Untrained neural network enabling fast and universal structured-illumination microscopy.

Structured-illumination microscopy (SIM) offers a twofold resolution enhancement beyond the optical diffraction limit. At present, SIM requires several raw structured-illumination (SI) frames to reconstruct a super-resolution (SR) image, especially the time-consuming reconstruction of speckle SIM, which requires hundreds of SI frames. Considering this, we herein propose an untrained structured-illumination reconstruction neural network (USRNN) with known illumination patterns to reduce the amount of raw data that is required for speckle SIM reconstruction by 20 times and thus improve its temporal resolution. Benefiting from the unsupervised optimizing strategy and CNNs' structure priors, the high-frequency information is obtained from the network without the requirement of datasets; as a result, a high-fidelity SR image with approximately twofold resolution enhancement can be reconstructed using five frames or less. Experiments on reconstructing non-biological and biological samples demonstrate the high-speed and high-universality capabilities of our method.

Gentisic acid prevents colorectal cancer metastasis via blocking GPR81-mediated DEPDC5 degradation.

BACKGROUND: Metastasis driven by epithelial-mesenchymal transition (EMT) remains a significant contributor to the poor prognosis of colorectal cancer (CRC), and requires more effective interventions. GPR81 signaling has been linked to tumor metastasis, while lacks an efficient specific inhibitor. PURPOSE: Our study aimed to investigate the effect and mechanism of Gentisic acid on colorectal cancer (CRC) metastasis. STUDY DESIGN: A lung metastasis mouse model induced by tail vein injection and a subcutaneous graft tumor model were used. Gentisic acid (GA) was administered by an intraperitoneal injection. HCT116 was treated with lactate to establish an in vitro model. METHODS: MC38 cells with mCherry fluorescent protein were injected into tail vein to investigate lung metastasis ability in vivo. GA was administered by intraperitoneal injection for 3 weeks. The therapeutic effect was evaluated by survival rates, histochemical analysis, RT-qPCR and live imaging. The mechanism was explored using small interfering RNA (siRNA), Western blotting, RT-qPCR and immunofluorescence. RESULTS: GA had a therapeutic effect on CRC metastasis and improved survival rates and pathological changes in dose-dependent manner. GA emerged as an GPR81 inhibitor, effectively suppressed EMT and mTOR signaling in CRC induced by lactate both in vivo and in vitro. Mechanistically, GA halted lactate-induce degradation of DEPDC5 through impeding the activation of Chaperone-mediated autophagy (CMA). CONCLUSION: CMA-mediated DEPDC5 degradation is crucial for lactate/GPR81-induced CRC metastasis, and GA may be a promising candidate for metastasis by inhibiting GPR81 signaling.

Vanillic acid restores homeostasis of intestinal epithelium in colitis through inhibiting CA9/STIM1-mediated ferroptosis.

The damage of integrated epithelial epithelium is a key pathogenic factor and closely associated with the recurrence of ulcerative colitis (UC). Here, we reported that vanillic acid (VA) exerted potent therapeutic effects on DSS-induced colitis by restoring intestinal epithelium homeostasis via the inhibition of ferroptosis. By the CETSA assay and DARTS assay, we identified carbonic anhydrase IX (CAIX, CA9) as the direct target of VA. The binding of VA to CA9 causes insulin-induced gene-2 (INSIG2) to interact with stromal interaction molecule 1 (STIM1), rather than SREBP cleavage-activating protein (SCAP), leading to the translocation of SCAP-SREBP1 from the endoplasmic reticulum (ER) to the Golgi apparatus for cleavage into mature SREBP1. The activation of SREBP1 induced by VA then significantly facilitated the transcription of stearoyl-CoA desaturase 1 (SCD1) to exert an inhibitory effect on ferroptosis. By inhibiting the excessive death of intestinal epithelial cells caused by ferroptosis, VA effectively preserved the integrity of intestinal barrier and prevented the progression of unresolved inflammation. In conclusion, our study demonstrated that VA could alleviate colitis by restoring intestinal epithelium homeostasis through CA9/STIM1-mediated inhibition of ferroptosis, providing a promising therapeutic candidate for UC.

High-throughput multiplexed fluorescence lifetime microscopy.

Fluorescence lifetime microscopy has been widely used in quantifying cellular interaction or histopathological identification of different stained tissues. A novel, to the best of our knowledge, approach for high-throughput multiplexed fluorescence lifetime imaging is presented. To establish a high-throughput fluorescence lifetime acquisition system, a uniformed illumination optical focus array was generated by a novel computer-generated hologram algorithm based on matrix triple product. This, in conjunction with an array detector and multichannel time-correlated single-photon counting, enables the full use of the acquisition ability of each detector. By utilizing interval segmentation of photon time detection, a high-throughput multiplexed fluorescence lifetime imaging is achieved. Experimental results demonstrate that this method achieves a fivefold increase in the collection throughput of fluorescence lifetime and is capable of simultaneous dual-target fluorescence lifetime measurement.

Modification and verification of the PMV model to improve thermal comfort prediction at low pressure.

The human body's thermal physiology changes due to atmospheric pressure, which significantly impacts the perception of thermal comfort. To quantify this effect, an improved version of the Predicted Mean Vote model (PMVp), was developed in this study to predict human thermal sensation under low atmospheric pressure conditions. The study employed environmental conditions of 0km/26°C, 3km/26°C, 4km/26°C, and 4km/21°C. Thirteen subjects were continuously monitored for exhaled CO2, inhaled O2, ambient temperature (ta), relative humidity (RH), air velocity (V), black globe temperature (tg), and altitude (H). The predictive performance of PMVp was evaluated by comparing the experimental results from this study with previous experiments. The findings demonstrate that PMVp exhibits lower root-mean-square errors (RMSE) than the original PMV model. Under the four experimental conditions, the RMSE values for PMVp were 0.311, 0.408, 0.123, and 0.375, while those for PMV were 1.251, 1.367, 1.106, and 1.716, respectively. Specifically, at a temperature range of 21∼27°C (altitude: 941m), the RMSE of PMVp (0.354) was smaller than PMV's. Furthermore, the study analyzed the sensitivity of PMVp to input parameters at an altitude of 4 km. PMVp exhibited considerable sensitivity to the metabolic rate (M) and thermal insulation of clothing (ICL). Consequently, a simple sensitivity scale was established: M>ICL>Ta≈V>Tr>H≈RH, indicating the relative importance of these parameters in influencing PMVp's response. The research findings provide comprehensive knowledge and a useful reference for developing a standard to design and evaluate indoor thermal environments in the plateau region.

Matrine suppresses NLRP3 inflammasome activation via regulating PTPN2/JNK/SREBP2 pathway in sepsis.

BACKGROUND: Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Abnormal activation of NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome plays a vital role in the pathogenesis of sepsis. Matrine is proved to show good anti-inflammatory properties, whereas its effect and the underlying molecular machinery on sepsis remains unclear. PURPOSE: The aim of this study is to evaluate the effect and mechanism of Matrine on sepsis. STUDY DESIGN: THP-1 cells and J774A.1 cells were stimulated by lipopolysaccharide (LPS) with nigericin or adenosine triphosphate (ATP) to establish an in vitro model. Cecal ligation and puncture (CLP)-induced sepsis mouse model was used. Matrine was given by gavage. METHODS: To investigate the NLRP3 inflammasome activation, phorbol myristate acetate (PMA)-induced THP-1 cells were first primed with LPS and then stimulated by matrine, followed by treatment with nigericin or ATP. The concentration of interleukin 1ß (IL-1ß) and interleukin 18 (IL-18) in the cell culture supernatant was detected. The mechanism was explored by cell death assay, immunoblots and immunofluorescence in vitro. C57BL/6 mice were intragastrically administered with matrine for 5 days before CLP. The therapeutic effect of matrine was evaluated by symptoms, pathological analysis, ELISA and RT-qPCR. RESULTS: Our results revealed that matrine inhibited IL-1ß and IL-18 secretion, suppressed caspase-1 activation, reduced cell death, and blocked ASC speck formation upon NLRP3 inflammasome activation. Furthermore, matrine restrains NLRP3 inflammasome activation as well as pyroptosis through regulating the protein tyrosine phosphatase non-receptor type 2 (PTPN2)/JNK/SREBP2 signaling. Matrine also prominently improved the symptoms and pathological changes with reduced levels of TNF-α, IL-1ß, and IL-6 in the lung tissues and serum in a dose-dependent manner. CONCLUSION: Matrine effectively alleviates the symptoms of CLP-induced sepsis in mice, restrains NLRP3 inflammasome activation by regulating PTPN2/JNK/SREBP2 signaling pathway, and may become a promising therapeutic agent for sepsis treatment.

IL-37 improves mice myocardial infarction via inhibiting YAP-NLRP3 signaling mediated macrophage programming.

OBJECTIVE: Myocardial infarction is the highest cause of cardiovascular death. Previous studies found that patients with myocardial infarction have elevated serum IL-37 and IL-37 treatment significantly alleviates adverse remodeling in myocardial infarction mice. However, the underlying mechanism of IL-37 in myocardial infarction is still unknown. Here we explored the underlying mechanism of IL-37 in attenuating myocardial infarction. METHODS: The myocardial infarction mice model was constructed by left anterior descending ligation and then submitted to recombinant IL-37 administration. The histology and cardiac function were detected by HE & Masson staining and echocardiography, respectively. The macrophage phenotypes were analyzed by flow cytometry and real-time PCR. The cytokines in serum and cell culture supernatant were determined by ELISA. In addition, THP-1 cells were used in vitro to investigate the underlying mechanisms. RESULTS: Infarcted mice showed increased inflammatory cell infiltration and impaired cardiac function. IL-37 treatment alleviated pro-inflammatory macrophage infiltration, tissue injury, and collagen deposition in hearts on day 3 and 7 after infarction in mice. In addition, IL-37 application modulated the balance between M1 and M2 macrophages in infarcted hearts. In vitro, THP-1 cell line polarization was also regulated by IL-37, companied by YAP phosphorylation and NLRP3 inactivation. Verteporfin, a YAP inhibitor, could abolish IL-37-induced NLRP3 inhibition and M2 macrophage polarization. CONCLUSION: Our results demonstrated that IL-37 achieves a favorable therapeutical function on myocardial infarction by modulating YAP-NLRP3 mediated macrophage programming, providing a promising drug for the treatment of myocardial infarction.

Paeoniflorin prevents aberrant proliferation and differentiation of intestinal stem cells by controlling C1q release from macrophages in chronic colitis.

The pathological features of inflammatory bowel disease necessitate therapeutic strategies aimed at restoring intestinal mucosal barrier function in addition to controlling inflammation. Paeoniflorin, a bioactive herbal constituent isolated from the root of Paeonia albiflora Pall, has been reported to protect against acute colitis in mice. However, the direct molecular target of paeoniflorin in preventing colitis remains elusive. Here, we evaluated the therapeutical effects of Paeoniflorin using IL-10-/- chronic colitis model, and explored the precise mechanism of action involved. Our results demonstrated that intragastric administration of Paeoniflorin significantly ameliorated inflammatory response and restored the aberrant intestinal proliferation and differentiation in IL-10-/-colitis mice. By utilizing a chemical biology approach, we identified C1qa, a crucial component of C1q, is the direct target of Paeoniflorin. Binding of Paeoniflorin to C1qa prevented the cleavage of C1q on macrophages, resulting in the aggregation of surface membrane-anchored C1q and the diminished C1q secretion. The excessive surface membrane-anchored C1q significantly enhanced the phagocytic capability of macrophages and promoted the elimination of infiltrated bacteria and inflammatory cells in mouse colon. The reduced C1q secretion conferred by Paeoniflorin dampened Wnt/ß-catenin signaling activation, thereby rectifying the aberrant proliferation and differentiation of intestinal stem cells (ISCs). In summary, our study demonstrates that Paeoniflorin can orchestrate mucosal healing and intestinal inflammation elimination through C1q-bridged macrophage-ISCs crosstalk, highlighting a novel strategy to treat chronic colitis by restoring mucosal homeostasis via targeting C1q.

Modulated pattern scanning microscopy.

In confocal microscopy, the effective optical transfer function (OTFeff) with Gaussian plane wave illumination covers very few high-frequency components, which prohibits further improvement of the resolution. We propose modulated pattern scanning microscopy (MPSM) to achieve super-resolution imaging. In MPSM, the phase of the illumination beam is modulated to reassign the OTFeff in the Fourier domain. The phase mask is designed using an optimization algorithm to obtain the fluorescence emission pattern with rich high-frequency components. Then, the postprocessing algorithms are adapted to retrieve the super-resolved images from the modulated recordings. Simulation and experiment demonstrate that MPSM increases the resolution approximately 1.3 times better than confocal microscopy. Compared with conventional deconvolution, MPSM exhibits a higher signal-to-noise ratio.

Identification and comparison of umami-peptides in commercially available dry-cured Spanish mackerels (Scomberomorus niphonius).

Dry-cured Spanish mackerel (DSM; Scomberomorus niphonius) is a popularity worldwide dry-cured marine fish product due to its salty and umami flavor. Umami peptides from eight commercial DSMs were identified and compared, and their molecular mechanisms were evaluated via molecular simulation. The results showed that the sequence of peptides varied in different DSMs, wherein only ten sequences were repeated across multiple samples and the remaining 19 were detected in only one sample. The sensory characteristics of eight repeated peptides were evaluated, and four were found to exhibit umami taste and umami-enhancing effects, including Arg-Asp, Asp-Gly-Val, Asp-Arg, and Asp-Lys. They all had a strong affinity for umami receptors, and several amino acid residues of the receptors were mobilized as binding sites to form hydrogen bonds and hydrophobic bonds in ligand-receptor interactions. These results indicated that DSM was rich in umami and umami-enhancing peptides, but their sequence were different in different DSMs.

Umami-enhancing effect of typical kokumi-active γ-glutamyl peptides evaluated via sensory analysis and molecular modeling approaches.

The umami-enhancing effect of typical kokumi-active γ-glutamyl peptides was verified by sensory evaluation. To investigate the umami-enhancing molecular mechanism of the peptide on monosodium glutamate (MSG) taste, a novel hypothetical receptor, taste type 1 receptor 3 (T1R3)-MSG complex, was constructed. These peptides demonstrated strong interactions with T1R3-MSG. Moreover, four amino acid residues, Glu-301, Ala-302, Thr-305, and Ser-306, were critical in ligand-receptor interactions. In detail, γ-Glu-γ-Glu-Val (γ-E-γ-EV) readily interacts with T1R3 through hydrogen bonds and hydrophobic interactions. While γ-E-γ-EV did not bind to MSG, γ-Glu-Val (γ-EV) and γ-Glu-Leu (γ-EL) showed high binding affinity to MSG and interacted with T1R3 through hydrophobic bonds suggesting that the interactions between dipeptides and T1R3-MSG were weaker than tripeptides. These results demonstrated that kokumi-active γ-glutamyl peptides could enhance the umami taste of MSG, and exhibit synergistic effects in activating T1R3. This study provides a theoretical reference for interactions between the novel umami-enhancing substances and umami receptor.

The application of L-glutaminase for the synthesis of the immunomodulatory γ-D-glutamyl-L-tryptophan and the kokumi-imparting γ-D-glutamyl peptides.

Glutaminase of Bacillus amyloliquefaciens has been used to synthesize the immunomodulatory γ-D-glutamyl-L-tryptophan (γ-D-Glu-L-Trp) and the kokumi-active γ-D-glutamyl peptides. The optimum yield of γ-D-Glu-L-Trp was 55.76 mM in corresponding to a minimum yield of by-product (γ-D-Glu-γ-D-Glu-L-Trp) in the presence of 75 mM D-Gln and 100 mM L-Trp. The glutaminase has a low Km values for the donors (D-Gln and L-Gln:5.53 and 0.98 mM), but high ones for the acceptors (L-Trp, L-Phe, L-Met, L-Val and γ-[D-Glu]( n =1,2,3)-L-Val/L-Phe/L-Met, ranging from 32.51 to 193.05 mM). The highest Km value appearing when n = 2 (γ-[D-Glu]( n =0,1,2)-L-Val/L-Phe/L-Met) suggested the rising difficulty for synthesis when the number of donor increases in the reaction mixtures. The γ-[D-Glu]( n =1,2,3)-L-Val/L-Phe/L-Met at 5 mM can impart the blank chicken broth an enhancing monthfulness, thickness, and umaminess taste.

Impact of meteorological and geographical factors on the distribution of leishmaniasis's vector in mainland China.

BACKGROUND: Phlebotomine sandfly (Diptera: Psychodidae) is best known for its role as the vector of the leishmaniasis. Leishmaniasis is a global disease, currently known to be affecting 88 countries and 12 million people worldwide. RESULTS: This study explored the impacts of climate factors and landscape on the local abundance of Phlebotomine sandfly in mainland China. A presence-only modelling method was used to evaluate this species' habitat preferences from environmental factors. Jackknife analysis revealed that several biologically meteorological variables, including the maximum temperature of the warmest quarter, the precipitation in the driest month, the daily average temperature and daily precipitation, would significantly affect the existence of this species. Moreover, the existence of Phlebotomine sandfly was significantly associated with grassland and forest. CONCLUSION: The results will improve scientific understanding of the risks of the spread of leishmaniasis over current infected areas and can be used to design more detailed surveillance programmes and more evidence-based control planning for Phlebotomine sandfly and leishmaniasis. © 2019 Society of Chemical Industry.

Gadolinium Doping Enhances the Photoacoustic Signal of Synthetic Melanin Nanoparticles: A Dual Modality Contrast Agent for Stem Cell Imaging.

In this paper, we show that gadolinium-loaded synthetic melanin nanoparticles (Gd(III)-SMNPs) exhibit up to a 40-fold enhanced photoacoustic signal intensity relative to synthetic melanin alone and higher than other metal-chelated SMNPs. This property makes these materials useful as dual labeling agents because Gd(III)-SMNPs also behave as magnetic resonance imaging (MRI) contrast agents. As a proof-of-concept, we used these nanoparticles to label human mesenchymal stem cells. Cellular uptake was confirmed with bright-field optical and transmission electron microscopy. The Gd(III)-SMNP-labeled stem cells continued to express the stem cell surface markers CD73, CD90, and CD105 and proliferate. The labeled stem cells were subsequently injected intramyocardially in mice, and the tissue was observed by photoacoustic and MR imaging. We found that the photoacoustic signal increased as the cell number increased (R 2 = 0.96), indicating that such an approach could be employed to discriminate between stem cell populations with a limit of detection of 2.3 × 104 cells in in vitro tests. This multimodal photoacoustic/MRI approach combines the excellent temporal resolution of photoacoustics with the anatomic resolution of MRI.

Multi-Scale Responses of Liquid Crystals Triggered by Interfacial Assemblies of Cleavable Homopolymers.

Liquid crystals (LCs) offer the basis of stimuli-responsive materials that can amplify targeted molecular events into macroscopic outputs. However, general and versatile design principles are needed to realize the full potential of these materials. To this end, we report the synthesis of two homopolymers with mesogenic side chains that can be cleaved upon exposure to either H2 O2 (polymer P1) or UV light (polymer P2). Optical measurements reveal that the polymers dissolve in bulk LC and spontaneously assemble at nematic LC-aqueous interfaces to impose a perpendicular orientation on the LCs. Subsequent addition of H2 O2 to the aqueous phase or exposure of the LC to UV was shown to trigger a surface-driven ordering transition to a planar orientation and an accompanying macroscopic optical output. Differences in the dynamics of the response to each stimulus are consistent with sequential processing of P1 at the LC-aqueous interface (H2 O2 ) and simultaneous transformation of P2 within the LC (UV). The versatility of the approach is demonstrated by creating stimuli-responsive LCs as films or microdroplets, and by dissolving mixtures of P1 and P2 into LCs to create LC materials that respond to two stimuli. Overall, our results validate a simple and generalizable approach to the rational design of polymers that can be used to program stimuli-responsiveness into LC materials.

High Relaxivity Gadolinium-Polydopamine Nanoparticles.

This study reports the preparation of a series of gadolinium-polydopamine nanoparticles (GdPD-NPs) with tunable metal loadings. GdPD-NPs are analyzed by nuclear magnetic relaxation dispersion and with a 7-tesla (T) magnetic resonance imaging (MRI) scanner. A relaxivity of 75 and 10.3 mM-1 s-1 at 1.4 and 7 T is observed, respectively. Furthermore, superconducting quantum interference device magnetometry is used to study intraparticle magnetic interactions and determine the GdPD-NPs consist of isolated metal ions even at maximum metal loadings. From these data, it is concluded that the observed high relaxivities arise from a high hydration state of the Gd(III) at the particle surface, fast rate of water exchange, and negligible antiferromagnetic coupling between Gd(III) centers throughout the particles. This study highlights design parameters and a robust synthetic approach that aid in the development of this scaffold for T1 -weighted, high relaxivity MRI contrast agents.

Mimicking Melanosomes: Polydopamine Nanoparticles as Artificial Microparasols.

A primary role of melanin in skin is the prevention of UV-induced nuclear DNA damage to human skin cells, where it serves to screen out harmful UV radiation. Melanin is delivered to keratinocytes in the skin after being excreted as melanosomes from melanocytes. Defects in melanin production in humans can cause diseases, many of which currently lack effective treatments due to their genetic origins (e.g., skin cancer, vitiligo, and albinism). The widespread prevalence of melanin-related diseases and an increasing interest in the performance of various polymeric materials related to melanin necessitates novel synthetic routes for preparing melanin-like materials. In this work, we prepared melanin-like nanoparticles (MelNPs) via spontaneous oxidation of dopamine, as biocompatible, synthetic analogues of naturally occurring melanosomes, and investigated their uptake, transport, distribution, and UV-protective capabilities in human keratinocytes. Critically, we demonstrate that MelNPs are endocytosed, undergo perinuclear aggregation, and form a supranuclear cap, or so-called microparasol in human epidermal keratinocytes (HEKa), mimicking the behavior of natural melananosomes in terms of cellular distribution and the fact that they serve to protect the cells from UV damage.

Simultaneous Enhancement of Photoluminescence, MRI Relaxivity, and CT Contrast by Tuning the Interfacial Layer of Lanthanide Heteroepitaxial Nanoparticles.

Nanoparticle (NP) based exogenous contrast agents assist biomedical imaging by enhancing the target visibility against the background. However, it is challenging to design a single type of contrast agents that are simultaneously suitable for various imaging modalities. The simple integration of different components into a single NP contrast agent does not guarantee the optimized properties of each individual components. Herein, we describe lanthanide-based core-shell-shell (CSS) NPs as triple-modal contrast agents that have concurrently enhanced performance compared to their individual components in photoluminescence (PL) imaging, magnetic resonance imaging (MRI), and computed tomography (CT). The key to simultaneous enhancement of PL intensity, MRI r1 relaxivity, and X-ray attenuation capability in CT is tuning the interfacial layer in the CSS NP architecture. By increasing the thickness of the interfacial layer, we show that (i) PL intensity is enhanced from completely quenched/dark state to brightly emissive state of both upconversion and downshifting luminescence at different excitation wavelengths (980 and 808 nm), (ii) MRI r1 relaxivity is enhanced by 5-fold from 11.4 to 52.9 mM-1 s-1 (per Gd3+) at clinically relevant field strength 1.5 T, and (iii) the CT Hounsfield Unit gain is 70% higher than the conventional iodine-based agents at the same mass concentration. Our results demonstrate that judiciously designed contrast agents for multimodal imaging can achieve simultaneously enhanced performance compared to their individual stand-alone structures and highlight that multimodality can be achieved without compromising on individual modality performance.

Polymer-Stabilized Perfluorobutane Nanodroplets for Ultrasound Imaging Agents.

In this paper, we describe a method for the stabilization of low-boiling point (low-bp) perfluorocarbons (PFCs) at physiological temperatures by an amphiphilic triblock copolymer which can emulsify PFCs and be cross-linked. After UV-induced thiol-ene cross-linking, the core of the PFC emulsion remains in liquid form even at temperatures exceeding their boiling points. Critically, the formulation permits vaporization at rarefactional pressures relevant for clinical ultrasound.

Structure and Function of Iron-Loaded Synthetic Melanin.

We describe a synthetic method for increasing and controlling the iron loading of synthetic melanin nanoparticles and use the resulting materials to perform a systematic quantitative investigation on their structure-property relationship. A comprehensive analysis by magnetometry, electron paramagnetic resonance, and nuclear magnetic relaxation dispersion reveals the complexities of their magnetic behavior and how these intraparticle magnetic interactions manifest in useful material properties such as their performance as MRI contrast agents. This analysis allows predictions of the optimal iron loading through a quantitative modeling of antiferromagnetic coupling that arises from proximal iron ions. This study provides a detailed understanding of this complex class of synthetic biomaterials and gives insight into interactions and structures prevalent in naturally occurring melanins.