Chlamydia psittaci infected cell studies by 4Pi Raman and atomic force microscopy.

Chlamydia psittaci is an avian bacterial pathogen that can cause atypical pneumonia in humans via zoonotic transmission. It is a Gram-negative intracellular bacterium that proliferates inside membrane bound inclusions in the cytoplasm of living eukaryotic cells. The study of such cells with C. psittaci inside without destroying them poses a significant challenge. We demonstrated in this work the utility of a combined multitool approach to analyze such complex samples. Atomic force microscopy was applied to obtain high-resolution images of the surface of infected cells upon entrance of bacteria. Atomic force microscopy scans revealed the morphological changes of the cell membrane of Chlamydia infected cells such as changes in roughness of cell membrane and the presence of micro vesicles. 4Pi Raman microscopy was used to image and probe the molecular composition of intracellular bacteria inside intact cells. Information about the structure of the inclusion produced by C. psittaci was obtained and it was found to have a similar molecular fingerprint as that of an intracellular lipid droplet but with less proteins and unsaturated lipids. The presented approach demonstrates complementarity of various microscopy-based approaches and might be useful for characterization of intracellular bacteria.

Three-dimensional co-culturing of stem cell-derived cardiomyocytes and cardiac fibroblasts reveals a role for both cell types in Marfan-related cardiomyopathy.

Pathogenic variants in the FBN1 gene, which encodes the extracellular matrix protein fibrillin-1, cause Marfan syndrome (MFS), which affects multiple organ systems, including the cardiovascular system. Myocardial dysfunction has been observed in a subset of patients with MFS and in several MFS mouse models. However, there is limited understanding of the intrinsic consequences of FBN1 variants on cardiomyocytes (CMs). To elucidate the CM-specific contribution in Marfan's cardiomyopathy, cardiosphere cultures of CMs and cardiac fibroblasts (CFs) are used. CMs and CFs were derived by human induced pluripotent stem cell (iPSC) differentiation from MFS iPSCs with a pathogenic variant in FBN1 (c.3725G>A; p.Cys1242Tyr) and the corresponding CRISPR-corrected iPSC line (Cor). Cardiospheres containing MFS CMs show decreased FBN1, COL1A2 and GJA1 expression. MFS CMs cultured in cardiospheres have fewer binucleated CMs in comparison with Cor CMs. 13% of MFS CMs in cardiospheres are binucleated and 15% and 16% in cardiospheres that contain co-cultures with respectively MFS CFs and Cor CFs, compared to Cor CMs, that revealed up to 23% binucleation when co-cultured with CFs. The sarcomere length of CMs, as a marker of development, is significantly increased in MFS CMs interacting with Cor CF or MFS CF, as compared to monocultured MFS CMs. Nuclear blebbing was significantly more frequent in MFS CFs, which correlated with increased stiffness of the nuclear area compared to Cor CFs. Our cardiosphere model for Marfan-related cardiomyopathy identified a contribution of CFs in Marfan-related cardiomyopathy and suggests that abnormal early development of CMs may play a role in the disease mechanism.

Optimization of hybrid gelatin-polysaccharide bioinks exploiting thiol-norbornene chemistry using a reducing additive.

Thiol-norbornene chemistry offers great potential in the field of hydrogel development, given its step growth crosslinking mechanism. However, limitations exist with regard to deposition-based bioprinting of thiol-containing hydrogels, associated with premature crosslinking of thiolated (bio)polymers resulting from disulfide formation in the presence of oxygen. More specifically, disulfide formation can result in an increase in viscosity thereby impeding the printing process. In the present work, hydrogels constituting norbornene-modified dextran (DexNB) combined with thiolated gelatin (GelSH) are selected as case study to explore the potential of incorporating the reducing agent tris(2-carboxyethyl)phosphine (TCEP), to prevent the formation of disulfides. We observed that, in addition to preventing disulfide formation, TCEP also contributed to premature, spontaneous thiol-norbornene crosslinking without the use of UV light as evidenced via1H-NMR spectroscopy. Herein, an optimal concentration of 25 mol% TCEP with respect to the amount of thiols was found, thereby limiting auto-gelation by both minimizing disulfide formation and spontaneous thiol-norbornene reaction. This concentration results in a constant viscosity during at least 24 h, a more homogeneous network being formed as evidenced using atomic force microscopy while retaining bioink biocompatibility as evidenced by a cell viability of human foreskin fibroblasts exceeding 70% according to ISO 10993-6:2016.

Gelatin-Based Hybrid Hydrogels as Matrices for Organoid Culture.

The application of liver organoids is very promising in the field of liver tissue engineering; however, it is still facing some limitations. One of the current major limitations is the matrix in which they are cultured. The mainly undefined and murine-originated tumor matrices derived from Engelbreth-Holm-Swarm (EHS) sarcoma, such as Matrigel, are still the standard culturing matrices for expansion and differentiation of organoids toward hepatocyte-like cells, which will obstruct its future clinical application potential. In this study, we exploited the use of newly developed highly defined hydrogels as potential matrices for the culture of liver organoids and compared them to Matrigel and two hydrogels that were already researched in the field of organoid research [i.e., polyisocyanopeptides, enriched with laminin-entactin complex (PIC-LEC) and gelatin methacryloyl (GelMA)]. The newly developed hydrogels are materials that have a physicochemical resemblance with native liver tissue. Norbornene-modified dextran cross-linked with thiolated gelatin (DexNB-GelSH) has a swelling ratio and macro- and microscale properties that highly mimic liver tissue. Norbornene-modified chondroitin sulfate cross-linked with thiolated gelatin (CSNB-GelSH) contains chondroitin sulfate, which is a glycosaminoglycan (GAG) that is present in the liver ECM. Furthermore, CSNB-GelSH hydrogels with different mechanical properties were evaluated. Bipotent intrahepatic cholangiocyte organoids (ICOs) were applied in this work and encapsulated in these materials. This research revealed that the newly developed materials outperformed Matrigel, PIC-LEC, and GelMA in the differentiation of ICOs toward hepatocyte-like cells. Furthermore, some trends indicate that an interplay of both the chemical composition and the mechanical properties has an influence on the relative expression of certain hepatocyte markers. Both DexNB-GelSH and CSNB-GelSH showed promising results for the expansion and differentiation of intrahepatic cholangiocyte organoids. The stiffest CSNB-GelSH hydrogel even significantly outperformed Matrigel based on ALB, BSEP, and CYP3A4 gene expression, being three important hepatocyte markers.

2D fibrillar osteoid niche mimicry through inclusion of visco-elastic and topographical cues in gelatin-based networks.

Given the clinical need for osteoregenerative materials incorporating controlled biomimetic and biophysical cues, a novel highly-substituted norbornene-modified gelatin was developed enabling thiol-ene crosslinking exploiting thiolated gelatin as cell-interactive crosslinker. Comparing the number of physical crosslinks, the degree of hydrolytic degradation upon modification, the network density and the chemical crosslinking type, the osteogenic effect of visco-elastic and topographical properties was evaluated. This novel network outperformed conventional gelatin-based networks in terms of osteogenesis induction, as evidenced in 2D dental pulp stem cell seeding assays, resulting from the presentation of both a local (substrate elasticity, 25-40 kPa) and a bulk (compressive modulus, 25-45 kPa) osteogenic substrate modulus in combination with adequate fibrillar cell adhesion spacing to optimally transfer traction forces from the fibrillar ECM (as evidenced by mesh size determination with the rubber elasticity theory) and resulting in a 1.7-fold increase in calcium production (compared to the gold standard gelatin methacryloyl (GelMA)).

Alginate-CaCO3 hybrid colloidal hydrogel with tunable physicochemical properties for cell growth.

Biomaterials composed of food polysaccharides are of great interest for future biomedical applications due to their great biocompatibility, tunable mechanical properties, and complex architectural designs that play a crucial role in the modulation of cell adhesion and proliferation. In this work, a facile approach was designed to obtain novel 3D alginate-CaCO3 hybrid hydrogel particles in situ. Controlling the gel concentration from 3 to 20 mg·mL-1 allows us to control the alginate-CaCO3 hydrogel particles' size and density (size variation from 1.86 to 2.34 mm and density from 1.22 to 1.29 mg/mm3). This variable also has a considerable influence on the mineralization process resulting in CaCO3 particles with varied sizes and amounts within the hydrogel beads. The measurements of Young's modulus showed that the inclusion of CaCO3 particles into the alginate hydrogel improved its mechanical properties, and Young's modulus of these hybrid hydrogel particles had a linear relationship with alginate content and hydrogel particle size. Cell experiments indicated that alginate-CaCO3 hybrid hydrogel particles can support osteoblastic cell proliferation and growth. In particular, the amount of hydroxyapatite deposition on the cell membrane significantly increased after the treatment of cells with hybrid hydrogel particles, up to 20-fold. This work offers a strategy for constructing inorganic particle-doped polysaccharide hybrid hydrogel scaffolds that provide the potential to support cell growth.

Effect of molar mass and alkyl chain length on the surface properties and biocompatibility of poly(alkylene terephthalate)s for potential cardiovascular applications.

Cardiovascular diseases are the leading cause of death worldwide. Treatments for occluded arteries include balloon angioplasty with or without stenting and bypass grafting surgery. Poly(ethylene terephthalate) is frequently used as a vascular graft material, but its high stiffness leads to compliance mismatch with the human blood vessels, resulting in altered hemodynamics, thrombus formation and graft failure. Poly(alkylene terephthalate)s (PATs) with longer alkyl chain lengths hold great potential for improving the compliance. In this work, the effect of the polymer molar mass and the alkyl chain length on the surface roughness and wettability of spin-coated PAT films was investigated, as well as the endothelial cell adhesion and proliferation on these samples. We found that surface roughness generally increases with increasing molar mass and alkyl chain length, while no trend for the wettability could be observed. All investigated PATs are non-cytotoxic and support endothelial cell adhesion and growth. For some PATs, the endothelial cells even reorganized into a tubular-like structure, suggesting angiogenic maturation. In conclusion, this research demonstrates the biocompatibility of PATs and their potential to be applied as materials serving cardiovascular applications.

Mechanobiology of Ferroptotic Cancer Cells as a Novel "Eat-Me" Signal: Regulating Efferocytosis through Layer-by-Layer Coating.

The importance of the clearance of dead cells is shown to have a regulatory role for normal tissue homeostasis and for the modulation of immune responses. However, how mechanobiological properties of dead cells affect efferocytosis remains largely unknown. Here, it is reported that the Young's modulus of cancer cells undergoing ferroptosis is reduced. To modulate their Young's modulus a layer-by-layer (LbL) nanocoating is developed. Scanning electron and fluorescence microscopy confirm coating efficiency of ferroptotic cells while atomic force microscopy reveals encapsulation of the dead cells increases their Young's modulus dependent on the number of applied LbL layers which increases their efferocytosis by primary macrophages. This work demonstrates the crucial role of mechanobiology of dead cells in regulating their efferocytosis by macrophages which can be exploited for the development of novel therapeutic strategies for diseases where modulation of efferocytosis can be potentially beneficial and for the design of drug delivery systems for cancer therapy.

High-throughput mechano-cytometry as a method to detect apoptosis, necroptosis, and ferroptosis.

In recent years, the importance of the investigation of regulated cell death (RCD) has significantly increased and different methods are proposed for the detection of RCD including biochemical as well as fluorescence assays. Researchers have shown that early stages of cell death could be detected by using AFM. Although AFM offers a high single-cell resolution and sensitivity, the throughput (<100 cells/h) limits a broad range of biomedical applications of this technique. Here, a microfluidics-based mechanobiology technique, named shear flow deformability cytometry (sDC), is used to investigate and distinguish dying cells from viable cells purely based on their mechanical properties. Three different RCD modalities (i.e., apoptosis, necroptosis, and ferroptosis) are induced in L929sAhFas cells and analysed using sDC. Using machine learning on the extracted parameters, it was possible to predict the dead or viable state with 92% validation accuracy. A significant decrease in elasticity can be noticed for each of these RCD modalities by analysing the deformation of the dying cells. Analysis of morphological characteristics such as cell size and membrane irregularities also indicated significant differences in the RCD induced cells versus control cells. These results highlight the importance of mechanical properties during RCD and the significance of label-free techniques, such as sDC, which can be used to detect regulated cell death and can be further linked with sorting of live and dead cells.

Gelatin-Based Hybrid Hydrogel Scaffolds: Toward Physicochemical Liver Mimicry.

There exists a clear need to develop novel materials that could serve liver tissue engineering purposes. Those materials need to be researched for the development of bioengineered liver tissue as an alternative to donor livers, as well as for materials that could be applied for scaffolds to develop an in vitro model for drug-induced liver injury (DILI) detection . In this paper, the hydrogels oxidized dextran-gelatin (Dexox-Gel) and norbornene-modified dextran-thiolated gelatin (DexNB-GelSH) were developed, and their feasibility toward processing via indirect 3D-printing was investigated with the aim to develop hydrogel scaffolds that physicochemically mimic native liver tissue. Furthermore, their in vitro biocompatibility was assessed using preliminary biological tests using HepG2 cells. Both materials were thoroughly physicochemically characterized and benchmarked to the methacrylated gelatin (GelMA) reference material. Due to inferior properties, Dexox-gel was not further processed into 3D-hydrogel scaffolds. This research revealed that DexNB-GelSH exhibited physicochemical properties that were in excellent agreement with the properties of natural liver tissue in contrast to GelMA. In combination with an equally good biological evaluation of DexNB-GelSH in comparison with GelMA based on an MTS proliferation assay and an albumin quantification assay, DexNB-GelSH can be considered promising in the field of liver tissue engineering.

The influence of Ca/Mg ratio on autogelation of hydrogel biomaterials with bioceramic compounds.

Hydrogels, which are versatile three-dimensional structures containing polymers and water, are very attractive for use in biomedical fields, but they suffer from rather weak mechanical properties. In this regard, biocompatible particles can be used to enhance their mechanical properties. The possibility of loading such particles with drugs (e.g. enzymes) makes them a particularly useful component in hydrogels. In this study, micro/nanoparticles containing various ratios of Ca2+/Mg2+ with sizes ranging from 1 to 8 µm were prepared and mixed with gellan gum (GG) solution to study the in-situ formation of hydrogel-particle composites. The particles provide multiple functionalities: 1) they efficiently crosslink GG to induce hydrogel formation through the release of the divalent cations (Ca2+/Mg2+) known to bind to GG polymer chains; 2) they enhance mechanical properties of the hydrogel from 2 up to 100 kPa; 3) the samples most efficiently promoting cell growth were found to contain two types of minerals: vaterite and hydroxymagnesite, which enhanced cells proliferation and hydroxyapatite formation. The results demonstrate that such composite materials are attractive candidates for applications in bone regeneration.

The type-1 ribosome-inactivating protein OsRIP1 triggers caspase-independent apoptotic-like death in HeLa cells.

Ribosome-inactivating proteins (RIPs) are capable of removing a specific adenine from 28S ribosomal RNA, thus inhibiting protein biosynthesis in an irreversible manner. In this study, recombinant OsRIP1, a type 1 RIP from rice (Oryza sativa L.), was investigated for its anti-proliferative properties. Human cervical cancer HeLa cells were incubated in the presence of OsRIP1 for 24-72 h. OsRIP1 treatment yielded an anti-proliferation response of the HeLa cells and resulted in apoptotic-like blebbing of the plasma membrane without causing DNA fragmentation. OsRIP1 labeled with FITC accumulated at the cell surface. Pull-down assays identified ASPP1 (Apoptosis-Stimulating Protein of p53 1) and IFITM3 (interferon-induced transmembrane protein 3) as potential interaction partners for OsRIP1. Transcript levels for several critical genes related to different signaling pathways were quantified by RT-qPCR. OsRIP1 provoked HeLa cells to undergo caspase-independent cell death, associated with a significant transcriptional upregulation of the apoptotic gene PUMA, interferon regulatory factor 1 (IRF1) and the autophagy-related marker LC3. No changes in caspase activities were observed. Together, these data suggest that apoptotic-like events were involved in OsRIP1-driven caspase-independent cell death that might trigger the IRF1 signaling pathway and LC3-mediated autophagy.

Potential of poly(alkylene terephthalate)s to control endothelial cell adhesion and viability.

Poly(ethylene terephthalate) (PET) is known for its various useful characteristics, including its applicability in cardiovascular applications, more precisely as synthetic bypass grafts for large diameter (≥ 6 mm) blood vessels. Although it is widely used, PET is not an optimal material as it is not interactive with endothelial cells, which is required for bypasses to form a complete endothelium. Therefore, in this study, poly(alkylene terephthalate)s (PATs) have been studied. They were synthesized via a single-step solution polycondensation reaction, which requires mild reaction conditions and avoids the use of a catalyst or additives like heat stabilizers. A homologous series was realized in which the alkyl chain length varied from 5 to 12 methylene groups (n = 5-12). Molar masses up to 28,000 g/mol were obtained, while various odd-even trends were observed with modulated differential scanning calorimetry (mDSC) and rapid heat-cool calorimetry (RHC) to access the thermal properties within the homologous series. The synthesized PATs have been subjected to in vitro cell viability assays using Human Umbilical Vein Endothelial Cells (HUVECs) and Human Dermal Microvascular Endothelial Cells (HDMECs). The results showed that HUVECs adhere and proliferate most pronounced onto PAT(n=9) surfaces, which could be attributed to the surface roughness and morphology as determined by atomic force microscopy (AFM) (i.e. Rq = 204.7 nm). HDMECs were investigated in the context of small diameter vessels and showed superior adhesion and proliferation after seeding onto PAT(n=6) substrates. These preliminary results already pave the way towards the use of PAT materials as substrates to support endothelial cell adhesion and growth. Indeed, as superior endothelial cell interactivity compared to PET was observed, time-consuming and costly surface modifications of PET grafts could be avoided by exploiting this novel material class.

Deep learning with digital holographic microscopy discriminates apoptosis and necroptosis.

Regulated cell death modalities such as apoptosis and necroptosis play an important role in regulating different cellular processes. Currently, regulated cell death is identified using the golden standard techniques such as fluorescence microscopy and flow cytometry. However, they require fluorescent labels, which are potentially phototoxic. Therefore, there is a need for the development of new label-free methods. In this work, we apply Digital Holographic Microscopy (DHM) coupled with a deep learning algorithm to distinguish between alive, apoptotic and necroptotic cells in murine cancer cells. This method is solely based on label-free quantitative phase images, where the phase delay of light by cells is quantified and is used to calculate their topography. We show that a combination of label-free DHM in a high-throughput set-up (~10,000 cells per condition) can discriminate between apoptosis, necroptosis and alive cells in the L929sAhFas cell line with a precision of over 85%. To the best of our knowledge, this is the first time deep learning in the form of convolutional neural networks is applied to distinguish-with a high accuracy-apoptosis and necroptosis and alive cancer cells from each other in a label-free manner. It is expected that the approach described here will have a profound impact on research in regulated cell death, biomedicine and the field of (cancer) cell biology in general.

AFM Analysis Enables Differentiation between Apoptosis, Necroptosis, and Ferroptosis in Murine Cancer Cells.

Regulated cell death (RCD) has a fundamental role in development, pathology, and tissue homeostasis. In order to understand the RCD mechanisms, it is essential to follow these processes in real time. Here, atomic force microscopy (AFM) is applied to morphologically and mechanically characterize four RCD modalities (intrinsic and extrinsic apoptosis, necroptosis, and ferroptosis) in murine tumor cell lines. The nano-topographical analysis revealed a distinct surface morphology in case of necroptosis, ∼ 200 nm membrane disruptions are observed. Using mechanical measurements, it is possible to detect the early onset of RCD. Combined elasticity and microrheology analysis allowed for a clear distinction between apoptotic and regulated necrotic cell death. Finally, immunofluorescence analysis of the cytoskeleton structure during the RCD processes confirm the measured mechanical changes. The results of this study not only demonstrate the possibility of early real-time cell death detection but also reveal important differences in the cytoskeletal dynamics between multiple RCD modalities.

Vaccination with early ferroptotic cancer cells induces efficient antitumor immunity.

BACKGROUND: Immunotherapy represents the future of clinical cancer treatment. The type of cancer cell death determines the antitumor immune response and thereby contributes to the efficacy of anticancer therapy and long-term survival of patients. Induction of immunogenic apoptosis or necroptosis in cancer cells does activate antitumor immunity, but resistance to these cell death modalities is common. Therefore, it is of great importance to find other ways to kill tumor cells. Recently, ferroptosis has been identified as a novel, iron-dependent form of regulated cell death but whether ferroptotic cancer cells are immunogenic is unknown. METHODS: Ferroptotic cell death in murine fibrosarcoma MCA205 or glioma GL261 cells was induced by RAS-selective lethal 3 and ferroptosis was analyzed by flow cytometry, atomic force and confocal microscopy. ATP and high-mobility group box 1 (HMGB1) release were detected by luminescence and ELISA assays, respectively. Immunogenicity in vitro was analyzed by coculturing of ferroptotic cancer cells with bone-marrow derived dendritic cells (BMDCs) and rate of phagocytosis and activation/maturation of BMDCs (CD11c+CD86+, CD11c+CD40+, CD11c+MHCII+, IL-6, RNAseq analysis). The tumor prophylactic vaccination model in immune-competent and immune compromised (Rag-2-/-) mice was used to analyze ferroptosis immunogenicity. RESULTS: Ferroptosis can be induced in cancer cells by inhibition of glutathione peroxidase 4, as evidenced by confocal and atomic force microscopy and inhibitors' analysis. We demonstrate for the first time that ferroptosis is immunogenic in vitro and in vivo. Early, but not late, ferroptotic cells promote the phenotypic maturation of BMDCs and elicit a vaccination-like effect in immune-competent mice but not in Rag-2-/- mice, suggesting that the mechanism of immunogenicity is very tightly regulated by the adaptive immune system and is time dependent. Also, ATP and HMGB1, the best-characterized damage-associated molecular patterns involved in immunogenic cell death, have proven to be passively released along the timeline of ferroptosis and act as immunogenic signal associated with the immunogenicity of early ferroptotic cancer cells. CONCLUSIONS: These results pave the way for the development of new therapeutic strategies for cancers based on induction of ferroptosis, and thus broadens the current concept of immunogenic cell death and opens the door for the development of new strategies in cancer immunotherapy.

Effects of fibrillin mutations on the behavior of heart muscle cells in Marfan syndrome.

Marfan syndrome (MFS) is a systemic disorder of connective tissue caused by pathogenic variants in the fibrillin-1 (FBN1) gene. Myocardial dysfunction has been demonstrated in MFS patients and mouse models, but little is known about the intrinsic effect on the cardiomyocytes (CMs). In this study, both induced pluripotent stem cells derived from a MFS-patient and the line with the corrected FBN1 mutation were differentiated to CMs. Several functional analyses are performed on this model to study MFS related cardiomyopathy. Atomic force microscopy revealed that MFS CMs are stiffer compared to corrected CMs. The contraction amplitude of MFS CMs is decreased compared to corrected CMs. Under normal culture conditions, MFS CMs show a lower beat-to-beat variability compared to corrected CMs using multi electrode array. Isoproterenol-induced stress or cyclic strain demonstrates lack of support from the matrix in MFS CMs. This study reports the first cardiac cell culture model for MFS, revealing abnormalities in the behavior of MFS CMs that are related to matrix defects. Based on these results, we postulate that impaired support from the extracellular environment plays a key role in the improper functioning of CMs in MFS.

Temperature Window for Encapsulation of an Enzyme into Thermally Shrunk, CaCO3 Templated Polyelectrolyte Multilayer Capsules.

Encapsulation of enzymes allows to preserve their biological activities in various environmental conditions, such as exposure to elevated temperature or to proteases. This is particularly relevant for in vivo applications, where proteases represent a severe obstacle to maintaining the activity of enzymes. Polyelectrolyte multilayer capsules are suitable for enzyme encapsulation, where CaCO3 particles and temperature-dependent capsule formation are the best templates and the most adequate method, respectively. In this work, these two areas are combined and, ALP (alkaline phosphatase), which is a robust and therapeutically relevant enzyme, is encapsulated into thermally shrunk polyelectrolyte multilayer (PDADMAC/PSS)4 capsules templated on calcium carbonate particles (original average diameter: ≈3.5 µm). The activity of the encapsulated enzyme and the optimal temperature range for encapsulation are investigated. The enzymatic activity is almost four times higher upon encapsulation when the temperature range for encapsulation is situated just above the glass transition temperature (40 °C), while its optimal conditions are dictated, on the one hand, by the enzyme activity (better at lower temperatures) and, on the other hand, by the size and mechanical properties of capsules (better at higher temperatures).

Identification and Analysis of Key Parameters for the Ossification on Particle Functionalized Composites Hydrogel Materials.

Developing materials for tissue engineering and studying the mechanisms of cell adhesion is a complex and multifactor process that needs analysis using physical chemistry and biology. The major challenge is the labor-intensive data mining as well as requirements of the number of advanced techniques. For example, hydrogel-based biomaterials with cell-binding sites, tunable mechanical properties, and complex architectures have emerged as a powerful tool to control cell adhesion and proliferation for tissue engineering. Composite hydrogels could be used for bone tissue regeneration, but they exhibit poor ossification properties. In current work, we have designed new osteoinductive gellan gum hydrogels by a thermal annealing approach and consequently functionalized them with Ca/Mg carbonate submicron particles. Determination of key parameters, which influence a successful hydroxyapatite generation, was done via the principal component analysis of 18 parameters (Young's modulus of the hydrogel and particles, particle size, and mass) and cell behavior at various time points (like viability, numbers of the cells, rate of alkaline phosphatase production, and cells area) obtained by characterizing such composite hydrogel. It is determined that the particles size and concentration of calcium ions have a dominant effect on the hydroxyapatite formation, because of providing local areas with a high Young's modulus in a hydrogel, a desirable property for cell adhesion. The detailed analysis presented here allows identifying hydrogels for cell growth applications, while on the other hand, material properties can be predicted, and their overall number can be minimized leading to efficient optimization of bone reconstruction and other cell growth applications.

Classification of analytics, sensorics, and bioanalytics with polyelectrolyte multilayer capsules.

Polyelectrolyte multilayer (PEM) capsules, constructed by LbL (layer-by-layer)-adsorbing polymers on sacrificial templates, have become important carriers due to multifunctionality of materials adsorbed on their surface or encapsulated into their interior. They have been also been used broadly used as analytical tools. Chronologically and traditionally, chemical analytics has been developed first, which has long been synonymous with all analytics. But it is not the only development. To the best of our knowledge, a summary of all advances including their classification is not available to date. Here, we classify analytics, sensorics, and biosensorics functionalities implemented with polyelectrolyte multilayer capsules and coated particles according to the respective stimuli and application areas. In this classification, three distinct categories are identified: (I) chemical analytics (pH; K+, Na+, and Pb2+ ion; oxygen; and hydrogen peroxide sensors and chemical sensing with surface-enhanced Raman scattering (SERS)); (II) physical sensorics (temperature, mechanical properties and forces, and osmotic pressure); and (III) biosensorics and bioanalytics (fluorescence, glucose, urea, and protease biosensing and theranostics). In addition to this classification, we discuss also principles of detection using the above-mentioned stimuli. These application areas are expected to grow further, but the classification provided here should help (a) to realize the wealth of already available analytical and bioanalytical tools developed with capsules using inputs of chemical, physical, and biological stimuli and (b) to position future developments in their respective fields according to employed stimuli and application areas. Graphical abstract.