Cell-laden microfibers for bottom-up tissue engineering

•Cell-laden microfibers (CLMs) are effective building blocks for tissue reconstruction.•Current formation technologies for CLM are summarized and classified.•CLM could apply to 3D tissue reconstruction, in vitro drug testing and in vivo implantation. Bottom-up tissue engineering, which utilizes hundred-micrometer-scale cellular constructs as building blocks, is a promising approach to reconstructing 3D, macroscopic and spatially organized tissues in vitro. Among the various types of cellular building blocks for reconstruction, cell-laden microfibers (CLMs) are recognized as an appropriate shape because many important human tissues and organs are composed of fiber-shaped or network-like structures. This review covers the current techniques in forming CLMs and typical cell culture conditions on or within the microfibers. We summarize CLMs for in vitro 3D tissue construction, in vitro pseudo tissue models for drug testing and in vivo implantation. Additionally, we discuss current challenges regarding CLM technologies and their potential applications.