Shape-defined solid micro-objects from poly(d,l-lactic acid) as cell-supportive counterparts in bottom-up tissue engineering

In bottom-up tissue engineering, small modular units of cells and biomaterials are assembled toward ​larger and more complex ones. In conjunction with a new implementation of this approach, a novel method to fabricate microscale objects from biopolymers by thermal imprinting on water-soluble sacrificial layers is presented. By this means, geometrically well-defined objects could be obtained without involving toxic agents in the form of photoinitiators. The micro-objects were used as cell-adhesive substrates and cell spacers in engineered tissues created by cell-guided assembly of the objects. Such constructs can be applied both for in vitro studies and clinical treatments. Clinically relevantly sized aggregates comprised of cells and micro-objects retained their viability up to 2 weeks of culture. The aggregation behavior of cells and objects showed to depend on the type and number of cells applied. To demonstrate the micro-objects’ potential for engineering vascularized tissues, small aggregates of human bone marrow stromal cells (hMSCs) and micro-objects were coated with a layer of human umbilical vein endothelial cells (HUVECs) and fused into larger tissue constructs, resulting in HUVEC-rich regions at the aggregates' interfaces. This three-dimensional network-type spatial cellular organization could foster the establishment of (premature) vascular structures as a vital prerequisite of, for example, bottom-up-engineered bone-like tissue.