POHANG, South Korea — A research team at the Pohang University of Science and Technology (POSTECH) has achieved a breakthrough in material science by turning a common manufacturing defect into a functional advantage. Led by Professor Hyoung Seop Kim from the Graduate School of Green Materials and Energy, the team has developed a technique to double the adhesion strength between metals and polymers by precisely controlling surface roughness during the 3D printing process.

The "Velcro" Effect: Rethinking Surface Roughness
In traditional additive manufacturing, the "roughness" or uneven surface created by melting metal powder with lasers (Laser Beam Powder Bed Fusion, or PBF-LB/M) is typically viewed as a defect that requires costly post-processing to smooth out. However, the POSTECH team viewed these microscopic peaks and valleys as a "programmable element" rather than a flaw.

By meticulously adjusting laser power, scanning speed, and hatch spacing, the researchers successfully controlled the surface roughness of titanium alloys within a range of 20 to 70 micrometers ($mu m$). This allows for "spatial surface design," where different areas of a single component can have varying degrees of grip.

When a liquid polymer, such as Polydimethylsiloxane (PDMS), is applied to these engineered surfaces, it seeps into the microscopic crevices. As it solidifies, it creates a mechanical "interlocking" structure—much like the hook-and-loop mechanism of Velcro. This physical bond, combined with the increased surface area, resulted in an adhesion strength more than 200% higher than that of smooth surfaces.

Why It Matters: Hybrid Structures Without Chemicals
The ability to fuse rigid metals with flexible polymers is a "Holy Grail" for several high-tech industries:

Soft Robotics: Creating robots with rigid internal frameworks and flexible "skin" or actuators.
Medical Devices: Developing implants that require a firm metal base but must integrate seamlessly with soft human tissue.
Aerospace & Automotive: Reducing vehicle weight by replacing heavy bolts with integrated metal-polymer hybrid parts.
Traditionally, joining these disparate materials required complex chemical treatments or toxic primers, which are often difficult to apply to complex 3D shapes. The POSTECH method eliminates these steps, offering a cleaner, more streamlined production route for multi-material structures.

Global Recognition and Future Impact
"The core of this research is that we can significantly enhance bonding performance simply by managing the textures that naturally occur during 3D printing," noted Professors Anna Lee and Dong-Sik Kim of the Department of Mechanical Engineering.

Professor Hyoung Seop Kim added that this technology opens new doors for "hybrid structural design," allowing engineers to customize the bonding strength of different sections within a single integrated part.

The study, supported by the National Research Foundation of Korea and the Ministry of Science and ICT, was recently published in Virtual and Physical Prototyping, a leading international journal in manufacturing and production engineering. As 3D printing moves toward mass production, this "innovation through imperfection" is expected to set a new standard for how we build the machines of tomorrow.