Water-stable three-dimensional ultrafine fibrous scaffolds from keratin for cartilage tissue engineering

Intrinsically water-stable scaffolds composed of ultrafine keratin fibers oriented randomly and evenly in three dimensions were electrospun for cartilage tissue engineering. Keratin has been recognized as a biomaterial that could substantially support the growth and development of multiple cell lines. Besides, three-dimensional (3D) ultrafine fibrous structures were preferred in tissue engineering due to their structural similarity to native extracellular matrices in soft tissues. Recently, we have developed a nontraditional approach to developing 3D fibrous scaffolds from alcohol-soluble corn protein, zein, and verified their structural advantages in tissue engineering. However, keratin with highly cross-linked molecular structures could not be readily dissolved in common solvents for fiber spinning, which required the remarkable drawability of solution. So far, 3D fibrous scaffolds from pure keratin for biomedical applications have not been reported. In this research, the highly cross-linked keratin from chicken feathers was de-cross-linked and disentangled into linear and aligned molecules with preserved molecular weights, forming highly stretchable spinning dope. The solution was readily electrospun into scaffolds with ultrafine keratin fibers oriented randomly in three dimensions. Due to the highly cross-linked molecular structures, keratin scaffolds showed intrinsic water stability. Adipose-derived mesenchymal stem cells could penetrate much deeper, proliferate, and chondrogenically differentiate remarkably better on the 3D keratin scaffolds than on 2D PLA fibrous scaffolds, 3D soy protein fibrous scaffolds, or 3D commercial nonfibrous scaffolds. In summary, the electrospun 3D ultrafine fibrous scaffolds from keratin could be promising candidates for cartilage tissue engineering.

Fabrication of PLLA/β-TCP nanocomposite scaffolds with hierarchical porosity for bone tissue engineering

Polymer and ceramic composite scaffolds play a crucial role in bone tissue engineering. In an attempt to mimic the architecture of natural extracellular matrix (ECM), poly(l-lactic acid)/β-tricalcium phosphate (PLLA/β-TCP) nanocomposite scaffolds with a hierarchical pore structure were fabricated by combining thermal induced phase separation and salt leaching techniques. The nanocomposite scaffold consisted of a nanofibrous PLLA matrix with a highly interconnected, high porosity (>93%) hierarchical pore structure with pore diameters ranging from 500nm to 300μm and a homogeneously distributed β-TCP nanoparticle phase. The nanofibrous PLLA matrix had a fiber diameter of 70-300nm. The nanocomposite scaffolds possess three levels of hierarchical structure: (1) porosity; (2) nanofibrous PLLA struts comprising the pore walls; and (3) β-TCP nanoparticle phase. The β-TCP nanoparticle phase improved the mechanical properties and bioactivity of the PLLA matrix. The nanocomposite scaffolds supported MG-63 osteoblast proliferation, penetration, and ECM deposition, indicating the potential of PLLA/β-TCP nanocomposite scaffolds with hierarchical porosity for bone tissue engineering applications.

Synthetic biodegradable functional polymers for tissue engineering: a brief review

Scaffolds play a crucial role in tissue engineering. Biodegradable polymers with great processing flexibility are the predominant scaffolding materials. Synthetic biodegradable polymers with well-defined structure and without immunological concerns associated with naturally derived polymers are widely used in tissue engineering. The synthetic biodegradable polymers that are widely used in tissue engineering, including polyesters, polyanhydrides, polyphosphazenes, polyurethane, and poly (glycerol sebacate) are summarized in this article. New developments in conducting polymers, photoresponsive polymers, amino-acid-based polymers, enzymatically degradable polymers, and peptide-activated polymers are also discussed. In addition to chemical functionalization, the scaffold designs that mimic the nano and micro features of the extracellular matrix (ECM) are presented as well, and composite and nanocomposite scaffolds are also reviewed.

Fabrication of nano-fibrous poly(L-lactic acid) scaffold reinforced by surface modified chitosan micro-fiber

To mimic the fibrillar structure of natural extracellular matrix and optimize the chemical composition of the scaffold, a nano-fibrous poly(L-lactic acid) (PLLA) scaffold reinforced by surface modified chitosan micro-fiber (MCTSF) was fabricated using the thermally induced phase separation method. The composite scaffold has a novel structure comprised of a nano-matrix with reinforcing micro-fibers, in which the nano-fibrous PLLA matrix promotes cell adhesion and proliferation, while the MCTSF provides the mechanical support and adjusts the biocompatibility. The morphology of the composite scaffold showed a nano-fibrous PLLA matrix (100-500 nm fiber diameter), an interconnected microporous structure (1.0-8.0 μm pore size), and high porosity (>90%). MCTSF were homogeneously distributed in the composite scaffold and had intimate interactions with PLLA matrix. As a result, the compressive modulus of PLLA/MCTSF (100:40, w/w) increased 4.7-fold compared with that of a pristine PLLA scaffold. The prepared composite scaffold also showed good properties including buffering the acidic degradation of PLLA during in vitro degradation, enhanced protein adsorption capacity, and good cytocompatibility, suggesting that the PLLA/MCTSF composite scaffolds are potential candidate materials in tissue engineering.

Biomimetic electrospun nanofibrous structures for tissue engineering

Biomimetic nanofibrous scaffolds mimicking important features of the native extracellular matrix provide a promising strategy to restore functions or achieve favorable responses for tissue regeneration. This review provides a brief overview of current state-of-the-art research designing and using biomimetic electrospun nanofibers as scaffolds for tissue engineering. It begins with a brief introduction of electrospinning and nanofibers, with a focus on issues related to the biomimetic design aspects. The review next focuses on several typical biomimetic nanofibrous structures (e.g. aligned, aligned to random, spiral, tubular, and sheath membrane) that have great potential for tissue engineering scaffolds, and describes their fabrication, advantages, and applications in tissue engineering. The review concludes with perspectives on challenges and future directions for design, fabrication, and utilization of scaffolds based on electrospun nanofibers.

Novel nanostructured biodegradable polymer matrices fabricated by phase separation techniques for tissue regeneration

Biomimetic nanostructures have a wide range of applications. In particular, biodegradable polymer nanostructures that mimic the subtleties of extracellular matrix may provide favorable cell interactions. In this study, a co-solvent system was developed to configure a thermodynamically metastable biodegradable polymer solution, from which novel nanostructured matrices subsequently formed via wet phase separation (quaternary) or a combination with thermally induced phase separation. Three-dimensional (3D) nanostructured porous matrices were further fabricated by combination with particle-leaching (100-300μm glucose). The new co-solvent system may generate matrices with reproducible nanostructures from a variety of biodegradable polymers such as poly(d,l-lactide) (PLA), poly(ε-caprolactone) (PCL) and PCL-based polyurethane. In vitro cell culture experiments were performed with mouse pre-osteoblasts (MC3T3-E1) and human bone marrow-derived mesenchymal stem cells (hBM-MSC) to evaluate the osteoinductive potential of PLA nanostructures. The results showed that nanofibrous (<100nm) membranes promoted the bone-related marker gene expression and matrix mineralization of MC3T3-E1 at 14days. Nanofibrous 3D matrices seeded with hBM-MSC without osteogenic induction supplements demonstrated a 2.5-fold increase in bone matrix deposition vs. the conventional microporous matrices after 14 and 21days. Antimicrobial nanofibers were further obtained by plasma-assisted coating of chitosan on PLA nanofibers. This study reveals a platform for fabricating novel biodegradable nanofibrous architecture, with potential in tissue regeneration.

Osteochondral tissue engineering: scaffolds, stem cells and applications

Osteochondral tissue engineering has shown an increasing development to provide suitable strategies for the regeneration of damaged cartilage and underlying subchondral bone tissue. For reasons of the limitation in the capacity of articular cartilage to self-repair, it is essential to develop approaches based on suitable scaffolds made of appropriate engineered biomaterials. The combination of biodegradable polymers and bioactive ceramics in a variety of composite structures is promising in this area, whereby the fabrication methods, associated cells and signalling factors determine the success of the strategies. The objective of this review is to present and discuss approaches being proposed in osteochondral tissue engineering, which are focused on the application of various materials forming bilayered composite scaffolds, including polymers and ceramics, discussing the variety of scaffold designs and fabrication methods being developed. Additionally, cell sources and biological protein incorporation methods are discussed, addressing their interaction with scaffolds and highlighting the potential for creating a new generation of bilayered composite scaffolds that can mimic the native interfacial tissue properties, and are able to adapt to the biological environment.

Collagen-templated bioactive titanium dioxide porous networks for drug delivery

A Type I collagen gel was used as a template for fabricating porous titanium dioxide networks. Conducting sol-gel chemistry within the template, followed by a mild solvothermal treatment (selected TiO(2)-collagen hybrids only), and then calcination to remove the template, produced anatase TiO(2) porous networks composed of mesoporous fibers. The collagen morphology was retained. TiO(2) fibers had walls up to 300 nm in thickness and hollow cores where the template was removed. Crystallite size, specific surface area (12.3-110 m(2) g(-1)), mesopore diameter (4.2-8.8 nm), and pore volume of the networks varied under different synthesis conditions; solvothermal treatment of the hybrid doubled the surface area and mesopore diameter of the final material. Biomineralization was studied by immersion in a simulated body fluid. All networks displayed in vitro bioactivity, and hence potential bone-bonding capability, with apatite clusters growing on the fibers. Drug delivery was assessed by the adsorption and release of anti-inflammatory ibuprofen. Ibuprofen was stored both at the fiber surface and in mesopores below 15 nm in diameter, while release was a sustained diffusion process. The network solvothermally treated as a hybrid adsorbed ibuprofen up to 58.9 mg g(-1). The TiO(2) networks compared favorably with literature drug delivery vehicles when ibuprofen loading was normalized against surface area. Therefore, porous TiO(2) networks have potential as materials for biomedical applications.

Fabrication of mesenchymal stem cells-integrated vascular constructs mimicking multiple properties of the native blood vessels

Mesenchymal stem cells (MSCs)-populated small diameter (6 mm) vascular constructs were fabricated. The constructs mimicked the native vessels in multiple levels, i.e. having similar structure and morphology to that of the extracellular matrix in the native blood vessels; recapitulating mechanical properties such as compliance and burst pressure of the native blood vessels; simulating the highly cellularized nature of the native blood vessels; and having an antithrombogenic lumen. The constructs were fabricated by simultaneously assembling poly(ester carbonate urethane) urea nanofibers and MSCs in an electrical field. The nanofibers had a diameter similar to that of the collagen and elastin fibers in the native blood vessels. MSCs were distributed evenly in the constructs. The constructs were highly cellularized when the cell loading density was exceeded 6 million/ml. The vascular constructs were strong and flexible with breaking strains of 144-202%, tensile strengths of 0.80-1.29 MPa, compliances of 13.23-21.96 × 10(-4 )mmHg(-1), stiffness indexes of 7.3-9.8, and burst pressures greater than 1700 mmHg. These mechanical properties were similar to those of the native blood vessels. In vitro platelet deposition experiments showed that platelet adhesion was remarkably decreased in the MSCs-populated constructs compared to that in the construct without MSCs. An increase in MSC density in the constructs further decreased platelet adhesion. When cultured in a spinner flask, MSCs maintained their mitochondria viability and cell number during a two-week culture period, as confirmed by MTT and dsDNA assays. These vascular constructs may hold the potential to regenerate functional small diameter vessels for cardiovascular tissue repair.

Biomimetic nanofibrous scaffolds for bone tissue engineering

Bone tissue engineering is a highly interdisciplinary field that seeks to tackle the most challenging bone-related clinical issues. The major components of bone tissue engineering are the scaffold, cells, and growth factors. This review will focus on the scaffold and recent advancements in developing scaffolds that can mimic the natural extracellular matrix of bone. Specifically, these novel scaffolds mirror the nanofibrous collagen network that comprises the majority of the non-mineral portion of bone matrix. Using two main fabrication techniques, electrospinning and thermally-induced phase separation, and incorporating bone-like minerals, such as hydroxyapatite, composite nanofibrous scaffolds can improve cell adhesion, stem cell differentiation, and tissue formation. This review will cover the two main processing techniques and how they are being applied to fabricate scaffolds for bone tissue engineering. It will then cover how these scaffolds can enhance the osteogenic capabilities of a variety of cell types and survey the ability of the constructs to support the growth of clinically relevant bone tissue.