Minimalist Tissue Engineering Approaches Using Low Material-Based Bioengineered Systems

Human Platelet Lysate-Derived Nanofibrils as Building Blocks to Produce Free-Standing Membranes for Cell Self-Aggregation

Amyloid-like fibrils are garnering keen interest in biotechnology as supramolecular nanofunctional units to be used as biomimetic platforms to control cell behavior. Recent insights into fibril functionality have highlighted their importance in tissue structure, mechanical properties, and improved cell adhesion, emphasizing the need for scalable and high-kinetics fibril synthesis. In this study, we present the instantaneous and bulk formation of amyloid-like nanofibrils from human platelet lysate (PL) using the ionic liquid cholinium tosylate as a fibrillating agent. The instant fibrillation of PL proteins upon supramolecular protein-ionic liquid interactions was confirmed from the protein conformational transition toward cross-β-sheet-rich structures. These nanofibrils were utilized as building blocks for the formation of thin and flexible free-standing membranes via solvent casting to support cell self-aggregation. These PL-derived fibril membranes reveal a nanotopographically rough surface and high stability over 14 days under cell culture conditions. The culture of mesenchymal stem cells or tumor cells on the top of the membrane demonstrated that cells are able to adhere and self-organize in a three-dimensional (3D) spheroid-like microtissue while tightly folding the fibril membrane. Results suggest that nanofibril membrane incorporation in cell aggregates can improve cell viability and metabolic activity, recreating native tissues' organization. Altogether, these PL-derived nanofibril membranes are suitable bioactive platforms to generate 3D cell-guided microtissues, which can be explored as bottom-up strategies to faithfully emulate native tissues in a fully human microenvironment.

Encapsulation of pristine and silica-coated human adipose-derived mesenchymal stem cells in gelatin colloidal hydrogels for tissue engineering and bioprinting applications

Colloidal gels assembled from gelatin nanoparticles (GNPs) as particulate building blocks show strong promise to solve challenges in cell delivery and biofabrication, such as low cell survival and limited spatial retention. These gels offer evident advantages to facilitate cell encapsulation, but research on this topic is still limited, which hampers our understanding of the relationship between the physicochemical and biological properties of cell-laden colloidal gels. Human adipose-derived mesenchymal stem cells were successfully encapsulated in gelatin colloidal gels and evaluated their mechanical and biological performance over 7 days. The cells dispersed well within the gels without compromising gel cohesiveness, remained viable, and spread throughout the gels. Cells partially coated with silica were introduced into these gels, which increased their storage moduli and decreased their self-healing capacity after 7 days. This finding demonstrates the ability to modulate gel stiffness by incorporating cells partially coated with silica, without altering the solid content or introducing additional particles. Our work presents an efficient method for cell encapsulation while preserving gel integrity, expanding the applicability of colloidal hydrogels for tissue engineering and bioprinting. Overall, our study contributes to the design of improved cell delivery systems and biofabrication techniques.

Tunable Light-Actuated Interpenetrating Networks of Silk Fibroin and Gelatin for Tissue Engineering and Flexible Biodevices

Soft materials with tunable properties are valuable for applications such as tissue engineering, electronic skins, and human-machine interfaces. Materials that are nature-derived offer additional advantages such as biocompatibility, biodegradability, low-cost sourcing, and sustainability. However, these materials often have contrasting properties that limit their use. For example, silk fibroin (SF) has high mechanical strength but lacks processability and cell-adhesive domains. Gelatin, derived from collagen, has excellent biological properties, but is fragile and lacks stability. To overcome these limitations, composites of gelatin and SF have been explored. However, mechanically robust self-supported matrices and electrochemically active or micropatterned substrates were not demonstrated. In this study, we present a composite of photopolymerizable SF and photogelatin, termed photofibrogel (PFG). By incorporating photoreactive properties in both SF and gelatin, control over material properties can be achieved. The PFG composite can be easily and rapidly formed into free-standing, high-resolution architectures with tunable properties. By optimizing the ratio of SF to gelatin, properties such as swelling, mechanical behavior, enzymatic degradation, and patternability are tailored. The PFG composite allows for macroscale and microscale patterning without significant swelling, enabling the fabrication of structures using photolithography and laser cutting techniques. PFG can be patterned with electrically conductive materials, making it suitable for cell guidance and stimulation. The versatility, mechanical robustness, bioactivity, and electrochemical properties of PFG are shown for skeletal muscle tissue engineering using C2C12 cells as a model. Overall, such composite biomaterials with tunable properties have broad potential in flexible bioelectronics, wound healing, regenerative medicine, and food systems.

Magnetic-Based Strategies for Regenerative Medicine and Tissue Engineering

The fabrication of biological substitutes to repair, replace, or enhance tissue- and organ-level functions is a long-sought goal of tissue engineering (TE). However, the clinical translation of TE is hindered by several challenges, including the lack of suitable mechanical, chemical, and biological properties in one biomaterial, and the inability to generate large, vascularized tissues with a complex structure of native tissues. Over the past decade, a new generation of "smart" materials has revolutionized the conventional medical field, transforming TE into a more accurate and sophisticated concept. At the vanguard of scientific development, magnetic nanoparticles (MNPs) have garnered extensive attention owing to their significant potential in various biomedical applications owing to their inherent properties such as biocompatibility and rapid remote response to magnetic fields. Therefore, to develop functional tissue replacements, magnetic force-based TE (Mag-TE) has emerged as an alternative to conventional TE strategies, allowing for the fabrication and real-time monitoring of tissues engineered in vitro. This review addresses the recent studies on the use of MNPs for TE, emphasizing the in vitro, in vivo, and clinical applications. Future perspectives of Mag-TE in the fields of TE and regenerative medicine are also discussed.

Close-to-native bone repair via tissue-engineered endochondral ossification approaches

In order to solve the clinical challenges related to bone grafting, several tissue engineering (TE) strategies have been proposed to repair critical-sized defects. Generally, the classical TE approaches are designed to promote bone repair via intramembranous ossification. Although promising, strategies that direct the osteogenic differentiation of mesenchymal stem/stromal cells are usually characterized by a lack of functional vascular supply, often resulting in necrotic cores. A less explored alternative is engineering bone constructs through a cartilage-mediated approach, resembling the embryological process of endochondral ossification. The remodeling of an intermediary hypertrophic cartilaginous template triggers vascular invasion and bone tissue deposition. Thus, employing this knowledge can be a promising direction for the next generation of bone TE constructs. This review highlights the most recent biomimetic strategies for applying endochondral ossification in bone TE while discussing the plethora of cell types, culture conditions, and biomaterials essential to promote a successful bone regeneration process.

Bioengineered Hierarchical Bonelike Compartmentalized Microconstructs Using Nanogrooved Microdiscs

Fabrication of vascularized large-scale constructs for regenerative medicine remains elusive since most strategies rely solely on cell self-organization or overly control cell positioning, failing to address nutrient diffusion limitations. We propose a modular and hierarchical tissue-engineering strategy to produce bonelike tissues carrying signals to promote prevascularization. In these 3D systems, disc-shaped microcarriers featuring nanogrooved topographical cues guide cell behavior by harnessing mechanotransduction mechanisms. A sequential seeding strategy of adipose-derived stromal cells and endothelial cells is implemented within compartmentalized, liquefied-core macrocapsules in a self-organizing and dynamic system. Importantly, our system autonomously promotes osteogenesis and construct's mineralization while promoting a favorable environment for prevascular-like endothelial organization. Given its modular and self-organizing nature, our strategy may be applied for the fabrication of larger constructs with a highly controlled starting point to be used for local regeneration upon implantation or as drug-screening platforms.

Duo Cadherin-Functionalized Microparticles Synergistically Induce Chondrogenesis and Cartilage Repair of Stem Cell Aggregates

Mesenchymal stem cell (MSC) aggregates incorporated with microparticles of functional materials have shown promising prospects in the field of cell therapy for cartilage repair. Given the importance of cadherins in modulating the stemness and chondrogenesis of MSCs, the use of transforming growth factor β1 (TGFβ1)-loaded poly (lactic-co-glycolic acid) (PLGA)-based composite microparticles inspired by duo cadherin (human E- and N-cadherin fusion proteins) to construct a bioartificial stem cell niche in engineered human MSC (hMSC) aggregates to promote chondrogenesis and cartilage regeneration is proposed. The hE/N-cadherin-functionalized PLGA/chitosan-heparin-TGFβ1 (Duo hE/N-cad@P/C-h-TGFβ1) microparticles spatiotemporally upregulates the endogenous E/N-cadherin expression of hMSC aggregates which further amplifies the chondrogenic differentiation and modulate paracrine and anti-inflammatory functions of hMSCs toward constructing a favorable microenvironment for chondrogenesis. The Duo hE/N-cad@P/C-h-TGFβ1 microparticles finely regulate the response of hMSCs to biochemical and mechanical signal stimuli in the microenvironment through the cadherin/catenin-Yes-associated protein signal transduction, which inhibits the hypertrophy of hMSC-derived chondrocytes. Furthermore, immunofluorescent and histological examinations show that the Duo hE/N-cad@P/C-h-TGFβ1 microparticles significantly improve regeneration of cartilage and subchondral bone in vivo. Together, the application of duo cadherin-functionalized microparticles is considered an innovative material-wise approach to exogenously activate hMSC aggregates for functional applications in regenerative medicine.

Dynamic Nanocomposite Microgel Assembly with Microporosity, Injectability, Tissue-Adhesion, and Sustained Drug Release Promotes Articular Cartilage Repair and Regeneration

Owing to the lack of blood vessels, nerves, and lymph, articular cartilage defect is difficult to self-repair. Although several cartilage tissue engineering products have been authorized for clinical use, there are still some problems such as large surgical wounds, weak adhesion with the host tissue, and the limited source of autologous chondrocytes. In this paper, a novel dynamic nanocomposite microgel assembly with excellent microporosity, injectability, tissue-adhesion, and sustained kartogenin (KGN) release is reported. Specifically, KGN-loaded cyclodextrin nanoparticles are synthesized through nanoemulsification and incorporated into bone marrow mesenchymal stem cell (BMSCs)-laden microgels via droplet-based microfluidics and photo-crosslinking, which are then bottom-up assembled via dynamic crosslinking between dopamine-modified hyaluronic acid and phenylboronic acid groups on microgel surface. Results reveal that the microgel assembly can avoid the cell endocytosis of nanoparticles, ensure the high BMSC viability during the regular cell culture, cryopreservation and injection process, promote the chondrogenic differentiation of BMSCs. In addition, animal expriment proves the newborn cartilages present the typical characteristics of articular cartilage. In brief, this microgel assembly not only offers convenience for clinical use (injectability, tissue adhesion) but also provides good microenvironments for chondrogenesis (controlled drug release, interconnected micropores), indicative of its promising application for cartilage repair and regeneration.

Freestanding Magnetic Microtissues for Tissue Engineering Applications

A long-sought goal in tissue engineering (TE) is the development of tissues able to recapitulate the complex architecture of the native counterpart. Microtissues, by resembling the functional units of living structures, can be used to recreate tissues' architecture. Howbeit, microfabrication methodologies fail to reproduce cell-based tissues with uniform shape. At the macroscale, complex tissues are already produced by magnetic-TE using solely magnetized cells as building materials. The enhanced extracellular matrix (ECM) deposition guaranties the conservation of tissues' architecture, leading to a successful cellular engraftment. Following the same rational, now the combination of a versatile microfabrication-platform is proposed with magnetic-TE to generate robust micro-tissues with complex architecture for TE purposes. Small tissue units with circle, square, and fiber-like shapes are designed with high fidelity acting as building blocks for engineering complex tissues. Notably, freestanding microtissues maintain their geometry after 7 days post-culturing, overcoming the challenges of microtissues fabrication. Lastly, the ability of microtissues in invading distinct tissue models while releasing trophic factors is substantiated in methacryloyl laminarin (LAM) and platelet lysates (PLMA) hydrogels. By simply using cells as building units and such microfabrication-platform, the fabrication of complex multiscale and multifunctional tissues with clinical relevance is envisaged, including for therapies or disease models.

Advances in microfabrication technologies in tissue engineering and regenerative medicine

BACKGROUND

Tissue engineering provides various strategies to fabricate an appropriate microenvironment to support the repair and regeneration of lost or damaged tissues. In this matter, several technologies have been implemented to construct close-to-native three-dimensional structures at numerous physiological scales, which are essential to confer the functional characteristics of living tissues.

METHODS

In this article, we review a variety of microfabrication technologies that are currently utilized for several tissue engineering applications, such as soft lithography, microneedles, templated and self-assembly of microstructures, microfluidics, fiber spinning, and bioprinting.

RESULTS

These technologies have considerably helped us to precisely manipulate cells or cellular constructs for the fabrication of biomimetic tissues and organs. Although currently available tissues still lack some crucial functionalities, including vascular networks, innervation, and lymphatic system, microfabrication strategies are being proposed to overcome these issues. Moreover, the microfabrication techniques that have progressed to the preclinical stage are also discussed.

CONCLUSIONS

This article aims to highlight the advantages and drawbacks of each technique and areas of further research for a more comprehensive and evolving understanding of microfabrication techniques in terms of tissue engineering and regenerative medicine applications.

Core-Shell Microcapsules: Biofabrication and Potential Applications in Tissue Engineering and Regenerative Medicine

The construction of biomaterial scaffolds that accurately recreate the architecture of living tissues in vitro is a major challenge in the field of tissue engineering and regenerative medicine. Core-shell microcapsules...

New insights into the biomimetic design and biomedical applications of bioengineered bone microenvironments

The bone microenvironment is characterized by an intricate interplay between cellular and noncellular components, which controls bone remodeling and repair. Its highly hierarchical architecture and dynamic composition provide a unique microenvironment as source of inspiration for the design of a wide variety of bone tissue engineering strategies. To overcome current limitations associated with the gold standard for the treatment of bone fractures and defects, bioengineered bone microenvironments have the potential to orchestrate the process of bone regeneration in a self-regulated manner. However, successful approaches require a strategic combination of osteogenic, vasculogenic, and immunomodulatory factors through a synergic coordination between bone cells, bone-forming factors, and biomaterials. Herein, we provide an overview of (i) current three-dimensional strategies that mimic the bone microenvironment and (ii) potential applications of bioengineered microenvironments. These strategies range from simple to highly complex, aiming to recreate the architecture and spatial organization of cell-cell, cell-matrix, and cell-soluble factor interactions resembling the in vivo microenvironment. While several bone microenvironment-mimicking strategies with biophysical and biochemical cues have been proposed, approaches that exploit the ability of the cells to self-organize into microenvironments with a high regenerative capacity should become a top priority in the design of strategies toward bone regeneration. These miniaturized bone platforms may recapitulate key characteristics of the bone regenerative process and hold great promise to provide new treatment concepts for the next generation of bone implants.

Microparticles orchestrating cell fate in bottom-up approaches

The modulation of cells in tissue formation is still one of the hardest tasks to achieve in Tissue Engineering. To control the cell response when undergoing their normal functions such as adhesion, differentiation, assembly, or maturation is vital the development of more successful solutions. Herein, we discuss how microparticles are being overlooked in their potential for controlling the cellular response. Until now, their role was quite often restricted to a reservoir of chemical compounds or as carriers for cell expansion. Nevertheless, microparticles design with the introduction of biophysical and biochemical cues can effectively modulate cell response.

Self-Organization Provides Cell Fate Commitment in MSC Sheet Condensed Areas via ROCK-Dependent Mechanism

Multipotent mesenchymal stem/stromal cells (MSC) are one of the crucial regulators of regeneration and tissue repair and possess an intrinsic program from self-organization mediated by condensation, migration and self-patterning. The ability to self-organize has been successfully exploited in tissue engineering approaches using cell sheets (CS) and their modifications. In this study, we used CS as a model of human MSC spontaneous self-organization to demonstrate its structural, transcriptomic impact and multipotent stromal cell commitment. We used CS formation to visualize MSC self-organization and evaluated the role of the Rho-GTPase pathway in spontaneous condensation, resulting in a significant anisotropy of the cell density within the construct. Differentiation assays were carried out using conventional protocols, and microdissection and RNA-sequencing were applied to establish putative targets behind the observed phenomena. The differentiation of MSC to bone and cartilage, but not to adipocytes in CS, occurred more effectively than in the monolayer. RNA-sequencing indicated transcriptional shifts involving the activation of the Rho-GTPase pathway and repression of SREBP, which was concordant with the lack of adipogenesis in CS. Eventually, we used an inhibitory analysis to validate our findings and suggested a model where the self-organization of MSC defined their commitment and cell fate via ROCK1/2 and SREBP as major effectors under the putative switching control of AMP kinase.

Multifunctional Scaffolds and Synergistic Strategies in Tissue Engineering and Regenerative Medicine

The increasing demand for organ replacements in a growing world with an aging population as well as the loss of tissues and organs due to congenital defects, trauma and diseases has resulted in rapidly evolving new approaches for tissue engineering and regenerative medicine (TERM). The extracellular matrix (ECM) is a crucial component in tissues and organs that surrounds and acts as a physical environment for cells. Thus, ECM has become a model guide for the design and fabrication of scaffolds and biomaterials in TERM. However, the fabrication of a tissue/organ replacement or its regeneration is a very complex process and often requires the combination of several strategies such as the development of scaffolds with multiple functionalities and the simultaneous delivery of growth factors, biochemical signals, cells, genes, immunomodulatory agents, and external stimuli. Although the development of multifunctional scaffolds and biomaterials is one of the most studied approaches for TERM, all these strategies can be combined among them to develop novel synergistic approaches for tissue regeneration. In this review we discuss recent advances in which multifunctional scaffolds alone or combined with other strategies have been employed for TERM purposes.