Search

At present, most carbon fibers are made from non-renewable polyacrylonitrile. Substantial efforts have been made to replace petroleum-based precursors for carbon fiber production. Interestingly, lignin is a carbon fiber precursor material that is cheap, highly available and sustainable. Submicron-scale lignin-based carbon nanofibers are used in numerous areas, such as electronic devices, batteries, supercapacitors and low-cost, high-performance structural composite materials. Trackspinning (TS) technology offers a way to scale up the versatile, but inefficient contact drawing technique to produce small-diameter lignin fibers from environmentally friendly aqueous solutions. In this study, the effects of TS based on probe drawing of low-concentration lignin nanofibers blended with poly(ethylene oxide) and glycerol in sodium hydroxide (NaOH) solution were investigated. The TS lignin fibers were well aligned and reached diameters as small as 500–1000 nm as the drawing length was increased. Lignin fiber macromolecular alignment was isotropic at low levels of draw, and the dichroic ratio increased from 1 to 2.25 with doubling of the drawing length. The most highly drawn trackspun lignin fibers had a mechanical strength of 3.92 MPa and a Young’s modulus of 2.15 GPa, which were similar to reported values for solvent-electrospun lignin nanofibers. These findings support the potential to utilize TS to produce small-diameter lignin fibers using a simple aqueous solvent approach.

Regenerated silk fibroin (SF) fiber is a multifaceted protein matrix suitable for engineering a wide variety of biological materials. Numerous artificial spinning systems have been developed to mimic the molecular structure and hierarchical properties found in native silks. Here, we show a bioinspired technique that can readily form nanofibers and induce both orientation and structure formation of crystalline β-sheet assemblies seen in natural silk. In this study, electrospun postdrawn SF nanofibers were fabricated using an automated track-drawing (TD) approach for the continuous production of highly aligned protein nanofibers. This one-step postdrawing process simulates the dominant pulling force seen in natural spinning. The mechanical performance of the postdrawn SF nanofibers with a draw ratio of 2 (DR2) via TD exhibited a 115% increase in Young's modulus and an 80% increase in ultimate tensile strength, compared with the undrawn SF fibers after water treatment. It was also determined that the intermolecular β-sheet content in DR2 nanofibers increased by 75%. This contribution led to higher glass-transition and degradation temperatures. These biomimetic fibers with structural hierarchy and mechanical properties may be used to build high-performance load-bearing and directionally propagating structures relevant in biomaterial and sustainable material applications.

This manuscript proposes a continuous and straightforward method for fabricating suspended micro- and nanodiameter polymer fibers using an automated single-step drawing system. Termed track spinning, the system is based on a simple manual fiber drawing process that is automated by using two oppositely rotating tracks. Fibers are continuously spun by direct contact of polymer solution coated tracks followed by mechanical drawing as the distance between the tracks increases. The device can draw single or multifilament arrays of micro- and nanofibers from many kinds of polymers and solvent combinations. To demonstrate, fibers were pulled from polymer solutions containing polyvinyl acetate (PVAc) and polyurethane (PU). Fiber morphology was smooth and uniform, and the diameter was sensitive to draw length and polymer solution/melt properties. Polymer nanofibers with diameters as small as 450 nm and length of 255 mm were produced. The track spinning method is able to form fibers from high viscosity solutions and melts that are not compatible with some other nanofiber fabrication methods. Further, the setup is simple and inexpensive to implement and nozzleless and does not require an electric field or high-velocity jets, and the tracks can be widened and patterned/textured to enhance fiber yield and manufacturing precision.

A novel fiber production system established using principles of the dip drawing process is outlined in this paper, known as track spinning (TS). This system can produce micro- and nanofibers from polymer solutions for use in a variety of applications including filtration and biomedical devices. The system features automated tracks operated by a programmable motion controller in combination with stepper motors to consistently produce nanofibers. Utilizing a lignin-based solution, nanofibers of approximately 700–800 nanometers diameter have been successfully achieved and replicated with this device. TS offers wider compatibility with various solutions, in addition to scalability to fit the needs of the application or product. The TS device could open the doors to wide scale, automated nanofiber production.

The study reports a nanomanufacturing method that facilitates post-drawing of electrospun polymer nanofibers. Post-drawing is critical in conventional microfiber processing to enhance mechanical strength, but has been difficult to implement with nanofibers. Here, a parallel automated track collector was designed to permit continuous processing of thousands of individual nanofibers per minute under highly controllable drawing conditions. Post-drawing systematically induced macromolecular alignment and altered the chemical bond composition of polycaprolactone nanofibers with increasing draw ratio. The strength and stiffness of fibers with a draw ratio of 4 were enhanced by 7 and 15 times respectively and their mechanical properties exceeded previously reported values for conventional and nanoscale polycaprolactone structures.

Energy harvested from human body movement can produce continuous, stable energy to portable electronics and implanted medical devices. The energy harvesters need to be light, small, inexpensive, and highly portable. Here we report a novel biocompatible device made of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers on flexible substrates. The nanofibers are prepared with electrospinning followed by a stretching process. This results in aligned nanofibers with diameter control. The assembled device demonstrates high mechanical-to-electrical conversion performance, with stretched PVDF-HFP nanofibers outperforming regular electrospun samples by more than 10 times. Fourier transform infrared spectroscopy (FTIR) reveals that the stretched nanofibers have a higher β phase content, which is the critical polymorph that enables piezoelectricity in polyvinylidene fluoride (PVDF). Polydimethylsiloxane (PDMS) is initially selected as the substrate material for its low cost, high flexibility, and rapid prototyping capability. Bombyx Mori silkworm silk fibroin (SF) and its composites are investigated as promising alternatives due to their high strength, toughness, and biocompatibility. A composite of silk with 20% glycerol demonstrates higher strength and larger ultimate strain than PDMS. With the integration of stretched electrospun PVDF-HFP nanofibers and flexible substrates, this pilot study shows a new pathway for the fabrication of biocompatible, skin-mountable energy devices.

A common method to precisely control the material properties is to evenly distribute functional nanomaterials within the substrate. For example, it is possible to mix a silk solution and nanomaterials together to form one tuned silk sample. However, the nanomaterials are likely to aggregate in the traditional manual mixing processes. Here we report a pilot study of utilizing specific microfluidic mixing designs to achieve a uniform nanomaterial distribution with minimal aggregation. Mixing patterns are created based on classic designs and then validated by experimental results. The devices are fabricated on polydimethylsiloxane (PDMS) using 3D printed molds and soft lithography for rapid replication. The initial mixing performance is validated through the mixing of two solutions with colored dyes. The microfluidic mixer designs are further analyzed by creating silk-based film samples. The cured film is inspected with scanning electron microscopy (SEM) to reveal the distribution uniformity of the dye particles within the silk material matrix. Our preliminary results show that the microfluidic mixing produces uniform distribution of dye particles. Because the microfluidic device can be used as a continuous mixing tool, we believe it will provide a powerful platform for better preparation of silk materials. By using different types of nanomaterials such as graphite (demonstrated in this study), graphene, carbon nanotubes, and magnetic nanoparticles, the resulting silk samples can be fine-tuned with desired electrical, mechanical, and magnetic properties.

Silk proteins are natural biopolymers that have extensive structural possibilities for chemical and mechanical modifications to facilitate novel properties, functions, and applications in the biomedical field. The versatile processability of silk fibroins (SF) into different forms such as gels, films, foams, membranes, scaffolds, and nanofibers makes it appealing in a variety of applications that require mechanically superior, biocompatible, biodegradable, and functionalizable biomaterials. There is no doubt that nature is the world’s best biological engineer, with simple, exquisite but powerful designs that have inspired novel technologies. By understanding the surface interaction of silk materials with living cells, unique characteristics can be implemented through structural modifications, such as controllable wettability, high-strength adhesiveness, and reflectivity properties, suggesting its potential suitability for surgical, optical, and other biomedical applications. All of the interesting features of SF, such as tunable biodegradation, anti-bacterial properties, and mechanical properties combined with potential self-healing modifications, make it ideal for future tissue engineering applications. In this review, we first demonstrate the current understanding of the structures and mechanical properties of SF and the various functionalizations of SF matrices through chemical and physical manipulations. Then the diverse applications of SF architectures and scaffolds for different regenerative medicine will be discussed in detail, including their current applications in bone, eye, nerve, skin, tendon, ligament, and cartilage regeneration.

Gold Nanoparticles (AuNP) were measured by Inductively Coupled Plasma–Mass Spectrometry (ICP-MS), Anodic Stripping Voltammetry (SV), and flame Atomic Absorption Spectrophotometry (AAS). Experiments investigated the relationships between counts per second (ICP-MS), absorbance (AAS), or μA (SV) and Au concentrations in solutions bearing AuNP with sizes of 5, 15, and 50 nm. Similarly the impact of the solution matrix was assessed using deionized water, 1.0 M HNO3, 1.0 M HCl (ICP-MS and AAS), and water containing the bacterium E. coli (∼106 organisms/mL) by all three types of instrumentation. Each instrument yielded linear calibration curves with a signal proportional to Au concentration over the concentration range 0.02 ppm to 1 ppm.The methods were all reliable when biomacromolecules or when organisms such as E.coli existed in the matrix. Comparing the limits of detection for the three methods, ICP-MS and SV were lower than AAS. Comparing cost, SV and AAS were less expensive than ICP-MS. Comparing time requ...

There is a pressing need for long-term, controlled drug release for sustained treatment of chronic or persistent medical conditions and diseases. Guided drug delivery is difficult because therapeutic compounds need to survive numerous transport barriers and binding targets throughout the body. Nanoscale protein-based polymers are increasingly used for drug and vaccine delivery to cross these biological barriers and through blood circulation to their molecular site of action. Protein-based polymers compared to synthetic polymers have the advantages of good biocompatibility, biodegradability, environmental sustainability, cost effectiveness and availability. This review addresses the sources of protein-based polymers, compares the similarity and differences, and highlights characteristic properties and functionality of these protein materials for sustained and controlled drug release. Targeted drug delivery using highly functional multicomponent protein composites to guide active drugs to the site of interest will also be discussed. A systematical elucidation of drug-delivery efficiency in the case of molecular weight, particle size, shape, morphology, and porosity of materials will then be demonstrated to achieve increased drug absorption. Finally, several important biomedical applications of protein-based materials with drug-delivery function-including bone healing, antibiotic release, wound healing, and corneal regeneration, as well as diabetes, neuroinflammation and cancer treatments-are summarized at the end of this review.