A comprehensive understanding of the key microenvironmental signals regulating bone regeneration is pivotal for the effective design of bioinspired orthopedic materials. Here, we identified citrate as an osteopromotive factor and revealed its metabonegenic role in mediating citrate metabolism and its downstream effects on the osteogenic differentiation of human mesenchymal stem cells (hMSCs). Our studies show that extracellular citrate uptake through solute carrier family 13, member 5 (SLC13a5) supports osteogenic differentiation via regulation of energy-producing metabolic pathways, leading to elevated cell energy status that fuels the high metabolic demands of hMSC osteodifferentiation. We next identified citrate and phosphoserine (PSer) as a synergistic pair in polymeric design, exhibiting concerted action not only in metabonegenic potential for orthopedic regeneration but also in facile reactivity in a fluorescent system for materials tracking and imaging. We designed a citrate/phosphoserine-based photoluminescent biodegradable polymer (BPLP-PSer), which was fabricated into BPLP-PSer/hydroxyapatite composite microparticulate scaffolds that demonstrated significant improvements in bone regeneration and tissue response in rat femoral-condyle and cranial-defect models. We believe that the present study may inspire the development of new generations of biomimetic biomaterials that better recapitulate the metabolic microenvironments of stem cells to meet the dynamic needs of cellular growth, differentiation, and maturation for use in tissue engineering.

Chloride is an essential electrolyte that maintains homeostasis within the body, where abnormal chloride levels in biological fluids may indicate various diseases such as Cystic Fibrosis. However, current analytical solutions for chloride detection fail to meet the clinical needs of both high performance and low material or labor costs, hindering translation into clinical settings. Here we present a new class of fluorescence chloride sensors derived from a facile citrate -based synthesis platform that utilize dynamic quenching mechanisms. Based on this low-cost platform, we demonstrate for the first time a selective sensing strategy that uses a single fluorophore to detect multiple halides simultaneously, promising both selectivity and automation to improve performance and reduce labor costs. We also demonstrate the clinical utility of citrate-based sensors as a new sweat chloride test method for the diagnosis of Cystic Fibrosis by performing analytical validation with sweat controls and clinical validation with sweat from individuals with or without Cystic Fibrosis. Lastly, molecular modeling studies reveal the structural mechanism behind chloride sensing, serving to expand this class of fluorescence sensors with improved chloride sensitivities. Thus citrate-based fluorescent materials may enable low-cost, automated multi-analysis systems for simpler, yet accurate, point-of-care diagnostics that can be readily translated into clinical settings. More broadly, a wide range of medical, industrial, and environmental applications can be achieved with such a facile synthesis platform, demonstrated in our citrate-based biodegradable polymers with intrinsic fluorescence sensing.

For the first time, a convenient copper-catalyzed azide-alkyne cycloaddition (CuAAC, click chemistry) was successfully introduced into injectable citrate-based mussel-inspired bioadhesives (iCMBAs, iCs) to improve both cohesive and wet adhesive strengths and elongate the degradation time, providing numerous advantages in surgical applications. The major challenge to developing such an adhesive was the mutual inhibition effect between the oxidant used for crosslinking catechol groups and the Cu(II) reductant used for CuAAC, which was successfully minimized by adding a biocompatible buffering agent typically used in cell culture, 4-(2-hydroxyethyl) -1-piperazineethanesulfonic acid (HEPES), as a copper chelating agent. Among the investigated formulations, the highest adhesion strength achieved (223.11 ± 15.94 kPa) was around 13 times higher than that of a commercially available fibrin glue (15.4 ± 2.8 kPa). In addition, dual-crosslinked (i.e. click crosslinking and mussel-inspired crosslinking) iCMBAs still preserved considerable antibacterial and antifungal capabilities that are beneficial for the bioadhesives used as hemostatic adhesives or sealants for wound management.