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.