Thiol-gelatin-norbornene bioink for laser‐based high‐definition bioprinting

Two-photon polymerization (2PP) is a lithography-based 3D printing method allowing the fabrication of 3D structures with sub-micrometer resolution. This work focuses on the characterization of gelatin-norbornene (Gel-NB) bioinks which enables the embedding of cells via 2PP. The high reactivity of the thiol-ene system allows 2PP processing of cell-containing materials at remarkably high scanning speeds (1000 mm s(-1)) placing this technology in the domain of bioprinting. Atomic force microscopy results demonstrate that the indentation moduli of the produced hydrogel constructs can be adjusted in the 0.2-0.7 kPa range by controlling the 2PP processing parameters. Using this approach gradient 3D constructs are produced and the morphology of the embedded cells is observed in the course of 3 weeks. Furthermore, it is possible to tune the enzymatic degradation of the crosslinked bioink by varying the applied laser power. The 3D printed Gel-NB hydrogel constructs show exceptional biocompatibility, supported cell adhesion, and migration. Furthermore, cells maintain their proliferation capacity demonstrated by Ki-67 immunostaining. Moreover, the results demonstrate that direct embedding of cells provides uniform distribution and high cell loading independently of the pore size of the scaffold. The investigated photosensitive bioink enables high-definition bioprinting of well-defined constructs for long-term cell culture studies

On-chip high-definition bioprinting of microvascular structures

'Organ-on-chip' devices which integrate three-dimensional (3D) cell culture techniques with microfluidic approaches have the capacity to overcome the limitations of classical 2D platforms. Although several different strategies have been developed to improve the angiogenesis within hydrogels, one of the main challenges in tissue engineering remains the lack of vascularization in the fabricated 3D models. The present work focuses on the high-definition (HD) bioprinting of microvascular structures directly on-chip using two-photon polymerization (2PP). 2PP is a nonlinear process, where the near-infrared laser irradiation will only lead to the polymerization of a very small volume pixel (voxel), allowing the fabrication of channels in the microvascular range (10-30 mu m in diameter). Additionally, 2PP not only enables the fabrication of sub-micrometer resolution scaffolds but also allows the direct embedding of cells within the produced structure. The accuracy of the 2PP printing parameters were optimized in order to achieve high-throughput and HD production of microfluidic vessel-on-chip platforms. The spherical aberrations stemming from the refractive index mismatch and the focusing depth inside the sample were simulated and the effect of the voxel compensation as well as different printing modes were demonstrated. Different layer spacings and their dependency on the applied laser power were compared both in terms of accuracy and required printing time resulting in a 10-fold decrease in structuring time while yielding well-defined channels of small diameters. Finally, the capacity of 2PP to create vascular structures within a microfluidic chip was tested with two different settings, by direct embedding of a co-culture of endothelial- and supporting cells during the printing process and by creating a supporting, cell-containing vascular scaffold barrier where the endothelial cell spheroids can be seeded afterwards. The functionality of the formed vessels was demonstrated with immunostaining of vascular endothelial cadherin (VE-Cadherin) endothelial adhesion molecules in both static and perfused culture

High-resolution 3D bioprinting of photo-cross-linkable recombinant collagen to serve tissue engineering applications

Various biopolymers, including gelatin, have already been applied to serve a plethora of tissue engineering purposes. However, substantial concerns have arisen related to the safety and the reproducibility of these materials due to their animal origin and the risk associated with pathogen transmission as well as batch-to-batch variations. Therefore, researchers have been focusing their attention toward recombinant materials that can be produced in a laboratory with full reproducibility and can be designed according to specific needs (e.g., by introducing additional RGD sequences). In the present study, a recombinant protein based on collagen type I (RCPhC1) was functionalized with photo-cross-linkable methacrylamide (RCPhC1-MA), norbornene (RCPhC1-NB), or thiol (RCPhC1-SH) functionalities to enable high-resolution 3D printing via two-photon polymerization (2PP). The results indicated a clear difference in 2PP processing capabilities between the chain-growth-polymerized RCPhC1-MA and the step-growth-polymerized RCPhC1-NB/SH. More specifically, reduced swelling-related deformations resulting in a superior CAD-CAM mimicry were obtained for the RCPhC1-NB/SH hydrogels. In addition, RCPhC1-NB/SH allowed the processing of the material in the presence of adipose tissue-derived stem cells that survived the encapsulation process and also were able to proliferate when embedded in the printed structures. As a consequence, it is the first time that successful HD bioprinting with cell encapsulation is reported for recombinant hydrogel bioinks. Therefore, these results can be a stepping stone toward various tissue engineering applications

Thiol-norbornene gelatin hydrogels : influence of thiolated crosslinker on network properties and high definition 3D printing

Photocrosslinkable gelatin hydrogels are excellent bioinks or biomaterial ink components to serve biofabrication applications. Especially the widely investigated gelatin-methacroyl (gel-MA) hydrogels hold an impressive track record. However, over the past decade, increasing attention is being paid to thiol-ene photo-click chemistry to obtain hydrogel networks benefitting from a faster reactivity (i.e. seconds vs minutes) along with superior biocompatibility and processability. In order to exploit this photo-click chemistry, often an ene-functionality (e.g. norbornene) is introduced onto gelatin followed by crosslinking in the presence of a multifunctional thiol (e.g. dithiothreitol). To date, very limited research has been performed on the influence of the applied thiolated crosslinker on the final hydrogel properties. Therefore, the present work assesses the influence of different thiolated crosslinkers on the crosslinking kinetics, mechanical properties and biological performance of the hydrogels upon encapsulation of primary adipose tissue-derived stem cells which indicated a cell viability exceeding 70%. Furthermore, the different formulations were processed using two-photon polymerization which indicated, in addition to differences in processing window and swelling ratio, a previously unreported phenomenon. At high intensities (i.e. 150 mW), the laser results in cleavage of the gelatin backbone even in the absence of distinct photo-cleavable functionalities. This can have potential to introduce channels or softer regions in gels to result in zones characterized by different degradation speeds or the formation of blood vessels. Consequently, the present study can be used to provide guidance towards tailoring the thiol-ene system towards the desired applications

(Photo-)crosslinkable gelatin derivatives for biofabrication applications

Over the recent decades gelatin has proven to be very suitable as an extracellular matrix mimic for bio-fabrication and tissue engineering applications. However, gelatin is prone to dissolution at typical cell culture conditions and is therefore often chemically modified to introduce (photo-)crosslinkable functionalities. These modifications allow to tune the material properties of gelatin, making it suitable for a wide range of biofabrication techniques both as a bioink and as a biomaterial ink (component). The present review provides a non-exhaustive overview of the different reported gelatin modification strategies to yield crosslinkable materials that can be used to form hydrogels suitable for biofabrication applications. The different crosslinking chemistries are discussed and classified according to their mechanism including chain-growth and step-growth polymerization. The step-growth polymerization mechanisms are further classified based on the specific chemistry including different (photo-)click chemistries and reversible systems. The benefits and drawbacks of each chemistry are also briefly discussed. Furthermore, focus is placed on different biofabrication strategies using either inkjet, deposition or light-based additive manufacturing techniques, and the applications of the obtained 3D constructs

3D printed micro-environments as biomimetic in vitro models

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersOne 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.1

Using HEP expertise for social & humanitarian impact

When humanitarian and social challenges from the United Nations, Red Cross and Non-Governmental Organisations meet HEP expertise impactful innovation becomes reality. THE Port association at CERN combines physicists and engineers working on HEP topics in their day job with researchers, refugees, entrepreneurs, artists, designers, humanitarian workers and other creative minds. During 60-hour-long curated hackathons they co-create new technology opportunities, identify new methods, materials and processes, that can be used in the humanitarian context and sometimes even feedback into HEP. Examples from the last 5 humanitarian hackathons at CERN, whose outcomes are now utilised by UN, ICRC and others as well as future initiatives for HEP society impact, are presented

Screening of two-photon activated photodynamic therapy sensitizers using a 3D osteosarcoma model

Photodynamic therapy (PDT) involves a photosensitizing agent activated with light to induce cell death. Two-photon excited PDT (TPE-PDT) offers numerous benefits compared to traditional one-photon induced PDT, including an increased penetration depth and precision. However, the in vitro profiling and comparison of two-photon photosensitizers (PS) are still troublesome. Herein, we report the development of an in vitro screening platform of TPE-PS using a 3D osteosarcoma cell culture. The platform was tested using three different two-photon (2P) active compounds - a 2P sensitizer P2CK, a fluorescent dye Eosin Y, and a porphyrin derivative (TPP). Their 2P absorption cross-sections (sigma(2PA)) were characterised using a fully automated z-scan setup. TPP exhibited a remarkably high sigma(2PA) at 720 nm (8865 GM) and P2CK presented a high absorption at 850 nm (405 GM), while Eosin Y had the lowest 2P absorption at the studied wavelengths (<100 GM). The cellular uptake of PS visualized using confocal laser scanning microscopy showed that both TPP and P2CK were internalized by the cells, while Eosin Y stayed mainly in the surrounding media. The efficiency of the former two TPE-PS was quantified using the PrestoBlue metabolic assay, showing a significant reduction in cell viability after two-photon irradiation. The possibility of damage localization was demonstrated using a co-culture of adipose derived stem cells together with osteosarcoma spheroids showing no signs of damage to the surrounding healthy cells after TPE-PDT