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

Abstract

Despite numerous advances in the field of tissue engineering and regenerative medicine, monitoring the formation of tissue regeneration and its metabolic variations during culture is still a challenge and mostly limited to bulk volumetric assays. Here, a simple method of adding capsules‐based optical sensors in cell‐seeded 3D scaffolds is presented and the potential of these sensors to monitor the pH changes in space and time during cell growth is demonstrated. It is shown that the pH decreased over time in the 3D scaffolds, with a more prominent decrease at the edges of the scaffolds. Moreover, the pH change is higher in 3D scaffolds compared to monolayered 2D cell cultures. The results suggest that this system, composed by capsules‐based optical sensors and 3D scaffolds with predefined geometry and pore architecture network, can be a suitable platform for monitoring pH variations during 3D cell growth and tissue formation. This is particularly relevant for the investigation of 3D cellular microenvironment alterations occurring both during physiological processes, such as tissue regeneration, and pathological processes, such as cancer evolution.

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

“…At 24 h, the majority of T3‐HPTS pH sensors were detected in close proximity or inside the cells and showed a diminished fluorescence emission at 458 nm excitation. In agreement with other studies based on different pH probes,[ 1a , 1b , 24 ] the change of fluorescence of HPTS might reflect the intracellular localization of the T3‐HPTS particles in an acidic environment [25] (e. g., endosomes or lysosomes), causing the observed decrease of emission from excitation at 458 nm. Additional experiments by electron microscopy aimed at deeply investigating the cell uptake of the T3‐HPTS sensors and their intracellular localization are currently underway in our laboratories.…”

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

“…Moreover, conventional techniques (such as pH-meter probes or microelectrodes) provide only an average pH value, not taking into consideration the local discrepancies and thus the gradients which may be present in a 3D cell culture system. Novel devices such as microneedle sensors, able to pierce the sample without serious damages, have been developed, however they do not resolve the need for large volumes of culture medium, and are limited in design regarding shape, mechanical properties and sterility [87].…”

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

“…Meanwhile, the BHEp fragments in POPC could accept the protons and effectively neutralize the acidity of citric acid during the early degradation stage, which was favor for cell attachment, proliferation, and tissue growth. [7] The pH of copolymers after immersing in Tris-HCL buffer and serum-free medium was presented in Figure 3f. Notably, after immersed in Tris-HCL buffer, POC sharply decreased solution pH from 7.40 to 7.20 within 1 h, while for POPC15 increased slightly.…”

“…It indicated that the alkaline BHEp fragments could self-neutralize the excessive citric acid biodegraded from POC segments and consequently improved the medium pH, which is beneficial to form suitable microenvironment and facilitate rBMSCs differentiation. [7,19]…”

“…However, the degradation of these polymers was difficult to control and their products were acidic, which would hamper cell proliferation and cause foreign body reaction, aseptic inflammation even implant failure. [6,7] Citrate plays a vital role in bone metabolism and bone formation as an intermediate in the Krebs cycle. [8] Served as calcium solubilizer, citrate interacted with apatite for bone biomineralization.…”