Fish scale collagen peptide was used as a precursor to prepare carbon dots using conventional hydrothermal (CDs-HT) and microwave methods (CDs-MW). The optical properties of CDs prepared using the two...

The preparation of carbon dots (CDs) from waste sh scales is an attractive and high-value transformation. In this study, sh scales were used as a precursor to prepare CDs, and the effects of hydrothermal and microwave methods on their uorescence properties and structures were evaluated.The microwave method was more conducive to the self-doping of nitrogen due to rapid and uniform heating. However, the low temperature associated with the microwave method resulted in the insu cient dissolution of the organic matter in sh scales; thus, the organic matter was di cult to completely dehydrate and condense, but formed nanosheet-like CDs, whose emission behavior had no signi cant correlation with excitation. Although the CDs prepared using the conventional hydrothermal had a lower doping amount of N element, the relative pyrrolic N content was higher, which was bene cial in improving their quantum yield. Additionally, the controllable high temperature and sealed environment used for the conventional hydrothermal could promote the dehydration and condensation of the organic matter in sh scales to form CDs with a higher degree of carbonization, uniform size, and higher C = O/COOH content. CDs prepared using the conventional hydrothermal exhibited higher quantum yield and excitation wavelength-dependent emission behavior. Declarations

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A skin wound represents a rupture caused by external damage or the existence of underlying pathological conditions. Sometimes, skin wound healing processes may place a heavy burden on patients, families, and society. Wound healing processes mainly consist of several continuous, dynamic, but overlapping stages, namely, the coagulation stage, inflammation stage, proliferation stage, and remodeling stage. Bacterial infection, excessive inflammation, impaired angiogenesis, and scar formation constitute the four significant factors impeding the recovery efficacy of skin wounds. This encourages scientists to develop multifunctional nanomedicines to meet challenging needs. As we know, mesenchymal stem cells (MSCs) have been widely explored for wound repair owing to their unique capability for self-renewal and multipotency. However, problems including immune concerns and legal restrictions should be properly resolved before MSC-based therapeutics are safely and widely used in clinics. Besides, maintaining the high viability/proliferation capability of MSCs during administration processes and therapy procedures is also one of the biggest technical bottlenecks. Extracellular vesicles (EVs) are cell-derived nanovesicles, that not only possess the basic characteristics and functions of their corresponding maternal cells but also contain several outstanding advantages including abundant sources, excellent biocompatibility, and convenient administration routes. Furthermore, the membrane surface and cavity are easy to flexibly modify to meet versatile application needs. Recently, MSC-derived EVs have emerged as promising therapeutics for skin wound repair. However, current reviews are too broad and rarely focused on the specific roles of EVs in the different stages of wound recovery. Therefore, it is quite necessary to demonstrate the significance of stem cell-derived EVs in promoting wound healing from several specific aspects. Here, this review primarily tries to provide critical comments on current advances in EVs derived from MSCs for wound repair, particularly elaborating on their impressive roles in effectively eliminating infections, inhibiting inflammation, promoting angiogenesis, and reducing scar formation. Last but not least, current limitations and future prospects of EVs derived from MSCs in the areas of wound repair are also objectively analyzed.

The preparation of carbon dots (CDs) from waste fish scales is an attractive and high-value transformation. In this study, fish scales were used as a precursor to prepare CDs, and the effects of hydrothermal and microwave methods on their fluorescence properties and structures were evaluated. The microwave method was more conducive to the self-doping of nitrogen due to rapid and uniform heating. However, the low temperature associated with the microwave method resulted in the insufficient dissolution of the organic matter in fish scales; thus, the organic matter was difficult to completely dehydrate and condense, but formed nanosheet-like CDs, whose emission behavior had no significant correlation with excitation. Although the CDs prepared using the conventional hydrothermal had a lower doping amount of N element, the relative pyrrolic N content was higher, which was beneficial in improving their quantum yield. Additionally, the controllable high temperature and sealed environment used for the conventional hydrothermal could promote the dehydration and condensation of the organic matter in fish scales to form CDs with a higher degree of carbonization, uniform size, and higher C = O/COOH content. CDs prepared using the conventional hydrothermal exhibited higher quantum yield and excitation wavelength-dependent emission behavior.