Functional Materials and Innovative Strategies for Wearable Thermal Management Applications

Abstract

Highlights:

1. This article systematically reviews the thermal management wearables with a specific emphasis on materials and strategies to regulate the human body temperature.

2. Thermal management wearables are subdivided into the active and passive thermal managing methods.

3. The strength and weakness of each thermal regulatory wearables are discussed in details from the view point of practical usage in real-life.

Abstract: Thermal management is essential in our body as it affects various bodily functions, ranging from thermal discomfort to serious organ failures, as an example of the worst-case scenario. There have been extensive studies about wearable materials and devices that augment thermoregulatory functionalities in our body, employing diverse materials and systematic approaches to attaining thermal homeostasis. This paper reviews the recent progress of functional materials and devices that contribute to thermoregulatory wearables, particularly emphasizing the strategic methodology to regulate body temperature. There exist several methods to promote personal thermal management in a wearable form. For instance, we can impede heat transfer using a thermally insulating material with extremely low thermal conductivity or directly cool and heat the skin surface. Thus, we classify many studies into two branches, passive and active thermal management modes, which are further subdivided into specific strategies. Apart from discussing the strategies and their mechanisms, we also identify the weaknesses of each strategy and scrutinize its potential direction that studies should follow to make substantial contributions to future thermal regulatory wearable industries.

Keywords: Active heat transfer; Passive heat transfer; Thermal management; Wearable device; Wearable materials.

Fig. 1

Passive thermal management methods: a high latent heat or high heat capacity materials to store heat from the external environment. b Thermal insulator that minimizes heat transfer to the human skin. c Thermally conductive material that exchanges heat with the air. d Photothermal material that absorbs solar energy and heats up the human skin. e Radiative cooling material that refrigerates the human skin by reflecting visible light and emitting infrared light toward space. f Evaporative cooling materials that facilitate liquid-to-vapor transition

Fig. 2

Active thermal management methods: a Joule heating. b Active microfluidic cooling. c Electro-, magnetocaloric cooling and heating. d Thermoelectric device cooling and heating

Fig. 3

Heat storage-based personal thermal management: a Phase-change hydrogels with thermal energy storage for personal healthcare. Reproduced with permission [7]. Copyright 2022, Elsevier. b Self-healable thermal energy storage for personal thermal management. Reproduced with permission [9]. Copyright 2023, Elsevier. c High heat storage and thermal diffusivity-based thermoregulation. Reproduced with permission [13]. Copyright 2023, Elsevier

Fig. 4

High thermal conductivity materials for passive thermal management: a Thermally conductive boron nitride composite that is aligned in the cross-plane direction. Reproduced with permission [98]. Copyright 2021, Springer Nature. b Thermally conductive liquid metal-elastomer composite that has the in-plane oriented alignment. Reproduced with permission [21]. Copyright 2017, PNAS. c Thermally conductive boron nanosheet composite that can be aligned both in the cross-plane and in-plane direction depending on the manufacturing method. Reproduced with permission [71]. Copyright 2022, Elsevier

Fig. 5

Thermal insulation for passive thermal management: a Aramid nanofiber aerogel for high-temperature (> 500 °C) thermal insulation. Reproduced with permission [14]. Copyright 2022, ACS Publications. b Hump-inspired fabric for firefighter thermal protection. Reproduced with permission [102]. Copyright 2023, Wiley–VCH. c Ceramic nanofiber aerogel with exceptional bendability and compressibility. Reproduced with permission [18]. Copyright 2020, Wiley–VCH

Fig. 6

Photothermal effect-based passive thermal management: a AM 1.5 G solar spectrum. The inset shows the schematic illustration of heated material by photothermal effect. b Wearable and transparent MXene & AgNP coating with light-driven healable properties. Reproduced with permission [20]. Copyright 2019, ACS publications. c Microneedle patches using bio-based materials for photothermal therapy. Reproduced with permission [21]. Copyright 2022, Wiley–VCH

Fig. 7

Sweat evaporation for passive thermoregulation: a Fouling-proof cooling (FP-Cool) fabric with sweat-wicking functionality for personal cooling. Reproduced with permission [26]. Copyright 2022, Wiley–VCH. b Hydrophobic/hydrophilic designed artificial sweating skin inspired by human body respiration. Reproduced with permission [27]. Copyright 2022, Wiley–VCH. c Biomimetic transpiration textile with one-way water transport. Reproduced with permission [29]. Copyright 2021, Wiley–VCH

Fig. 8

Personal radiative cooling for passive thermal management: a Nanoprocessed silk-based radiative cooling textile. Reproduced under the terms of CC BY [31]. Copyright 2021, Springer Nature. b Janus textile with radiative cooling and solar heating functionalities for all-day outdoor personal thermal management. Reproduced with permission [33]. Copyright 2021, ACS publications. c Hierarchical fibrous membrane that utilizes radiative and evaporative heat dissipation for enhancing the cooling performance. Reproduced with permission [37]. Copyright 2022, ACS publications

Fig. 9

Joule heating for active thermal management: a Transparent liquid metal electrodes for the heater. Reproduced with permission [38]. Copyright 2022, ELSEVIER. b Stretchable and transparent Kirigami patterned electrodes for the heater. Reproduced with permission [39]. Copyright 2019, ACS publications. c Smart MXene fabric heater for healthcare and medical therapy. Reproduced with permission [40]. Copyright 2020, ACS publications. d Highly stretchable Cu nanowire heater for virtual reality applications. Reproduced with permission [41]. Copyright 2020, Royal Society of Chemistry

Fig. 10

Microfluidic cooling for active thermal management: a An adaptive robotic skin with a microfluidic cooling device. Reproduced with permission [43]. Copyright 2022, Wiley–VCH. b A liquid metal mold-based 3D flexible microfluidics [45]. Copyright 2022, Frontiers Media

Fig. 11

Caloric effect for active thermal management. a Flexible and freestanding gadolinium film for magnetocaloric applications [46]. Copyright 2020, Wiley–VCH. b Pb0.82Ba0.08La0.1Zr0.9Ti0.1O3 (PBLZT) thin film‐based flexible EC device [104]. Copyright 2019, Elsevier. c 0.65(0.94Na0.5Bi0.5TiO₃-0.06BaTiO₃)-0.35SrTiO₃ (NBBST) film‐based flexible EC device [49]. Copyright 2020, ACS Publications. d Ba0.85Ca0.15Zr0.1Ti0.9O₃ (BCZT) ceramic network—P(VDF-TrFE-CFE) polymer matrix composite EC device. Reproduced with permission [107]. Copyright 2022, Springer Nature

Fig. 12

Thermoelectric effect for active thermal management: a Stretchable skin-like thermoelectric device for virtual reality applications. Reproduced with permission [52]. Copyright 2020, Wiley–VCH. b Soft and compliant thermoelectric generators with high performance. Reproduced with permission [54]. Copyright 2020, Springer Nature. c Soft multi-modal thermoelectric skin [55]. Copyright 2022, Elsevier