Scalable and Uniform Fabrication of Dexamethasone-Eluting Depot-Engineered Stem Cell Spheroids as a Microtissue Construct to Target Bone Regeneration

Engineered 3D mesenchymal stem cell aggregates with multifunctional prowess for bone regeneration: Current status and future prospects

BACKGROUND

Impaired efficacy of in vitro expanded mesenchymal stem cells (MSCs) is a universal and thorny situation, which cast a shadow on further clinical translation of exogenous MSCs. Moreover, the relatively lengthy healing process, host metabolic heterogeneity and the sophisticated cell recognition and crosstalk pose rigorous challenges towards MSC-based bone regeneration strategies. Three-dimensional (3D) cell aggregates facilitate more robust intercellular communications and cell-extracellular matrix (ECM) interactions, providing a better mimicry of microarchitectures and biochemical milieus in vivo, which is conducive for stemness maintenance and downstream bone formation.

AIM OF REVIEW

This review enunciates the phenotypic features of MSCs in aggregates, which deepens the knowledge of the MSC fate determination in 3D microenvironment. By summarizing current empowerment methods and biomaterial-combined techniques for establishing functionalized MSC aggregates, this review aims to spark innovative and promising solutions for exalting the translational value of MSCs and improve their therapeutic applications in bone tissue repair.

KEY SCIENTIFIC CONCEPTS OF REVIEW

3D aggregates optimize regenerative behaviors of in vitro cultured MSCs including cell adhesion, viability, proliferation, pluripotency and immunoregulation capacity, etc. Biomaterials hybridization endows MSC aggregates with tailored mechanical and biological properties, which offers more possibilities in adapting various clinical scenarios.

Developing fibrin-based biomaterials/scaffolds in tissue engineering

Tissue engineering technology has advanced rapidly in recent years, offering opportunities to construct biologically active tissues or organ substitutes to repair or even enhance the functions of diseased tissues and organs. Tissue-engineered scaffolds rebuild the extracellular microenvironment by mimicking the extracellular matrix. Fibrin-based scaffolds possess numerous advantages, including hemostasis, high biocompatibility, and good degradability. Fibrin scaffolds provide an initial matrix that facilitates cell migration, differentiation, proliferation, and adhesion, and also play a critical role in cell-matrix interactions. Fibrin scaffolds are now widely recognized as a key component in tissue engineering, where they can facilitate tissue and organ defect repair. This review introduces the properties of fibrin, including its composition, structure, and biology. In addition, the modification and cross-linking modes of fibrin are discussed, along with various forms commonly used in tissue engineering. We also describe the biofunctionalization of fibrin. This review provides a detailed overview of the use and applications of fibrin in skin, bone, and nervous tissues, and provides novel insights into future research directions for clinical treatment.

Injectable Nano-Micro Composites with Anti-bacterial and Osteogenic Capabilities for Minimally Invasive Treatment of Osteomyelitis

The effective management of osteomyelitis remains extremely challenging due to the difficulty associated with treating bone defects, the high probability of recurrence, the requirement of secondary surgery or multiple surgeries, and the difficulty in eradicating infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Hence, smart biodegradable biomaterials that provide effective and precise local anti-infection effects and can promote the repair of bone defects are actively being developed. Here, a novel nano-micro composite is fabricated by combining calcium phosphate (CaP) nanosheets with drug-loaded GelMA microspheres via microfluidic technology. The microspheres are covalently linked with vancomycin (Van) through an oligonucleotide (oligo) linker using an EDC/NHS carboxyl activator. Accordingly, a smart nano-micro composite called "CaP@MS-Oligo-Van" is synthesized. The porous CaP@MS-Oligo-Van composites can target and capture bacteria. They can also release Van in response to the presence of bacterial micrococcal nuclease and Ca2+, exerting additional antibacterial effects and inhibiting the inflammatory response. Finally, the released CaP nanosheets can promote bone tissue repair. Overall, the findings show that a rapid, targeted drug release system based on CaP@MS-Oligo-Van can effectively target bone tissue infections. Hence, this agent holds potential in the clinical treatment of osteomyelitis caused by MRSA.