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Yang et al. Soft Sci 2024;4:9 https://dx.doi.org/10.20517/ss.2023.43 Page 13 of 26

cryopreservation or exert enhanced damage to tumor cells in cryotherapy, determined by specific
manipulation. Our laboratory has been striving to push forward the application of LMs in cryobiological
applications and has made some significant progress in recent years, which will be presented in this section.

LM-mediated vitrification of cell suspensions
With the aim of no ice formation through the whole procedure, vitrification has been more widely
investigated and holds the potential of increasing cell viability and scaling up the size of cryopreserved
specimens [19,23,24,74,77] . On account of the acknowledged fact that the rewarming process is more challenging
than the cooling process, high rewarming rates are crucial to successful vitrification. Inspired by the
significant PT conversion effect of LMNPs, Hou et al. applied them as nanoscale heat sources that realized
[87]
uniform and rapid rewarming of vitrified cell suspensions [Figure 5A i] . Moreover, the cell suspensions
loaded with LMNPs showed mitigated devitrification compared with the control group [Figure 5A ii]. They
utilized ultrasonication to prepare LMNPs, followed by the centrifugal screening of the particles and
lyophilization of the supernatant, which ensured a uniform size distribution of the LMNPs. The in vitro
biocompatibility test was consistent with the work presented above. The calculated PT conversion efficiency
was 52%, which was higher than long-studied gold nanomaterials and in accordance with the previously
reported value . This consistency probably also suggested that surface modification might have little
[47]
influence on the PT efficiency of LMNPs. Benefiting from the “nanowarming” technique of LMNPs, the
CPA recipe they applied was free of dimethyl sulfoxide (DMSO), which is widely considered to be toxic to
[23]
cells ; at the same time, the total CPA concentration was far lower than commercial recipes . With a
[90]
minimum dose of LMNPs (0.1 mg/mL), the viability of rewarmed cells exceeded 70%. Even in the
experimental groups without laser irradiation, the cell viability was still uplifted with a higher dose of
LMNPs [Figure 5A iii], probably ascribed to heat transfer enhancement of the suspension. The resuscitated
stem cells were evaluated in multiple dimensions, including attachment efficiency, proliferation, expression
of critical antigens and genes, and multi-directional differentiation ability. To demonstrate the potential of
this technique in large-scale specimen cryopreservation, they further vitrified and rewarmed murine tails,
resulting in better protection efficacy from the point of view of histological morphology analysis.

This work primarily exploited LMNPs as functional materials in cryopreservation protocol, which mainly
made differences from three aspects: (i) No DMSO was added to the CPA recipe; (ii) Dispersing uniformly
in CPA to increase the thermal conductivity of suspension; (iii) Serving as PT sensitizers to rapidly rewarm
the vitrified specimens to avoid recrystallization. Combining their thermal properties, modifiability,
softness, and biocompatibility, LMs hold great prospects in the field of cryopreservation.

LM-enhanced tumor thermotherapy
LM-mediated ice-fire ablation
Combining high thermal conductivity, PT effect, and conformability, Hou et al. proposed an LM-based
hybrid platform to improve the efficacy of tumor therapy , which comprised two major parts: (i) They
[53]
prepared pasty LM-Cu composites to apply a conformal coating on the skin to enhance the heat transfer. As
shown in Figure 5B i, the simulation result indicated that LM paste coating could result in deeper
penetration of cold energy into the tumor. They injected LMNPs into the tumor and radiated the tumor
with NIR to implement PT therapy (PTT) [Figure 5B ii]. The near-infrared thermograph demonstrated the
phenomenal PTT effect aroused by LMNPs. Furthermore, to further exploit the therapeutic effect of the LM
[53]
platform, Hou et al. combined these two modes successively . The tumor cells underwent drastic
temperature change from extreme hypothermia to hyperthermia, which would also cause intensive thermal
stress to ultimately kill tumor cells [Figure 5B iii]. The experimental result manifested that LM platform-
mediated cryoablation combined with PTT realized better tumor elimination efficiency than each therapy
alone [Figure 5B iv]. Besides, only in the combined therapy group the tumor did not recur.