Engineering macrophage responses through 3D scaffold microarchitecture.

Area of Science:

• Biomaterials Science
• Immunology
• Tissue Engineering

Background:

• Biomaterial implantation triggers foreign body reaction, involving macrophage polarization into M1 (pro-inflammatory) or M2 (anti-inflammatory) phenotypes.
• Controlling macrophage behavior is crucial for tissue regeneration, with growing interest in tailoring biomaterial physical properties.
• The role of 3D microstructures in modulating macrophage behavior and immune responses remains unclear.

Purpose of the Study:

• To investigate how 3D scaffold microstructure, specifically pore size, influences macrophage behavior and polarization.
• To determine if 3D microstructures can be engineered to promote desired immune responses for tissue engineering and drug development.

Main Methods:

• Fabrication of 3D scaffolds with distinct large (50 × 50 × 20 μm³) and small (15 × 15 × 15 μm³) pores using two-photon polymerization.
• Assessment of macrophage cytoskeletal organization and metabolic activity in response to the scaffolds.
• Evaluation of macrophage polarization markers (Arg1 and iNOS) under combined scaffold and chemical stimulation.

Main Results:

• Both large and small pore scaffolds influenced macrophage cytoskeletal organization and metabolic activity.
• The scaffolds alone were immunologically inert and did not induce spontaneous macrophage polarization.
• In combination with chemical stimuli, large pores slightly upregulated anti-inflammatory Arg1, while small pores markedly increased pro-inflammatory iNOS expression.

Conclusions:

• 3D microstructures offer tunable control over macrophage behavior, distinct from intrinsic material properties.
• Precisely engineered 3D scaffolds can balance pro- and anti-inflammatory macrophage phenotypes.
• These findings open avenues for 3D scaffolds in *in vivo* tissue engineering to prevent fibrosis and in *in vitro* platforms for anti-inflammatory drug screening.