Preface

Recently, 3D bioprinting has drawn increasing attention and progressed vastly with the advancement in printing technologies and functional bioinks in the field of tissue engineering and regenerative medicine. 3D bioprinting is considered as one of the most modern technologies that gives high hope for the biomaterial scientists, biomedical engineers and clinicians to develop functional complex tissues and organ constructs in vitro for drug screening and tissue regeneration. With advanced biofabrication techniques and biomaterials, the researchers are able to create complex tissues or large organs with biomimetic structures and/or functionalities. The 3D bioprinting process generally involves the deposition of cell-laden hydrogel biomaterials (bioinks) in well-arranged layers to obtain a 3D construct that is capable of creating functional tissues or organs.

Typical 3D bioprinting techniques include pneumatic or screw-based extrusion printing techniques such as direct ink writing (DIW), laser-induced forward transfer, inkjet bioprinting and stereolithography (SLA). For all 3D bioprinting techniques, the primary component is the cell-laden bioink, generally hydrogels, which function as an extracellular matrix to produce engineered/artificial living tissues. Hence, the selection of the bioink, i.e. hydrogel and encapsulated cells, is highly critical to obtain the desired results. In bioink preparation, the hydrogels play a dominant role by encapsulating cells for the protection of cells during bioprinting. Besides, the hydrogels as a bioink mimic the biological and physico-chemical properties of the native tissues to provide the necessary environment for cells to attach, grow and proliferate, leading to tissue regeneration. Furthermore, they offer the convenient environment by providing proper nutrient transport, waste removal, and oxygen/carbon dioxide exchange. To obtain these functionalities, the hydrogel should be synthesized with adequate synthetic methodologies and have physically appropriate and cell-compatible features such as in situ gelation and self-assembly. Properties such as rheology, degradability or mechanical strength can be obtained by polymer synthesis as well as the chemical modification of natural polymers. Apart from these, the hydrogels can yield shear thinning properties during 3D printing processes even while accommodating living cells and without significantly affecting their biocompatibility.

This book covers hydrogel synthesis, characterization, 3D printing processing, rheological properties, tissue engineering applications, intellectual property and FDA approval, and basically outlines the current status of injectable and 3D bioprinting hydrogels and their 3D bioprinting starting from bioinks in line with the targeted applications. This book also focuses on more in-depth explanations about injectable and bioprintable hydrogels such as their various forms and synthesis methods as well as the characterization of different properties. It also covers issues with respect to intellectual property and Food and Drug Administration (FDA) approval. We believe that the in-depth explanations in this book can benefit a number of audiences, including graduate school level students and the majority of researchers working in the areas of advanced injectable hydrogels, 3D bioprinting, tissue/organ engineering research, and drug screening research.

We as editors sincerely express our gratitude to the authors for their great expertise and valuable contributions to bioprinting hydrogel-related chapters and to their lab members for the contributions involving research and writing the chapters. We would like to give our special appreciation to their families for their continuous support and love. Insup Noh would like to thank scientific mentors, Professor Jeffrey A. Hubbell at the University of Chicago and Professor Elazer R. Edelman at the Massachusetts Institute of Technology and at Harvard Medical School, USA.

Xiumei Wang would like to thank scientific mentor, Prof. Fuzhai Cui at Tsinghua University, China and Prof. Shuguang Zhang at the Massachusetts Institute of Technology, USA.

Sandra van Vlierberghe would like to thank scientific mentor, Prof. Em. Etienne Schacht, and her valuable team members at the Polymer Chemistry & Biomaterials Group at Ghent University (Belgium).

Insup Noh

Xiumei Wang

Sandra van Vlierberghe