Browsing by Subject "Electrospinning"

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Development of multifunctional electrospun wraps for bone healing
(2020-11-17) Buie, Taneidra Walker; Cosgriff-Hernandez, Elizabeth; Suggs, Laura; Zoldan, Janeta; Laverty, David
The Masquelet technique is a two-staged procedure that uses an induced biological membrane and bone graft to reconstruct critical-sized bone defects. However, unpredictable clinical outcomes result due to the variable durability and the transient vascular network of the induced membrane, as well as high incidences of osteomyelitis. To this end, we have engineered a resorbable multifunctional electrospun wrap that guides formation of the induced membrane with improved durability and enhanced angiogenesis while simultaneously preventing infection. We achieve this by developing and combining an antimicrobial poly(lactic-co-glycolic) acid (PLGA) mesh and an angiogenic crosslinked gelatin mesh. We first confirmed the ability of electrospun PLGA to provide sustained release of gentamicin sulfate or gallium maltolate above its minimum inhibitory concentration (MIC). Studies that evaluated antimicrobial activity indicated that osteomyelitis-derived bacteria was not susceptible to released gallium maltolate at the hypothesized MIC and further established the accurate gallium maltolate MIC. The inhibitory concentration of each antimicrobial on osteoblasts was compared to the respective MIC to determine if they were safe and effective at released concentrations. Results concluded that the gentamicin sulfate-loaded PLGA mesh is safer and more effective mesh. Next, the bioactivity retention of vascular endothelial growth factor (VEGF) released from electrospun photo-crosslinked gelatin-methacrylate was confirmed. Subcutaneous implantation of the VEGF-loaded mesh in a rat corroborated resorption and the capacity for sustained release. A multifunctional electrospun wrap was then engineered to prevent osteomyelitis and guide formation of the induced membrane by combining the antimicrobial and angiogenic platforms with co-electrospinning. The combination of the two fiber populations was confirmed microscopically and offered independently tuned bimodal release of gentamicin sulfate and VEGF. Overall, this work provides the fundamentals to advance the development of a multifunctional electrospun wrap that can guide formation of the induced membrane and prevent osteomyelitis for improved clinical outcomes with the Masquelet technique. This work offers a substrate that can recruit and support cellular adhesion, provide a template for matrix deposition and tissue remodeling, and enable bimodal release of bioactive agents. These studies also enhance the capacity of electrospun platforms to serve as stand-alone therapies or combinatorial therapies in various bone regeneration applications.
Flame retardant polyamide 6 nanocomposites and nanofibers : processing and characterization
(2012-05) Yin, Xiaoli; Koo, Joseph H.; Krifa, Mourad
Polyamide 6 (PA6) was melt-blended with an intumescent flame retardant (FR) and nanoparticles (multi-wall carbon nanotubes [MWNTs] and nanoclays) to produce multi-component FR-PA6 nanocomposites. Thermal, flammability properties, char residue morphology, and mechanical properties of FR-PA6 nanocomposites were characterized. The flame retardant properties were enhanced according to UL 94 and microscale combustion calorimeter (MCC) measurements, whereas the thermal stability was decreased. Mechanical properties of the bulk material, especially elongation at break, were severely reduced, with the exception of tensile modulus which increased significantly. FR-PA6 nanofibers were processed via electrospinning. Electrospinnability, morphology of the nanofibers, combustion, and thermal properties were also analyzed. As for the bulk-form nanocomposite, improved combustion properties of these nanofibers were successfully achieved though thermal stability was compromised. With proper FR additive, the synergism between MWNTs and nanoclays was observed in PA6 resin.
Functional nanocomposite fibers through electrospinning : flame retardant and superhydrophobic
(2012-05) Wu, Hao; Krifa, Mourad; Koo, Joseph H.
Flame retardant (FR) intumescent additives and montmorillonite (MMT) organoclay incorporated nylon-6 nanocomposite (FR-NC-PA6) fibers with a diameter of about 200 nm were fabricated by electrospinning. Before electrospinning, dispersion and exfoliation of the FR additive and MMT in nylon-6 were achieved by twin-screw extrusion. Tensile, TGA and UL-94 flammability tests were first performed using injection-molded bulk samples. The tensile modulus of FR-NC-PA6 was 45% higher than that of neat PA6, but tensile strength and elongation at break decreased by 23% and 98.7%, respectively. It is worth noting that although the TGA results show that FR-NC-PA6 has a slightly earlier decomposition temperature than neat PA6, it did not drip under fire and had the best rating (V-0) in UL 94 test, while neat PA6 is only rated as V-2. SEM and EDX of char residues after the UL 94 test clearly show the oxygen-rich protective char layer on the surface. These results indicate the advantage of using clay and FR additive in bulk-form PA6. Flammability of electrospun nanocomposite fibers was characterized by Micro-combustion calorimeter (MCC), a small-scale test to screen flammability of polymer materials. The MCC results show that the nano-fillers in both bulk and fiber form could effectively improve flame retardant properties of the material. Electrospun fibers had similar combustion properties as bulk materials. In addition to FR applications, superhydrophobic surface was another area that was explored using the electrospun nanocomposite fibers. Static water contact angle (WCA) test showed that samples with 5wt% clay even without plasma treatment greatly improved the WCA to 140°, probably due to the barrier effect of nanoclay platelets. Plasma treatment was used to modify the surface energy, further improving WCA to as high as 160°. However, fiber structure was partially etched away when overexposed to the plasma. This etching effect increased the surface roughness. Clay incorporated samples had higher level of surface roughness and better resistance to plasma etching compared to neat nylon 6.
Nanostructured PVDF-TrFE based piezoelectric pressure sensors on catheter for cardiovascular applications
(2012-12) Sharma, Tushar; Zhang, John X. J.; Gill, Brijesh S.
The objective of this research is to develop a new class of miniaturized sensors on-catheter technology through the integration of functional nanomaterials and flexible microsystems, with high sensitivity, fast recovery time, reduced form factor, for in situ blood pressure and flow monitoring with minimal invasiveness. Real-time endovascular pressure measurement techniques are crucial to evaluate the hemodynamics, which indicates the physiological state of the cardiovascular system. Current technology relies on fluid filled catheter coupled to remote transducers to measure endovascular pressures and gradients. The fluid filled catheters are bulky, inherently inaccurate due to the tubing mechanical resonance, and with low signal integrity due to the vibration noises from the environment. Silicon based conventional pressure sensors have complications due to issues of catheter stiffness, biocompatibility or small form factor integration. We propose a paradigm shift in designing the endovascular pressure sensing technology, through developing compact flexible sensing structures using nanoengineered piezoelectric polymers which can be integrated on catheters without consuming the internal lumen space. We focused on designing novel nanostructures using PVDF-TrFE (Polyvinyledene fluoride trifluoroethylene), with well controlled [Beta]-crystalline phase to significantly improve the resulting sensor performance. The research objectives include: (1) Thin-film structures for higher piezoelectric effect without any mechanical stretching or poling requirements, (2) High density highly-aligned electrospun nanofibers through electrospinning towards enhanced sensitivity; (3) Core-shell electrospun nanofiber for tapping the near [Beta]-crystalline phase formation and high cyrstallinity by virtue of inherent stress and stretching involved in the fabrication procedure. For pressure sensor design and characterization, we worked on two main form factors designs: thin-film, and aligned electrospun nanofiber based sensors patterned on catheter tips which are ready to be deployed in intra-vascular environment. Testing results showed promising results from PVDF based pressure sensors. The average sensitivity of the PVDF sensors was found to be four times higher than commercial pressure sensor while the PVDF sensor had five fold shorter response time than commercial pressure sensor, making the PVDF sensors highly suitable for real-time pressure measurements using catheters.