A single-axis space simulator for testing the OGO altitude control system

Single axis space simulator for OGO attitude control system test

Novel Nanofiber Structures and Advanced Tissue Engineering Applications

Extracellular matrix (ECM) nanofibers such as collagen and elastin make up an important component of natural tissues. These structural components serve to impart mechanical strength and provide locations for cell attachment and biomolecule storage. Cells respond to their structural environment in a wide variety of ways beyond physical support, and it has been demonstrated that this environment directly modulates cell behaviors such as, morphology, differentiation, ECM production, attachment, and migration. ECM nanofibers also play an important role as a template for tissue formation during development, remodeling, and regeneration. Nanofiber based tissue engineering strategies aim to mimic the geometry of the natural fibrous component of the ECM to promote tissue regeneration. Nanofiber based approaches are of special interest in regeneration of aligned tissues such as, nerve, blood vessel, muscle, and connective tissue because they are able to promote aligned morphologies in resident cells. While there are many different nanofiber fabrication methods available, the electrospinning method may be the most promising due its simplicity, versatility and scalability. Many different types of materials can be easily electrospun into nanofibers with a wide variety of morphologies, sizes, and structural arrangements. However, the potential of the electrospinning method in tissue engineering applications is limited by the available assembly techniques. It was our goal to investigate new technologies that allow more precise assembly of electrospun nanofibers into useful complex structures. First, the parallel plate technique for collecting aligned nanofiber arrays was investigated systematically. Results of this study provided valuable insights into the relationships of fiber length to collection rate and collecting plate size, which were used in designing novel loose fiber collection technologies. One of our technologies utilizes parallel mobile tracks to collect and distribute aligned electrospun nanofibers into loose 3D arrays. Advantages of this technology include indefinitely continuous steady state nanofiber collection, and the capability to simultaneously collect nanofibers from an electrospinning jet in one location and assemble them into complex structures at another. In addition, nanofibers are allowed an indefinite amount of time to dry between collection and assembly, thus eliminating complications related to fiber-to-fiber adhesions. This technology demonstrates potential in complex nanofiber structure assembly, and in industrial scale up. Precision assembly, facilitated by the mobile track technology, led to the development of technologies to fabricate composite nanofiber/protein matrix thin films. These composites combined the strengths of each component as a scaffold for regenerating different types of tissues. Precision assembly technologies also facilitated the development of hybrid two components fibrous structures with finely tuned biomimetic microstructures. The mechanical properties of these structures were similar to those of natural tissues. It was demonstrated that the biomimetic mechanical properties of the hybrid materials were derived from precise nanofiber arrangement at the mechanical properties were highly responsive to subtle changes nanofiber arrangement. Nanofibrous structures were evaluated as tissue engineering scaffolds in vitro and in vitro. C2C12 myoblasts seeded on aligned nanofibers scaffolds attached, aligned, and grew to confluence to form thin cell/nanofiber sheets and cell/nanofiber/protein matrix films. Three dimensional skeletal muscle scaffolds were further assembled by stacking these constructs layer-by-layer or by assembling them into 3D bundled structures. Integration of multilayered grafts with natural muscle was evaluated in vivo. Tubular vascular grafts were also fabricated with biomimetic wavy stiff nanofibers and straight elastic fibers. These grafts demonstrated a remarkably similar mechanical profile to natural blood vessels when the microstructure was optimized. In vivo evaluation of vascular grafts was conducted in a rabbit carotid artery replacement model. Our studies indicate that advances in nanofiber assembly allow for the design of tissue engineering scaffolds with improved control over fiber density, placement, and microstructure. These advances offer the potential for the design of better tissue engineering scaffolds for regeneration of many tissues such as skeletal muscle, blood vessels, nerve, tendon, skin, and so on

Fabrication of three dimensional aligned nanofiber array

Disclosed are methods of forming three dimensional arrays of aligned nanofibers in an open, loose structure of any desired depth. The arrays are formed according to an electrospinning process utilizing two parallel conducting plates to align the fibers and rotating tracks to distribute the fibers throughout the array. Arrays can be used as formed, for instance in tissue engineering applications as three dimensional scaffolding constructs. As-formed arrays can be combined with other materials to form a composite 3-D structure. For instance, composite polymeric materials can be electrospun to form composite nanofibers within the array. Multiple polymeric materials can be electrospun at different areas of the array to form a composite array including materially different nanofibers throughout the array. The arrays can be loaded with other fibrous or non-fibrous materials to form a composite array. Arrays can also be rolled to form a uniaxial fiber bundle

Fabrication of Three Dimensional Aligned Nanofiber Array

Disclosed are methods of forming three dimensional arrays of aligned nanofibers in an open, loose structure of any desired depth. The arrays are formed according to an electrospinning process utilizing two parallel conducting plates to align the fibers and rotating tracks to distribute the fibers throughout the array. Arrays can be used as formed, for instance in tissue engineering applications as three dimensional scaffolding constructs. As-formed arrays can be combined with other materials to form a composite 3-D structure. For instance, composite polymeric materials can be electrospun to form composite nanofibers within the array. Multiple polymeric materials can be electrospun at different areas of the array to form a composite array including materially different nanofibers throughout the array. The arrays can be loaded with other fibrous or non-fibrous materials to form a composite array. Arrays can also be rolled to form a uniaxial fiber bundle

Role of Draw Rate and Molecular Weight when Electrospun Nanofibers are Post-Drawn with Residual Solvent

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

Effects of Fiber Density and Strain Rate on the Mechanical Properties of Electrospun Polycaprolactone Nanofiber Mats.

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\u27s 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/

Precisely Assembled Nanofiber Arrays as a Platform to Engineer Aligned Cell Sheets for Biofabrication

A hybrid cell sheet engineering approach was developed using ultra-thin nanofiber arrays to host the formation of composite nanofiber/cell sheets. It was found that confluent aligned cell sheets could grow on uniaxially-aligned and crisscrossed nanofiber arrays with extremely low fiber densities. The porosity of the nanofiber sheets was sufficient to allow aligned linear myotube formation from differentiated myoblasts on both sides of the nanofiber sheets, in spite of single-side cell seeding. The nanofiber content of the composite cell sheets is minimized to reduce the hindrance to cell migration, cell-cell contacts, mass transport, as well as the foreign body response or inflammatory response associated with the biomaterial. Even at extremely low densities, the nanofiber component significantly enhanced the stability and mechanical properties of the composite cell sheets. In addition, the aligned nanofiber arrays imparted excellent handling properties to the composite cell sheets, which allowed easy processing into more complex, thick 3D structures of higher hierarchy. Aligned nanofiber array-based composite cell sheet engineering combines several advantages of material-free cell sheet engineering and polymer scaffold-based cell sheet engineering; and it represents a new direction in aligned cell sheet engineering for a multitude of tissue engineering applications

Synthetic vascular tissue and method of forming same

Disclosed are composite materials that can more closely mimic the mechanical characteristics of natural elastic tissue, such as vascular tissue. Disclosed materials include a combination of elastic nanofibers and non-elastic nanofibers. Also disclosed are a variety of methods for forming the composite materials. Formation methods generally include the utilization of electrospinning methods to form a fibrous composite construct including fibers of different mechanical characteristics

Annealing post-drawn polycaprolactone (PCL) nanofibers optimizes crystallinity and molecular alignment and enhances mechanical properties and drug release profiles

Post-drawn PCL nanofibers can be molecularly tuned to have a variety of mechanical properties and drug release profiles depending on the temperature and time of annealing, which has implications for regenerative medicine and drug delivery applications. Post-drawing polycaprolactone (PCL) nanofibers has previously been demonstrated to drastically increase their mechanical properties. Here the effects of annealing on post-drawn PCL nanofibers are characterized. It is shown that room temperature storage and in vivo temperatures increase crystallinity significantly on the order of weeks, and that high temperature annealing near melt significantly increases crystallinity and molecular orientation on the order of minutes. The kinetics of crystallization were assessed using an anneal and quench approach. High temperature annealing also increased the ultimate tensile strength and toughness of the fibers and changed the release profile of a model drug absorbed in PCL nanofibers from first-order to zero-order kinetics

Protein-Based Fiber Materials in Medicine: A Review

Fibrous materials have garnered much interest in the field of biomedical engineering due to their high surface-area-to-volume ratio, porosity, and tunability. Specifically, in the field of tissue engineering, fiber meshes have been used to create biomimetic nanostructures that allow for cell attachment, migration, and proliferation, to promote tissue regeneration and wound healing, as well as controllable drug delivery. In addition to the properties of conventional, synthetic polymer fibers, fibers made from natural polymers, such as proteins, can exhibit enhanced biocompatibility, bioactivity, and biodegradability. Of these proteins, keratin, collagen, silk, elastin, zein, and soy are some the most common used in fiber fabrication. The specific capabilities of these materials have been shown to vary based on their physical properties, as well as their fabrication method. To date, such fabrication methods include electrospinning, wet/dry jet spinning, dry spinning, centrifugal spinning, solution blowing, self-assembly, phase separation, and drawing. This review serves to provide a basic knowledge of these commonly utilized proteins and methods, as well as the fabricated fibers’ applications in biomedical research