INTRODUCTION

Tissue engineering (TE) strategies have been actively seeking for an optimal approach for the development of suitable articular cartilage tissue replacements, given that the current treatment options do not constitute a feasible long-term solution (Correa & Lietman, 2017). Considerable efforts have been made to improve scaffolds design – choice of material and fabrication technique, topography and three-dimensional (3D) anisotropic design – for functional cartilage tissue formation support, as well as effective cell incorporation and subsequent interaction of host cells within the construct (Camarero-Espinosa et al., 2016; Griffith & Swartz, 2006). Electrospinning, for instance, has been widely employed for the fabrication of fibrous scaffolds for cartilage TE, not only due to its simplicity and versatility, but also the ECM-mimicking nanofibers produced, known to trigger a suitable chondrocyte response (Girão et al., 2018; Jin et al., 2018; Jun et al., 2018; McCullen et al., 2012; Reboredo et al., 2016; Steele et al., 2014). Still, the pores generated by electrospinning are usually too small to allow effective cell migration into the inner regions of the scaffold, particularly in 3D designs, resulting in poor and time dependent cellular infiltration, and ultimately, in the production of non-functional tissue constructs (Bueno et al., 2007; Griffon et al., 2011; Rnjak-Kovacina & Weiss, 2011; Villalona et al., 2010). In this regard, a logical conclusion would be to directly incorporate the cells into the fibers mesh during scaffolds production in order to fabricate functional and homogeneous tissue constructs, by overcoming the challenges of cell infiltration through small pores by literally surrounding the cells with the fiber matrix as it is produced. Indeed, there are reports of successful development of cell-laden scaffolds by combining fiber electrospinning with cell electrospraying (Canbolat et al., 2011; H. Chen et al., 2015; Paletta et al., 2011; Stankus et al., 2006). Cell electrospraying, or bio-electrospraying, a concept first introduced in 2005 by Jayasingheet al , enables the deposition of living cells onto specific targets by exposing the cell suspension to an external high intensity electric field (Jayasinghe et al., 2006; Jayasinghe & Townsend-Nicholson, 2006). The principle underlying electrospraying involves the application of voltage on a capillary holding the flow of liquid media, resulting in the ejection of a liquid microjet of charged droplets onto an oppositely charged collector. Moreover, when an electric potential difference threshold between the capillary and the collector is achieved, a stable conical liquid meniscus is formed – Taylor cone (Hartman et al., 1999; Kavadiya & Biswas, 2018; Morad et al., 2016; Rosell-Llompart et al., 2018). Concerning cell electrospraying, the establishment of this stable cone-jet is crucial for the control of the precise cell placement, and it requires certain operational conditions, such as a particular flow rate, surface tension, conductivity and voltage (Hartman et al., 1999). Still, it is necessary to understand how the exposure to the electric field, as well as shear stress of passing through the cell electrospraying apparatus may affect cell viability and function. So far, neuronal cells (Eddaoudi et al., 2010; Jayasinghe & Townsend-Nicholson, 2006; Townsend-Nicholson & Jayasinghe, 2006), smooth muscle cells (Jayasinghe et al., 2007; Odenwälder et al., 2007; Patel et al., 2008), lymphocytes (Kempski et al., 2008), mononuclear cells (Hall et al., 2008), primary cardiac myocytes and endothelial cells (Barry et al., 2008; Ng et al., 2011), kidney cells (Kwok et al., 2008), embryonic stem cells (Abeyewickreme et al., 2009), mesenchymal stem cells (Mongkoldhumrongkul et al., 2009) to hematopoietic stem cells (Bartolovic et al., 2010), and even for multicellular organisms (Clarke & Jayasinghe, 2008) have been electrosprayed and survived with no significant influence on a genetic, genomic and physiological level. Yet, so far, no study has reported the bio-electrospray of chondrocyte suspensions. So, the aim of the present study is to understand the impact of the electrospraying process and the respective parameters on the viability and proliferative behavior of chondrocytes, so that this technology might be implemented for the fabrication of chondrocyte-laden scaffolds for cartilage TE.