Standard in vitro evaluations of engineered bone substitutes are not sufficient to predict in vivo preclinical model outcomes

Bone microphysiological models for biomedical research

Bone related disorders are highly prevalent, and many of these pathologies still do not have curative and definitive treatment methods. This is due to a complex interplay of multiple factors, such as the crosstalk between different tissues and cellular components, all of which are affected by microenvironmental factors. Moreover, these bone pathologies are specific, and current treatment results vary from patient to patient owing to their intrinsic biological variability. Current approaches in drug development to deliver new drug candidates against common bone disorders, such as standard two-dimensional (2D) cell culture and animal-based studies, are now being replaced by more relevant diseases modelling, such as three-dimension (3D) cell culture and primary cells under human-focused microphysiological systems (MPS) that can resemble human physiology by mimicking 3D tissue organization and cell microenvironmental cues. In this review, various technological advancements for in vitro bone modeling are discussed, highlighting the progress in biomaterials used as extracellular matrices, stem cell biology, and primary cell culture techniques. With emphasis on examples of modeling healthy and disease-associated bone tissues, this tutorial review aims to survey current approaches of up-to-date bone-on-chips through MPS technology, with special emphasis on the scaffold and chip capabilities for mimicking the bone extracellular matrix as this is the key environment generated for cell crosstalk and interaction. The relevant bone models are studied with critical analysis of the methods employed, aiming to serve as a tool for designing new and translational approaches. Additionally, the features reported in these state-of-the-art studies will be useful for modeling bone pathophysiology, guiding future improvements in personalized bone models that can accelerate drug discovery and clinical translation.

Genetic Profiling of MC3T3-E1 Cells in Different Media: Implications for In Vitro Screening Development

Background/Objectives: The translation of in vitro biomaterial evaluations into successful clinical applications often fails due to discrepancies with in vivo results. Previously, we demonstrated that differences in culture medium conditions influence the bone formation process. This study aimed to investigate the influence of culture media on gene expression during calcification induction in osteoblasts. Methods: Using MC3T3-E1 cells cultured in α Minimum Essential Medium without L-ascorbic acid (αMEM(-)) and Dulbecco's Modified Eagle Medium (DMEM), we screened gene expression profiles through microarray analysis and validated key findings with quantitative PCR. Additionally, we compared these gene expression patterns with those in primary osteoblasts (POBs) cultured under the same medium conditions. Results: The results revealed distinct gene expression profiles in MC3T3-E1 cells depending on the culture medium, while POBs exhibited minimal differences between media, except for the gene Alpl. In αMEM(-), Alpl expression in POBs was significantly increased approximately 4-fold via calcification stimulation (p < 0.0001). POBs cultured in DMEM showed calcification appearance differing from the αMEM(-) condition, even though no significant increase in Alpl expression via calcification stimulation was observed. Conclusions: Differences in media appear to remarkably impact osteoblast gene expression and mineralization. These findings may help improve biomaterial evaluation when transitioning from in vitro assessments to in vivo evaluations. Moreover, our results suggest the possibility that gene expression differences observed in MC3T3-E1 cells reflect the diverse bone formation processes in vivo. Focusing on these genes could facilitate the development of screening methods for bone formation, supporting future clinical applications in orthopedics.

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.

Integrating bioprinting, cell therapies and drug delivery towards in vivo regeneration of cartilage, bone and osteochondral tissue

The biological and biomechanical functions of cartilage, bone and osteochondral tissue are naturally orchestrated by a complex crosstalk between zonally dependent cells and extracellular matrix components. In fact, this crosstalk involves biomechanical signals and the release of biochemical cues that direct cell fate and regulate tissue morphogenesis and remodelling in vivo. Three-dimensional bioprinting introduced a paradigm shift in tissue engineering and regenerative medicine, since it allows to mimic native tissue anisotropy introducing compositional and architectural gradients. Moreover, the growing synergy between bioprinting and drug delivery may enable to replicate cell/extracellular matrix reciprocity and dynamics by the careful control of the spatial and temporal patterning of bioactive cues. Although significant advances have been made in this direction, unmet challenges and open research questions persist. These include, among others, the optimization of scaffold zonality and architectural features; the preservation of the bioactivity of loaded active molecules, as well as their spatio-temporal release; the in vitro scaffold maturation prior to implantation; the pros and cons of each animal model and the graft-defect mismatch; and the in vivo non-invasive monitoring of new tissue formation. This work critically reviews these aspects and reveals the state of the art of using three-dimensional bioprinting, and its synergy with drug delivery technologies, to pattern the distribution of cells and/or active molecules in cartilage, bone and osteochondral engineered tissues. Most notably, this work focuses on approaches, technologies and biomaterials that are currently under in vivo investigations, as these give important insights on scaffold performance at the implantation site and its interaction/integration with surrounding tissues.

Enhancing the correlation between in vitro and in vivo experiments in dental implant osseointegration: investigating the role of Ca ions

This study delves into the osteogenic potential of a calcium-ion modified titanium implant surface, unicCa, employing state-of-the-art proteomics techniques both in vitro (utilizing osteoblasts and macrophage cell cultures) and in vivo (in a rabbit condyle model). When human osteoblasts (Hobs) were cultured on unicCa surfaces, they displayed a marked improvement in cell adhesion and differentiation compared to their unmodified counterparts. The proteomic analysis also revealed enrichment in functions associated with cell migration, adhesion, extracellular matrix organization, and proliferation. The analysis also underscored the involvement of key signalling pathways such as PI3K-Akt and mTOR. In the presence of macrophages, unicCa initially exhibited improvement in immune-related functions and calcium channel activities at the outset (1 day), gradually tapering off over time (3 days). Following a 5-day implantation in rabbits, unicCa demonstrated distinctive protein expression profiles compared to unmodified surfaces. The proteomic analysis highlighted shifts in adhesion, immune response, and bone healing-related proteins. unicCa appeared to influence the coagulation cascade and immune regulatory proteins within the implant site. In summary, this study provides a comprehensive proteomic analysis of the unicCa surface, drawing correlations between in vitro and in vivo results. It emphasizes the considerable potential of unicCa surfaces in enhancing osteogenic behavior and immunomodulation. These findings significantly contribute to our understanding of the intricate molecular mechanisms governing the interplay between biomaterials and bone cells, thereby facilitating the development of improved implant surfaces for applications in bone tissue engineering.

β-TCP from 3D-printed composite scaffolds acts as an effective phosphate source during osteogenic differentiation of human mesenchymal stromal cells

Introduction: Human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) are often combined with calcium phosphate (CaP)-based 3D-printed scaffolds with the goal of creating a bone substitute that can repair segmental bone defects. In vitro, the induction of osteogenic differentiation traditionally requires, among other supplements, the addition of β-glycerophosphate (BGP), which acts as a phosphate source. The aim of this study is to investigate whether phosphate contained within the 3D-printed scaffolds can effectively be used as a phosphate source during hBM-MSC in vitro osteogenesis. Methods: hBM-MSCs are cultured on 3D-printed discs composed of poly (lactic-co-glycolic acid) (PLGA) and β-tricalcium phosphate (β-TCP) for 28 days under osteogenic conditions, with and without the supplementation of BGP. The effects of BGP removal on various cellular parameters, including cell metabolic activity, alkaline phosphatase (ALP) presence and activity, proliferation, osteogenic gene expression, levels of free phosphate in the media and mineralisation, are assessed. Results: The removal of exogenous BGP increases cell metabolic activity, ALP activity, proliferation, and gene expression of matrix-related (COL1A1, IBSP, SPP1), transcriptional (SP7, RUNX2/SOX9, PPARγ) and phosphate-related (ALPL, ENPP1, ANKH, PHOSPHO1) markers in a donor dependent manner. BGP removal leads to decreased free phosphate concentration in the media and maintained of mineral deposition staining. Discussion: Our findings demonstrate the detrimental impact of exogenous BGP on hBM-MSCs cultured on a phosphate-based material and propose β-TCP embedded within 3D-printed scaffold as a sufficient phosphate source for hBM-MSCs during osteogenesis. The presented study provides novel insights into the interaction of hBM-MSCs with 3D-printed CaP based materials, an essential aspect for the advancement of bone tissue engineering strategies aimed at repairing segmental defects.