Encapsulation of biologics in self-assembled fibers as biostructural units for tissue engineering

Electrospinning and Cell Fibers in Biomedical Applications

Human body tissues such as muscle, blood vessels, tendon/ligaments, and nerves have fiber-like fascicle morphologies, where ordered organization of cells and extracellular matrix (ECM) within the bundles in specific 3D manners orchestrates cells and ECM to provide tissue functions. Through engineering cell fibers (which are fibers containing living cells) as living building blocks with the help of emerging "bottom-up" biomanufacturing technologies, it is now possible to reconstitute/recreate the fiber-like fascicle morphologies and their spatiotemporally specific cell-cell/cell-ECM interactions in vitro, thereby enabling the modeling, therapy, or repair of these fibrous tissues. In this article, a concise review is provided of the "bottom-up" biomanufacturing technologies and materials usable for fabricating cell fibers, with an emphasis on electrospinning that can effectively and efficiently produce thin cell fibers and with properly designed processes, 3D cell-laden structures that mimic those of native fibrous tissues. The importance and applications of cell fibers as models, therapeutic platforms, or analogs/replacements for tissues for areas such as drug testing, cell therapy, and tissue engineering are highlighted. Challenges, in terms of biomimicry of high-order hierarchical structures and complex dynamic cellular microenvironments of native tissues, as well as opportunities for cell fibers in a myriad of biomedical applications, are discussed.

Electrochemical Glue for Binding Chitosan–Alginate Hydrogel Fibers for Cell Culture

Three-dimensional organs and tissues can be constructed using hydrogels as support matrices for cells. For the assembly of these gels, chemical and physical reactions that induce gluing should be induced locally in target areas without causing cell damage. Herein, we present a novel electrochemical strategy for gluing hydrogel fibers. In this strategy, a microelectrode electrochemically generated HClO or Ca2+, and these chemicals were used to crosslink chitosan–alginate fibers fabricated using interfacial polyelectrolyte complexation. Further, human umbilical vein endothelial cells were incorporated into the fibers, and two such fibers were glued together to construct “+”-shaped hydrogels. After gluing, the hydrogels were embedded in Matrigel and cultured for several days. The cells spread and proliferated along the fibers, indicating that the electrochemical glue was not toxic toward the cells. This is the first report on the use of electrochemical glue for the assembly of hydrogel pieces containing cells. Based on our results, the electrochemical gluing method has promising applications in tissue engineering and the development of organs on a chip.

Observations that suggest a contribution of altered dermal papilla mitochondrial function to androgenetic alopecia

Androgenetic alopecia (AGA) is a prevalent hair loss condition in males that develops due to the influence of androgens and genetic predisposition. With the aim of elucidating genes involved in AGA pathogenesis, we modelled AGA with three-dimensional culture of keratinocyte-surrounded dermal papilla (DP) cells. We co-cultured immortalised balding and non-balding human DP cells (DPC) derived from male AGA patients with epidermal keratinocyte (NHEK) using multi-interfacial polyelectrolyte complexation technique. We observed up-regulated mitochondria-related gene expression in balding compared to non-balding DP aggregates which indicated altered mitochondria metabolism. Further observation of significantly reduced electron transport chain complex activity (complex I, IV and V), ATP levels and ability to uptake metabolites for ATP generation demonstrated compromised mitochondria function in balding DPC. Balding DP was also found to be under significantly higher oxidative stress than non-balding DP. Our experiments suggest that application of antioxidants lowers oxidative stress levels and improve metabolite uptake in balding DPC. We postulate that the observed up-regulation of mitochondria-related genes in balding DP aggregates resulted from an over-compensatory effort to rescue decreased mitochondrial function in balding DP through the attempted production of new functional mitochondria. In all, our three-dimensional co-culturing revealed mitochondrial dysfunction in balding DPC, suggesting a metabolic component in the etiology of AGA.

Biofabrication of natural hydrogels for cardiac, neural, and bone Tissue engineering Applications

Natural hydrogels are one of the most promising biomaterials for tissue engineering applications, due to their biocompatibility, biodegradability, and extracellular matrix mimicking ability. To surpass the limitations of conventional fabrication techniques and to recapitulate the complex architecture of native tissue structure, natural hydrogels are being constructed using novel biofabrication strategies, such as textile techniques and three-dimensional bioprinting. These innovative techniques play an enormous role in the development of advanced scaffolds for various tissue engineering applications. The progress, advantages, and shortcomings of the emerging biofabrication techniques are highlighted in this review. Additionally, the novel applications of biofabricated natural hydrogels in cardiac, neural, and bone tissue engineering are discussed as well.

Self-assembly of multiscale anisotropic hydrogels through interfacial polyionic complexation

Polysaccharides are explored for various tissue engineering applications due to their inherent cytocompatibility and ability to form bulk hydrogels. However, bulk hydrogels offer poor control over their microarchitecture and multiscale hierarchy, parameters important to recreate extracellular matrix-mimetic microenvironment. Here, we developed a versatile platform technology to self-assemble oppositely charged polysaccharides into multiscale fibrous hydrogels with controlled anisotropic microarchitecture. We employed polyionic complexation through microfluidic flow of positively charged polysaccharide, chitosan, along with one of the three negatively charged polysaccharides: alginate, gellan gum, and kappa carrageenan. These hydrogels were composed of microscale fibers, which in turn were made of submicron fibrils confirming multiscale hierarchy. Fibrous hydrogels showed strong tensile mechanical properties, which were further modulated by encapsulation of shape-specific antioxidant cerium oxide nanoparticles (CNPs). Specifically, hydrogels with chitosan and gellan gum showed more than eight times higher tensile strength compared to the other two pairs. Incorporation of sphere-shaped cerium oxide nanoparticles in chitosan and gellan gum further reinforced fibrous hydrogels and increased their tensile strength by 40%. Altogether, our automated hydrogel fabrication platform allows fabrication of bioinspired biomaterials with scope for one-step encapsulation of small molecules and nanoparticles without chemical modification or use of chemical crosslinkers.

Microfibers as Physiologically Relevant Platforms for Creation of 3D Cell Cultures

Microfibers have received much attention due to their promise for creating flexible and highly relevant tissue models for use in biomedical applications such as 3D cell culture, tissue modeling, and clinical treatments. A generated tissue or implanted material should mimic the natural microenvironment in terms of structural and mechanical properties as well as cell adhesion, differentiation, and growth rate. Therefore, the mechanical and biological properties of the fibers are of importance. This paper briefly introduces common fiber fabrication approaches, provides examples of polymers used in biomedical applications, and then reviews the methods applied to modify the mechanical and biological properties of fibers fabricated using different approaches for creating a highly controlled microenvironment for cell culturing. It is shown that microfibers are a highly tunable and versatile tool with great promise for creating 3D cell cultures with specific properties.

Electrospun alginate nanofibres impregnated with silver nanoparticles: Preparation, morphology and antibacterial properties

Silver nanoparticles are amongst the most valuable nanoparticles with interesting properties, such as a non-toxic nature and high antibacterial efficiency, making them applicable for tissue scaffold, protective clothing and wound dressing. In this study, silver nanoparticles (AgNPs) have been synthesized using chitosan as reducing and stabilizing agent. The formation of silver nanoparticles was confirmed by UV-vis, and the TEM showed that different shapes were obtained depending on the heating duration. The chitosan/AgNPs was coated onto an electrospun alginate membrane to produce stable polyelectrolyte complex (PEC) nanofibre composites with high antibacterial efficiency. These composites were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). AgNPs were successfully impregnated into the PEC nanofibre composite, while there was complexation between the electrospun alginate and the chitosan/AgNPs composite. PEC demonstrated a good antibacterial activity against both gram negative and gram positive bacteria with acceptable water vapour transmission within the range required for the treatment of injuries or wounds.

Cell-microenvironment interactions and architectures in microvascular systems

In the past decade, significant advances have been made in the design and optimization of novel biomaterials and microfabrication techniques to generate vascularized tissues. Novel microfluidic systems have facilitated the development and optimization of in vitro models for exploring the complex pathophysiological phenomena that occur inside a microvascular environment. To date, most of these models have focused on engineering of increasingly complex systems, rather than analyzing the molecular and cellular mechanisms that drive microvascular network morphogenesis and remodeling. In fact, mutual interactions among endothelial cells (ECs), supporting mural cells and organ-specific cells, as well as between ECs and the extracellular matrix, are key driving forces for vascularization. This review focuses on the integration of materials science, microengineering and vascular biology for the development of in vitro microvascular systems. Various approaches currently being applied to study cell-cell/cell-matrix interactions, as well as biochemical/biophysical cues promoting vascularization and their impact on microvascular network formation, will be identified and discussed. Finally, this review will explore in vitro applications of microvascular systems, in vivo integration of transplanted vascularized tissues, and the important challenges for vascularization and controlling the microcirculatory system within the engineered tissues, especially for microfabrication approaches. It is likely that existing models and more complex models will further our understanding of the key elements of vascular network growth, stabilization and remodeling to translate basic research principles into functional, vascularized tissue constructs for regenerative medicine applications, drug screening and disease models.

Hard tissue regeneration using bone substitutes: an update on innovations in materials

Bone is a unique organ composed of mineralized hard tissue, unlike any other body part. The unique manner in which bone can constantly undergo self-remodeling has created interesting clinical approaches to the healing of damaged bone. Healing of large bone defects is achieved using implant materials that gradually integrate with the body after healing is completed. Such strategies require a multidisciplinary approach by material scientists, biological scientists, and clinicians. Development of materials for bone healing and exploration of the interactions thereof with the body are active research areas. In this review, we explore ongoing developments in the creation of materials for regenerating hard tissues.

Composite pullulan-dextran polysaccharide scaffold with interfacial polyelectrolyte complexation fibers: a platform with enhanced cell interaction and spatial distribution

Hydrogels are highly preferred in soft tissue engineering because they recapitulate the hydrated extracellular matrix. Naturally derived polysaccharides, like pullulan and dextran, are attractive materials with which to form hydrophilic polymeric networks due to their non-immunogenic and non-antigenic properties. However, their inherent hydrophilicity prevents adherent cell growth. In this study, we modified pullulan-dextran scaffolds with interfacial polyelectrolyte complexation (IPC) fibers to improve their ability to support adherent cell growth. We showed that the pullulan-dextran-IPC fiber composite scaffold laden with extracellular matrix protein has improved cell adhesion and proliferation compared to the plain polysaccharide scaffold. We also demonstrated the zero-order release kinetics of the biologics bovine serum albumin and vascular endothelial growth factor (VEGF) incorporated in the composite scaffold. Lastly, we showed that the VEGF released from the composite scaffold retained its capacity to stimulate endothelial cell growth. The incorporation of IPC fibers in the pullulan-dextran hydrogel scaffold improved its functionality and biological activity, thus enhancing its potential in tissue engineering applications.

The synergistic effect of nanotopography and sustained dual release of hydrophobic and hydrophilic neurotrophic factors on human mesenchymal stem cell neuronal lineage commitment

A combination of nanotopography and controlled release is a potential platform for neuronal tissue engineering applications. Previous studies showed that combining both physical and chemical guidance was more effective than individual cues in the directional promotion of neurite outgrowth. Nanotopography can direct human mesenchymal stem cells (hMSCs) into neuronal lineage, while controlled release of neurotrophic factors can deliver temporally controlled biochemical signals. Hypothesizing that the synergistic effect will enhance neuronal lineage commitment of hMSCs, a fabrication method for multiple neurotrophic factors delivery from a single nanopatterned (350 nm gratings), poly-ɛ-caprolactone (PCL) film was developed and evaluated. Our results showed a synergistic effect on hMSC differentiation cultured on substrates with both nanotopographical and biochemical cues. The protein/drug encapsulation into PCL nanopatterned films was first optimized using a hydrophilic model protein, bovine serum albumin. The hydrophobic retinoic acid (RA) molecule was directly incorporated into PCL films. To achieve sustained release, hydrophilic nerve growth factor (NGF) was first encapsulated within polyelectrolyte complexation fibers before they were embedded within the nanopatterned PCL film. Our results showed that nanotopography on the fabricated polymer films remained intact, while release of bioactive RA and NGF was sustained over a period of 3 weeks. Under the combinatorial effect of physical and biochemical cues, we observed an enhanced upregulation of neuronal genes such as microtubule-associated protein 2 (MAP2) and neurofilament light (NFL) as compared with sustained delivery of individual cues and bolus delivery. Quantitative polymerase chain reaction analysis showed that MAP2 and NFL gene upregulation in hMSCs was most pronounced on the nanogratings with sustained release of both RA and NGF. The fabricated platforms supported the sustained delivery of multiple neurotrophins, including both hydrophobic and hydrophilic therapeutic agents, while providing surface patterning versatility for application in neural regeneration and tissue engineering.

Patterned prevascularised tissue constructs by assembly of polyelectrolyte hydrogel fibres

The in vivo efficacy of engineered tissue constructs depends largely on their integration with the host vasculature. Prevascularisation has been noted to facilitate integration of the constructs via anastomosis of preformed microvascular networks. Here we report a technique to fabricate aligned, spatially defined prevascularised tissue constructs with endothelial vessels by assembling individually tailored cell-laden polyelectrolyte hydrogel fibres. Stable, aligned endothelial vessels form in vitro within these constructs in 24 h, and these vessels anastomose with the host circulation in a mouse subcutaneous model. We create vascularised adipose and hepatic tissues by co-patterning the respective cell types with the preformed endothelial vessels. Our study indicates that the formation of aligned endothelial vessels in a hydrogel is an efficient prevascularisation approach in the engineering of tissue constructs.

Engineering cell matrix interactions in assembled polyelectrolyte fiber hydrogels for mesenchymal stem cell chondrogenesis

Cell-cell and cell-matrix interactions are important events in directing stem cell chondrogenesis, which can be promoted in matrix microenvironments presenting appropriate ligands. In this study, interfacial polyelectrolyte complexation (IPC) based hydrogels were employed, wherein the unique formation of submicron size fibers facilitated spatial orientation of ligands within such hydrogels. The influence of aligned, collagen type I (Col I) presentation in IPC hydrogel on chondrogenic differentiation of human mesenchymal stem cells (MSC) was investigated. Early morphological dynamics, onset of N-cadherin/β-catenin mediated chondrogenic induction and differentiation were compared between MSCs encapsulated in IPC-Col I and IPC-control (without Col I) hydrogels, and a conventional Col I hydrogel. MSCs in IPC-Col I hydrogel aligned and packed uniformly, resulting in enhanced cell-cell interactions and cellular condensation, facilitating superior chondrogenesis and the generation of mature hyaline neocartilage, with notable downregulation of fibrocartilaginous marker. Inhibition study using function blocking β1-integrin antibodies reversed the aforementioned outcomes, indicating the importance of coupling integrin mediated cell-matrix interactions and N-cadherin/β-catenin mediated downstream signaling events. This study demonstrated the significance of oriented ligand presentation for MSC chondrogenesis, and the importance of facilitating an orderly sequence of differentiation events, initiated by proximal interactions between MSCs and the extracellular matrix for robust neocartilage formation.

2,5-Dimethoxy 2,5-dihydrofuran crosslinked chitosan fibers enhance bone regeneration in rabbit femur defects

Chitosan fibers were fabricated via pH induced neutralization and precipitation in a 5 w/v% NaOH bath.

Follicular dermal papilla structures by organization of epithelial and mesenchymal cells in interfacial polyelectrolyte complex fibers

The hair follicle is a regenerating organ that produces a new hair shaft during each growth cycle. Development and cycling of the hair follicle is governed by interactions between the epithelial and mesenchymal components. Therefore, development of an engineered 3D hair follicle would be useful for studying these interactions to identify strategies for treatment of hair loss. We have developed a technique suitable for assembly of different cell types in close proximity in fibrous hydrogel scaffolds with resolutions of ∼50 μm. By assembly of dermal papilla (DP) and keratinocytes, structures similar to the native hair bulb arrangement are formed. Gene expression of these constructs showed up-regulation of molecules involved in epithelial-mesenchymal interactions of the hair follicle. Implantation of the follicular structures in SCID mice led to the formation of hair follicle-like structures, thus demonstrating their hair inductive ability. The transparency of the fiber matrix and the small dimensions of the follicular structures allowed the direct quantitation of DP cell proliferation by confocal microscopy, clearly illustrating the promoting or inhibitory effects of hair growth regulating agents. Collectively, our results suggested a promising application of these 3D engineered follicular structures for in vitro screening and testing of drugs for hair growth therapy.

Improvement in nerve regeneration through a decellularized nerve graft by supplementation with bone marrow stromal cells in fibrin

Acellular nerve grafting is often inferior as well as an inadequate alternative to autografting for the repair of long gaps in peripheral nerves. Moreover, the injection method is not perfect. During the injection of cells, the syringe can destroy the acellular nerve structure and the limited accumulation of seed cells. To resolve this problem, we constructed a nerve graft by acellular nerve grafting. Bone marrow-mesenchymal stromal cells (BM-MSCs) were affixed with fibrin glue and injected inside or around the graft, which was then used to repair a 15-mm nerve defect in rats. The acellular nerve graft maintained its structure and composition, and its tensile strength was decreased, as determined by two-photon microscopy and a tensile testing device. In vitro, MSCs embedded in fibrin glue survived and secreted growth factors such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). We repaired 15-mm Sprague-Dawley rat sciatic nerve defects using this nerve graft construction, and MSCs injected around the graft helped improve nerve regeneration and functional recovery of peripheral nerve lesions as determined by functional analysis and histology. Therefore, we conclude that supplying MSCs in fibrin glue around acellular nerves is successful in maintaining the nerve structure and can support nerve regeneration similar to the direct injection of MSCs into the acellular nerve for long nerve defects but may avoid destroying the nerve graft. The technique is simple and is another option for stem cell transplantation.

In vivo bioactivity of rhBMP-2 delivered with novel polyelectrolyte complexation shells assembled on an alginate microbead core template

Electrostatic interactions between polycations and polyanions are being explored to fabricate polyelectrolyte complexes (PEC) that could entrap and regulate the release of a wide range of biomolecules. Here, we report the in vivo application of PEC shells fabricated from three different polycations: poly-l-ornithine (PLO), poly-l-arginine (PLA) and DEAE-dextran (DEAE-D) to condense heparin on the surface of alginate microbeads and further control the delivery of recombinant human bone morphogenetic protein 2 (rhBMP-2) in spinal fusion application. We observed large differences in the behavior of PEC shells fabricated from the cationic polyamino acids (PLO and PLA) when compared to the cationic polysaccharide, DEAE-D. Whereas DEAE-D-based PEC shells eroded and released rhBMP-2 over 2 days in vitro, PLO- and PLA-based shells retained at least 60% of loaded rhBMP-2 after 3 weeks of incubation in phosphate-buffered saline. In vivo implantation in a rat model of posterolateral spinal fusion revealed robust bone formation in the PLO- and PLA-based PEC shell groups. This resulted in a significantly enhanced mechanical stability of the fused segments. However, bone induction and biomechanical stability of spine segments implanted with DEAE-D-based carriers were significantly inferior to both PLO- and PLA-based PEC shell groups (p<0.01). From these results, we conclude that PEC shells incorporating native heparin could be used for growth factor delivery in functional bone tissue engineering application and that PLA- and PLO-based complexes could represent superior options to DEAE-D for loading and in vivo delivery of bioactive BMP-2 in this approach.

Multicomponent fibers by multi-interfacial polyelectrolyte complexation

In multi-interfacial polyelectrolyte complexation (MIPC), fusion of nascent fibers from multiple interfaces brings the interfaces to a point from which a composite fiber is drawn. MIPC applied to two, three, and four polyelectrolyte complex interfaces leads to various patterned multicomponent fibers. Cells encapsulated in these fibers exhibit migration, aggregation and spreading in relation to the initial cell or matrix pattern.

A 3D microfibrous scaffold for long-term human pluripotent stem cell self-renewal under chemically defined conditions

Realizing the potential of human pluripotent stem cell (hPSC)-based therapy requires the development of defined scalable culture systems with efficient expansion, differentiation and isolation protocols. We report an engineered 3D microfiber system that efficiently supports long-term hPSCs self-renewal under chemically defined conditions. The unique feature of this system lies in the application of a 3D ECM-like environment in which cells are embedded, that affords: (i) uniform high cell loading density in individual cell-laden constructs (∼10(7) cells/ml); (ii) quick recovery of encapsulated cells (<10min at 37°C) with excellent preservation of cell viability and 3D multicellular structure; (iii) direct cryopreservation of the encapsulated cells in situ in the microfibers with >17-fold higher cell viability compared to those cultured on Matrigel surface; (iv) long-term hPSC propagation under chemically defined conditions. Four hPSC lines propagated in the microfibrous scaffold for 10 consecutive passages were capable of maintaining an undifferentiated phenotype as demonstrated by the expression of stem cell markers and stable karyotype in vitro and the ability to form derivatives of the three germ layers both in vitro and in vivo. Our 3D microfibrous system has the potential for large-scale cultivation of transplantable hESCs and derivatives for clinical applications.

Modified polyelectrolyte complex fibrous scaffold as a matrix for 3D cell culture

The paradigm of scaffold tissue engineering relies on the provision of an appropriate environment for cell growth, which includes both structural support and the presentation of cellular signals. In terms of biosignal presentation, fibrous scaffolds by interfacial polyelectrolyte complexation (IPC) offer a clear advantage over other scaffold types as IPC scaffolds are formed using an aqueous-based, room-temperature process compatible with the incorporation of biological molecules. This paper establishes two primary methods for the chemical and biochemical modification of these scaffolds: (i) physical entrapment of the bioactive component, and (ii) covalent binding of the bioactive component. For the first method, extracellular matrix (ECM) proteins, collagen, fibronectin and laminin were drawn into the IPC fiber. For the second method, the cell adhesion peptide, RGD, was chemically conjugated to a thiol-active maleimidylated form of the scaffold. Immobilization of the bioactive components was characterized by confocal fluorescence microscopy, scanning electron microscopy (SEM) and BCA protein assay. The ECM proteins were distributed throughout the bulk and surface of the fiber. The ratio of covalently bound to physisorbed RGD was approximately 2:3. The performance of the various scaffolds as a matrix to maintain the differentiated function of primary hepatocytes showed that albumin levels in the supernatant were in the order of RGD-modified scaffold>collagen Type I-modified scaffold>fibronectin- or laminin-modified scaffold>unmodified scaffold>plate, while no clear trend in urea production could be discerned. Thus, IPC scaffolds offered a promising platform for the presentation of signals to cells, in this case, to influence their differentiated function.

Collagen-based fibrous scaffold for spatial organization of encapsulated and seeded human mesenchymal stem cells

Living tissues consist of groups of cells organized in a controlled manner to perform a specific function. Spatial distribution of cells within a three-dimensional matrix is critical for the success of any tissue-engineering construct. Fibers endowed with cell-encapsulation capability would facilitate the achievement of this objective. Here we report the synthesis of a cell-encapsulated fibrous scaffold by interfacial polyelectrolyte complexation (IPC) of methylated collagen and a synthetic terpolymer. The collagen component was well distributed in the fiber, which had a mean ultimate tensile strength of 244.6+/-43.0 MPa. Cultured in proliferating medium, human mesenchymal stem cells (hMSCs) encapsulated in the fibers showed higher proliferation rate than those seeded on the scaffold. Gene expression analysis revealed the maintenance of multipotency for both encapsulated and seeded samples up to 7 days as evidenced by Sox 9, CBFA-1, AFP, PPARgamma2, nestin, GFAP, collagen I, osteopontin and osteonectin genes. Beyond that, seeded hMSCs started to express neuronal-specific genes such as aggrecan and MAP2. The study demonstrates the appeal of IPC for scaffold design in general and the promise of collagen-based hybrid fibers for tissue engineering in particular. It lays the foundation for building fibrous scaffold that permits 3D spatial cellular organization and multi-cellular tissue development.

Scaffolding in tissue engineering: general approaches and tissue-specific considerations

Scaffolds represent important components for tissue engineering. However, researchers often encounter an enormous variety of choices when selecting scaffolds for tissue engineering. This paper aims to review the functions of scaffolds and the major scaffolding approaches as important guidelines for selecting scaffolds and discuss the tissue-specific considerations for scaffolding, using intervertebral disc as an example.

Tissue compatibility of interfacial polyelectrolyte complexation fibrous scaffold: evaluation of blood compatibility and biocompatibility

Interfacial polyelectrolyte complexation (PEC) fiber has been proposed as a biostructural unit and biological construct for tissue engineering applications, with its ability to incorporate proteins, drug molecules, DNA nanoparticles, and cells. In this study, we evaluated the biocompatibility and blood compatibility of PEC fiber in order to assess its potential for in vivo applications in tissue engineering. Although chitosan-alginate PEC fibrous scaffold was found to be thrombogenic, the blood compatibility of the scaffold could be significantly improved by incorporating a small amount of heparin in the polyelectrolyte solution during fiber formation. The platelet microparticle production and platelet adhesion on the chitosan-alginate-heparin fibrous scaffold were comparable to those on the resting control. In vitro cytotoxicity test showed that the scaffold was not toxic to human mesenchymal stem cells (hMSCs). In the in vivo biocompatibility test in rats, no acute inflammation was observed in the subcutaneously or intramuscularly implanted specimens. Good cell infiltration and vascularization were observed after 2 months of implantations. Enhanced extracellular matrix (ECM) deposition was observed when hMSCs were cultured in the transforming growth factor-beta3 (TGF-beta3)-encapsulated PEC fibrous scaffold in vitro, or when the TGF-beta3-encapsulated PEC was implanted intramuscularly in vivo. The results showed that this versatile PEC fibrous scaffold could be used in various tissue engineering applications for its good biocompatible and blood compatible properties.

Proliferation and differentiation of human mesenchymal stem cell encapsulated in polyelectrolyte complexation fibrous scaffold

A biofunctional scaffold was constructed with human mesenchymal stem cells (hMSCs) encapsulated in polyelectrolyte complexation (PEC) fibers. Human MSCs were either encapsulated in PEC fibers and constructed into a fibrous scaffold or seeded on PEC fibrous scaffolds. The proliferation, chondrogenic and osteogenic differentiation of the encapsulated and seeded hMSCs were compared for a culture period of 5.5 weeks. Gene expression and extracellular matrix production showed evidences of chondrogenesis and osteogenesis in the cell-encapsulated scaffolds and cell-seeded scaffolds when the samples were cultured in the chondrogenic and osteogenic differentiation media, respectively. However, better cell proliferation and differentiation were observed on the hMSC-encapsulated scaffolds compared to the hMSC-seeded scaffolds. The study demonstrated that the cell-encapsulated PEC fibers could support proliferation and chondrogenic and osteogenic differentiation of the encapsulated-hMSCs. Together with our previous works, which demonstrated the feasibility of PEC fiber in controlled release of drug, protein and gene delivery, the reported PEC fibrous scaffold system will have the potential in composing a multi-component system for various tissue-engineering applications.

Nonviral gene delivery from nonwoven fibrous scaffolds fabricated by interfacial complexation of polyelectrolytes

We investigated a novel nonwoven fibrous scaffold as a vehicle for delivery of DNA. Fibers were formed by polyelectrolyte complexation of water-soluble chitin and alginate, and PEI-DNA nanoparticles were encapsulated during the fiber drawing process. Nanoparticles released from the fibers over time retained their bioactivity and successfully transfected cells seeded on the scaffold in a sustained manner. Transgene expression in HEK293 cells and human dermal fibroblasts seeded on the transfecting scaffolds was significant even after 2 weeks of culture compared to 3-day expression in two-dimensional controls. Fibroblasts seeded on scaffolds containing DNA encoding basic fibroblast growth factor (bFGF) demonstrated prolonged secretion of bFGF at levels significantly higher than baseline. This work establishes the potential of this fibrous scaffold as a matrix capable of delivering genes to direct and support cellular development in tissue engineering.

Encapsulation of adult human mesenchymal stem cells within collagen-agarose microenvironments

Reliable control over the process of cell differentiation is a major challenge in moving stem cell-based therapies forward. The composition of the extracellular matrix (ECM) is known to play an important role in modulating differentiation. We have developed a system to encapsulate adult human mesenchymal stem cells (hMSC) within spherical three-dimensional (3D) microenvironments consisting of a defined mixture of collagen Type I and agarose polymers. These protein-based beads were produced by emulsification of liquid hMSC-matrix suspensions in a silicone fluid phase and subsequent gelation to form hydrogel beads, which were collected by centrifugation and placed in culture. Bead size and size distribution could be varied by changing the encapsulation parameters (impeller speed and blade separation), and beads in the range of 30-150 microns in diameter were reliably produced. Collagen concentrations up to 40% (wt/wt) could be incorporated into the bead matrix. Visible light and fluorescence microscopy confirmed that the collagen matrix was uniformly distributed throughout the beads. Cell viability post-encapsulation was in the range of 75-90% for all bead formulations (similar to control slab gels) and remained at this level for 8 days in culture. Fluorescent staining of the actin cytoskeleton revealed that hMSC spreading increased with increasing collagen concentration. This system of producing 3D microenvironments of defined matrix composition therefore offers a way to control cell-matrix interactions and thereby guide hMSC differentiation. The bead format allows the use of small amounts of matrix proteins, and such beads can potentially be used as a cell delivery vehicle in tissue repair applications.

Controlled release from fibers of polyelectrolyte complexes

Controlled release systems for delicate compounds, such as proteins, often suffer the drawbacks of decreased bioactivity and low encapsulation efficiency. This study introduces the concept of producing drug-loaded fibers from interfacial polyelectrolyte complexation. Chitosan-alginate fibers were produced by pulling from the interface between two polyelectrolyte solutions at room temperature. Depending on the component properties, the release time of encapsulated components from these fibers can range from hours to weeks. Dexamethasone was completely released within 2 h, whereas charged compounds such as BSA, PDGF-bb, and avidin showed sustained release for 3 weeks. The fibers were able to release PDGF-bb in a steady fashion for over 3 weeks without an initial burst. Furthermore, the bioactivity of PDGF-bb was retained over this period. Release kinetics could be controlled by the inclusion of heparin, which contains specific binding sites for various growth factors. By varying the alginate/heparin ratios in the anionic polyelectrolyte solution, the release of PDGF-bb could be significantly altered. In this study, interfacial polyelectrolyte complexation has been demonstrated to be a promising technique for producing drug-loaded fibers with high encapsulation efficiency, sustained release kinetics, and capacity to retain the bioactivity of the encapsulants.