Solution Blow Spinning of Polycaprolactone—Rheological Determination of Spinnability and the Effect of Processing Conditions on Fiber Diameter and Alignment

Abstract

The growing popularity of solution blow spinning as a method for the production of fibrous tissue engineering scaffolds and the vast range of polymer–solvent systems available for the method raises the need to study the effect of processing conditions on fiber morphology and develop a method for its qualitative assessment. Rheological approaches to determine polymer solution spinnability and image analysis approaches to describe fiber diameter and alignment have been previously proposed, although in a separate manner and mostly for the widely known, well-researched electrospinning method. In this study, a series of methods is presented to determine the processing conditions for the development of submicron fibrous scaffolds. Rheological methods are completed with extensive image analysis to determine the spinnability window for a polymer–solvent system and qualitatively establish the influence of polymer solution concentration and collector rotational speed on fiber morphology, diameter, and alignment. Process parameter selection for a tissue engineering scaffold target application is discussed, considering the varying structural properties of the native extracellular matrix of the tissue of interest.

Shear and elongational rheometry for determination of spinnability window of polymer solutions in solution blow spinning

“…Using zero shear viscosity values determined for PLLA and PU solutions, one can determine the polymer concentration regimes for the respective polymer solutions. 16,19 Figure 2 shows the zero shear viscosity and relaxation time dependence on polymer solution concentration and corresponding concentration regimes for both investigated polymers. The presented approach with a zero shear viscosity plot is common to determine critical overlap concentration c*.…”

“…In previous work, we established that it is often impossible in practice to measure the viscosity of liquids at a very low shear rate. Thus, zero shear viscosity was calculated by extrapolating apparent viscosities measured for a range of higher shear rates, within the measurement capabilities of the rheometer, to a shear rate approaching zero 19 . The Carreau 34 regression model was used to extrapolate experimental data to zero shear viscosity η 0 : where η —apparent viscosity (Pa s); τ —shear stress (N m −2 ); —shear rate (s −1 ); η ∞ —infinite shear viscosity (Pa s); η 0 —zero shear viscosity (Pa s); λ —time constant (s); n —material constant (−).…”

“…Thus, zero shear viscosity was calculated by extrapolating apparent viscosities measured for a range of higher shear rates, within the measurement capabilities of the rheometer, to a shear rate approaching zero. 19 The Carreau 34 regression model was used to extrapolate experimental data to zero shear viscosity η 0 :…”

“…Up to now, investigated approaches to the determination of the ‘spinnability window’ for electrospinning and SBS require complex theoretical analysis and additional experiments. Such experiments include shear rheology leading to the determination of zero shear rate viscosity, viscosity number, and critical overlap polymer concentration 19–22 . In most cases, a semi‐dilute regime above the critical overlap concentration of the polymer in the solution is considered a ‘spinnability window’ 21 .…”

“…Such experiments include shear rheology leading to the determination of zero shear rate viscosity, viscosity number, and critical overlap polymer concentration. [19][20][21][22] In most cases, a semi-dilute regime above the critical overlap concentration of the polymer in the solution is considered a 'spinnability window'. 21 However, methods for describing processes commonly used in chemical engineering offer a simplified solution.…”