A fundamental limitation with current approaches aiming to bioprint tissues and organs is an inability to generate constructs with truly biomimetic composition and structure, resulting in the development of engineered tissues that cannot execute their specific function in vivo. This is perhaps unsurprising, as many tissues and organs continue to mature postnatally, often taking many years to attain the compositional and structural complexity that is integral to their function. A potential solution to this challenge is to engineer tissues that are more representative of an earlier stage of development, using bioprinting to not only generate such constructs, but to also provide them with guiding structures and biochemical cues that supports their maturation into fully functional tissues or organs within damaged or diseased in vivo environments. It has recently been demonstrated that such developmental processes are better recapitulated in ‘microtissues’ or ‘organoids formed from self-organizing (multi)cellular aggregates, motivating their use as biological building blocks for the engineering of larger scale tissues and organ. The main goal of micro2MACRO (m2M) is to develop a new bioprinting platform capable of spatially patterning numerous cellular aggregates or microtissues into scaled-up, personalised durable load-bearing grafts and guiding their (re)modelling into fully functional tissues in vivo within damaged or diseased environments. This will be achieved using a converged bioprinting approach capable of rapidly depositing cells and microtissues into guiding scaffold structures with high spatial resolution in a rapid, reliable, reproducible and quantifiable manner. These guiding structures will then function to direction the fusion and remodelling of cellular aggregates and microtissues into structurally organised tissues in vitro and in vivo, as well as providing medium-term (3-5 years) mechanical support to the regenerating tissue.

Despite advances in organ transplantation technology, there is still a huge shortage of transplantable organs. Yearly, 25% of patients with end-stage liver disease on the donor waiting list die, emphasizing the need for alternatives to organ donations, such as bioprinting. Bioprinting presents a promising approach for creating organs from scratch, yet, it faces significant hurdles due to technical and biological challenges, combined with lacking standardized procedures and materials. In NEOLIVER, we will develop large, dense, and vascularized fully functional bioprinted constructs suitable for transplantation. We will achieve this by establishing a GMP-conform manufacturing line for standardized production, ensuring unparalleled quality and safety for future patients. More specifically, by using patient-derived organoids and supporting cells including endothelial cells, we will generate millions of multicellular spheroids as building blocks for bioprinting. Through laser induced forward transfer (LIFT) bioprinting techniques we will create a vascularized liver construct via precise spatial deposition of spheroids and vessels at high density. By integrating this technology with extrusion-based bioprinted vessels for blood supply, we will generate the world's first autologous bioprinted liver, ready for transplantation. To show the safety and efficacy, we will transplant the bioprinted liver constructs in immune-deficient pigs. This, combined with a clinical validation plan, upscaling strategy and Health Technology Assessment (including patient acceptance), will prepare the bioprinted liver constructs for first-in-human trials. Thus, NEOLIVER presents a disruptive alternative to donor organs for patients dealing with end-stage liver disease.