Key Takeaways & Executive Findings
- •• Self-reinforced network of metal-organic frameworks nanoparticles significantly improved the mechanical strength and durability of the hydrogel. • Biomimetic lubricating hydrogels with architectural and compositional gradients enabled by multi-material 3D printing. • Slippery hydrogel meniscus substitutes with complicated gradient structures and reliable cushioning layers were manufactured. • The gradient architecture stiffness can be modulated by controlling the spatial distribution of MOFs, achieving low friction (~0.1141) and high fracture strength (~2.50 MPa).
Abstract
The development of gradient lubrication materials is critical for numerous biomedical applications, particularly in magnifying mechanical properties and service longevity. Herein, we present an innovative approach to fabricate biomimetic gradient lubrication hydrogel through the synergistic integration of three-dimensional (3D) printed metal–organic frameworks (MOFs) nanoparticle network hydrogel skeletons with bio-inspired lubrication design. Specifically, robust hydrogel skeletons were engineered through single or multi-material 3D printing, followed by the in situ growth of MOFs nanoparticles within this hydrogel network to create a reinforced, load-bearing architecture. Subsequently, biomimetic lubrication capability was enabled by mechanically coupling another lubricating hydrogel within 3D-printed MOFs nanoparticle network hydrogel skeleton. The superficial layer is highly lubricious to ensure low coefficient of friction (~ 0.1141) and wear resistance (40,000 cycles), while the deeper layer is stiffer to afford the obligatory mechanical support (fracture strength ~ 2.50 MPa). Furthermore, the gradient architecture stiffness of the hydrogel can be modulated by manipulating the spatial distribution of MOFs within the 3D-printed hydrogel skeleton. As a proof-of-concept, biomimetic gradient hydrogel meniscus structures with C- and O-shaped configurations were constructed by leveraging multi-material 3D printing, demonstrating exceptional lubrication performance. This innovative biomimetic design opens new avenues for creating implantable biomedical gradient lubricating materials with reinforced mechanical and lubrication performance.
1. Introduction
Hydrogels, composed of water-filled, three-dimensional cross-linked polymer chains, have been extensively investigated for their unique properties, such as high water content, tunable mechanics, and favorable biocompatibility [1–3]. Moreover, hydrogel’s attributes like soft, wet, and slippery resemble biological tissues, making them an ideal candidate for multitudinous biomedical applications [4–6], particularly in tissue replacements and artificial organs [7, 8]. Despite these benefits, however, conventional hydrogels often suffer from drawbacks in mechanical strength, wear resistance, and durable lubrication, which restricts their usability in many applications, particularly those involving repetitive, dynamic, and long-term load-bearing circumstances.
To overcome these limitations, several approaches have been developed to ameliorate the performance of hydrogels, such as microphase separation [9, 10], hydrogen bond [11, 12], crystalline domain [13–15], and reinforcement with nanomaterials [16]. Surprisingly, the incorporation of nanomaterials or nanoparticles into the hydrogel network will exceedingly strengthen their mechanical properties. Among the numerous hydrogel’s nanoparticle reinforcements, the integration of MOFs nanoparticles into hydrogels enables the establishment of self-reinforcing networks, which is considerably beneficial in strengthening the overall mechanical strength and load-bearing capacity [17–19]. Furthermore, the MOFs network within the hydrogel is more resistant to deformation under mechanical stress, which is conductive to mitigate wear and reduce friction [20, 21]. Therefore, the self-reinforcing nature of the MOFs nanoparticles is a critical factor in the durability and longevity of the hydrogel.
Unlike much prior research that primarily exploit MOFs nanoparticles as reinforcing fillers [22, 23], here the MOFs nanoparticle network serves as a multifunctional cross-linking point within the hydrogel matrix that enables the significant enhancement of the mechanical performance of engineered hydrogels. To date, the fabrication of MOFs nanoparticle-reinforced hydrogels can be achieved through several manners, including in situ growth of MOFs within the hydrogel matrix, or by embedding pre-synthesized MOFs into the hydrogel network [24–26]. While the integration of MOFs within the hydrogel network is able to reinfo...
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Desheng Liu, Yixian Wang, Changcheng Bai, Danli Hu, Xingxing Yang, Yaozhong Lu, Tao Wu, Fei Zhai, Pan Jiang, Xiaolong Wang, Weimin Liu (2026). Biomimetic Gradient Lubrication Hydrogel Contrived by Self-Reinforced MOFs Nanoparticle Network. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-02001-x
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Frequently Asked Questions
What is the main innovation of this hydrogel?
The main innovation is the use of a self-reinforced MOFs nanoparticle network within a 3D-printed hydrogel skeleton, which significantly enhances mechanical strength and durability while providing biomimetic gradient lubrication.
How was the gradient lubrication achieved?
The gradient lubrication was achieved by mechanically coupling a lubricating hydrogel layer onto a 3D-printed MOFs-reinforced hydrogel skeleton, creating a superficial low-friction layer and a stiffer deeper layer for mechanical support.
What are the key performance metrics of the hydrogel?
The hydrogel exhibits a low coefficient of friction of approximately 0.1141, wear resistance over 40,000 cycles, and a fracture strength of about 2.50 MPa.
What applications could this hydrogel have?
This hydrogel is particularly suited for biomedical applications such as implantable meniscus substitutes, where both lubrication and mechanical support are critical.
How is the stiffness gradient controlled?
The stiffness gradient is controlled by manipulating the spatial distribution of MOFs within the 3D-printed hydrogel skeleton, allowing for tailored mechanical properties.
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