An Elastin-derived composite matrix for enhanced vascularized and innervated bone tissue reconstruction: from material development to preclinical evaluation.

Despite progress in bone tissue engineering, reconstruction of large bone defects remains an important clinical challenge. Here, we developed a biomaterial designed to recruit bone cells, endothelial cells, and neuronal fibers within the same matrix, enabling bone tissue regeneration. The bioactive matrix is based on modified elastin-like polypeptides (ELPs) grafted with laminin-derived adhesion peptides IKVAV and YIGSR, and the SNA15 peptide for retention of hydroxyapatite (HA) particles. The composite matrix shows suitable porosity, interconnectivity, biocompatibility for endothelial cells, and the ability to support neurites outgrowth by sensory neurons. Subcutaneous implantation led to the formation of osteoid tissue, characterized by the presence of bone cells, vascular networks, and neuronal structures, while minimizing inflammation. Using a rat femoral condyle defect model, we performed longitudinal micro-CT analysis, which demonstrates a significant increase in the volume of mineralized tissue when using the ELP-based matrix compared to empty defects and a commercially available control (Collapat). Furthermore, visible blood vessel networks and nerve fibers are observed within the lesions after a period of two weeks. By incorporating multiple key components that support cell growth, mineralization, and tissue integration, this ELP-based composite matrix provides a holistic and versatile solution to enhance bone tissue regeneration. This article is protected by copyright. All rights reserved.

Development of Novel Polysaccharide Membranes for Guided Bone Regeneration: In Vitro and In Vivo Evaluations.

INTRODUCTION: Guided bone regeneration (GBR) procedures require selecting suitable membranes for oral surgery. Pullulan and/or dextran-based polysaccharide materials have shown encouraging results in bone regeneration as bone substitutes but have not been used to produce barrier membranes. The present study aimed to develop and characterize pullulan/dextran-derived membranes for GBR. MATERIALS AND METHODS: Two pullulan/dextran-based membranes, containing or not hydroxyapatite (HA) particles, were developed. In vitro, cytotoxicity evaluation was performed using human bone marrow mesenchymal stem cells (hBMSCs). Biocompatibility was assessed on rats in a subcutaneous model for up to 16 weeks. In vivo, rat femoral defects were created on 36 rats to compare the two pullulan/dextran-based membranes with a commercial collagen membrane (Bio-Gide®). Bone repair was assessed radiologically and histologically. RESULTS: Both polysaccharide membranes demonstrated cytocompatibility and biocompatibility. Micro-computed tomography (micro-CT) analyses at two weeks revealed that the HA-containing membrane promoted a significant increase in bone formation compared to Bio-Gide®. At one month, similar effects were observed among the three membranes in terms of bone regeneration. CONCLUSION: The developed pullulan/dextran-based membranes evidenced biocompatibility without interfering with bone regeneration and maturation. The HA-containing membrane, which facilitated early bone regeneration and offered adequate mechanical support, showed promising potential for GBR procedures.

Injectable bone cement containing carboxymethyl cellulose microparticles as a silver delivery system able to reduce implant-associated infection risk.

In the challenging quest for a solution to reduce the risk of implant-associated infections in bone substitution surgery, the use of silver ions is promising regarding its broad spectrum on planktonic, sessile as well as multiresistant bacteria. In view of controlling its delivery in situ at the desired dose, we investigated its encapsulation in carboxymethyl cellulose (CMC) microparticles by spray-drying and included the latter in the formulation of a self-setting calcium phosphate bone cement. We implemented an original step-by-step methodology starting from the in vitro study of the antibacterial properties and cytotoxicity of two silver salts of different solubility in aqueous medium and then in the cement to determine the range of silver loading able to confer anti-biofilm and non-cytotoxic properties to the biomaterial. A dose-dependent efficiency of silver was demonstrated on the main species involved in bone-implant infection (S. aureus and S. epidermidis). Loading silver in microspheres instead of loading it directly inside the cement permitted to avoid undesired silver-cement interactions during setting and led to a faster release of silver, i.e. to a higher dose released within the first days combining anti-biofilm activity and preserved cytocompatibility. In addition, a combined interest of the introduction of about 10% (w/w) silver-loaded CMC microspheres in the cement formulation was demonstrated leading to a fully injectable and highly porous (77%) cement, showing a compressive strength analogous to cancellous bone. This injectable silver-loaded biomimetic composite cement formulation constitutes a versatile bone substitute material with tunable drug delivery properties, able to fight against bone implant associated infection. STATEMENT OF SIGNIFICANCE: This study is based on two innovative scientific aspects regarding the literature: i) Choice of silver ions as antibacterial agent combined with their way of incorporation: Carboxymethylcellulose has never been tested into bone cement to control its drug loading and release properties. ii) Methodology to formulate an antibacterial and injectable bone cement: original and multidisciplinary step-by-step methodology to first define, through (micro)biological tests on two silver salts with different solubilities, the targeted range of silver dose to include in carboxymethylcellulose microspheres and, then optimization of silver-loaded microparticles processing to fulfill requirements (encapsulation efficiency and size). The obtained fully injectable composite controls the early delivery of active dose of silver (from 3 h and over 2 weeks) able to fight against bone implant-associated infections.

Comparison of amniotic membrane versus the induced membrane for bone regeneration in long bone segmental defects using calcium phosphate cement loaded with BMP-2.

Thanks to its biological properties, the human amniotic membrane (HAM) combined with a bone substitute could be a single-step surgical alternative to the two-step Masquelet induced membrane (IM) technique for regeneration of critical bone defects. However, no study has directly compared these two membranes. We first designed a 3D-printed scaffold using calcium phosphate cement (CPC). We assessed its suitability in vitro to support human bone marrow mesenchymal stromal cells (hBMSCs) attachment and osteodifferentiation. We then performed a rat femoral critical size defect to compare the two-step IM technique with a single-step approach using the HAM. Five conditions were compared. Group 1 was left empty. Group 2 received the CPC scaffold loaded with rh-BMP2 (CPC/BMP2). Group 3 and 4 received the CPC/BMP2 scaffold covered with lyophilized or decellularized/lyophilized HAM. Group 5 underwent a two- step induced membrane procedure with insertion of a polymethylmethacrylate (PMMA) spacer followed by, after 4 weeks, its replacement with the CPC/BMP2 scaffold wrapped in the IM. Micro-CT and histomorphometric analysis were performed after six weeks. Results showed that the CPC scaffold supported the proliferation and osteodifferentiation of hBMSCs in vitro. In vivo, the CPC/BMP2 scaffold very efficiently induced bone formation and led to satisfactory healing of the femoral defect, in a single-step, without autograft or the need for any membrane covering. In this study, there was no difference between the two-step induced membrane procedure and a single step approach. However, the results indicated that none of the tested membranes further enhanced bone healing compared to the CPC/BMP2 group.

Assessment of fresh and preserved amniotic membrane for guided bone regeneration in mice.

Thanks to its biological properties, the human amniotic membrane (HAM) can be used as a barrier membrane for guided bone regeneration (GBR). However, no study has assessed the influence of the preservation method of HAM for this application. This study aimed to establish the most suitable preservation method of HAM for GBR. Fresh (F), cryopreserved (C) lyophilized (L), and decellularized and lyophilized (DL) HAM were compared. The impact of preservation methods on collagen and glycosaminoglycans (GAG) content was evaluated using Masson's trichrome and alcian blue staining. Their suture retention strengths were assessed. In vitro, the osteogenic potential of human bone marrow mesenchymal stromal cells (hBMSCs) cultured on the four HAMs was evaluated using alkaline phosphatase staining and alizarin red quantification assay. In vivo, the effectiveness of fresh and preserved HAMs for GBR was assessed in a mice diaphyseal bone defect after 1 week or 1 month healing. Micro-CT and histomorphometric analysis were performed. The major structural components of HAM (collagen and GAG) were preserved whatever the preservation method used. The tearing strength of DL-HAM was significantly higher. In vitro, hBMSCs seeded on DL-HAM displayed a stronger ALP staining, and alizarin red staining quantification was significantly higher at Day 14. In vivo, L-HAM and DL-HAM significantly enhanced early bone regeneration. One month after the surgery, only DL-HAM slightly promoted bone regeneration. Several preserving methods of HAM have been studied for bone regeneration. Here, we have demonstrated that DL-HAM achieved the most promising results for GBR.

Towards an in vitro model of the glomerular barrier unit with an innovative bioassembly method.

BACKGROUND: The development of an artificial glomerular unit may be pivotal for renal pathophysiology studies at a multicellular scale. Using a tissue engineering approach, we aimed to reproduce in part the specific glomerular barrier architecture by manufacturing a glomerular microfibre (Mf). METHODS: Immortalized human glomerular cell lines of endothelial cells (GEnCs) and podocytes were used. Cells and a three-dimensional (3D) matrix were characterized by immunofluorescence with confocal analysis, Western blot and polymerase chain reaction. Optical and electron microscopy were used to study Mf and cell shapes. We also analysed cell viability and cell metabolism within the 3D construct at 14 days. RESULTS: Using the Mf manufacturing method, we repeatedly obtained a cellularized Mf sorting human glomerular cells in 3D. Around a central structure made of collagen I, we obtained an internal layer composed of GEnC, a newly formed glomerular basement membrane rich in α5 collagen IV and an external layer of podocytes. The cell concentration, optimal seeding time and role of physical stresses were modulated to obtain the Mf. Cell viability and expression of specific proteins (nephrin, synaptopodin, vascular endothelial growth factor receptor 2 (VEGFR2) and von Willebrandt factor (vWF)) were maintained for 19 days in the Mf system. Mf ultrastructure, observed with EM, had similarities with the human glomerular barrier. CONCLUSION: In summary, with our 3D bio-engineered glomerular fibre, GEnC and podocytes produced a glomerular basement membrane. In the future, this glomerular Mf will allow us to study cell interactions in a 3D system and increase our knowledge of glomerular pathophysiology.

Comparison of the impact of preservation methods on amniotic membrane properties for tissue engineering applications.

Human amniotic membrane (hAM) is considered as an attractive biological scaffold for tissue engineering. For this application, hAM has been mainly processed using cryopreservation, lyophilization and/or decellularization. However, no study has formally compared the influence of these treatments on hAM properties. The aim of this study was to develop a new decellularization-preservation process of hAM, and to compare it with other conventional treatments (fresh, cryopreserved and lyophilized). The hAM was decellularized (D-hAM) using an enzymatic method followed by a detergent decellularization method, and was then lyophilized and gamma-sterilized. Decellularization was assessed using DNA staining and quantification. D-hAM was compared to fresh (F-hAM), cryopreserved (C-hAM) and lyophilized/gamma-sterilized (L-hAM) hAM. Their cytotoxicity on human bone marrow mesenchymal stem cells (hBMSCs) and their biocompatibility in a rat subcutaneous model were also evaluated. The protocol was effective as judged by the absence of nuclei staining and the residual DNA lower than 50 ng/mg. Histological staining showed a disruption of the D-hAM architecture, and its thickness was 84% lower than fresh hAM (p < 0.001). Despite this, the labeling of type IV and type V collagen, elastin and laminin were preserved on D-hAM. Maximal force before rupture of D-hAM was 92% higher than C-hAM and L-hAM (p < 0.01), and D-hAM was 37% more stretchable than F-hAM (p < 0.05). None of the four hAM were cytotoxic, and D-hAM was the most suitable scaffold for hBMSCs proliferation. Finally, D-hAM was well integrated in vivo. In conclusion, this new hAM decellularization process appears promising for tissue engineering applications.

Layer-by-layer bioassembly of poly(lactic) acid membranes loaded with coculture of HBMSCs and EPCs improves vascularization in vivo.

Layer-by-layer (LBL) BioAssembly method was developed to enhance the control of cell distribution within 3D scaffolds for tissue engineering applications. The objective of this study was to evaluate in vivo the development of blood vessels within LBL bioassembled membranes seeded with human primary cells, and to compare it to cellularized massive scaffolds. Poly(lactic) acid (PLA) membranes fabricated by fused deposition modeling were seeded with monocultures of human bone marrow stromal cells or with cocultures of these cells and endothelial progenitor cells. Then, four cellularized membranes were assembled in LBL constructs. Early osteoblastic and endothelial cell differentiation markers, alkaline phosphatase, and von Willebrand's factor, were expressed in all layers of assemblies in homogenous manner. The same kind of LBL assemblies as well as cellularized massive scaffolds was implanted subcutaneously in mice. Human cells were observed in all scaffolds seeded with cells, but not in the inner parts of massive scaffolds. There were significantly more blood vessels observed in LBL bioassemblies seeded with cocultures compared to all other samples. LBL bioassembly of PLA membranes seeded with a coculture of human cells is an efficient method to obtain homogenous cell distribution and blood vessel formation within the entire volume of a 3D composite scaffold.

Cell and tissue responses at the interface with a chitosan hydrogel intended for vascular applications: in vitro and in vivo exploration.

AIMS: The need for small caliber vessels to treat cardiovascular diseases has grown. However, synthetic polymers perform poorly in small-diameter applications. Chitosan hydrogels can provide a novel biological scaffold for vascular engineering. The goal of this study was to explore host cell and tissue behavior at the interface with chitosan-based scaffolds in vitro and in vivo. METHODS AND RESULTS: in vitro, we assessed the ability of endothelial cells lining chitosan hydrogels to produce tissue factor (TF), thrombomodulin (TM) and nitric oxide. We showed that endothelial cells behave as a native endothelium since under stimulation, TF and TM expression increased and decreased, respectively. Endothelial cells seeded on chitosan produced nitric oxide, but no change was observed under stimulation. After in vivo subcutaneous implantation of chitosan hydrogels in rats, macrophage activation phenotypes, playing a crucial role in biomaterial/tissue, were explored by immunohistochemistry. Our results suggested a balance between pro- and anti-inflammatory signals since we observed an inflammatory response in favor of macrophage M2 phenotype. CONCLUSION: in vitro exploration of endothelial cell response at the interface with chitosan hydrogel showed a functional endothelium and in vivo exploration of tissue response revealed a biointegration of chitosan hydrogels.

Colorectal wall regeneration resulting from the association of chitosan hydrogel and stromal vascular fraction from adipose tissue.

Chitosan hydrogel and adipose derived stem cells (ADCS) have been reported as the optimal partnership for colorectal tissue engineering. In that field, the aim of the current experiment was to assess the interest of seeding ADSC on chitosan hydrogel patches in an in vivo comparative study and on a tube intended replace a colonic segment in an in vivo feasibility study. In the comparative study, a 2 × 3 cm colonic wall defect was performed in 20 swine and repaired by suturing a chitosan hydrogel patch: acellular matrix (group A, n = 10) versus matrix seeded with autologous stromal vascular fraction (SVF) (group B, n = 10). In the feasibility study, a circular colonic section was performed and a 2-cm-length chitosan hydrogel tube (seeded with autologous SVF) was implanted between the two edges of the colon in 3 pigs. Graft areas were explanted at 8 weeks for examinations. Endpoints were technical feasibility, fibrosis ratio, and smooth muscle layer regeneration. A complete coverage of the patched area was observed with an ad integrum regeneration of the colonic wall including smooth muscle cells layer around a thin fibrosis scare. Fibrosis ratio was significantly lower group B: 13% versus 55% (p = 0.013). Segmental colonic replacement appeared accurate. Our data confirmed in a large animal model the healing effect of chitosan on colorectal tissue. The very low rate of the fibrosis ratio in the cellularized group emphasizes inflammatory control effect of the chitosan hydrogel and SVF association. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 460-467, 2018.

A new composite hydrogel combining the biological properties of collagen with the mechanical properties of a supramolecular scaffold for bone tissue engineering.

Tissue engineering is a promising alternative to autografts, allografts, or biomaterials to address the treatment of severe and large bone lesions. Classically, tissue engineering products associate a scaffold and cells and are implanted or injected into the lesion. These cells must be embedded in an appropriate biocompatible scaffold, which offers a favourable environment for their survival and differentiation. Here, we designed a composite hydrogel composed of collagen I, an extracellular matrix protein widely used in several therapeutic applications, which we associated with a physical hydrogel generated from a synthetic small amphiphilic molecule. This composite showed improved mechanical and biological characteristics as compared with gels obtained from each separate compound. Incorporation of the physical hydrogel prevented shrinkage of collagen and cell diffusion out of the gel and yielded a gel with a higher elastic modulus than those of gels obtained with each component alone. The composite hydrogel allowed cell adhesion and proliferation in vitro and long-term cell survival in vivo. Moreover, it promoted the differentiation of human adipose-derived stem cells in the absence of any osteogenic factors. In vivo, cells embedded in the composite gel and injected subcutaneously in immunodeficient mice produced lamellar osteoid tissue and differentiated into osteoblasts. This study points this new composite hydrogel as a promising scaffold for bone tissue engineering applications.

Injectable and Gellable Chitosan Formulations Filled with Cellulose Nanofibers for Intervertebral Disc Tissue Engineering.

The development of non-cellularized injectable suspensions of viscous chitosan (CHI) solutions (1.7⁻3.3% (w/w)), filled with cellulose nanofibers (CNF) (0.02⁻0.6% (w/w)) of the type nanofibrillated cellulose, was proposed for viscosupplementation of the intervertebral disc nucleus pulposus tissue. The achievement of CNF/CHI formulations which can gel in situ at the disc injection site constitutes a minimally-invasive approach to restore damaged/degenerated discs. We studied physico-chemical aspects of the sol and gel states of the CNF/CHI formulations, including the rheological behavior in relation to injectability (sol state) and fiber mechanical reinforcement (gel state). CNF-CHI interactions could be evidenced by a double flow behavior due to the relaxation of the CHI polymer chains and those interacting with the CNFs. At high shear rates resembling the injection conditions with needles commonly used in surgical treatments, both the reference CHI viscous solutions and those filled with CNFs exhibited similar rheological behavior. The neutralization of the flowing and weakly acidic CNF/CHI suspensions yielded composite hydrogels in which the nanofibers reinforced the CHI matrix. We performed evaluations in relation to the biomedical application, such as the effect of the intradiscal injection of the CNF/CHI formulation in pig and rabbit spine models on disc biomechanics. We showed that the injectable formulations became hydrogels in situ after intradiscal gelation, due to CHI neutralization occurring in contact with the body fluids. No leakage of the injectate through the injection canal was observed and the gelled formulation restored the disc height and loss of mechanical properties, which is commonly related to disc degeneration.

Prolonged delivery of BMP-2 by a non-polymer hydrogel for bone defect regeneration.

Bone morphogenetic protein 2 (BMP-2) is a potent inducer of bone formation that is currently used in a limited number of clinical indications to treat extensive bone loss. Extending the field of applications of this molecule requires design of the delivery system to protect the protein from early degradation and allow a slow long-term release. This study describes the use of a non-polymer hydrogel, based on the self-assembly of small amphiphilic glycosyl-nucleolipids into micellar structures, as a new type of delivery system for BMP-2. BMP-2 was readily encapsulated in glycosyl-nucleosyl-fluorinated (GNF)-based gels and slowly released in vitro, while maintaining its osteogenic activity. When hydrogel pieces containing fluorophore-tagged BMP-2 were deposited onto a calvaria defect in mouse, the signal detected in living mice gradually decreased and was still detectable at 3 weeks. Gel-embedded protein promoted significant calvarial bone defect regeneration at 8 weeks after surgery. In contrast, when a solution of BMP-2 without hydrogel was injected into the defects, the fluorescence signal decreased rapidly and no significant bone formation was observed. The unique property of the GNF-based hydrogel as an injectable delivery system for low doses of BMP-2 was revealed in a subcutaneous model of ectopic bone formation. Injected BMP-2-laden GNF hydrogel blocks elicited the formation of cancellous bone, showing all the typical features of remodeling bone that contains bone marrow. These results show that this GNF-based hydrogel is an easy-to-use, efficient delivery system for BMP-2 and osteogenic material to support bone regeneration.

Influence of the three-dimensional culture of human bone marrow mesenchymal stromal cells within a macroporous polysaccharides scaffold on Pannexin 1 and Pannexin 3.

Because cell interactions play a fundamental role for cell differentiation, we investigated the expression of Pannexin 1 and Pannexin 3 in human bone marrow mesenchymal stromal cells (HBMSCs) in a three-dimensional (3D) microenvironment provided by a polysaccharide-based macroporous scaffold. The pannexin (Panx) family consists of three members, Panx1, Panx2, and Panx3. The roles of Panx large-pore ion and metabolite channels are recognized in many physiological and pathophysiological scenarios, but the role of these proteins in human physiological processes is still under investigation. Our study demonstrates that HBMSCs cultured within 3D scaffolds have induced Panx1 and Panx3 expression, compared with two-dimensional culture and that the Panx3 gene expression profile correlates with those of bone markers on mesenchymal stromal cells culture into the 3D scaffold. We showed that Panx1 is involved in the HBMSCs 3D cell-cell organization, as acting on the size of cellular aggregates, demonstrated by the use of Probenecid and the mimetic peptide 10panx1 as specific inhibitors. Inhibition of Panx3 using siRNA strategy shows to reduce the expression of osteocalcin as osteoblast-specific marker by HBMSCs cultured in 3D conditions, suggesting a role of this Panx in osteogenesis. Moreover, we evaluated Panx1 and Panx3 expression within the cellularized scaffolds upon subcutaneous implantation in NOG (NOD/Shi-scid/IL-2Rγnull ) mice, where we could observe a more intense expression in the constructs than in the surrounding tissues in vivo. This study provides new insights on the expression of pannexins in HBMSCs on a 3D microenvironment during the osteogenic differentiation, in vitro and in vivo.

Layer-by-layer bioassembly of cellularized polylactic acid porous membranes for bone tissue engineering.

The conventional tissue engineering is based on seeding of macroporous scaffold on its surface ("top-down" approach). The main limitation is poor cell viability in the middle of the scaffold due to poor diffusion of oxygen and nutrients and insufficient vascularization. Layer-by-Layer (LBL) bioassembly is based on "bottom-up" approach, which considers assembly of small cellularized blocks. The aim of this work was to evaluate proliferation and differentiation of human bone marrow stromal cells (HBMSCs) and endothelial progenitor cells (EPCs) in two and three dimensions (2D, 3D) using a LBL assembly of polylactic acid (PLA) scaffolds fabricated by 3D printing. 2D experiments have shown maintain of cell viability on PLA, especially when a co-cuture system was used, as well as adequate morphology of seeded cells. Early osteoblastic and endothelial differentiations were observed and cell proliferation was increased after 7 days of culture. In 3D, cell migration was observed between layers of LBL constructs, as well as an osteoblastic differentiation. These results indicate that LBL assembly of PLA layers could be suitable for BTE, in order to promote homogenous cell distribution inside the scaffold and gene expression specific to the cells implanted in the case of co-culture system.

The proangiogenic potential of a novel calcium releasing composite biomaterial: Orthotopic in vivo evaluation.

Insufficient angiogenesis remains a major hurdle in current bone tissue engineering strategies. An extensive body of work has focused on the use of angiogenic factors or endothelial progenitor cells. However, these approaches are inherently complex, in terms of regulatory and methodologic implementation, and present a high cost. We have recently demonstrate the potential of electrospun poly(lactic acid) (PLA) fiber-based membranes, containing calcium phosphate (CaP) ormoglass particles, to elicit angiogenesis in vivo, in a subcutaneous model in mice. Here we have devised an injectable composite, containing CaP glass-ceramic particles, dispersed within a (Hydroxypropyl)methyl cellulose (HPMC) matrix, with the capacity to release calcium in a more sustained fashion. We show that by tuning the release of calcium in vivo, in a rat bone defect model, we could improve both bone formation and increase angiogenesis. The bone regeneration kinetics was dependent on the Ca2+ release rate, with the faster Ca2+ release composite gel showing improved bone repair at 3weeks, in relation to control. In the same line, improved angiogenesis could be observed for the same gel formulation at 6weeks post implantation. This methodology allows to integrate two fundamental processes for bone tissue regeneration while using a simple, cost effective, and safe approach. STATEMENT OF SIGNIFICANCE: In current bone tissue engineering approaches the achievement of sufficient angiogenesis, during tissue regeneration, is a major limitation in order to attain full tissue functionality. Recently, we have shown that calcium ions, released by the degradation of calcium phosphate ormoglasses (CaP), are effective angiogenic promoters, in both in vitro and in a subcutaneous implantation model. Here, we devised an injectable composite, containing CaP glass-ceramic particles, dispersed within a HPMC matrix, enabling the release of calcium in a more sustained fashion. We show that by tuning the release of calcium in vivo, in a rat bone defect model, we could improve both bone formation and increase angiogenesis. This simple and cost effective approach holds great promise to translate to the clinics.

An easy-to-use and versatile method for building cell-laden microfibres.

Fibre-shaped materials are useful for creating different functional three-dimensional (3D) structures that could mimic complex tissues. Several methods (e.g. extrusion, laminar flow or electrospinning) have been proposed for building hydrogel microfibres, with distinctive cell types and with different degrees of complexity. However, these methods require numerous protocol adaptations in order to achieve fibre fabricating and lack the ability to control microfibre alignment. Here, we present a simple method for the production of microfibers, based on a core shell approach, composed of calcium alginate and type I collagen. The process presented here allows the removal of the calcium alginate shell, after only 24 hours of culture, leading to stable and reproducible fibre shaped cellular constructs. With time of culture cells show to distribute preferentially to the surface of the fibre and display a uniform cellular orientation. Moreover, when cultured inside the fibres, murine bone marrow mesenchymal stem cells show the capacity to differentiate towards the osteoblastic lineage, under non-osteoinductive culture conditions. This work establishes a novel method for cellular fibre fabrication that due to its inherent simplicity can be easily upscaled and applied to other cell types.

The proangiogenic potential of a novel calcium releasing biomaterial: Impact on cell recruitment.

In current bone tissue engineering strategies the achievement of sufficient angiogenesis during tissue regeneration is still a major limitation in order to attain full functionality. Several strategies have been described to tackle this problem, mainly by the use of angiogenic factors or endothelial progenitor cells. However, when facing a clinical scenario these approaches are inherently complex and present a high cost. As such, more cost effective alternatives are awaited. Here, we demonstrate the potential of electrospun poly(lactic acid) (PLA) fiber-based membranes, containing calcium phosphate ormoglass (CaP) particles, to elicit angiogenesis in vivo, in a subcutaneous model in mice. We show that the current approach elicited the local expression of angiogenic factors, associated to a chemotactic effect on macrophages, and sustained angiogenesis into the biomaterial. As both PLA and CaP are currently accepted for clinical application these off-the-shelf novel membranes have great potential for guided bone regeneration applications. STATEMENT OF SIGNIFICANCE: In current bone tissue engineering approaches the achievement of sufficient angiogenesis, during tissue regeneration, is a major limitation in order to attain full tissue functionality. Recently, our group has found that calcium ions released by the degradation of calcium phosphate ormoglasses (CaP) are effective angiogenic promoters. Based on this, in this work we successfully produced hybrid fibrous mats with different contents of CaP nanoparticles and thus with different calcium ion release rates, using an ormoglass - poly(lactic acid) blend approach. We show that these matrices, upon implantation in a subcutaneous site, could elicit the local expression of angiogenic factors, associated to a chemotactic effect on macrophages, and sustained angiogenesis into the biomaterial, in a CaP dose dependent manner. This off-the-shelf cost effective approach presents great potential to translate to the clinics.

Colorectal tissue engineering: A comparative study between porcine small intestinal submucosa (SIS) and chitosan hydrogel patches.

OBJECTIVE: Tissue engineering may provide new operative tools for colorectal surgery in elective indications. The aim of this study was to define a suitable bioscaffold for colorectal tissue engineering. METHODS: We compared 2 bioscaffolds with in vitro and in vivo experiments: porcine small intestinal submucosa (SIS) versus chitosan hydrogel matrix. We assessed nontoxicity of the scaffold in vitro by using human adipose-derived stem cells (hADSC). In vivo, a 1 × 2-cm colonic wall defect was created in 16 rabbits. Animals were divided randomly into 2 groups according to the graft used, SIS or chitosan hydrogel. Graft area was explanted at 4 and 8 weeks. The end points of in vivo experiments were technical feasibility, behavior of the scaffold, in situ putative inflammatory effect, and the quality of tissue regeneration, in particular smooth muscle layer regeneration. RESULTS: In vitro, hADSC attachment and proliferation occurred on both scaffolds without a substantial difference. After proliferation, hADSCs kept their mesenchymal stem cell characteristics. In vivo, one animal died in each group. Eight weeks after implantation, the chitosan scaffold allowed better wound healing compared with the SIS scaffold, with more effective control of inflammatory activity and an integral regeneration of the colonic wall including the smooth muscle cell layer. CONCLUSION: The outcomes of in vitro experiments did not differ greatly between the 2 groups. Macroscopic and histologic findings, however, revealed better wound healing of the colonic wall in the chitosan group suggesting that the chitosan hydrogel could serve as a better scaffold for colorectal tissue engineering.

Labeling and qualification of endothelial progenitor cells for tracking in tissue engineering: An in vitro study.

PURPOSE: In order to track location and distribution of endothelial cells (ECs) within scaffolds in vitro, we chose lentiPGK-TdTomato transduction of human endothelial progenitor cells (EPCs) isolated and differentiated from cord blood. Because transduction could have a functional impact on cell behavior, we checked different parameters for qualification of labeled- EPCs as well as their use for potential applications in the context of vascular and bone tissue engineering. METHODS: After isolation and expansion, EPCs were classically characterized then transduced with the lentiviral vector containing the TdTomato protein gene under the control of the phosphoglycerate kinase (PGK) promoter. Conventional karyotyping, differentiation capacity, viability, proliferation assays were performed with labeled and unlabeled EPCs. Scaffolds and co-cultures were explored with labeled EPCs, in static or shear stress conditions. RESULTS: Our results show that cell labeling did not affect cell adhesion nor induce cell death. Cell labeling did not induce more chromosomal aberrations. Phenotypical characterization was not affected. In the context of tissue engineering applications, labeled EPCs maintained their ability to line 2D or 3D scaffolds, withstand physiological arterial shear stress, and form tubular networks in co-cultures with human osteoblast progenitor cells. CONCLUSIONS: It is possible to label human EPCs with TdTomato without affecting their behavior by the transduction procedure. This creates an important tool for numerous applications. Our results provide a qualification of labeled EPCs in comparison with unlabeled ones for vascular and bone tissue engineering.