Noninvasive brain–computer interfaces (BCIs) show great potential in applications including sleep monitoring, fatigue alerts, neurofeedback training, etc. While noninvasive BCIs do not impose any procedural risk to users (as opposed to invasive BCIs), the acquisition of high-quality electroencephalograms (EEGs) in the long term has been challenging due to the limitations of current electrodes. Herein, we developed a semidry double-layer hydrogel electrode that not only records EEG signals at a resolution comparable to that of wet electrodes but is also able to withstand up to 12 h of continuous EEG acquisition. The electrode comprises dual hydrogel layers: a conductive layer that features high conductivity, low skin-contact impedance, and high robustness; and an adhesive layer that can bond to glass or plastic substrates to reduce motion artifacts in wearing conditions. Water retention in the hydrogel is stable, and the measured skin-contact impedance of the hydrogel electrode is comparable to that of wet electrodes (conductive paste) and drastically lower than that of dry electrodes (metal pin). Cytotoxicity and skin irritation tests show that the hydrogel electrode has excellent biocompatibility. Finally, the developed hydrogel electrode was evaluated in both N170 and P300 event-related potential (ERP) tests on human volunteers. The hydrogel electrode captured the expected ERP waveforms in both the N170 and P300 tests, showing similarities in the waveforms generated by wet electrodes. In contrast, dry electrodes fail to detect the triggered potential due to low signal quality. In addition, our hydrogel electrode can acquire EEG for up to 12 h and is ready for recycled use (7-day tests). Altogether, the results suggest that our semidry double-layer hydrogel electrodes are able to detect ERPs in the long term in an easy-to-use fashion, potentially opening up numerous applications in real-life scenarios for noninvasive BCI.

The efficacy of messenger RNA (mRNA)-based vaccines or therapies relies on delivery vehicles that can transport them into the cytosol of cells. Lipid nanoparticles (LNPs) are the most clinically advanced carrier for mRNA. The chemical structure of an ionizable lipid is critical for the delivery efficiency of the LNPs. Herein, we synthesize a new ionizable lipid containing fluorinated alkyl chains (F-L319) and evaluate its mRNA delivery efficiency compared to its hydrocarbon counterpart (L319). While LNPs formulated with F-L319 alone showed decreased mRNA encapsulation and delivery efficiencies in comparison to the L319-LNP, we found that combining the appropriate ratios of F-L319 and L319 as hybrid ionizable lipids in LNPs (hybrid-LNPs) greatly enhanced mRNA delivery efficiency both in vitro and in vivo. Upon intravenous injection, the hybrid-LNP showed targeted mRNA expression in the spleen. Mechanistic studies indicate that the enhanced mRNA delivery of the hybrid-LNP is attributed to both improved mRNA encapsulation and cellular uptake. Collectively, fluorination of ionizable lipids represents a promising strategy to improve the delivery efficiency of LNPs.

MRNA technology holds immense promise as an innovative therapeutic approach with applications spanning infectious disease vaccines, cancer immunotherapy, protein replacement, and gene editing. However, practical use of mRNA has been hindered by challenges such as low cellular stability and transient protein expression. For addressing these, we propose a novel strategy to optimize mRNA sequences, particularly in the untranslated region, by inserting adenylate/uridylate-rich elements (AU-rich elements) to enhance stability and protein expression. Our investigation revealed that integrating AU-rich elements between the open reading frame (ORF) and the 3' untranslated region (3' UTR) significantly enhances RNA stability compared with other insertion sites. We identified cytoplasmic Human antigen R (HuR) as an essential RNA-binding protein responsible for promoting mRNA stability and translation, confirmed through HuR knockdown experiments and pull-down assays between AU-rich elements and HuR. Through rational design, we optimized the sequence of natural AU-rich elements and identified the essential "AUUUA" element, which, with certain repeats, can increase protein expression up to 5-fold. To demonstrate the universality of AU-rich element sequences in enhancing mRNA translation, we switched the coding proteins from luciferase to EGFP, mCherry, and ovalbumin (OVA), finding that both natural and engineered AU-rich element sequences amplify the expression of these proteins. In conclusion, leveraging the functionalities of RNA-binding proteins and the natural regulation of RNA stability in the untranslated region represents a novel strategy to enhance mRNA pharmacokinetics in the cytoplasm, expanding the potential applications of mRNA in therapeutic drugs.

Non-invasive brain–computer interfaces (NI-BCIs) have garnered significant attention due to their safety and wide range of applications. However, developing non-invasive electroencephalogram (EEG) electrodes that are highly sensitive, comfortable to wear, and reusable has been challenging due to the limitations of conventional electrodes. Here, we introduce a simple method for fabricating semi-dry hydrogel EEG electrodes with antibacterial properties, enabling long-term, repeatable acquisition of EEG. By utilizing N-acryloyl glycinamide and hydroxypropyltrimethyl ammonium chloride chitosan, we have prepared electrodes that not only possess good mechanical properties (compression modulus 65 kPa) and anti-fatigue properties but also exhibit superior antibacterial properties. These electrodes effectively inhibit the growth of both Gram-negative (E. coli) and Gram-positive (S. epidermidis) bacteria. Furthermore, the hydrogel maintains stable water retention properties, resulting in an average contact impedance of <400 Ω measured over 12 h, and an ionic conductivity of 0.39 mS cm⁻¹. Cytotoxicity and skin irritation tests have confirmed the high biocompatibility of the hydrogel electrodes. In an N170 event-related potential (ERP) test on human volunteers, we successfully captured the expected ERP signal waveform and a high signal-to-noise ratio (20.02 dB), comparable to that of conventional wet electrodes. Moreover, contact impedance on the scalps remained below 100 kΩ for 12 h, while wet electrodes became unable to detect signals after 7–8 h due to dehydration. In summary, our hydrogel electrodes are capable of detecting ERPs over extended periods in an easy-to-use manner with antibacterial properties. This reduces the risk of bacterial infection associated with prolonged reuse and expands the potential of NI-BCIs in daily life.

The efficacy of mRNA-based vaccines and therapies relies on lipid nanoparticles (LNPs) as carriers to deliver mRNA into cells. The chemical structure of ionizable lipids (ILs) within LNPs is crucial in determining their delivery efficiency. In this study, we synthesized 623 alkyne-bearing ionizable lipids using the A3 coupling reaction and assessed their effectiveness in mRNA delivery. ILs with specific structural features—18-carbon alkyl chains, a cis-double bond, and ethanolamine head groups—demonstrated superior mRNA delivery capabilities. Variations in saturation, double bond placement, and chain length correlated with decreased efficacy. Alkynes positioned adjacent to nitrogen atoms in ILs reduced the acid dissociation constant (pKa) of LNPs, thereby hindering mRNA delivery efficiency. Conversion of alkynes to alkanes significantly enhanced mRNA delivery of ILs both in vitro and in vivo. Moreover, combining optimized ILs with cKK-E12 yields synergistic LNPs that showed markedly augmented mRNA expression levels in vivo. Overall, our study provides insights into the structure–function relationships of ILs, providing a foundation for the rational design of ILs to enhance the efficacy of LNPs in mRNA delivery.

Lipid nanoparticles (LNPs) are the most clinically relevant vehicles for mRNA vaccines. Despite the great successes, the toxicity caused by the high dose of lipid components still represents a great challenge. The suboptimal loading capacity of mRNA in LNPs not only compromises the vaccine’s efficacy but also heightens the risk of non-specific immune responses, accelerates clearance caused by anti-PEG IgG/IgM. These problems underscore the urgent need for improving mRNA loading capacity in LNPs to provide dose-sparing effects. Herein, we develop a metal ion mediated mRNA enrichment strategy to efficiently form a high-density mRNA core, and manganese ion (Mn²⁺) exhibits a unique capability to match the need. The prepared Mn-mRNA nanoparticle is subsequently coated with lipids to form the resulting nanosystem, L@Mn-mRNA, which achieved nearly twice the mRNA loading capacity compared to conventional mRNA vaccine formulations (LNP-mRNA). Remarkably, L@Mn-mRNA also demonstrates a 2-fold increase in cellular uptake efficiency compared to LNP-mRNA, attributed to the enhanced stiffness provided by the Mn-mRNA core. By combining improved mRNA loading with superior cellular uptake, L@Mn-mRNA achieves significantly enhanced antigen-specific immune responses and therapeutic efficacy as vaccines. We elucidate the mechanism behind Mn-mRNA construction and optimize the L@Mn-mRNA formulations, and this method is suitable for types of lipids and mRNAs. Moreover, L@Mn-mRNA also reduces the risk of anti-PEG IgG/IgM generation. Thus, this strategy holds significant potential as a platform for the next generation of lipid-based mRNA vaccines.