Faster Drum Rotation Tightens Nanofiber Alignment and Boosts Piezoelectric Output

A spinning drum may sound like an unlikely dial for controlling electricity, but a team of bioengineers at the University of Connecticut has shown that turning it faster is enough to make biodegradable plastic fibers generate measurably more voltage. In a detailed methods study published in Frontiers in Biomaterials Science, researchers led by I’jaaz Muhammad, Katherine Miller, Gang Ge, Thanh D. Nguyen, and Kevin W.-H. Lo describe a standardized electrospinning protocol in which collector rotation speed alone tunes the alignment of poly(L-lactic acid), or PLLA, nanofibers — and with it, their piezoelectric performance.

Piezoelectric materials convert mechanical strain into electrical signals, and piezoelectric polymers are prized wherever flexibility matters: flexible electronics, wearable sensors, energy harvesters, and electrically active biomaterial scaffolds. PLLA occupies a special niche in this landscape because it is biocompatible, biodegradable, mechanically compliant, and intrinsically piezoelectric. The Connecticut groups have previously used PLLA nanofiber systems for biodegradable transducers, cartilage repair, wound healing, and osteoinductive scaffolds, exploiting the materials’ ability to generate therapeutic electrical cues under mechanical or ultrasound stimulation.

The team’s fabrication method of choice was electrospinning, one of the most widely used techniques for producing polymer nanofibers. In this process, a high electric field pulls a droplet of polymer solution out of a needle toward a grounded collector, drawing continuous fibers that range from micro- to nanoscale diameter. Electrospun nanofiber mats resemble the native extracellular matrix more closely than bulk films, and the elongation the polymer jet experiences during spinning can induce the molecular alignment and crystallinity that underpin piezoelectricity in PLLA.

Among the many parameters that shape nanofiber performance, fiber alignment has attracted particular interest because it governs mechanical anisotropy, crystal organization, and piezoelectric response. Randomly deposited fibers yield isotropic mats, whereas aligned fibers offer enhanced directionality in mechanical properties and more uniform electromechanical behavior. In PLLA, tighter alignment is thought to facilitate enhanced chain orientation, improved stress transfer, and greater piezoelectric output under load. Rotating collectors are a common alignment tool, but the authors note that specifics — solution preparation, ambient environment, collector configuration, speed determination, alignment quantification, and piezoelectric validation — are often omitted or relegated to supplementary material, hampering reproducibility and cross-study comparison.

The new protocol closes that gap with a fully specified workflow. The researchers dissolved PL38 polymer in chloroform — a validated replacement for methylene chloride, whose research and consumer uses the EPA banned as of May 5, 2025 — and spun the solution at 14 kV from a 20-gauge needle positioned a fixed 8.573 centimeters from a foil-wrapped rotating drum. Humidity was held between 25 and 35 percent inside the spinning chamber, adjusted with dry air or ultrapure water as needed, while flow rate, polymer concentration, and tip-to-collector distance were kept constant so that collector speed stood as the only deliberate variable.

After spinning, the films underwent an overnight evaporation step on the drum, followed by a two-stage annealing sequence: first at 105 °C to drive off residual solvent, then sandwiched between Teflon films at 160 °C to stabilize the material. For some applications the team cryosectioned the annealed sheets into individual nanofibers, embedding them in O.C.T. compound, freezing at −80 °C, and cutting 0.25-micrometer sections perpendicular to the fiber direction before washing away the embedding medium and lyophilizing the product.

Alignment was quantified rather than eyeballed. Scanning electron microscopy images taken at ×5 kV and ×5000 magnification were processed with a MATLAB two-dimensional structure tensor approach, producing normalized orientation histograms from 0 to 180 degrees. The key metric was orientation spread, where lower values indicate tighter alignment. When the drum spun at 1000 rpm, the fibers were visibly more random, and the orientation spread measured 19.57 degrees. At 2000 rpm it narrowed to 14.68 degrees, and at 4000 rpm the mats displayed aligned fiber bundles with a spread of just 11.23 degrees. The authors attribute this trend to stronger directional pull and increased shear forces on the polymer jet at higher speeds, which suppress the jet oscillations responsible for random deposition.

Structural analysis supported the mechanistic story. Fourier transform infrared spectroscopy showed consistent chemical composition across all samples, but within the 850–940 per centimeter region associated with piezoelectric activity, films spun at 2000 and 4000 rpm showed stronger beta-phase peaks. Quantified by integrating spectral regions, the relative beta-phase content rose from 56 percent at 1000 rpm to 61 percent at 2000 rpm and 62 percent at 4000 rpm, at the expense of the alpha phase. By contrast, X-ray diffraction revealed no differences in peak position or intensity across samples, and differential scanning calorimetry showed similar thermal behavior in all films, each with a characteristic melting endotherm near 180 °C — suggesting the piezoelectric gains arise from molecular packing and phase organization rather than changes in bulk crystallinity.

The functional payoff was unambiguous. Measured with a quasi-static d33 meter under a 0.05 newton compressive force, the effective piezoelectric coefficient climbed from 3.37 pC/N at 1000 rpm to 4.13 pC/N at 2000 rpm and 5.92 pC/N at 4000 rpm — roughly a 76 percent increase across the speed range. Open-circuit voltage output, recorded with an oscilloscope while ultrasound at 1 MHz and 0.5 W/cm² pressed on gel-coupled samples fitted with aluminum foil electrodes, rose from 15 mV to 20 mV to 35 mV. Samples were soaked in deionized water before testing to suppress triboelectric artifacts, ensuring the signals reflected genuine piezoelectric response.

The authors are candid about the method’s limits. Collector speed does not act alone: polymer concentration, solvent system, flow rate, applied voltage, tip-to-collector distance, temperature, and humidity all influence final fiber morphology, so each system requires systematic optimization. At extremely high rotational speeds, fibers can suffer instability, breakage, or nonuniform deposition, degrading mat quality. Alignment also does not correlate linearly with piezoelectricity — crystalline phase content, dipole alignment, fiber diameter, and device design all contribute — so morphological evaluation must be paired with structural and functional characterization. Practical troubleshooting guidance, from drum release coatings to syringe pump replacement every three years and desiccator storage that keeps performance stable for roughly two months, rounds out the protocol. With those caveats, the team argues the framework offers a simple, reproducible dial for designing tunable scaffolds, wearable sensors, and mechanically triggered energy harvesters, and could extend to other polymers, piezoelectric composites, multilayer structures, and scaled-up setups.

Subject of Research: Collector speed-controlled fiber alignment and piezoelectric properties of electrospun PLLA nanofibers

Article Title: Tuning the structure-piezoelectric property relationship in electrospun PLLA nanofibers through collector-induced fiber alignment

Article References: Muhammad, I., Miller, K., Ge, G., Nguyen, T. D., & Lo, K. W.-H. (2026). Tuning the structure-piezoelectric property relationship in electrospun PLLA nanofibers through collector-induced fiber alignment. Frontiers in Biomaterials Science, 5, Article 1967187. https://doi.org/10.3389/fbiom.2026.1967187

Image Credits: AI Generated

DOI: 10.3389/fbiom.2026.1967187

Keywords: electrospinning, PLLA, nanofibers, piezoelectricity, fiber alignment, biomaterials, energy harvesting, wearable sensors, tissue scaffolds, rotating collector, beta phase, biodegradable polymers