Evaluation of type II collagen scaffolds reinforced by poly(epsilon-caprolactone) as tissue-engineered trachea

A novel composite scaffold comprising a poly(epsilon-caprolactone) (PCL) stent and a type II collagen sponge for tissue-engineered trachea was developed. The PCL stent with surface grooves was fabricated by casting and freeze drying the PCL solution in a mold container. The grooves on the stent were filled by the type II collagen with crosslinking treatment (ring-shaped collagen sponge). The rabbit chondrocytes (3 x 10(6) cells for each ring) were seeded onto the collagen sponge of the scaffold. The cell-scaffold constructs were implanted subcutaneously in the dorsum of nude mice. After 4 and 8 weeks, constructs were harvested and dedicated for measurement of mechanical properties, histology, and biochemical assays. It was found that the constructs were strong enough to retain their tubular shape against extrinsic forces in the dorsum of nude mice. The gross appearance of the constructs revealed cartilage-like tissue at 8 weeks, with modulus higher than that of native trachea. Histological and biochemical analyses of the tissue-engineered tracheal cartilage revealed evenly spaced lacunae embedded in the matrix, with abundant proteoglycans and type II collagen. The stent-sponge composite facilitated the proliferation of chondrocytes and was expected to provide adequate mechanical strength, and therefore was a promising material for use in trachea tissue engineering.     

Biomechanical and angiogenic properties of tissue-engineered rat trachea using genipin cross-linked decellularized tissue

In this study, the obtainment and characterization of decellularized rat tracheal grafts are described. The detergent-enzymatic method, already used to develop bioengineered pig and human trachea scaffolds, has been applied to rat tracheae in order to obtain airway grafts suitable to be used to improve our knowledge on the process of tissue-engineered airway transplantation and regeneration. The results demonstrated that, after 9 detergent-enzymatic cycles, almost complete decellularized tracheae, retaining the hierarchical and mechanical properties of the native tissues with strong in vivo angiogenic characteristics, could be obtained. Moreover, to improve the mechanical properties of decellularized tracheae, genipin is here considered as a naturally derived cross-linking agent. The results demonstrated that the treatment increased mechanical properties, in term of secant modulus, without neither altering the pro-angiogenic properties of decellularized airway matrices or eliciting an in vivo inflammatory response.     

Biological and MRI characterization of biomimetic ECM scaffolds for cartilage tissue regeneration

Osteoarthritis is the most common joint disorder affecting millions of people. Most scaffolds developed for cartilage regeneration fail due to vascularization and matrix mineralization. In this study we present a chondrogenic extracellular matrix (ECM) incorporated collagen/chitosan scaffold (chondrogenic ECM scaffold) for potential use in cartilage regenerative therapy. Biochemical characterization showed that these scaffolds possess key pro-chondrogenic ECM components and growth factors. MRI characterization showed that the scaffolds possess mechanical properties and diffusion characteristics important for cartilage tissue regeneration. In vivo implantation of the chondrogenic ECM scaffolds with bone marrow derived mesenchymal stem cells (MSCs) triggered chondrogenic differentiation of the MSCs without the need for external stimulus. Finally, results from in vivo MRI experiments indicate that the chondrogenic ECM scaffolds are stable and possess MR properties on par with native cartilage. Based on our results, we envision that such ECM incorporated scaffolds have great potential in cartilage regenerative therapy. Additionally, our validation of MR parameters with histology and biochemical analysis indicates the ability of MRI techniques to track the progress of our ECM scaffolds non-invasively in vivo; highlighting the translatory potential of this technology.     

The impact of PLGA scaffold orientation on in vitro cartilage regeneration

The success of in vitro cartilage regeneration provides a promising approach for cartilage repair. However, the currently engineered cartilage in vitro is unsatisfactory for clinical application due to non-homogeneous structure, inadequate thickness, and poor mechanical property. It has been widely reported that orientation of scaffolds can promote cell migration and thus probably contributes to improving tissue regeneration. This study explored the impact of microtubular oriented scaffold on in vitro cartilage regeneration. Porcine articular chondrocytes were seeded into microtubule-oriented PLGA scaffolds and non-oriented scaffolds respectively. A long-term in vitro culture followed by a long-term in vivo implantation was performed to evaluate the influence of scaffold orientation on cartilage regeneration. The current results showed that the oriented scaffolds could efficiently promote cell migration towards the inner region of the constructs. After 12 weeks of in vitro culture, the chondrocyte-scaffold constructs in the oriented group formed thicker cartilage with more homogeneous structure, stronger mechanical property, and higher cartilage matrix content compared to the non-oriented group. Furthermore, the in vitro engineered cartilage based on oriented scaffolds showed better cartilage formation in terms of size, wet weight, and homogeneity after 12-week in vivo implantation in nude mice. These results indicated that the longitudinal microtubular orientation of scaffolds can efficiently improve the structure and function of in vitro engineered cartilage.     

Controlling stem cell-mediated bone regeneration through tailored mechanical properties of collagen scaffolds

Mechanical properties of the extracellular matrix (ECM) play an essential role in cell fate determination. To study the role of mechanical properties of ECM in stem cell-mediated bone regeneration, we used a 3D in vivo ossicle model that recapitulates endochondral bone formation. Three-dimensional gelatin scaffolds with distinct stiffness were developed using 1-Ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride (EDC) mediated zero-length crosslinking. The mechanical strength of the scaffolds was significantly increased by EDC treatment, while the microstructure of the scaffold was preserved. Cell behavior on the scaffolds with different mechanical properties was evaluated in vitro and in vivo. EDC-treated scaffolds promoted early chondrogenic differentiation, while it promoted both chondrogenic and osteogenic differentiation at later time points. Both micro-computed tomography and histologic data demonstrated that EDC-treatment significantly increased trabecular bone formation by transplanted cells transduced with AdBMP. Moreover, significantly increased chondrogenesis was observed in the EDC-treated scaffolds. Based on both in vitro and in vivo data, we conclude that the high mechanical strength of 3D scaffolds promoted stem cell mediated bone regeneration by promoting endochondral ossification. These data suggest a new method for harnessing stem cells for bone regeneration in vivo by tailoring the mechanical properties of 3D scaffolds.     

A functional biphasic biomaterial homing mesenchymal stem cells for in vivo cartilage regeneration

Cartilage regeneration after trauma is still a great challenge for clinicians and researchers due to many reasons, such as joint load-bearing, synovial movement and the paucity of endogenous repair cells. To overcome these limitations, we constructed a functional biomaterial using a biphasic scaffold platform and a bone-derived mesenchymal stem cells (BMSCs)-specific affinity peptide. The biphasic scaffold platform retains more cells homogeneously within the sol–gel transition of chitosan and provides sufficient solid matrix strength. This biphasic scaffold platform is functionalized with an affinity peptide targeting a cell source of interest, BMSCs. The presence of conjugated peptide gives this system a biological functionality towards BMSC-specific homing both in vitro and in vivo. The functional biomaterial can stimulate stem cell proliferation and chondrogenic differentiation during in vitro culture. Six months after in vivo implantation, compared with routine surgery or control scaffolds, the functional biomaterials induced superior cartilage repair without complications, as indicated by histological observations, magnetic resonance imaging and biomechanical properties. Beyond cartilage repair, this functional biphasic scaffold may provide a biomaterial framework for one-step tissue engineering strategy by homing endogenous cells to stimulate tissue regeneration.     

Mechano growth factor (MGF) and transforming growth factor (TGF)-β3 functionalized silk scaffolds enhance articular hyaline cartilage regeneration in rabbit model

Damaged cartilage has poor self-healing ability and usually progresses to scar or fibrocartilaginous tissue, and finally degenerates to osteoarthritis (OA). Here we demonstrated that one of alternative isoforms of IGF-1, mechano growth factor (MGF) acted synergistically with transforming growth factor β3 (TGF-β3) embedded in silk fibroin scaffolds to induce chemotactic homing and chondrogenic differentiation of mesenchymal stem cells (MSCs). Combination of MGF and TGF-β3 significantly increased cell recruitment up to 1.8 times and 2 times higher than TGF-β3 did in vitro and in vivo. Moreover, MGF increased Collagen II and aggrecan secretion of TGF-β3 induced hMSCs chondrogenesis, but decreased Collagen I in vitro. Silk fibroin (SF) scaffolds have been widely used for tissue engineering, and we showed that methanol treated pured SF scaffolds were porous, similar to compressive module of native cartilage, slow degradation rate and excellent drug released curves. At 7days after subcutaneous implantation, TGF-β3 and MGF functionalized silk fibroin scaffolds (STM) recruited more CD29+/CD44 + cells (P < 0.05). Similarly, more cartilage-like extracellular matrix and less fibrillar collagen were detected in STM scaffolds than that in TGF-β3 modified scaffolds (ST) at 2 months after subcutaneous implantation. When implanted into articular joints in a rabbit osteochondral defect model, STM scaffolds showed the best integration into host tissues, similar architecture and collagen organization to native hyaline cartilage, as evidenced by immunostaining of aggrecan, collagen II and collagen I, as well as Safranin O and Masson's trichrome staining, and histological evalution based on the modified O'Driscoll histological scoring system (P < 0.05), indicating that MGF and TGF-β3 might be a better candidate for cartilage regeneration. This study demonstrated that TGF-β3 and MGF functionalized silk fibroin scaffolds enhanced endogenous stem cell recruitment and facilitated in situ articular cartilage regeneration, thus providing a novel strategy for cartilage repair.     

The use of ASCs engineered to express BMP2 or TGF-β3 within scaffold constructs to promote calvarial bone repair

Calvarial bone healing is difficult and grafts comprising adipose-derived stem cells (ASCs) and PLGA (poly(lactic-co-glycolic acid)) scaffolds barely heal rabbit calvarial defects. Although calvarial bone forms via intramembranous ossification without cartilage templates, it was suggested that chondrocytes/cartilages promote calvarial healing, thus we hypothesized that inducing ASCs chondrogenesis and endochondral ossification involving cartilage formation can improve calvarial healing. To evaluate this hypothesis and selectively induce osteogenesis/chondrogenesis, rabbit ASCs were engineered to express the potent osteogenic (BMP2) or chondrogenic (TGF-β3) factor, seeded into either apatite-coated PLGA or gelatin sponge scaffolds, and allotransplanted into critical-size calvarial defects. Among the 4 ASCs/scaffold constructs, gelatin constructs elicited in vitro chondrogenesis, in vivo osteogenic metabolism and calvarial healing more effectively than apatite-coated PLGA, regardless of BMP2 or TGF-β3 expression. The BMP2-expressing ASCs/gelatin triggered better bone healing than TGF-β3-expressing ASCs/gelatin, filling ≈86% of the defect area and ≈61% of the volume at week 12. The healing proceeded via endochondral ossification, instead of intramembranous pathway, as evidenced by the formation of cartilage that underwent osteogenesis and hypertrophy. These data demonstrated ossification pathway switching and significantly augmented calvarial healing by the BMP2-expressing ASCs/gelatin constructs, and underscored the importance of growth factor/scaffold combinations on the healing efficacy and pathway.     

Regeneration of canine tracheal cartilage by slow release of basic fibroblast growth factor from gelatin sponge

We investigated the efficiency of basic fibroblast growth factor (b-FGF) released from a gelatin sponge in the regeneration of tracheal cartilage. A 1-cm gap was made in the midventral portion of each of 10 consecutive cervical tracheal cartilages (rings 4 to 13) in 15 experimental dogs. In the control group (n = 5), the resulting gap was left blank. In the gelatin group (n = 5), a gelatin sponge alone was implanted in the gap. In the b-FGF group (n = 5), a gelatin sponge containing 100 mug b-FGF solution was implanted in the gap. We euthanatized one of the five dogs in each group at 1 month after implantation and one at 3 months and examined the implant sites macroscopically and microscopically. In the control and gelatin groups, no regenerated cartilage was observed in the tracheal cartilage gap at 1 or 3 months. The distances between the cartilage stumps had shrunk. In the b-FGF group, fibrous cartilage had started to regenerate from both host cartilage stumps at 1 month. At 3 months, regenerated fibrous cartilage filled the gap and had connected each of the stumps. The regenerated cartilage was covered with regenerated perichondrium originating from the host perichondrium. Shrinkage of the distance between the host cartilage stumps was not observed in the b-FGF group. We succeeded in inducing cartilage regeneration in the gaps in canine tracheal cartilage rings by using the slow release of b-FGF from a gelatin sponge. The regenerated cartilage induced by b-FGF was fibrous cartilage.     

Comparison of tracheal reconstruction with allograft,fresh xenograft and artificial trachea scaffold in a rabbit model

This study evaluated the possibility of tracheal reconstruction with allograft, pig-to-rabbit fresh xenograft or use of a tissue-engineered trachea, and compared acute rejection of three different transplanted tracheal segments in rabbits. Eighteen healthy New Zealand White rabbits weighing 2.5–3.1 kg were transplanted with three different types of trachea substitutes. Two rabbits and two alpha 1, 3-galactosyltransferase gene-knockout pigs weighing 5 kg were used as donors. The rabbits were divided into three groups: an allograft control group consisting of rabbit-to-rabbit allotransplantation animals (n?=?6), a fresh xenograft group consisting of pig-to-rabbit xenotransplantation animals (n?=?6), and an artificial trachea scaffold group (n?=?6). All animals were monitored for 4 weeks for anastomotic complications or infection. The recipients were sacrificed at 28 days after surgery and the grafts were evaluated. On bronchoscopy, all of the fresh xenograft group animals showed ischemic and necrotic changes at 28 days after trachea replacement. The allograft rabbits and the tissue-engineered rabbits showed mild mucosal granulation. The levels of interleukin-2 and interferon-γ in the fresh xenograft group were higher than in other groups. Histopathologic examination of the graft in the fresh xenograft rabbits showed ischemic and necrotic changes, including a loss of epithelium, mucosal granulation, and necrosis of cartilaginous rings. The pig-to-rabbit xenografts showed more severe acute rejection within a month than the rabbits with allograft or artificial trachea-mimetic graft. In addition, the artificial tracheal scaffold used in the present experiment is superior to fresh xenograft and may facilitate tracheal reconstruction in the clinical setting.     

3D打印与组织工程技术在气管替代治疗中的应用与热点

背景:由于缺乏满意的气管替代物,功能性气管重建仍然是一个外科挑战。目的:综述组织工程气管支架的研究热点、临床应用及主要存在的问题。方法:以"3D Printing,tissue-engineered trachea,trachea reconstruction,tracheal replacement;3D打印气管,组织工程气管,气管重建,气管替代"为关键词,检索PubMed、Medline、万方数据库2004至2019年发表的相关文献,共纳入47篇文献进行分析总结。结果与结论:目前气管重建的方式主要有人工气管移植、同种异体移植、自体组织移植和组织工程气管移植。人工气管移植通常引起气管破裂、感染和狭窄而导致移植失败;同种异体移植需要长期的免疫抑制治疗,移植后由于血管再生不足引起的坏死和感染往往导致死亡;自体组织复制气管结构和功能的能力有限且存在手术创伤;组织工程气管通过选择合适的支架材料,在支架中均匀地植入种子细胞,可以模拟与天然气管相似的生物结构和功能,似乎是气管替代物的理想选择。将3D打印技术与组织工程技术相结合,利用生物降解材料打印完整的气管支架,再植入间充质干细胞培育的组织工程气管,为解决长段气管缺损问题提供了新思路。     

The effect of mechanical stimulation on the maturation of TDSCs-poly(L-lactide-co-e-caprolactone)/collagen scaffold constructs for tendon tissue engineering

Mechanical stimulation plays an important role in the development and remodeling of tendons. Tendon-derived stem cells (TDSCs) are an attractive cell source for tendon injury and tendon tissue engineering. However, these cells have not yet been fully explored for tendon tissue engineering application, and there is also lack of understanding to the effect of mechanical stimulation on the maturation of TDSCs-scaffold construct for tendon tissue engineering. In this study, we assessed the efficacy of TDSCs in a poly(L-lactide-co-ε-caprolactone)/collagen (P(LLA-CL)/Col) scaffold under mechanical stimulation for tendon tissue engineering both in vitro and in vivo, and evaluated the utility of the transplanted TDSCs-scaffold construct to promote rabbit patellar tendon defect regeneration. TDSCs displayed good proliferation and positive expressed tendon-related extracellular matrix (ECM) genes and proteins under mechanical stimulation in vitro. After implanting into the nude mice, the fluorescence imaging indicated that TDSCs had long-term survival, and the macroscopic evaluation, histology and immunohistochemistry examinations showed high-quality neo-tendon formation under mechanical stimulation in vivo. Furthermore, the histology, immunohistochemistry, collagen content assay and biomechanical testing data indicated that dynamically cultured TDSCs-scaffold construct could significantly contributed to tendon regeneration in a rabbit patellar tendon window defect model. TDSCs have significant potential to be used as seeded cells in the development of tissue-engineered tendons, which can be successfully fabricated through seeding of TDSCs in a P(LLA-CL)/Col scaffold followed by mechanical stimulation.     

Tracheal cartilage regeneration and new bone formation by slow release of bone morphogenetic protein (BMP)-2

We investigated the efficiency of bone morphogenetic protein (BMP)-2 released slowly from gelatin sponge for tracheal cartilage regeneration. A 1-cm gap was made in the mid-ventral portion of each of 10 consecutive tracheal cartilages. In the control group (n = 4), the resulting gap was left untreated. In the gelatin group (n = 4), plain gelatin was implanted in the gap. In the BMP-2 group (n = 4), gelatin containing 100 microg BMP-2 was implanted. We euthanatized all dogs in each group at 1, 3, 6, and 12 months after the implantation, respectively, and then examined the implant site macro- and microscopically. In the BMP-2 group, regenerated fibrous cartilage and newly formed bone were observed at 1 and 12 months. Regenerated cartilage was observed at the ends of the host cartilage stumps, with newly formed bone in the middle portion. The gaps were filled with regenerated cartilage and newly formed bone. At 3 and 6 months, regenerated cartilage, but not newly formed bone, was evident. The regenerated cartilage was covered with perichondrium and showed continuity with the host cartilage. We succeeded in inducing cartilage regeneration and new bone formation in canine trachea by slow release of 100 microg BMP-2 from gelatin.     

Experimental study of bone morphogenetic proteins-2 slow release from an artificial trachea made of biodegradable materials: evaluation of stenting time

We manufactured an artificial trachea that slowly releases bone morphogenetic protein 2 (BMP-2) and used it to replace a section of the canine trachea. We made a three-layered prosthesis composed of an outer layer of gelatin sponge, a middle layer of collagen sponge, and an inner silicone tube. BMP-2 solution was soaked into the gelatin sponge layer. An approximately 3 cm length of the canine trachea was resected, and the artificial trachea was inserted into the resulting gap and anastomosed. The implanted portion was covered by periosteum. At 2, 4, and 8 weeks after surgery, the inner silicone tube was removed. Soon after removal of the silicone tube at 2 and 4 weeks, the dogs died of choking because of collapse of the trachea. One dog whose silicone tube was removed at 8 weeks was able to survive without choking. At 6 months after removal of the silicone tube, the bronchoscopic findings revealed that the gap in the trachea had been closed by regenerated tissue and covered by mucosa. We have demonstrated that our artificial trachea slowly releasing BMP-2 requires at least 8 weeks to achieve regeneration of solid tissue to support the tracheal gap.     

Perichondrium directed cartilage formation in silk fibroin and chitosan blend scaffolds for tracheal transplantation

The purpose of this study was to investigate the potential of silk fibroin and chitosan blend (SFCS) biological scaffolds for the purpose of cartilage tissue engineering with applications in tracheal tissue reconstruction. The capability of these scaffolds as cell carrier systems for chondrocytes was determined in vitro and cartilage generation in vivo on engineered chondrocyte-scaffold constructs with and without a perichondrium wrapping was tested in an in vivo nude mouse model. SFCS scaffolds supported chondrocyte adhesion, proliferation, and differentiation, determined as features of the cells based on the spherical cell morphology, increased accumulation of glycosaminoglycans, and increased collagen type II deposition with time within the scaffold framework. Perichondrium wrapping significantly (P<0.001) improved chondrogenesis within the cell-scaffold constructs in vivo. In vivo implantation for 6weeks did not generate cartilage structures resembling native trachea, although cartilage-like structures were present. The mechanical properties of the regenerated tissue increased due to the deposition of chondrogenic matrix within the SFCS scaffold structural framework of the trachea. The support of chondrogenesis by the SFCS tubular scaffold construct resulted in a mechanically sound structure and thus is a step towards an engineered trachea that could potentially support the growth of an epithelial lining resulting in a tracheal transplant with properties resembling those of the fully functional native trachea.     

Histological maturation of vascular smooth muscle cells in in situ tissue-engineered vasculature

The goal of regenerative medicine is to achieve histological and functional recovery to the level of the original tissue. For this purpose, we have developed a biodegradable scaffold to create cell-free in-situ tissue-engineered vasculature (iTEV) with good long-term results. However, the regeneration process of vascular smooth muscle cells (VSMCs) over time has yet to be examined. To evaluate the regeneration ability of VSMCs, the inferior vena cava of experimental animals was replaced with iTEV, and tested at 1, 3, 6, 12, and 24 months (n = 6 each) after implantation. Six animals were enrolled to compare 24-month iTEV and native vasculature in single individual samples. There were no complications throughout the study. Immunohistology, protein expression analysis, and biochemical findings indicate that iTEV can gradually regenerate and develop into a mature vessel within 24 months using our biodegradable scaffold. These results provide a time course for the regeneration of VSMCs within the tissue-engineered vascular autograft constructed using a biodegradable scaffold.     

Functional biomaterials for cartilage regeneration

The injury and degeneration of articular cartilage and associated arthritis are leading causes of disability worldwide. Cartilage tissue engineering as a treatment modality for cartilage defects has been investigated for over 20 years. Various scaffold materials have been developed for this purpose, but has yet to achieve feasibility and effectiveness for widespread clinical use. Currently, the regeneration of articular cartilage remains a formidable challenge, due to the complex physiology of cartilage tissue and its poor healing capacity. Although intensive research has been focused on the developmental biology and regeneration of cartilage tissue and a diverse plethora of biomaterials have been developed for this purpose, cartilage regeneration is still suboptimal, such as lacking a layered structure, mechanical mismatch with native cartilage and inadequate integration between native tissue and implanted scaffold. The ideal scaffold material should have versatile properties that actively contribute to cartilage regeneration. Functional scaffold materials may overcome the various challenges faced in cartilage tissue engineering by providing essential biological, mechanical, and physical/chemical signaling cues through innovative design. This review thus focuses on the complex structure of native articular cartilage, the critical properties of scaffolds required for cartilage regeneration, present strategies for scaffold design, and future directions for cartilage regeneration with functional scaffold materials.     

间充质干细胞构建组织工程化气管的研究与应用

背景：间充质干细胞诸多特有的良好生物学特性使得其在组织工程化气管研究中成为理想的种子细胞来源。 目的：总结间充质干细胞在构建组织工程化气管领域的研究现状、进展、存在的问题及展望。 方法：由作者检索PubMed数据库及CNKI数据库1979至2012年,在英文标题和摘要中以“mesenchymal stem cells, tissue-engineered trachea”和“tracheal chondrocytes, tracheal epithelial cells, tracheal vascular endothelial cells” 检索,中文文献检索中以“间充质干细胞、组织工程化气管、气管软骨细胞、气管上皮细胞和气管血管内皮细胞”为关键词,选择与组织工程化气管相关的文章,同一领域文献则选择近期发表或发表在权威杂志的文章,共纳入51篇。 结果与结论：组织工程化气管种子细胞研究主要包括软骨细胞、上皮细胞和血管内皮细胞。实验已证实, 间充质干细胞可定向分化为软骨细胞,细胞因子在诱导间充质干细胞分化为软骨过程中起着关键作用。目前尚未发现合适的诱导因子能特异性诱导间充质干细胞定向分化气管上皮细胞。有研究发现间充质干细胞具有向上皮细胞分化的潜能。间充质干细胞在体内或体外特殊条件下可诱导分化为血管内皮细胞,为间充质干细胞作为种子细胞分化血管内皮细胞应用于组织工程化气管起到借鉴作用。     

Blood vessel formation in the tissue-engineered bone with the constitutively active form of HIF-1α mediated BMSCs

The successful clinical outcome of the implanted tissue-engineered bone is dependent on the establishment of a functional vascular network. A gene-enhanced tissue engineering represents a promising approach for vascularization. Our previous study indicated that hypoxia-inducible factor-1α (HIF-1α) can up-regulate the expression of vascular endothelial growth factor (VEGF) and stromal-derived factor 1 (SDF-1) in bone mesenchymal stem cells (BMSCs). The angiogenesis is a co-ordinated process that requires the participation of multiple angiogenic factors. To further explore the angiogenic effect of HIF-1α mediated stem cells, in this study, we systematically evaluated the function of HIF-1α in enhancing BMSCs angiogenesis in vitro and in vivo. A constitutively active form of HIF-1α (CA5) was inserted into a lentivirus vector and transduced into BMSCs, and its effect on vascularization and vascular remodeling was further evaluated in a rat critical-sized calvarial defects model with a gelatin sponge (GS) scaffold. The expression of the key angiogenic factors including VEGF, SDF-1, basic fibroblast growth factor (bFGF), placental growth factor (PLGF), angiopoietin 1 (ANGPT1), and stem cell factor (SCF) at both mRNAs and proteins levels in BMSCs were significantly enhanced by HIF-1α overexpression compared to the in vitro control group. In addition, HIF-1α-over expressing BMSCs showed dramatically improved blood vessel formation in the tissue-engineered bone as analyzed by photography of specimen, micro-CT, and histology. These data confirm the important role of HIF-1α in angiogenesis in tissue-engineered bone. Improved understanding of the mechanisms of angiogenesis may offer exciting therapeutic opportunities for vascularization, vascular remodeling, and bone defect repair using tissue engineering strategies in the future.     

Cartilage regeneration using slow release of bone morphogenetic protein-2 from a gelatin sponge to treat experimental canine tracheomalacia: a preliminary report

We investigated whether saber sheath-type tracheomalacia could be treated by the slow release of bone morphogenetic protein (BMP)-2 from a gelatin sponge. A 1 cm gap was made in the middle portion of each of 10 consecutive tracheal cartilage rings in the canine cervix (control group, n = 3), then a gelatin sponge containing 12 microg of BMP-2 solution was implanted in the gap (12 microg group, n = 3). In another group (120 microg + P group, n = 3), the implanted gelatin sponge contained 120 microg of BMP-2 solution, and the gap was covered with periosteum. All of the control dogs developed saber sheath-type tracheomalacia, whereas tracheomalacia was not observed in the 12 microg and 120 microg + P groups. In the 12 microg group, fibrous cartilage was observed at the ends of the cartilage stumps. In the 120 microg + P group, newly formed bone and cartilage were observed to form a bridge between the cartilage stumps. The regeneration of cartilage or bone induced by the slow release of BMP-2 from a gelatin sponge might be useful for treatment of tracheomalacia.