Corrugated round fibers to improve cell adhesion and proliferation in tissue engineering scaffolds

Progress and challenges of graphene and its congeners for biomedical applications

Nanomaterials by virtue of their small size and enhanced surface area, present unique physicochemical properties that enjoy widespread applications in bioengineering, biomedicine, biotechnology, disease diagnosis, and therapy. In recent years, graphene and its derivatives have attracted a great deal of attention in various applications, including photovoltaics, electronics, energy storage, catalysis, sensing, and biotechnology owing to their exceptional structural, optical, thermal, mechanical, and electrical. Graphene is a two-dimensional sheet of sp2 hybridized carbon atoms of atomic thickness, which are arranged in a honeycomb crystal lattice structure. Graphene derivatives are graphene oxide (GO) and reduced graphene oxide (rGO), which are highly oxidized and less oxidized forms of graphene, respectively. Another form of graphene is graphene quantum dots (GQDs), having a size of less than 20 nm. Contemporary graphene research focuses on using graphene nanomaterials for biomedical purposes as they have a large surface area for loading biomolecules and medicine and offer the potential for the conjugation of fluorescent dyes or quantum dots for bioimaging. The present review begins with the synthesis, purification, structure, and properties of graphene nanomaterials. Then, we focussed on the biomedical application of graphene nanomaterials with special emphasis on drug delivery, bioimaging, biosensing, tissue engineering, gene delivery, and chemotherapy. The implications of graphene nanomaterials on human health and the environment have also been summarized due to their exposure to their biomedical applications. This review is anticipated to offer useful existing understanding and inspire new concepts to advance secure and effective graphene nanomaterials-based biomedical devices.

Novel electrospun polyurethane scaffolds containing bioactive glass nanoparticles

In the present study, polyurethane (PU) nanocomposite scaffolds containing bioactive glass nanoparticles (BG-NPs) were successfully fabricated through the electrospinning process. The BG-NPs were synthesized through the sol–gel method. PU solutions (10% w/v) containing different weight percentages of the BG-NPs (5, 10 and 15 wt.%) in dimethylformamide/tetrahydrofuran were prepared. To determine both the size of BG-NPs and the diameter of the nanofibers, transmission electron microscopy and scanning electron microscopy were carried out. The surface morphology, mechanical properties, bioactivity and degradation rate of the scaffolds were studied. Fourier transform infrared spectroscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy confirmed the presence of BG within the scaffolds. The tensile strength of nanocomposite scaffolds was in the range 5–8 MPa, which is in good agreement with the tensile strength of cancellous bone tissue. MG63 cells attached to and proliferated well within the scaffolds; therefore, cellular growth was also improved in the nanocomposite scaffolds. Based on the results, the novel PU/BG-NP (10 wt.%) nanocomposite scaffold has a great potential to be applied in cancellous bone tissue engineering.

Engineered scaffolds based on mesenchymal stem cells/preosteoclasts extracellular matrix promote bone regeneration

Recently, extracellular matrix-based tissue-engineered bone is a promising approach to repairing bone defects, and the seed cells are mostly mesenchymal stem cells. However, bone remodelling is a complex biological process, in which osteoclasts perform bone resorption and osteoblasts dominate bone formation. The interaction and coupling of these two kinds of cells is the key to bone repair. Therefore, the extracellular matrix secreted by the mesenchymal stem cells alone cannot mimic a complex bone regeneration microenvironment, and the addition of extracellular matrix by preosteoclasts may contribute as an effective strategy for bone regeneration. Here, we established the mesenchymal stem cell/preosteoclast extracellular matrix -based tissue-engineered bones and demonstrated that engineered-scaffolds based on mesenchymal stem cell/ preosteoclast extracellular matrix significantly enhanced osteogenesis in a 3 mm rat femur defect model compared with mesenchymal stem cell alone. The bioactive proteins released from the mesenchymal stem cell/ preosteoclast extracellular matrix based tissue-engineered bones also promoted the migration, adhesion, and osteogenic differentiation of mesenchymal stem cells in vitro. As for the mechanisms, the iTRAQ-labeled mass spectrometry was performed, and 608 differentially expressed proteins were found, including the IGFBP5 and CXCL12. Through in vitro studies, we proved that CXCL12 and IGFBP5 proteins, mainly released from the preosteoclasts, contributed to mesenchymal stem cells migration and osteogenic differentiation, respectively. Overall, our research, for the first time, introduce pre-osteoclast into the tissue engineering of bone and optimize the strategy of constructing extracellular matrix-based tissue-engineered bone using different cells to simulate the natural bone regeneration environment, which provides new sight for bone tissue engineering.

Solvent-Induced Nanotopographies of Single Microfibers Regulate Cell Mechanotransduction

The extracellular matrix (ECM) is a dynamic three-dimensional (3D) fibrous network, surrounding all cells in vivo. Fiber manufacturing techniques are employed to mimic the ECM but still lack the knowledge and methodology to produce single fibers approximating cell size with different surface topographies to study cell-material interactions. Using solvent-assisted spinning (SAS), the potential to continuously produce single microscale fibers with unlimited length, precise diameter, and specific surface topographies was demonstrated. By applying solvents with different solubilities and volatilities, fibers with smooth, grooved, and porous surface morphologies are produced. Due to their hierarchical structures, the porous fibers are the most hydrophobic, followed by the grooved and the smooth fibers. The fiber diameter is increased by increasing the polymer concentration or decreasing the collector rotational speed. Moreover, SAS offers the advantage to control the interfiber distance and angle to fabricate multilayered 3D constructs. This report shows for the first time that the micro- and nanoscale topographies of single fibers mechanically regulate cell behavior. Fibroblasts, grown on fibers with grooved topographical features, stretch and elongate more compared to smooth and porous fibers, whereas both porous and grooved fibers induce nuclear translocation of yes-associated protein. The presented technique, therefore, provides a unique platform to study the interaction between cells and single ECM-like fibers in a precise and reproducible manner, which is of great importance for new material developments in the field of tissue engineering.

Corrosion behavior and cytocompatibility of a Co–Cr and two Ni–Cr dental alloys before and after the pretreatment with a biological saline solution

Objectives. The aim of this study was to evaluate the corrosion behavior and cytocompatibility of a Co–Cr and two Ni–Cr dental alloys before and after the pretreatment with a biological saline solution.

Salt-responsive polyzwitterionic materials for surface regeneration between switchable fouling and antifouling properties

Development of smart regenerative surface is a highly challenging but important task for many scientific and industrial applications. Specifically, very limited research efforts were made for surface regeneration between bio-adhesion and antifouling properties, because bioadhesion and antifouling are the two highly desirable but completely opposite properties of materials. Herein, we developed salt-responsive polymer brushes of poly(3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium-3-yl) propane-1-sulfonate) (polyVBIPS), which can be switched reversibly and repeatedly between protein capture/release and surface wettability in a controllable manner. PolyVBIPS brush has demonstrated its switching ability to resist both protein adsorption from 100% blood plasma/serum and bacterial attachment in multiple cycles. PolyVBIPS brush also exhibits reversible surface wettability from ∼40° to 25° between in PBS and in 1M NaCl solutions in multiple cycles. Overall, the salt-responsive behaviors of polyVBIPS brushes can be interpreted by the "anti-polyelectrolyte effect", i.e. polyVBIPS brushes adopt a collapsed chain conformation at low ionic strengths to achieve surface adhesive, but an extended chain conformation at high ionic strength to realize antifouling properties. We expect that polyVBIPS will provide a simple, robust, and promising system for the fabrication of smart surfaces with biocompatible, reliable, and regenerative properties.

STATEMENT OF SIGNIFICANCE

Unlike many materials with "one-time switching" capability for surface regeneration, we developed a new regenerative surface of zwitterionic polymer brush, which exhibits a reversible salt-induced switching property between a biomolecule-adhesive state and a biomolecule repellent state in complex media for multiple cycles. PolyVBIPS is easily synthesized and can be straightforward coated on the surface, which provides a simple, robust, and promising system for the fabrication of smart surfaces with biocompatible, reliable, regenerative properties.

Providing the right cues in nerve guidance conduits: Biofunctionalization versus fiber profile to facilitate oriented neuronal outgrowth

Following peripheral nerve injury, rapid and spatially oriented axonal outgrowth from the proximal nerve stump is required for successful tissue regeneration. Regenerative strategies such as introducing fiber bundles into the nerve guidance conduits improve the directional growth of neurons and Schwann cells. Recently, it has been proposed that fiber profiling increases cell alignment and could accelerate neuronal growth. Here, we evaluate the impact of fiber profiling on the extent of neurite outgrowth in vitro as compared to non-profiled round fibers. We developed novel profiled trilobal poly(lactic acid) (PLA) fibers and systematically tested their potency to support nerve regeneration in vitro. The profiled fibers did not improve neurite outgrowth as compared to the round fibers. Instead, we show that growing neurites are merely guided by the type and quantity of proteins adsorbed on the polymer surface. Together this data has significant implications for in vivo experiments focusing on directional regrowth of severed axons across lesion sites during peripheral nerve regeneration.

Chitosan-collagen porous scaffold and bone marrow mesenchymal stem cell transplantation for ischemic stroke

In this study, we successfully constructed a composite of bone marrow mesenchymal stem cells and a chitosan-collagen scaffold in vitro, transplanted either the composite or bone marrow mesenchymal stem cells alone into the ischemic area in animal models, and compared their effects. At 14 days after co-transplantation of bone marrow mesenchymal stem cells and the hitosan-collagen scaffold, neurological function recovered noticeably. Vascular endothelial growth factor expression and nestin-labeled neural precursor cells were detected in the ischemic area, surrounding tissue, hippocampal dentate gyrus and subventricular zone. Simultaneously, a high level of expression of glial fibrillary acidic protein and a low level of expression of neuron-specific enolase were visible in BrdU-labeled bone marrow mesenchymal stem cells. These findings suggest that transplantation of a composite of bone marrow mesenchymal stem cells and a chitosan-collagen scaffold has a neuroprotective effect following ischemic stroke.

Combined additive manufacturing approaches in tissue engineering

Advances introduced by additive manufacturing (AM) have significantly improved the control over the microarchitecture of scaffolds for tissue engineering. This has led to the flourishing of research works addressing the optimization of AM scaffolds microarchitecture to optimally trade-off between conflicting requirements (e.g. mechanical stiffness and porosity level). A fascinating trend concerns the integration of AM with other scaffold fabrication methods (i.e. "combined" AM), leading to hybrid architectures with complementary structural features. Although this innovative approach is still at its beginning, significant results have been achieved in terms of improved biological response to the scaffold, especially targeting the regeneration of complex tissues. This review paper reports the state of the art in the field of combined AM, posing the accent on recent trends, challenges, and future perspectives.

The Effect of Electrospun Gelatin Fibers Alignment on Schwann Cell and Axon Behavior and Organization in the Perspective of Artificial Nerve Design

Electrospun fibrous substrates mimicking extracellular matrices can be prepared by electrospinning, yielding aligned fibrous matrices as internal fillers to manufacture artificial nerves. Gelatin aligned nano-fibers were prepared by electrospinning after tuning the collector rotation speed. The effect of alignment on cell adhesion and proliferation was tested in vitro using primary cultures, the Schwann cell line, RT4-D6P2T, and the sensory neuron-like cell line, 50B11. Cell adhesion and proliferation were assessed by quantifying at several time-points. Aligned nano-fibers reduced adhesion and proliferation rate compared with random fibers. Schwann cell morphology and organization were investigated by immunostaining of the cytoskeleton. Cells were elongated with their longitudinal body parallel to the aligned fibers. B5011 neuron-like cells were aligned and had parallel axon growth when cultured on the aligned gelatin fibers. The data show that the alignment of electrospun gelatin fibers can modulate Schwann cells and axon organization in vitro, suggesting that this substrate shows promise as an internal filler for the design of artificial nerves for peripheral nerve reconstruction.

Wound healing in urology

Wound healing is a dynamic and complex phenomenon of replacing devitalized tissues in the body. Urethral healing takes place in four phases namely inflammation, proliferation, maturation and remodelling, similar to dermal healing. However, the duration of each phase of wound healing in urology is extended for a longer period when compared to that of dermatology. An ideal wound dressing material removes exudate, creates a moist environment, offers protection from foreign substances and promotes tissue regeneration. A single wound dressing material shall not be sufficient to treat all kinds of wounds as each wound is distinct. This review includes the recent attempts to explore the hidden potential of growth factors, stem cells, siRNA, miRNA and drugs for promoting wound healing in urology. The review also discusses the different technologies used in hospitals to treat wounds in urology, which make use of innovative biomaterials synthesised in regenerative medicines like hydrogels, hydrocolloids, foams, films etc., incorporated with growth factors, drug molecules or nanoparticles. These include surgical zippers, laser tissue welding, negative pressure wound therapy, and hyperbaric oxygen treatment.

Biomaterials-based nanofiber scaffold: targeted and controlled carrier for cell and drug delivery

Nanofiber scaffold formulations (diameter less than 1000 nm) were successfully used to deliver the drug/cell/gene into the body organs through different routes for an effective treatment of various diseases. Various fabrication methods like drawing, template synthesis, fiber-mesh, phase separation, fiber-bonding, self-assembly, melt-blown, and electrospinning are successfully used for fabrication of nanofibers. These formulations are widely used in various fields such as tissue engineering, drug delivery, cosmetics, as filter media, protective clothing, wound dressing, homeostatic, sensor devices, etc. The present review gives a detailed account on the need of the nanofiber scaffold formulation development along with the biomaterials and techniques implemented for fabrication of the same against innumerable diseases. At present, there is a huge extent of research being performed worldwide on all aspects of biomolecules delivery. The unique characteristics of nanofibers such as higher loading efficiency, superior mechanical performance (stiffness and tensile strength), controlled release behavior, and excellent stability helps in the delivery of plasmid DNA, large protein drugs, genetic materials, and autologous stem-cell to the target site in the future.

Bone tissue engineering scaffolding: computer-aided scaffolding techniques

Tissue engineering is essentially a technique for imitating nature. Natural tissues consist of three components: cells, signalling systems (e.g. growth factors) and extracellular matrix (ECM). The ECM forms a scaffold for its cells. Hence, the engineered tissue construct is an artificial scaffold populated with living cells and signalling molecules. A huge effort has been invested in bone tissue engineering, in which a highly porous scaffold plays a critical role in guiding bone and vascular tissue growth and regeneration in three dimensions. In the last two decades, numerous scaffolding techniques have been developed to fabricate highly interconnective, porous scaffolds for bone tissue engineering applications. This review provides an update on the progress of foaming technology of biomaterials, with a special attention being focused on computer-aided manufacturing (Andrade et al. 2002) techniques. This article starts with a brief introduction of tissue engineering (Bone tissue engineering and scaffolds) and scaffolding materials (Biomaterials used in bone tissue engineering). After a brief reviews on conventional scaffolding techniques (Conventional scaffolding techniques), a number of CAM techniques are reviewed in great detail. For each technique, the structure and mechanical integrity of fabricated scaffolds are discussed in detail. Finally, the advantaged and disadvantage of these techniques are compared (Comparison of scaffolding techniques) and summarised (Summary).

A Method for Scale-Up of Grooved Nanofibers via Flat Off-Centered Core-Shell Structure Spinneret

An approach to the scale-up of grooved nanofibers via a flat off-centered core-shell structure spinneret has been developed in this study. The spinneret with a flat surface involves shell-holes and off-centered core-needles. The position of the core-needle in the hole and the electrospinning process do influence the formation and structure of the grooved nanofibers. The production rate of the core-shell nanofibers can be enhanced by increasing the hole and needle number of the spinneret. This novel design is expected to provide a promising method towards the massive production of grooved nanofibers.