Evaluation of processed bovine cancellous bone matrix seeded with syngenic osteoblasts in a critical size calvarial defect rat model

INTRODUCTION: Biologic bone substitutes may offer alternatives to bone grafting procedures. The aim of this study was to evaluate a preformed bone substitute based on processed bovine cancellous bone (PBCB) with or without osteogenic cells in a critical size calvarial defect rat model. METHODS: Discs of PBCB (Tutobone) were seeded with second passage fibrin gel-immobilized syngenic osteoblasts (group A, n = 40). Cell-free matrices (group B, n = 28) and untreated defects (group C; n=28) served as controls. Specimens were explanted between day 0 and 4 months after implantation and were subjected to histological and morphometric evaluation. RESULTS: At 1 month, bone formation was limited to small peripheral areas. At 2 and 4 months, significant bone formation, matrix resorption as well as integration of the implants was evident in groups A and B. In group C no significant regeneration of the defects was observed. Morphometric analysis did not disclose differences in bone formation in matrices from groups A and B. Carboxyfluorescine-Diacetate-Succinimidylester (CFDA) labeling demonstrated low survival rates of transplanted cells. DISCUSSION: Osteoblasts seeded into PBCB matrix display a differentiated phenotype following a 14 days cell culture period. Lack of initial vascularization may explain the absence of added osteogenicity in constructs from group A in comparison to group B. PBCB is well integrated and represents even without osteogenic cells a promising biomaterial for reconstruction of critical size calvarial bone defects.     

间充质干细胞在脂肪性供肝肝移植中的应用与展望

骨髓间充质干细胞（BMSC）是一种具有多向分化能力且能无限增殖的间质细胞,在肝脏疾病的作用已经得到证实。肝移植是目前治疗终末期肝病最为有效的方法,随着脂肪性供肝等边缘性供肝的增加,如何使边缘性供肝更好的发挥功能,成为了新的研究热点。研究BMSC对脂肪性供肝肝移植术后肝脏功能恢复的影响将为其在临床上的应用提供依据。     

Primary vascularization of the graft determines the immunodominance of murine minor H antigens during organ transplantation

Grafts can be rejected even when matched for MHC because of differences in the minor histocompatibility Ags (mH-Ags). H4- and H60-derived epitopes are known as immunodominant mH-Ags in H2(b)-compatible BALB.B to C57BL/6 transplantation settings. Although multiple explanations have been provided to explain immunodominance of Ags, the role of vascularization of the graft is yet to be determined. In this study, we used heart (vascularized) and skin (nonvascularized) transplantations to determine the role of primary vascularization of the graft. A higher IFN-γ response toward H60 peptide occurs in heart recipients. In contrast, a higher IFN-γ response was generated against H4 peptide in skin transplant recipients. Peptide-loaded tetramer staining revealed a distinct antigenic hierarchy between heart and skin transplantation: H60-specific CD8(+) T cells were the most abundant after heart transplantation, whereas H4-specific CD8(+) T cells were more abundant after skin graft. Neither the tissue-specific distribution of mH-Ags nor the draining lymph node-derived dendritic cells correlated with the observed immunodominance. Interestingly, non-primarily vascularized cardiac allografts mimicked skin grafts in the observed immunodominance, and H60 immunodominance was observed in primarily vascularized skin grafts. However, T cell depletion from the BALB.B donor prior to cardiac allograft induces H4 immunodominance in vascularized cardiac allograft. Collectively, our data suggest that immediate transmigration of donor T cells via primary vascularization is responsible for the immunodominance of H60 mH-Ag in organ and tissue transplantation.     

Feasibility and potential of in utero foetal membrane-derived cell transplantation

Cells isolated from foetal membranes of human term placenta display multiple properties, including some features of stem/progenitor cells, together with immunomodulatory actions and the ability to secrete bioactive soluble factors. Whilst such properties support the potential applicability of these cells in transplantation settings aimed at regenerating/repairing tissues in adults, theoretically, using these cells in prenatal treatment strategies may also be achievable. To assess the feasibility of a foetal membrane-derived cell-based therapeutic treatment during foetal development, we firstly addressed the question of whether in utero transplantation using these cells was possible. To this end, we assessed postnatal microchimerism after transplantation of amniotic membrane-derived cells (a mixture of both mesenchymal stromal/stem cells and epithelial cells) in foetal sheep. Transplantation was performed with or without human umbilical cord blood mononuclear cells and chorionic membrane-derived mesenchymal stromal/stem cells, and was followed by a postnatal booster cell injection. Lambs were euthanized 2–4 months postnatally and their organs/tissues were analysed for microchimerism through detection of human DNA. Human DNA was found in almost all tissues of all of the lambs, with the seemingly random appearance of human cells in some of the analysed tissues suggesting long-term human microchimerism and donor cell migration after in utero/postnatal booster xenotransplation. Differences in microchimerism tissue distribution between animals transplanted with different cell types are discussed. This pilot study adds to ongoing efforts by different investigators to explore the potential of in utero cellular transplantation, and warrants further investigation of using foetal membrane-derived cells for prenatal cell therapies.     

Stable hepatocyte transplantation using fibrin matrix

Fibrin matrix, a naturally derived biodegradable polymer matrix, was evaluated as a scaffold for hepatocyte transplantation in an athymic mouse model. One week after transplantation, opaque conglomerates of the transplanted hepatocytes and fibrin matrix were found on the intestinal mesentery, whereas no transplanted hepatocytes were observed in control groups (transplantation of hepatocytes suspended in culture medium). The hepatocytes in the conglomerates retained hepatocyte-specific functions, as examined with histochemical and immunohistochemical stainings. Stable hepatocyte engraftment may thus be achieved by hepatocyte transplantation using fibrin matrix.     

Fetal and adult liver stem cells for liver regeneration and tissue engineering

For the development of innovative cell-based liver directed therapies, e.g. liver tissue engineering, the use of stem cells might be very attractive to overcome the limitation of donor liver tissue. Liver specific differentiation of embryonic, fetal or adult stem cells is currently under investigation. Different types of fetal liver (stem) cells during development were identified, and their advantageous growth potential and bipotential differentiation capacity were shown. However, ethical and legal issues have to be addressed before using fetal cells. Use of adult stem cells is clinically established, e.g. transplantation of hematopoietic stem cells. Other bone marrow derived liver stem cells might be mesenchymal stem cells (MSC). However, the transdifferentiation potential is still in question due to the observation of cellular fusion in several in vivo experiments. In vitro experiments revealed a crucial role of the environment (e.g. growth factors and extracellular matrix) for specific differentiation of stem cells. Co-cultured liver cells also seemed to be important for hepatic gene expression of MSC. For successful liver cell transplantation, a novel approach of tissue engineering by orthotopic transplantation of gel-immobilized cells could be promising, providing optimal environment for the injected cells. Moreover, an orthotopic tissue engineering approach using bipotential stem cells could lead to a repopulation of the recipients liver with healthy liver and biliary cells, thus providing both hepatic functions and biliary excretion. Future studies have to investigate, which stem cell and environmental conditions would be most suitable for the use of stem cells for liver regeneration or tissue engineering approaches.     

Endothelial progenitor cells are integrated in newly formed capillaries and alter adjacent fibrovascular tissue after subcutaneous implantation in a fibrin matrix

Vascularization of bioartificial matrices is crucial for successful tissue engineering. Endothelial progenitor cells (EPC) have shown vascularization potential in ischemic conditions and may also support blood vessel formation in tissue-engineered matrices. The aim of our study was to investigate the impact of a well-characterized murine embryonal EPC line (T17b-EPC) on vascularization and fibrovascular granulation tissue formation after suspension in a fibrine matrix followed by subcutaneous implantation in a separation chamber in rats. EPC were fluorescently labelled in vitro prior to implantation. After 3, 7 or 14 days, animals were killed followed by explantation and histological analysis of the constructs. Before the end of the experiment, Bandeirea Simplicifolia lectin was intravenously injected to mark the vascular ingrowth into the implanted constructs. The transplanted cells were histologically detected at all time-points and located almost exclusively within the fibrin matrix at day 3 but the number of cells in the clot continuously decreased over day 7 to day 14. Conversely, cells were detected within the newly formed granulation tissue in increasing numbers from day 3 over day 7 to day 14. Transplanted cells were also found in the intermuscular septa. Cell viability was confirmed by use of an EPC clone expressing β-galactosidase. Fluorescence microscopy demonstrated integration of the transplanted cells in newly formed blood vessels within the fibrovascular granulation tissue adjacent to the fibrin clot. Presence of cells in the fibrin clot lead to thicker granulation tissue and an increased blood vessel diameter compared to cell-free controls. Organ standard controls showed presence of the transplanted cells in spleens at day 14 after transplantation. In summary, EPC exhibited biological activity after subcutaneous implantation in a fibrin matrix by migration from the fibrin clot into the granulation tissue and along intermuscular septae, undergoing differentiation into mature endothelial cells and integration into newly formed blood vessels and altering fibrovascular granulation tissue development. EPC may hold promise to modulate blood vessel formation in bioartificial matrices.     

Repetitive transplantation of different cell types sequentially improves heart function after infarction

Cell-based therapy is considered a novel and potentially new strategy in regenerative medicine. But the efficacy of cell-based therapy has been limited by the poor survival of the transplanted cells in an ischaemic environment. The goal of the present study is to present a possibility to increase survival of the transplanted cardiomyocytes, by increasing the vascularization of the infarcted area. First, we injected endothelial progenitor cells (EPCs) to augment the vascular density in infarcted areas and to improve the benefit of a subsequent Tx of foetal cardiomyocytes. Serial echocardiography indeed showed significant improvement of the left ventricular function after application of EPC and a significant additive improvement after Tx of foetal cardiomyocytes. In contrast, repetitive EPC transplantation as a control group did not show an additional improvement after the second transplantation. Histologically, cells could be readily detected after Tx by BrdU-staining for EPC and by carboxy-fluorescein diacetate succinimidyl ester (CFSE)-staining for foetal cardiomyocytes. Staining for CD31 revealed a significant increase in vessel density in the infarction area compared with medium controls, possibly contributing to the benefit of transplanted foetal cardiomyocytes. Notably, a significant increase in the number of apoptotic cells was observed in cell-transplanted hearts accompanied by an increase in proliferation, collagen content and neutrophil infiltration, suggesting an active remodelling concomitant with sustained inflammatory processes. In conclusion, repetitive Tx of different cell types after myocardial infarction in rat hearts significantly improved left ventricular function and could represent a feasible option to enhance the benefit of cell therapy.     

Intracerebral transplantation of foetal neural stem cells improves brain dysfunction induced by intracerebral haemorrhage stroke in mice

Intracerebral haemorrhage (ICH) can lead to secondary insults and severe neurological deficits. Transplantation of neural stem cells (NSCs) was suggested as an alternative to improve ICH-induced neurological dysfunction. The present study aimed at investigating the therapeutic role and long-term survival of foetal NSCs and potential role of foetal NSCs-produced factors in ICH. Our results demonstrated that foetal NSCs could differentiate into neural axons and dendrites and astrocytes in both in vitro and in vivo conditions, demonstrated by positive double or triple staining with Hoechst, neuronal specific nuclear protein, neurofilaments and glial fibrillary acidic protein. Intracerebral transplantation of foetal NSCs 3 days after ICH induction by intrastriatal administration of bacterial collagenase could improve the functional performance in the limb-placing test and shorten the duration of the recovery from ICH-induced neural disorders. The foetal NSCs may also produce neurotrophic and/or neuroprotective factors during culture, because the culture medium alone could partially improve functional performance. Thus, our data suggest that the foetal NSCs may be one of the therapeutic candidates for ICH.     

Cryopreservation of isolated human hepatocytes for transplantation: State of the art

Hepatocytes isolated from unused donor livers are being used for transplantation in patients with acute liver failure and liver-based metabolic defects. As large numbers of hepatocytes can be prepared from a single liver and hepatocytes need to be available for emergency and repeated treatment of patients it is essential to be able to cryopreserve and store cells with good thawed cell function. This review considers the current status of cryopreservation of human hepatocytes discussing the different stages involved in the process. These include pre-treatment of cells, freezing solution, cryoprotectants and freezing and thawing protocols. There are detrimental effects of cryopreservation on hepatocyte structure and metabolic function, including cell attachment, which is important to the engraftment of transplanted cells in the liver. Cryopreserved human hepatocytes have been successfully used in clinical transplantation, with evidence of replacement of missing function. Further optimisation of hepatocyte cryopreservation protocols is important for their use in hepatocyte transplantation.     

Islet transplantation in type I diabetes mellitus

For most patients with type I diabetes, insulin therapy and glucose monitoring are sufficient to maintain glycemic control. However, hypoglycemia is a potentially lethal side effect of insulin treatment in patients who are glycemically labile or have hypoglycemia-associated autonomic failure [1]. For those patients, an alternative therapy is beta cell replacement via pancreas or islet transplantation. Pancreas transplants using cadaveric donor organs reduce insulin dependence but carry risks involved in major surgery and chronic immunosuppression. Islet transplantation, in which islets are isolated from donor pancreases and intravenously infused, require no surgery and can utilize islets isolated from pancreases unsuitable for whole organ transplantation. However, islet transplantation also requires immunosuppression, and standard steroid regimens may be toxic to beta cells [2]. The 2000 Edmonton Trial demonstrated the first long-term successful islet transplantation by using a glucocorticoid-free immunosuppressive regimen (sirolimus and tacrolimus). The Clinical Islet Transplantation (CIT) Consortium seeks to improve upon the Edmonton Protocol by using anti-thymocyte globulin (ATG) and TNFα antagonist (etanercept). The trials currently in progress, in addition to research efforts to find new sources of islet cells, reflect enormous potential for islet transplantation in treatment of type I diabetes.     

Additive effect of endothelial progenitor cell mobilization and bone marrow mononuclear cell transplantation on angiogenesis in mouse ischemic limbs

Summary The methods of therapeutic angiogenesis include endothelial progenitor cell (EPC) mobilization with cytokines [e.g., granulocyte colony-stimulating factor (G-CSF)] and bone marrow mononuclear cell (BMMNC) transplantation. Combined angiogenic therapies may be superior to a single angiogenic therapy for the treatment of limb ischemia. Therefore, we investigated whether the angiogenic efficacy of a combination of two angiogenic strategies is superior to either strategy alone. One day after the surgical induction of hindlimb ischemia, mice were randomized to receive either no treatment, EPC mobilization with G-CSF administration, BMMNC transplantation using a fibrin matrix, or a combination of EPC mobilization with BMMNC transplantation using a fibrin matrix. EPC mobilization with G-CSF or BMMNC transplantation using a fibrin matrix significantly increased the microvessel density compared with no treatment. Importantly, a combination of EPC mobilization with BMMNC transplantation using a fibrin matrix further increased the densities of microvessels and BrdU-positive capillaries compared to either strategy alone. Basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF) expression was higher in the EPC mobilization with G-CSF or BMMNC transplantation group than in the no treatment group. The combination therapy of EPC mobilization with G-CSF and BMMNC transplantation resulted in more extensive expression of bFGF and VEGF than the single therapy of either EPC mobilization with G-CSF treatment or BMMNC transplantation. This study demonstrates that the combination therapy of BMMNC transplantation and EPC mobilization potentiates the angiogenic efficacy of either single therapy in mouse limb ischemia models.     

Immune reconstitution in patients with Fanconi anemia after allogeneic bone marrow transplantation

Background aimsFanconi anemia is an autosomal recessive or X-linked genetic disorder characterized by bone marrow (BM) failure/aplasia. Failure of hematopoiesis results in depletion of the BM stem cell reservoir, which leads to severe anemia, neutropenia and thrombocytopenia, frequently requiring therapeutic interventions, including hematopoietic stem cell transplantation (HSCT). Successful BM transplantation (BMT) requires reconstitution of normal immunity.MethodsIn the present study, we performed a detailed analysis of the distribution of peripheral blood subsets of T, B and natural killer (NK) lymphocytes in 23 patients with Fanconi anemia before and after BMT on days +30, +60, +100, +180, +270 and +360. In parallel, we evaluated the effect of related versus unrelated donor marrow as well as the presence of graft-versus-host disease (GVHD).ResultsAfter transplantation, we found different kinetics of recovery for the distinct major subsets of lymphocytes. NK cells were the first to recover, followed by cytotoxic CD8⁺ T cells and B cells, and finally CD4⁺ helper T cells. Early lymphocyte recovery was at the expense of memory cells, potentially derived from the graft, whereas recent thymic emigrant (CD31⁺ CD45RA⁺) and naive CD4⁺ or CD8⁺ T cells rose only at 6 months after HSCT, in the presence of immunosuppressive GVHD prophylactic agents. Only slight differences were observed in the early recovery of cytotoxic CD8⁺ T cells among those cases receiving a graft from a related donor versus an unrelated donor. Patients with GVHD displayed a markedly delayed recovery of NK cells and B cells as well as of regulatory T cells and both early thymic emigrant and total CD4⁺ T cells.ConclusionsOur results support the utility of post-transplant monitoring of a peripheral blood lymphocyte subset for improved follow-up of patients with Fanconi anemia undergoing BMT.     

Hepatic tissue engineering: from transplantation to customized cell-based liver directed therapies from the laboratory

Today, liver transplantation is still the only curative treatment for liver failure due to end-stages liver diseases. Donor organ shortage, high cost and the need of immunosuppressive medications are still the major limitations in the field of liver transplantation. Thus, alternative innovative cell-based liver directed therapies, e.g. liver tissue engineering, are under investigation with the aim, that in future an artificial liver tissue could be created and be used for the replacement of the liver function in patients. Using cells instead of organs in this setting should permit (i) expansion of cells in an in vitro phase, (ii) genetic or immunological manipulation of cells for transplantation, (iii) tissue typing and cryopreservation in a cell bank, and (iv) the ex vivo genetic modification of patient's own cells prior re-implantation. Function and differentiation of liver cells are influenced by the three-dimensional organ architecture. The use of polymeric matrices permits the three dimensional formation of a neo-tissue and specific stimulation by adequate modification of the matrix-surface which might be essential for appropriate differentiation of transplanted cells. Additionally, culturing hepatocytes on three dimensional matrices permits culture in a flow bioreactor system with increased function and survival of the cultured cells. Based on bioreactor technology, bioartificial liver devices (BAL) are developed for extracorporeal liver support. Although BALs improved clinical and metabolic conditions, increased patient survival rates have not been proven yet. For intra-corporeal liver replacement, a concept which combines Tissue Engineering using three-dimensional, highly porous matrices with cell transplantation could be useful. In such a concept, whole liver mass transplantation, long term engraftment and function as well as correction of a metabolic defect in animal models could be achieved with a principally reversible procedure. Future studies have to investigate, which environmental conditions and transplantation system would be most suitable for the development of artificial functional liver tissue including blood supply for a potential use in a clinical setting.     

Germ cell transplantation in goats

Transplantation of spermatogonial stem cells provides a unique approach for the study of spermatogenesis and manipulation of the male germ line. This technique may also offer an alternative to the currently inefficient methods of producing transgenic domestic animals. We have recently established the technique of spermatogonial transplantation, originally developed in laboratory rodents, in pigs, and this study was aimed to extend the technique to the goat. Isolated donor testis cells were infused into the seminiferous tubules of anesthetized recipient goats through an ultrasonographically-guided catheter inserted into the rete testis. Donor cells were obtained by enzymatic digestion of freshly collected testes from immature goats (either from the recipients' contralateral testis or from unrelated donors). Prior to transplantation, testis cells were labeled with a fluorescent marker to allow identification after transplantation. Recipient testes were examined for the presence and localization of labeled donor cells at 3-week intervals up to 12 weeks after transplantation. Labeled donor cells were found in the seminiferous tubules of all testes, comprising 10-35% of the examined tubules. Histological examination of the recipient testes did not reveal evident tissue damage, except for limited fibrotic changes at the site of needle insertion. Likewise there were no detectable local or systemic signs of immunologic reactions to the transplantations. These results indicate that germ cell transplantation is technically feasible in immature male goats and that donor-derived cells are retained in the recipient testis for at least three months and through puberty. This study represents the first report of germ cell transplantation in goats.     

Noninvasive high-resolution in vivo imaging of cell biology in the anterior chamber of the mouse eye

There is clearly a demand for an experimental platform that enables cell biology to be studied in intact vascularized and innervated tissue in vivo. This platform should allow observations of cells noninvasively and longitudinally at single-cell resolution. For this purpose, we use the anterior chamber of the mouse eye in combination with laser scanning microscopy (LSM). Tissue transplanted to the anterior chamber of the eye is rapidly vascularized, innervated and regains function. After transplantation, LSM through the cornea allows repetitive and noninvasive in vivo imaging at cellular resolution. Morphology, vascularization, cell function and cell survival are monitored longitudinally using fluorescent proteins and dyes. We have used this system to study pancreatic islets, but the platform can easily be adapted for studying a variety of tissues and additional biological parameters. Transplantation to the anterior chamber of the eye takes 25 min, and in vivo imaging 1-5 h, depending on the features monitored.     

单倍体造血干细胞移植对儿童重型再生障碍性贫血治疗的并发症分析

目的分析儿童重型再生障碍性贫血(SAA)单倍体造血干细胞移植和同胞全相合移植并发症发生率。方法回顾性分析2010年1月1日至2018年12月31日于苏州大学附属儿童医院进行治疗的SAA患儿(56例),分为治疗组(单倍体造血干细胞移植,35例),对照组(同胞全相合移植,21例)。其中患儿年龄、诊断距离移植时间、总单个核细胞数、总CD34+细胞数、中位随访时间、粒细胞植入时间、血小板植入时间及等级资料[供受体血型相合程度、急性移植物抗宿主病(aGVHD)分级、广泛性慢性移植物抗宿主病(cGVHD)分级、出血性膀胱炎分级、渗漏综合征分级]采用Mann-Whitney U检验。性别、疾病种类、供体与受体性别、预处理方案、CD20单抗的使用、HLA配型、供体来源、移植物来源、植入综合征、巨细胞病毒(CMV)血症、EB病毒(EBV)血症、死亡人数、植入失败人数和骨髓增殖不良人数使用卡方检验进行组间分析。生存曲线以及累积发生率用Kaplan-Meier法绘制,并使用Log-rank检验分析组间差异。结果与对照组比较,治疗组CD19+B细胞的重建延迟,而CD16+CD56+NK细胞数量移植后6个月开始增加,逐渐达到对照组的水平。与对照组比较,治疗组aGVHD、cGVHD、植入综合征和骨髓增殖不良累积发生率(14.29﹪±7.64﹪比57.14﹪±8.36﹪,11.67﹪±7.75﹪比61.59﹪±9.65﹪,9.53﹪±6.41﹪比74.86﹪±7.43﹪,0.0﹪比14.29﹪±5.91﹪)均升高,差异具有统计学意义(P<0.05),两组CMV与EBV感染,5年总体生存率(OS)、无失败生存率(FFS)、无GVHD失败存活率(GFFS)、Ⅲ-Ⅳ度aGVHD及广泛性cGVHD累积发生率比较差异无统计意义(P>0.05)。结论单倍体移植是治疗儿童SAA的有效治疗方案,但与同胞全合造血干细胞移植比较,其GVHD发生率较高,植入综合征和骨髓增殖不良的发生率较高,优化单倍体移植方案有望降低并发症,提高儿童重型再生障碍性贫血的生活质量。     

移植途径对大鼠骨髓间充质干细胞归巢及肝功能恢复的影响

目的 探讨移植途径对骨髓间充质干细胞（MSCs）归巢及促进肝切除大鼠肝再生的影响.方法 建立肝切除大鼠模型,随机分为3 组,即肝切除对照组、尾静脉移植组和门静脉移植组.移植组分别经尾静脉和门静脉注射DAPI 标记的MSCs 约1.5×106/ 只,分别于第3 天和第9 天后采血清检测肝功能,第9 天处死大鼠取肝脏标本,并通过荧光显微镜观察两种移植途径对MSCs 向肝脏迁移的影响.结果 门静脉移植组（18.1 ± 3.4）个细胞/100 倍视野到肝脏归巢及定植的 MSCs 多于尾静脉移植组（7.6 ± 2.0）个细胞/100 倍视野,差异有统计学意义（P 〈 0.01）.术后第9 天各组大鼠肝功能均有好转,丙氨酸氨基转移酶（ALT）及天冬氨酸氨基转移酶（AST）3 组之间对比差异无统计学意义（F = 2.822,1.046,P = 0.057,0.365,P 〉 0.05）;但两移植组与单纯肝切除组比较血浆白蛋白（ALB）均有明显升高,差异具有统计学意义（F = 6.259,P = 0.006）;尾静脉移植组与门静脉移植组两移植组之间相比,差异无统计学意义（P 〉 0.05）.结论 移植途径对 MSCs 归巢、定植到肝脏有一定影响,门静脉途径优于外周静脉,MSCs 移植对肝大部切除大鼠肝功能恢复具有促进作用.     

ECM concentration and cell-mediated traction forces play a role in vascular network assembly in 3D bioprinted tissue

Tissue vascularization is critical to enable oxygen and nutrient supply. Therefore, establishing expedient vasculature is necessary for the survival of tissue after transplantation. The use of biomechanical forces, such as cell-induced traction forces, may be a promising method to encourage growth of the vascular network. Three-dimensional (3D) bioprinting, which offers unprecedented versatility through precise control over spatial distribution and structure of tissue constructs, can be used to generate capillary-like structures in vitro that would mimic microvessels. This study aimed to develop an in vitro, 3D bioprinted tissue model to study the effect of cellular forces on the spatial organization of vascular structures and tissue maturation. The developed in vitro model consists of a 3D bioprinted polycaprolactone (PCL) frame with a gelatin spacer hydrogel layer and a gelatin–fibrin–hyaluronic acid hydrogel layer containing normal human dermal fibroblasts and human umbilical vein endothelial cells printed as vessel lines on top. The formation of vessel-like networks and vessel lumens in the 3D bioprinted in vitro model was assessed at different fibrinogen concentrations with and without inhibitors of cell-mediated traction forces. Constructs containing 5 mg/ml fibrinogen had longer vessels compared to the other concentrations of fibrinogen used. Also, for all concentrations of fibrinogen used, most of the vessel-like structures grew parallel to the direction the PCL frame-mediated tensile forces, with very few branching structures observed. Treatment of the 3D bioprinted constructs with traction inhibitors resulted in a significant reduction in length of vessel-like networks. The 3D bioprinted constructs also had better lumen formation, increased collagen deposition, more elaborate actin networks, and well-aligned matrix fibers due to the increased cell-mediated traction forces present compared to the non-anchored, floating control constructs. This study showed that cell traction forces from the actomyosin complex are critical for vascular network assembly in 3D bioprinted tissue. Strategies involving the use of cell-mediated traction forces may be promising for the development of bioprinting approaches for fabrication of vascularized tissue constructs.