Bioprinting in Vascularization Strategies

Abstract

Three-dimensional (3D) printing technology has revolutionized tissue engineering field because of its excellent potential of accurately positioning cell-laden constructs. One of the main challenges in the formation of functional engineered tissues is the lack of an efficient and extensive network of microvessels to support cell viability. By printing vascular cells and appropriate biomaterials, the 3D printing could closely mimic in vivo conditions to generate blood vessels. In vascular tissue engineering, many various approaches of 3D printing have been developed, including selective laser sintering and extrusion methods, etc. The 3D printing is going to be the integral part of tissue engineering approaches; in comparison with other scaffolding techniques, 3D printing has two major merits: automation and high cell density. Undoubtedly, the application of 3D printing in vascular tissue engineering will be extended if its resolution, printing speed, and available materials can be improved.

Keywords: Neovascularization; Three-dimensional printings; Tissue engineering; Tissue scaffolds.

Fig. 1

Blood vessel formation in vitro and in vivo. (A) A schematic process of in vivo blood vessels development, vasculogenesis and angiogenesis, the two main mechanisms of blood vessel development. Vasculogenesis gives rise to the early vascular network during embryogenesis. Angiogenesis remodels and develops the vascular network through biochemical cues containing budding tumors, hypoxia conditions, and growth factor gradient[24]. (B) A schematic process of fabrication to make microfluidic patterning and laterally confined microfluidic patterning devices using soft lithography method. In the first step, a microfluidic device (a patterned polydimethylsiloxane [PDMS] mold) and the glass were exposed to plasma treatment and bonded to each other. Then a solution of fibronectin was introduced to the device. In the next step, a solution of endothelial cells was entered to the inlet section of the system. When most of the cells attached to the surface (about 1 hour), the PDMS mold was separated to obtain a PDMS surface containing patterned cells. In the following, the PDMS mold was immersed in the culture media and then a layer of hydrogel was coated on the patterned surface[32].

Fig. 2

Extrusion printing method. (A) A schematic picture of two large channel structures and deposition of fibrin and cell, which were developed using the 3D bioprinter. (B) Florescent microscopic images of two large channels, and the mixture of fibrin cell placed between channels. Green dots show green fluorescent protein-ECs that were cultured within fibrin, and red dots indicate red fluorescent protein-ECs that were seeded on the two large channels[55].

Fig. 3

Selective laser sintering (SLS) methods. (A) A schematic picture of a SLS printer; (B) environmental scanning electron microscopy photos of three different samples, non-coated (a and b) and polycaprolactone-coated (c and d); (C) Wimasis image analysis ofv titanium implant’s crosssection with green fluorescent protein-osteoblasts seeded in different times: (a) one day, (b) three days, and (c) seven days.

Fig. 4

Stereolithography method of printing. (A) direct and (B) indirect or mask-based stereolithography. (C) An illustration of stereolithography to fabricate vessels in Huber et al.’s[71] study. A laser beam was polarized, expanded and then directed through a microscope objective.

Fig. 5

The process of the microchannel formation inside the gel using the 3D printing of sacrificial materials (SM). At first, a computer-based plan of a SM is fabricated using the 3D printing. Then this 3D construct was immersed in a solution of an appropriate biomaterial and certain cells. After gelation of the biomaterial, the 3D constructs were immersed in culture media, which flows inside the channel, dissolves SM, and creates microchannel within the scaffolds.