Engineered dermal equivalent tissue in vitro by assembly of microtissue precursors

Tissue-engineered constructs can be fabricated by the assembly of smaller building blocks in order to mimic much of the native biology that is often made from repeating functional units. Our aim was to real- ize a three-dimensional (3-D) tissue-like construct in vitro by inducing the assembly of functional micro- metric tissue precursors (lTPs). lTPs were obtained by dynamic cell seeding of bovine fibroblasts on porous gelatine microcarriers using a spinner flask bioreactor. During the dynamic seeding, cells adhered, proliferated and synthesized a thin layer of extracellular matrix (ECM) in and around the macroporous beads, generating the lTPs. The analysis showed that the ECM produced was rich in type I collagen. The cells and ECM layer around the lTPs allowed their biological sintering via cell-cell and cell-matrix interaction after only a few days of dynamic seeding. The assembling ability of lTPs was exploited by placing them in a maturation chamber. After 1 week of culture disc-shaped constructs (1 cm in diameter, 1 mm in thickness) of completely assembled lTPs were collected. The biohybrid obtained presented both a homogeneous and compact aspect. Moreover, histological and immunohistochemical analyses revealed an abundant ECM, rich in type I collagen, interconnecting the lTPs. The results obtained in this survey pave the way to realizing a 3-D dermal tissue equivalent by means of a bottom-up tissue engineering approach.