Electrospinning of linear and highly branched segmented poly(urethane urea)s

Nanofibers Produced by Electrospinning of Ultrarigid Polymer Rods Made from Designed Peptide Bundlemers

Mimicking the hierarchical assembly of natural fiber materials is an important design challenge in the manufacturing of nanostructured materials with biomolecules such as peptides. Here, we produce nanofibers with control of structure over multiple length scales, ranging from peptide molecule assembly into supramolecular building blocks called "bundlemers," to rigid-rod formation through a covalent connection of bundlemer building blocks, and, ultimately, to uniaxially oriented fibers made with the rigid-rod polymers. The peptides are designed to physically assemble into coiled-coil bundles, or bundlemers, and to covalently interact in an end-to-end fashion to produce the rigid-rod polymer. The resultant rodlike polymer exhibits a rigid, cylindrical nanostructure confirmed by transmission electron microscopy (TEM) and, correspondingly, exhibits shear-thinning behavior at low shear rates observed in many nanoscopic rod systems. The rigid-rod chains are further organized into final fiber materials via electrospinning processing, all the while preserving their unique rodlike structural characteristics. Morphological and structural investigations of the nanofibers through scanning electron microscopy, transmission electron microscopy, and X-ray scattering, as well as molecular characterization via Fourier transform infrared (FTIR) and Raman spectroscopy, show that continuous nanofibers are composed of oriented rigid-rod chains constituted by α-helical peptides within bundle building blocks. Mechanical properties of electrospun fibers are also presented. The ability to produce nanofibers from the oriented rigid-rod polymer reveals bundlemer chains as a viable tool for the development of new fiber materials with targeted structure and properties.

Guide to electrospinning denatured whole chain collagen from hoki fish using benign solvents

Tissue engineering requires the design and manufacture of biomimetic scaffolds. Collagen-derived nanofibrous scaffolds have been intensively studied because collagen, in the form of fibrils, is one of the main components of the extra cellular matrix (ECM). Several collagen materials have been used in electrospinning studies including mammalian extracted Type I collagen and gelatin formulations. Denatured whole chain collagen (DWCC) can be prepared by heat denaturing acid-soluble collagen extracted from cold-water fish skin. This product provides a consistent source of collagen with a controlled molecular weight profile and intact alpha chains including telopeptides. In this work, we studied DWCC-water-acid systems in order to determine the effect of solution composition on nanofibre morphology. Whereas measurement of the classical physical properties of concentrated solutions failed to predict and only partially explained the electrospinning behavior of collagen derived polymers, hydrodynamic properties provided insight. All the samples are presented in ternary diagrams to map the electrospinnability of the systems. These "electrospinning maps" provide an informative resource to electrospinning collagen-derived product for biomedical or commercial applications and a practical alternative to complicated models developed for synthetic polymers.

Biocompatible, degradable thermoplastic polyurethane based on polycaprolactone-block-polytetrahydrofuran-block-polycaprolactone copolymers for soft tissue engineering

Biodegradable synthetic polymers have been widely used as tissue engineering scaffold materials. Even though they have shown excellent biocompatibility, they have failed to resemble the low stiffness and high elasticity of soft tissues because of the presence of massive rigid ester bonds. Herein, we synthesized a new thermoplastic polyurethane elastomer (CTC-PU(BET)) using poly ester ether triblock copolymer (polycaprolactone-block-polytetrahydrofuran-block-polycaprolactone triblock copolymer, PCTC) as the soft segment, aliphatic diisocyanate (hexamethylene diisocyanate, HDI) as the hard segment, and degradable diol (bis(2-hydroxyethyl) terephthalate, BET) as the chain extender. PCTC inhibited crystallization and reduced the melting temperature of CTC-PU(BET), and BET dramatically enhanced the thermal decomposition and hydrolytic degradation rate when compared with conventional polyester-based biodegradable TPUs. The CTC-PU(BET) synthesized in this study possessed a low tensile modulus and tensile strength of 2.2 MPa and 1.3 MPa, respectively, and an elongation-at-break over 700%. Meanwhile, it maintained a 95.3% recovery rate and 90% resilience over ten cycles of loading and unloading. In addition, the TPU could be electrospun into both random and aligned fibrous scaffolds consisting of major microfibers and nanobranches. 3T3 fibroblast cell culture confirmed that these scaffolds outperformed the conventional biodegradable TPU scaffolds in terms of substrate-cellular interactions and cell proliferation. Considering the advantages of this TPU, such as ease of synthesis, low cost, low stiffness, high elasticity, controllable degradation rate, ease of processability, and excellent biocompatibility, it has great prospects to be used as a tissue engineering scaffold material for soft tissue regeneration.

Poly(triphenyl ethene) and poly(tetraphenyl ethene): synthesis, aggregation-induced emission property and application as paper sensors for effective nitro-compounds detection

This paper reports two structurally unique aggregation-induced emission (AIE) polymers that are fully constructed by AIE luminogen tetraphenyl or triphenyl ethene units. Their applications as paper sensors are studied.

Tailored star poly (ε-caprolactone) wet-spun scaffolds for in vivo regeneration of long bone critical size defects

One of the most challenging requirements of a successful bone tissue engineering approach is the development of scaffolds specifically tailored to individual tissue defects. Besides materials chemistry, well-defined scaffold’s structural features at the micro- and macro-levels are needed for optimal bone in-growth. In this study, polymeric fibrous scaffolds with a controlled internal network of pores and modelled on the anatomical shape and dimensions of a critical size bone defect in a rabbit’s radius model were developed by employing a computer-aided wet-spinning technique. The tailored scaffolds made of star poly(ε-caprolactone) or star poly(ε-caprolactone)–hydroxyapatite composite material were implanted into 20-mm segmental defects created in radial diaphysis of New Zealand white rabbits. Bone regeneration and tissue response were assessed by X-rays and histological analysis at 4, 8 and 12 weeks after surgery. No signs of macroscopic and microscopic inflammatory reactions were detected, and the developed scaffolds showed a good ability to support and promote the bone regeneration process. However, no significant differences in osteoconductivity were observed between star poly(ε-caprolactone) and star poly(ε-caprolactone)–hydroxyapatite scaffolds. Long-term study on implanted star poly(ε-caprolactone) scaffolds confirmed the presence of signs of bone regeneration and remodelling, particularly evident at 24 weeks.

Electrospun aggregation-induced emission active POSS-based porous copolymer films for detection of explosives

Electrospun AIE-active POSS-based copolymer films exhibit an approximately 9-fold increase in response to explosive vapors compared to dense films.

Fibrous star poly(ε-caprolactone) melt-electrospun scaffolds for wound healing applications

Polymeric fibrous scaffolds based on the biocompatible and biodegradable three-arm-branched star poly(ε-caprolactone) (Mw = 189,000 g/mol) were prepared by a melt electrospinning technique. The possibility of processing polymers without the use of organic solvents is one of the main advantages over solution electrospinning. Scaffolds were biologically tested for their ability of supporting skin tissue regeneration. For this purpose, mouse embryo fibroblast (BALB/3T3 clone A31) and human keratinocyte (HaCaT) cell lines were selected as models, and seeded onto the polymeric supports both as single and co-culture. Cell viability, proliferation, and collagen production were assessed by WST-1 assay and Direct Red 80 dye, respectively. Cell morphology and colonization of the supports were evaluated by scanning electron microscopy and confocal laser scanning microscopy. Results highlighted that the star poly(ε-caprolactone) scaffolds were able to promote collagen production by fibroblasts. In co-culture studies, scaffolds supported adhesion, proliferation, and spatial organization of both cell lines. By virtue of the observed results, the developed polymeric scaffolds appeared suitable as biodegradable and biocompatible three-dimensional supports for skin tissue regeneration in wound healing dressing.

Electrospinning and crosslinking of low-molecular-weight poly(trimethylene carbonate-co-(L)-lactide) as an elastomeric scaffold for vascular engineering

The growth of suitable tissue to replace natural blood vessels requires a degradable scaffold material that is processable into porous structures with appropriate mechanical and cell growth properties. This study investigates the fabrication of degradable, crosslinkable prepolymers of l-lactide-co-trimethylene carbonate into porous scaffolds by electrospinning. After crosslinking by γ-radiation, dimensionally stable scaffolds were obtained with up to 56% trimethylene carbonate incorporation. The fibrous mats showed Young's moduli closely matching human arteries (0.4-0.8MPa). Repeated cyclic extension yielded negligible change in mechanical properties, demonstrating the potential for use under dynamic physiological conditions. The scaffolds remained elastic and resilient at 30% strain after 84days of degradation in phosphate buffer, while the modulus and ultimate stress and strain progressively decreased. The electrospun mats are mechanically superior to solid films of the same materials. In vitro, human mesenchymal stem cells adhered to and readily proliferated on the three-dimensional fiber network, demonstrating that these polymers may find use in growing artificial blood vessels in vivo.

Structural characterization, mechanical properties, and in vitro cytocompatibility evaluation of fibrous polycarbonate urethane membranes for biomedical applications

This paper reports the electrospinning of a series of oxidatively stable polycarbonate urethanes (PCU) [carbothane (ECT), bionate (EBN), and chronoflex (ECF)] using N,N-dimethyl formamide and tetrahydrofuran as the mixed solvent. The nonwoven membranes were characterized for their structure, performance, and compatibility with cells. Scanning electron microscope was utilized to study the structural morphology and fiber diameter. Microcomputed tomography (micro-CT) was used to characterize the 3D architecture, pore size distribution, and percentage porosity. All the membranes displayed a porous architecture with average fiber diameter in the range of 1.5-2 μm. Static mechanical tests on the membranes revealed that the tensile strength was greater than 7 MPa and the dynamic mechanical tests showed that the average storage modulus (E(i) ) is 2 MPa at 37°C. PCU membranes were subjected to accelerated in vitro degradation for 90 days in 20% hydrogen peroxide/0.1M cobalt chloride solution. Mechanical characterization of the membranes postdegradation confirmed a 64% reduction in tensile strength for EBN at the end of 90 days where as ECF and ECT did not show any significant mechanical property deterioration in the oxidative medium. Cytotoxicity of the membranes was evaluated using L929 fibroblast cells and the results indicated that all the PCU membranes were cytocompatible and showed good adherence to L929 cells. Accordingly, these results highlight the potential of these fibrous PCU membranes for biomedical applications but further in vivo correlation studies are required for better understanding of the biodegradation and biological efficacy.

Physical and in vitro biological evaluation of a PA 6/MWCNT electrospun composite for biomedical applications

Significant progress in the study of scaffolds for cell growth has taken place that has led to the development of a wide variety of metallic, polymeric, ceramic, and composite biomaterials. This article describes the fabrication and characterization of an electrospun net with tunable morphological and mechanical properties composed by aligned fibers of polyamide 6 (PA 6) and carboxyl-functionalized multi-walled carbon nanotubes (MWCNT). Physical and short-term biological properties of the nets were evaluated, focusing on the effect of the filler addition. The production technique used, induced the alignment of MWCNT within the nanofiber axis and the formation of a roughness on the fiber’s surface. The proliferation and activation of MG63 cell line osteoblasts were enhanced due to surface modification caused by the filler addition compared to the purely PA 6 networks.

Gemini surfactant electrospun membranes

Our research demonstrates electrospun nonwoven fibrous scaffolds from a low molar mass gemini ammonium surfactant, N,N'-didodecyl-N,N,N',N'-tetramethyl-N,N'-ethanediyldiammonium dibromide (12-2-12). Cryogenic transmission electron microscopy (cryo-TEM) and solution rheological experiments revealed micellar morphological transitions of 12-2-12 in water and water:methanol (1:1 vol). The microstructure of 12-2-12 in water transitioned from entangled, cylindrical, threadlike micelles to branched threadlike micelles, and a viscoelastic, entangled, highly branched network of threadlike micelles with increasing concentration finally formed. In sharp contrast, the solution behavior of 12-2-12 in water:methanol produced a drastically different micellar microstructure compared to that in water, and the morphology transitioned from partitioned, globular micelles to overlapped micelles at an overlap concentration (C*) of 11 wt %. Electrospinning 12-2-12 from water did not produce fibers at any concentration; however, electrospinning 12-2-12 in water:methanol at concentrations greater than 2C* produced hydrophilic continuous fibers with diameters ranging from 0.9 to 7 microm. High surface area scaffolds with hydrophilic surfaces offer potential as charged controlled-release membranes, tissue engineering scaffolds, and coatings for biologically compatible devices.

Fabrication and characterization of prosurvival growth factor releasing, anisotropic scaffolds for enhanced mesenchymal stem cell survival/growth and orientation

Scaffolds that not only mimic the mechanical and structural properties of the target tissue but also support cell survival/growth are likely necessary for the development of mechanically functional cardiovascular tissues. To reach these goals, we have generated scaffolds that are elastic to approximate soft tissue mechanical properties, are nanofibrous to mimic fibrous nature of extracellular matrix (ECM), have aligned structure to guide cellular alignment, and are capable of releasing insulin-like growth factor (IGF-1) to administrate cellular growth and survival. We have developed a technique that can quickly fabricate (<3 h) such scaffolds by simultaneously electrospinning elastase-sensitive polyurethaneurea nanofibers, encapsulating IGF-1 into poly(lactide-co-glycolide) (PLGA) microspheres and assembling them into scaffolds. Scaffold morphology, mechanical properties, degradation with or without elastase, and bioactivity of the released IGF-1 were assessed. The scaffolds had degree of alignment approximately 70%. They were flexible and relatively strong, with tensile strengths of 3.4-11.1 MPa, elongations at break of 71-88%, and moduli of 2.3-7.9 MPa at the alignment direction. IGF-1 release profile and bioactivity were dependent on PLGA content and molecular weight and IGF-1 loading. The released IGF-1 remained bioactive for 4 weeks. The fabricated nanofibers were elastase-sensitive with weight remaining <59% after a 4-week degradation in the presence of elastase. Mesenchymal stem cells (MSCs) were seeded on the scaffolds and cultured either under normal culture conditions (21% O(2), 5% CO(2), and 20% fetal bovine serum (FBS)) or hypoxia/nutrient starvation conditions (5% O(2), 5% CO(2), and 1% FBS) to evaluate the effect of IGF-1 loading on cell growth and survival. Under normal culture conditions, MSCs were found to align on the scaffolds with a degree of alignment matching that of the scaffold. The IGF-1 loaded scaffolds enhanced MSC growth during a 7-day culture period, with higher IGF-1 content showing better stimulus effect. Under hypoxia/nutrient starvation conditions, the IGF-1 loaded scaffolds were found to significantly improve MSC survival.

Surface depletion of the fluorine content of electrospun fibers of fluorinated polyurethane

For materials containing fluorine, it has been generally accepted that fluorinated segments or end groups tend to aggregate in the outer surface because of the low surface energy, which endows the fluorinated materials with special surface properties such as self-cleaning, superhydrophobicity, and so forth. However, for the electrospun fibrous membranes of polyurethane elastomers containing perfluoropolyether segments (FPU), abnormal fluorine aggregations in the core of the electrospun fibers were observed. The XPS analysis indicated a rather low fluorine content at the surface of the electrospun FPU fibers. Further study with dynamic light scattering and fluorescence showed that FPU chains can form aggregates in the concentrated solution. Therefore, it can be deduced that the rapid evaporation of solvent and fast formation of fibers during the electrospinning process could result in the freeze-in of the aggregated chain conformation and the depletion of fluorine units on the surface of the electrospun FPU fibers.

Electrospinning: A Fascinating Method for the Preparation of Ultrathin Fibers

Electrospinning is a highly versatile method to process solutions or melts, mainly of polymers, into continuous fibers with diameters ranging from a few micrometers to a few nanometers. This technique is applicable to virtually every soluble or fusible polymer. The polymers can be chemically modified and can also be tailored with additives ranging from simple carbon-black particles to complex species such as enzymes, viruses, and bacteria. Electrospinning appears to be straightforward, but is a rather intricate process that depends on a multitude of molecular, process, and technical parameters. The method provides access to entirely new materials, which may have complex chemical structures. Electrospinning is not only a focus of intense academic investigation; the technique is already being applied in many technological areas.