Paper Number
AC22 

Session
Additive Manufacturing and Composites

Title
Imparting extensibility to jammed colloidal inks for direct-ink-writing printability

Presentation Date and Time
October 13, 2022 (Thursday) 10:35

Track / Room
Track 7 / Ontario

Authors (Click on name to view author profile)

  1. Saengow, Chaimongkol (University of Illinois at Urbana-Champaign, Beckman Institute for Advanced Science and Technology)
  2. Wagoner Johnson, Amy J. (University of Illinois at Urbana-Champaign, Urbana, Mechanical Science and Engineering)
  3. Ewoldt, Randy H. (University of Illinois at Urbana-Champaign, Mechanical Science and Engineering)

Author and Affiliation Lines (in printed abstract book)
Chaimongkol Saengow1, Amy J. Wagoner Johnson2 and Randy H. Ewoldt2
1Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL 61801; 2Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Saengow, Chaimongkol

Keywords
experimental methods; additive manufacturing; biomaterials; composite rheology; jammed systems

Text of Abstract
We describe an experimental study of jammed colloidal inks for direct-write 3D printing used to fabricate implantable lattice-structured bone scaffolds. The inks consist of an aqueous suspension of hydroxyapatite particles (the main mineral of bone) sized 1-2µm which creates a paste-like yield-stress fluid, in addition to other stabilizing components, and an extra addition of particles of polymethyl methacrylate (PMMA, 5.96 ± 2.00µm in diameter) to create microporosity in the final structure. The PMMA particles are burned off to create the final microporous structure, thus giving rise to additional capillarity effects thought to improve cell incorporation in the implanted scaffold. This baseline formulation of ink is difficult to print due to brittle filament rupture if the nozzle speed is not closely matched to the average velocity of the extruded ink. Thixotropy and sample heterogeneity make the speed matching even more challenging throughout the printing session. Guided by the hypothesis that creating higher extensional viscosity and extensibility of yield stress fluids can enable more robust printing [1], we examine two methods to impart extensibility: (i) incorporating polymer additives, and (ii) coating particles with polyelectrolytes to increase interparticle attraction. Hydroxypropyl methylcellulose is used as the polymer additive, tested at different loading. Polyacrylic acid and polyethylenimine are coated onto the particles in a negative and positive manner, and pH is modulated to control extensibility. Our results show quantify how printability, e.g. in terms of speed tolerance, is improved by the ink extensibility, mapping printability to the rheological design requirements [2] of extensional strain-to-break and yield stress. [1] Rauzan, BM, AZ Nelson, RH Ewoldt, and RG Nuzzo, “Particle-free emulsions for 3D printing elastomers,” Advanced Functional Materials, 28, 1707032 (2018) [2] Ewoldt, RH, and C Saengow, “Designing complex fluids,” Annual Review of Fluid Mechanics, 54, 413-441 (2022)