Ratiometric Fluorescent Microgels for Sensing Extracellular Microenvironment pH during Biomaterial Degradation

Abstract

Bone regeneration has attracted extensive attention in the field of regenerative medicine. The influence of biomaterial on the extracellular environment is important for regulating the biological functions of cells for tissue regeneration. Among the various influencing factors, we had previously demonstrated that the extracellular pH value in the local microenvironment during biomaterial degradation affected the balance of bone formation and resorption. However, there is a lack of techniques for conveniently detecting the pH of the extracellular environment. In light of the development of fluorescent pH-sensing probes, herein, we fabricated a novel ratiometric fluorescent microgel (F-MG) for real-time and spatiotemporal monitoring of microenvironment pH. F-MGs were prepared from polyurethane with a size of around 75 μm by loading with pH-sensitive bovine serum albumin nanoparticles (BNPs) and pH-insensitive Nile red as a reference. The pH probes exhibited reversible fluorescence response to pH change and worked in a linear range of 6–10. F-MGs were biocompatible and could be used for long-term pH detection. It could be used to map interfacial pH on biomaterials during their degradation through pseudocolored images formed by the fluorescence intensity ratio between the green fluorescence of BNPs and the red fluorescence of Nile red. This study provided a useful tool for studying the influence of biomaterial microenvironment on biological functions of surrounding cells.

A targeted fluorescent nanosensor for ratiometric pH sensing at the cell surface

“…Furthermore, the small size of the particles allows local pH imaging with high resolution. This is in contrast to other particulate sensors, which have larger particles in the µm range, hindering the ability to image and detect pH at a cellular resolution 29 . The zeta potential analysis revealed a negative charge of approximately − 63 mV and − 66 mV for the precursor NP and the NR-loaded NP, respectively.…”

“…Consequently, most of them are better suited for intracellular rather than extracellular pH sensing applications 27 . One possible approach is the immobilization of the probe encased in thin films or gels 28 , 29 . This does enable pH sensing in the extracellular region but confines measurement to the interface where the gel adheres to the cell surface.…”

A library of Rhodamine6G-based pH-sensitive fluorescent probes with versatile in vivo and in vitro applications

“…Real-time microenvironment monitoring is a major priority for implantable biomaterials, particularly when it can be achieved without causing major modification of the material's chemistry and properties. 31,85,86 In theory, this approach could be used to non-invasively image deposition of extracellular matrix or changes in the supply of nutrients or removal of acidic metabolites. While specific biologic applications were not pursued in the current manuscript, we have demonstrated the feasibility of incorporation of Compound ( 27) into two distinct biomaterial structures.…”

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

“…The system was used to study, through colorimetric maps, local extracellular pH during biomaterial degradation because this phenomenon could significantly affect the surrounding cells; for example, it could affect the balance between bone formation and resorption. 237 Fluorescent microparticles were also included in a polymer layer to create an integrated sensor for monitoring the oxygen gradients of hypoxic tumors. In particular, silica microparticles were first absorbed with oxygen-sensitive (Ru(dpp) 3 Cl 2 ) and insensitive (Nile Blue chloride) fluorophores and then mixed with polydimethylsiloxane (PDMS).…”