The 3D Printing of Freestanding PLLA Thin Layers and Improving First Layer Consistency through the Introduction of Sacrificial PVA

Abstract

Fused filament fabrication (FFF) is an inexpensive way of producing objects through a programmed layer-by-layer deposition. For multi-layer, macro-scaled prints, acceptable printing is achieved provided, amongst other factors, first layer adhesion is sufficient to fix a part to the surface during printing. However, in the deposition of structures with a single or few layers, first layer consistency is significantly more important and is an issue that has been previously overlooked. As layer-to-bed adhesion is prioritised in first layer printing, thin layer structures are difficult to remove without damage. The deposition of controllable thin structures has potential in tissue engineering through the use of bioactive filaments and incorporation of microfeatures into complex, patient-specific scaffolds. This paper presents techniques to progress the deposition of thin, reproducible structures. The linear thickness variation of 3D-printed single PVA and PLLA layers is presented as a function of extrusion factor and the programmed vertical distance moved by the nozzle between layers (the layer separation). A sacrificial PVA layer is shown to significantly improve first layer consistency, reducing the onus on fine printer calibration in the deposition of single layers. In this way, the linear variation in printed single PLLA layers with bed deviation is drastically reduced. Further, this technique is used to demonstrate the printing of freestanding thin layers of ~25 µm in thickness.

Induced Birefringence in 3D Printing: Concealing Information Optically within Printed Objects

“…Single PLLA layers were printed on a PVA support layer detailed in our previous work. [ 25 ] Figure shows the measured birefringence of single PLLA layers for a range of programmed layer separations ( L PLLA = 50, 75, 100, and 125 µm) deposited at an extrusion factor e PLLA = 0.01 and print speeds v p = 1000, 2000, 4000, and 6000 mm min −1 . Birefringence is shown to increase with print speed across all layer separations.…”

“…The required printing speeds, in the range of thousands of millimetres per minute are quite high for an average printed part. Thirdly, the disconnect between extrusion feed rates and transverse printing speeds (addressed by the introduction of an extrusion factor previously [ 25 ] ) have made distinguishing the influence of parameters on part properties difficult. Fourthly, the difference in induced birefringence is only clearly distinguished at lower layer separations, owing to an increased strain rate during deposition.…”

“…Where the extrusion factor, e , ensures volume of extruded material is conserved across all print speeds [ 25 ] $$\[ \begin{array}{*{20}{c}}{e\;{\rm{ = }}\;{\rm{length}}\;{\rm{of}}\;{\rm{filament}}\;{\rm{extruded}}{\rm{/horizontal}}\;{\rm{nozzle}}\;{\rm{displacement}}}\end{array} \]$$…”

“…Deposition is controlled by an extrusion factor, which fixes the amount of material ejected by a print head (measured by the length of filament extruded) to the distance travelled by the print head across the printing surface. [ 25 ] In this way, variations in molecular alignment can be achieved without altering deposition dimensions. The alignment demonstrated here contrasts with that previously reported as it constitutes a transition in the accommodation of strain during deposition.…”

“…Current attempts which demonstrate steganography during 3D printing necessitate the altering of a 3D printed structure to encode this information, by either using different materials, omitting printing regions or selectively offsetting layers. [ 25–27 ] These techniques are not optimal, as variations through negative space, offsets or material changes weaken the printed structure with voids and compromising inter‐layer bonding. Alternatively, the optical properties of printed material can be harnessed to manipulate light to reveal data.…”