**2. Biomaterials and stem cells**

Tissues in the human organism are generated, maintained and repopulated by stem cells. These are specialized cells capable of cell renewal and are able to differentiate into the different cell types in the human body. Stem cells have several differentiation programs, therefore, they possess information to allow them to become any cell in the body or a restricted cell type with a specialized function. These abilities make stem cells extremely useful for biomedical applications and regenerative medicine and have become the main molecular tool for these purposes [22].

Stem cells are derived from three primary sources, the embryonic origin, the mesenchymal origin and the so-called induced pluripotent stem cells. Cells from the embryonic origin are obtained from the inner cell mass of the blastocyst. They are considered a very important cell source for cell replacement therapies and have been used in regenerative medicine approaches by virtue of their ability to differentiate into any adult cell type [18]. Ethical considerations have restricted their use in many countries.

to the surface of the material shows an exponential increase in their contact area, which can enhance significantly the physicochemical properties. In this regard, nano-sized particles (ranging from 1 to 100 nm) have been considered as an effective strategy for pharmaceutical

Nanotechnology research has been intensively developed over the last decades; it is rapidly expanding and providing significant contributions to materials science. The main reasons for its success are the interesting properties of nanostructures that have led to greater efficacy systems, based on their physical dimension, shape, and composition [3]. Nowadays, these materials represent a broad potential for market growth, and recently these are commercialized as nanotechnology-enhanced products [4]. In the majority of these products, the presence of nanoparticles (NPs) is related to the addition of reinforcing agents such as additives,

The overall standings of NPs as additives involve organic systems, such as polymers [5], lipids [6], dendrimers [7], nano gels [8], nano emulsions [9], supramolecular structures [10] and others [11, 12]. In particular, inorganic NPs used for tissue regeneration such as carbon nanostructures (graphene, carbon nanotubes, fullerenes) [13], metallic nanoparticles, (such as silver, copper gold, titanium dioxide), quantum dots [14], and magnetic nanoparticles [15]

Recent advances in the use of nano-sized particles in pharmaceutics involves the design of controlled drug delivery systems [16], biomarkers as diseases detection [2], pathogen/protein identification [17], molecule separation/purification [18] and regenerative medicine approaches [17, 19, 20]. Recent studies have been focused in biomedicine in order to execute multidisciplinary research, combining topics such as chemistry, biology, physics, engineering and materials science; associated with the design of functional systems, addressed to the tissue regeneration responses in organisms. The development of tissue engineered systems from health sciences is aimed to promote specific cell growth to replace tissue damage, associated

In this chapter, the recent trends in the use of nanostructured systems combined with biopolymers will be discussed, divided into three parts: biomaterials and STEM cells, bio-nanocomposites and the current clinical cases where these systems were employed; aiming to emphasize the future challenge and perspectives in the design of biocompatible and nontoxic nanocomposites with high efficiency as promoter for tissue regeneration and many other biomedical applications.

Tissues in the human organism are generated, maintained and repopulated by stem cells. These are specialized cells capable of cell renewal and are able to differentiate into the different cell types in the human body. Stem cells have several differentiation programs, therefore, they possess information to allow them to become any cell in the body or a restricted cell type with a specialized function. These abilities make stem cells extremely useful for biomedical applications and regenerative medicine and have become the main molecular tool for these purposes [22].

with diseases such as cancer, trauma, hepatitis or congenital malformations [21].

carriers, antibacterial and skin regenerator systems [1, 2].

to improve physical/chemical or antibacterial characteristics.

have also been described.

28 Tissue Regeneration

**2. Biomaterials and stem cells**

Cells from the mesenchymal origin, as opposed to embryonic stem cells, come from adult organisms, and these cells can differentiate into cell lineages organ-specific, the use of these cells in regenerative medicine makes them very appropriated because the lack of ethical concerns of obtaining cells from embryos. As in other tissues, cartilage self-renewal potential is limited due to the absence of a dense population of progenitor cells, multipotent mesenchymal stem cells, have been used therapeutically for the purposes of cartilage repair. Arthrosis of the carpometacarpal joint is common in postmenopausal women and requires surgical treatment; mesenchymal stem cells have been therapeutically used as connective tissue progenitor donors isolated from the anterior and posterior iliac crest. Treatment with mesenchymal stem cells is a very effective therapeutic alternative, the patient avoids surgery and greatly improves articular function and diminishes pain [23].

The so-called induced pluripotent stem cells are adult cells with a modified genetic program, which have gained potency due to transcription factor transfection. According to Mall and Wernig [24], cell reprogramming makes now possible to change cell fate and transform adult skin cells into neurons, hepatocytes or cardiac cells. This approach is useful for many biomedical applications from studying disease progression as well as the efficacy and safety of newly developed drugs even before animal testing on clinical trials [24].

Stem cells have been successfully used to develop organoids. Organoids are stem cell 3D cultures resembling real organs. Cells in this array have interactions with each other, as well as with the extracellular matrix, which are not seen in petri dish monolayer culture [25]. An example in the advance of organoids came from the idea to perform functional studies in human brains, which is not that easy to address due to difficulties to perform studies in whole human brains or the inaccuracies of using postmortem tissue, therefore, researchers were in need of an *in vitro* model system that would mimic the characteristics of the brain during development. Three-dimensional *in vitro* brain models are arising, and more importantly, how they are now used to study the evolution of the brain and the associated neural disorders [26].

Stem cells have clinical potential for injury treatments and degenerative diseases. The challenge of the use of nanomaterials in these systems is related to the optimal control of microenvironment conditions to transplant cells [27]. The combined use of stem cells and nanoparticles has improved cell proliferation and differentiation, used in different diseases, such as ischemic stroke, spinal cord, multiple sclerosis, Parkinson, Alzheimer, and others [28].

In order to recapitulate the function and structure of the native extracellular matrix (ECM) to generate functional tissue, researchers have developed new biodegradable and biocompatible synthetic of natural polymer structures called scaffolds [29]. The supporting scaffold temporarily replaces the function of the ECM, supporting the 3D geometry and providing the appropriated structural conformation, enabling cell adherence, and facilitating the conformation of a tissue with its functional properties [30]. The microscopic structure must allow nutrient diffusion as well as the efflux of metabolites no longer needed to the cell through the scaffold. Finally, the scaffold must have good mechanical properties, enabling handling during culture in bioreactors and transplantation into the host [30].

Confocal imaging is a very useful to imaging technique in biomedical research, offering the ability to visualize different cell structures and their interaction with nanomaterials by using fluorescent dyes, as well allowing the creation of Z-stacks to recreate the three-dimensional architecture. Confocal imaging has been used to analyze the safety of dental nanostructured materials made from methacrylate monomers [37]. Another approach of engineered tissues has been the generation of oral soft and non-soft tissue. Recent advances involve the regeneration of whole teeth. Cells dissociated from epithelium and mesenchymal tissue of tooth buds were used to create a bioengineered tooth in vitro: cells were seeded to biodegradable polyglycolic/polylactide scaffolds having the shape of a tooth and implanted to rat hosts for

Trends in Tissue Regeneration: Bio-Nanomaterials http://dx.doi.org/10.5772/intechopen.75401 31

The use of cell combined with nanostructured materials has greatly improved translational research making now areas like biomedical research and nanomedicine, important contributors of many peer-reviewed papers, publications and funding in these areas have had an exponential increase since 2011. It is expected even a more dramatic increase in the years to come [39]. In accordance with these new developments, another branch of research has been developed, *nanotoxicology*. This increase in published data now has to be proved innocuous to the biological system or organism where is going to be applied. Eventually, this will lead to more research to discover the advantages or disadvantages of using nanostructured materials with potential biomedical applications. Toxicity of nanomaterials has to be verified at different levels, whereas is about the systemic effects or the inflammatory and immunological

Biomaterials research has been concerned with the use of nanomaterials to enhance the tissue regeneration process. In this regard, nanomaterials can be classified into organic and inorganic systems. Diversity in organic materials derived mainly from polymers, such as polysaccharides, collagen, and chitosan have been recently used with different morphologies into the biomedical application and stem cell differentiation [19]. In particular, the use of polymer NPs as carriers or drug delivery systems is promising materials used as neuroprotectors to avoid acute ischemic stroke, which is actually considered one of the most common causes of death worldwide [40]. Nanostructured drug delivery systems offer many advantages, such as the avoidance of drug degradation, the possibility to improve the pharmacokinetic profile and

NPs from different materials have been functionalized with bioactive molecules in order to describe their effects in cells and tissues. Bio-composites of silica NPs with fluorescent compounds from the tree *Eysenhardtia polystachya* were internalized into MCF-7 breast cancer cells and observed with confocal microscopy to analyze their possible anti-tumor effect [41].

Cells interact with each other through their own synthesized ECM, which provides support and allows proliferation and differentiation processes. In consequence, ECM produces high membrane adherence with specific ligands associated with signaling pathways and possible migration, which can regulate the cell growth [42, 43]. Our body possesses natural ECM, mainly

30 weeks and tooth structures were obtained [38].

**3. Bio-nanocomposites**

the specificity at nano scale.

response toward them, as well as the intra or extracellular effects [39].

One of the biggest health issues worldwide is organ failure derived from disease or a traumatic event; this has been resolved by transplantation of organs from living or deceased patient donors. The list of donors and recipients has increased in the last years and there are many patients on waiting lists for organ donation [31]. According to Gilpin and Yang [31], tissue engineering consists of three important aspects: the participating cells, the signaling molecules used and the scaffold. Scaffolds can be natural or synthetic. Natural scaffolds are derived from decellularization processes using chemical, enzymatic or physical methods. The resulting decellularized scaffold has to be recellularized either with one or different type of cells, in other cases induced pluripotent stem cells are used to recapitulate organ functionality [31–33].

For more than 20 years, scientists started developing nano-bio-materials and it is thought that nano bio-composites will be more important than non-nanometric materials at the physiological level. The advancement in biomedical research due to the incorporation in biomaterials to biological models has had a great impact in health sciences [34].

Decellularized scaffolds have been improved by combining them with biomaterials, not only to provide the extracellular matrix required for the cells to proliferate and differentiate but also to provide structural, biochemical and biomechanical support to the regenerated organ. Cheng et al. [35], developed silk-based scaffolds for bone regeneration, but their therapeutic efficacy was not optimal, therefore they developed a composite material of mesoporous bioactive glass/silk scaffold to improve mesenchymal stem cell regeneration activity in a rodent model for postmenopausal osteoporosis. They proved that the composite material provided the optimal environment for mesenchymal stem cell differentiation, attachment, and proliferation as treatment of osteoporotic defects [35]. Sterling and Guelcher [36] proposed another example of scaffolds to heal fractures derive for osteoporosis. In this research, the authors have argued that bone autografts (bone sample from the same patient), that have been used to improve fractured bone healing, have some pitfalls due to the limited amounts of bone that can be harvested, instead, hybrid scaffolds have been fabricated made with silk and calcium phosphate to stimulate bone formation and to reverse bone loss. The same group has shown that local delivery of recombinant bone morphogenic protein from microspheres made with polylactic glycolic acid has improved the mechanical properties of vertebrae in animal models [36].

We have been addressing some examples of the use of nanomaterials in conjunction with biological models or cells, but we are also going to show how these systems have to be visualized for further biomedical characterization.

Regarding tissue engineering, once the bio-engineered tissue is developed, it has to be evaluated in its structure and function. Histological and histochemical techniques have been used. For example, it is important not only to evaluate the 3D structure of scaffolds and its possible interaction with cells prior deciding on a biological or clinical application, but also the functionality of the cells contained the manufactured tissues. Different imaging techniques can be used to assure the efficiency of the biocomposites, such as ultrasound, microscopy, magnetic resonance imaging (MRI), and other optical imaging techniques [20].

Confocal imaging is a very useful to imaging technique in biomedical research, offering the ability to visualize different cell structures and their interaction with nanomaterials by using fluorescent dyes, as well allowing the creation of Z-stacks to recreate the three-dimensional architecture. Confocal imaging has been used to analyze the safety of dental nanostructured materials made from methacrylate monomers [37]. Another approach of engineered tissues has been the generation of oral soft and non-soft tissue. Recent advances involve the regeneration of whole teeth. Cells dissociated from epithelium and mesenchymal tissue of tooth buds were used to create a bioengineered tooth in vitro: cells were seeded to biodegradable polyglycolic/polylactide scaffolds having the shape of a tooth and implanted to rat hosts for 30 weeks and tooth structures were obtained [38].

The use of cell combined with nanostructured materials has greatly improved translational research making now areas like biomedical research and nanomedicine, important contributors of many peer-reviewed papers, publications and funding in these areas have had an exponential increase since 2011. It is expected even a more dramatic increase in the years to come [39]. In accordance with these new developments, another branch of research has been developed, *nanotoxicology*. This increase in published data now has to be proved innocuous to the biological system or organism where is going to be applied. Eventually, this will lead to more research to discover the advantages or disadvantages of using nanostructured materials with potential biomedical applications. Toxicity of nanomaterials has to be verified at different levels, whereas is about the systemic effects or the inflammatory and immunological response toward them, as well as the intra or extracellular effects [39].
