Tissue Engineering

Culturing cells in 3D scaffolds can help model a physiological process. The property of the substrate used for such scaffolds has been shown to modify and determine stem cell lineage. Using this knowledge, in-vitro 3D stem cell culture models with ex-vivo bone tissue investigations can offer insight and inspiration for the development of novel therapies for bone defects. Although many different scaffolds have been created for bone tissue repair, in situ cell level mechanics are not always given consideration as the main design target. Overall, the ideal tissue engineering solution to bone regeneration would incorporate cells of osteogenic potential into a synthetic bone scaffold in order to reduce the need for external factors added such as drugs or growth factors. Attention to the mechanical aspects of the bone to be studied as well as the cells to be placed within the scaffold is fundamental. In this chapter, we will explore studies investigating the role of cell communication in bone mechanosensing, including the roles of different bone cells in the process of bone adaptation and repair, and the use of this knowledge in creating a novel tissue engineering strategy for the repair of acute bone defects.

In tissue regenerative implants, porosity allowing the ingrowth of cells and tissue is a key factor for the long-term success. While vital for healing and tissue regeneration, the use of highly porous structures may adversely affect the mechanical properties of the scaffold, in particular when viscoelastic polymeric materials are used. In the case of biodegradable scaffold materials, the effect of the degradation process on mechanical and structural properties of the scaffold is yet another aspect to be considered. Both tissue ingrowth and biodegradation are concurrent transient processes which change the mechanical and structural properties of the implanted device over time. Ingrowth of cells and tissue typically results in an increase in structural stiffness whereas scaffold degradation leads to loss of mechanical properties and potentially to structural disintegration. The aim of the research presented in this chapter was the investigation of the change of mechanical properties of a biodegradable, electro-spun polyester-urethane scaffold for soft tissue regeneration during hydrolytic degradation and the development of a constitutive model that is suitable for capturing these changes.

A large range of biodegradable polymers are used to produce scaffolds for tissue engineering, which temporarily replace the biomechanical functions of a biologic tissue while it progressively regenerates its capacities. However, the mechanical behavior of biodegradable materials during its degradation, which is an important aspect of the scaffold design, is still an unexplored subject. For a biodegradable scaffold, performance will decrease along its degradation, ideally in accordance to the regeneration of the biologic tissue, avoiding the stress shielding effect or the premature rupture. In this chapter, a new numerical approach to predict the mechanical behavior of complex 3D scaffolds during degradation time (the 4th dimension) is presented. The degradation of mechanical properties should ideally be compatible to the tissue regeneration. With this new approach, an iterative process of optimization is possible to achieve an ideal solution in terms of mechanical behavior and degradation time. The scaffold can therefore be pre-validated in terms of functional compatibility. An example of application of this approach is demonstrated at the end of this chapter.

Many studies demonstrate the relevance of the mechanical properties of molecules and living cells to physiological function. Therefore, several techniques have been developed to probe the rheology of biological materials. Among them are based on the analysis of embedded probe fluctuations. However, novel applications using this robust tool are still lacking, despite the fact that the study of living matter routinely demonstrate new phenomena, not immediately characterized by existing analytical tools developed in physics. Hence, we derive novel robust tools to adapt ways of probing non-linear and non-equilibrium phenomena for biological samples. We propose designs of optical tweezer systems using two-beam tandems by dual-wavelength and single-wavelength splitting, for the study of microrheology in bulk down to single biopolymer or protein based on the fluctuation spectra of embedded or attached probes. We generalize, for the first time, calculations for winding turn probabilities to account for unfolding events in single fibrous biopolymers, which is modeled using a newly derived worm-like-chain model re-expressed by fractional strain expansion. The ensuing probe fluctuations are taken as originating from a damped harmonic oscillator. The approach described here offer new ways of characterizing biopolymer rheology using parameters based on folding turns and a newly derived WLC expansion for non-linear stretching.

Scaffolds play a pivotal role in tissue engineering, promoting the synthesis of neo extra-cellular matrix (ECM), and providing temporary mechanical support for the cells during tissue regeneration. Advances introduced by additive manufacturing techniques have significantly improved the ability to regulate scaffold architecture, enhancing the control over scaffold shape and porosity. Thus, considerable research efforts have been devoted to the fabrication of 3D porous scaffolds with optimized micro-architectural features. This chapter gives an overview of the methods for the design of additively manufactured scaffolds and their applicability in tissue engineering (TE). Along with a survey of the state of the art, the Authors will also present a recently developed method, called Load-Adaptive Scaffold Architecturing (LASA), which returns scaffold architectures optimized for given applied mechanical loads systems, once the specific stress distribution is evaluated through Finite Element Analysis (FEA).

Tissue Engineering is a promising emerging field that studies the intrinsic regenerative potential of the human body and uses it to restore functionality of damaged organs or tissues unable of self-healing due to illness or ageing. In order to achieve regeneration using Tissue Engineering strategies, it is first necessary to study the properties of the native tissue and determine the cause of tissue failure; second, to identify an optimum population of cells capable of restoring its functionality; and third, to design and manufacture a cellular microenvironment in which those specific cells are directed towards the desired cellular functions. The design of the artificial cellular niche has a tremendous importance, because cells will feel and respond to both its biochemical and biophysical properties very differently. In particular, the artificial niche will act as a physical scaffold for the cells, allowing their three-dimensional spatial organization; also, it will provide mechanical stability to the artificial construct; and finally, it will supply biochemical and mechanical cues to control cellular growth, migration, differentiation and synthesis of natural extracellular matrix. During the last decades, many scientists have made great contributions to the field of Tissue Engineering. Even though this research has frequently been accompanied by vast investments during extended periods of time, yet too often these efforts have not been enough to translate the advances into new clinical therapies. More and more scientists in this field are aware of the need of rational experimental designs before carrying out complex, expensive and time-consuming in vitro and in vivo trials. This review highlights the importance of computer modeling and novel biofabrication techniques as critical key players for a rational design of artificial cellular niches in Tissue Engineering.

Stereolithography is an additive technique that produces three-dimensional (3D) solid objects using a multi-layer procedure through the selective photo-initiated curing reaction of a liquid photosensitive material. Stereolithographic processes have been widely employed in Tissue Engineering for the fabrication of temporary constructs, using natural and synthetic polymers, and polymer-ceramic composites. These processes allow the fabrication of complex structures with a high accuracy and precision at physiological temperatures, incorporating cells and growth factors without significant damage or denaturation. Despite recent advances on the development of novel biomaterials and biocompatible crosslinking agents, the main limitation of these techniques are the lack number of available photocrosslinkable materials, exhibiting appropriate biocompatibility and biodegradability. This chapter gives an overview of the current state-of-art of materials and stereolithographic techniques to produce constructs for tissue regeneration, outlining challenges for future research.