3D Bioprinting of Human Adipose-Derived Stem Cells and Their Tenogenic Differentiation in Clinical-Grade Medium

Bacterial Cellulose: A Sustainable Source for Hydrogels and 3D-Printed Scaffolds for Tissue Engineering

Bacterial cellulose is a biocompatible biomaterial with a unique macromolecular structure. Unlike plant-derived cellulose, bacterial cellulose is produced by certain bacteria, resulting in a sustainable material consisting of self-assembled nanostructured fibers with high crystallinity. Due to its purity, bacterial cellulose is appealing for biomedical applications and has raised increasing interest, particularly in the context of 3D printing for tissue engineering and regenerative medicine applications. Bacterial cellulose can serve as an excellent bioink in 3D printing, due to its biocompatibility, biodegradability, and ability to mimic the collagen fibrils from the extracellular matrix (ECM) of connective tissues. Its nanofibrillar structure provides a suitable scaffold for cell attachment, proliferation, and differentiation, crucial for tissue regeneration. Moreover, its mechanical strength and flexibility allow for the precise printing of complex tissue structures. Bacterial cellulose itself has no antimicrobial activity, but due to its ideal structure, it serves as matrix for other bioactive molecules, resulting in a hybrid product with antimicrobial properties, particularly advantageous in the management of chronic wounds healing process. Overall, this unique combination of properties makes bacterial cellulose a promising material for manufacturing hydrogels and 3D-printed scaffolds, advancing the field of tissue engineering and regenerative medicine.

4-Axis 3D-Printed Tubular Biomaterials Imitating the Anisotropic Nanofiber Orientation of Porcine Aortae

Many of the peculiar properties of the vasculature are related to the arrangement of anisotropic proteinaceous fibers in vessel walls. Understanding and imitating these arrangements can potentially lead to new therapies for cardiovascular diseases. These can be pre-surgical planning, for which patient-specific ex vivo anatomical models for endograft testing are of interest. Alternatively, therapies can be based on tissue engineering, for which degradable in vitro cell growth substrates are used to culture replacement parts. In both cases, materials are desirable that imitate the biophysical properties of vessels, including their tubular shapes and compliance. This work contributes to these demands by offering methods for the manufacturing of anisotropic 3D-printed nanofibrous tubular structures that have similar biophysical properties as porcine aortae, that are biocompatible, and that allow for controlled nutrient diffusion. Tubes of various sizes with axial, radial, or alternating nanofiber orientation along the blood flow direction are manufactured by a customized method. Blood pressure-resistant, compliant, stable, and cell culture-compatible structures are obtained, that can be degraded in vitro on demand. It is suggested that these healthcare materials can contribute to the next generation of cardiovascular therapies of ex vivo pre-surgical planning or in vitro cell culture.

3D Printed Scaffolds Manufactured with Biosilica from Marine Sponges for Bone Healing in a Cranial Defect in Rats

The inorganic part of marine sponges, called Biosilica (BS), presents an osteogenic potential and the ability of consolidating fractures. Moreover, 3D printing technique is highly effective for manufacturing scaffolds for tissue engineering proposals. Thus, the aims of this study were to characterize the 3D rinted scaffolds, to evaluate the biological effects in vitro and to investigate the in vivo response using an experimental model of cranial defects in rats. The physicochemical characteristics of 3D printed BS scaffolds were analyzed by FTIR, EDS, calcium assay, evaluation of mass loss and pH measurement. For in vitro analysis, the MC3T3-E1 and L929 cells viability was evaluated. For the in vivo evaluation, histopathology, morphometrical and immunohistochemistry analyses were performed in a cranial defect in rats. After the incubation, the 3D printed BS scaffolds presented lower values in pH and mass loss over time. Furthermore, the calcium assay showed an increased Ca uptake. The FTIR analysis indicated the characteristic peaks for materials with silica and the EDS analysis demonstrated the main presence of silica. Moreover, 3D printed BS demonstrated an increase in MC3T3-E1 and L929 cell viability in all periods analyzed. In addition, the histological analysis demonstrated no inflammation in days 15 and 45 post-surgery, and regions of newly formed bone were also observed. The immunohistochemistry analysis demonstrated increased Runx-2 and OPG immunostaining. Those findings support that 3D printed BS scaffolds may improve the process of bone repair in a critical bone defect as a result of stimulation of the newly formed bone.

Classification, processing, and applications of bioink and 3D bioprinting: A detailed review

With the advancement in 3D bioprinting technology, cell culture methods can design 3D environments which are both, complex and physiologically relevant. The main component in 3D bioprinting, bioink, can be split into various categories depending on the criterion of categorization. Although the choice of bioink and bioprinting process will vary greatly depending on the application, general features such as material properties, biological interaction, gelation, and viscosity are always important to consider. The foundation of 3D bioprinting is the exact layer-by-layer implantation of biological elements, biochemicals, and living cells with the spatial control of the implantation of functional elements onto the biofabricated 3D structure. Three basic strategies underlie the 3D bioprinting process: autonomous self-assembly, micro tissue building blocks, and biomimicry or biomimetics. Tissue engineering can benefit from 3D bioprinting in many ways, but there are still numerous obstacles to overcome before functional tissues can be produced and used in clinical settings. A better comprehension of the physiological characteristics of bioink materials and a higher level of ability to reproduce the intricate biologically mimicked and physiologically relevant 3D structures would be a significant improvement for 3D bioprinting to overcome the limitations.

Recent Advances in Decellularized Matrix-Derived Materials for Bioink and 3D Bioprinting

As an emerging 3D printing technology, 3D bioprinting has shown great potential in tissue engineering and regenerative medicine. Decellularized extracellular matrices (dECM) have recently made significant research strides and have been used to create unique tissue-specific bioink that can mimic biomimetic microenvironments. Combining dECMs with 3D bioprinting may provide a new strategy to prepare biomimetic hydrogels for bioinks and hold the potential to construct tissue analogs in vitro, similar to native tissues. Currently, the dECM has been proven to be one of the fastest growing bioactive printing materials and plays an essential role in cell-based 3D bioprinting. This review introduces the methods of preparing and identifying dECMs and the characteristic requirements of bioink for use in 3D bioprinting. The most recent advances in dECM-derived bioactive printing materials are then thoroughly reviewed by examining their application in the bioprinting of different tissues, such as bone, cartilage, muscle, the heart, the nervous system, and other tissues. Finally, the potential of bioactive printing materials generated from dECM is discussed.

A novel extrusion-based 3D bioprinting system for skeletal muscle tissue engineering

Three-dimensional (3D) bioprinting is an emerging technology, which turned out to be an optimal tool for tissue engineering approaches. To date, different printing systems have been developed. Among them, the extrusion-based approach demonstrated to be the most suitable for skeletal muscle tissue engineering, due to its ability to produce and deposit printing fibers in a parallel pattern that well mimic the native skeletal muscle tissue architecture. In tissue bioengineering, a key role is played by biomaterials, which must possess the key requisite of 'printability'. Nevertheless, this feature is not often well correlated with cell requirements, such as motives for cellular adhesion and/or absorbability. To overcome this hurdle, several efforts have been made to obtain an effective bioink by combining two different biomaterials in order to reach a good printability besides a suitable biological activity. However, despite being efficient, this strategy reveals several outcomes limitations. We report here the development and characterization of a novel extrusion-based 3D bioprinting system, and its application for correction of volumetric muscle loss (VML) injury in a mouse model. The developed bioprinting system is based on the use of PEG-Fibrinogen, a unique biomaterial with excellent biocompatibility, well-suited for skeletal muscle tissue engineering. With this approach, we obtained highly organized 3D constructs, in which murine muscle progenitors were able to differentiate into muscle fibers arranged in aligned bundles and capable of spontaneously contracting when culturedin vitro. Furthermore, to evaluate the potential of the developed system in future regenerative medicine applications, bioprinted constructs laden with either murine or human muscle progenitors were transplanted to regenerate theTibialis Anteriormuscle of a VML murine model, one month after grafting.

Nanocomposite bioinks for 3D bioprinting

Three-dimensional (3D) bioprinting is an advanced technology to fabricate artificial 3D tissue constructs containing cells and hydrogels for tissue engineering and regenerative medicine. Nanocomposite reinforcement endows hydrogels with superior properties and tailored functionalities. A broad range of nanomaterials, including silicon-based, ceramic-based, cellulose-based, metal-based, and carbon-based nanomaterials, have been incorporated into hydrogel networks with encapsulated cells for improved performances. This review emphasizes the recent developments of cell-laden nanocomposite bioinks for 3D bioprinting, focusing on their reinforcement effects and mechanisms, including viscosity, shear-thinning property, printability, mechanical properties, structural integrity, and biocompatibility. The cell-material interactions are discussed to elaborate on the underlying mechanisms between the cells and the nanomaterials. The biomedical applications of cell-laden nanocomposite bioinks are summarized with a focus on bone and cartilage tissue engineering. Finally, the limitations and challenges of current cell-laden nanocomposite bioinks are identified. The prospects are concluded in designing multi-component bioinks with multi-functionality for various biomedical applications. STATEMENT OF SIGNIFICANCE: 3D bioprinting, an emerging technology of additive manufacturing, has been one of the most innovative tools for tissue engineering and regenerative medicine. Recent developments of cell-laden nanocomposite bioinks for 3D bioprinting, and cell-materials interactions are the subject of this review paper. The reinforcement effects and mechanisms of nanocomposites on viscosity, printability and biocompatibility of bioinks and 3D printed scaffolds are addressed mainly for bone and cartilage tissue engineering. It provides detailed information for further designing and optimizing multi-component bioinks with multi-functionality for specialized biomedical applications.

Adipose tissue in bone regeneration - stem cell source and beyond

Adipose tissue (AT) is recognized as a complex organ involved in major home-ostatic body functions, such as food intake, energy balance, immunomodulation, development and growth, and functioning of the reproductive organs. The role of AT in tissue and organ homeostasis, repair and regeneration is increasingly recognized. Different AT compartments (white AT, brown AT and bone marrow AT) and their interrelation with bone metabolism will be presented. AT-derived stem cell populations - adipose-derived mesenchymal stem cells and pluripotent-like stem cells. Multilineage differentiating stress-enduring and dedifferentiated fat cells can be obtained in relatively high quantities compared to other sources. Their role in different strategies of bone and fracture healing tissue engineering and cell therapy will be described. The current use of AT- or AT-derived stem cell populations for fracture healing and bone regenerative strategies will be presented, as well as major challenges in furthering bone regenerative strategies to clinical settings.

3D Bioprinting of Biomimetic Bilayered Scaffold Consisting of Decellularized Extracellular Matrix and Silk Fibroin for Osteochondral Repair

Recently, three-dimensional (3D) bioprinting technology is becoming an appealing approach for osteochondral repair. However, it is challenging to develop a bilayered scaffold with anisotropic structural properties to mimic a native osteochondral tissue. Herein, we developed a bioink consisting of decellularized extracellular matrix and silk fibroin to print the bilayered scaffold. The bilayered scaffold mimics the natural osteochondral tissue by controlling the composition, mechanical properties, and growth factor release in each layer of the scaffold. The in vitro results show that each layer of scaffolds had a suitable mechanical strength and degradation rate. Furthermore, the scaffolds encapsulating transforming growth factor-beta (TGF-β) and bone morphogenetic protein-2 (BMP-2) can act as a controlled release system and promote directed differentiation of bone marrow-derived mesenchymal stem cells. Furthermore, the in vivo experiments suggested that the scaffolds loaded with growth factors promoted osteochondral regeneration in the rabbit knee joint model. Consequently, the biomimetic bilayered scaffold loaded with TGF-β and BMP-2 would be a promising strategy for osteochondral repair.

Advances in the application of mesenchymal stem cells, exosomes, biomimetic materials, and 3D printing in osteoporosis treatment

Owing to an increase in the aging population, osteoporosis has become a severe public health concern, with a high prevalence among the elderly and postmenopausal adults. Osteoporosis-related fracture is a major cause of morbidity and mortality in elderly and postmenopausal adults, posing a considerable socioeconomic burden. However, existing treatments can only slow down the process of osteoporosis, reduce the risk of fractures, and repair fractures locally. Therefore, emerging methods for treating osteoporosis, such as mesenchymal stem cell transplantation, exosome-driving drug delivery systems, biomimetic materials, and 3D printing technology, have received increasing research attention, with significant progress. Mesenchymal stem cells (MSCs) are pluripotent stem cells that can differentiate into different types of functional cells. Exosomes play a key role in regulating cell microenvironments through paracrine mechanisms. Bionic materials and 3D printed scaffolds are beneficial for the reconstruction and repair of osteoporotic bones and osteoporosis-related fractures. Stem cells, exosomes, and biomimetic materials represent emerging technologies for osteoporosis treatment. This review summarizes the latest developments in these three aspects.

Clay Minerals as Bioink Ingredients for 3D Printing and 3D Bioprinting: Application in Tissue Engineering and Regenerative Medicine

The adaptation and progress of 3D printing technology toward 3D bioprinting (specifically adapted to biomedical purposes) has opened the door to a world of new opportunities and possibilities in tissue engineering and regenerative medicine. In this regard, 3D bioprinting allows for the production of tailor-made constructs and organs as well as the production of custom implants and medical devices. As it is a growing field of study, currently, the attention is heeded on the optimization and improvement of the mechanical and biological properties of the so-called bioinks/biomaterial inks. One of the strategies proposed is the use of inorganic ingredients (clays, hydroxyapatite, graphene, carbon nanotubes and other silicate nanoparticles). Clays have proven to be useful as rheological and mechanical reinforcement in a wide range of fields, from the building industry to pharmacy. Moreover, they are naturally occurring materials with recognized biocompatibility and bioactivity, revealing them as optimal candidates for this cutting-edge technology. This review deals with the use of clays (both natural and synthetic) for tissue engineering and regenerative medicine through 3D printing and bioprinting. Despite the limited number of studies, it is possible to conclude that clays play a fundamental role in the formulation and optimization of bioinks and biomaterial inks since they are able to improve their rheology and mechanical properties, thus improving printability and construct resistance. Additionally, they have also proven to be exceptionally functional ingredients (enhancing cellular proliferation, adhesion, differentiation and alignment), controlling biodegradation and carrying/releasing actives with tissue regeneration therapeutic activities.

The Lack of a Representative Tendinopathy Model Hampers Fundamental Mesenchymal Stem Cell Research

Overuse tendon injuries are a major cause of musculoskeletal morbidity in both human and equine athletes, due to the cumulative degenerative damage. These injuries present significant challenges as the healing process often results in the formation of inferior scar tissue. The poor success with conventional therapy supports the need to search for novel treatments to restore functionality and regenerate tissue as close to native tendon as possible. Mesenchymal stem cell (MSC)-based strategies represent promising therapeutic tools for tendon repair in both human and veterinary medicine. The translation of tissue engineering strategies from basic research findings, however, into clinical use has been hampered by the limited understanding of the multifaceted MSC mechanisms of action. In vitro models serve as important biological tools to study cell behavior, bypassing the confounding factors associated with in vivo experiments. Controllable and reproducible in vitro conditions should be provided to study the MSC healing mechanisms in tendon injuries. Unfortunately, no physiologically representative tendinopathy models exist to date. A major shortcoming of most currently available in vitro tendon models is the lack of extracellular tendon matrix and vascular supply. These models often make use of synthetic biomaterials, which do not reflect the natural tendon composition. Alternatively, decellularized tendon has been applied, but it is challenging to obtain reproducible results due to its variable composition, less efficient cell seeding approaches and lack of cell encapsulation and vascularization. The current review will overview pros and cons associated with the use of different biomaterials and technologies enabling scaffold production. In addition, the characteristics of the ideal, state-of-the-art tendinopathy model will be discussed. Briefly, a representative in vitro tendinopathy model should be vascularized and mimic the hierarchical structure of the tendon matrix with elongated cells being organized in a parallel fashion and subjected to uniaxial stretching. Incorporation of mechanical stimulation, preferably uniaxial stretching may be a key element in order to obtain appropriate matrix alignment and create a pathophysiological model. Together, a thorough discussion on the current status and future directions for tendon models will enhance fundamental MSC research, accelerating translation of MSC therapies for tendon injuries from bench to bedside.