolic acid and a 50:50 poly (l-lactic-co-ε-caprolactone) copolymer. Patients were followed up with postoperatively in a multidisciplinary clinic. Median patient age at operation was 5.5 years and the mean follow-up period was 11.1 years. There was no graft-related mortality during the follow-up period. There was also no evidence of aneurysmal formation, graft rupture, graft infection, or calcification. Seven (28%) patients had asymptomatic graft stenosis and underwent successful balloon angioplasty. Stenosis is the primary complication of the tissue-engineered vascular graft. Avoidance of anticoagulation therapy would improve patients' quality of life. Tissue-engineered vascular grafts have feasibility in pediatric cardiovascular surgery.
Genetically modified mouse models provide a versatile and efficient platform to extend our understanding of the underlying disease processes and evaluate potential treatments for congenital heart ...valve diseases. However, applications have been limited to the gene and molecular levels due to the small size of murine heart valves, which prohibits the use of standard mechanical evaluation and in vivo imaging methods. We have developed an integrated imaging/computational mechanics approach to evaluate, for the first time, the functional mechanical behavior of the murine pulmonary heart valve (mPV). We utilized extant mPV high resolution µCT images of 1-year-old healthy C57BL/6J mice, with mPVs loaded to 0, 10, 20 or 30 mmHg then chemically fixed to preserve their shape. Individual mPV leaflets and annular boundaries were segmented and key geometric quantities of interest defined and quantified. The resulting observed inter-valve variations were small and consistent at each TVP level. This allowed us to develop a high fidelity NURBS-based geometric model. From the resultant individual mPV geometries, we developed a mPV shape-evolving geometric model (SEGM) that accurately represented mPV shape changes as a continuous function of transvalvular pressure. The SEGM was then integrated into an isogeometric finite element based inverse model that estimated the individual leaflet and regional mPV mechanical behaviors. We demonstrated that the mPV leaflet mechanical behaviors were highly anisotropic and nonlinear, with substantial leaflet and regional variations. We also observed the presence of strong axial mechanical coupling, suggesting the important role of the underlying collagen fiber architecture in the mPV. When compared to larger mammalian species, the mPV exhibited substantially different mechanical behaviors. Thus, while qualitatively similar, the mPV exhibited important functional differences that will need to accounted for in murine heart valve studies. The results of this novel study will allow detailed murine tissue and organ level investigations of semi-lunar heart valve diseases.
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