Fabrication and functionality of porous fibers prepared from microbial polyesters

PHAs are synthesized by microorganisms using renewable feedstocks such as sugars and plant oils and biodegrade into water and carbon dioxide through microbial action. They combine sustainability with thermoplastic processability and crystallinity, making them attractive alternatives to petroleum-derived plastics for applications where environmental impact and end-of-life disposal are important.

The elasticity is not produced by a conventional thermoplastic elastomer mechanism or block copolymer morphology. Instead, synchrotron X-ray analysis shows that elasticity originates from reversible changes in hierarchical structure, including crystalline orientation, lamellar spacing, and deformation of amorphous regions, all of which recover after unloading.

Real-time wide-angle and small-angle X-ray scattering allows structural evolution to be monitored while the fibers are stretched. These measurements reveal reversible changes in crystal orientation, lattice parameters, and lamellar long period, providing direct insight into how molecular-scale and nanoscale structural changes produce macroscopic elasticity.

The fibers are fabricated using a microcrystal nucleation drawing process. After melt spinning, the polymer is rapidly cooled below its glass transition temperature, held near that temperature for a controlled period, and then drawn. The holding time strongly influences pore formation, allowing the internal porous structure to be tailored.

The pores deform during stretching by increasing their aspect ratio while remaining largely discontinuous within the fiber. This pore deformation supplements the reversible deformation of the polymer's hierarchical structure, contributing to the overall extensibility without fundamentally changing the elastic recovery mechanism.

The combination of elasticity and controlled porosity improves knot performance. Elastic recovery helps tighten the knot automatically, while collapse of the internal pores reduces knot size. Smaller, more secure knots can lessen the amount of implanted material and potentially reduce tissue irritation while maintaining reliable fixation.

High-resolution laboratory X-ray computed tomography provides non-destructive visualization of the internal pore structure before and after knot formation. The technique clearly shows pore collapse within the knot while confirming that pores remain intact outside the compressed region, directly linking internal structural changes to functional performance.