Electrospun Fibrous Scaffolds for Bone and Cartilage Tissue Generation: Recent Progress and Future Developments

A Temperature-Based Easy-Separable (TempEasy) 3D Hydrogel Coculture System

Interactions between different cell types are crucial for their behavior in tissues, but are rarely considered in 3D in vitro cell culture experiments. One reason is that such coculture experiments are sometimes difficult to perform in 3D or require specialized equipment or know-how. Here, a new 3D cell coculture system is introduced, TempEasy, which is readily applied in any cell culture lab. The matrix material is based on polyisocyanide hydrogels, which closely resemble the mechanical characteristics of the natural extracellular matrix. Gels with different gelation temperatures, seeded with different cells, are placed on top of each other to form an indirect coculture. Cooling reverses gelation, allowing cell harvesting from each layer separately, which benefits downstream analysis. To demonstrate the potential of TempEasy , human adipose stem cells (hADSCs) with vaginal epithelial fibroblasts are cocultured. The analysis of a 7-day coculture shows that hADSCs promote cell-cell interaction of fibroblasts, while fibroblasts promote proliferation and differentiation of hADSCs. TempEasy provides a straightforward operational platform for indirect cocultures of cells of different lineages in well-defined microenvironments.

Advances in Field-Assisted 3D Printing of Bio-Inspired Composites: From Bioprototyping to Manufacturing

Biocomposite systems evolve to superior structural strategies in adapting to their living environments, using limited materials to form functionality superior to their inherent properties. The synergy of physical-field and Three-dimensional （3D） printing technologies creates unprecedented opportunities that overcome the limitations of traditional manufacturing methods and enable the precise replication of bio-enhanced structures. Here, an overview of typical structural designs in biocomposite systems, their functions and properties, are provided and the recent advances in bio-inspired composites using mechanical, electrical, magnetic, and ultrasound-field-assisted 3D printing techniques are highlighted. Finally, in order to realize the preparation of bionic functional devices and equipment with more superior functions, here an outlook on the development of field-assisted 3D printing technology from three aspects are provided: Materials, technology, and post-processing.

Enhanced chondrogenic differentiation of bone marrow mesenchymal stem cells on gelatin/glycosaminoglycan electrospun nanofibers with different amount of glycosaminoglycan

Tissue engineering is a new technique to help damaged cartilage treatment using cells and scaffolds. In this study we tried to evaluate electrospun scaffolds composed of gelatin/glycosaminoglycan (G/GAG) blend nanofibers in chondrogenesis of bone marrow-derived mesenchymal stem cells (BMMSCs). Scaffolds were fabricated by electrospinning technique with different concentration of glycosaminoglycan (0%, 5%, 10%, and 15%) in gelatin matrix. BMMSCs were cultured on the scaffolds for chondrogenesis process. MTT assay was done for scaffold's biocompatibility and cells viability evaluation. Alcian blue staining was carried out to determine the release of GAG and reverse transcription polymerase chain reaction (RT-PCR) was done for expression of COL2A1 and also immunocytochemistry assay were used to confirm expression of type II collagen. Scaffold with 15% GAG showed better result for biocompatibility (p =0.02). Scanning electron microscopy (SEM) micrographs showed that MSCs have good attachment to the scaffolds. Alcian blue staining result confirmed that cells produce GAG during differentiation time different from GAG in the scaffolds. Also the results for RT-PCR showed the expression of COL2A1 marker. Immunocytochemistry assay for type II collagen confirm that this protein expressed. Scaffold comprising 15% GAG is better results for chondrogenesis and it can be a good applicant for cartilage tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 38-48, 2019.

Recent Progress of Fabrication of Cell Scaffold by Electrospinning Technique for Articular Cartilage Tissue Engineering

As a versatile nanofiber manufacturing technique, electrospinning has been widely employed for the fabrication of tissue engineering scaffolds. Since the structure of natural extracellular matrices varies substantially in different tissues, there has been growing awareness of the fact that the hierarchical 3D structure of scaffolds may affect intercellular interactions, material transportation, fluid flow, environmental stimulation, and so forth. Physical blending of the synthetic and natural polymers to form composite materials better mimics the composition and mechanical properties of natural tissues. Scaffolds with element gradient, such as growth factor gradient, have demonstrated good potentials to promote heterogeneous cell growth and differentiation. Compared to 2D scaffolds with limited thicknesses, 3D scaffolds have superior cell differentiation and development rate. The objective of this review paper is to review and discuss the recent trends of electrospinning strategies for cartilage tissue engineering, particularly the biomimetic, gradient, and 3D scaffolds, along with future prospects of potential clinical applications.

3-D mineralized silk fibroin/polycaprolactone composite scaffold modified with polyglutamate conjugated with BMP-2 peptide for bone tissue engineering

In the field of bone tissue engineering, an ideal three-dimensional (3-D) scaffold should not only structurally mimic the extracellular matrix (ECM) in large tissues but also mechanically support the bone healing process and provide biochemical cues to induce osteogenesis. In this study, we investigated the feasibility of functionalisation of scaffolds by coupling polyglutamate acid conjugated with BMP-2 peptide onto silk fibroin (SF)/polycaprolactone (PCL) (SF/PCL) blend nanofibers. The morphology, composition, and mineralisation, were confirmed by FE-SEM, XRD, and FT-IR spectroscopy. The FE-SEM images revealed that wet-electrospun nanofibrous scaffolds exhibited inter-connected nano/micro-pores at different levels, and a different morphology was observed on the 3-D SF/PCL scaffold after mineralisation. Furthermore, the binding property and release behaviour of the peptide were investigated on this mineralized structure, and adipose-derived stem cells were seeded on the composite scaffolds to assay their cytocompatibility and osteogenic differentiation capacities. Results suggest that the polyglutamate motif (repetitive glutamate amino acids) exhibited markedly improved binding properties to mineralized nanofibers, and the mineralized 3-D scaffolds with the conjugated with peptide enhances the mRNA expression of osteogenic genes. The sponge-like 3-D nanofibrous scaffold mechanically and biochemically mimics the regenerative process for applications in bone tissue engineering, including the regeneration of calvarial defects.

An ECM-Mimicking, Mesenchymal Stem Cell-Embedded Hybrid Scaffold for Bone Regeneration

While biologically feasible, bone repair is often inadequate, particularly in cases of large defects. The search for effective bone regeneration strategies has led to the emergence of bone tissue engineering (TE) techniques. When integrating electrospinning techniques, scaffolds featuring randomly oriented or aligned fibers, characteristic of the extracellular matrix (ECM), can be fabricated. In parallel, mesenchymal stem cells (MSCs), which are capable of both self-renewing and differentiating into numerous tissue types, have been suggested to be a suitable option for cell-based tissue engineering therapies. This work aimed to create a novel biocompatible hybrid scaffold composed of electrospun polymeric nanofibers combined with osteoconductive ceramics, loaded with human MSCs, to yield a tissue-like construct to promote in vivo bone formation. Characterization of the cell-embedded scaffolds demonstrated their resemblance to bone tissue extracellular matrix, on both micro- and nanoscales and MSC viability and integration within the electrospun nanofibers. Subcutaneous implantation of the cell-embedded scaffolds in the dorsal side of mice led to new bone, muscle, adipose, and connective tissue formation within 8 weeks. This hybrid scaffold may represent a step forward in the pursuit of advanced bone tissue engineering scaffolds.

Substrate-bound CCL21 and ICAM1 combined with soluble IL-6 collectively augment the expansion of antigen-specific murine CD4+ T cells

Immune processes within the complex microenvironment of the lymph node involve multiple intercellular, cell-matrix, and paracrine interactions, resulting in the expansion of antigen-specific T cells. Inspired by the lymph node microenvironment, we aimed to develop an ex vivo "synthetic immune niche" (SIN), which could effectively stimulate the proliferation of antigen-activated CD4⁺ T cells. This engineered SIN consisted of surfaces coated with the chemokine C-C motif ligand 21 (CCL21) and with the intercellular adhesion molecule 1 (ICAM1), coupled with the soluble cytokine interleukin 6 (IL-6) added to the culture medium. When activated by ovalbumin-loaded dendritic cells, OT-II T cells growing on regular uncoated culture plates form nonadherent, dynamic clusters around the dendritic cells. We found that functionalization of the plate surface with CCL21 and ICAM1 and the addition of IL-6 to the medium dramatically increases T-cell proliferation and transforms the culture topology from that of suspended 3-dimensional cell clusters into a firm, substrate-attached monolayer of cells. Our findings demonstrate that the components of this SIN collectively modulate T-cell interactions and augment both the proliferation and survival of T cells in an antigen-specific manner, potentially serving as a powerful approach for expanding immunotherapeutic T cells.

The Good the Bad and the Ugly of Glycosaminoglycans in Tissue Engineering Applications

High sulfation, low cost, and the status of heparin as an already FDA- and EMA- approved product, mean that its inclusion in tissue engineering (TE) strategies is becoming increasingly popular. However, the use of heparin may represent a naïve approach. This is because tissue formation is a highly orchestrated process, involving the temporal expression of numerous growth factors and complex signaling networks. While heparin may enhance the retention and activity of certain growth factors under particular conditions, its binding 'promiscuity' means that it may also inhibit other factors that, for example, play an important role in tissue maintenance and repair. Within this review we focus on articular cartilage, highlighting the complexities and highly regulated processes that are involved in its formation, and the challenges that exist in trying to effectively engineer this tissue. Here we discuss the opportunities that glycosaminoglycans (GAGs) may provide in advancing this important area of regenerative medicine, placing emphasis on the need to move away from the common use of heparin, and instead focus research towards the utility of specific GAG preparations that are able to modulate the activity of growth factors in a more controlled and defined manner, with less off-target effects.

A Bioinspired Ultraporous Nanofiber-Hydrogel Mimic of the Cartilage Extracellular Matrix

A true biomimetic of the cartilage extracellular matrix (ECM) could greatly contribute to our ability to regenerate this tissue in a mechanically demanding, often inflamed environment. Articular cartilage is a composite tissue made of cells and fibrillar proteins embedded in a hydrophilic polymeric meshwork. Here, a polyanionic functionalized alginate is used to mimic the glycosaminoglycan component of the native ECM. To create the fibrillar component, cryoelectrospinning of poly(ε-caprolactone) on a -78 °C mandrel, subsequently treated by O₂ plasma, is used to create a stable, ultraporous and hydrophillic nanofiber network. In this study, cell-laden, fiber-reinforced composite scaffolds thicker than 1.5 mm can be created by infiltrating a chondrocyte/alginate solution into the fiber mesh, which is then physically cross-linked. The fibrillar component significantly reinforces the chondroinductive, but mechanically weak sulfated alginate hydrogels. This allows the production of a glycosaminoglycan- and collagen type II-rich matrix by the chondrocytes as well as survival of the composite in vivo. To further enhance the system, the electrospun component is loaded with dexamethasone, which protected the cells from an IL-1β-mediated inflammatory insult.

A synergistic approach to the design, fabrication and evaluation of 3D printed micro and nano featured scaffolds for vascularized bone tissue repair

3D bioprinting has begun to show great promise in advancing the development of functional tissue/organ replacements. However, to realize the true potential of 3D bioprinted tissues for clinical use requires the fabrication of an interconnected and effective vascular network. Solving this challenge is critical, as human tissue relies on an adequate network of blood vessels to transport oxygen, nutrients, other chemicals, biological factors and waste, in and out of the tissue. Here, we have successfully designed and printed a series of novel 3D bone scaffolds with both bone formation supporting structures and highly interconnected 3D microvascular mimicking channels, for efficient and enhanced osteogenic bone regeneration as well as vascular cell growth. Using a chemical functionalization process, we have conjugated our samples with nano hydroxyapatite (nHA), for the creation of novel micro and nano featured devices for vascularized bone growth. We evaluated our scaffolds with mechanical testing, hydrodynamic measurements and in vitro human mesenchymal stem cell (hMSC) adhesion (4 h), proliferation (1, 3 and 5 d) and osteogenic differentiation (1, 2 and 3 weeks). These tests confirmed bone-like physical properties and vascular-like flow profiles, as well as demonstrated enhanced hMSC adhesion, proliferation and osteogenic differentiation. Additional in vitro experiments with human umbilical vein endothelial cells also demonstrated improved vascular cell growth, migration and organization on micro-nano featured scaffolds.

Cold Atmospheric Plasma Modified Electrospun Scaffolds with Embedded Microspheres for Improved Cartilage Regeneration

Articular cartilage is prone to degeneration and possesses extremely poor self-healing capacity due to inherent low cell density and the absence of a vasculature network. Tissue engineered cartilage scaffolds show promise for cartilage repair. However, there still remains a lack of ideal biomimetic tissue scaffolds which effectively stimulate cartilage regeneration with appropriate functional properties. Therefore, the objective of this study is to develop a novel biomimetic and bioactive electrospun cartilage substitute by integrating cold atmospheric plasma (CAP) treatment with sustained growth factor delivery microspheres. Specifically, CAP was applied to a poly(ε-caprolactone) electrospun scaffold with homogeneously distributed bioactive factors (transforming growth factor-β1 and bovine serum albumin) loaded poly(lactic-co-glycolic) acid microspheres. We have shown that CAP treatment renders electrospun scaffolds more hydrophilic thus facilitating vitronectin adsorption. More importantly, our results demonstrate, for the first time, CAP and microspheres can synergistically enhance stem cell growth as well as improve chondrogenic differentiation of human marrow-derived mesenchymal stem cells (such as increased glycosaminoglycan, type II collagen, and total collagen production). Furthermore, CAP can substantially enhance 3D cell infiltration (over two-fold increase in infiltration depth after 1 day of culture) in the scaffolds. By integrating CAP, sustained bioactive factor loaded microspheres, and electrospinning, we have fabricated a promising bioactive scaffold for cartilage regeneration.

Engineering a biomimetic three-dimensional nanostructured bone model for breast cancer bone metastasis study

Traditional breast cancer (BrCa) bone metastasis models contain many limitations with regards to controllability, reproducibility and flexibility of design. In this study, a novel biomimetic bone microenvironment was created by integrating hydroxyapatite (HA) and native bioactive factors deposited by osteogenic induction of human bone marrow mesenchymal stem cells (MSCs) within a cytocompatible chitosan hydrogel. It was found that a 10% nanocrystalline HA (nHA) chitosan scaffold exhibited the highest BrCa adhesion and proliferation when compared to chitosan scaffolds with 20% nHA, 10% and 20% microcrystalline HA as well as amorphous HA. This 3-D tunable bone scaffold can provide a biologically relevant environment, increase cell-cell and cell-matrix interactions as found in native bone, and retain the behavior of BrCa cells with different metastasis potential (i.e. highly metastatic MDA-MB-231, less metastatic MCF-7 and transfected MDA-MB-231). The co-culture of MSCs and MDA-MB-231 in this bone model illustrated that MSCs have the capacity to upregulate the expression of the well-known metastasis-associated gene metadherin within BrCa cells. In summary, this study illustrates the ability of our 3-D bone model to create a biomimetic environment conducive to recapitulating the behavior of metastatic BrCa cells, making it a promising tool for in vitro BrCa cell bone metastasis study and for the discovery of potential therapeutics.

Three-dimensional printing of nanomaterial scaffolds for complex tissue regeneration

Three-dimensional (3D) printing has recently expanded in popularity, and become the cutting edge of tissue engineering research. A growing emphasis from clinicians on patient-specific care, coupled with an increasing knowledge of cellular and biomaterial interaction, has led researchers to explore new methods that enable the greatest possible control over the arrangement of cells and bioactive nanomaterials in defined scaffold geometries. In this light, the cutting edge technology of 3D printing also enables researchers to more effectively compose multi-material and cell-laden scaffolds with less effort. In this review, we explore the current state of 3D printing with a focus on printing of nanomaterials and their effect on various complex tissue regeneration applications.

Cell encapsulation in a magnetically aligned collagen-GAG copolymer microenvironment

Engineered tissue microenvironments impart specialized cues that drive distinct cellular phenotypes and function. Microenvironments with defined properties, such as mechanical properties and fibril alignment, can elicit specific cellular responses that emulate those observed in vivo. Collagen- and glycosaminoglycan (GAG)-based tissue matrices have been popularized due to their biological ubiquity in a broad range of tissues and the ability to tune structure and mechanical properties through a variety of processes. Here, we investigate the combined effects of static magnetic fields, and GAG and cell encapsulation, on the structure (e.g. collagen fibril orientation) and material properties of collagen matrices. We found that magnetic fields align the collagen-GAG matrix, alter equilibrium mechanical properties and provide a method for encapsulating cells within a three-dimensional aligned matrix. Cells are encapsulated prior to polymerization, allowing for controlled cell density and eliminating the need for cell seeding. Increased relative GAG concentrations reduced the ability to magnetically align collagen fibrils, in part through a mechanism involving increased viscosity and polymerization time of the collagen-GAG solution. This work provides a functional design space for the development of pure collagen and hybrid collagen-GAG matrices in the presence of magnetic fields. Additionally, this work shows that magnetic fields are effective for the fabrication of collagen constructs with controlled fibril orientation, and can be coupled with GAG incorporation to modulate mechanical properties and the response of embedded cells.

Structure and properties of PLLA/β-TCP nanocomposite scaffolds for bone tissue engineering

One of the key components of tissue engineering is a scaffold with suitable morphology, outstanding mechanical properties, and favorable biocompatibility. In this study, β-tricalcium phosphate (β-TCP) nanoparticles were synthesized and incorporated with poly(L-lactic acid) (PLLA) to fabricate nanocomposite scaffolds by the thermally induced phase separation method. The PLLA/β-TCP nanocomposite scaffolds showed a continuous nanofibrous PLLA matrix with strut diameters of 100-750 nm, interconnected micropores with pore diameters in the range of 0.5-10 μm, and high porosity (>92 %). β-TCP nanoparticles were homogeneously dispersed in the PLLA matrix, which significantly improved the compressive modulus and protein adsorption capacity. The prepared nanocomposite scaffolds provided a suitable microenvironment for osteoblast attachment and proliferation, demonstrating the potential of the PLLA/β-TCP nanocomposite scaffolds in bone tissue engineering applications.

Development of novel three-dimensional printed scaffolds for osteochondral regeneration

As modern medicine advances, various methodologies are being explored and developed in order to treat severe osteochondral defects in joints. However, it is still very challenging to cure the osteochondral defects due to their poor inherent regenerative capacity, complex stratified architecture, and disparate biomechanical properties. The objective of this study is to create novel three-dimensional (3D) printed osteochondral scaffolds with both excellent interfacial mechanical properties and biocompatibility for facilitating human bone marrow mesenchymal stem cell (MSC) growth and chondrogenic differentiation. For this purpose, we designed and 3D printed a series of innovative bi-phasic 3D models that mimic the osteochondral region of articulate joints. Our mechanical testing results showed that our bi-phasic scaffolds with key structures have enhanced mechanical characteristics in compression (a maximum Young's modulus of 31 MPa) and shear (a maximum fracture strength of 5768 N/mm(2)) when compared with homogenous designs. These results are also correlated with numerical simulation. In order to improve their biocompatibility, the scaffolds' surfaces were further modified with acetylated collagen (one of the main components in osteochondral extracellular matrix). MSC proliferation results demonstrated that incorporation of a collagen, along with biomimetically designed micro-features, can greatly enhance MSC growth after 5 days in vitro. Two weeks' chondrogenic differentiation results showed that our novel scaffolds (dubbed "key" scaffolds), both with and without surface collagen modification, displayed enhanced chondrogenesis (e.g., 130%, 114%, and 236% increases in glycosaminoglycan, type II collagen deposition, and total protein content on collagen-modified key scaffolds when compared with homogeneous controls).

Engineering of synthetic cellular microenvironments: implications for immunity

In this article, we discuss novel synthetic approaches for studying the interactions of cells with their microenvironment. Notably, critical cellular processes such as growth, differentiation, migration, and fate determination, are tightly regulated by interactions with neighboring cells, and the surrounding extracellular matrix. Given the huge complexity of natural cellular environments, and their rich molecular and physical diversity, the mission of understanding "environmental signaling" at a molecular-mechanistic level appears to be extremely challenging. To meet these challenges, attempts have been made in recent years to design synthetic matrices with defined chemical and physical properties, which, artificial though they may be, could reveal basic "design principles" underlying the physiological processes. Here, we summarize recent developments in the characterization of the chemical and physical properties of cell sensing and adhesion, as well as the design and use of engineered, micro- to nanoscale patterned and confined environments, for systematic, comprehensive modulation of the cells' environment. The power of these biomimetic surfaces to highlight environmental signaling events in cells, and in immune cells in particular, will be discussed.

Design of biomimetic and bioactive cold plasma-modified nanostructured scaffolds for enhanced osteogenic differentiation of bone marrow-derived mesenchymal stem cells

The objective of this study was to design a biomimetic and bioactive tissue-engineered bone construct via a cold atmospheric plasma (CAP) treatment for directed osteogenic differentiation of human bone morrow mesenchymal stem cells (MSCs). Porous nanocrystalline hydroxyapatite/chitosan scaffolds were fabricated via a lyophilization procedure. The nanostructured bone scaffolds were then treated with CAP to create a more favorable surface for cell attachment, proliferation, and differentiation. The CAP-modified scaffolds were characterized via scanning electron microscope, Raman spectrometer, contact angle analyzer, and white light interferometer. In addition, optimal CAP treatment conditions were determined. Our in vitro study shows that MSC adhesion and infiltration were significantly enhanced on CAP modified scaffolds. More importantly, it was demonstrated that CAP-modified nanostructured bone constructs can greatly promote total protein, collagen synthesis, and calcium deposition after 3 weeks of culture, thus making them a promising implantable scaffold for bone regeneration. Moreover, the fibronectin and vitronection adsorption experiments by enzyme-linked immunosorbent assay demonstrated that more adhesion-mediated protein adsorption on the CAP-treated scaffolds. Since the initial specific protein absorption on scaffold surfaces can lead to further recruitment as well as activation of favorable cell functions, it is suggested that our enhanced stem cell growth and osteogenic function may be related to more protein adsorption resulting from surface roughness and wettability modification. The CAP modification method used in this study provides a quick one-step process for cell-favorable tissue-engineered scaffold architecture remodeling and surface property alteration.

Advancements in electrospinning of polymeric nanofibrous scaffolds for tissue engineering

Polymeric nanofibers have potential as tissue engineering scaffolds, as they mimic the nanoscale properties and structural characteristics of native extracellular matrix (ECM). Nanofibers composed of natural and synthetic polymers, biomimetic composites, ceramics, and metals have been fabricated by electrospinning for various tissue engineering applications. The inherent advantages of electrospinning nanofibers include the generation of substrata with high surface area-to-volume ratios, the capacity to precisely control material and mechanical properties, and a tendency for cellular in-growth due to interconnectivity within the pores. Furthermore, the electrospinning process affords the opportunity to engineer scaffolds with micro- to nanoscale topography similar to the natural ECM. This review describes the fundamental aspects of the electrospinning process when applied to spinnable natural and synthetic polymers; particularly, those parameters that influence fiber geometry, morphology, mesh porosity, and scaffold mechanical properties. We describe cellular responses to fiber morphology achieved by varying processing parameters and highlight successful applications of electrospun nanofibrous scaffolds when used to tissue engineer bone, skin, and vascular grafts.

Enhanced human bone marrow mesenchymal stem cell functions in novel 3D cartilage scaffolds with hydrogen treated multi-walled carbon nanotubes

Cartilage tissue is a nanostructured tissue which is notoriously hard to regenerate due to its extremely poor inherent regenerative capacity and complex stratified architecture. Current treatment methods are highly invasive and may have many complications. Thus, the goal of this work is to use nanomaterials and nano/microfabrication methods to create novel biologically inspired tissue engineered cartilage scaffolds to facilitate human bone marrow mesenchymal stem cell (MSC) chondrogenesis. To this end we utilized electrospinning to design and fabricate a series of novel 3D biomimetic nanostructured scaffolds based on hydrogen (H2) treated multi-walled carbon nanotubes (MWCNTs) and biocompatible poly(L-lactic acid) (PLLA) polymers. Specifically, a series of electrospun fibrous PLLA scaffolds with controlled fiber dimension were fabricated in this study. In vitro MSC studies showed that stem cells prefer to attach in the scaffolds with smaller fiber diameter. More importantly, the MWCNT embedded scaffolds showed a drastic increase in mechanical strength and a compressive Young's modulus matching to natural cartilage. Furthermore, our MSC differentiation results demonstrated that incorporation of the H2 treated carbon nanotubes and poly-L-lysine coating can induce more chondrogenic differentiations of MSCs than controls. After two weeks of culture, PLLA scaffolds with H2 treated MWCNTs and poly-L-lysine can achieve the highest glycosaminoglycan synthesis, making them promising for further exploration for cartilage regeneration.

Chitosan for gene delivery and orthopedic tissue engineering applications

Gene therapy involves the introduction of foreign genetic material into cells in order exert a therapeutic effect. The application of gene therapy to the field of orthopaedic tissue engineering is extremely promising as the controlled release of therapeutic proteins such as bone morphogenetic proteins have been shown to stimulate bone repair. However, there are a number of drawbacks associated with viral and synthetic non-viral gene delivery approaches. One natural polymer which has generated interest as a gene delivery vector is chitosan. Chitosan is biodegradable, biocompatible and non-toxic. Much of the appeal of chitosan is due to the presence of primary amine groups in its repeating units which become protonated in acidic conditions. This property makes it a promising candidate for non-viral gene delivery. Chitosan-based vectors have been shown to transfect a number of cell types including human embryonic kidney cells (HEK293) and human cervical cancer cells (HeLa). Aside from its use in gene delivery, chitosan possesses a range of properties that show promise in tissue engineering applications; it is biodegradable, biocompatible, has anti-bacterial activity, and, its cationic nature allows for electrostatic interaction with glycosaminoglycans and other proteoglycans. It can be used to make nano- and microparticles, sponges, gels, membranes and porous scaffolds. Chitosan has also been shown to enhance mineral deposition during osteogenic differentiation of MSCs in vitro. The purpose of this review is to critically discuss the use of chitosan as a gene delivery vector with emphasis on its application in orthopedic tissue engineering.

Enhancing the biological performance of osteoconductive nanocomposite scaffolds through negative voltage electrospinning

Aim: To investigate negative voltage electrospinning of fibrous nanocomposite scaffolds bearing negative electric charges (N-poled), and determine whether and how retained negative charges could influence the biological performance of scaffolds for bone tissue engineering. Materials & methods: Poly(D,L-lactic acid) was used as the polymer matrix and carbonated hydroxyapatite nanospheres were the osteoconductive phase in the electrospun nanocomposite scaffolds. N-poled nanocomposite scaffolds were formed using negative voltage electrospinning, while conventional positive voltage electrospinning produced fibrous nanocomposite scaffolds bearing positive electric charges (P-poled). N-poled and P-poled scaffolds were systematically characterized and their biological performance was investigated through in vitro cell culture experiments. Results & conclusion: N-poled and P-poled scaffolds retained charges for different periods of time after electrospinning. Both types of scaffolds supported cell spreading and promoted filopodia formation. Compared with P-poled scaffolds, N-poled scaffolds enhanced cell proliferation, alkaline phosphatase activity and mineralization. N-poled scaffolds offer distinct advantages for bone tissue engineering.

Application of tissue engineering to the immune system: development of artificial lymph nodes

The goal of tissue engineering and regenerative medicine is to develop synthetic versions of human organs for transplantation, in vitro toxicology testing and to understand basic mechanisms of organ function. A variety of different approaches have been utilized to replicate the microenvironments found in lymph nodes including the use of a variety of different bio-materials, culture systems, and the application of different cell types to replicate stromal networks found in vivo. Although no system engineered so far can fully replicate lymph node function, progress has been made in the development of microenvironments that can promote the initiation of protective immune responses. In this review we will explore the different approaches utilized to recreate lymph node microenvironments and the technical challenges required to recreate a fully functional immune system in vitro.