3D printed architected lattice structures by material jetting

1. Introduction

• Architected lattices seek to retain strength and stiffness at low weight, with potential economic, energy, and environmental savings.The introduction frames these designs as inspired by natural structures such as bones and teeth.Source: §1 · p. 2
• The review focuses on recent architected lattice studies using photopolymer Material Jetting, especially commercial Polyjet and MultiJet techniques.It also considers their high resolution, rigid and soft curable resins in one print, morphing capabilities, and simplified post-processing.Source: §1 · p. 2
• The review covers MJ process effects, lattice experiments and models, manufacturing challenges, and mechanical-performance comparisons using Ashby plots.Its lattice survey distinguishes single-material designs from multi-material designs, including reinforced, graded, and active structures.Source: §1 · p. 3

2. Material Jetting (MJ) technology overview

• MJ produces parts with 13–16-micron layers and ±0.06–0.1% accuracy for lengths under ≈100 mm, but tray size is <1 m and minimum wall thickness should be >= 0.6 mm.Compared with material extrusion, MJ has less surface roughness, fewer staircase defects, and less waste; thin features may be fragile or warp during post-processing.Source: §2 · p. 3
• MJ printers deposit base and support droplets concurrently, level layers with a roller and wiper, then harden them using UV curing.Higher UV energy increases polymerization and cross-linking density, influencing resin glass-transition temperature.Source: §2 · p. 3
• Typical MJ resins have a Tg of about 50°C, so printed parts may show viscoelastic behavior at ambient temperature.Part orientation affects the relaxation modulus E(t), which also varies over time; low-viscosity resins facilitate nozzle flow and spreading.Source: §2 · p. 4
• Polyjet uses soluble gel supports, while MultiJet uses bulk wax supports, so their removal methods and cleaning conditions differ.For thin or intricate Polyjet lattices, chemical support removal requires visual inspection to protect fragile features; MultiJet wax is removed with heat and solvent baths.Source: §2 · p. 4
• MJ can combine polymers with different stiffness or color in one print, and commercial resins range from near 200% elongation at break for rubber-like resins to 10% for plastics.Polymer-rubber combinations span Shore hardness A30–A95, though some resins have poor mechanical performance and degrade over time.Source: §2 · p. 4
• Current photocurable materials are generally not eco-friendly or recyclable, and the available MJ resin range remains limited.Bio-based monomers, photocurable bio-resins, and cell-laden hydrogels are among the alternatives under investigation.Source: §2 · p. 4

3.1. Architected lattice materials overview

• Stretch-dominated lattices offer high initial strength and stiffness, while bending-dominated lattices reach larger strains and sustain extended post-yield stress plateaus.Relative density, nodal connectivity, effective Young’s modulus, yield strength, and fracture strength are identified as factors controlling lattice properties.Source: §3.1 · pp. 4–5

3.2. Material jetting process effects on mechanical properties of 3D printed lattices

• Print orientation, UV curing, post-processing, and storage conditions affect material and lattice performance, despite material jetting’s relatively low reported anisotropy.Parts built parallel to the tray generally showed the highest tensile properties, while perpendicular builds had the lowest; flexible Tango+ and RGD8625 were exceptions for tensile modulus.Source: §3.2 · pp. 5–6

3.3.1. Rigid-based material architected lattices

• Interpenetrating FCC+RD lattices absorbed six times more energy than isolated FCC or RD structures, while single-material designs also tune strength, toughness, and porosity.Rigid-based examples include semi-plate lattices with enhanced load-bearing capability and TPMS scaffolds whose lower relative density reduced Young’s modulus by about 30% and yield stress by 10–20%.Source: §3.3.1 · pp. 6–7

3.3.2. Soft lattices and instability control

• Flexible lattices accommodate large deformations and use geometry and buckling behavior to tailor stiffness, deformation, and force response.Sea-sponge-inspired grids resisted buckling around 6% strain; other soft cellular structures activated multiple buckling modes while adjusting force and amplitude without extra fixtures or boundary conditions.Source: §3.3.2 · pp. 7–8

3.3.3. Auxetic and shape programmable lattices

• Auxetic designs exhibit tunable negative Poisson’s ratios, while heat-responsive structures can recover or transform shape under specified stimuli.Reported NPR ranges were approximately −0.1 to −0.7; a previously stretched shell changed from flat to closed-curved after about 80 seconds in contact with a heat source.Source: §3.3.3 · pp. 9–10

3.3.4. Wave propagation control lattices

• Material-jetted lattices have been used to prototype acoustic and optical devices and vibration-control structures, including metastructures with bandwidth improved up to 160%.Examples include 40 kHz airborne-ultrasound lenses, dielectric beam-steering lenses, and tunable sinusoidal lattices with multiple band gaps.Source: §3.3.4 · p. 10

3.4. Multi-material 3D printed lattices

• Material jetting combines photopolymers in one print, producing strong interfaces and smooth property transitions for reinforced and multifunctional lattices.Soft infills in glassy lattices delay densification, with higher energy-absorption efficiency expected; distributions of rigid and rubbery phases can tune elastic modulus, Poisson’s ratio, and instability behavior.Source: §3.4 · p. 10, §3.4.1 · p. 10, §3.4.2 · pp. 10–11

3.4.3. Functionally graded and active lattices

• Functionally graded and active lattices use spatial material distributions and stimulus-responsive combinations to tune mechanical behavior and create morphing structures.Flexible-covered, rigid-core Voronoi struts improved energy absorption up to 38 times relative to single-material strut lattices without reducing stiffness and strength; graded auxetic patterns also prevented wrinkles and lateral displacement at the elbow during bending.Source: §3.4.3 · pp. 11–12

4.1. MJ architected lattices: Printing process and experimental work challenges

• MJ-specific defects, anisotropy, curing, and post-curing can separate model predictions from measured lattice properties, motivating broader tests and constitutive modeling.The review also identifies fatigue, aging, large-strain behavior, failure, dynamic loading, and multimaterial-interface validation as research needs.Source: §4.1 · pp. 12–13

4.2.1. Geometrical limits

• Horizontal ligaments below 1 mm bent during jetting, and 0.5 mm ligaments broke readily during support removal; 1 mm provided a safer geometry margin.The tested cubic lattices used VeroBlack and SUP706B on a Stratasys J750 with heavy grid support.Source: §4.2.1 · p. 14, Figure 10 · p. 15

4.2.2. Cost analysis

• For 4×4×4 octet lattices, estimated MJ cost was 3.67 $/cm3 in High-Mix Glossy mode, and printing took 25.92–48.65 hours versus 123.12–290.93 hours for FDM.The estimate included model and support materials, energy, and machine depreciation; labor and additional post-processing costs were excluded.Source: §4.2.2 · pp. 14–15
• For High-Mix Glossy printing, the 4×4×4 octet lattice cost about $3.67/cm3 versus $9.46/cm3 for a unit cell, making series production more cost-effective.MJ layer heights were 14–27 microns, compared with 0.05–0.15 mm for the FDM modes considered.Source: §4.2.2 · pp. 14–15
• At near-full tray capacity, estimated MJ cost was $2.60–$2.87/cm3, about 30–40% below the smaller 4×4×4 lattice.The review attributes the reduction to more objects being fabricated during a single horizontal print-head pass.Source: §4.2.2 · p. 15

4.3. MJ architected lattices: outcomes and potential

• Single-material lattices approached the stiffness of metal foams and biomaterials, while graded TPMS combined foam-like modulus with lower density.Some MJ lattices also showed yield strengths exceeding metal and ceramic foams at comparable density.Source: §4.3 · p. 16
• SEA reached 30 J/g in tailored honeycombs and radially graded TPMS, while several lattice types achieved toughness comparable to foams and some ceramics.Reported MJ lattice SEA exceeded values for polymeric or metal foams and steel tubes.Source: §4.3 · p. 16, Figure 12 · p. 17
• MJ lattices also exhibit tunable Poisson’s ratios and shape programmability, with proposed vibration-control applications requiring further research.Reported Poisson’s ratios range from 0 to -0.4 in flexible digital-material lattices, and from 1 to -0.5 in hierarchical honeycombs.Source: §4.3 · p. 17

5. Concluding remarks

• The review compares MJ lattice properties with existing materials in Ashby plots and reports modulus, yield strength, and density approaching biomaterials and high-performing elastomers.Reported toughness ranges were close to those of foams.Source: §5 · pp. 17–18
• Biomedical and energy-absorption applications are the most achieved design targets, while shape-programmable materials and vibration-control devices remain future research targets.The review also identifies UV intensity during curing and aging effects as areas needing more experimental work.Source: §5 · p. 18
• Despite high printing costs, MJ offers high resolution, reduced anisotropy, multimaterial printing, and cost effectiveness for series production or full-tray capacity.The conclusion also calls for more sustainable alternatives, including novel bio-resins.Source: §5 · p. 18

6. Funding

• SM, NMP, and DM acknowledge support from the European Commission under the H2020 FET Open “Boheme” grant No. 863179.Source: §6 · p. 18
• SM, NMP, and DM also acknowledge the Italian Ministry of Education, University and Research “Departments of Excellence” grant L. 232/2016.Source: §6 · p. 18
• DM acknowledges ERC-ADG-2021-101052956-BEYOND financial support.Source: §6 · p. 18

A.1 MJ technology

• This review focuses on PolyJet and MultiJet, two photopolymer-based MJ techniques.Both are used to manufacture automotive, aerospace, and medical components.Source: §A.1 · pp. 21–22
• MJ nozzles deposit photopolymer droplets as voxels onto a build tray, where UV light cures them; support grids hold overhangs and floating parts.PolyJet uses soluble gel supports, while MultiJet uses wax supports removed by heat.Source: §A.1 · p. 22
• Support removal and UV curing can affect dimensional precision and mechanical properties, while fast, uniform curing is needed for bonding across layers.The section notes that alkaline cleaning solutions can adversely affect final part properties.Source: §A.1 · p. 22
• Curing thickness depends on surface light energy, critical energy, and penetration depth, informing layer increments and UV settings for resolution.The section gives hc = Dp · ln(El ÷ Ecr).Source: §A.1 · p. 22

A.2 Manufacturing process e

• MJ can combine rigid and soft photopolymers into hybrids with intermediate stiffness or flexibility and varied hardness; Table 3 covers common Polyjet and MultiJet base materials.The passage also names these hybrids Digital Materials, Multi-Material Composites, and Functionally Graded Materials, with viscoelastic properties varying by particle distribution.Source: §A.2 · p. 22, Table 3 · p. 23
• Compressive-dominated lattices made from rigid VeroWhite are recommended over bending-dominated lattices for improved strength or energy absorption.Build orientation, strut buckling, and scaling effects also affect lattice performance.Source: §A.2 · p. 23
• Aging in glassy photopolymers increased ultimate tensile strength while reducing elongation at break; fatigue behavior remains difficult to link to process parameters.Surface flaws, voids, and shear forces tend to reduce fatigue life at elastomeric and multi-material interfaces; glossy finishes and crack orientation also affect fatigue behavior.Source: §A.2 · p. 23
• A 60.86% time saving was reported for 30-micron high-speed printing versus 16-micron high-quality-matte models, alongside enhanced interlayer bonding but reduced resolution.Source: §A.2 · p. 24

B.1 3D printing techniques

• Micro-stereolithography can produce structures at resolutions close to 5 microns.Source: §B.1 · p. 24
• Photopolymerization techniques used to print metamaterials at the microscale include SPPW, TPL, and CLIP.Source: §B.1 · p. 24
• For metals, SLS, SLM, EBM, and DED are identified as widely used techniques.Source: §B.1 · p. 24

B.2 Manufacturing effects on lattices

• Offset nodes, strut waviness, incomplete struts, roughness, and residual porosity are manufacturing imperfections that can reduce mechanical performance through stress and strain concentrations.Source: §B.2 · p. 24
• Anisotropy is reported at approximately 50% for FDM, 10% for SLS, 1% for SLA, and 2% for MJ, varying by technique.Source: §B.2 · p. 24
• Further research is needed to develop accurate models of printing defects; photopolymerization findings and methods may extend to MJ for estimating mechanical performance.Source: §B.2 · p. 24

Appendix C Cost estimation of architected lattices via MJ

• The case study estimates MJ costs for a 30×30×30 mm octet-truss unit cell and its 4×4×4 lattice arrangement using a Stratasys J750 and GrabCAD Print.The unit cell has a real volume of 5.33 cm3, and the lattice arrangement has a real volume of 341.30 cm3.Source: Appendix C · p. 24
• The MJ estimate includes material waste, printing energy, machine depreciation, and one hour of labor, using late-2021 Italian material and machine prices and March 2022 energy prices.The estimate uses a waste factor of 1.76 and assumes eight-year depreciation, 57% annual utilization, and a technician wage of $15 per hour.Source: Appendix C · pp. 24–25
• FDM costs are estimated for the same samples using a Prusa i3 MK3S, two layer-thickness settings, Prusament PC Blend filament, and soluble supports.Printing time and material weights were estimated with Prusa Slicer.Source: Appendix C · p. 25

Appendix D Constitutive models for material jetting architected lattices

• Table 4 groups finite-element models by printing material.Its caption identifies the table’s scope as models used to simulate the mechanical response of material-jetting architected lattices.Source: Table 4 · p. 25
• Flexible Arruda–Boyce models are listed for FLX9795-DM, Tango+ [120], Agilus30, TangoBlack, and FLX95595-DM.Source: Appendix D · pp. 25–26
• Other entries list Neo-Hookean models for FLX985 and FLX9795-DM, Hyperfoam for Tango+ [96], and a nonlinear Weeger et al. model for Tango+.Source: Appendix D · pp. 25–26

• Other reported functions include stiffness in one direction with high compliance in others, and tunable Poisson’s ratio and programmable shape changes.Source: Appendix E · pp. 27, 29
• Reviewed applications include medical implants and scaffolds, impact and crash devices, soft robotics, and vibration isolation.Source: Appendix E · pp. 27–28
• Tuning the gradient yields high energy-absorption efficiency in architected lattices.Source: Appendix E · p. 27
• Some lattices achieve higher strength and energy-storage levels than truss topologies.Source: Appendix E · p. 27
• Lattice outcomes include energy absorption through plastic dissipation and mitigation of acoustic effects.Source: Appendix E · pp. 27–28
• Soft-lattice designs report variable negative Poisson’s ratio, improved stiffness and fracture toughness over open-cell foams, and high indentation resistance.Source: Appendix E · p. 28
• Sinusoidal-strut lattices enable multiple and omnidirectional bandgaps tailored for wave-propagation control.Source: Appendix E · p. 30

Appendix E Relevant aspects of the reviewed material jetting architected lattices

• Meta-structures provide scale-independent elastic-wave control, wide- and ultrawide-band attenuation, and multiple tunable low-frequency band gaps.The cited outcomes also include control in all directions and underwater acoustic applications.Source: Appendix E · p. 30
• Void and geometric features control buckling and Poisson’s ratio, including negative ratios under low compression and controlled zero-energy behavior.The ratio is described as tunable across directions and by geometrical features.Source: Appendix E · pp. 30–31
• Interpenetrating composites with rubbery matrices improve properties, while auxetic lattices show enhanced strength and energy absorption.The passages also report improved energy absorption for cellular composites.Source: Appendix E · p. 31
• Graded bending-dominated lattices improve energy absorption by up to 38 times compared with single-material counterparts.The passages describe this as an energy-absorption improvement.Source: Appendix E · pp. 31–32
• Architected lattices enable tunable negative thermal expansion coefficients and are described as resistant to thermal fatigue.The passages indicate that the coefficients can be extended to any direction.Source: Appendix E · p. 32
• Printing effects, orientation, and scaling significantly affect mechanical properties; hierarchical deformation can dissipate energy while preserving shape.The passages identify anisotropy among the printing effects considered.Source: Appendix E · p. 33