Vascular patches tissue-engineered with autologous bone marrow-derived cells and decellularized tissue matrices

Cardiovascular patches applied in congenital cardiac surgery: Current materials and prospects

Congenital Heart Defects (CHDs) are the most common congenital anomalies, affecting between 4 and 75 per 1000 live births. Cardiovascular patches (CVPs) are frequently used as part of the surgical armamentarium to reconstruct cardiovascular structures to correct CHDs in pediatric patients. This review aims to evaluate the history of cardiovascular patches, currently available options, clinical applications, and important features of these patches. Performance and outcomes of different patch materials are assessed to provide reference points for clinicians. The target audience includes clinicians seeking data on clinical performance as they make choices between different patch products, as well as scientists and engineers working to develop patches or synthesize new patch materials.

Adipose-Derived Stem Cells in Reinforced Collagen Gel: A Comparison between Two Approaches to Differentiation towards Smooth Muscle Cells

Scaffolds made of degradable polymers, such as collagen, polyesters or polysaccharides, are promising matrices for fabrication of bioartificial vascular grafts or patches. In this study, collagen isolated from porcine skin was processed into a gel, reinforced with collagen particles and with incorporated adipose tissue-derived stem cells (ASCs). The cell-material constructs were then incubated in a DMEM medium with 2% of FS (DMEM_part), with added polyvinylalcohol nanofibers (PVA_part sample), and for ASCs differentiation towards smooth muscle cells (SMCs), the medium was supplemented either with human platelet lysate released from PVA nanofibers (PVA_PL_part) or with TGF-β1 + BMP-4 (TGF + BMP_part). The constructs were further endothelialised with human umbilical vein endothelial cells (ECs). The immunofluorescence staining of alpha-actin and calponin, and von Willebrand factor, was performed. The proteins involved in cell differentiation, the extracellular matrix (ECM) proteins, and ECM remodelling proteins were evaluated by mass spectrometry on day 12 of culture. Mechanical properties of the gels with ASCs were measured via an unconfined compression test on day 5. Gels evinced limited planar shrinkage, but it was higher in endothelialised TGF + BMP_part gel. Both PVA_PL_part samples and TGF + BMP_part samples supported ASC growth and differentiation towards SMCs, but only PVA_PL_part supported homogeneous endothelialisation. Young modulus of elasticity increased in all samples compared to day 0, and PVA_PL_part gel evinced a slightly higher ratio of elastic energy. The results suggest that PVA_PL_part collagen construct has the highest potential to remodel into a functional vascular wall.

Vascular Remodeling of Clinically Used Patches and Decellularized Pericardial Matrices Recellularized with Autologous or Allogeneic Cells in a Porcine Carotid Artery Model

Background: Cardiovascular surgery is confronted by a lack of suitable materials for patch repair. Acellular animal tissues serve as an abundant source of promising biomaterials. The aim of our study was to explore the bio-integration of decellularized or recellularized pericardial matrices in vivo. Methods: Porcine (allograft) and ovine (heterograft, xenograft) pericardia were decellularized using 1% sodium dodecyl sulfate ((1) Allo-decel and (2) Xeno-decel). We used two cell types for pressure-stimulated recellularization in a bioreactor: autologous adipose tissue-derived stromal cells (ASCs) isolated from subcutaneous fat of pigs ((3) Allo-ASC and (4) Xeno-ASC) and allogeneic Wharton’s jelly mesenchymal stem cells (WJCs) ((5) Allo-WJC and (6) Xeno-WJC). These six experimental patches were implanted in porcine carotid arteries for one month. For comparison, we also implanted six types of control patches, namely, arterial or venous autografts, expanded polytetrafluoroethylene (ePTFE Propaten® Gore®), polyethylene terephthalate (PET Vascutek®), chemically stabilized bovine pericardium (XenoSure®), and detoxified porcine pericardium (BioIntegral® NoReact®). The grafts were evaluated through the use of flowmetry, angiography, and histological examination. Results: All grafts were well-integrated and patent with no signs of thrombosis, stenosis, or aneurysm. A histological analysis revealed that the arterial autograft resembled a native artery. All other control and experimental patches developed neo-adventitial inflammation (NAI) and neo-intimal hyperplasia (NIH), and the endothelial lining was present. NAI and NIH were most prominent on XenoSure® and Xeno-decel and least prominent on NoReact®. In xenografts, the degree of NIH developed in the following order: Xeno-decel > Xeno-ASC > Xeno-WJC. NAI and patch resorption increased in Allo-ASC and Xeno-ASC and decreased in Allo-WJC and Xeno-WJC. Conclusions: In our setting, pre-implant seeding with ASC or WJC had a modest impact on vascular patch remodeling. However, ASC increased the neo-adventitial inflammatory reaction and patch resorption, suggesting accelerated remodeling. WJC mitigated this response, as well as neo-intimal hyperplasia on xenografts, suggesting immunomodulatory properties.

Decellularized bovine aorta as a promising 3D elastin scaffold for vascular tissue engineering applications

Aim: To evaluate the suitability of using aorta elastin scaffold, in combination with human adipose-derived mesenchymal stem cells (hAd-MSCs), as an approach for cardiovascular tissue engineering. Materials & Methods: Human adipose-derived MSCs were seeded on elastin samples of decellularized bovine aorta. The samples were cultured in vitro to investigate the inductive effects of this scaffold on the cells. The results were evaluated using histological, and immunohistochemical methods, as well as MTT assay, DNA content, reverse transcription-PCR and scanning electron microscopy. Results: Histological staining and DNA content confirmed the efficacy of decellularization procedure (82% DNA removal). MTT assay showed the construct's ability to support cell viability and proliferation. Cell differentiation was confirmed by reverse transcription-PCR and positive immunohistochemistry for alfa smooth muscle actin and von Willebrand. Conclusion: The prepared aortic elastin samples act as a potential scaffold, in combination with MSCs, for applications in cardiovascular tissue engineering. Further experiments in animal models are required to confirm this.

CD146 expression regulates osteochondrogenic differentiation of human adipose-derived stem cells

Tissue engineering aims to develop innovative approaches to repair tissue defects. The use of adipose-derived stem cells (ASCs) in tissue regeneration was extensively investigated for osteochondrogenesis. Among the ASC population, ASCs expressing the CD146 were demonstrated to be multipotent and considered as perivascular stem cells, although the functional role of CD146 expression in these cells remains unclear. Herein, we investigated the influence of CD146 expression on osteochondrogenic differentiation of ASCs. Our results showed that, in two-dimensional culture systems, sorted CD146⁺ ASCs proliferated less and displayed higher adipogenic and chondrogenic potential than CD146^- ASCs. The latter demonstrated a higher osteogenic capacity. Besides this, CD146⁺ ASCs in three-dimensional Matrigel/endothelial growth medium (EGM) cultures showed the highest angiogenic capability. When cultured in three-dimensional collagen scaffolds, CD146⁺ ASCs showed a spontaneous chondrogenic differentiation, further enhanced by the EGM medium's addition. Finally, CD146^- ASCs seeded on hexafluoroisopropanol silk scaffolds displayed a greater spontaneous osteogenetic capacity. Altogether, these findings demonstrated a functional and relevant influence of CD146 expression in ASC properties and osteochondrogenic commitment. Exploiting the combination of specific differentiation properties of ASC subpopulations and appropriate culture systems could represent a promising strategy to improve the efficacy of new regenerative therapies.

The Real Need for Regenerative Medicine in the Future of Congenital Heart Disease Treatment

Bioabsorbable materials made from polymeric compounds have been used in many fields of regenerative medicine to promote tissue regeneration. These materials replace autologous tissue and, due to their growth potential, make excellent substitutes for cardiovascular applications in the treatment of congenital heart disease. However, there remains a sizable gap between their theoretical advantages and actual clinical application within pediatric cardiovascular surgery. This review will focus on four areas of regenerative medicine in which bioabsorbable materials have the potential to alleviate the burden where current treatment options have been unable to within the field of pediatric cardiovascular surgery. These four areas include tissue-engineered pulmonary valves, tissue-engineered patches, regenerative medicine options for treatment of pulmonary vein stenosis and tissue-engineered vascular grafts. We will discuss the research and development of biocompatible materials reported to date, the evaluation of materials in vitro, and the results of studies that have progressed to clinical trials.

Polysaccharide-based tissue-engineered vascular patches

Coronary artery and peripheral vascular diseases are the leading cause of morbidity and mortality worldwide and often require surgical intervention to replace damaged blood vessels, including the use of vascular patches in endarterectomy procedures. Tissue engineering approaches can be used to obtain biocompatible and biodegradable materials directed to this application. In this work, dense or porous scaffolds constituted of chitosan (Ch) complexed with alginate (A) or pectin (P) were fabricated and characterized considering their application as tissue-engineered vascular patches. Scaffolds fabricated with alginate presented higher culture medium uptake capacity (up to 17 g/g) than materials produced with pectin. A degradation study of the patches in the presence of lysozyme showed longer-term stability for Ch-P-based scaffolds. Pectin-containing matrices presented higher elastic modulus (around 280 kPa) and ability to withstand larger deformations. Moreover, these materials demonstrated better performance when tested for hemocompatibility, with lower levels of platelet adhesion and activation. Human smooth muscle cells (HSMC) adhered, spread and proliferated better on matrices produced with pectin, probably as a consequence of cell response to higher stiffness of this material. Thus, the outcomes of this study demonstrate that Ch-P-based scaffolds present superior characteristics for the application as vascular patches. Despite polysaccharides are yet underrated in this field, this work shows that biocompatible tridimensional structures based on these polymers present high potential to be applied for the reconstruction and regeneration of vascular tissues.

Vessel graft fabricated by the on-site differentiation of human mesenchymal stem cells towards vascular cells on vascular extracellular matrix scaffold under mechanical stimulation in a rotary bioreactor

Although a significant number of studies on vascular tissue engineering have been reported, the current availability of vessel substitutes in the clinic remains limited mainly due to the mismatch of their mechanical properties and biological functions with native vessels. In this study, a novel approach to fabricating a vessel graft for vascular tissue engineering was developed by promoting differentiation of human bone marrow mesenchymal stem cells (MSCs) into endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) on a native vascular extracellular matrix (ECM) scaffold in a rotary bioreactor. The expression levels of CD31 and vWF, and the LDL uptake capacity as well as the angiogenesis capability of the EC-like cells in the dynamic culture system were significantly enhanced compared to the static system. In addition, α-actin and smoothelin expression, and contractility of VSMC-like cells harvested from the dynamic model were much higher than those in a static culture system. The combination of on-site differentiation of stem cells towards vascular cells in the natural vessel ECM scaffold and maturation of the resulting vessel construct in a dynamic cell culture environment provides a promising approach to fabricating a clinically applicable vessel graft with similar mechanical properties and physiological functions to those of native blood vessels.

Induced Pluripotent Stem Cell-Derived Endothelial Cells: Overview, Current Advances, Applications, and Future Directions

Endothelial cells are prevalent in our bodies and serve multiple functions. By lining the vasculature, they provide a barrier to tissues and facilitate the transport of molecules and cells. They also maintain hemostasis and modulate blood flow by reacting to chemokines and releasing signal molecules. Thus, endothelial dysfunction leads to a wide variety of diseases, including atherosclerosis and coronary artery disease. In today's era of stem cell research, induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) have emerged for research and engineering purposes. They are not only tools for studying disease states but are also a crucial part of efforts to engineer vessel and organ grafts. As the techniques in cell culture, microfluidics, and personalized medicine concomitantly improve, the potential for iPSC-ECs is enormous. We review functions of endothelium in our bodies, the development and uses of iPSC-ECs, and the possible avenues to explore in the future.

Evaluation of recellularization on decellularized aorta scaffolds engineered by ultrasonication treatment

Aortic scaffolds prepared using sonication decellularization treatment has provided a successful medium for repopulation with vascular smooth muscle cells (VSMCs). The objective of this study is to explore the potential of tissue decellularization using ultrasonication treatment and its recellularization before implantation of the cell-seeded scaffolds into host. Aorta tissue samples are decellularized in 2% SDS with sonication for 10 hours and compared with the native tissues. The 4',6-diamidino-2-phenylindole (DAPI) staining was used to evaluate the decellularization and Hematoxylin-Eosin (H-E) staining was used to compare the VSMCs infiltrations onto the decellularized tissues at day-0 and day-6 after cell-seeding. The results histologically showed complete DNA removal from scaffolds after decellularization and subsequent recellularization resulted in successful VSMCs infiltration. Accordingly, the decellularized tissues treated with 2% SDS in sonication demonstrated successful VSMCs repopulation afterward and is speculated to have less toxicity and able to be effectively implanted into host.

The effect of decellularized tissue engineered constructs on periodontal regeneration

AIM

To evaluate the effect of decellularized tissue engineered constructs on cell differentiation in vitro and periodontal regeneration in vivo.

MATERIALS AND METHODS

Periodontal ligament cell (PDLC) sheets were loaded on polycaprolactone (PCL) scaffolds and then decellularized. Constructs were assessed for their effect on allogenic PDLC and mesenchymal stem cell (MSC) differentiation in vitro, as evaluated by gene expression of bone and periodontal ligament tissue markers post-seeding. Expression of MSC marker STRO-1 was assessed by immunostaining. Decellularized constructs were evaluated in a rat periodontal defect model to assess their biocompatibility and tissue integration. Microcomputed topography (μCT) and histological assessment were performed to assess the regenerative potential of the constructs at 2 and 4 weeks postoperatively.

RESULTS

There was upregulation of bone marker gene expression by PDLCs especially on the 14th day. MSCs lacked bone markers expression, but showed increased collagen I marker expression on day 14. STRO-1 expression by the MSCs decreased over the three timepoints when seeded on decellularized sheets. Histological assessment demonstrated the biocompatibility of the decellularized constructs in vivo. More new attachment formation was observed on the decellularized constructs compared to scaffold only controls.

CONCLUSION

Decellularized tissue engineered constructs are capable of inducing cell differentiation in vitro and have the potential to facilitate periodontal regeneration in vivo.

Development and characterization of hybrid tubular structure of PLCL porous scaffold with hMSCs/ECs cell sheet

Tissue engineering offers an alternate approach to providing vascular graft with potential to grow similar with native tissue by seeding autologous cells into biodegradable scaffold. In this study, we developed a combining technique by layering a sheet of cells onto a porous tubular scaffold. The cell sheet prepared from co-culturing human mesenchymal stem cells (hMSCs) and endothelial cells (ECs) were able to infiltrate through porous structure of the tubular poly (lactide-co-caprolactone) (PLCL) scaffold and further proliferated on luminal wall within a week of culture. Moreover, the co-culture cell sheet within the tubular scaffold has demonstrated a faster proliferation rate than the monoculture cell sheet composed of MSCs only. We also found that the co-culture cell sheet expressed a strong angiogenic marker, including vascular endothelial growth factor (VEGF) and its receptor (VEGFR), as compared with the monoculture cell sheet within 2 weeks of culture, indicating that the co-culture system could induce differentiation into endothelial cell lineage. This combined technique would provide cellularization and maturation of vascular construct in relatively short period with a strong expression of angiogenic properties.

Enhanced Cartilaginous Tissue Formation with a Cell Aggregate-Fibrin-Polymer Scaffold Complex

Cell density is one of the factors required in the preparation of engineered cartilage from mesenchymal stem cells (MSCs). Additionally, it is well known for having a significant role in chemical and physical stimulations when stem cells undergo chondrogenic differentiation. Here, we developed an engineered cartilage with a cell aggregate-hydrogel-polymer scaffold complex capable of inducing the effective regeneration of cartilage tissue similar to natural cartilage while retaining a high mechanical strength, flexibility, and morphology. Cell aggregates were generated by the hanging drop method with rabbit bone marrow stromal cells (BMSCs), and poly (lactide-co-caprolactone) (PLCL) scaffolds were fabricated with 78.3 ± 5.3% porosity and a 300⁻500 μm pore size with a gel-pressing method. We prepared the cell aggregate-fibrin-poly (lactide-co-caprolactone) (PLCL) scaffold complex, in which the cell aggregates were evenly dispersed in the fibrin, and they were immobilized onto the surface of the polymer scaffold while filling up the pores. To examine the chondrogenic differentiation of seeded BMSCs and the formation of chondral extracellular matrix onto the complexes, they were cultured in vitro or subcutaneously implanted into nude mice for up to eight weeks. The results of the in vitro and in vivo studies revealed that the accumulation of the chondral extracellular matrices was increased on the cell aggregate-fibrin-PLCL scaffold complexes (CAPs) compared to the single cell-fibrin-PLCL scaffold complexes (SCPs). Additionally, we examined whether the mature and well-developed cartilaginous tissues and lacunae structures typical of mature cartilage were evenly distributed in the CAPs. Consequently, the cell aggregates in the hybrid scaffolds of fibrin gels and elastic PLCL scaffolds can induce themselves to differentiate into chondrocytes, maintain their phenotypes, enhance glycosaminoglycan (GAG) production, and improve the quality of cartilaginous tissue formed in vitro and in vivo.

Experimental Evaluation of Kidney Regeneration by Organ Scaffold Recellularization

The rising number of patients needing renal replacement therapy, alongside the significant clinical and economic limitations of current therapies, creates an imperative need for new strategies to treat kidney diseases. Kidney bioengineering through the production of acellular scaffolds and recellularization with stem cells is one potential strategy. While protocols for obtaining organ scaffolds have been developed successfully, scaffold recellularization is more challenging. We evaluated the potential of in vivo and in vitro kidney scaffold recellularization procedures. Our results show that acellular scaffolds implanted in rats cannot be repopulated with host cells, and in vitro recellularization is necessary. However, we obtained very limited and inconsistent cell seeding when using different infusion protocols, regardless of injection site. We also obtained experimental and theoretical data indicating that uniform cell delivery into the kidney scaffolds cannot be obtained using these infusion protocols, due to the permeability of the extracellular matrix of the scaffold. Our results highlight the major physical barriers that limit in vitro recellularization of acellular kidney scaffolds and the obstacles that must be investigated to effectively advance this strategy for regenerative medicine.

Evaluation of small-diameter vascular grafts reconstructed from decellularized aorta sheets

Following small-diameter vascular grafting, blood vessels fail to retain excellent antithrombotic function and therefore require application of antithrombogenic drugs. We have previously reported early attachment of endothelial cells to the luminal surface of high hydrostatic pressure (HHP)-decellularized arteries after transplantation. In addition, the graft retained antithrombotic function by endothelialization and remained open for several weeks. To fabricate tube grafts of optimal size and shape for small-diameter vascular grafting, we evaluated decellularized porcine aorta sheets as a suitable antithrombogenic material. Porcine aortic sheets were decellularized using detergent-based or HHP methods. The HHP-, but not detergent-based-, decellularized aortic sheets were verified to be acellular, and the mechanical properties of the native aortic sheet remained intact. To fabricate vascular grafts, the decellularized aortic sheets were rolled into tubes and secured using fibrin glue bonding. After implantation into a rat carotid artery model, the tubular grafts withstood normal blood pressure, mechanical beating, and pulsatile flow. After 3 weeks, the tubular grafts remained patent and recipient cell infiltration and cell attachment were observed on the luminal surface. These results indicate that HHP-decellularized aortic sheets may be useful as an antithrombogenic material for tubular vascular grafts. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1293-1298, 2017.

The scaffold microenvironment for stem cell based bone tissue engineering

Bone tissue engineering uses the principles and methods of engineering and life sciences to study bone structure, function and growth mechanism for the purposes of repairing, maintaining and improving damaged bone tissue.

Deconstructing the Tissue Engineered Vascular Graft: Evaluating Scaffold Pre-Wetting, Conditioned Media Incubation, and Determining the Optimal Mononuclear Cell Source

Stenosis limits widespread use of tissue-engineered vascular grafts (TEVGs), and bone marrow mononuclear cell (BM-MNC) seeding attenuates this complication. Yet seeding is a multistep process, and the singular effects of each component are unknown. We investigated which components of the clinical seeding protocol confer graft patency and sought to identify the optimal MNC source. Scaffolds composed of polyglycolic acid and ε-caprolactone/ι-lactic acid underwent conditioned media (CM) incubation (n = 25) and syngeneic BM-MNC (n = 9) or peripheral blood (PB)-MNC (n = 20) seeding. TEVGs were implanted for 2 weeks in the mouse IVC. CM incubation and PB-MNC seeding did not increase graft patency compared to control scaffolds prewet with PBS (n = 10), while BM-MNC seeding reduced stenosis by suppressing inflammation and smooth muscle cell, myofibroblast, and pericyte proliferation. IL-1β, IL-6, and TNFα were elevated in the seeded BM-MNC supernatant. Further, BM-MNC seeding reduced platelet activation in a dose-dependent manner, possibly contributing to TEVG patency.

Preparation of decellularized vascular matrix by co-crosslinking of procyanidins and glutaraldehyde

BACKGROUND

Vascular extracellular matrices (vECMs) have shown potential for small-diameter blood vessel tissue engineering applications. However, problems such as chemical instability and easy calcification are still remained. Chemical crosslinking using crosslinkers such as glutaraldehyde (GA) can improve mechanical properties and proteolysis resistance of vECMs, but leads to calcification and cytotoxicity. Procyanidins (PC) can crosslink ECMs with anti-calcification property and cytocompatibility, but the mechanical properties and chemical stability are unsatisfactory.

OBJECTIVE

A novel co-crosslinking technique using PC and GA was developed, which combines the advantages of both PC and GA for enhancing mechanical properties and stability of vECMs with reduced calcification and cytotoxicity.

METHODS

Fresh carotid were decellularized and then crosslinked by PC and subsequent GA for 6 h respectively. The mechanical properties, dynamic release of PC, enzymatic degradation, calcification and cytotoxicity of crosslinked samples were evaluated.

RESULTS

The co-crosslinked vECMs showed enhanced tensile strength, chemical and biological stability, comparable anti-calcification property as compared to pure PC-crosslinked samples. Cytotoxicity assay showed that the co-crosslinked vECMs were cytocompatible for supporting the adhesion and proliferation of HUVECs.

CONCLUSIONS

Co-crosslinking with PC and GA might be a useful method for preparation of vECM scaffolds with potential applications in small-diameter blood vessel tissue engineering.

Characterization of Tensile Mechanical Behavior of MSCs/PLCL Hybrid Layered Sheet

A layered construct was developed by combining a porous polymer sheet and a cell sheet as a tissue engineered vascular patch. The primary objective of this study is to investigate the influence of mesenchymal stem cells (MSCs) sheet on the tensile mechanical properties of porous poly-(l-lactide-co-ε-caprolactone) (PLCL) sheet. The porous PLCL sheet was fabricated by the solid-liquid phase separation method and the following freeze-drying method. The MSCs sheet, prepared by the temperature-responsive dish, was then layered on the top of the PLCL sheet and cultured for 2 weeks. During the in vitro study, cellular properties such as cell infiltration, spreading and proliferation were evaluated. Tensile test of the layered construct was performed periodically to characterize the tensile mechanical behavior. The tensile properties were then correlated with the cellular properties to understand the effect of MSCs sheet on the variation of the mechanical behavior during the in vitro study. It was found that MSCs from the cell sheet were able to migrate into the PLCL sheet and actively proliferated into the porous structure then formed a new layer of MSCs on the opposite surface of the PLCL sheet. Mechanical evaluation revealed that the PLCL sheet with MSCs showed enhancement of tensile strength and strain energy density at the first week of culture which is characterized as the effect of MSCs proliferation and its infiltration into the porous structure of the PLCL sheet. New technique was presented to develop tissue engineered patch by combining MSCs sheet and porous PLCL sheet, and it is expected that the layered patch may prolong biomechanical stability when implanted in vivo.

An in vivo study of a gold nanocomposite biomaterial for vascular repair

Currently vascular repairs are treated using synthetic or biologic patches, however these patches have an array of complications, including calcification, rupture, re-stenosis, and intimal hyperplasia. An active patch material composed of decellularized tissue conjugated to gold nanoparticles (AuNPs) was developed and the long term biocompatibility and cellular integration was investigated. Porcine abdominal aortic tissue was decellularized and conjugated with 100 nm gold nanoparticles (AuNP). These patches were placed over a longitudinal arteriotomy of the thoracic aorta in six pigs. The animals were monitored for six months. Gross, histological, and immunohistochemical analyses of the patches were performed after euthanasia. Grossly there was minimal scar tissue with the patches still visible on the outer surface of the vessel. The inner lumen was smooth with a seamless transition from patch to native tissue. Histology demonstrated infiltration of host cells into the patch material. The immunohistochemical results demonstrated an endothelial cell layer forming over the patch within the vessel. Smooth muscle cells were repopulating the biomaterial in all animals. These results demonstrated that the AuNP biomaterial patch integrated well with the host tissue and did not failed over the six month implantation time.

Repair of spinal cord injury by implantation of bFGF-incorporated HEMA-MOETACL hydrogel in rats

There is no effective strategy for the treatment of spinal cord injury (SCI). An appropriate combination of hydrogel materials and neurotrophic factor therapy is currently thought to be a promising approach. In this study, we performed experiments to evaluate the synergic effect of implanting hydroxyl ethyl methacrylate [2-(methacryloyloxy)ethyl] trimethylammonium chloride (HEMA-MOETACL) hydrogel incorporated with basic fibroblast growth factor (bFGF) into the site of surgically induced SCI. Prior to implantation, the combined hydrogel was surrounded by an acellular vascular matrix. Sprague-Dawley rats underwent complete spinal cord transection at the T-9 level, followed by implantation of bFGF/HEMA-MOETACL 5 days after transection surgery. Our results showed that the bFGF/HEMA-MOETACL transplant provided a scaffold for the ingrowth of regenerating tissue eight weeks after implantation. Furthermore, this newly designed implant promoted both nerve tissue regeneration and functional recovery following SCI. These results indicate that HEMA-MOETACL hydrogel is a promising scaffold for intrathecal, localized and sustained delivery of bFGF to the injured spinal cord and provide evidence for the possibility that this approach may have clinical applications in the treatment of SCI.

Polymer-Based Reconstruction of the Inferior Vena Cava in Rat: Stem Cells or RGD Peptide?

As part of a program targeted at developing a resorbable valved tube for replacement of the right ventricular outflow tract, we compared three biopolymers (polyurethane [PU], polyhydroxyalkanoate (the poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-4-hydroxyvalerate) [PHBVV]), and polydioxanone [PDO]) and two biofunctionalization techniques (using adipose-derived stem cells [ADSCs] or the arginine-glycine-aspartate [RGD] peptide) in a rat model of partial inferior vena cava (IVC) replacement. Fifty-three Wistar rats first underwent partial replacement of the IVC with an acellular electrospun PDO, PU, or PHBVV patch, and 31 nude rats subsequently underwent the same procedure using a PDO patch biofunctionalized either by ADSC or RGD. Results were assessed both in vitro (proliferation and survival of ADSC seeded onto the different materials) and in vivo by magnetic resonance imaging (MRI), histology, immunohistochemistry [against markers of vascular cells (von Willebrand factor [vWF], smooth muscle actin [SMA]), and macrophages ([ED1 and ED2] immunostaining)], and enzyme-linked immunosorbent assay (ELISA; for the expression of various cytokines and inducible NO synthase). PDO showed the best in vitro properties. Six weeks after implantation, MRI did not detect significant luminal changes in any group. All biopolymers were evenly lined by vWF-positive cells, but only PDO and PHBVV showed a continuous layer of SMA-positive cells at 3 months. PU patches resulted in a marked granulomatous inflammatory reaction. The ADSC and RGD biofunctionalization yielded similar outcomes. These data confirm the good biocompatibility of PDO and support the concept that appropriately peptide-functionalized polymers may be successfully substituted for cell-loaded materials.

Bacterial nanocellulose as a new patch material for closure of ventricular septal defects in a pig model

OBJECTIVES

Current materials for closure of cardiac defects such as ventricular septal defects (VSDs) are associated with compliance mismatch and a chronic inflammatory response. Bacterial nanocellulose (BNC) is a non-degradable biomaterial with promising properties such as high mechanical strength, favourable elasticity and a negligible inflammatory reaction. The aim of this study was the evaluation of a BNC patch for VSD closure and the investigation of its in vivo biocompatibility in a chronic pig model.

METHODS

Young's modulus and tensile strength of BNC patches were determined before and after blood exposure. Muscular VSDs were created and closed with a BNC patch on the beating heart in an in vivo pig model. Hearts were explanted after 7, 30 or 90 days. Macropathology, histology and immunohistochemistry were performed.

RESULTS

Young's modulus and tensile strength of the BNC patch decreased after blood contact from 6.3 ± 1.9 to 3.86 ± 2.2 MPa (P < 0.01) and 0.33 ± 0.06 to 0.26 ± 0.06 MPa (P < 0.01), respectively, indicating the development of higher elasticity. Muscular VSDs were closed with a BNC patch without residual shunting. After 90 days, a mild chronic inflammatory reaction was present. Moreover, there was reduced tissue overgrowth in comparison with polyester. Proceeding cellular organization characterized by fibromuscular cells, production of extracellular matrix, neoangiogenesis and complete neoendothelialization were found. There were no signs of thrombogenicity.

CONCLUSIONS

BNC patches can close VSDs with good mid-term results and its biocompatibility can be considered as satisfactory. Its elasticity increases in the presence of blood, which might be advantageous. Therefore, it has potential to be used as an alternative patch material in congenital heart disease.

Bioengineered vascular scaffolds: the state of the art

To date, there is increasing clinical need for vascular substitutes due to accidents, malformations, and ischemic diseases. Over the years, many approaches have been developed to solve this problem, starting from autologous native vessels to artificial vascular grafts; unfortunately, none of these have provided the perfect vascular substitute. All have been burdened by various complications, including infection, thrombogenicity, calcification, foreign body reaction, lack of growth potential, late stenosis and occlusion from intimal hyperplasia, and pseudoaneurysm formation. In the last few years, vascular tissue engineering has emerged as one of the most promising approaches for producing mechanically competent vascular substitutes. Nanotechnologies have contributed their part, allowing extraordinarily biostable and biocompatible materials to be developed. Specifically, the use of electrospinning to manufacture conduits able to guarantee a stable flow of biological fluids and guide the formation of a new vessel has revolutionized the concept of the vascular substitute. The electrospinning technique allows extracellular matrix (ECM) to be mimicked with high fidelity, reproducing its porosity and complexity, and providing an environment suitable for cell growth. In the future, a better knowledge of ECM and the manufacture of new materials will allow us to "create" functional biological vessels - the base required to develop organ substitutes and eventually solve the problem of organ failure.

Mussel-inspired cell-adhesion peptide modification for enhanced endothelialization of decellularized blood vessels

Enhanced endothelialization of tissue-engineered blood vessels is essential for vascular regeneration and function of engineered vessels. In this study, mussel-inspired surface chemistry of polydopamine (pDA) coatings are applied to functionalize decellularized vein matrix (DVM) with extracellular matrix-derived cell adhesion peptides (RGD and YIGSR). DVMs engineered with pDA-peptides enhance focal adhesion, metabolic activity, and endothelial differentiation of human endothelial progenitor cells (EPCs) derived from cord blood and embryonic stem cells compared with EPCs on non-coated or pDA-coated DVMs. These results indicate that pDA-peptide functionalization may contribute to enhanced, rapid endothelialization of DVM surfaces by promoting adhesion, proliferation, and differentiation of circulating EPCs. Ultimately, this approach may be useful for improving in vivo patency and function of decellularized matrix-based blood vessels.

Endothelial outgrowth cells: function and performance in vascular grafts

The clinical need for vascular grafts continues to grow. Tissue engineering strategies have been employed to develop vascular grafts for patients lacking sufficient autologous vessels for grafting. Restoring a functional endothelium on the graft lumen has been shown to greatly improve the long-term patency of small-diameter grafts. However, obtaining an autologous source of endothelial cells for in vitro endothelialization is invasive and often not a viable option. Endothelial outgrowth cells (EOCs), derived from circulating progenitor cells in peripheral blood, provide an alternative cell source for engineering an autologous endothelium. This review aims at highlighting the role of EOCs in the regulation of processes that are central to vascular graft performance. To characterize EOC performance in vascular grafts, this review identifies the characteristics of EOCs, defines functional performance criteria for EOCs in vascular grafts, and summarizes the existing work in developing vascular grafts with EOCs.

Influence of nanoparticle-embedded polymeric surfaces on cellular adhesion, proliferation, and differentiation

The development of functional substrates to direct cellular organization is important for biomedical applications such as regenerative medicine and biorobotics. In this study, we prepared freestanding polymeric ultrathin films (nanofilms) consisting of poly(lactic acid) (PLA) and magnetic nanoparticles (MNPs), and evaluated the effects of their surface properties on the organization of cardiac-like rat myoblasts (H9c2). We changed surface properties of the PLA nanofilms (i.e., roughness and wettability) as a function of MNPs concentration. We found that the incorporation of MNPs into the nanofilms enhanced both proliferation and adhesion of H9c2 cells. Through the morphological assessment of the differentiated H9c2 cells, we also found that the presence of MNPs significantly increased the fusion index and the surface area of myotubes. In conclusion, the embedding of MNPs is a simple method to tailor the physicochemical properties of the polymeric nanofilms, yet it is an effective approach to enhance the cellular morphogenesis in the field of cardiac tissue engineering for regenerative medicine and biorobotics applications.

The fetal porcine aorta and mesenteric acellular matrix as small-caliber tissue engineering vessels and microvasculature scaffold

BACKGROUND

The extracellular matrix (ECM) is characterized by not only well-preserved scaffolds of organs and vascularized tissues, but also by extremely low immunogenicity during allo- or xeno-implantation. This study aimed to establish a model of a composite microvasculature network scaffold with a small-caliber-dominant vascular pedicle by decellularizing fetal porcine aorta and the conterminous mesentery.

METHODS

The aorta and the conterminous mesenteric vascular system originating from the inferior mesenteric artery were harvested from fetal pigs at late gestation. All of the cellular components were removed by sequential treatment with Triton X-100 and sodium dodecyl sulfate. After the degree of decellularization was assessed, the fetal porcine aorta and mesenteric acellular matrix (FPAMAM) were transplanted into dogs.

RESULTS

Gross and histologic examination demonstrated the removal of cellular constituents with preservation of ECM architecture, including macrochannels and microchannels. The residual DNA content in the FPAMAM was less than 2 %. The aorta and microchannels were perfused well, and the fetal porcine aorta had good patency for more than 3 months.

CONCLUSIONS

The integrity of the FPAMAM provided a scaffold for the reconstruction of a rich vascular network with numerous segmentally radiating branches. Decellularized fetal porcine vascular tissue might be a potential alternative for xenogeneic transplantation based on its optimized properties and low immunogenicity.

LEVEL OF EVIDENCE II

This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Exploring the application of stem cells in tendon repair and regeneration

PURPOSE

To conduct a systematic review of the current evidence for the effects of stem cells on tendon healing in preclinical studies and human studies.

METHODS

A systematic search of the PubMed, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Cochrane, and Embase databases was performed for stem cells and tendons with their associated terminology. Data validity was assessed, and data were collected on the outcomes of trials.

RESULTS

A total of 27 preclinical studies and 5 clinical studies met the inclusion criteria. Preclinical studies have shown that stem cells are able to survive and differentiate into tendon cells when placed into a new tendon environment, leading to regeneration and biomechanical benefit to the tendon. Studies have been reported showing that stem cell therapy can be enhanced by molecular signaling adjunct, mechanical stimulation of cells, and the use of augmentation delivery devices. Studies have also shown alternatives to the standard method of bone marrow-derived mesenchymal stem cell therapy. Of the 5 human studies, only 1 was a randomized controlled trial, which showed that skin-derived tendon cells had a greater clinical benefit than autologous plasma. One cohort study showed the benefit of stem cells in rotator cuff tears and another in lateral epicondylitis. Two of the human studies showed how stem cells were successfully extracted from the humerus and, when tagged with insulin, became tendon cells.

CONCLUSIONS

The current evidence shows that stem cells can have a positive effect on tendon healing. This is most likely because stem cells have regeneration potential, producing tissue that is similar to the preinjury state, but the results can be variable. The use of adjuncts such as molecular signaling, mechanical stimulation, and augmentation devices can potentially enhance stem cell therapy. Initial clinical trials are promising, with adjuncts for stem cell therapy in development.

Blood derived stem cells: an ameliorative therapy in veterinary ophthalmology

Stem cell technology has evoked considerable excitement among people interested in the welfare of animals, as it has suggested the potential availability of new tools for several pathologies, including eye disease, which in many cases is considered incurable. One such example is ulcerative keratitis, which is very frequent in horses. Because some of these corneal ulcers can be very severe, progress rapidly and, therefore, can be a possible cause of vision loss, it is important to diagnose them at an early stage and administer an appropriate treatment, which can be medical, surgical, or a combination of both. The therapeutic strategy should eradicate the infection in order to reduce or stop destruction of the cornea. In addition, it should support the corneal structures and control the uveal reaction, and the pain associated with it, in order to minimize scarring. In this study, we address how stem cells derived from peripheral blood can be used also in ophthalmological pathologies. Our results demonstrate that this treatment protocol improved eye disease in four horse cases, including corneal ulcers and one case of retinal detachment. In all cases, we detected a decrease in the intense inflammatory reaction as well as the restoration of the epithelial surface of the central cornea.

A new clinical approach: use of blood-derived stem cells (BDSCs) for superficial digital flexor tendon injuries in horses

AIMS

In this study, we present an innovative therapy using stem cells that were obtained from the peripheral blood of racehorses affected by uninduced superficial digital flexor tendon (SDFT) injuries.

MAIN METHODS

Blood-derived stem cells (BDSCs) were generated from the blood samples of three horses in the presence of macrophage colony-stimulating factor (M-CSF). The racehorses received a single autologous BDSC treatment, which resulted in the successful repair of the tendons injuries.

KEY FINDINGS

The results demonstrated that the BDSCs injection into the damaged tendon stimulated the regeneration of normal tissue. Furthermore, a relationship may exist between the speed and the quality of new tissue formation and the welfare and management of the treated animals.

SIGNIFICANCE

This study demonstrates that stem cell technology offers new tools for tissue repair that in many cases is considered incurable, and provides additional evidence that BDScs injections increase the speed and quality of the regeneration process in different animal tissues.

Biomaterials to prevascularize engineered tissues

Tissue engineering promises to restore tissue and organ function following injury or failure by creating functional and transplantable artificial tissues. The development of artificial tissues with dimensions that exceed the diffusion limit (1-2 mm) will require nutrients and oxygen to be delivered via perfusion (or convection) rather than diffusion alone. One strategy of perfusion is to prevascularize tissues; that is, a network of blood vessels is created within the tissue construct prior to implantation, which has the potential to significantly shorten the time of functional vascular perfusion from the host. The prevascularized network of vessels requires an extracellular matrix or scaffold for 3D support, which can be either natural or synthetic. This review surveys the commonly used biomaterials for prevascularizing 3D tissue engineering constructs.

Preparation of decellularized and crosslinked artery patch for vascular tissue-engineering application

There is an urgent clinical need of tissue-engineering (TE) vascular grafts, so this study was for developing a fast and simple way of producing TE vascular scaffold. The TE vascular scaffold was prepared with pepsin, DNase and RNase enzymatic decellularization and crosslinked with 0.1, 1, 5% glutaraldehyde (GA), respectively. The samples were underwent analyses of burst pressure; suture strength; cytotoxicity; enzymatic degradation in vitro; degradation in vivo; rehydration; biocompatibilities detected with hematoxylin and eosin (H&E), scan electron microscope, immunohistochemistry both in vivo and in vitro; macrophage infiltration and calcification using Von Kossa staining. After being decellularized the scaffold had a complete removal of cellular components, an intact collagen structure. The burst pressure and suture strength were similar to native artery. 0.1% GA crosslinked scaffold showed less cytotoxicity than 1 and 5% GA groups (P < 0.05) and was resistance to enzymatic degradation in vitro. Once being implanted, 0.1% GA group was resistant to degradation and formed endothelium, smooth muscle and adventitia with few macrophages infiltration. However, there appeared calcification in implants compared with that in native artery. This study demonstrated that DVPs producing methods by enzymatic decellularizing and crosslinking with 0.1% GA could be used for clinical TE vascular graft manufacture.

Hyaluronic acid biodegradable material for reconstruction of vascular wall: a preliminary study in rats

The objective of this preliminary study was to develop a reabsorbable vascular patch that did not require in vitro cell or biochemical preconditioning for vascular wall repair. Patches were composed only of hyaluronic acid (HA). Twenty male Wistar rats weighing 250-350 g were used. The abdominal aorta was exposed and isolated. A rectangular breach (1 mm × 5 mm) was made on vessel wall and arterial defect was repaired with HA made patch. Performance was assessed at 1, 2, 4, 8, and 16 weeks after surgery by histology and immunohistochemistry. Extracellular matrix components were evaluated by molecular biological methods. After 16 weeks, the biomaterial was almost completely degraded and replaced by a neoartery wall composed of endothelial cells, smooth muscle cells, collagen, and elastin fibers organized in layers. In conclusion, HA patches provide a provisional three-dimensional support to interact with cells for the control of their function, guiding the spatially and temporally multicellular processes of artery regeneration.

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.

Histological and immunohistochemical evaluation of autologous cultured bone marrow mesenchymal stem cells and bone marrow mononucleated cells in collagenase-induced tendinitis of equine superficial digital flexor tendon

The aim of this study was to compare treatment with cultured bone marrow stromal cells (cBMSCs), bone marrow Mononucleated Cells (BMMNCs), and placebo to repair collagenase-induced tendinitis in horses. In six adult Standardbred horses, 4000 IU of collagenase were injected in the superficial digital flexor tendon (SDFT). Three weeks after collagenase treatment, an average of either 5.5 x 10(6) cBMSCs or 1.2 x 10(8) BMMNCs, fibrin glue, and saline solution was injected intralesionally in random order. In cBMSC- and BMMNCS-treated tendons, a high expression of cartilage oligomeric matrix protein (COMP) and type I collagen, but low levels of type III collagen were revealed by immunohistochemistry, with a normal longitudinally oriented fiber pattern. Placebo-treated tendons expressed very low quantities of COMP and type I collagen but large numbers of randomly oriented type III collagen fibers. Both cBMSC and BMMNCS grafts resulted in a qualitatively similar heling improvement of tendon extracellular matrix, in terms of the type I/III collagen ratio, fiber orientation, and COMP expression.

The development of a tissue-engineered artery using decellularized scaffold and autologous ovine mesenchymal stem cells

Alternatives to using native arteries in vascular surgery are urgently needed. Vessels made from synthetic polymers have shortcomings such as thrombosis, rejection, intimal hyperplasia, calcification, infection, chronic inflammation and no growth potential. Tissue-engineered blood vessels (TEBV) may overcome these problems. We developed a tissue-engineered artery using autologous bone marrow derived mesenchymal stem cells (MSCs) and a decellularized arterial scaffold. Vascular smooth muscle cell (SMCs)-like cells and endothelial cell (ECs)-like cells were differentiated from MSCs in vitro. We constructed TEBV by seeding these autologous cells onto decellularized ovine carotid arteries and interposed into the carotid arteries in an ovine host models. The scaffold retained the main structural components of a blood vessel, such as collagen and elastin. The TEBVs were patent, anti-thrombogenic, and mechanically stable for 5 months in vivo, whereas non-seeded grafts occluded within 2 weeks. Histological, immunohistochemical, and electron microscopic analyses of the TEBVs demonstrated the existence of endothelium, smooth muscle and the presence of collagen and elastin both at 2 and 5 months, respectively. MSCs labeled with a fluorescent dye prior to implantation were detected in the harvested TE artery 2 months after implantation, indicating that the MSCs survived and contributed to the vascular tissue regeneration. Therefore, TEBVs can be assembled from autologous MSCs and decellularized bioscaffold.

Electrospun scaffolds for stem cell engineering

Stem cells interact with and respond to a myriad of signals emanating from their extracellular microenvironment. The ability to harness the regenerative potential of stem cells via a synthetic matrix has promising implications for regenerative medicine. Electrospun fibrous scaffolds can be prepared with high degree of control over their structure creating highly porous meshes of ultrafine fibers that resemble the extracellular matrix topography, and are amenable to various functional modifications targeted towards enhancing stem cell survival and proliferation, directing specific stem cell fates, or promoting tissue organization. The feasibility of using such a scaffold platform to present integrated topographical and biochemical signals that are essential to stem cell manipulation has been demonstrated. Future application of this versatile scaffold platform to human embryonic and induced pluripotent stem cells for functional tissue repair and regeneration will further expand its potential for regenerative therapies.