Electrospun nanofiber yarns possess desirable biological properties, making them promising candidates for novel suture materials if they can achieve the mechanical performance required for tissue approximation. Nanofibers mimic the size scale of native extracellular matrix proteins, promoting tissue regeneration, favorable immune modulation, and enhanced extracellular matrix production, thereby facilitating improved healing outcomes. They also support cellular adhesion, proliferation, and differentiation, effects that are further enhanced through fiber alignment. Although electrospun yarns have previously been produced using self-bundling techniques, existing methods lack control over fabrication and post-processing parameters, resulting in limited mechanical performance. This study presents a nanoyarn fabrication method that enables controlled alignment and post-drawing to enhance mechanical properties. Nanoyarns produced using this approach were compared with monofilament counterparts and a commercial absorbable suture to evaluate performance as a novel suture material. The method generated uniform nanoyarns with diameter coefficients of variation of 8-30%, consistent with conventional staple yarns. Mechanical testing demonstrated that post-drawing increased Young's modulus, ultimate tensile strength, and tenacity. Functional testing further showed reduced tissue damage and improved knot stability relative to commercial monofilament sutures. Overall, these findings demonstrate the potential of a parallel-track system to fabricate uniform, aligned, and mechanically suitable nanoyarns for suture applications.

Continuous high‐strength polymer nanofiber yarns can be assembled into textiles suitable for numerous applications that benefit from the high surface‐area‐to‐volume ratio of the component nanofibers. Electrospun nanofibers have been used to make multifiber twisted yarns (MFTYs). Traditionally, electrospun nanoyarns are made using self‐bundling methods or cone spinning. However, these approaches inhibit ordered fiber architecture or postprocessing of filaments prior to yarn fabrication limiting yarn length, uniformity, and mechanical strength. A spinning process utilizing automated parallel track collection is capable of manufacturing MFTYs with microarchitecture control and integration of individual fiber postdrawing prior to yarn assembly. The advantage of this process is the ability to optimize electrospinning parameters, postprocessing parameters, and yarn spinning parameters independently. Polycaprolactone (PCL) fibers are electrospun with various parameters and made into long MFTYs that retain up to 50% of the strength of individual component nanofibers. Mechanical testing shows relationships between spinning parameters and yarn strength. The tenacity of PCL MFTYs exceeds the tenacity of most reported self‐bundled nanofiber yarns by an order of magnitude or more. Thus, the alternative nanoyarn fabrication method presented in this work is able to produce yarns with highly tunable parameters with a significant increase in mechanical strength compared to other electrospun nanoyarns.

Electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers possess desirable mechanical and piezoelectric properties, making them promising candidates for smart textiles if they can be assembled into continuous yarns. This study presents a manufacturing approach that enables the production of electrospun PVDF-HFP nanofiber yarns using an automated parallel track system and an adjustable roll-to-roll collector. Results show that this approach has potential for PVDF yarn manufacturing on a commercial scale. Electrospun yarns have previously been fabricated with self-bundling methods, but current technologies are limited by production limitations such as the lack of tight control over assembly parameters and the absence of a postdrawing process. Postdrawing was applied here to individual fibers before yarn spinning to enhance fiber strength by over two times and yarn strength by 39%. The piezoelectrical performance of yarns was enhanced by up to 45% with postdrawing. Continuous PVDF-HFP yarns with specific strength approaching 50,000 N m/kg and a relative β phase content of 97% are promising candidates for piezoelectric nanofiber-based smart textiles, which can be integrated into various wearable devices and intelligent garments.

Polycaprolactone (PCL) is an inexpensive polymer used in numerous biomedical applications due to its biocompatibility and gradual biodegradation. While PCL scaffolds with diverse topographical features are well characterized, it is challenging to functionalize PCL constructs with bioactive peptides. In this study, a thiol-norbornene click chemistry was used to immobilize thiolated peptides onto PCL surfaces. PCL was mixed with varying amounts of poly(ethylene glycol) (PEG) modified with norbornene (Nor), and the presence of Nor in PCL-Nor blends was confirmed with 1H NMR spectroscopy. These blends reduced PCL film surface roughness and had no effect on nanofiber diameter. Mesenchymal stem cells (MSCs) cultured on PCL-Nor films and nanofibers functionalized with thiolated RGD peptides adhered and adopted morphologies concomitant with the underlying surface topographies. This study shows that PCL-Nor blends can be used to form rigid PCL structures amenable to photopatterning with any thiolated molecule including bioactive peptides, thereby expanding the functionality of PCL-based biomaterials.

Laser zone-drawing is shown to significantly enhance control over nanofiber properties. This study investigates the dynamics of nanofiber laser zone-drawing. It is hypothesized that the equilibrium between heating and cooling guides fiber temperature. The high heating rate of laser irradiation and the high convective cooling rate of nanofibers facilitate fast heating and cooling kinetics. Results showed fiber thinning in the presence of laser irradiation until reaching a steady-state diameter. Final fiber diameter is correlated to laser power independent of initial fiber diameter. The relationship between final fiber diameter and laser power is used to estimate the heat transfer coefficient, which is used to create a computational model of the thermodynamic system. These simulations predict rapid heating and cooling up to 36 000 K min-1 for the lowest fiber diameters tested experimentally. While laser-induced softening of polymer nanofibers is described in detail, the forces driving fiber drawing, particularly under different thermal kinetics, remain unexplored. This research showcases the capabilities of laser zone-drawing in nanofiber manufacturing and facilitates future investigations aimed at enhancing fiber processing by producing highly aligned molecular structures via rapid cooling. This work signifies a pivotal methodological leap, promising transformative nanofiber materials useful across multiple industries including aerospace, electronics, and biomedicine.

Electrospun polycaprolactone nanofibers were enzymatically degraded to evaluate the effect of post-draw processing and tension on the rate of degradation. Electrospun polycaprolactone (PCL) nanofibers were drawn to increasing lengths, then submerged in pseudomonas lipase (PS Lipase) solution for a 7-day period. The degradation process and extent of deterioration were evaluated by changes in mass, tensile strength, percent crystallinity, molecular weight, and macromolecular chain alignment on day 0, 3, and 7. The rate of degradation was dependent on the percent crystallinity of the fiber and the degree of alignment in crystalline and amorphous portions of the fiber. Post-drawn PCL fibers maintained mass and tensile strength over 7 days in PS Lipase, while undrawn fibers, degraded within 1 day. Pretension in fibers before enzymatic incubation was critical to maintain the macromolecular structure and tensile strength over the degradation period. Loss of mass and mechanical strength without molecular weight reduction indicated that degradation occured via surface erosion of the material over time rather than enzyme penetration and bulk degradation. Measurement of crystallinity and chain alignment illustrated the effect of automated track drawing on the progression of crystal growth and chain alignment, as well as the changes in macromolecular structure which occurred during the multi-day degradation period.

The postdrawing process is poorly understood for polymer nanofibers due to the difficulty of manipulating nanofiber structures. Here, an angled track system facilitates postdrawing of individual nanofibers with control of parameters including molecular weight, draw rate, draw ratio, and solvent evaporation time. In this study, the effects of molecular weight, draw rate, and relative residual solvent content on final nanofiber properties are investigated. Molecular weight is first investigated to clarify any influence polymer chain length can have on drawing in facilitating or hindering chain extensibility. Polyacrylonitrile nanofibers with 50 and 150 kDa molecular weights behave similarly with postdrawing resulting in reduced diameters and enhanced mechanics. Since solvent quantity during drawing is a time sensitive component it is meaningful to assess the impact of draw rate on the chemical and structural makeup of postdrawn fibers. Chemical bond vibrations and chain orientation are sensitive to draw rate when polycaprolactone nanofibers are dried for 3 minutes prior to postdrawing, but this dependency to draw rate is not observed when fibers are postdrawn immediately upon collection. These findings demonstrate that the amount of retained solvent at collection is relevant to this postprocessing approach, and highlights the dynamics of solvent evaporation during postdrawing.

A parallel automated track collector is integrated with a rationally designed centrifugal spinning head to collect aligned polyacrylonitrile (PAN) nanofibers. Centrifugal spinning is an extremely promising nanofiber fabrication technology due to high production rates. However, continuous oriented fiber collection and processing presents challenges. Engineering solutions to these two challenges are explored in this study. A 3D-printed head design, optimized through a computational fluid dynamics simulation approach, is utilized to limit unwanted air currents that disturb deposited nanofibers. An automated track collecting device has pulled deposited nanofibers away from the collecting area. This results in a continuous supply of individual aligned nanofibers as opposed to the densely packed nanofiber mesh ring that is deposited on conventional static post collectors. The automated track collector allows for simple integration of the postdraw processing step that is critical to polymer fiber manufacturing for enhancing macromolecular orientation and mechanical properties. Postdrawing has enhanced the mechanical properties of centrifugal spun PAN nanofibers, which have different crystalline properties compared with conventional PAN microfiber. These technological developments address key limitations of centrifugal spinning that can facilitate high production rate commercial fabrication of highly aligned, high-performance polymer nanofibers.

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.

Centrifugal spinning is a fiber spinning method capable of producing fibers in the nanoscale diameter range from a multitude of polymers, including polyacrylonitrile (PAN). With a traditional centrifugal spinner, fiber can be rapidly spun and collected on static collection posts. However, the use of posts inevitably forms a dense fiber “ring” that is incompatible with roll-to-roll manufacturing processes. In this work, factors that influence throughput and scalability of highly aligned centrifugally spun PAN fibers are explored. A custom centrifugal setup is used to vertically translate collected fibers during the spinning process to distribute them over a large surface area. In addition, factors that affect PAN fiber diameter during the spinning process are investigated, including spinneret to collector distance, rotational speed, and humidity. Resulting data demonstrates that these factors can be independently optimized to reliably produce quality PAN fiber in the nanoscale diameter range. Furthermore, the fiber mass collection rate can be increased without affecting sample quality when the vertical translation speed is increased. This work demonstrates the potential scalability of centrifugal spinning to quickly produce large amounts of highly aligned nanofiber in a cheap, efficient, and reliable manner, and also lends the ability to be collected in a roll-to-roll fashion.

The precise mechanical properties of many tissues are highly dependent on both the composition and arrangement of the nanofibrous extracellular matrix. It is well established that collagen nanofibers exhibit a crimped microstructure in several tissues such as blood vessel, tendon, and heart valve. This collagen fiber arrangement results in the classic non-linear ‘J-shaped’ stress strain curve characteristic of these tissues. Synthetic biomimetic fibrous materials with a crimped microstructure similar to natural collagen demonstrate similar mechanical properties to natural tissues. The following work describes a nanofabrication method based on electrospinning used to fabricate two component hybrid electrospun fibrous materials that mimic the microstructure and mechanical properties of vascular tissue. The properties of these samples can be precisely and predictably optimized by modifying fabrication parameters. Tubular grafts with biomimetic microstructure were constructed to demonstrate the potential of this fabrication method in vascular graft replacement applications. It was possible to closely match both the overall geometry and the compliance of specific blood vessels by optimizing graft microstructure.

PCL nanofiber crystallinity is significantly increased in all orientations after annealing.

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.

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.

This study examines the effects of electrospun polycaprolactone (PCL) fiber density and strain rate on nanofiber mat mechanical properties. An automated track collection system was employed to control fiber number per mat and promote uniform individual fiber properties regardless of the duration of collection. Fiber density is correlated to the mechanical properties of the nanofiber mats. Young's modulus was reduced as fiber density increased, from 14,901 MPa for samples electrospun for 30 s (717 fibers +/- 345) to 3,615 MPa for samples electrospun for 40 min (8,310 fibers +/- 1,904). Ultimate tensile strength (UTS) increased with increasing fiber density, where samples electrospun for 30 s resulted in a UTS of 594 MPa while samples electrospun for 40 min demonstrated a UTS of 1,250 MPa. An average toughness of 0.239 GJ/m(3)was seen in the 30 s group, whereas a toughness of 0.515 GJ/m(3)was observed at 40 min. The ultimate tensile strain for samples electrospun for 30 s was observed to be 0.39 and 0.48 for samples electrospun for 40 min. The relationships between UTS, Young's modulus, toughness, and ultimate tensile strain with increasing fiber density are the result of fiber-fiber interactions which leads to network mesh interactions.

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.

This paper reports the molecular organization and mechanical properties of electrospun, post-drawn polyacrylonitrile (PAN) nanofibers. Without post-drawing, the polymer chain was kinked and oriented in hexagonal crystalline structures. Immediate post-drawing in the semi-solid state disrupted the crystal structures and chain kink at maximum draw ratio. Structural re-orientation at maximum draw resulted in a 500% increase in Young's modulus and a 100% increase in ultimate tensile strength. By applying post-drawing to electrospinning it may be possible to obtain PAN fibers and PAN-derived carbon fibers with enhanced mechanical properties compared to available fabrication technologies.

Three-dimensional cell spheroid models can be used to predict the effect of drugs and therapeutics and to model tissue development and regeneration. The utility of these models is enhanced by high throughput 3D spheroid culture technologies allowing researchers to efficiently culture numerous spheroids under varied experimental conditions. Detailed analysis of high throughput spheroid culture is much less efficient and generally limited to narrow outputs, such as metabolic viability. We describe a microarray approach that makes traditional histological embedding/sectioning/staining feasible for large 3D cell spheroid sample sets. Detailed methodology to apply this technology is provided. Analysis of the technique validates the potential for efficient histological analysis of up to 96 spheroids in parallel. By integrating high throughput 3D spheroid culture technologies with advanced immunohistochemical techniques, this approach will allow researchers to efficiently probe expression of multiple biomarkers with spatial localization within 3D structures. Quantitative comparison of staining will have improved inter- and intra-experimental reproducibility as multiple samples are collectively processed, stained, and imaged on a single slide.

This study reports the effects of post-draw processing on the structural and functional properties of electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers. Previous studies have independently demonstrated the potential of the electrospinning process or the post-drawing process to enhance the piezoelectric properties of PVDF nanofiber, and thin film structures respectively. However, post drawing electrospun nanofibers has been difficult to achieve. To overcome this limitation, a parallel automated track device was implemented to post-draw thousands of individual PVDF-HFP electrospun nanofibers per minute. Relationships were established showing that yield strength, Young's modulus, and piezoelectric output were enhanced with increasing draw ratio. The normalized voltage output of PVDF-HFP nanofibers post-drawn to a draw ratio of 3 increased by four-fold compared to undrawn control. We hypothesize that polymer chain and crystal alignment in the direction of the fiber axis, which were increased by post drawing, resulted in enhanced voltage output of PVDF-HFP nanofibers under mechanical stimulation.