Terry W. J. Steele

Colloidally stable, citrate-functionalized Mn–Zn ferrite nanoparticles deliver kilowatt per gram heating efficiency and enable induction curing of aqueous acrylate resins.

Magnetic induction heating of Curie nanoparticles (CNPs), termed “Spinheat”, offers a rapid, temperature-failsafe alternative to conventional curing of adhesives, which consumes substantial energy and requires prolonged heating. Mn−Zn ferrite CNPs combine tunable Curie temperatures (Tc) with heat generation under an alternating magnetic field (AMF), making them suitable transducers. An aqueous coprecipitation route was developed to prepare Mn−Zn ferrite (MnxZn1−xFe2O4, 0 ≤ x ≤ 1) CNPs, achieving a recovered-mass yield of ∼98%. Across the series of Mn−Zn ferrites, Tc was tuned from 107 to 334 °C, and the dry-state specific absorption rate (SAR) was correlated with composition, structure, particle and crystallite sizes, and magnetic properties. As-synthesized Mn0.9Zn0.1Fe2O4 (particle size ∼12 nm) exhibited the highest dry-powder SAR of 11 W/g at 140 Oe and 400 kHz (intrinsic loss power of 0.22 nH·m2/kg), exceeding prior dry-powder reports by more than tenfold. Annealing increased saturation magnetization but markedly reduced the SAR in the Mn-rich compositions, accompanied by particle growth from ∼5−15 nm to 300−400 nm. CNPs with Tc near 190 °C enabled 5 min induction curing of a commercial epoxy adhesive, achieving ∼19 MPa lap-shear strength (vs ∼15 MPa for oven curing), no discoloration, and ∼1.6% of the oven energy. These findings highlight the potential of Mn−Zn ferrite CNPs prepared via coprecipitation for rapid, energy-efficient adhesive and resin processing.

Antibacterial coatings are needed to reduce surface contamination in clinical and textile environments, but many existing antimicrobial coatings rely on the release of biocides, creating concerns about toxicity and antimicrobial resistance, or require metal ions, harsh chemicals, and complex multi-step fabrication processes that limit practical deployment. In this study, six catechol aldehyde isomers were grafted onto bactericidal branched polyethylenimine (bPEI) using Schiff-base click chemistry to create one-component, metal-free coating solutions. Upon exposure to air and moisture, these solutions crosslinked into quinone-based networks that formed uniform films on cellulose substrates through simple dip-coating. Evaluation using colony-forming-unit counts, zone-of-inhibition assays, and ¹H NMR leachate analysis distinguished contact-killing activity from antibacterial effects caused by diffusion. All coatings exhibited low leaching, losing no more than 7.6% of their mass after aqueous exposure, while maintaining antibacterial performance after brief water and ethanol rinses. Notably, the bPEI-g-(3,5-DBA) formulation matched the strong contact-bactericidal activity of unmodified bPEI, achieving more than a three-log reduction in bacterial count. The results demonstrate that catechol substitution patterns can be used to control the balance between diffusible and surface-retained antibacterial activity, offering a versatile strategy for designing durable, wash-resistant, air-activated antibacterial coatings.

Conventional strategies for upcycling plastic waste into high-performance materials are energy-intensive and lack precise thermal control.

Current photoinitiators like (diphenylphosphoryl)(mesityl)methanone (TPO) are being regulatory phased out due to issues related to solubility, cytotoxicity, and leaching. Diazirines, a class of three-membered-ring photoinitiators, have been identified to address limitations of solubility, leaching, and toxicity effects as compared to TPO. Herein, two water-soluble diazirines are exposed to human keratinocyte (Ker-CT) cells for cytotoxicity evaluation. Exposure conditions are limited to initiator concentrations of 0.17–17 mM before (0 J) and after (10 J) UVA irradiation. Diazirine benchmarked to TPO maintained >90% cell viability at concentrations up to 17 mM, compared to a 20% reduction with TPO at 0.17 mM post-UVA. (4-(3-(trifluoromethyl)-3H-diazirin-3-yl)phenyl)methanol and 4-(3-(trifluoromethyl)-3H-diazirin-3-yl)benzoic acid (DzOH and DzCOOH) did not elevate mitochondrial superoxide above baseline levels. Elevated intracellular ROS levels correlated to diazirine dose, which could be due to controlled oxidative signaling. DzOH exhibited potential mitochondrial superoxide scavenging behavior under stimulated conditions. Diazirine-derived diazoalkanes spontaneously react with acrylamide monomers to form stable, non-toxic pyrazoline structures. Thus, the benign side product of UVA exposure mitigates the cytotoxicity associated with residual acrylamide. Incorporation of these diazirines into poly(ethylene glycol) diacrylate (PEGDA) - 575 hydrogels resulted in biocompatible materials with tunable water content (0–80 wt %) and negligible toxic leachates. Furthermore, cytotoxicity studies revealed cell type–dependent responses, with HeLa cells showing greater sensitivity than keratinocytes, suggesting potential for selective biological interactions. Overall, this study highlights water-soluble diazirine photoinitiators with low cytotoxicity, reactive oxygen species-modulating properties, and intrinsic detoxification capability.

Catechol grafted macromolecules have attributes that overlap what's needed within non‐toxic bioadhesives. However, decades of research have failed to make commercial progress as a general tissue adhesive. The major impediments include reliance on harmful crosslinking additives, long‐term shelf‐stability, and variability in preparation (e.g. two component mixing). This can arguably be assigned to the over‐reliance on just one catechol crosslinker based on L‐dopamine. Herein, we evaluate catechol scaffolds and oxidation processes that side‐step these limitations and provide one‐component (1C) bioadhesive designs. These 1C designs hypothesize activation via surface contact and oxygen exposure. The branched polyethylenimine (PEI) dendrimer serves as a model macromolecule, easily grafted via Schiff‐base click chemistry. One of the optimized formulations, PEI‐(5‐OMe‐3,4‐DBA) ₂₀ , in which 20% of the primary amine groups of PEI are grafted with 5‐methoxy‐3,4‐dihydroxybenzaldehyde (5‐OMe‐3,4‐DBA) through Schiff‐base linkages, initiates crosslinking immediately after air/O ₂ exposure, but remains stable in anaerobic environments. Structural evaluation confirms PEI‐(5‐OMe‐3,4‐DBA) ₂₀ undergoes spontaneous conversion to quinones, supported by aromatic CH integration ( ¹ H‐NMR) and first order decay of 5‐OMe catechol Schiff‐base (UV–vis). Gelation time occurs in 〈 1 min with shear strengths of 26 kPa on wetted collagen substrates.

Spinheat processing is an emerging rapid, energy-efficient directed energy technique for curing adhesives and resins: suitable magnetic nanoparticles are added to an adhesive or resin, and the composite is subjected to an alternating magnetic field (AMF). The AMF heats up the nanoparticles, resulting in the curing of the surrounding adhesive. Mn-Zn ferrite Curie nanoparticles (CNP) have been studied for Spinheat applications, in part because their Curie temperature (TC) acts as a temperature cut-off for failsafe curing. However, currently there is no gram scale method of producing such CNP. Hence, the auto-combustion technique was selected for its facile nature with low reaction time, energy demand of less than 2 kJ per gram of CNP synthesized, and potential scalability. The specific absorption rate (SAR) of CNP needs to be maximized to minimize CNP loading. Hence, a suite of MnxZn1-xFe2O4 (x = 0.1-0.9) nanoparticles were synthesized by a glycine-assisted auto-combustion synthesis route. The influence of Mn/Zn substitution, fuel ratio and heat-treatment on the crystal structure, morphology, and magnetic properties were studied. These characteristics were correlated with the SAR. The CNP exhibited TC values ranging from 132 to 334 °C with varying Mn/Zn ratio. The as-prepared Mn0.9Zn0.1Fe2O4 and Mn0.7Zn0.3Fe2O4 CNP, with a higher glycine content displayed a dry-powder SAR of 15.4 W/g and 9.7 W/g, respectively, under an alternating magnetic field (AMF) of strength 200 Oe and frequency 404 kHz. The Mn0.7Zn0.3Fe2O4 CNP, with a TC matching the curing temperature (265 °C) of a commercial adhesive, could bond wood and ABS substrates in less than 10 min using the Spinheat method, compared to 16 h by conventional curing, without compromising structural strength. Thus, Mn-Zn ferrite nanoparticles produced by the auto-combustion technique are suitable for Spinheat applications.

Diazirine-grafted polycaprolactone adhesive, CaproGlu, can be photoactivated using sunlight as a stimulus and shows the potential of a film-forming sunscreen or a component thereof. Herein, the structure–property relationships of molecular weight, activation temperature, and inclusion of a photocatalyst on the film-forming capabilities of CaproGlu are investigated. Using polycaprolactone of molecular weight 1000 Da allows for a non-inferior storage modulus and elasticity compared to a paste-like formulation while retaining the fluidity required for easy spreading. Increasing the activation temperature of CaproGlu results in lower viscosity and requires a larger dosage of light energy for gelation. The inclusion of an iridium photocatalyst allows for faster photoactivation kinetics with non-inferior rheological properties compared to controls. Preliminary skin sensitization assays show negative results for both CaproGlu and IrPC formulations, supporting the potential for topical usage.

Magnetic nanoparticles with tunable Curie temperature (Tc) enable rapid, temperature-failsafe magnetic induction heating. Such particles are referred to as Curie nanoparticles (CNP). Applications include the emerging Spinheat approach to adhesive and polymer curing, hyperthermia and catalysis. MnxZn1-xFe2O4 CNP are attractive for such applications. However, a single scalable synthesis route that produces phase-pure CNP with controlled stoichiometry across the full composition range (x = 0 to 1) has not been reported. Here, we report a polyol-assisted sol-gel method, utilizing an ethylene glycol-glycerol system, that can produce a complete series of MnxZn1-xFe2O4 (x = 0 to 1) CNP. This route yielded phase-pure cubic spinel nanocrystals with crystallite sizes of 4-8 nm, stoichiometric deviations below 10%, and Tc tunable from 85 °C to 328 °C. The saturation magnetization (Ms) was the primary predictor of the specific absorption rate (SAR). The maximum dry-powder SAR was 6.9 W g-1 for the composition of Mn0.9Zn0.1Fe2O4. As a functional demonstration, this CNP was incorporated into a commercial epoxy. Magnetic induction heating reduced the curing time by 86% with an energy consumption of 3.1 MJ Kg-1, while preserving lap-shear adhesive strength comparable to conventionally cured controls. These results show, for the first time, that Tc-tuned MnxZn1-xFe2O4 CNP can be produced for magnetic induction-heating applications for the advanced manufacturing of polymer and adhesive based systems.