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Microfluidic technology has become a valuable tool to the scientific community, allowing researchers to study fine cellular mechanisms with higher variable control compared with conventional systems. It has evolved tremendously, and its applicability and flexibility made its usage grow exponentially and transversely to several research fields. This has been particularly noticeable in neuroscience research, where microfluidic platforms made it possible to address specific questions extending from axonal guidance, synapse formation, or axonal transport to the development of 3D models of the CNS to allow pharmacological testing and drug screening. Furthermore, the continuous upgrade of microfluidic platforms has allowed a deeper study of the communication occurring between different neuronal and glial cells or between neurons and other peripheral tissues, both in physiological and pathological conditions. Importantly, the evolution of microfluidic technology has always been accompanied by the development of new computational tools addressing data acquisition, analysis, and modeling.

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Innervation has proven to be critical in bone homeostasis/regeneration due to the effect of soluble factors, produced by nerve fibers, associated with changes in the activity of bone cells. Thus, in this study, we have established and characterized a coculture system comprising sensory neurons and osteoblasts to mimic the in vivo scenario where nerve fibers can be found in a bone microenvironment. Embryonic or adult primary dorsal root ganglion (DRG) and MC3T3-E1 osteoblastic cells were cocultured in compartmentalized microfluidic platforms and morphological and functional tests were performed. The time of adhesion and readout of axonal outgrowth were improved by the alignment of DRG with the axis of microgrooves, which showed to be a crucial step for the designed experiments. Cocultures of entire DRG from adult origin with osteoblasts were performed, showing extended DRG projections towards the axonal compartment, reaching osteoblastic cells. Immunocytochemistry showed that the neurites present within the osteoblastic compartment were immunoreactive to synapsin and calcitonin gene-related peptide suggesting the presence of specialized structures involved in this crosstalk. This evidence was further confirmed by electron microscopy where varicosities were detected as well as electron dense structures in neurite membranes. Aiming to mimic the properties of tissue extracellular matrices, MC3T3-E1 cells were seeded in the axonal side upon laminin, collagen or within 3D functionalized alginate matrices and axonal outgrowth was clearly observed. In order to analyze and quantify data with reproducible image analysis, a semi-automated algorithm was also developed. The collagen and laminin substrates displayed a higher amount of axons reaching the axonal side. Overall, the established method revealed to be a suitable tool to study the interaction between the peripheral nervous system and bone cells in different contexts mimicking the in vivo scenario.

This study aims at assessing the influence of the competitive preadsorption of human serum albumin (HSA) and human plasma fibronectin (FN) from binary solutions and 10% plasma on MC3T3-E1 osteoblast adhesion and morphology on two types of TiO2 substrates. One was commercially pure titanium with a titanium oxide layer formed in an H2O2 solution and the other TiO2 sputtered on Si (Sousa et al., Langmuir 2004; 20:9745-9754.). The strategy applied in the present investigation was to compare osteoblast adhesion to surfaces preadsorbed with HSA, FN, HSA/FN = 1, HSA/FN = 200, and 10% plasma. The adsorption of proteins was evaluated measuring the amount and the effectiveness of binding with radiolabeled proteins, 125 I-FN and 125 I-HSA. Our results indicated that MC3T3-E1 osteoblast adhesion correlates well with the amounts of FN and HSA adsorbed on TiO2 surfaces. Also, we found that fewer osteoblasts adhered to both substrates preadsorbed with HSA, HSA/FN = 200, and 10% plasma, after 4 and 24 h, than to the surfaces preadsorbed with FN and HSA/FN = 1. For the latter, FN was able to compensate the inhibitory effect of HSA on osteoblast adhesion. Therefore, the presence of lower amounts of coadsorbed albumin may improve presentation of FN in a more integrin-recognized conformation, suggesting that some degree of molecular packing prevents loss of integrin-binding activity. FN reversibility does not seem to be dependent on the HSA/FN adsorption mass ratio in solution, suggesting that FN competitively adsorbs to TiO2 in a favorable conformation and does not suffers subsequent conformational changes allowing exchange with other FN molecules in solution.

Cell adhesion, migration, and proliferation of a few anchorage-dependent cells cultured on chitosan (Ch) matrices are influenced by the degree of N-acetylation (DA) of Ch. In the present work, we examined the influence of the DA on the attachment, spreading, proliferation, and osteogenic differentiation of rat bone marrow stromal cells (rBMSCs). Ch membranes were characterized in terms of surface morphology, roughness, and wettability, and in terms of adsorption of an adhesive protein, fibronectin (Fn). Chs with DAs in the range of 4 to 49% were used. Among the Ch samples, the DA of 4% led to the highest Fn surface concentration, both from single protein solution and from diluted serum. Furthermore, the levels of Fn adsorbed from serum found for this DA were threefold higher than for the tissue culture polystyrene control, indicating that in the presence of competitive proteins Ch is more specific toward Fn adsorption than tissue culture polystyrene. rBMSCs cultured on Ch carrying a DA of 4% were able to spread, proliferate, and differentiate, reaching a higher level of osteogenic differentiation than on the control, despite the lower cell attachment observed for all Ch samples. Because the Ch sample with a DA of 4% showed the highest Fn adsorption from serum, we suggest that cell adhesion, spreading, and osteogenic differentiation of rBMSCs on Ch may be mediated by the adsorbed layer of Fn.

Stem cell-based mediated therapies represent very promising approaches for tissue regeneration and are already applied with success in clinics. These therapeutic approaches consist of the in vitro manipulation of stem cells and their consequent administration to patients as living and dynamic biological agents. Nevertheless, the deregulation of stem cells function might result in the generation of pathologies such as tumours or accelerated senescence. Moreover, different stem cells sources are needed for regeneration of specific tissues. It is thus fundamental to understand the mechanisms regulating the physiology of stem cells. Microfluidic technology can be used to mimic in vivo scenarios and allow the study of stem cell physiology at both single cell and whole stem cell niche levels. This review focuses on the potential sources of stem and progenitor cells for orofacial regeneration and the use of microfluidic technologies for the study of stem cells behaviour and stem cell niches, in the light of regenerative medicine. Keywords:Microfluidics, stem cells, stem cell niches, orofacial regeneration, tooth, innervation, trigeminal ganglia, regenerative medicine. IntroductionThe development of organs and tissues that belong to the orofacial complex proceeds through a series of inductive interactions between cells originated from the epithelium, mesoderm and cranial neural crest-derived mesenchyme (Mao et al., 2012;Mitsiadis and Graf, 2009;Mitsiadis and Papagerakis, 2011). Orofacial organs are highly diverse and exert fundamental and specific functions such as breathing, chewing, speech, smell, and sight (Mao et al., 2012). The physiological functions of these organs are compromised by traumatic injuries, congenital and infectious diseases, and cancer (Mao et al., 2012;Scheller et al., 2009). Furthermore, these pathologies are often accompanied by intensive pain and aesthetic deformities. Therefore, the treatment of compromised pathological orofacial tissues and organs should guarantee restoration of both functionality and aesthetics, which constitutes an enormous clinical challenge. Moreover, organ structure, function, aesthetics, and pain should be managed simultaneously during the regenerative care, a situation that is more complex than in other compartments of the body (Scheller et al., 2009).Biological regeneration is proving an increasingly attractive alternative and complement to traditional surgical techniques for prosthetic replacement of tissues and organs. Cell-based therapeutic approaches are already applied with success in clinics and consist of in vitro manipulation of stem cells and their consequent administration to patients as living and dynamic biological agents. Stem cells are characterised by their potential to self-replicate and their capacity to differentiate into a vast variety of cell types that form the diverse tissues. Therefore, stem cells guarantee tissue repair and regeneration throughout life. During the last decades, a plethora of adult stem cell populations have been isolate...

Neuropeptide Y (NPY) has recently emerged as a potential regulator of bone homeostasis. However, the relevance of NPY's role in osteoblast activity and the biological functions involving NPY receptors in bone homeostasis remain to be clarified. Here we report that chronically elevated NPY levels leaded to a modulation of the level of Y2 receptor expression marked with a transient down and upregulation according to the stage of osteoblast differentiation. We also show that NPY is a negative regulator of Y1 receptor expression. The pharmacological activation of Y2 receptor with its agonist resulted in similar effect. Functional analysis also revealed the osteogenic potential of NPY with osteoblast phenotype markers being significantly enhanced in osteoprogenitor cells stimulated by NPY, probably due to the down-regulation of Y1 receptor. In contrasts, these cells exhibit a reduction in calcium deposition in extracellular matrix most likely mediated via Y2 receptor signalling. Furthermore, we show that NPY modulates receptor activator of nuclear factor kB (NF-kB) (RANK) ligand and osteoprotegerin, two key factors regulating bone remodelling. Specifically, NPY inhibits the transcriptional activity of RANKL promoter in osteoprogenitor cells and enhances OPG expression in osteoblasts at early stages of differentiation. However, NPY effect on OPG seemed to be unrelated to Y2 receptor activation. Taken together the present data supported the contribution of NPY pathway in bone homeostasis via a direct action on osteoblasts cells.