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Page 18 of 27 He et al. Soft Sci 2024;4:37 https://dx.doi.org/10.20517/ss.2024.32

Osteoarthritis affects millions of people worldwide. Synergistic therapy provides long-term joint lubrication
without shear thinning and mitigates systemic toxicity associated with oral administration. Wu et al.
[110]
developed a core-shell MOFs-based hydrogel . The poly(N-isopropylacrylamide) (pNIPAm) can be
programmatically grown on the surface of the MOFs. The reversible swelling and collapsing behavior of the
composites can be controlled by temperature, allowing for thermal-responsive drug release. When utilized
as water lubrication additives, the composites significantly reduce the coefficient and wear volume. In cell
culture studies with HeLa and BEAS-2B cells, the composites demonstrated excellent biocompatibility.
Additionally, cobalt (Co) ions are known to promote angiogenesis and bone regeneration. Sun et al.
fabricated 2-ethylimidazole (eIm)-doped ZIF-67 and furtherly create nanocomposite hydrogels . By
[111]
changing the linker composition, the releasing of the Co ions from the nanocomposite hydrogels can be
controlled, and hybrid hydrogels can release Co ions for up to 21 days. The in vitro study demonstrates that
the nanocomposite hydrogels can promote bone regeneration and show their neovascularization abilities
and good biocompatibility.

The challenges in tumor treatment, such as incomplete tumor removal and systemic toxicity, limit its
[112]
effectiveness. Kaur et al. fabricated plasmonically active hydrogels that can controllably release drugs .
The plasmonic hydrogels showed viscoelastic and self-healing properties due to the interaction between
ZIF-8 and carboxymethyl CS. Benefiting from the size of ultrasmall gold nanoparticles, the nanoparticles
can be checked in the urine, which proves the PHG can be degraded. Light is used wildly on the treatment
of the tumor including photothermal therapy and photodynamic therapy. Li et al. encapsulated liquid metal
[eutectic gallium indium (EGaIn)] nanoparticles in the MOFs (ZIF-8) and fabricated nanoparticle
composite materials [liquid metal supraparticles (LMSPs)] . The nanoparticles possess the performance of
[113]
stable photothermal and controllable Zn(II) ions releasing. Furthermore, they combined LMSPs with
alginate-based hydrogels to fabricate injectable hybrid hydrogels. The hybrid composite hydrogels
performed at the capacity of safety, stability and biodegradation. Zhang et al. reported MOFs-based
hydrogels as intelligent nanobots [FeSe –Ce6/MOF@Aichi hemagglutinin/polyethyleneimine/
2
CpG@hexahydrophthalic anhydride nanoparticles (FSMH)] that can the intracellular redox balance and
[114]
trigger the immune response in cancer cells . The FSMH can convert hydrogen peroxide into hydroxyl
radicals, thereby reducing intracellular oxidative stress. The negative charges on the hydrogel ensure the
system remains highly stable in blood circulation. Unlike traditional MOF materials, beta-cyclodextrin-
based MOFs offer brilliant properties compared to conventional MOFs. Shao et al. integrated beta-
cyclodextrin-based MOFs with polymers to fabricate two complexes with distinct morphologies and
structures . By employing the hydrophobic molecule curcumin, the hybrid materials are proven to possess
[115]
the ability to stabilize the included drug and controll the drug releasing .
[116]
Other application
The application of MOF-based hydrogels has expanded beyond the above uses, demonstrating versatility in
various fields. This section highlights several innovative developments in MOF-based hydrogels for
different applications.

One notable example is the use of 3D printing technology. Liu et al. developed stretchable and tough MOF-
based hydrogels by combining hydrogels with MOF ligands to create 3D printing ink. They characterized
the ink and optimized parameters to adjust the modulus, strength, and toughness of the printed
structures . Similarly, Zhang et al. created MOF-802@PVA hydrogel composites that exhibit excellent
[117]
proton conductivity and stability, making them promising for energy-related applications, although
conductivity decreases at higher temperatures .
[118]