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Page 4 of 33 Ren et al. Soft Sci. 2026, 6, 6

Figure 2. Schematic illustration of (A) DIW, (B) FDM, (C) SLA, (D) DLP, and (E) TPP. DIW: Direct ink writing; FDM: fused deposition
modeling; SLA: stereolithography; DLP: digital light processing; TPP: two-photon polymerization; PNG: portable network graphics.

Table 1. Quantitative metrics of common AM techniques used in soft microrobotics
Representative lateral Representative layer
Method Representative speed Ref.
feature size thickness
DIW ~100-1,200 μm ~10-300 μm ~1-100 mm/s Sol et al. [24]
FDM ~200-800 μm ~100-300 μm mm/s-tens of mm/s Dezaki et al. [25]
Layer-by-layer; generally higher throughput
SLA ~10-50 μm ~10-100 μm Paunović et al. [26]
than serial micro-writing
Layer-by-layer projection; often faster than
DLP ~25-100 μm ~10-100 μm Chaudhary et al. [27]
scanning approaches
Serial writing; high precision but limited
TPP ~0.1-1 μm ~0.1-2 μm Ren et al. [28]
throughput
AM: Additive manufacturing; DIW: direct ink writing; FDM: fused deposition modeling; SLA: stereolithography; DLP: digital light processing; TPP:
two-photon polymerization.

Cheng et al. employed alginate as a biocompatible rheological modifier to fabricate free-form structures of
chemically and physically crosslinked hydrogels using the DIW method, thereby overcoming fragility and
mold-constrained geometries . By co-tuning ink composition and tool paths, they achieved biomimetic
[49]
prototypes such as moving tentacles, beating and pumping heart structures, and phototactic tendrils,
collectively demonstrating geometric multifunctionality, mechanical tunability, and stimulus-response-
driven behavior. Sol et al. synthesized a humidity-responsive cholesteric liquid crystal oligomer ink and
demonstrated printed devices that combine structural color with processable actuation . By controlling
[24]
post-processing and local environments, they achieved hydrochromic coatings on complex 3D shapes and
scallop-like actuators that reversibly open and close under alternating wet and dry conditions. Extending
functionality toward system-level integration, Zhang et al. formulated ion-conducting, electroluminescent,