Electrostatic Flocking of Insulative and Biodegradable Polymer Microfibers for Biomedical Applications

Abstract

Electrostatic flocking, a textile engineering technique, uses Coulombic driving forces to propel conductive microfibers toward an adhesive-coated substrate, leaving a forest of aligned fibers. Though an easy way to induce anisotropy along a surface, this technique is limited to microfibers capable of accumulating charge. This study reports a novel method, utilizing principles from the percolation theory to make electrically insulative polymeric microfibers flockable. A variety of well-mixed, conductive materials are added to multiple insulative and biodegradable polymer microfibers during wet spinning, which enables nearly all types of polymer microfibers to accumulate sufficient charges required for flocking. Biphasic, biodegradable scaffolds are fabricated by flocking silver nanoparticle (AgNP)-filled poly( -caprolactone) (PCL) microfibers onto substrates made from 3D printing, electrospinning, and thin-film casting. The incorporation of AgNP into PCL fibers and use of chitosan-based adhesive enables antimicrobial activity against methicillin-resistant Staphylococcus aureus. The fabricated scaffolds demonstrate both favorable in vitro cell response and new tissue formation after subcutaneous implantation in rats, as evident by newly formed blood vessels and infiltrated cells. This technology opens the door for using previously unflockable polymer microfibers as surface modifiers or standalone structures in various engineering fields.

Electrostatic flocking of salt-treated microfibers and nanofiber yarns for regenerative engineering

“…Continuous PCL fibers were prepared with phase-separation wet spinning as previously reported [ 12 ]. First, 20% w/v PCL (Mw ​= ​80 ​kDa, Sigma-Aldrich, St. Louis, MO, USA) and 0.5% w/v F-127 (Sigma-Aldrich, St. Louis, MO, USA) were dissolved in a 4:1 (v/v) mix dichloromethane to N, N -dimethylformamide (DCM: DMF) (BDH Chemicals, Dawsonville, GA, USA) and stirred until a homogeneous solution with uniform viscosity was achieved.…”

“…Electrostatic flocking generally followed previous studies [ 12 ]. In both MF and NFY scaffolds, the adhesive layers served as the substrates.…”

“…RH was controlled in the flocking chamber by using a Hunter 31004 Cool Mist Ultrasonic Humidifier (Hunter Fan Company, Memphis, TN) with deionized H 2 O and RH readings were taken with a RH meter (Fisherbrand™ Traceable™, Fisher Scientific, Waltham, MA). Flock yield was calculated as the fraction of fibers lifted relative to the number of fibers sieved onto the charging electrode, based on an equation previously reported [ 10 , 12 ]. …”

“…Noting the favorable in vitro and in vivo responses and tunable porosity and fiber density, flocked materials may offer an advantage over other tissue engineering and regenerative medicine approaches in some applications. The establishment of fully degradable flocked scaffolds using both chitosan and poly(ε-caprolactone) (PCL) demonstrated that inherently or charge-modified fibers could effectively accumulate charge necessary for flocking [ 6 , 12 ]. Charge accumulation typically relies on the hydrophilicity of the flock fiber surfaces [ 13 ].…”

“…Recently, McCarthy et al. demonstrated that hydrophobic and electrically insulative polymers could accumulate sufficient charge by utilizing conductive fractional fillers following principles of the Percolation Theory [ 12 , 14 ]. Another method to induce conductivity on a fiber surface may be the implementation of a salt-based system that ionizes under sufficient humidities [ 15 ].…”