Collagen Nanoyarns: Hierarchical Three-Dimensional Biomaterial Constructs.

Hierarchical fibrous scaffolds (HFS) consist of nanoscale fibers arranged in larger macroscale structures, much in the same pattern as in native tissue such as tendon and bone. Creation of continuous macroscale nanofiber yarns has been made possible using modified electrospinning set-ups that combine electrospinning with techniques such as twisting, drawing, and winding. In this paper, a modified electrospinning setup was used to create continuous yarns of twisted type I collagen nanofibers, also known as collagen nanoyarns (CNY), from collagen solution prepared in acetic acid. Fabricated CNYs were cross-linked and characterized using SEM imaging and mechanical testing, while denaturation of collagen and dissolution of the scaffolds were assessed using circular dichroism (CD) and UV-vis spectroscopy, respectively. HeLa cells were then cultured on the nanoyarns for 24 h to assess cell adhesion on the scaffolds. Scanning electron micrographs revealed a twisted nanofiber morphology with an average nanofiber diameter of 213 ± 60 nm and a yarn diameter of 372 ± 23 µm that shrank by 35% after covalent cross-linking. Structural denaturation assessment of native collagen using circular dichroism (CD) spectroscopy showed that 60% of the triple-helical collagen content in CNYs was retained. Cross-linking of CNYs significantly improved their mechanical properties as well as stability in buffered saline with no sign of degradation for 14 days. In addition, CNY strength and stiffness increased significantly with cross-linking although in the wet state, significant loss in these properties, with a corresponding increase in elasticity, was observed. HeLa cells cultured on cross-linked CNYs for 24 h adhered to the yarn surface and oriented along the nanofiber alignment axis, displaying the characteristic spindle-like morphology of cells grown on surfaces with aligned topography. Collectively, the results demonstrate the promising potential of collagen nanoyarns as a new class of shapable biomaterial scaffold and building block for generating macroscale fiber-based tissues.

On the Effect of Sweat on Sheet Resistance of Knitted Conductive Yarns in Wearable Antenna Design.

Researchers are looking for new methods to integrate sensing capabilities into textiles while maintaining the durability, flexibility, and comfort of the garment. One method for imparting sensing capabilities into garments is through coupling conductive yarns with the radio frequency identification (RFID) technology. These smart devices have exhibited promising results for short-term use. However, long-term studies of their performance are still needed to evaluate their performance over a longer period. Like all garments, wearable sensors are susceptible to environmental factors during use. These factors can lead to dielectric coupling and corrosion of conductive yarns, which has the potential to degrade the performance of the device. This letter analyzes the effect of sweat and moisture on silver-coated nylon yarn by extracting the sheet resistance at 913 MHz from transmission line measurements. HFSS simulation shows the level of perturbation in antenna performance as sheet resistance increased with each cycle of sweat-immersion, washing, and drying.

Overcoming the inhibitory effects of urea to improve the kinetics of microbial-induced calcium carbonate precipitation (MICCP) by Lysinibacillus sphaericus strain MB284.

Among different microbial-induced calcium carbonate precipitation (MICCP) mechanisms utilized for biomineralization, ureolysis leads to the greatest yields of calcium carbonate. Unfortunately, it is reported that urea-induced growth inhibition can delay urea hydrolysis but it is not clear how this affects MICCP kinetics. This study investigated the impact of urea addition on the MICCP performance of Lysinibacillus sphaericus MB284 not previously grown on urea (thereafter named bio-agents), compared with those previously cultured in urea-rich media (20 g/L) (hereafter named bio-agents+ or bio-agents-plus). While it was discovered that initial urea concentrations exceeding 3 g/L temporarily hindered cell growth and MICCP reactions for bio-agents, employing bio-agents+ accelerated the initiation of bacterial growth by 33% and led to a 1.46-fold increase in the initial yield of calcium carbonate in media containing 20 g/L of urea. The improved tolerance of bio-agents+ to urea is attributed to the presence of pre-produced endogenous urease, which serves to reduce the initial urea concentration, alleviate growth inhibition, and expedite biomineralization. Notably, elevating the initial concentration of bio-agents+ from OD600 of 0.01 to 1, housing a higher content of endogenous urease, accelerated the initiation of MICCP reactions and boosted the ultimate yield of biomineralization by 2.6 times while the media was supplemented with 20 g/L of urea. These results elucidate the advantages of employing bio-agents+ with higher initial cell concentrations to successfully mitigate the temporary inhibitory effects of urea on biomineralization kinetics, offering a promising strategy for accelerating the production of calcium carbonate for applications like bio self-healing of concrete.

Fabrication and characterization of electrospun semiconductor nanoparticle-polyelectrolyte ultra-fine fiber composites for sensing applications.

Fluorescent composite fibrous assembles of nanoparticle-polyelectrolyte fibers are useful multifunctional materials, utilized in filtration, sensing and tissue engineering applications, with the added benefits of improved mechanical, electrical or structural characteristics over the individual components. Composite fibrous mats were prepared by electrospinning aqueous solutions of 6 wt% poly(acrylic acid) (PAA) loaded with 0.15 and 0.20% v/v, carboxyl functionalized CdSe/ZnS nanoparticles (SNPs). The resulting fluorescent composite fibrous mats exhibits recoverable quenching when exposed to high humidity. The sensor response is sensitive to water concentration and is attributed to the change in the local charges around the SNPs due to deprotonation of the carboxylic acids on the SNPs and the surrounding polymer matrix.

Selective detection of hexachromium ions by localized surface plasmon resonance measurements using gold nanoparticles/chitosan composite interfaces.

Selective removal of hexavalent chromium ions from aqueous solutions using a chitosan/gold nanoparticles composite film was demonstrated. Localized surface plasmon resonance (LSPR) was used to measure the interface stability and detect the incorporation of chromium ions over time. The effects of pH, ethylenediaminetetraacetic acid (EDTA), and various foreign ions such as trivalent chromium, sodium, calcium, phosphate, sulfate and chloride on the adsorption of hexavalent chromium were investigated.

Localized surface plasmon resonance of gold nanoparticle-modified chitosan films for heavy-metal ions sensing.

Gold nanoparticles (Au NPs) were entrapped within, and in between, a cross-linked thin chitosan film, casted onto a glass substrate. The glass/chitosan/Au NPs interface was formed by casting Au NPs-chitosan solutions onto flat glass supports, followed by exposure to Au NPs in solution and repeating the casting procedure for the desired number of layers. The optical properties of the resulting interfaces and their ability to sense various heavy metal ions, such as Fe3+ and Cu2+, were investigated utilizing the phenomenon of localized surface plasmon resonance (LSPR) visualized by UV/V is absorption spectroscopy. The interfaces investigated showed different optical behavior to the presence of the different metal ions. An increase of the LSRP absorption maximum at lamdamax = 517 nm was observed upon Fe3+ binding with a detection limit of 0.5 microM and a linear range up to approximately 2 microM. Due to a lower binding capability of Cu2+, the detection limit is 0.5 mM with a linear range up to approximately 5 mM.

Carboxymethyl chitosan as a matrix material for platinum, gold, and silver nanoparticles.

Carboxymethyl chitosan (CMC) was evaluated for its use in the synthesis and stabilization of catalytic nanoparticles for the first time. Many studies have reported on the ability of chitosan to bind with metal ions and support metal nanoparticles. CMC has a higher reported chelation capacity than chitosan, which has potential implications for improved catalyst formation and immobilization. Platinum, gold, and silver nanoparticles were synthesized in both chitosan and CMC. Particle size, morphology, and aggregation were examined using transmission electron microscopy (TEM). Complexation of nanoparticles was studied through Fourier transform infrared spectroscopy (FTIR). Similar nanoparticle size distributions were observed in the two polymers; however, CMC was observed to have higher rates of aggregation. This indicates that the carboxymethyl groups did not change nanoparticle formation; however, poor cross-linking and a limited anchoring ability of CMC led to the inability to immobilize the catalyst materials effectively.

Structurally colored thiol chitosan thin films as a platform for aqueous heavy metal ion detection.

Thin films of the polysaccharide chitosan and several chitosan derivatives, including conjugates of l-cysteine, thioglycolic acid, and 2-iminothiolane, were produced from dilute acidic solutions. Attempts to produce a fourth conjugate using lipoic acid resulted in the synthesis of partially N-acetylated chitosan ethanoate. These biopolymer films were exposed to solutions containing 50 ppm concentrations of various metal ion and counterion analytes. Analyte-induced changes in film thicknesses and refractive indices were measured using a spectroscopic ellipsometer, and shifts in film color were quantified using a reflectance spectrometer. The modified chitosans were generally more sensitive to change in response to pure water but also showed varied response to several ions of interest, including Cr(III) and Cr(VI), Hg(II), Ni(II), and others. The potential for tuning film response was demonstrated by varying the concentration of sulfur groups in the thioglycolic acid conjugate, leading to increased specificity for Hg(II).

Thin chitosan films as a platform for SPR sensing of ferric ions.

Homogeneous chitosan films of various thicknesses (10-65 nm) were deposited on thin gold films through spin coating. The resulting interfaces were characterized using surface plasmon resonance (SPR), AFM, profilometry and cyclic voltammetry. The strong chelating properties of chitosan films to Fe(3+) were investigated using cyclic voltammetry. Through SPR measurements, an affinity constant between chitosan and Fe(3+) of 9.49 x 10(5) M(-1) was determined with a detection limit as low as 250 ppb.

Antibacterial properties of electrospun Ti3C2T z (MXene)/chitosan nanofibers.

Electrospun natural polymeric bandages are highly desirable due to their low-cost, biodegradability, non-toxicity and antimicrobial properties. Functionalization of these nanofibrous mats with two-dimensional nanomaterials is an attractive strategy to enhance the antibacterial effects. Herein, we demonstrate an electrospinning process to produce encapsulated delaminated Ti3C2T z (MXene) flakes within chitosan nanofibers for passive antibacterial wound dressing applications. In vitro antibacterial studies were performed on crosslinked Ti3C2T z /chitosan composite fibers against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) - demonstrating a 95% and 62% reduction in colony forming units, respectively, following 4 h of treatment with the 0.75 wt% Ti3C2T z - loaded nanofibers. Cytotoxicity studies to determine biocompatibility of the nanofibers indicated the antibacterial MXene/chitosan nanofibers are non-toxic. The incorporation of Ti3C2T z single flakes on fiber morphology was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy equipped with an energy-dispersive detector (TEM-EDS). Our results suggest that the electrospun Ti3C2T z /chitosan nanofibers are a promising candidate material in wound healing applications.

Variable piezoelectricity of electrospun chitin.

Investigations into the piezoelectricity of natural polymers is a continuing area of interest due to their potential role in the complex interplay of mechanical and electrical forces present in biological organisms. Their synthetic counterparts, when electrospun using the air gap electrospinning method, are known to have increased crystallinity and tensile strength as compared to randomly aligned nanofibers composed of the same constituent polymers. Using the air gap electrospinning method with the naturally-occurring, semi-crystalline polymer chitin, the nanofibers were determined to have a 300% increase in tensile strength over randomly collected ones. Additionally, a 400% increase in piezoelectric response in the aligned nanofiber chitin mats was measured. The increased tensile strength and piezoelectricity in aligned chitin nanofibers is a consequence of an increase in α-chitin crystallinity in the nanofibers induced by the air gap collection method.

Investigation of nanoyarn preparation by modified electrospinning setup.

Higher ordered structures of nanofibers, including nanofiber-based yarns and cables, have a variety of potential applications, including wearable health monitoring systems, artificial tendons, and medical sutures. In this study, twisted assemblies of polyacrylonitrile (PAN), polyvinylidene fluoride trifluoroethylene (PVDF-TrFE), and polycaprolactone (PCL) nanofibers were fabricated via a modified electrospinning setup, consisting of a rotating cone-shaped copper collector, two syringe pumps, and two high voltage power supplies. The fiber diameters and twist angles varied as a function of the rotary speed of the collector. Mechanical testing of the yarns revealed that PVDF-TrFe and PCL yarns have a higher strain-to-failure than PAN yarns, reaching 307% for PCL nanoyarns. For the first time, the porosity of nanofiber yarns was studied as a function of twist angle, showing that PAN nanoyarns are more porous than PCL yarns.

Synthesis of macromolecular mimics of small leucine-rich proteoglycans with a poly(ethylene glycol) core and chondroitin sulphate bristles.

Small leucine-rich proteoglycans (SLRPs) are a class of molecules prevalent in almost all tissues types and are thought to be responsible for collagen organization and macro-scale biological properties. However, when they are dysfunctional or degraded, severe pathological phenotypes are observed. Here we investigate macromolecular mimics to SLRPs using poly(ethylene glycol) (PEG) as a core (replacing the protein core of natural SLRPs) and chondroitin sulphate (CS) bristle(s) in an end-on attachment (via epoxide-amine reactions), mimicking the physical structure of the natural SLRPs. Poly(ethylene glycol)-diglycidyl ether (PEG-DEG) and ethylene glycol-diglycidyl ether (EG-DGE) monomers were used to incorporate CS bristles into a macromolecule that closely mimics the SLRP biglycan structure in a grafting-to strategy. The kinetics of these reactions was studied along with the specific viscosity and cytocompatibility of resulting CS macromolecules. Structures were found to incorporate two CS chains (similar to biglycan) on average and exhibited cytocompatibility equivalent to or better than CS-only controls.

Osteoblast biocompatibility of premineralized, hexamethylene-1,6-diaminocarboxysulfonate crosslinked chitosan fibers.

Biopolymer-ceramic composites are thought to be particularly promising materials for bone tissue engineering as they more closely mimic natural bone. Here, we demonstrate the fabrication by electrospinning of fibrous chitosan-hydroxyapatite composite scaffolds with low (1 wt %) and high (10 wt %) mineral contents. Scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and unidirectional tensile testing were performed to determine fiber surface morphology, elemental composition, and tensile Young's modulus (E) and ultimate tensile strength (σUTS ), respectively. EDS scans of the scaffolds indicated that the fibers, crosslinked with either hexamethylene-1,6-diaminocarboxysulfonate (HDACS) or genipin, have a crystalline hydroxyapatite mineral content at 10 wt % additive. Moreover, FESEM micrographs showed that all electrospun fibers have diameters (122-249 nm), which fall within the range of those of fibrous collagen found in the extracellular matrix of bone. Young's modulus and ultimate tensile strength of the various crosslinked composite compositions were in the range of 116-329 MPa and 2-15 MPa, respectively. Osteocytes seeded onto the mineralized fibers were able to demonstrate good biocompatibility enhancing the potential use for this material in future bone tissue engineering applications.

Osteoblast biocompatibility of novel chitosan crosslinker, hexamethylene-1,6-diaminocarboxysulfonate.

Chitosan is a naturally occurring polysaccharide, which has proven to be an attractive candidate for bone tissue engineering, due to its ability to promote osteoblast mineralization. Electrospinning has become a well-established cell scaffold processing technique, as it produces a high surface area to volume fibrous material that can mimic the three dimensionality of the extracellular matrix of a cell. In this study, we have investigated the osteoblast response to two different chemically crosslinked (hexamethylene-1,6-diaminocarboxysulfonate (HDACS) and genipin) electrospun chitosan scaffolds and their film counterparts in order to determine how material chemistry influences cellular behavior in conjunction with material topology. In addition, material properties of each fiber scaffold such as porosity and tensile strength were considered. MLO-A5 osteoblast cells grown on chitosan-HDACS scaffolds were found to display a more organized cellular network, along with significantly more filopodia extensions, compared to those grown on chitosan-genipin scaffolds. After 2 days of growth on chitosan-HDACS fibers, a higher level of alkaline phosphatase expression in MLO-A5 cells was reported compared to that of either chitosan-genipin fibers or films. These results indicate that not only chemistry, but also surface topology is an important effecter of cellular behavior. Ultimately, chitosan-HDACS fiber scaffolds provided an adequate substrate for osteoblast attachment and proliferation.

Fabrication and characterization of 3D hydrogel microarrays to measure antigenicity and antibody functionality for biosensor applications.

We report the fabrication, characterization and evaluation of three-dimensional (3D) hydrogel thin films used to measure protein binding (antigenicity) and antibody functionality in a microarray format. Protein antigenicity was evaluated using the protein toxin, staphylococcal enterotoxin B (SEB), as a model on highly crosslinked hydrogel thin films of polyacrylamide and on two-dimensional (2D) glass surfaces. Covalent crosslinking conditions were optimized and quantified. Interrogation of the modified 3D hydrogel was measured both by direct coupling of a Cy5-labeled SEB molecule and Cy5-anti-SEB antibody binding to immobilized unlabeled SEB. Antibody functionality experiments were conducted using three chemically modified surfaces (highly crosslinked polyacrylamide hydrogels, commercially available hydrogels and 2D glass surfaces). Cy3-labeled anti-mouse IgG (capture antibody) was microarrayed onto the hydrogel surfaces and interrogated with the corresponding Cy5-labeled mouse IgG (antigen). Five different concentrations of Cy5-labeled mouse IgG were applied to each microarrayed surface and the fluorescence quantified by scanning laser confocal microscopy. Experimental results showed fluorescence intensities 3-10-fold higher for the 3D films compared to analogous 2D surfaces with attomole level sensitivity measured in direct capture immunoassays. However, 2D surfaces reported equal or greater sensitivity on a per-molecule basis. Reported also are the immobilization efficiencies, inter-and intra-slide variability and detection limits.

A reagentless electrochemical biosensor based on a protein scaffold.

Apo-myoglobin, labeled with the environmentally sensitive redox probe RuII(NH3)4(1,10-phenanthroline-5-maleimide)2+, was immobilized onto gold electrodes modified with 11-mercaptoundecanoic acid and subsequently labeled with biotin; avidin binding to the immobilized biotin was specifically and quantitatively detected by a change in cyclic voltammetry of the co-immobilized probe.

Various-sourced pectin and polyethylene oxide electrospun fibers.

Pectin, a naturally occurring and biorenewable polysaccharide, is derived from plant cell wall tissue and used in applications ranging from food processing to biomedical engineering. Due to extraction methods and source variation, there is currently no consensus in literature as to the exact structure of pectin. Here, we have studied key material properties of electrospun pectin blends with polyethylene oxide (PEO) (1:1, v/v) in order to demonstrate the fabrication of a fibrous and less toxic material system, as well as to understand the effects of source variability on the resulting fibrous mats. The bulk pectin degree of esterification (DE) estimated using FTIR (bulk apple pomace (AP)=28%, bulk citrus peel (CP)=86% and bulk sugar beet pulp (SBP)=91%) was shown to inversely correlate with electrospun fiber crystallinity determined using XRD (PEO-AP=37%, PEO-CP=28% and PEO-SBP=23%). This in turn affected the trend observed for the mean fiber diameter (n=50) (PEO-AP=124 ± 26 nm, PEO-CP=493 ± 254 nm and PEO-SBP=581 ± 178 nm) and elastic tensile moduli (1.6 ± 0.2 MPa, 4.37 ± 0.64 MPa and 2.49 ± 1.46 MPa, respectively) of the fibrous mats. Electrospun fibers containing bulk AP had the lowest DE, highest crystallinity, smallest mean fiber diameter, and lowest tensile modulus compared to either the bulk CP or bulk SBP. Bound water in PEO-CP fiber and bulk pectin impurities in PEO-SPB were observed to influence fiber branching and mean diameter distributions, which in turn influenced the fiber tensile properties. These results indicate that pectin, when blended with PEO in water, produces submicron fibrous mats with pectin influencing the blend fiber properties. Moreover, the source of pectin is an important variable in creating electrospun blend fibrous mats with desired material properties.

Non-covalent crosslinkers for electrospun chitosan fibers.

Electrospun chitosan fibers have numerous potential in biomedical, food, and pharmaceutical applications. However, the mats formed are often not chemically stable in a wide range of pHs unless crosslinked. Here, we report on the use of glycerol phosphate (GP), tripolyphosphate (TPP) and tannic acid (TA) as a new set of non-covalent crosslinkers for electrospun chitosan fibers. Crosslinking with or without heat or base activation were performed either prior to (one-step or activated one-step) or after (two-step or activated two-step) electrospinning with either GP or TA. TPP crosslinking was performed in two-step and activated two-step. FESEM, FTIR and UV-vis transmittance at 600 nm were used to determine fiber surface morphology, chemical interactions and solubility in 1M AA (pH 3), water (~pH 6) and 1 M NaOH (pH 13), respectively. Crosslinking of chitosan with GP and TA yields fibers with a mean diameter range of 145-334 nm and 143-5554 nm, respectively. TPP crosslinking produced branched fibers with mean diameters of 117-462 nm range. Two-step chitosan-TA did not dissolve in 1M AA even after 72 h while all chitosan-TPP, activated two-step chitosan-TA and two-step heat activated chitosan-GP fibers survived in water after 72 h.

New crosslinkers for electrospun chitosan fibre mats. Part II: mechanical properties.

Few studies exist on the mechanical performance of crosslinked electrospun chitosan (CS) fibre mats. In this study, we show that the mat structure and mechanical performance depend on the different crosslinking agents genipin, epichlorohydrin (ECH), and hexamethylene-1,6-diaminocarboxysulphonate (HDACS), as well as the post-electrospinning heat and base activation treatments. The mat structure was imaged by field emission scanning electron microscopy and the mechanical performance was tested in tension. The elastic modulus, tensile strength, strain at failure and work to failure were found to range from 52 to 592 MPa, 2 to 30 MPa, 2 to 31 per cent and 0.041 to 3.26 MJ m(-3), respectively. In general, neat CS mats were found to be the stiffest and the strongest, though least ductile, while CS-ECH mats were the least stiff, weakest, but the most ductile, and CS-HDACS fibre mats exhibited intermediary mechanical properties. The mechanical performance of the mats is shown to reflect differences in the fibre diameter, number of fibre-fibre contacts formed within the mat, as well as varying intermolecular bonding and moisture content. The findings reported here complement the chemical properties of the mats, described in part I of this study.