Mechanical Enhancement of Bioinspired Polydopamine Nanocoatings

Abstract

Inspired by the catechol and amine-rich adhesive proteins of mussels, polydopamine (pDA) has become one of the most widely employed methods for functionalizing material surfaces, powered in part by the versatility and simplicity of pDA film deposition that takes place spontaneously on objects immersed in an alkaline aqueous solution of dopamine monomer. Despite the widespread adoption of pDA as a multifunctional coating for surface modification, it exhibits poor mechanical performance. Attempts to modify the physical properties of pDA by incorporation of oxidizing agents, cross-linkers, or carbonization of the films at ultrahigh temperatures have been reported; however, improving mechanical properties with mild post-treatments without sacrificing the functionality and versatility of pDA remains a challenge. Here, we demonstrate thermal annealing at a moderate temperature (130 °C) as a facile route to enhance mechanical robustness of pDA coatings. Chemical spectroscopy, X-ray scattering, molecular force spectroscopy, and bulk mechanical analyses indicate that monomeric and oligomeric species undergo further polymerization during thermal annealing, leading to fundamental changes in molecular and bulk mechanical behavior of pDA. Considerable improvements in scratch resistance were noted in terms of both penetration depth (32% decrease) and residual depth (74% decrease) for the annealed pDA coating, indicating the enhanced ability of the annealed coating to resist mechanical deformations. Thermal annealing resulted in significant enhancement in the intermolecular and cohesive interactions between the chains in the pDA structure, attributed to cross-linking and increased entanglements, preventing desorption and detachment of the chains from the coating. Importantly, improvements in pDA mechanical performance through thermal annealing did not compromise the ability of pDA to support secondary coating reactions as evidenced by electroless deposition of a metal film adlayer on annealed pDA.

Polydopamine-Lysophosphatidate-Functionalised Titanium: A Novel Hybrid Surface Finish for Bone Regenerative Applications

“…Significant peaks were present at all of the randomly selected points in the Raman spectra at Stokes shifts around the 1410cm −1 and 1590cm −1 . This is in keeping with previous reports (e.g., [29]) for PDA film deposition on Ti ( Figure 3A). These peaks were totally absent for the control Ti blank sample.…”

“…The high-resolution N1s analysis provides insight on the possible linking mechanism between FHBP and PDA, which is assumed to be a Schiff-base reaction ( Figure 3C-E). The N1s peaks were deconvoluted with three distinctive amine functional groups by referring to the previous report [29]: primary amine (R-NH 2 ) at 401.9 eV, secondary amine (R 2 -NH) at 399.9 eV and tertiary amine (=N-R) at 398.8 eV. As a result, we could identify the primary amine groups (16%) in the PDA structure ( Figure 3C), which should be originated from the un-indolised dopamine unit, as proposed by Liebscher et al [30].…”

Laser-induced graphitization of polydopamine leads to enhanced mechanical performance while preserving multifunctionality

“…At 500 µN, the scratch depth of a 37 nm thick LAPDA film was only 2.1 ± 0.8 nm, whereas the scratch depth of a pristine PDA film under the same conditions was the full thickness of the film (248 nm). This represents more than a 100-fold increase in scratch resistance, which is more effective than the conventional thermal annealing approach showing a 2.5-fold increase 16 . To further put the scratch resistance of LAPDA in perspective, we also performed scratching experiments on bare TiO 2 and quartz substrates at a load of 500 µN, producing average scratch depths of 16.8 ± 1.2 nm for TiO 2 and 10.5 ± 1.0 nm for quartz.…”

“…Many prior efforts have been made to address the aforementioned challenges. For example, posttreatment approaches have been proposed to transform mechanical characteristics of the PDA, including mild thermal annealing 16 , molecular integration of metal ions 17 , and introduction of a cross-linker 18 . However, even these methods do not offer dramatic improvements in wear resistance.…”

Bioinspired Interface Design of Sewable, Weavable, and Washable Fiber Zinc Batteries for Wearable Power Textiles

“…This is consistent with the results reported in the literature that as much as 20% of PDA comprises unpolymerized monomeric or oligomeric species. [37,38] Previous research showed that organic quinone-based electrode materials in AZBs may incline to www.afm-journal.de www.advancedsciencenews.com…”