3D printed micro-environments as biomimetic in vitro models

Abstract

One of the main challenges of current biomedical research and drug development is the lack of available physiological in vitro models. Traditionally in vitro research was performed using two-dimensional cell culture methods. However, there has been an increasing evidence that culturing cells under planar conditions do not recapitulate the complexity of the three-dimensional (3D) environment cells experience in the body, which often results in increased drug response at preclinical research phase. Multiple different approaches have been developed over the last decades to introduce 3D microenvironments for cells, either by “bottom up” or “top down” technologies. In the bottom up method, the cells self-assemble without any mechanical support and form aggregates (spheroids), while the top down production of 3D cell cultures involves the use of scaffolds which later on can be seeded with cells. Two photon-polymerization (2PP) is a high-definition 3D printing approach, where the absorption of femtosecond-pulsed laser radiation leads to localized cross-linking of photosensitive materials within the focal volume enabling the direct embedding of cells inside photosensitive hydrogels at high structural resolution in accordance to a computer assisted designs. Structures can be printed within the bulk of the material eradicating the need of a layer-by-layer deposition, which is required in other 3D printing technologies. One of the main bottlenecks of using 2PP for biofabrication is the lack available biocompatible photoinitiators and bioinks. The aim of the thesis is to establish the printing conditions and material compositions which allows the embedding of cells directly into the bioink, while maintaining cell viability. Several different materials can be employed as bioinks for 2PP including natural and synthetic photopolymers. One of the main advantages of natural hydrogels is that they are often derived from the non-cellular compartment of the tissues, the extracellular matrix, therefore they contain the necessary biological and mechanical cues the cells require. The ultimate goal of this thesis is to use 2PP platform to create biomimetic tissue models and disease models and study cell behaviour in complex 3D environment.