Laser
carbonization of polymers is an emerging technique that enables
directly patterning conductive carbon electrodes for a plethora of
flexible devices, including supercapacitors and sensors. While these
laser-induced nanocarbon (LINC) patterns were previously shown to
have various hierarchical porous and fibrous graphene-based morphologies,
the fundamental mechanisms underlying the formation of specific LINC
morphologies is still largely missing. Here, we present a method for
lasing polyimide films with spatially controlled gradients of optical
energy flux. Combined with Gaussian beam modeling, our approach uniquely
enables continuously sweeping different laser fluence values as a
spatial map along the laser path. We find that above the fluence value
of 5 J/cm2, progressive carbonization and swelling results
in porous LINC. We also identify two additional thresholds that correspond
to morphological transitions: first, from isotropic porous morphology
to anisotropic networks at 12 J/cm2; second, from anisotropic
networks to aligned nanofibers at 17 J/cm2. Our results
show that anisotropic cellular networks are the most electrically
conducting and have the highest quality sp2 carbon. However,
the aligned woolly nanofiber morphology is electrically insulating
along the length of the lased lines, although they exhibit the highest
degree of carbonization with the least heteroatom content. Hence,
our results provide insights into the fluence-dependence of the physicochemical
processes underlying LINC formation. Moreover, our approach enables
generating a morphology diagram for LINC, which facilitates precise
tunability of both the morphology and properties of LINC patterns,
based on easy-to-control processing parameters, such as laser power
and degree of beam defocusing.
Spider major ampullate silk fibers have been shown to display a unique combination of relatively high fracture strength and toughness compared to other fibers and show potential for tissue engineering scaffolds. While it is not possible to mass produce native spider silks, the potential ability to produce fibers from recombinant spider silk fibers could allow for an increased innovation rate within tissue engineering and regenerative medicine. In this pilot study, we improved upon a prior fabrication route by both changing the expression host and additives to the fiber pulling precursor solution to improve the performance of fibers. The new expression host for producing spidroin protein mimics, protozoan parasite Leishmania tarentolae, has numerous advantages including a relatively low cost of culture, rapid growth rate and a tractable secretion pathway. Tensile testing of hand pulled fibers produced from these spidroin-like proteins demonstrated that additives could significantly modify the fiber’s mechanical and/or antimicrobial properties. Cross-linking the proteins with glutaraldehyde before fiber pulling resulted in a relative increase in tensile strength and decrease in ductility. The addition of ampicillin into the spinning solution resulted in the fibers being able to inhibit bacterial growth.
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