Bone metabolism is regulated by osteoblasts, osteoclasts, osteocytes, and stem cells. Pathologies such as osteoporosis, osteoarthritis, osteonecrosis, and traumatic fractures require effective treatments that favor bone formation and regeneration. Among these, cell therapy based on mesenchymal stem cells (MSC) has been proposed. MSC are osteoprogenitors, but their regenerative activity depends in part on their paracrine properties. These are mainly mediated by extracellular vesicle (EV) secretion. EV modulates regenerative processes such as inflammation, angiogenesis, cell proliferation, migration, and differentiation. Thus, MSC-EV are currently an important tool for the development of cell-free therapies in regenerative medicine. This review describes the current knowledge of the effects of MSC-EV in the different phases of bone regeneration. MSC-EV has been used by intravenous injection, directly or in combination with different types of biomaterials, in preclinical models of bone diseases. They have shown great clinical potential in regenerative medicine applied to bone. These findings should be confirmed through standardization of protocols, a better understanding of the mechanisms of action, and appropriate clinical trials. All that will allow the translation of such cell-free therapy to human clinic applications.

Hard-to-heal chronic wounds associated with aging and high-prevalence pathologies, such as diabetes, are a global health problem. Therefore, it is necessary to advance effective treatments to accelerate wound healing. Among these potential treatments are new therapies based on mesenchymal stem cells (MSC) and their secretomes, including extracellular vesicles (EV). They have an important therapeutic potential for the treatment of chronic ulcers, due to their immunomodulatory activity, as well as their ability to induce angiogenesis, cell proliferation and cell migration. The use of MSC-derived EV in regenerative medicine involves cell-free therapies that decrease risks associated with cell therapies, such as the potential development of tumors. However, the short half-life of MSC-EV is a limitation for their clinical use. A therapeutic strategy to increase the regenerative efficiency of EV in wounds is to encapsulate them in biomaterials. The latter must protect and progressively release EV in damaged tissues, optimizing healing. Biomaterials that can be used include hydrogels. These, in addition to acting as a vehicle for sustained application of EV, can create favorable environments for wound healing. Thus, the aim of this review is to critically describe the latest advances in the development of such therapeutic strategies. It highlights the significance and clinical potential of these new therapies, as well as the need to develop clinical trials, to ascertain their performance.

Three-dimensional bioprinting is a new advance in tissue engineering and regenerative medicine. Bioprinting allows manufacturing three-dimensional (3D) structures that mimic tissues or organs. The bioinks used are mainly made of natural or synthetic polymers that must be biocompatible, printable, and biodegradable. These bioinks may incorporate progenitor cells, favoring graft implantation and regeneration of injured tissues. However, the natures of biomaterials, bioprinting processes, a lack of vascularization, and immune responses are factors that limit the viability and functionality of implanted cells and the regeneration of damaged tissues. These limitations can be addressed by incorporating extracellular vesicles (EV) into bioinks. Indeed, EV from progenitor cells may have regenerative capacities, being similar to those of their source cells. Therefore, their combinations with biomaterials can be used in cell-free therapies. Likewise, they can complement the manufacture of bioinks by increasing the viability, differentiation, and regenerative ability of incorporated cells. Thus, the main objective of this review is to show how the use of 3D bioprinting technology can be used for the application of EV in regenerative medicine by incorporating these nanovesicles into hydrogels used as bioinks. To this end, the latest advances derived from in vitro and in vivo studies have been described. Together, these studies show the high therapeutic potential of this strategy in regenerative medicine.

Background: The prevention and treatment of bone loss and osteoporotic fractures is a public health challenge. Combined with normobaric hypoxia, whole-body vibration has a high clinic potential in bone health and body composition. The effect of this therapy may be mediated by its action on bone marrow mesenchymal stem cells (MSCs). Objectives: Evaluate the effects of cyclic low-vibration stimuli and/or hypoxia on bone marrow-derived human MSC differentiation. Methods: MSCs were exposed four days per week, two hours/day, to hypoxia (3% O₂) and/or vibration before they were induced to differentiate or during differentiation into osteoblasts or adipocytes. Gene and protein expression of osteoblastic, adipogenic, and cytoskeletal markers were studied, as well as extracellular matrix mineralization and lipid accumulation. Results: early osteoblastic markers increased in undifferentiated MSCs, pretreated in hypoxia and vibration. This pretreatment also increased mRNA levels of osteoblastic genes and beta-catenin protein in the early stages of differentiation into osteoblasts without increasing mineralization. When MSCs were exposed to vibration under hypoxia or normoxia during osteoblastic differentiation, mineralization increased with respect to cultures without vibrational stimuli. In MSCs differentiated into adipocytes, both in those pretreated as well as exposed to different conditions during differentiation, lipid formation decreased. Changes in adipogenic gene expression and increased beta-catenin protein were observed in cultures treated during differentiation. Conclusions: Exposure to cyclic hypoxia in combination with low-intensity vibratory stimuli had positive effects on osteoblastic differentiation and negative ones on adipogenesis of bone marrow-derived MSCs. These results suggest that in elderly or frail people with difficulty performing physical activity, exposure to normobaric cyclic hypoxia and low-density vibratory stimuli could improve bone metabolism and health.

Diabetes mellitus may adversely affect the regenerative capacities of tissues, including skin healing and bone health (osteoporosis). Dipeptidyl peptidase-4 (DPP4) inhibitors (DPP4i) are antidiabetic drugs that increase the half-life of incretins, improving glucose levels. Several proteins that regulate important physiological processes are also substrates of DPP4. Therefore, DPP4i may have multiple effects. The aim of this work was to study if DPP4i sitagliptin affects regenerative capacities in a diabetic animal model. Thus, its effects on skin wound healing were evaluated. Likewise, if it produces changes in serum composition that might affect the viability and differentiation of endothelial cells and mesenchymal stem cells (MSC). Diabetic rats were dorsally wounded and treated with sitagliptin. At day six, CD34⁺ cells and endothelial progenitor cells (EPC) were quantified in blood by flow cytometry. At day 14, blood serum and wound samples were obtained for histological analyses. In vitro studies of viability, apoptosis and angiogenesis in human umbilical-cord vein endothelial cells (HUVEC) and MSC capabilities of differentiation into adipocytes or osteoblasts were tested using rat sera. Sitagliptin treatments accelerated wound closure, decreased wound inflammation, and increased circulating EPC. Serum from sitagliptin-treated rats increased angiogenesis in HUVEC, while in MSC, it negatively affected osteogenic differentiation, promoting adipogenesis. Sitagliptin treatment may have positive effects on ulcer healing in diabetics. However, the possible changes produced in serum composition may negatively affect bone formation. Therefore, sitagliptin may affect regenerative capacity and induce different responses in progenitor cells, depending on their niche.