Extracellular matrix deposition and scaffold biodegradation in an in vitro three‐dimensional model of bone by X‐ray computed microtomography

The development of an in vitro model of bone and the optimization of tools for determining the biological processes occurring during bone repair remains a major goal in the field of bone tissue engineering. Recently, a model based on a three‐dimensional co‐culture of osteoblasts and osteoclast precursors in Skelite^TM scaffolds was developed. Although induction of osteoblast and osteoclast differentiation was observed, a complete evaluation of bone deposition and biodegradation processes was missing due to technical limitations. In the current study, both X‐ray computed microtomography and histological analysis were used to monitor these two key biological processes in the same in vitro model. Either osteoblasts or a combination of osteoblasts and osteoclasts were seeded on Skelite^TM scaffolds. Scaffold biodegradation and increased bone deposition together with a more organized extracellular matrix were observed in the co‐cultures, highlighting the role of osteoclasts in the determination and regulation of bone deposition. Results confirmed the potential and relevance of co‐culturing osteoblasts and osteoclasts to resemble native tissue. The combination of X‐ray computed microtomography and histology presented in this study could be useful in future studies for the validation and development of new in vitro culture systems for bone tissue engineering. Copyright © 2012 John Wiley & Sons, Ltd.     

Fabrication of porous scaffolds by three‐dimensional plotting of a pasty calcium phosphate bone cement under mild conditions

The major advantage of hydroxyapatite (HA)‐forming calcium phosphate cements (CPCs) used as bone replacement materials is their setting under physiological conditions without the necessity for thermal treatment that allows the incorporation of biological factors. In the present study, we have combined the biocompatible consolidation of CPCs with the potential of rapid prototyping (RP) techniques to generate calcium phosphate‐based scaffolds with defined inner and outer morphology. We demonstrate the application of the RP technique three‐dimensional (3D) plotting for the fabrication of HA cement scaffolds. This was realized by utilizing a paste‐like CPC (P‐CPC) which is stable as a malleable paste and whose setting reaction is initiated only after contact with aqueous solutions. The P‐CPC showed good processability in the 3D plotting process and allowed the fabrication of stable 3D structures of different geometries with adequate mechanical stability and compressive strength. The cytocompatibility of the plotted P‐CPC scaffolds was demonstrated in a cell culture experiment with human mesenchymal stem cells. The mild conditions during 3D plotting and post‐processing and the realization of the whole procedure under sterile conditions make this approach highly attractive for fabrication of individualized implants with respect to patient‐specific requirements by simultaneous plotting of biological components. Copyright © 2012 John Wiley & Sons, Ltd.     

猪小肠与犬食管脱细胞基质（ECM）构建组织工程化人工食管的比较研究

背景骨髓间充质干细胞（BMSCs）具有多向分化潜能,来源广泛、分离方便、增殖迅速,是目前公认的组织工程最佳种子细胞;脱细胞基质膜（ECM）有良好的组织相容性,充足的孔隙率,利于种子细胞的附着、增殖,并诱导细胞沿“模具”的性状生长、分化,是组织工程的理想支架材料。目的为比较研究骨髓间充质干细胞在体外在不同的支架材料上复合生长情况,分别与猪小肠脱细胞基质（IECM）;犬自体食管脱细胞基质（EECM）和人工补片（ePTFE）做对比研究。方法使用物理方法和化学方法制备ECM,扫描电镜观察其表面结构。体外提取分离培养犬骨髓间充质干细胞,做流式细胞学鉴定后,取第三代BMSCs分别与IECM、EECM、ePTFE复合培养,HE染色和扫描电镜观察。结果 ECM为白色菲薄,半透明的膜状物,扫描电镜可见其清晰的纤维网状结构,具有良好的立体三维空间结构,并且之间相互连通。BMSCs经流式细胞学鉴定CD29、CD44、CD90、CD105表达率几乎100%,而CD34、CD45几乎不表达。BMSCs与载体支架复合培养15d后,做HE染色切片观察,细胞与IECM、EECM复合生长率良好,与ePTFE较差。结论复合培养后的IECM组与EECM组生物性状较为接近,同时IECM的来源更加广泛,是组织工程化人工食管支架材料的更好选择。     

Effectiveness of tissue engineered three‐dimensional bioactive graft on bone healing and regeneration: an in vivo study with significant clinical value

Several strategies have been used to promote bone repair, with many failing due to the lack of osteoinduction. This report describes an approach for promoting bone healing that attempts to overcome prior shortcomings. First, the role was compared of different concentrations of gelatine (Gel), nanostructured‐hydroxyapatite (nHA), simvastatin (Sim) and nHA‐Sim particles on healing of small femoral bone defects in rabbits. The effective concentration of each was studied, and then a three‐dimensional porous scaffold was designed using Gel, nHA and Sim, which was then cross‐linked with genipin. Morphology, degradation profile and Sim delivery properties of the scaffolds were evaluated in vitro. Then, the scaffolds were subcutaneously tested in vivo to determine their biocompatibility, biodegradability and osteogenic properties. Finally, the scaffolds were implanted in a large radial bone defect model in rabbits and their effect on bone regeneration was investigated. The Gel, nHA and Sim with concentrations of 1, 1 and 5 mg/femoral hole were effective during bone healing respectively, and the Sim showed the most osteoinduction and osteoconduction when compared to controls. The Gel‐Sim and Gel‐nHA‐Sim scaffolds continuously and homogenously released Sim into the simulated body fluid in vitro. Subcutaneously, the scaffolds were biocompatible, biodegradable and able to produce ectopic bone after 30 days. Thirty and 60 days after implantation of the scaffolds in radial bone defects, they were completely degraded and replaced with the new bone that had significantly superior morphology, mineral density, bioelectrical, biophysical and micromechanical properties compared with controls. Such bioactive grafts may be a suitable option for bone reconstruction, healing and repair.     

Design,fabrication and in vitro evaluation of a novel polymer‐hydrogel hybrid scaffold for bone tissue engineering

The development of a bone mechanically‐compatible and osteoinductive scaffold is important for bone tissue engineering applications, particularly for the repair and regeneration of large area critically‐sized bone defects. Although previous studies with weight‐bearing scaffolds have shown promising results, there is a clear need to develop better osteoinductive strategies for effective scaffold‐based bone regeneration. In this study, we designed and fabricated a novel polymer‐hydrogel hybrid scaffold system in which a load‐bearing polymer matrix and a peptide hydrogel allowed for the synergistic combination of mechanical strength and great potential for osteoinductivity in a single scaffold. The hybrid scaffold system promoted increased pre‐osteoblastic cell proliferation. Further, we biotinylated human recombinant bone morphogenetic protein 2 (rhBMP2), and characterized the biotin addition and its effect on rhBMP2 biological activity. The biotinylated rhBMP2 was tethered to the hybrid scaffold using biotin‐streptavidin complexation. Controlled release studies demonstrated increased rhBMP2 retention with the tethered rhBMP2 hybrid scaffold group. In vitro evaluation of the hybrid scaffold was performed with rat bone marrow stromal cells and mouse pre‐osteoblast cell line MC3T3‐E1 cells. Gene expression of alkaline phosphatase (ALP), collagen I (Col I), osteopontin (OPN), bone sialoprotein (BSP), Runx‐2 and osteocalcin (OC) increased in MC3T3‐E1 cells seeded on the rhBMP2 tethered hybrid scaffolds over the untethered counterparts, demonstrating osteoinductive potential of the hybrid graft. These findings suggest the possibility of developing a novel polymer‐hydrogel hybrid system that is weight bearing and osteoinductive for effective bone tissue engineering. Copyright © 2012 John Wiley & Sons, Ltd.     

Design and characterization of a tissue‐engineered bilayer scaffold for osteochondral tissue repair

Treatment of full‐thickness cartilage defects relies on osteochondral bilayer grafts, which mimic the microenvironment and structure of the two affected tissues: articular cartilage and subchondral bone. However, the integrity and stability of the grafts are hampered by the presence of a weak interphase, generated by the layering processes of scaffold manufacturing. We describe here the design and development of a bilayer monolithic osteochondral graft, avoiding delamination of the two distinct layers but preserving the cues for selective generation of cartilage and bone. A highly porous polycaprolactone‐based graft was obtained by combining solvent casting/particulate leaching techniques. Pore structure and interconnections were designed to favour in vivo vascularization only at the bony layer. Hydroxyapatite granules were added as bioactive signals at the site of bone regeneration. Unconfined compressive tests displayed optimal elastic properties and low residual deformation of the graft after unloading (< 3%). The structural integrity of the graft was successfully validated by tension fracture tests, revealing high resistance to delamination, since fractures were never displayed at the interface of the layers (n = 8). Ectopic implantation of grafts in nude mice, after seeding with bovine trabecular bone‐derived mesenchymal stem cells and bovine articular chondrocytes, resulted in thick areas of mature bone surrounding ceramic granules within the bony layer, and a cartilaginous alcianophilic matrix in the chondral layer. Vascularization was mostly observed in the bony layer, with a statistically significant higher blood vessel density and mean area. Thus, the easily generated osteochondral scaffolds, since they are mechanically and biologically functional, are suitable for tissue‐engineering applications for cartilage repair. Copyright © 2012 John Wiley & Sons, Ltd.     

Ovine bone‐ and marrow‐derived progenitor cells and their potential for scaffold‐based bone tissue engineering applications in vitro and in vivo

Recently, research has focused on bone marrow derived multipotent mesenchymal precursor cells (MPC) and osteoblasts (OB) for clinical use in bone engineering. Prior to clinical application, cell based treatment concepts need to be evaluated in preclinical, large animal models. Sheep in particular are considered a valid model for orthopaedic and trauma related research. However, only sheep aged > 6 years show secondary osteon formation characteristic of human bone. Osteogenic cells isolated from animals of this age group remain poorly characterized. In the present study, ex vivo expanded MPC isolated from ovine bone marrow proliferated at a higher rate than OB derived from tibial compact bone as assessed in standard 2D cultures. MPC expressed the respective phenotypic profile typical for different mesenchymal cell populations (CD14^?/CD31^?/CD45^?/CD29⁺/CD44⁺/CD166⁺) and showed a multilineage differentiation potential. When compared to OB, MPC had a higher mineralization potential under standard osteogenic culture conditions and expressed typical bone related markers such as osteocalcin, osteonectin and type I collagen at the mRNA and protein level. After 4 weeks in 3D culture, MPC constructs demonstrated higher cell density and mineralization, whilst cell viability on the scaffolds was assessed > 90%. Cells displayed a spindle‐like morphology and formed interconnected networks. In contrast, when implanted subcutaneously into NOD/SCID mice, MPC presented a lower osteogenic potential than OB. In summary, this study provides a detailed characterisation of ovine MPC and OB from a bone engineering perspective and suggests that MPC and OB provide promising means for future bone disease related treatment applications. Copyright © 2010 John Wiley & Sons, Ltd.     

Osteoblastic differentiation and potent osteogenicity of three‐dimensional hBMSC‐BCP particle constructs

Bone tissue engineering usually consists of associating osteoprogenitor cells and macroporous scaffolds. This study investigated the in vitro osteoblastic differentiation and resulting in vivo bone formation induced by a different approach that uses particles as substrate for human bone marrow stromal cells (hBMSCs), in order to provide cells with a higher degree of freedom and allow them to synthesize a three‐dimensional (3D) environment. Biphasic calcium phosphate (BCP) particles (35 mg, ~175 µm in diameter) were therefore associated with 4 × 10⁵ hBMSCs. To discriminate the roles of BCP properties and cell‐synthesized 3D environments, inert glass beads (GBs) of similar size were used under the same conditions. In both cases, high cell proliferation and extensive extracellular matrix (ECM) production resulted in the rapid formation of thick cell‐synthesized 3D constructs. In vitro, spontaneous osteoblastic differentiation was observed in the 3D constructs at the mRNA and protein levels by monitoring the expression of Runx2, BMP2, ColI, BSP and OCN. The hBMSC–BCP particle constructs implanted in the subcutis of nude mice induced abundant ectopic bone formation after 8 weeks (~35%, n = 5/5). In comparison, only fibrous tissue without bone was observed in the implanted hBMSC–GB constructs (n = 0/5). Furthermore, little bone formation (~3%, n = 5/5) was found in hBMSC–macroporous BCP discs (diameter 8 × 3 mm). This study underlines the lack of correspondence between bone formation and in vitro differentiation assays. Furthermore, these results highlight the importance of using BCP as well as a 3D environment for achieving high bone yield of interest for bone engineering. Copyright © 2012 John Wiley & Sons, Ltd.     

The effects of different vascular carrier patterns on the angiogenesis and osteogenesis of BMSC–TCP‐based tissue‐engineered bone in beagle dogs

Bone repair using tissue‐engineered bone (TEB) in a large defect or accompanied by a poor recipient vascular bed is a long‐standing challenge. Surgical vascular carrier patterns of vascular bundle (VB) and arteriovenous loop (AV loop) have been shown to improve the vascularization and repair capacity of TEB. However, the effects of these different vascular carrier patterns on angiogenesis and osteogenesis in TEB have never been evaluated. Here, TEB was constructed with bone marrow mesenchymal stem cells (BMSCs) and β‐TCP and prevascularized by the VB or AV loop technique in beagle dogs. The vascularization and bone formation in TEB were quantitatively compared using Microfil perfusion, histological examination and CT and micro‐CT analyses. The distribution and constitution of the neovasculature were analysed to determine the underlying mechanism of angiogenesis. The results showed that prevascularized TEB generated bone tissue faster and more homogeneously than untreated TEB. The VB technique was found to strike a better balance between bone regeneration and β‐TCP scaffold degradation than the AV loop strategy, which resulted in more vascularization but less bone yield, due to faster degradation of the β‐TCP scaffold. This study indicates that a suitable triangular relationship, composed of bone regeneration, scaffold degradation and vasculature, is critical to TEB construction. Copyright © 2015 John Wiley & Sons, Ltd.     

Glottic regeneration with a tissue‐engineering technique,using acellular extracellular matrix scaffold in a canine model

Acellular extracellular matrix scaffold derived from porcine urinary bladder (UBM) is decellularized material that has shown success for constructive remodelling of various tissues and organs. The regenerative effects of UBM were reported for the tympanic membrane, oesophagus, trachea, larynx, pleura and pericardium in animal studies, with promising results. The aim of this study was to investigate the regenerative effects of UBM on hemilarynx, using a canine model. A left partial hemilaryngectomy was performed and the surgical defects were reconstructed by insertion of UBM scaffold. Although local infection was observed in one dog in 1 week after implantation of the scaffold, all dogs showed good re‐epithelialization with minimum complication in 1 month. The effect of regeneration of the larynx was evaluated 6 months after the operation. The excised larynx experiments were performed to measure phonation threshold pressure (PTP), normalized mucosal wave amplitude (NMWA) and normalized glottal gap (NGG). The results of the measurements showed that PTP was normal or near normal in two cases and NMWA was within normal range in three cases, although there were individual variations. Histological examination was completed to evaluate structural changes in the scaffold with the appearance of the new cartilaginous structure. However, the regenerated vocal fold mucosa was mostly scarred. The UBM scaffold has shown to be biocompatible, biodegradable and useful for tissue regeneration of the hemilarynx, with possible restoration of function of the vocal fold. The vocal fold mucosa was scarred, which is the next challenge to be addressed. Copyright © 2014 John Wiley & Sons, Ltd.     

Poly‐ε‐caprolactone scaffold and reduced in vitro cell culture: beneficial effect on compaction and improved valvular tissue formation

Tissue‐engineered heart valves (TEHVs), based on polyglycolic acid (PGA) scaffolds coated with poly‐4‐hydroxybutyrate (P4HB), have shown promising in vivo results in terms of tissue formation. However, a major drawback of these TEHVs is compaction and retraction of the leaflets, causing regurgitation. To overcome this problem, the aim of this study was to investigate: (a) the use of the slowly degrading poly‐ε‐caprolactone (PCL) scaffold for prolonged mechanical integrity; and (b) the use of lower passage cells for enhanced tissue formation. Passage 3, 5 and 7 (P3, P5 and P7) human and ovine vascular‐derived cells were seeded onto both PGA–P4HB and PCL scaffold strips. After 4 weeks of culture, compaction, tissue formation, mechanical properties and cell phenotypes were compared. TEHVs were cultured to observe retraction of the leaflets in the native‐like geometry. After culture, tissues based on PGA–P4HB scaffold showed 50–60% compaction, while PCL‐based tissues showed compaction of 0–10%. Tissue formation, stiffness and strength were increased with decreasing passage number; however, this did not influence compaction. Ovine PCL‐based tissues did render less strong tissues compared to PGA–P4HB‐based tissues. No differences in cell phenotype between the scaffold materials, species or cell passage numbers were observed. This study shows that PCL scaffolds may serve as alternative scaffold materials for human TEHVs with minimal compaction and without compromising tissue composition and properties, while further optimization of ovine TEHVs is needed. Reducing cell expansion time will result in faster generation of TEHVs, providing more rapid treatment for patients. Copyright © 2013 John Wiley & Sons, Ltd.     

Characterization of human cultured periosteal sheets expressing bone‐forming potential: in vitro and in vivo animal studies

Our recent clinical studies have demonstrated that autologous implantation of human cultured periosteal (hCP) sheets in combination with porous hydroxylapatite (HAp) particles at the site of periodontal bone defects strikingly facilitates tissue regeneration. To better understand how the hCP sheet functions at the implantation site, we have now examined its biochemical and morphological characteristics in vitro and its ectopic osteoinductivity in nude mice. Cultured human periosteal tissue segments produced periosteal cells that migrated out from the central region within 4–8 days and grew more rapidly with longer culture times. Alkaline phosphatase activity increased in parallel with actual osteoblastic induction. Cytokine array assays demonstrated that osteoblastic induction downregulated IL‐6 and thrombopoietin, but upregulated IL‐8, IL‐13, IGF‐I and IGFBP‐2 in hCP sheets. When differentiated hCP sheets were implanted alone, areas of osteoid and mineralized tissue were formed within 2 weeks, but non‐induced, immature hCP sheets did not produce much mineralization. These findings suggest that mature hCP sheets potentially function not only as seeds of ectopic bone formation without the need of synthetic tissue scaffolds, but also as living drug‐delivery systems, to influence cells near implantation sites by producing several important cytokines. These two major characteristics indicate that a mature hCP sheet is a promising osteoinductive biomaterial, even without conventional scaffolds for periodontal regenerative therapy. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparing the osteogenic potential of bone marrow and tendon‐derived stromal cells to repair a critical‐sized defect in the rat femur

Despite significant advancements in bone tissue‐engineering applications, the clinical impact of bone marrow stromal cells (BMSCs) for the treatment of large osseous defects remains limited. Therefore, other cell sources are under investigation for their osteogenic potential to repair bone. In this study, tendon‐derived stromal cells (TDSCs) were evaluated in comparison to BMSCs to support the functional repair of a 5 mm critical‐sized, segmental defect in the rat femur. Analysis of the trilineage differentiation capacity of TDSCs and BMSCs cultured on collagen sponges revealed impaired osteogenic differentiation and mineral deposition of TDSCs in vitro, whereas chondrogenic and adipogenic differentiation was evident for both cell types. Radiographic assessment demonstrated that neither cell type significantly improved the healing rate of a challenging 5 mm segmental femoral defect. Transplanted TDSCs and BMSCs both led to the formation of only small amounts of bone in the defect area, and histological evaluation revealed non‐mineralized, collagen‐rich scar tissue to be present within the defect area. Newly formed lamellar bone was restricted to the defect margins, resulting in closure of the medullary cavity. Interestingly, in comparison to BMSCs, significantly more TDSC‐derived cells were present at the osteotomy gap up to 8 weeks after transplantation and were also found to be located within newly formed lamellar bone, suggesting their capacity to directly contribute to de novo bone formation. To our knowledge, this is the first study investigating the in vivo capacity of TDSCs to regenerate a critical‐sized defect in the rat femur. Copyright © 2015 John Wiley & Sons, Ltd.     

PDLA/PLLA and PDLA/PCL nanofibers with a chitosan‐based hydrogel in composite scaffolds for tissue engineered cartilage

Osteoarthritis (OA) is the most prevalent musculoskeletal disease in humans, causing pain, loss of joint motility and function, and severely reducing the standard of living of patients. Cartilage tissue engineering attempts to repair the damaged tissue of individuals suffering from OA by providing mechanical support to the joint as new tissue regenerates. The aim of this study was to create composite three dimensional scaffolds comprised of electrospun poly(D,L‐lactide)/poly(L‐lactide) (PDLA/PLLA) or poly(D,L‐lactide)/polycaprolactone (PDLA/PCL) with salt leached pores and an embedded chitosan hydrogel to determine the potential of these scaffolds for cartilage tissue engineering. PDLA/PLLA‐hydrogel scaffolds displayed the largest compressive moduli followed by PDLA/PCL‐hydrogel scaffolds. Dynamic mechanical tests showed that the PDLA/PLLA scaffolds had no appreciable recovery while PDLA/PCL scaffolds did exhibit some recovery. Primary canine chondrocytes produced both collagen type II and proteoglycans (primary components of extracellular matrix in cartilage) while being cultured on scaffolds composed of electrospun PDLA/PCL. As a result, a composite electrospun embedded hydrogel scaffold shows promise for treating individuals suffering from OA. Copyright © 2012 John Wiley & Sons, Ltd.     

Gelatin‐ and hydroxyapatite‐based cryogels for bone tissue engineering: synthesis,characterization, in vitro and in vivo biocompatibility

The aim of this study was the synthesis and characterization of gelatin‐ and hydroxyapatite (osteoconductive component of bone)‐based cryogels for tissue‐engineering applications. Preliminary in vitro and in vivo biocompatibility tests were conducted. Gelatin‐ and hydroxyapatite‐based cryogels of varying concentrations were synthesized using glutaraldehyde as the crosslinking agent. Chemical structure, pore morphology, pore size distribution, mechanical properties, swelling characteristics and degradation profiles of the synthesized cryogels were demonstrated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), mercury porosimetry, a mechanical test device, swelling ratio tests and weight loss measurements, respectively. In vitro cell viability and in vivo biocompatility tests were performed in order to show the performance of the cryogels in the biological environment. Changing the concentrations of gelatin, hydroxyapatite and crosslinker changed the chemical structure, pore size and pore size distribution of the cryogels, which in turn resulted in the ultimate behaviour (mechanical properties, swelling ratio, degradation profile). In vitro cell culture tests showed the viability of the cells. The cryogels did not show any cytotoxic effects on the cells. Clinical outcomes and the gross pathological results demonstrated that there was no necrosis noted in the abdominal and thoracic regions at the end of implantation and the implanted cryogel was found to be non‐irritant and non‐toxic at 12 weeks of implantation. Copyright © 2013 John Wiley & Sons, Ltd.     

Gelatin coating increases in vivo bone formation capacity of three‐dimensional 45S5 bioactive glass‐based crystalline scaffolds

Recent studies have demonstrated that surface characteristics, porosity, and mechanical strength of three‐dimensional 45S5‐type bioactive glass (BG)‐based scaffolds are directly correlated with osteogenic properties. Three‐dimensional BG‐based scaffolds obtained from maritime natural sponges (MNSs) as sacrificial templates exhibit the required morphological properties; however, no in vivo data about the osteogenic features are available. In this study, uncoated (Group A) and gelatin‐coated (Group B) crystalline MNS‐obtained BG‐based scaffolds were evaluated mechanically and seeded with human mesenchymal stem cells prior to subcutaneous implantation in immunodeficient mice. Before implantation and after explantation, micro‐computed tomography scans were conducted, and scaffolds were finally subjected to histomorphometry. Scaffolds of both groups showed bone formation. However, Group B scaffolds performed distinctly better as indicated by a significant increase in scaffold volume (8.95%, p = 0.039) over the implantation period compared with a nonsignificant increase of 5.26% in Group A scaffolds in micro‐computed tomography analysis. Furthermore, percentage bone area was 10.33% (±1.18%) in the Group B scaffolds, which was significantly (p = 0.007) higher compared with the 8.53% (±0.77%) in the Group A scaffolds in histomorphometry. Compressive strength was enhanced significantly by gelatin coating (9 ± 2 vs. 4 ± 1 MPa; p = 0.029). The presence of gelatin on the remnant parts was verified by scanning electron microscopy and X‐ray spectroscopy, demonstrating the coatings' resilience. MNS‐obtained BG‐based scaffolds were thus confirmed to exhibit osteogenic properties in vivo that can significantly be enhanced by gelatin coating.     

Biocompatibility evaluation of tissue‐engineered valved venous conduit by reseeding autologous bone marrow‐derived endothelial progenitor cells and multipotent adult progenitor cells into heterogeneous decellularized venous matrix

Clinical treatment of chronic deep venous insufficiency remains difficult despite the availability of various therapies. Previous experimental efforts have demonstrated that the tissue‐engineered valvedvenous conduit (TEVV) is a promising option to replace the damaged venous valve. The aim of the present study was to evaluate the TEVV by reseeding bone marrow‐derived endothelial progenitor cells and multipotent adult progenitor cells into acellular matrix according to International Standard ISO10993, and to clarify their interactions with blood, the local effect after implantation both in vitro and vivo, and immunogenicity. The results showed that the 2‐cm long TEVV did not cause haemolysis in vitro and remained patent without thrombosis formation in vivo. However, the luminal surface of TEVV was partially covered by multilayer cells. Compared with the native ovine femoral vein segment, the TEVV beneath the mouse skin produced significant mononuclear cell infiltration, with serum interleukin‐6 and tumour necrosis factor‐α similar to normal. The TEVV maintained its structural integrity, while the native ovine femoral vein segments fell apart at postoperative week nine. The TEVV implantation did not change serum immunoglobulin G. In addition, the seeds and extracts of the scaffold did not affect the proliferation of mouse lymphocytes. These findings suggest that the histocompatibility, haemocompatibility and immunogenicity of this TEVV are acceptable owing to complete removal of the cellular components of autologous seeds and residues of chemical regents, thus providing an experimental basis for further clinical translation. Copyright © 2014 John Wiley & Sons, Ltd.     

Functional analysis in vivo of engineered valved venous conduit with decellularized matrix and two bone marrow‐derived progenitors in sheep

Tissue engineering has been considered a promising approach for creating grafts to replace autologous venous valves. Here, ovine bone marrow‐derived endothelial progenitor cells (EPCs) and multipotent adult progenitor cells (MAPCs) were harvested and then loaded into decellularized venous matrix to create tissue‐engineered (TE) valved vein. Subsequently, the ovine femoral veins containing the valve were removed and replaced by TE grafts or acellular matrix only. The morphology and function were analysed for up to 1 year by ultrasonography, angiography, H&E staining and scanning electron microscopy (SEM). The differentiation of seeded cells was traced immunofluorochemically. The results showed that decellularized venous matrix could initially and feebly attract endogenous cells, but failed afterwards and were insufficient to restore valve function. On the contrary, the seeded cells differentiated into endothelial cells (ECs) in vivo and formed a monolayer endothelium, and smooth muscle cells within the scaffold therefore produced TE grafts comparable to the native vein valve. This TE graft remained patent and sufficient after implantation into the venous circuit of the ovine lower extremity for at least 6 months. Unfortunately, cells seeded on the luminal surface and both sides of the leaflets lost their biological functions at 12 months, resulting in thrombosis formation and leading to complete occlusion of the TE grafts and impotent venous valves. These findings suggest that this TE valved venous conduit can function physiologically in vivo in the medium term. Before translating this TE venous valve into clinical practice, the durability should be improved and thrombogenicity should be suppressed. Copyright © 2016 John Wiley & Sons, Ltd.