Magnetic field application or mechanical stimulation via magnetic microparticles does not enhance chondrogenesis in mesenchymal stem cell sheets

Static magnetic fields in regenerative medicine

All organisms on Earth live in the weak but ubiquitous geomagnetic field. Human beings are also exposed to magnetic fields generated by multiple sources, ranging from permanent magnets to magnetic resonance imaging (MRI) in hospitals. It has been shown that different magnetic fields can generate various effects on different tissues and cells. Among them, stem cells appear to be one of the most sensitive cell types to magnetic fields, which are the fundamental units of regenerative therapies. In this review, we focus on the bioeffects of static magnetic fields (SMFs), which are related to regenerative medicine. Most reports in the literature focus on the influence of SMF on bone regeneration, wound healing, and stem cell production. Multiple aspects of the cellular events, including gene expression, cell signaling pathways, reactive oxygen species, inflammation, and cytoskeleton, have been shown to be affected by SMFs. Although no consensus yet, current evidence indicates that moderate and high SMFs could serve as a promising physical tool to promote bone regeneration, wound healing, neural differentiation, and dental regeneration. All in vivo studies of SMFs on bone regeneration and wound healing have shown beneficial effects, which unravel the great potential of SMFs in these aspects. More mechanistic studies, magnetic field parameter optimization, and clinical investigations on human bodies will be imperative for the successful clinical applications of SMFs in regenerative medicine.

Magnetic Hydroxyapatite Nanoparticles in Regenerative Medicine and Nanomedicine

This review focuses on the latest advancements in magnetic hydroxyapatite (mHA) nanoparticles and their potential applications in nanomedicine and regenerative medicine. mHA nanoparticles have gained significant interest over the last few years for their great potential, offering advanced multi-therapeutic strategies because of their biocompatibility, bioactivity, and unique physicochemical features, enabling on-demand activation and control. The most relevant synthetic methods to obtain magnetic apatite-based materials, either in the form of iron-doped HA nanoparticles showing intrinsic magnetic properties or composite/hybrid compounds between HA and superparamagnetic metal oxide nanoparticles, are described as highlighting structure-property correlations. Following this, this review discusses the application of various magnetic hydroxyapatite nanomaterials in bone regeneration and nanomedicine. Finally, novel perspectives are investigated with respect to the ability of mHA nanoparticles to improve nanocarriers with homogeneous structures to promote multifunctional biological applications, such as cell stimulation and instruction, antimicrobial activity, and drug release with on-demand triggering.

MECHANOBIOLOGICAL APPROACHES FOR STIMULATING CHONDROGENESIS OF STEM CELLS

Chondrogenesis is the process of differentiation of stem cells into mature chondrocytes. Such a process consists of chemical, functional, and structural changes which are initiated and mediated by the host environment of the cells. To date, the mechanobiology of chondrogenesis has not been fully elucidated. Hence, experimental activity is focused on recreating specific environmental conditions for stimulating chondrogenesis, and to look for a mechanistic interpretation of the mechanobiological response of cells in the cartilaginous tissues. There are a large number of studies on the topic that vary considerably in their experimental protocols used for providing environmental cues to cells for differentiation, making generalizable conclusions difficult to ascertain. The main objective of this contribution is to review the mechanobiological stimulation of stem cell chondrogenesis and methodological approaches utilized to date to promote chondrogenesis of stem cells in-vitro. In-vivo models will also be explored, but this area is currently limited. An overview of the experimental approaches used by different research groups may help the development of unified testing methods that could be used to overcome existing knowledge gaps, leading to an accelerated translation of experimental findings to clinical practice.

The Application of Bioreactors for Cartilage Tissue Engineering: Advances, Limitations, and Future Perspectives

Tissue engineering (TE) has brought new hope for articular cartilage regeneration, as TE can provide structural and functional substitutes for native tissues. The basic elements of TE involve scaffolds, seeded cells, and biochemical and biomechanical stimuli. However, there are some limitations of TE; what most important is that static cell culture on scaffolds cannot simulate the physiological environment required for the development of natural cartilage. Recently, bioreactors have been used to simulate the physical and mechanical environment during the development of articular cartilage. This review aims to provide an overview of the concepts, categories, and applications of bioreactors for cartilage TE with emphasis on the design of various bioreactor systems.

High-Throughput Magnetic Actuation Platform for Evaluating the Effect of Mechanical Force on 3D Tumor Microenvironment

Accurately replicating and analyzing cellular responses to mechanical cues is vital for exploring metastatic disease progression. However, many of the existing in vitro platforms for applying mechanical stimulation seed cells on synthetic substrates. To better recapitulate physiological conditions, a novel actuating platform is developed with the ability to apply tensile strain on cells at various amplitudes and frequencies in a high-throughput multi-well culture plate using a physiologically-relevant substrate. Suspending fibrillar fibronectin across the body of the magnetic actuator provides a matrix representative of early metastasis for 3D cell culture that is not reliant on a synthetic substrate. This platform enables the culturing and analysis of various cell types in an environment that mimics the dynamic stretching of lung tissue during normal respiration. Metabolic activity, YAP activation, and morphology of breast cancer cells are analyzed within one week of cyclic stretching or static culture. Further, matrix degradation is significantly reduced in breast cancer cell lines with metastatic potential after actuation. These new findings demonstrate a clear suppressive cellular response due to cyclic stretching that has implications for a mechanical role in the dormancy and reactivation of disseminated breast cancer cells to macrometastases.

Efficacy of pulsed electromagnetic fields and electromagnetic fields tuned to the ion cyclotron resonance frequency of Ca2+ on chondrogenic differentiation

Previous studies provide strong evidence for the therapeutic effect of electromagnetic fields (EMFs) on different tissues including cartilage. Diverse exposure parameters applied in scientific reports and the unknown interacting mechanism of EMF with biological systems make EMF studies challenging. In 1985, Liboff proposed that when magnetic fields are tuned to the cyclotron resonance frequencies of critical ions, the motion of ions through cell membranes is enhanced, and thus biological effects appear. Such exposure system consists of a weak alternating magnetic field (B₁ ) in the presence of a static magnetic field (B₀ ) and depends on the relationship between the magnitudes of B₀ and B₁ and the angular frequency Ω. The purpose of the present study is to determine the chondrogenic potential of EMF with regards to pulsed EMF (PEMF) and the ion cyclotron resonance (ICR) theory. We used different stimulating systems to generate EMFs in which cells are either stimulated with ubiquitous PEMF parameters, frequently reported, or parameters tuned to satisfy the ICR for Ca²⁺ (including negative and positive control groups). Chondrogenesis was analysed after 3 weeks of treatment. Cell stimulation under the ICR condition showed positive results in the context of glycosaminoglycans and type II collagen synthesis. In contrast, the other electromagnetically stimulated groups showed no changes compared with the control groups. Furthermore, gene expression assays revealed an increase in the expression of chondrogenic markers (COL2A1, SOX9, and ACAN) in the ICR group. These results suggest that the Ca²⁺ ICR condition can be an effective factor in inducing chondrogenesis.

Recent advances in bioreactors for cell-based therapies

Bioreactors have become indispensable tools in the cell-based therapy industry. Various forms of bioreactors are used to maintain well-controlled microenvironments to regulate cell growth, differentiation, and tissue development. They are essential for providing standardized, reproducible cell-based products for regenerative medicine applications or to establish physiologically relevant in vitro models for testing of pharmacologic agents. In this review, we discuss three main classes of bioreactors: cell expansion bioreactors, tissue engineering bioreactors, and lab-on-a-chip systems. We briefly examine the factors driving concerted research endeavors in each of these areas and describe the major advancements that have been reported in the last three years. Emerging issues that impact the commercialization and clinical use of bioreactors include (i) the need to scale up to greater cell quantities and larger graft sizes, (ii) simplification of in vivo systems to function without exogenous stem cells or growth factors or both, and (iii) increased control in the manufacture and monitoring of miniaturized systems to better capture complex tissue and organ physiology.