The aim of this chapter is to provide the reader with an outline of the methods most commonly used to characterize samples, taken from studies involving physical metallurgy, using techniques allied with transmission electron microscopy. In the main, rather than provide full and comprehensive details on all methods including various imaging techniques, diffraction methods, and analytical spectroscopies, it is the attempt of the coauthors to outline techniques, and then provide ways in which difficulties in interpretation may be avoided.

Delivery of mRNA (mRNA) to the central nervous system (CNS) remains a significant challenge. Herein, we design a library of furan-derived lipids and, to our knowledge, for the first time, leverage the meningeal lymphatic vessels (MLVs) route to achieve efficient delivery of mRNA to the brain. These furan-derived lipids were engineered with different furan cores, functional groups, and tails. We found that tetrahydrofuran (THF)-derived lipid nanoparticles (LNPs) generally displayed exceptional mRNA delivery compared to their furan-based counterparts. Specifically, LNPs formulated with four-acetal-tail mono-THF-derived lipid F10T5 and four-acetal-tail di-THF-derived lipid F11T6 demonstrated significantly higher mRNA delivery efficiency to the brain compared with FDA-approved SM102 LNPs. The data revealed that these LNPs bypassed the blood-brain barrier (BBB) via the lymphatic pathway, traveling from deep cervical lymph nodes (dCLNs) to the meninges and subsequently entering brain cells. Collectively, this work provides valuable insights into engineering LNPs and exploring alternative approaches for the delivery of mRNA to the brain.

Superatomic clusters have long attracted attention as active components in a broad range of optical and electronic technologies, making the discovery and understanding of new cluster-based materials an important frontier. Here, we establish the optimized synthesis and properties of a metastable palladium selenide Pd3Se10 phase comprised of Pd6Se20 cube-like clusters. The solution-phase electrochemically balanced reaction between Pd2+ and sodium polyselenide precursor mixtures, under precise reaction conditions, enables the formation of a crystalline product in high yields. The Raman fingerprint of Pd6Se20 shows that the cluster is also present in amorphous products that form at lower reaction temperatures. Pd3Se10 is stable up to 340 degrees C, above which it disproportionates into Se and orthorhombic PdSe2. Finally, the optical absorption, electronic resistivity, and photoconductivity measurements indicate that crystalline Pd3Se10 is semiconducting with a 1.18 eV indirect gap. Overall, this understanding opens a pathway toward accessing a new superatomic building block which has potential in optoelectronic devices.

Dendritic cells (DCs) are essential for inducing effective antitumor T cell responses. However, the immunosuppressive tumor microenvironment (TME) hinders DC recruitment and maturation, facilitating tumor progression and spread. This study investigates the synergistic potential of immunogenic cell death (ICD), triggered by chemotherapeutic-derived lipid nanoparticles (LNPs), in combination with Flt3L and CD40L mRNA delivery to enhance DC mobilization and activation, reprogram the TME, and ultimately promote robust antitumor T cell responses. The optimized LNP formulation, GEM5Q7, efficiently delivered mRNA and induced ICD in melanoma cells. Intratumoral administration of GEM5Q7, encapsulating Flt3L and CD40L mRNAs, elevated pro-inflammatory cytokine and chemokine secretion, driving the infiltration and activation of cross-presenting DCs, which are critical for priming T cells. In a subcutaneous melanoma model, this approach led to significant tumor suppression and a 40 % complete response rate. This strategy holds promise for enhancing cancer immunotherapies by reprogramming the TME and inducing durable antitumor T cell immunity.

Spinal cord injury (SCI) is a devastating neurological disorder that results in severe disability and imposes a high social and economic burden. Effective recovery from SCI requires comprehensive neural repair strategies, including neurogenesis and neuroprotection. Inspired by the structure of phospholipids in nature, we developed a library of biomimetic ionizable lipids, containing aminophosphate, aminophosphoramidate, or aminophosphonate groups (AP lipids). Then, we formulated these AP lipids into lipid nanoparticles (LNPs) and examined their mRNA delivery efficiency in neurons and astrocytes. Among these AP LNPs, AP60 LNP showed superior delivery efficiency compared to FDA approved D-Lin-MC3-DMA (MC3) LNP. To achieve longer protein expression, the circular RNA was used in LNPs. Additionally, we developed a two-step method for circular RNA production, providing a simple yet highly efficient approach. By combining these innovations, a circular RNA loaded aminophosphonate-derived lipids nanoparticles delivery system (CROSS) was constructed. To explore a therapeutic regimen, CROSS-loaded with circular Sox2, Ascl1, and GDNF RNAs were administered locally and intravenously in SCI model, which led to the restoration of bladder function and significant motor function recovery. In summary, the CROSS platform provided a novel and effective strategy for treating SCI.

Lipid nanoparticle-messenger RNA formulations have garnered significant attention for their therapeutic potential in infectious diseases, cancer and genetic disorders. However, effective mRNA delivery to the central nervous system (CNS) remains a formidable challenge. To overcome this limitation, a class of brain-targeting lipids (BLs) is developed by incorporating brain-targeting small molecules with amino lipids and formulated them with helper lipids to generate brain-targeting lipid nanoparticles (BLNPs) for mRNA delivery. Screening studies led to a lead formulation, TD5 BLNPs, outperforming FDA-approved DLin-MC3-DMA LNPs in delivering mRNA to the brain upon intrathecal injection. Specifically, a single intrathecal injection of TD5 BLNP-GFP mRNA led to GFP expression in 29.6% of neurons and 38.1% of astrocytes across the brain. In an Ai14 mouse model, TD5 BLNP-Cre recombinase mRNA treatment induced tdTomato expression in ≈30% of neurons and 40% of astrocytes across major brain regions. Notably, delivery of Cas9 mRNA/sgRNA complex using TD5 BLNPs achieved effective genome editing in the brain. Additionally, TD5 BLNPs showed comparable safety profiles to MC3 LNPs, indicating promising biocompatibility. Overall, this TD5 BLNP formulation effectively delivers mRNA to brain tissues via intrathecal injection and facilitates efficient expression in both neurons and astrocytes, presenting a potential strategy for treating CNS diseases.

Lipid nanoparticle (LNP)-mRNA vaccines have demonstrated protective capability in combating SARS-CoV-2. Their extensive deployment across the global population leads to the broad presence of T-cell immunity against the SARS-CoV-2 spike protein, presenting an opportunity to harness this immunological response as a universal antigen target for cancer treatment. Herein, we design and synthesize a series of amino alcohol- or amino acid-derived ionizable lipids (AA lipids) and develop an LNP-RNA-based antigen presentation platform to redirect spike-specific T-cell immunity against cancer in mouse models. First, in a prime-boost regimen, AA2 LNP encapsulating spike mRNA elicit stronger T-cell immunity against the spike epitopes compared to FDA-approved LNPs (ALC-0315 and SM-102), highlighting the superior delivery efficiency of AA2 LNP. Next, AA15V LNP efficiently delivers self-amplifying RNAs (saRNAs) encoding spike epitope-loaded single-chain trimer (sSE-SCT) MHC I molecules into tumor tissues, thereby inducing the presentation of spike epitopes. Our results show that a single intratumoral (i.t.) treatment of AA15V LNP-sSE-SCTs suppresses tumor growth and extends the survival of B16F10 melanoma and A20 lymphoma tumor-bearing mice vaccinated with AA2 LNP-spike mRNA. Additionally, AA15V LNP-sSE-SCTs enable SE-SCT expression in ex vivo human glioblastoma and lung cancer samples, suggesting its potential in clinical translation.

The identification and differentiation of the mineral phases, hydroxyapatite (HA, Ca10(PO4)6(OH)2) and octacalcium phosphate (OCP, Ca8H2(PO4)6), remains challenging because of their similar composition and chemical structure. In this research, electron energy-loss spectroscopy (EELS) analyses revealed indicators to distinguish HA and OCP and these were applied to examine mineral development in enamel from mouse incisors. Reference EELS data for HA and OCP was established with commercial HA and synthesized OCP. An evaluation of electron damage and a mitigation strategy of multipass imaging was conducted, and the electron dose limitation of OCP was identified. New insights into the mechanism of electron beam damage on the apatite crystal were obtained. With the characterization of the energy-loss spectra and the EELS simulation, the oxygen K-edge was found to be one of the indicators for the differentiation of HA from OCP. The second indicator, the Ca/P ratio, was calculated with a calibrated experimental factor of K exp. Elemental mapping was done to establish the different Ca/P ratio of HA and OCP, and the boundary between these mineral forms. EELS analysis was performed on developing enamel in wild-type (WT) and Mmp20 knockout (KO) mice. This research establishes a protocol for EELS analysis on biological specimens and demonstrates the power and potential of EELS in biomaterial characterization.

Magnons, quanta of spin wave excitations in magnetically ordered materials, have been identified as candidates for several potentially transformative technologies in recent years. Macroscopic techniques, such as neutron scattering or Raman spectroscopy, can be used to identify and analyze magnons, but provide relatively delocalized information about the sample. Understanding how the bonding and local structure of a material interacts with, and influences, the magnon population in a material is a crucial step toward the ability to produce any real-world application utilizing magnons. By leveraging the combined spatial resolution of scanning transmission electron microscopy (STEM) and the energy resolution of monochromated electron energy-loss spectroscopy (EELS) nanoscale analysis of magnons can be performed. While the weak interaction of magnons with the electron beam makes magnon EELS challenging on reasonable timescales, magnon-phonon coupling can be leveraged to understand magnons through their effect on the more easily measured phonons. Here, we examine yttrium iron garnet (YIG) flakes, and demonstrate non-linear, temperature-dependent shifts in the phonon frequencies, consistent with previously described magnon-phonon coupling effects. The ability to measure the temperature-dependence of vibrational frequencies with high precision in individual nanoscale flakes, demonstrates the ability to study magnon-phonon coupling in the STEM with unprecedented spatial resolution.

The systemic delivery of mRNA molecules to the central nervous system is challenging as they need to cross the blood-brain barrier (BBB) to reach into the brain. Here we design and synthesize 72 BBB-crossing lipids fabricated by conjugating BBB-crossing modules and amino lipids, and use them to assemble BBB-crossing lipid nanoparticles for mRNA delivery. Screening and structure optimization studies resulted in a lead formulation that has substantially higher mRNA delivery efficiency into the brain than those exhibited by FDA-approved lipid nanoparticles. Studies in distinct mouse models show that these BBB-crossing lipid nanoparticles can transfect neurons and astrocytes of the whole brain after intravenous injections, being well tolerated across several dosage regimens. Moreover, these nanoparticles can deliver mRNA to human brain ex vivo samples. Overall, these BBB-crossing lipid nanoparticles deliver mRNA to neurons and astrocytes in broad brain regions, thereby being a promising platform to treat a range of central nervous system diseases.

The precise control of mechanochemical activation within deep tissues using non-invasive ultrasound holds profound implications for advancing our understanding of fundamental biomedical sciences and revolutionizing disease treatments1-4. However, a theory-guided mechanoresponsive materials system with well-defined ultrasound activation has yet to be explored5,6. Here we present the concept of using porous hydrogen-bonded organic frameworks (HOFs) as toolkits for focused ultrasound (FUS) programmably triggered drug activation to control specific cellular events in the deep brain, through on-demand scission of the supramolecular interactions. A theoretical model is developed to potentially visualize the mechanochemical scission and ultrasound mechanics, providing valuable guidelines for the rational design of mechanoresponsive materials to achieve programmable control. To demonstrate the practicality of this approach, we encapsulate the designer drug clozapine N-oxide (CNO) into the optimal HOF nanocrystals for FUS-gated release to activate engineered G-protein-coupled receptors in the ventral tegmental area (VTA) of mice and rats and hence achieve targeted neural circuit modulation even at depth 9 mm with a latency of seconds. This work demonstrates the capability of ultrasound to precisely control molecular interactions and develops ultrasound-programmable HOFs to non-invasively and spatiotemporally control cellular events, thereby facilitating the establishment of precise molecular therapeutic possibilities.

In alignment with the Materials Genome Initiative and as the product of a workshop sponsored by the US National Science Foundation, we define a vision for materials laboratories of the future in alloys, amorphous materials, and composite materials; chart a roadmap for realizing this vision; identify technical bottlenecks and barriers to access; and propose pathways to equitable and democratic access to integrated toolsets in a manner that addresses urgent societal needs, accelerates technological innovation, and enhances manufacturing competitiveness. Spanning three important materials classes, this article summarizes the areas of alignment and unifying themes, distinctive needs of different materials research communities, key science drivers that cannot be accomplished within the capabilities of current materials laboratories, and open questions that need further community input. Here, we provide a broader context for the workshop, synopsize the salient findings, outline a shared vision for democratizing access and accelerating materials discovery, highlight some case studies across the three different materials classes, and identify significant issues that need further discussion.

Magnetic skyrmions, which are stable, topologically protected spin structures, have garnered significant interest for their potential in revolutionizing spintronic applications. This study reveals the room-temperature coexistence of Néel-type and Bloch-Néel hybrid skyrmions in [Pt/Co/Cu] multilayers grown by molecular beam epitaxy (MBE). Pulse current is used to switch the skyrmion type and modulate the stability of the skyrmions. The thermal effect on the stability of the skyrmions due to the current pulse is also investigated. The work unveils a broad magnetic phase space, offering unprecedented control over skyrmion states in metallic multilayers with broken inversion symmetry. These findings pave the way for diverse applications in spintronics, including binary data encoding, and provide a novel framework for the manipulation of multi-type skyrmions.

In 1966, Pierre-Gilles de Gennes proposed a non-volatile mechanism for switching superconductivity on and off in a magnetic device. This involved a superconductor (S) sandwiched between ferromagnetic (F) insulators in which the net magnetic exchange field could be controlled through the magnetisation-orientation of the F layers. Because superconducting switches are attractive for a range of applications, extensive studies have been carried out on $F/S/F$ structures. Although these have demonstrated a sensitivity of the superconducting critical temperature ($T_{c}$) to parallel (P) and antiparallel (AP) magnetisation-orientations of the F layers, corresponding shifts in $T_c$ (i.e., ${\Delta}T_c = T_{c,AP} - T_{c,P}$) are lower than predicted with ${\Delta}T_c$ only a small fraction of $T_{c,AP}$, precluding the development of applications. Here, we report $EuS/Au/Nb/EuS$ structures where EuS is an insulating ferromagnet, Nb is a superconductor and Au is a heavy metal. For P magnetisations, the superconducting state in this structure is quenched down to the lowest measured temperature of 20 mK meaning that ${\Delta}T_c/T_{c,AP}$ is practically 1. The key to this so-called absolute switching effect is a sizable spin-mixing conductance at the $EuS/Au$ interface which ensures a robust magnetic proximity effect, unlocking the potential of $F/S/F$ switches for low power electronics.

Aurivillius structured Bi6Ti3Fe1.5Mn0.5O18 (B6TFMO) has emerged as a rare room temperature multiferroic, exhibiting reversible magnetoelectric switching of ferroelectric domains under cycled magnetic fields. This layered oxide presents exceptional avenues for advancing data storage technologies owing to its distinctive ferroelectric and ferrimagnetic characteristics. Despite its immense potential, a comprehensive understanding of the underlying mechanisms driving multiferroic behavior remains elusive. Herein, we employ atomic resolution electron microscopy to elucidate the interplay of octahedral tilting and atomic-level structural distortions within B6TFMO, associating these phenomena with functional properties. Fundamental electronic features at varying bonding environments within this complex system are scrutinized using electron energy loss spectroscopy (EELS), revealing that the electronic nature of the Ti4+ cations within perovskite BO6 octahedra is influenced by position within the Aurivillius structure. Layer-by-layer EELS analysis shows an ascending crystal field splitting (Δ) trend from outer to center perovskite layers, with an average increase in Δ of 0.13 ± 0.06 eV. Density functional theory calculations, supported by atomic resolution polarization vector mapping of B-site cations, underscore the correlation between the evolving nature of Ti4+ cations, the extent of tetragonal distortion and ferroelectric behavior. Integrated differential phase contrast imaging unveils the position of light oxygen atoms in B6TFMO for the first time, exposing an escalating degree of octahedral tilting toward the center layers, which competes with the magnitude of BO6 tetragonal distortion. The observed octahedral tilting, influenced by B-site cation arrangement, is deemed crucial for juxtaposing magnetic cations and establishing long-range ferrimagnetic order in multiferroic B6TFMO.

Metal halide perovskites have garnered considerable interest for their potential uses in high-efficiency photonics, particularly in the construction of on-chip lasers. Despite extensive efforts to understand the mechanisms underlying perovskite-based lasing, no clear consensus has emerged. Moreover, the fabrication of practical lasing emitters requires the challenging integration of a low-defect active material into a device architecture with minimized complexity. In this study, we demonstrate a simple, multimode lasing emitter composed of a millimeter-scale single-crystalline thin film of CsPbBr3. Dislocations, created during vapor-based film deposition, function as lasing cavity walls and form close-packed sets of resonators with random sizes at two orthogonal orientations within the thin film. Collecting ensemble temperature and power-dependent lasing characteristics of multiple, independent lasing modes in a single sample enables a statistical analysis of the underlying lasing mechanism. Our results reveal that the power-dependent red-shift in the stimulated emission envelope is caused by coupling between the radiatively recombining excitons and the collective oscillations of a photoexcited electron-hole plasma within the perovskite.

Since the approval of the lipid nanoparticles (LNP)-mRNA vaccines against the SARS-CoV-2 virus, there has been an increased interest in the delivery of mRNA through LNPs. However, current LNP formulations contain PEG lipids, which can stimulate the generation of anti-PEG antibodies. The presence of these antibodies can potentially cause adverse reactions and reduce therapeutic efficacy after administration. Given the widespread deployment of the COVID-19 vaccines, the increased exposure to PEG may necessitate the evaluation of alternative LNP formulations without PEG components. In this study, we investigated a series of polysarcosine (pSar) lipids as alternatives to the PEG lipids to determine whether pSar lipids could still provide the functionality of the PEG lipids in the ALC-0315 and SM-102 LNP systems. We found that complete replacement of the PEG lipid with a pSar lipid can increase or maintain mRNA delivery efficiency and exhibit similar safety profiles in vivo.