The main components used to engineer functional kidney
constructs are living cells, scaffolding system based on biomaterials,
bioactive factors, and appropriate microenvironments that facilitate cellular behaviors. A well-orchestrated combination of
these components is of critical significance in creating engineered
tissues or organs for the development of functional substitutes
[10]. Engineering of kidney tissue constructs may involve scaffolding
systems and/or bioactive factors alone, wherein the body’s natural
healing ability to regenerate is utilized to guide or direct new
tissue growth. When cells are utilized, donor tissue is dissociated
into individual single cells that are either, implanted directly into
the host or expanded in culture or attached to a scaffolding system
and re-implanted after expansion
Several TE and RM approaches have been introduced to improve
renal functions. Due to the difficulty in regenerating damaged
renal structures, particularly glomerulus [11], early studies have
focused replacing pathological renal tissues with functional engineered
constructs containing renal cells [12,13]. Implantation of
these constructs in vivo showed the formation of renal structures
that produce urine-like fluid [13]. The results suggest the possibility
of using engineered renal constructs for augmenting renal function.
With the advances in stem cell biology and cell culture
techniques, additional fundamental studies have been performed
to identify specific cell types that contribute to the restoration of
renal function (e.g. filtration) [11]. For instance, podocyte, which
is a critical cell population in the glomerulus, plays a major role
in the glomerular filtration barrier among other cell types such
as mesangial and endothelial cells [14]. However, podocytes are
known to have limited proliferation capacity in the damaged kidney,
and the depletion degree of podocyte up to 20–40% and 60%
leads to scarring and glomerulosclerosis, respectively [15]. Due to
the low proliferation capacity of podocyte in the diseased kidney,
investigations have focused on developing methods to accelerate
podocyte regeneration, which include activation of podocytes by
exogenously administered bioactive factors [11] or infusion of cultured
cells [16] into the damaged kidney. These strategies were
targeted to specifically regenerate certain renal function (e.g. filtration).
Likewise, many studies have aimed to achieve targeted specific
renal functions using various cell sources, scaffolding system
and bioactive factors.