Direct sound printing

Abstract

Photo- and thermo-activated reactions are dominant in Additive Manufacturing (AM) processes for polymerization or melting/deposition of polymers. However, ultrasound activated sonochemical reactions present a unique way to generate hotspots in cavitation bubbles with extraordinary high temperature and pressure along with high heating and cooling rates which are out of reach for the current AM technologies. Here, we demonstrate 3D printing of structures using acoustic cavitation produced directly by focused ultrasound which creates sonochemical reactions in highly localized cavitation regions. Complex geometries with zero to varying porosities and 280 μm feature size are printed by our method, Direct Sound Printing (DSP), in a heat curing thermoset, Poly(dimethylsiloxane) that cannot be printed directly so far by any method. Sonochemiluminescnce, high speed imaging and process characterization experiments of DSP and potential applications such as remote distance printing are presented. Our method establishes an alternative route in AM using ultrasound as the energy source.

Fig. 1. DSP concept and printed parts.

a DSP process schematic. b Detailed view of UAMR, bubbles are created in low-pressure zones. c Printed “DSP” letters. c1 porous/transparent structure of the printed part (the scale bar is 200 μm). c2–4, SEM pictures of the microstructure of the printed parts (the scale bar is 100 μm). d Printed impellers, transparent and porous. e–h Printed maple leaf, gear, shell and honey comb, respectively. i Molded microfluidic channel using 3D printed PDMS mold. (HIFU: high-intensity ultrasound).

Fig. 2. Observation of UAMR during insonication of the build chamber.

a and b Front and side view of the observation setup which constitutes a high speed and DSLR camera. c and d Acoustic pressure in the build chamber, P, at h = 30 mm and h = 22 mm, respectively. e Footage from high-speed imaging (e1-a to e9-a) of area A and DSLR camera (e1-c to e9-c) for h = 30 mm where the acoustic focal is at the platform location (e1-b to e9-b are the magnified views of e1-a to e9-a, respectively) (DSLR: digital single-lens reflex, PCD: passive cavitation detector, UAMR: ultra-active micro reactor, PDMS: polydimethylsiloxane). f Footage from high speed imaging (f1-12) for h = 22 mm and v = 0. For all cases, f = 2.15 MHz, DC = 100%, and Power = 210 W.

Fig. 3. Porous and transparent printing observation of UAMR on the platform during insonication of the build chamber.

a–d Porous printing progress in progressive times. v = 300 mm/min, and h = 30 mm e–g Transparent printing progress in progressive times, v = 240 mm/min, Power=20 W, DC = 50%.(other experimental conditions are the same as Fig. 2). (UAMR: ultra-active micro reactor).

Fig. 4. Process, material and microstructure characterization.

a–d Raman spectrums of reference (molded) and printed PDMS for different mixing ratios. e and f IR bands comparison of Si-H (2162 cm⁻¹) and vinyl (1597 cm⁻¹) stretches for maxing ratio 13:1 and 17:1, respectively. g–i XY resolution investigation for mixing ratio 15:1. j–l XY resolution investigation for mixing ratio 10:1. m UV–Vis spectrum comparison among printed and molded specimen for different mixing ratios. n and o Samples of pore size distributions for printed objects in 10:1 ratio with frequencies 2 MHz and 3.1 MHz, respectively. Transducer H-316 (natural frequency: 2.5 MHz) is used for printing. p and q Stress–strain curves and Young’s Modulus comparison, respectively, of printed and molded specimen for different mixing ratios. r Microscopic picture of a Chlamydomonas reinhardtii at 7th day of cell culture of a printed petridish. s Cell concentration of Chlamydomonas reinhardtii after every day for 7 days for the printed and molded petridishes.

Fig. 5. Potential applications of DSP.

a Light-based AM and small cure depth for opaque printing materials. b DSP and deep penetration of ultrasound in opaque printing materials. c Printing opaque micro/nano composites by DSP. d The concept of an ideal DSP technology for noninvasive inside body printing. e in-vitro/ex-vivo prove of concept setup. f Tissue phantom of human skin and muscle. g A printed maple leaf using the tissue phantom. h Real porcine tissue compromising skin, fat and muscle. i Printed maple leaf using the porcine tissue. j and k Printed ear and nose using the tissue phantom. (HIFU: high-intensity focused ultrasound, UAMR: ultra-active micro reactor, PDMS: polydimethylsiloxane).