Melt Electrospinning Writing of PLGA for Tissue Engineering Applications
Polymer Materials
Final Report Abstract
This project led to several discoveries that have broader implications in polymer thermal-processing research. We used a high-resolution 3D printing technology, called melt electrowriting, to fabricate highly porous structures for biomedical applications. The first discovery in this context is that the Taylor Cone volume (i.e., the electrified jet just under the nozzle) is an excellent characteristic to monitor the melt electrowriting stability. Since melt electrowriting balances multiple parameters, it is common to begin operation with unstable conditions. A better understanding of this balance is achieved using high-resolution cameras to visualize the printing jet stability profiles in different electrical fields. This information, in turn, allows the detection and correction of manufacturing defects for accurate jet placement on the collector, and the in-process assessment of fiber diameter. A second discovery was that heated polymers will stabilize after an initial period, and not continue to degrade as seen with the same polymers heated to higher temperatures. We found that a degradable polymer could be printed for 25-days in a very stable manner, and the only slight changes that occurred were in the first 5 days. As a polymer of interest to this project, PLGA, this instability lasted 4 hours and after this was stable out to 24h. We found that the thermal processing of degradable polymers is a complex balance of both physical and chemical changes that result from extended heating times (days) at moderately low temperatures (just above the melting point). This is not reflected in the existing publish thermal degradation data that relies on substantial heat (100°C above the melting point) being applied to a polymer for a short period of time (minutes). In the interest of reducing the processing temperature, we further identified an additive that provides elastomeric properties to a polymer, PLGA, that is typically ductile. This meant that the printed material could be repeatedly deformed, and it kept recovering to its original position after releasing forces. This was an unexpected outcome as the focus of the research was to minimize degradation and not to change the mechanical properties of the polymer. The establishment of a working principle of this high resolution technology was also achieved using a filament-driven head, fitted onto a multi-axis robot arm so that it can print onto a sphere. The important change in using a low-cost filament approach has broad implications for accessibility since such printers are economical and widely available. This last aspect of the project promised to make melt electrowriting more available to interested researchers. Several characterization methodologies were additionally established to measure changes in polymer properties and composition with heating time. This includes methods such as measuring the speed of the printing jet and gel permeation chromatography, differential scanning calorimetry and rheology.
Publications
- (2021) Convergence of machine vision and melt electrowriting. Adv Mater, 2100519
Mieszczanek P, Robinson TM, Dalton PD, Hutmacher DW
(See online at https://doi.org/10.1002/adma.202100519) - (2021) The multi-week thermal stability of medical-grade poly(ɛ-caprolactone) during melt electrowriting. Small, 2104193
Boehm C, Stahlhut P, Weichhold J, Hrynevich A, Teßmar J, Dalton PD
(See online at https://doi.org/10.1002/smll.202104193)
