3D-Printed Enzyme-Embedded Plastics

Abstract

A simple and environmentally friendly approach toward the thermoplastic processing of rapidly degradable plastic-enzyme composites using three-dimensional (3D) printing techniques is described. Polycaprolactone/Amano lipase (PCL/AL) composite films (10 mm × 10 mm; height [h] = ∼400 μm) with an AL loading of 0.1, 1.0, and 5.0% were prepared via 3D printing techniques that entail direct mixing in the solid state and thermal layer-by-layer extrusion. It was found that AL can tolerate in situ processing temperatures up to 130 °C in the solid-state for 60 min without loss of enzymatic activity. The composites were degraded in phosphate buffer (8 mg/mL, composite to buffer) for 7 days at 37 °C and the resulting average percent total weight loss (WLavg %) was found to be 5.2, 92.9, and 100%, for the 0.1, 1.0, and 5.0% films, respectively. The degradation rates of PCL/AL composites were found to be faster than AL applied externally in the buffer. Thicker PCL/AL 1.0% films (10 mm × 10 mm; h = ∼500 μm) were also degraded over a 7 day period to examine how the weight loss occurs over time with 3.0, 18.1, 36.4, 46.4, and 70.2% weight loss for days 1, 2, 3, 4, and 7, respectively. Differential scanning calorimetry (DSC) analysis shows that the film’s percent crystallinity (D xtal%) increases over time with D xtal% = 46.5 for day 0 and 53.1% for day 7. Scanning electron microscopy (SEM) analysis found that film erosion begins at the surface and that water can penetrate the interior via surface pores activating the enzymes embedded in the film. Controlled release experiments utilizing dye-loaded PCL/AL/dye (AL = 1.0%; dye = 0.1%) composites were degraded over a 7 day period with the bulk of the dye released by the fourth day. The PCL/AL multimaterial objects containing AL-resistant polylactic acid (PLA) were also printed and degraded to demonstrate the application of this material on more complex structures.

Microbial enzymes will offer limited solutions to the global plastic pollution crisis

“…Nevertheless, very promising examples have been published recently for poly‐(L‐lactic acid) (PLA) films and for using embedded proteinase K for self‐degradation (Huang et al, 2020 ). Recently, a very convincing study has demonstrated that using 3D printing with a lipase implemented in PCL as composite films could be a highly attractive technological advancement (Greene et al, 2021 ). Furthermore, the implementation of lipase and/or proteinase K as nano‐dispersed enzymes into PCL and PLA films was shown to be a highly efficient and advanced technology for polymer degradation (DelRe et al, 2021 ).…”

Advances in 3D Gel Printing for Enzyme Immobilization

“…However, depending on the ultimate application goals, entrapping enzymes inside the thermoplastic matrix may be beneficial. Greene et al [ 82 ] mixed solid-state lipase enzyme powder together with dry ground polycaprolactone (PCL) powder and melt-extruded the “thermal paste” in an FDM-like 3D printer. Dry solid enzymes were able to well tolerate the 130 °C processing temperature for 60 min.…”

Trends in Polymer Degradation Across All Scales

“…[ 61 ] An elegant strategy from the research team around Greene utilized heat stable Amano lipase which displayed enzymatic activity even after exposure to 130 °C for 60 min. [ 62 ] Mixing of enzyme and PCL in the solid‐state and thermal layer‐by‐layer extrusion enabled successful 3D printing of enzyme embedded plastics. Importantly, enzyme embedded thin films degraded significantly faster compared to external addition of the same enzyme and enabled 100% weight loss after 7 d in an aqueous buffer at 37 °C.…”

“…Degradation rates of polyesters often depend on the ratio of crystalline to amorphous sections [ 70 ] and crystalline domains are often left untouched by embedded enzymes. [ 62,71 ] For example, a lipase derived from L. plantarum with Tween 20 in chloroform for dispersion into PCL matrices resulted in enzymatic activity predominantly on the amorphous regions of the PCL films. This was confirmed by measuring the crystallinity of the material, showing an increase from 39% to 95% over 8 d as a strong indicator that the crystalline segments are not degraded.…”