Probing the pH Microenvironment of Mesenchymal Stromal Cell Cultures on Additive-Manufactured Scaffolds

Facile One Pot Synthesis of Hybrid Core-Shell Silica-Based Sensors for Live Imaging of Dissolved Oxygen and Hypoxia Mapping in 3D Cell Models

Fluorescence imaging allows for noninvasively visualizing and measuring key physiological parameters like pH and dissolved oxygen. In our work, we created two ratiometric fluorescent microsensors designed for accurately tracking dissolved oxygen levels in 3D cell cultures. We developed a simple and cost-effective method to produce hybrid core-shell silica microparticles that are biocompatible and versatile. These sensors incorporate oxygen-sensitive probes (Ru(dpp) or PtOEP) and reference dyes (RBITC or A647 NHS-Ester). SEM analysis confirmed the efficient loading and distribution of the sensing dye on the outer shell. Fluorimetric and CLSM tests demonstrated the sensors' reversibility and high sensitivity to oxygen, even when integrated into 3D scaffolds. Aging and bleaching experiments validated the stability of our hybrid core-shell silica microsensors for 3D monitoring. The Ru(dpp)-RBITC microparticles showed the most promising performance, especially in a pancreatic cancer model using alginate microgels. By employing computational segmentation, we generated 3D oxygen maps during live cell imaging, revealing oxygen gradients in the extracellular matrix and indicating a significant decrease in oxygen level characteristics of solid tumors. Notably, after 12 h, the oxygen concentration dropped to a hypoxic level of PO2 2.7 ± 0.1%.

Nanoclay Reinforced Integrated Scaffold for Dual-Lineage Regeneration of Cartilage and Subchondral Bone

Tissue engineering is theoretically considered a promising approach for repairing osteochondral defects. Nevertheless, the insufficient osseous support and integration of the cartilage layer and the subchondral bone frequently lead to the failure of osteochondral repair. Drawing from this, it was proposed that incorporating glycine-modified attapulgite (GATP) into poly(1,8-octanediol-co-citrate) (POC) scaffolds via the one-step chemical cross-linking is proposed to enhance cartilage and subchondral bone defect repair simultaneously. The effects of the GATP incorporation ratio on the physicochemical properties, chondrocyte and MC3T3-E1 behavior, and osteochondral defect repair of the POC scaffold were also evaluated. In vitro studies indicated that the POC/10% GATP scaffold improved cell proliferation and adhesion, maintained cell phenotype, and upregulated chondrogenesis and osteogenesis gene expression. Animal studies suggested that the POC/10% GATP scaffold has significant repair effects on both cartilage and subchondral bone defects. Therefore, the GATP-incorporated scaffold system with dual-lineage bioactivity showed potential application in osteochondral regeneration.

Psidium guajava L. phenolic compound-reinforced lamellar scaffold for tracheal tissue engineering

The aim of this work was to develop a dense lamellar scaffold, as a biomimetic material with potential applications in the regeneration of tracheal tissue after surgical tumor resection. The scaffolds were produced by plastic compression technique, exploiting the use of total phenolic compounds (TPC) from Psidium guajava Linn as a potential cross-linking agent in a polymeric mixture based on collagen (COL), silk fibroin (SF), and polyethylene glycol 400 (PEG 400). Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) confirmed the chemical interactions between the polymers and the cross-linking of TPC between COL and SF. Morphological analyses showed scaffolds with porosity, interconnectivity, and a porous surface structure with a gyroid-like geometry. The analysis of the anisotropic degree resulted in anisotropic structures (0.1% TFC and 0.3% TFC) and an isotropic structure (0.5% TFC). In the mechanical properties, it was evidenced greater resistance for the 0.3% TFC formulation. The addition of TPC percentages did not result in a significant difference (p > 0.05) in swelling capacity and disintegration rate. The results confirmed that TPC were able to modulate the morphological, morphometric, and mechanical properties of scaffolds. Thus, this study describes a potential new material to improve the regeneration of major tracheal structures after surgical tumor removal.

Fluorescent nano- and microparticles for sensing cellular microenvironment: past, present and future applications

The tumor microenvironment (TME) demonstrates distinct hallmarks, including acidosis, hypoxia, reactive oxygen species (ROS) generation, and altered ion fluxes, which are crucial targets for early cancer biomarker detection, tumor diagnosis, and therapeutic strategies. Various imaging and sensing techniques have been developed and employed in both research and clinical settings to visualize and monitor cellular and TME dynamics. Among these, ratiometric fluorescence-based sensors have emerged as powerful analytical tools, providing precise and sensitive insights into TME and enabling real-time detection and tracking of dynamic changes. In this comprehensive review, we discuss the latest advancements in ratiometric fluorescent probes designed for the optical mapping of pH, oxygen, ROS, ions, and biomarkers within the TME. We elucidate their structural designs and sensing mechanisms as well as their applications in in vitro and in vivo detection. Furthermore, we explore integrated sensing platforms that reveal the spatiotemporal behavior of complex tumor cultures, highlighting the potential of high-resolution imaging techniques combined with computational methods. This review aims to provide a solid foundation for understanding the current state of the art and the future potential of fluorescent nano- and microparticles in the field of cellular microenvironment sensing.

pH-sensing hybrid hydrogels for non-invasive metabolism monitoring in tumor spheroids

The constant increase in cancer incidence and mortality pushes biomedical research towards the development of in vitro 3D systems able to faithfully reproduce and effectively probe the tumor microenvironment. Cancer cells interact with this complex and dynamic architecture, leading to peculiar tumor-associated phenomena, such as acidic pH conditions, rigid extracellular matrix, altered vasculature, hypoxic condition. Acidification of extracellular pH, in particular, is a well-known feature of solid tumors, correlated to cancer initiation, progression, and resistance to therapies. Monitoring local pH variations, non-invasively, during cancer growth and in response to drug treatment becomes extremely important for understanding cancer mechanisms. Here, we describe a simple and reliable pH-sensing hybrid system, based on a thermoresponsive hydrogel embedding optical pH sensors, that we specifically apply for non-invasive and accurate metabolism monitoring in colorectal cancer (CRC) spheroids. First, the physico-chemical properties of the hybrid sensing platform, in terms of stability, rheological and mechanical properties, morphology and pH sensitivity, were fully characterized. Then, the proton gradient distribution in the spheroids proximity, in the presence or absence of drug treatment, was quantified over time by time lapse confocal light scanning microscopy and automated segmentation pipeline, highlighting the effects of the drug treatment in the extracellular pH. In particular, in the treated CRC spheroids the acidification of the microenvironment resulted faster and more pronounced over time. Moreover, a pH gradient distribution was detected in the untreated spheroids, with more acidic values in proximity of the spheroids, resembling the cell metabolic features observed in vivo in the tumor microenvironment. These findings promise to shed light on mechanisms of regulation of proton exchanges by cellular metabolism being essential for the study of solid tumors in 3D in vitro models and the development of personalized medicine approaches.

Probing Single-Cell Fermentation Fluxes and Exchange Networks via pH-Sensing Hybrid Nanofibers

The homeostatic control of their environment is an essential task of living cells. It has been hypothesized that, when microenvironmental pH inhomogeneities are induced by high cellular metabolic activity, diffusing protons act as signaling molecules, driving the establishment of exchange networks sustained by the cell-to-cell shuttling of overflow products such as lactate. Despite their fundamental role, the extent and dynamics of such networks is largely unknown due to the lack of methods in single-cell flux analysis. In this study, we provide direct experimental characterization of such exchange networks. We devise a method to quantify single-cell fermentation fluxes over time by integrating high-resolution pH microenvironment sensing via ratiometric nanofibers with constraint-based inverse modeling. We apply our method to cell cultures with mixed populations of cancer cells and fibroblasts. We find that the proton trafficking underlying bulk acidification is strongly heterogeneous, with maximal single-cell fluxes exceeding typical values by up to 3 orders of magnitude. In addition, a crossover in time from a networked phase sustained by densely connected "hubs" (corresponding to cells with high activity) to a sparse phase dominated by isolated dipolar motifs (i.e., by pairwise cell-to-cell exchanges) is uncovered, which parallels the time course of bulk acidification. Our method addresses issues ranging from the homeostatic function of proton exchange to the metabolic coupling of cells with different energetic demands, allowing for real-time noninvasive single-cell metabolic flux analysis.

Nanocomposite Hydrogels as Functional Extracellular Matrices

Over recent years, nano-engineered materials have become an important component of artificial extracellular matrices. On one hand, these materials enable static enhancement of the bulk properties of cell scaffolds, for instance, they can alter mechanical properties or electrical conductivity, in order to better mimic the in vivo cell environment. Yet, many nanomaterials also exhibit dynamic, remotely tunable optical, electrical, magnetic, or acoustic properties, and therefore, can be used to non-invasively deliver localized, dynamic stimuli to cells cultured in artificial ECMs in three dimensions. Vice versa, the same, functional nanomaterials, can also report changing environmental conditions-whether or not, as a result of a dynamically applied stimulus-and as such provide means for wireless, long-term monitoring of the cell status inside the culture. In this review article, we present an overview of the technological advances regarding the incorporation of functional nanomaterials in artificial extracellular matrices, highlighting both passive and dynamically tunable nano-engineered components.

Simultaneous recording of electrical and metabolic activity of cardiac cells in vitro using an organic charge modulated field effect transistor array

In vitro electrogenic cells monitoring is an important objective in several scientific and technological fields, such as electrophysiology, pharmacology and brain machine interfaces, and can represent an interesting opportunity in other translational medicine applications. One of the key aspects of cellular cultures is the complexity of their behavior, due to the different kinds of bio-related signals, both chemical and electrical, that characterize these systems. In order to fully understand and exploit this extraordinary complexity, specific devices and tools are needed. However, at the moment this important scientific field is characterized by the lack of easy-to-use, low-cost devices for the sensing of multiple cellular parameters. To the aim of providing a simple and integrated approach for the study of in vitro electrogenic cultures, we present here a new solution for the monitoring of both the electrical and the metabolic cellular activity. In particular, we show here how a particular device called Micro Organic Charge Modulated Array (MOA) can be conveniently engineered and then used to simultaneously record the complete cell activity using the same device architecture. The system has been tested using primary cardiac rat myocytes and allowed to detect the metabolic and electrical variations thar occur upon the administration of different drugs. This first example could lay the basis for the development of a new generation of multi-sensing tools that can help to efficiently probe the multifaceted in vitro environment.

3D Culture Modeling of Metastatic Breast Cancer Cells in Additive Manufactured Scaffolds

Cancer biology research is increasingly moving toward innovative in vitro 3D culture models, as conventional and current 2D cell cultures fail to resemble in vivo cancer biology. In the current study, porous 3D scaffolds, designed with two different porosities along with 2D tissue culture polystyrene (TCP) plates were used with a model breast cancer human cell line. The 3D engineered system was evaluated for the optimal seeding method (dynamic versus static), adhesion, and proliferation rate of MDA-MB-231 breast cancer cells. The expression profiles of proliferation-, stemness-, and dormancy-associated cancer markers, namely, ki67, lamin A/C, SOX2, Oct3/4, stanniocalcin 1 (STC1), and stanniocalcin 2 (STC2), were evaluated in the 3D cultured cells and compared to the respective profiles of the cells cultured in the conventional 2D TCP. Our data suggested that static seeding was the optimal seeding method with porosity-dependent efficiency. Moreover, cells cultured in 3D scaffolds displayed a more dormant phenotype in comparison to 2D, which was manifested by the lower proliferation rate, reduced ki67 expression, increased lamin A/C expression, and overexpression of STCs. The possible relationship between the cell affinity to different extracellular matrix (ECM) proteins and the RANK expression levels was also addressed after deriving collagen type I (COL-I) and fibronectin (FN) MDA-MB-231 filial cell lines with enhanced capacity to attach to the respective ECM proteins. The new derivatives exhibited a more mesenchymal like phenotype and higher RANK levels in relation to the parental cells, suggesting a relationship between ECM cell affinity and RANK expression. Therefore, the present 3D cell culture model shows that cancer cells on printed scaffolds can work as better representatives in cancer biology and drug screening related studies.

Tissue-engineered bones with adipose-derived stem cells - composite polymer for repair of bone defects

Background: Development of alternative bone tissue graft materials based on tissue engineering technology has gradually become a research focus. Engineered bone composed of biodegradable, biosafe and bioactive materials is attractive, but also challenging. Materials & methods: An adipose-derived stem cell/poly(L-glutamic acid)/chitosan composite scaffold was further developed for construction of biodegradable and bone-promoting tissue-engineered bone. A series of composite scaffold materials with different physical properties such as structure, pore size, porosity and pore diameter was developed. Results: The composite scaffold showed good biodegradability and water absorption, and exhibited an excellent ability to promote bone differentiation. Conclusion: This type of biodegradable scaffold is expected to be applied to the field of bone repair or bone tissue engineering.

Biosensors to Monitor Cell Activity in 3D Hydrogel-Based Tissue Models

Three-dimensional (3D) culture models have gained relevant interest in tissue engineering and drug discovery owing to their suitability to reproduce in vitro some key aspects of human tissues and to provide predictive information for in vivo tests. In this context, the use of hydrogels as artificial extracellular matrices is of paramount relevance, since they allow closer recapitulation of (patho)physiological features of human tissues. However, most of the analyses aimed at characterizing these models are based on time-consuming and endpoint assays, which can provide only static and limited data on cellular behavior. On the other hand, biosensing systems could be adopted to measure on-line cellular activity, as currently performed in bi-dimensional, i.e., monolayer, cell culture systems; however, their translation and integration within 3D hydrogel-based systems is not straight forward, due to the geometry and materials properties of these advanced cell culturing approaches. Therefore, researchers have adopted different strategies, through the development of biochemical, electrochemical and optical sensors, but challenges still remain in employing these devices. In this review, after examining recent advances in adapting existing biosensors from traditional cell monolayers to polymeric 3D cells cultures, we will focus on novel designs and outcomes of a range of biosensors specifically developed to provide real-time analysis of hydrogel-based cultures.

Regulation of Inflammatory Response and Osteogenesis to Citrate-Based Biomaterials through Incorporation of Alkaline Fragments

A proper pH microenvironment is crucial to mobilizing regeneration function of biomaterials. Neutralizing the acidity in bone defects with alkaline substances is a promising strategy to create favorable environments for cell proliferation and bone repair. In this study, to neutralize the acidity and reduce the inflammation caused by the rapid release of citric acid, a novel citrate-based biodegradable elastomeric poly(citric acid-1,8-octanediol-1,4-bis(2-hydroxyethyl)piperazine (BHEp)) (POPC) is synthesized with the introduction of the alkaline fragment BHEp, and then POPC/β-tricalcium phosphate (β-TCP) porous scaffolds are fabricated by 3D printing technique. The results reveal that the alkaline fragment BHEp effectively corrects the acid environment and improves the biocompatibility, cells affinity and promoted cell adhesion, and proliferation of POPC. Furthermore, the improved pH of POPC15/β-TCP (PTCP15) enhances the adhesion and the proliferation of rabbit bone marrow mesenchymal stem cells, and the expression of osteogenesis-related genes. Moreover, PTCP15 scaffolds relieve inflammatory response and switch RAW 264.7 toward a prohealing extreme. The rat femoral defect model further demonstrates good biocompatibility and enhanced bone regeneration of PTCP15. In conclusion, the results offer a promising approach for biodegradable polymers to address the degradation acidity issue. Meanwhile, a positive regulation strategy is provided for biopolymer to enhance cell proliferation, osteogenic differentiation, and bone repair.

Highly Sensitive Fluorescent pH Microsensors Based on the Ratiometric Dye Pyranine Immobilized on Silica Microparticles

Pyranine (HPTS) is a remarkably interesting pH-sensitive dye that has been used for plenty of applications. Its high quantum yield and extremely sensitive ratiometric fluorescence against pH change makes it a very favorable for pH-sensing applications and the development of pH nano-/microsensors. However, its strong negative charge and lack of easily modifiable functional groups makes it difficult to use with charged substrates such as silica. This study reports a methodology for noncovalent HPTS immobilization on silica microparticles that considers the retention of pH sensitivity as well as the long-term stability of the pH microsensors. The study emphasizes the importance of surface charge for governing the sensitivity of the immobilized HPTS dye molecules on silica microparticles. The importance of the immobilization methodology, which preserves the sensitivity and stability of the microsensors, is also assessed.

Optical and magnetic resonance imaging approaches for investigating the tumour microenvironment: state-of-the-art review and future trends

The tumour microenvironment (TME) strongly influences tumorigenesis and metastasis. Two of the most characterized properties of the TME are acidosis and hypoxia, both of which are considered hallmarks of tumours as well as critical factors in response to anticancer treatments. Currently, various imaging approaches exist to measure acidosis and hypoxia in the TME, including magnetic resonance imaging (MRI), positron emission tomography and optical imaging. In this review, we will focus on the latest fluorescent-based methods for optical sensing of cell metabolism and MRI as diagnostic imaging tools applied both in vitro and in vivo. The primary emphasis will be on describing the current and future uses of systems that can measure intra- and extra-cellular pH and oxygen changes at high spatial and temporal resolution. In addition, the suitability of these approaches for mapping tumour heterogeneity, and assessing response or failure to therapeutics will also be covered.