The effect of controlled release of PDGF-BB from heparin-conjugated electrospun PCL/gelatin scaffolds on cellular bioactivity and infiltration. Biomaterials. 2012;33:6709-6720. [PMID: 22770570 DOI: 10.1016/j.biomaterials.2012.06.017]

Development of Injectable Fucoidan and Biological Macromolecules Hybrid Hydrogels for Intra-Articular Delivery of Platelet-Rich Plasma

Platelet-rich plasma (PRP) is rich in growth factors and has commonly been utilized in the repair and regeneration of damaged articular cartilage. However, the major drawbacks of direct PRP injection are unstable biological fixation and fast or burst release of growth factors. Fucoidan is a heparinoid compound that can bind growth factors to control their release rate. Furthermore, fucoidan can reduce arthritis through suppressing inflammatory responses and thus it has been reported to prevent the progression of osteoarthritis, promote bone regeneration and accelerate healing of cartilage injury. Injectable hydrogels can be used to deliver cells and growth factors for an alternative, less invasive treatment of cartilage defects. In this study, hyaluronic acid (HA) and fucoidan (FD) was blended with gelatin (GLT) and the GLT/HA/FD hybrid was further cross-linked with genipin (GP) to prepare injectable GP-GLT/HA/FD hydrogels. The gelation rate was affected by the GP, GLT, HA and FD concentrations, as well as the pH values. The addition of HA and FD to GLT networks improved the mechanical strength of the hydrogels and facilitated the sustained release of PRP growth factors. The GP-GLT/HA/FD hydrogel showed adequate injectability, shape-persistent property and strong adhesive ability, and was more resistant to enzymatic degradation. The PRP-loaded GP-GLT/HA/FD hydrogel promoted cartilage regeneration in rabbits, which may lead to an advanced PRP therapy for enhancing cartilage repair.

Nanoparticle-modified chitosan-agarose-gelatin scaffold for sustained release of SDF-1 and BMP-2

Background

Stromal cell-derived factor 1 (SDF-1) is an important chemokine for stem cell mobilization, and plays a critical role in mobilization of mesenchymal stem cells (MSCs). Bone morphogenetic protein 2 (BMP-2) plays a critical role in osteogenesis of MSCs. However, the use of SDF-1 and BMP-2 in bone tissue engineering is limited by their short half-lives and rapid degradation in vitro and in vivo.

Methods

The chitosan oligosaccharide/heparin nanoparticles (CSO/H NPs) were first prepared via self-assembly. Chitosan-agarose-gelatin (CAG) Scaffolds were then synthesized via gelation technology using cross-linked chitosan, agarose, and gelatin, and were modified by CSO/H NPs. The encapsulation efficiency and release kinetics of SDF-1 and BMP-2 were quantified using an enzyme-linked immunosorbent assay. A CCK-8 assays were used to evaluate biocompatibility of NP-modified scaffolds. The biological activity of the loaded SDF-1 and BMP-2 was evaluated using the transwell migration assay and osteogenic induction assay. An animal MSC recruitment model was used to study the ability of SDF-1 released from NP-modified scaffolds to induce migration of MSCs.

Results

In this study, we developed a novel nanoparticle-modified CAG scaffold for the delivery of SDF-1 and BMP-2. CCK-8 assays demonstrated excellent biocompatibility of NP-modified scaffolds. In addition, we investigated the release of SDF-1 and BMP-2 from NP-modified scaffolds, and evaluated the effect of released SDF-1 on MSC migration. The effect of released BMP-2 on MSC osteogenesis was also examined. In vitro cell migration assays showed that SDF-1 released from NP-modified scaffolds retained its migration activity; osteogenesis studies demonstrated that released BMP-2 exhibited a strong ability to induce differentiation towards osteoblasts. Our in vivo recruitment assays showed continuous chemotactic response of MSCs to SDF-1 released from the NP-modified scaffold.

Conclusion

The simplicity of synthesizing CSO/H NP-modified CAG scaffolds, combined with its high cytokine loading capacity and sustained release effect, renders NP-modified CAG scaffold an attractive candidate for sustained release of SDF-1 and BMP-2 to promote bone repair and regeneration.

Heparinized PCL/keratin mats for vascular tissue engineering scaffold with potential of catalytic nitric oxide generation

Heparins are capable of improving blood compatibility, enhancing HUVEC viability, while inhibiting HUASMC proliferation. Combination of biodegradable poly(ε-caprolactone) (PCL) with keratin and heparins would provide an anticoagulant and endothelialization supporting environment for vascular tissue engineering. Herein, PCL and keratin were first coelectrospun and then covalently conjugated with heparins. The resulting mats were surface-characterized by ATR-FTIR, SEM, WCA, and XPS. Cell viability data showed that the heparinized PCL/keratin mats could motivate the adhesion and growth of HUVEC, while inhibit HUASMC proliferation. In addition, these mats could prolong blood clotting time and reduce platelet adhesion as well as no erythrolysis. Interestingly, these mats could catalyze the NO donor in blood to release NO, which could enhance endothelial cell growth, while decrease smooth muscle cell proliferation and platelet adhesion. In summary, the heparinized mats would be a good candidate as a scaffold for vascular tissue engineering. This study is novel in that we prepared a type of heparinized tissue scaffold that could catalyze the NO donor to release NO to regulate endothelialization without angiogenesis and thrombus formation.

Platelet-derived growth factor-coated decellularized meniscus scaffold for integrative healing of meniscus tears

The aim of this study was to examine the potential of platelet-derived growth factor (PDGF)-coated decellularized meniscus scaffold in mediating integrative healing of meniscus tears by inducing endogenous cell migration. Fresh bovine meniscus was chemically decellularized and covalently conjugated with heparin and PDGF-BB. In vitro PDGF release kinetics was measured. The scaffold was transplanted into experimental tears in avascular bovine meniscus explants and cultured for 2 and 4 weeks. The number migrating and proliferating cells at the borderline between the scaffold and injured explant and PDGF receptor-β (PDGFRβ) expressing cells were counted. The alignment of the newly produced ECM and collagen was analyzed by Safranin-O, picrosirius red staining, and differential interference contrast (DIC). Tensile testing of the explants was performed after culture for 2 and 4 weeks. Heparin conjugated scaffold showed immobilization of high levels of PDGF-BB, with sustained release over 2 weeks. Insertion of the PDGF-BB treated scaffold in defects in avascular meniscus led to increased PDGFRβ expression, cell migration and proliferation into the defect zone. Safranin-O, picrosirius red staining and DIC showed tissue integration between the scaffold and injured explants. Tensile properties of injured explants treated with PDGF-BB coated scaffold were significantly higher than in the scaffold without PDGF. In conclusion, PDGF-BB-coated scaffold increased PDGFRβ expression and promoted migration of endogenous meniscus cells to the defect area. New matrix was formed that bridged the space between the native meniscus and the scaffold and this was associated with improved biomechanical properties. The PDGF-BB-coated scaffold will be promising for clinical translation to healing of meniscus tears.

STATEMENT OF SIGNIFICANCE

Meniscus tears are the most common injury of the knee joint. The most prevalent forms that occur in the inner third typically do not spontaneously heal and represent a major risk factor for the development of knee osteoarthritis. The goal of this project was to develop an approach that is readily applicable for clinical use. We selected a natural and readily available decellularized meniscus scaffold and conjugated it with PDGF, which we had previously found to have strong chemotactic activity for chondrocytes and progenitor cells. The present results show that insertion of the PDGF-conjugated scaffold in defects in avascular meniscus led to endogenous cell migration and proliferation into the defect zone with tissue integration between the scaffold and injured explants and improved tensile properties. This PDGF-conjugated scaffold will be promising for a translational approach to healing of meniscus tears.

Evaluating the angiogenic potential of a novel temperature-sensitive gel scaffold derived from porcine skeletal muscle tissue

Our previous study fabricated decellularized porcine muscle tissues (DPMTs) and demonstrated that DPMTs with few cell residues possess highly preserved protein components and good biocompatibility. In the physical state, skeletal muscle equips an abundant vascular network due to the vast demand of energy from aerobic metabolism. Vascular bioactive factors which are rich in skeletal muscle tissues may contribute to the angiogenic effect of DPMTs. However, implanting DPMTs in vivo in a less invasive way is unfeasible. Hence, the purpose of this study was to fabricate DPMTs into hydrogel and investigate the effects of DPMT gel on promoting neovessel formation in vitro and in vivo. The results demonstrated that the surface topographies of the DPMT gel were looser and more homogeneous than the DPMTs. The rates of retained VEGF, bFGF, and PDGF-BB in DPMT gel were almost half of the corresponding content in fresh skeletal muscle tissues. Human umbilical endothelial cells displayed better proliferation ability and enhanced the formation of neovascular loops when seeded on DPMT gel compared to small intestinal submucosa gels at the same concentration of 2% (W/V). Furthermore, the increased neovessel formation was detected after subcutaneous injection of DPMT gel. Taken together, these findings suggested that DPMT gel may possess the potential of promoting neovascular formation.

The effects of biomimetically conjugated VEGF on osteogenesis and angiogenesis of MSCs (human and rat) and HUVECs co-culture models

The purpose of this work was to investigate if the biomimetically conjugated VEGF and HUVECs co-culture could modulate the osteogenic and angiogenic differentiation of MSCs derived from rat and human bone marrow (rMSCs and hMSCs). After treated by ammonia plasma, Poly(lactic-co-glycolic acid) (PLGA) electrospun nanofibers were immobilized with VEGF through heparin to fulfil the sustained release. The proliferation capacity of rMSCs and hMSCs on neat PLGA nanofibers (NF) and VEGF immobilized NF (NF-VEGF) surfaces were assessed by CCK-8 and compared when MSCs were mono-cultured and co-cultured with HUVECs. The effect of VEGF and HUVECs co-culturing on osteogenic and angiogenic differentiation of rMSCs and hMSCs were investigated by calcium deposits and CD31 expression on NF and NF-VEGF surfaces. The results indicated that VEGF has been biomimetically immobilized onto PLGA nanofibers surface and kept sustained release successfully. The CD31 staining results showed that both VEGF and HUVECs co-culture could enhance the angiogenesis of rMSCs and hMSCs. However, the proliferation and osteogenic differentiation of MSCs when cultured with VEGF and HUVECs showed a species dependent response. Taken together, VEGF immobilization and co-culture with HUVECs promoted angiogenesis of MSCs, indicating a good strategy for vascularization in bone tissue engineering.

Heparin-Eluting Electrospun Nanofiber Yarns for Antithrombotic Vascular Sutures

The surgical connection of blood vessels, anastomosis, is a critical procedure in many reparative, transplantation, and reconstructive surgical procedures. However, effective restoration of circulation is complicated by pathological clotting (thrombosis) or progressive occlusion due to excess cell proliferation that often leads to additional surgeries and increases morbidity and mortality risk for patients. Pharmaceutical agents have been tested to prevent these complications, but many have unacceptable systemic side effects. Therefore, an alternative approach to deliver these drugs at the site of injury in a controlled manner is necessary. The objective of this study was to develop electrospun nanofibers composed of polyester poly(lactide- co-glycolide) (PLGA), poly(ethylene oxide) (PEO), and positively charged copolymer, poly(lactide- co-glycolide)- graft-polyethylenimine (PgP) for electrostatic binding and release of heparin for application as an antithrombotic microvascular suture. PgP was synthesized with different coupling ratios between PLGA and branched polyethylenimine (bPEI) to obtain PgP₁ (∼1 PLGA grafted to 1 bPEI) and PgP_3.7 (∼3.7 PLGA grafted to 1 bPEI). Nanofiber yarns (PLGA/PEO/PgP₁ and PLGA/PEO/PgP_3.7) were fabricated by electrospinning. Heparin immobilization on the positively charged nanofiber yarns was visualized using fluorescein-conjugated heparin (F-Hep), and the amount of immobilized F-Hep was higher on both PLGA/PEO/PgP_3.7 and PLGA/PEO/PgP₁ than yarns without PgP (PLGA/PEO). We also found that F-Hep was released from both PgP-containing yarns in a sustained manner over 20 days, while over 60% of F-Hep was released within 4 h from PLGA/PEO. Finally, we observed that heparin-eluting nanofiber yarns with both PgP₁ and PgP_3.7 showed significantly longer clotting times than nanofiber yarns without PgP. The clotting time of PLGA/PEO/PgP_3.7 was not significantly different than that of free heparin (0.5 μg/mL). These results show that heparin-eluting electrospun nanofiber yarns may offer a basis for the development of microvascular sutures with anticoagulant activity.

Enhanced survival and insulin secretion of insulinoma cell aggregates by incorporating gelatin hydrogel microspheres

Introduction

The objective of this study is to evaluate the survival and glucose-induced insulin secretion of rat-derived insulinoma cells (INS-1) from their aggregates incorporating different size of gelatin hydrogel microspheres comparing with microspheres-free cell aggregates.

Methods

The gelatin hydrogel microspheres were prepared by the conventional w/o emulsion method. The INS-1 cells were cultured in a V-bottomed well, combining with or without the gelatin hydrogel microspheres to form their aggregates with or without microspheres.

Results

When the cell viability, the live cell number, the reductase activity, and the insulin secretion of cell aggregates were evaluated 7 or 14 days after incubation, the cell aggregates incorporating gelatin hydrogel microspheres showed higher cell viability, reductase activity and a larger number of live cells. The cell aggregates incorporating larger size and number of gelatin hydrogel microspheres secreted a larger amount of insulin, compared with those incorporating smaller size and number of microspheres or without microspheres.

Conclusion

It is conceivable that the incorporation of gelatin hydrogel microspheres in cell aggregates is promising to improve their survival and insulin secretion function.

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INS-1 cell aggregates incorporating gelatin hydrogel microspheres are prepared.

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Gelatin hydrogel microspheres incorporation improves cell viability and glucose-induced insulin secretion of cell aggregates.

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The size and number of gelatin hydrogel microspheres affected the cell condition and function.

Modifications of silk film for dual delivery

Silk biomaterials can be designed to provide an architectural framework comparable to connate extracellular matrix in order to boost cell growth and eventual tissue regeneration. Silk (Bombyx mori) fibroins self-assemble into hydrophobic crystalline β sheets, which provide mechanical strength and tunable degradability. The next generation of tissue engineering scaffolds aim to provide spatially controlled modulation of cell adhesion and differentiation, which can be achieved by spatially controlled surface functionalization of the scaffolds. In this respect, it is even more important to be able to release molecules at timescales ranging from hours to days, as many biological processes require signals early on to initiate processes, and over prolonged periods to sustain them. Unfortunately, achieving spatio-temporal control over multiple release profiles from silk based substrates is challenging due to their intrinsic slow release behaviour. Here, we report a simple strategy that provides spatio-temporal control over the release of drugs from silk films (SFs). We have developed a UV based strategy to modify the SFs with nanogels, which can provide a fast as well as slow release profile from a single platform. We demonstrate that the release profile of encapsulated molecules on the SF substrate can be tuned from fast (within hours) to slow (within days), thus resulting in a dual release system, which can be eventually utilized to deliver bioactive molecules at specific regions with different rates to achieve the desired multiple biological effects.

Biomaterial-driven in situ cardiovascular tissue engineering-a multi-disciplinary perspective

There is a persistent and growing clinical need for readily-available substitutes for heart valves and small-diameter blood vessels. In situ tissue engineering is emerging as a disruptive new technology, providing ready-to-use biodegradable, cell-free constructs which are designed to induce regeneration upon implantation, directly in the functional site. The induced regenerative process hinges around the host response to the implanted biomaterial and the interplay between immune cells, stem/progenitor cell and tissue cells in the microenvironment provided by the scaffold in the hemodynamic environment. Recapitulating the complex tissue microstructure and function of cardiovascular tissues is a highly challenging target. Therein the scaffold plays an instructive role, providing the microenvironment that attracts and harbors host cells, modulating the inflammatory response, and acting as a temporal roadmap for new tissue to be formed. Moreover, the biomechanical loads imposed by the hemodynamic environment play a pivotal role. Here, we provide a multidisciplinary view on in situ cardiovascular tissue engineering using synthetic scaffolds; starting from the state-of-the art, the principles of the biomaterial-driven host response and wound healing and the cellular players involved, toward the impact of the biomechanical, physical, and biochemical microenvironmental cues that are given by the scaffold design. To conclude, we pinpoint and further address the main current challenges for in situ cardiovascular regeneration, namely the achievement of tissue homeostasis, the development of predictive models for long-term performances of the implanted grafts, and the necessity for stratification for successful clinical translation.

Progress and perspectives in bioactive agent delivery via electrospun vascular grafts

The review discusses the progress in the design and synthesis of bioactive agents incorporated into vascular grafts obtained by the electrospinning process.

Recent advances in multiaxial electrospinning for drug delivery

Electrospun fibers have seen an insurgence in biomedical applications due to their unique characteristics. Coaxial and triaxial electrospinning techniques have added new impetus via fabrication of multilayered nano and micro-size fibers. These techniques offer the possibility of forming fibers with features such as blending, reinforced core, porous and hollow structure. The unique fabrication process can be used to tailor the mechanical properties, biological properties and release of various factors, which can potentially be useful in various controlled drug delivery applications. Harvesting these advantages, various polymers and their combinations have been explored in a number of drug delivery and tissue regeneration applications. New advances have shown the requirement of drug-polymer compatibility in addition to drug-solvent compatibility. We summarize recent findings using both hydrophilic and hydrophobic (or lipophilic) drugs in hydrophobic or hydrophilic polymers on release behavior. We also describe the fundamental forces involved during the electrospinning process providing insight to the factors to be considered to form fibers. Also, various modeling efforts on the drug release profiles are summarized. In addition new developments in the immune response to the electrospun fibers, and advances in scale-up issues needed for industrial size manufacturing.

Pharmacology of Heparin and Related Drugs

Heparin has been recognized as a valuable anticoagulant and antithrombotic for several decades and is still widely used in clinical practice for a variety of indications. The anticoagulant activity of heparin is mainly attributable to the action of a specific pentasaccharide sequence that acts in concert with antithrombin, a plasma coagulation factor inhibitor. This observation has led to the development of synthetic heparin mimetics for clinical use. However, it is increasingly recognized that heparin has many other pharmacological properties, including but not limited to antiviral, anti-inflammatory, and antimetastatic actions. Many of these activities are independent of its anticoagulant activity, although the mechanisms of these other activities are currently less well defined. Nonetheless, heparin is being exploited for clinical uses beyond anticoagulation and developed for a wide range of clinical disorders. This article provides a "state of the art" review of our current understanding of the pharmacology of heparin and related drugs and an overview of the status of development of such drugs.

Hybrid Polycaprolactone/Alginate Scaffolds Functionalized with VEGF to Promote de Novo Vessel Formation for the Transplantation of Islets of Langerhans

Although regarded as a promising treatment for type 1 diabetes, clinical islet transplantation in the portal vein is still hindered by a low transplantation outcome. Alternative transplantation sites have been proposed, but the survival of extra-hepatically transplanted islets of Langerhans critically depends on quick revascularization after engraftment. This study aims at developing a new 3D scaffold platform that can actively boost vascularization and may find an application for extra-hepatic islet transplantation. The construct consists of a 3D ring-shaped polycaprolactone (PCL) scaffold with heparinized surface to electrostatically bind vascular endothelial growth factor (VEGF), surrounding a hydrogel core for islets encapsulation. Heparin immobilization improves the amount of VEGF retained by the construct, up to 3.6 fold, compared to untreated PCL scaffolds. In a chicken chorioallanthoic membrane model, VEGF immobilized on the construct enhances angiogenesis in close proximity and on the surface of the scaffolds. After 7 days, islets encapsulated in the alginate core show functional response to glucose stimuli comparable to free-floating islets. Thus, the developed platform has the potential to support rapid vascularization and islet endocrine function.

Creating Hierarchical Topographies on Fibrous Platforms Using Femtosecond Laser Ablation for Directing Myoblasts Behavior

Developing an artificial extracellular matrix that closely mimics the native tissue microenvironment is important for use as both a cell culture platform for controlling cell fate and an in vitro model system for investigating the role of the cellular microenvironment. Electrospinning, one of the methods for fabricating structures that mimic the native ECM, is a promising technique for creating fibrous platforms. It is well-known that align or randomly distributed electrospun fibers provide cellular contact guidance in a single pattern. However, native tissues have hierarchical structures, i.e., topographies on the micro- and nanoscales, rather than a single structure. Thus, we fabricated randomly distributed nanofibrous (720 ± 80 nm in diameter) platforms via a conventional electrospinning process, and then we generated microscale grooves using a femtosecond laser ablation process to develop engineered fibrous platforms with patterned hierarchical topographies. The engineered fibrous platforms can regulate cellular adhesive morphology, proliferation, and distinct distribution of focal adhesion proteins. Furthermore, confluent myoblasts cultured on the engineered fibrous platforms revealed that the direction of myotube assembly can be controlled. These results indicate that our engineered fibrous platforms may be useful tools in investigating the roles of nano- and microscale topographies in the communication between cells and ECM.

Importance of dual delivery systems for bone tissue engineering

Bone formation is a complex process that requires concerted function of multiple growth factors. For this, it is essential to design a delivery system with the ability to load multiple growth factors in order to mimic the natural microenvironment for bone tissue formation. However, the short half-lives of growth factors, their relatively large size, slow tissue penetration, and high toxicity suggest that conventional routes of administration are unlikely to be effective. Therefore, it seems that using multiple bioactive factors in different delivery systems can develop new strategies for improving bone tissue regeneration. Combination of these factors along with biomaterials that permit tunable release profiles would help to achieve truly spatiotemporal regulation during delivery. This review summarizes the various dual-control release systems that are used for bone tissue engineering.

Nanogel containing electrospun nanofibers as a platform for stable loading of proteins

We designed polysaccharide nanogel-containing nanofibers by electrospinning. This system have a great potential for protein delivery systems.

Bicomponent electrospun scaffolds to design extracellular matrix tissue analogs

In the last decade, bicomponent fibers have been proposed to fabricate bio-inspired systems for tissue repair, regenerative medicine, medical healthcare and clinical applications. In comparison with monocomponent fibers, key advantage concerns their ability of self-adapting to the physiological conditions through an extended pattern of signals--morphological, chemical and physical ones--confined at the single fiber level. Hydrophobic/hydrophilic phases may be variously organized by tuneable processing modes (i.e., blending, core/shell, interweaving) thus offering different benefits in terms of biological activity, fluid sorption and molecular transport properties (first generation). The possibility to efficiently graft cell-adhesive proteins and peptide sequences onto the fiber surface mediated by spacers or impregnating hydrogels allows to trigger cell late activities by a controlled and sustained release in vitro of specific biomolecules (i.e., morphogens, growth factors). Here, we introduce an overview of current approaches based on bicomponent fiber use as extra cellular matrix analogs with cell-instructive functions and hierarchal organization of living tissues.

Smooth Muscle Cell Alignment and Phenotype Control by Melt Spun Polycaprolactone Fibers for Seeding of Tissue Engineered Blood Vessels

A method has been developed to induce and retain a contractile phenotype for vascular smooth muscle cells, as the first step towards the development of a biomimetic blood vessel construct with minimal compliance mismatch. Melt spun PCL fibers were deposited on a mandrel to form aligned fibers of 10 μm in diameter. The fibers were bonded into aligned arrangement through dip coating in chitosan solution. This formed a surface of parallel grooves, 10 μm deep by 10 μm across, presenting a surface layer of chitosan to promote cell surface interactions. The aligned fiber surface was used to culture cells present in the vascular wall, in particular fibroblasts and smooth muscle cells. This topography induced “surface guidance” over the orientation of the cells, which adopted an elongated spindle-like morphology, whereas cells on the unpatterned control surface did not show such orientation, assuming more rhomboid shapes. The preservation of VSMC contractile phenotype on the aligned scaffold was demonstrated by the retention of α-SMA expression after several days of culture. The effect was assessed on a prototype vascular graft prosthesis fabricated from polylactide caprolactone; VSMCs aligned longitudinally along a fiberless tube, whereas, for the aligned fiber coated tubes, the VSMCs aligned in the required circumferential orientation.

The scope and sequence of growth factor delivery for vascularized bone tissue regeneration

Bone regeneration is a complex process, that in vivo, requires the highly coordinated presentation of biochemical cues to promote the various stages of angiogenesis and osteogenesis. Taking inspiration from the natural healing process, a wide variety of growth factors are currently being released within next generation tissue engineered scaffolds (in a variety of ways) in order to heal non-union fractures and bone defects. This review will focus on the delivery of multiple growth factors to the bone regeneration niche, specifically 1) dual growth factor delivery signaling and crosstalk, 2) the importance of growth factor timing and temporal separation, and 3) the engineering of delivery systems that allow for temporal control over presentation of soluble growth factors. Alternative methods for growth factor presentation, including the use of gene therapy and platelet-rich plasma scaffolds, are also discussed.

A novel tissue-engineered trachea with a mechanical behavior similar to native trachea

A novel tissue-engineered trachea was developed with appropriate mechanical behavior and substantial regeneration of tracheal cartilage. We designed hollow bellows scaffold as a framework of a tissue-engineered trachea and demonstrated a reliable method for three-dimensional (3D) printing of monolithic bellows scaffold. We also functionalized gelatin sponge to allow sustained release of TGF-β1 for stimulating tracheal cartilage regeneration and confirmed that functionalized gelatin sponge induces cartilaginous tissue formation in vitro. A tissue-engineered trachea was then created by assembling chondrocytes-seeded functionalized gelatin sponges into the grooves of bellows scaffold and it showed very similar mechanical behavior to that of native trachea along with substantial regeneration of tracheal cartilage in vivo. The tissue-engineered trachea developed here represents a novel concept of tracheal substitute with appropriate mechanical behavior similar to native trachea for use in reconstruction of tracheal stenosis.

Novel stable cytokine delivery system in physiological pH solution: chitosan oligosaccharide/heparin nanoparticles

Background

Cell therapy is a promising strategy for tissue regeneration. Key to this strategy is mobilization and recruitment of exogenous or autologous stem/progenitor cells by cytokines. However, there is no effective cytokine delivery system available for clinic application, in particular for myocardial regeneration. The aim of this study was to develop a novel cytokine delivery system that is stable in solution at physiological pH.

Methods

Four groups of self-assembled chitosan oligosaccharide/heparin (CSO/H) nanoparticles were prepared with various volume ratios of chitosan oligosaccharide to heparin (5:2, 5:4, 4:15, 1:5) and characterized by laser diffraction, particle size analysis, and transmission electron microscopy. The encapsulation efficiency and loading content of two cytokines, ie, stromal cell-derived factor (SDF)-1α and vascular endothelial growth factor (VEGF) were quantified using an enzyme-linked immunosorbent assay. The biological activity of the loaded SDF-1α and VEGF was evaluated using the transwell migration assay and MTT assay. The dispersion profiles for the cytokine-loaded nanoparticles were quantified using fluorescence molecular tomography.

Results

CSO/H nanoparticles were prepared successfully in solution with physiological pH. The particle sizes in the four treatment groups were in the range of 96.2–210.5 nm and the zeta potential ranged from −29.4 mV to 24.2 mV. The loading efficiency in the CSO/H nanoparticle groups with the first three ratios was more than 90%. SDF-1α loaded into CSO/H nanoparticles retained its migration activity and VEGF loaded into CSO/H nanoparticles continued to show proliferation activity. The in vivo dispersion test showed that the CSO/H nanoparticles enabled to VEGF to accumulate locally for a longer period of time.

Conclusion

CSO/H nanoparticles have a high cytokine loading capacity and allow cytokines to maintain their bioactivity for longer, are stable in an environment with physiological pH, and may be a promising cytokine delivery system for tissue regeneration.

Layer-by-layer paper-stacking nanofibrous membranes to deliver adipose-derived stem cells for bone regeneration

Bone tissue engineering through seeding of stem cells in three-dimensional scaffolds has greatly improved bone regeneration technology, which historically has been a constant challenge. In this study, we researched the use of adipose-derived stem cell (ADSC)-laden layer-by-layer paper-stacking polycaprolactone/gelatin electrospinning nanofibrous membranes for bone regeneration. Using this novel paper-stacking method makes oxygen distribution, nutrition, and waste transportation work more efficiently. ADSCs can also secrete multiple growth factors required for osteogenesis. After the characterization of ADSC surface markers CD29, CD90, and CD49d using flow cytometry, we seeded ADSCs on the membranes and found cells differentiated, with significant expression of the osteogenic-related proteins osteopontin, osteocalcin, and osteoprotegerin. During 4 weeks in vitro, the ADSCs cultured on the paper-stacking membranes in the osteogenic medium exhibited the highest osteogenic-related gene expressions. In vivo, the paper-stacking scaffolds were implanted into the rat calvarial defects (5 mm diameter, one defect per parietal bone) for 12 weeks. Investigating with microcomputer tomography, the ADSC-laden paper-stacking membranes showed the most significant bone reconstruction, and from a morphological perspective, this group occupied 90% of the surface area of the defect, produced the highest bone regeneration volume, and showed the highest bone mineral density of 823.06 mg/cm(3). From hematoxylin and eosin and Masson staining, the new bone tissue was most evident in the ADSC-laden scaffold group. Using quantitative polymerase chain reaction analysis from collected tissues, we found that the ADSC-laden paper-stacking membrane group presented the highest osteogenic-related gene expressions of osteocalcin, osteopontin, osteoprotegerin, bone sialoprotein, runt-related transcription factor 2, and osterix (two to three times higher than the control group, and 1.5 times higher than the paper-stacking membrane group in all the genes). It is proposed that ADSC-laden layer-by-layer paper-stacking scaffolds could be used as a way of promoting bone defect treatment.

Extracellular matrix-inspired BMP-2-delivering biodegradable fibrous particles for bone tissue engineering

A heparin conjugated fibrous particle resembling the structure of an extracellular matrix was developed. The BMP-2 loaded particles promoted osteogenic differentiation and healing of a bone defect, in vitro and in vivo.

3D tissue-engineered model of Ewing's sarcoma

Despite longstanding reliance upon monolayer culture for studying cancer cells, and numerous advantages from both a practical and experimental standpoint, a growing body of evidence suggests that more complex three-dimensional (3D) models are necessary to properly mimic many of the critical hallmarks associated with the oncogenesis, maintenance and spread of Ewing's sarcoma (ES), the second most common pediatric bone tumor. And as clinicians increasingly turn to biologically-targeted therapies that exert their effects not only on the tumor cells themselves, but also on the surrounding extracellular matrix, it is especially important that preclinical models evolve in parallel to reliably measure antineoplastic effects and possible mechanisms of de novo and acquired drug resistance. Herein, we highlight a number of innovative methods used to fabricate biomimetic ES tumors, encompassing both the surrounding cellular milieu and the extracellular matrix (ECM), and suggest potential applications to advance our understanding of ES biology, preclinical drug testing, and personalized medicine.

In vitro and in vivo studies of BMP-2-loaded PCL-gelatin-BCP electrospun scaffolds

To confirm the effect of recombinant human bone morphogenetic protein-2 (BMP-2) for bone regeneration, BMP-2-loaded polycaprolactone (PCL)-gelatin (Gel)-biphasic calcium phosphate (BCP) fibrous scaffolds were fabricated using the electrospinning method. The electrospinning process to incorporate BCP nanoparticles into the PCL-Gel scaffolds yielded an extracellular matrix-like microstructure that was a hybrid system composed of nano- and micro-sized fibers. BMP-2 was homogeneously loaded on the PCL-Gel-BCP scaffolds for enhanced induction of bone growth. BMP-2 was initially released at high levels, and then showed sustained release behavior for 31 days. Compared with the PCL-Gel-BCP scaffold, the BMP-2-loaded PCL-Gel-BCP scaffold showed improved cell proliferation and cell adhesion behavior. Both scaffold types were implanted in rat skull defects for 4 and 8 weeks to evaluate the biological response under physiological conditions. Remarkable bone regeneration was observed in the BMP-2/PCL-Gel-BCP group. These results suggest that BMP-2-loaded PCL-Gel-BCP scaffolds should be considered for potential bone tissue engineering applications.

Monocyte chemoattractant protein-1 released from polycaprolactone/chitosan hybrid membrane to promote angiogenesis in vivo

We have fabricated a hybrid membrane composed of polycaprolactone and a natural polysaccharide, chitosan. The incorporation of chitosan enabled heparinization of the material via electrostatic interaction between heparin and chitosan. More importantly, since multiple cytokines have exhibited binding affinity towards heparin, heparinization of the polycaprolactone/chitosan compound also facilitated immobilization of monocyte chemoattractant protein-1, which is a well-reported pro-angiogenic chemokine. Results demonstrated that the heparinized polycaprolactone/chitosan membrane with monocyte chemoattractant protein-1 immobilization was able to release monocyte chemoattractant protein-1 in a controlled and sustained manner. Bioactivity of the released monocyte chemoattractant protein-1 was uncompromised as shown by a chemotaxis chamber assay using isolated rat peripheral blood mononuclear cells. Enhanced local angiogenesis was subsequently observed in vivo after subcutaneous implantation of the heparinized polycaprolactone/chitosan membrane with monocyte chemoattractant protein-1-releasing property and the mechanisms underlying the angiogenic role of monocyte chemoattractant protein-1 were also investigated. We propose that the monocyte chemoattractant protein-1-induced local capillary formation is attributable to increased recruitment of macrophages, particularly the alternatively activated M2 macrophages, which have been implicated in wound healing. Moreover, a direct effect of monocyte chemoattractant protein-1 on angiogenesis was also observed, mainly via monocyte chemoattractant protein-1-stimulated vascular endothelial growth factor expression and activity. In summary, we report here a feasible way to fabricate a polycaprolactone/chitosan hybrid material that could be functionalized with angiogenic signalling agents, such as monocyte chemoattractant protein-1. Implantation of this material promoted angiogenesis and may therefore be developed into scaffold or dressing materials in treating local ischemia injuries or cutaneous wound.

Heparinized PLLA/PLCL nanofibrous scaffold for potential engineering of small-diameter blood vessel: tunable elasticity and anticoagulation property

The success of tissue engineered vascular grafts depends greatly on the synthetic tubular scaffold, which can mimic the architecture, mechanical, and anticoagulation properties of native blood vessels. In this study, small-diameter tubular scaffolds were fabricated with different weight ratios of poly(l-lactic acid) (PLLA) and poly(l-lactide-co-ɛ-caprolactone) (PLCL) by means of thermally induced phase separation technique. To improve the anticoagulation property of materials, heparin was covalently linked to the tubular scaffolds by N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide coupling chemistry. The as-prepared PLLA/PLCL scaffolds retained microporous nanofibrous structure as observed in the neat PLLA scaffolds, and their structural and mechanical properties can be fine-tuned by changing the ratio of two components. The scaffold containing 60% PLCL content was found to be the most promising scaffold for engineering small-diameter blood vessel in terms of elastic properties and structural integrity. The heparinized scaffolds showed higher hydrophilicity, lower protein adsorption ability, and better in vitro anticoagulation property than their untreated counterparts. Pig iliac endothelial cells seeded on the heparinized scaffold showed good cellular attachment, spreading, proliferation, and phenotypic maintenance. Furthermore, the heparinized scaffolds exhibited neovascularization after subcutaneous implantation into the New Zealand white rabbits for 1 and 2 months. Taken together, the heparinized PLLA/PLCL nanofibrous scaffolds have the great potential for vascular tissue engineering application.

Post-transcriptional regulation in osteoblasts using localized delivery of miR-29a inhibitor from nanofibers to enhance extracellular matrix deposition

MicroRNAs are important post-transcriptional regulators of skeletal biology, and miRNA-based therapeutics have the potential to aid bone repair. However, efficient tools for delivering miRNA mimics or inhibitors to specific target tissues are limited. Polymeric nanofibers closely mimic natural extracellular matrix (ECM) morphology, and are attractive candidates for supporting delivery of cells and bone-anabolic reagents. It is hypothesized that gelatin nanofibers could be used for the localized transient delivery of miRNA-based therapeutics, using miR-29a inhibitor as a prototype to increase ECM deposition. miR-29 family members are negative regulators of ECM synthesis, targeting the mRNAs of selected collagens and osteonectin/SPARC. Inhibiting miR-29 activity may therefore increase ECM production by cells. miR-29a inhibitor-loaded gelatin nanofibers, prepared by electrospinning, demonstrated continuous release of miRNA inhibitor over 72h. Pre-osteoblastic murine MC3T3-E1 cell line seeded on miR-29a inhibitor-loaded nanofibers synthesized more osteonectin, indicating efficient inhibitor delivery. These cells also displayed increased Igf1 and Tgfb1 mRNA. Moreover, primary bone marrow stromal cells from transgenic pOBCol3.6cyan reporter mice, grown on miR-29a inhibitor scaffolds, displayed increased col3.6 cyan expression as well as collagen production. This study demonstrates that ECM mimicking nanostructured scaffolds, in conjunction with bioactive miRNA-based therapeutics, may serve as a novel platform for developing biologically active localized cell delivery systems.

Sensitive detection of platelet-derived growth factor through surface-enhanced Raman scattering

A surface-enhanced Raman scattering (SERS) assay using two different nanomaterials has been demonstrated for highly sensitive and selective detection of platelet-derived growth factor (PDGF). Gold nanoparticles (Au NPs; 13 nm) are conjugated with aptamer (Apt) and 4-mercaptobenzoic acid (MBA) as the recognition element and reporter, respectively, while Au pearl necklace nanomaterials (Au PNNs) are used for generating reproducible and enhanced SERS signal of 4-MBA. The Apt/MBA-Au NPs bind PDGF through a specific interaction between Apt and PDGF in a fashion of 2:1, leading to concentration of the analyte and removal of the sample matrix. Through electrostatic interaction, the PDGF-Apt/MBA-Au NPs complexes form aggregates with Au PNNs, leading to an enhanced Raman signal of 4-MBA. Au PNNs allow enhancement factors up to 1.3 × 10(7) and relative standard deviations of Raman signals for 4-MBA down to 15% (five measurements). The assay allows detection of PDGF BB down to 0.5 pM, with linearity of the Raman signal of 4-MBA against the concentration of PDGF over 1-50 pM. Having advantages of sensitivity and reproducibility, this assay has been further applied for the determination of the concentration of PDGF in urine samples, showing its great potential for ultrasensitive analysis of target proteins in biological samples.

“Ins” and “Outs” of mesenchymal stem cell osteogenesis in regenerative medicine

Repair and regeneration of bone requires mesenchymal stem cells that by self-renewal, are able to generate a critical mass of cells with the ability to differentiate into osteoblasts that can produce bone protein matrix (osteoid) and enable its mineralization. The number of human mesenchymal stem cells (hMSCs) diminishes with age and ex vivo replication of hMSCs has limited potential. While propagating hMSCs under hypoxic conditions may maintain their ability to self-renew, the strategy of using human telomerase reverse transcriptase (hTERT) to allow for hMSCs to prolong their replicative lifespan is an attractive means of ensuring a critical mass of cells with the potential to differentiate into various mesodermal structural tissues including bone. However, this strategy must be tempered by the oncogenic potential of TERT-transformed cells, or their ability to enhance already established cancers, the unknown differentiating potential of high population doubling hMSCs and the source of hMSCs (e.g., bone marrow, adipose-derived, muscle-derived, umbilical cord blood, etc.) that may provide peculiarities to self-renewal, differentiation, and physiologic function that may differ from non-transformed native cells. Tissue engineering approaches to use hMSCs to repair bone defects utilize the growth of hMSCs on three-dimensional scaffolds that can either be a base on which hMSCs can attach and grow or as a means of sequestering growth factors to assist in the chemoattraction and differentiation of native hMSCs. The use of whole native extracellular matrix (ECM) produced by hMSCs, rather than individual ECM components, appear to be advantageous in not only being utilized as a three-dimensional attachment base but also in appropriate orientation of cells and their differentiation through the growth factors that native ECM harbor or in simulating growth factor motifs. The origin of native ECM, whether from hMSCs from young or old individuals is a critical factor in “rejuvenating” hMSCs from older individuals grown on ECM from younger individuals.