Frontiers in Biomaterials

Stem cells have attracted great interest of biomedical scientists and clinicians due to their unique abilities of self-renewal and multipotential differentiation. With the most current technologies, stem cells have been isolated from almost all types of tissue, including embryonic stem cells, somatic stem cells, and induced pluripotent stem cells. The mechanisms of cells behavior have been fully studied. In combination with tissue engineering skills, stem cells have been investigated in a better environment by simulating the three-dimensional environment. However, the long-term safety and efficiency of stem cell-based outcomes should be further evaluated prior to any clinical application.

Dental/orofacial tissue engineering is an emerging field that offers alternative solutions for dental problems resulting from pathologies such as caries, trauma, periodontal disease and others. Various stem cell types such as bone marrow stem cells (BMSCs) and adipose tissue-derived stem cells (ADSCs) can be employed as cell sources for dental tissue repair. In particular, dental tissue-derived stem cells such as dental pulp stem cells (DPSCS) and dental follicle stem cells (DFSCs) can be utilized due to their favorable origin and properties. On the other hand, natural and synthetic polymers are used to fabricate 3D dental tissue scaffolds to support cellular activities. Several bioregulators such as cytokines and growth factors can also be incorporated to induce cells interaction and cell-scaffold integration. The literature on the regeneration of dental tissues via tissue engineering principles presents numerous results that are superior to the traditional methods, which are vital for advancing dental therapy. Herein, the types, properties, and applications of dental stem cells (DSCs) were reviewed, as well as the tissue engineering and regeneration strategies for different types of dental tissues.

Cardiovascular disease is one of the leading causes of death worldwide. Transplantation is the conventional treatment, but it has to be alleviated due to scarcity of donors. The emerging field of cardiac tissue engineering aims to develop innovative strategies for the treatment of cardiovascular diseases, through engineering of biomimetic tissue substitutes. Among the different strategies, scaffold-based approaches hold great promises, such as the use of rationally designed porous scaffolds that will effectively guide the development of seeded cells into the formation of functional cardiac tissues. Properly selected biomaterials used for scaffold fabrication promote the interactions among homogeneous or heterogeneous cell types while they maintain biomechanical properties of the microenvironment. Here we review the stateof- art progress in porous scaffold-based fabrication of cardiac tissues and vascular grafts. While extensive achievements have been consolidated in the past decade, with further advancements we envision the applications of cardiac tissue engineering in the areas of drug screening, disease modeling, and in vivo regenerative therapy.

Liver and kidney are among the most demanded organs for transplantation. There is currently no tissue engineered liver or kidney that has been used as a clinical product. One of the main reasons is due to the structural and functional complexity of these organs. In recent years, several studies have demonstrated significant progress in development of an engineered 3D tissues and decellularization from the original organ. 3D printing bio-microelectromechanical system (BioMEMS) and organ-on-a-chip technology can help to provide a biological in vitro model for studying fundamental organ biology, organ disease, toxicology and drug discovery. Despite promising approaches have been used by many research groups within last decades, how to construct a fully functional liver or kidney tissue still reminds a big challenge. In this chapter we will review the most recent advances in liver and kidney tissue engineering, respectively.

Skin substitutes as an alternative to skin grafts provide immediate protective barrier against the environment and have critical medical applications to patients with extensive burns. Their initial role is to facilitate repair and reconstruction of skin layers and in more advanced approaches to maintain normal functionality and aesthetics of normal skin. Depending on their design, skin substitutes can act as temporary covers or permanent skin replacements with the main goals of reducing the need for donor sites and to decrease the risk of infection. Moreover, they minimize scarring and also can facilitate angiogenesis. However, current skin substitutes do not restore the normal skin anatomy and they lack skin appendages like sweat glands, hair follicles as well as immune cells. Recent progresses in stem cell biology and engineering techniques hold promise for simulating more advanced skin equivalents with the potential to serve as a drug screening and immune competent models.

Musculoskeletal system mainly includes bone, cartilage, tendon, ligament, and skeletal muscle, which supports the body and connects tissues and organs together. Musculoskeletal disorders, including degenerative diseases and trauma injuries lead to the loss of part tissue, and always accompanied with pain. With the development of biomaterials, developmental biology, nanomedicine and orthopedic therapy strategies, tissue engineering of musculoskeletal system has been well investigated in the past two decades. Many musculoskeletal tissue repair strategies have achieved success in animal models, with part of them entered clinical trials which will benefit patients in the future.