Osteocyte culture in microfluidic devices

In vitro development and optimization of cell-laden injectable bioprinted gelatin methacryloyl (GelMA) microgels mineralized on the nanoscale

Bone defects may occur in different sizes and shapes due to trauma, infections, and cancer resection. Autografts are still considered the primary treatment choice for bone regeneration. However, they are hard to source and often create donor-site morbidity. Injectable microgels have attracted much attention in tissue engineering and regenerative medicine due to their ability to replace inert implants with a minimally invasive delivery. Here, we developed novel cell-laden bioprinted gelatin methacrylate (GelMA) injectable microgels, with controllable shapes and sizes that can be controllably mineralized on the nanoscale, while stimulating the response of cells embedded within the matrix. The injectable microgels were mineralized using a calcium and phosphate-rich medium that resulted in nanoscale crystalline hydroxyapatite deposition and increased stiffness within the crosslinked matrix of bioprinted GelMA microparticles. Next, we studied the effect of mineralization in osteocytes, a key bone homeostasis regulator. Viability stains showed that osteocytes were maintained at 98 % viability after mineralization with elevated expression of sclerostin in mineralized compared to non-mineralized microgels, showing that mineralization can effectively enhances osteocyte maturation. Based on our findings, bioprinted mineralized GelMA microgels appear to be an efficient material to approximate the bone microarchitecture and composition with desirable control of sample injectability and polymerization. These bone-like bioprinted mineralized biomaterials are exciting platforms for potential minimally invasive translational methods in bone regenerative therapies.

In vitro development and optimization of cell-laden injectable bioprinted gelatin methacryloyl (GelMA) microgels mineralized on the nanoscale

Bone defects may occur in different sizes and shapes due to trauma, infections, and cancer resection. Autografts are still considered the primary treatment choice for bone regeneration. However, they are hard to source and often create donor-site morbidity. Injectable microgels have attracted much attention in tissue engineering and regenerative medicine due to their ability to replace inert implants with a minimally invasive delivery. Here, we developed novel cell-laden bioprinted gelatin methacrylate (GelMA) injectable microgels, with controllable shapes and sizes that can be controllably mineralized on the nanoscale, while stimulating the response of cells embedded within the matrix. The injectable microgels were mineralized using a calcium and phosphate-rich medium that resulted in nanoscale crystalline hydroxyapatite deposition and increased stiffness within the crosslinked matrix of bioprinted GelMA microparticles. Next, we studied the effect of mineralization in osteocytes, a key bone homeostasis regulator. Viability stains showed that osteocytes were maintained at 98% viability after mineralization with elevated expression of sclerostin in mineralized compared to non-mineralized microgels, indicating that mineralization effectively enhances osteocyte maturation. Based on our findings, bioprinted mineralized GelMA microgels appear to be an efficient material to approximate the bone microarchitecture and composition with desirable control of sample injectability and polymerization. These bone-like bioprinted mineralized biomaterials are exciting platforms for potential minimally invasive translational methods in bone regenerative therapies.

Experimental measurements and CFD modelling of hydroxyapatite scaffolds in perfusion bioreactors for bone regeneration

In the field of bone tissue engineering, particular interest is devoted to the development of 3D cultures to study bone cell proliferation under conditions similar to in vivo ones, e.g. by artificially producing mechanical stresses promoting a biological response (mechanotransduction). Of particular relevance in this context are the effects generated by the flow shear stress, which governs the nutrients delivery rate to the growing cells and which can be controlled in perfusion reactors. However, the introduction of 3D scaffolds complicates the direct measurement of the generated shear stress on the adhered cells inside the matrix, thus jeopardizing the potential of using multi-dimensional matrices. In this study, an anisotropic hydroxyapatite-based set of scaffolds is considered as a 3D biomimetic support for bone cells deposition and growth. Measurements of sample-specific flow resistance are carried out using a perfusion system, accompanied by a visual characterization of the material structure. From the obtained results, a subset of three samples is reproduced using 3D-Computational Fluid Dynamics (CFD) techniques and the models are validated by virtually replicating the flow resistance measurement. Once a good agreement is found, the analysis of flow-induced shear stress on the inner B-HA structure is carried out based on simulation results. Finally, a statistical analysis leads to a simplified expression to correlate the flow resistance with the entity and extensions of wall shear stress inside the scaffold. The study applies CFD to overcome the limitations of experiments, allowing for an advancement in multi-dimensional cell cultures by elucidating the flow conditions in 3D reactors.

Microfluidic Co-culture Platforms for Studying Osteocyte Regulation of Other Cell Types under Dynamic Mechanical Stimulation

PURPOSE OF REVIEW

Osteocytes are the most abundant cell type in bone. These unique cells act primarily as mechanosensors and play crucial roles in the functional adaptation of bone tissue. This review aims to summarize the recent microfluidic studies on mechanically stimulated osteocytes in regulating other cell types.

RECENT FINDINGS

Microfluidics is a powerful technology that has been widely employed in recent years. With the advantages of microfluidic platforms, researchers can mimic multicellular environments and integrate dynamic systems to study osteocyte regulation under mechanical stimulation. Microfluidic platforms have been developed to investigate mechanically stimulated osteocytes in the direct regulation of multiple cell types, including osteoclasts, osteoblasts, and cancer cells, and in the indirect regulation of cancer cells via endothelial cells. Overall, these microfluidic studies foster the development of treatment approaches targeting osteocytes under mechanical stimulation.

Perfused Platforms to Mimic Bone Microenvironment at the Macro/Milli/Microscale: Pros and Cons

As life expectancy increases, the population experiences progressive ageing. Ageing, in turn, is connected to an increase in bone-related diseases (i.e., osteoporosis and increased risk of fractures). Hence, the search for new approaches to study the occurrence of bone-related diseases and to develop new drugs for their prevention and treatment becomes more pressing. However, to date, a reliable in vitro model that can fully recapitulate the characteristics of bone tissue, either in physiological or altered conditions, is not available. Indeed, current methods for modelling normal and pathological bone are poor predictors of treatment outcomes in humans, as they fail to mimic the in vivo cellular microenvironment and tissue complexity. Bone, in fact, is a dynamic network including differently specialized cells and the extracellular matrix, constantly subjected to external and internal stimuli. To this regard, perfused vascularized models are a novel field of investigation that can offer a new technological approach to overcome the limitations of traditional cell culture methods. It allows the combination of perfusion, mechanical and biochemical stimuli, biological cues, biomaterials (mimicking the extracellular matrix of bone), and multiple cell types. This review will discuss macro, milli, and microscale perfused devices designed to model bone structure and microenvironment, focusing on the role of perfusion and encompassing different degrees of complexity. These devices are a very first, though promising, step for the development of 3D in vitro platforms for preclinical screening of novel anabolic or anti-catabolic therapeutic approaches to improve bone health.

A facile surface modification of poly(dimethylsiloxane) with amino acid conjugated self-assembled monolayers for enhanced osteoblast cell behavior

Polydimethylsiloxane (PDMS) is a biocompatible synthetic polymer and used in various applications due to its low toxicity and tunable surface properties. However, PDMS does not have any chemical cues for cell binding. Plasma treatment, protein coating or surface modification with various molecules have been used to improve its surface characteristics. Still, these techniques are either last for a very limited time or have very complicated experimental procedures. In the present study, simple and one-step surface modification of PDMS is successfully accomplished by the preparation of hydrophilic and hydrophobic amino acid conjugated self-assembled monolayers (SAMs) for enhanced interactions at the cell-substrate interface. Synthesis of histidine and leucine conjugated (3-aminopropyl)-triethoxysilane (His-APTES and Leu-APTES) were confirmed with proton nuclear magnetic resonance spectroscopy (¹H NMR) and optimum conditions for the modification of PDMS with SAMs were investigated by X-ray photoelectron spectroscopy (XPS) analysis, combined with water contact angle (WCA) measurements. Results indicated that both SAMs enhanced cellular behavior in vitro. Furthermore, hydrophilic His-APTES modification provides a superior environment for the osteoblast maturation with higher alkaline phosphatase activity and mineralization. As histidine, leucine, and functional groups of these SAMs are naturally found in biological systems, modification of PDMS with them increases its cell-substrate surface biomimetic properties. This study establishes a successful modification of PDMS for in vitro cell studies, offering a biomimetic and easy procedure for potential applications in microfluidics, cell-based therapies, or drug investigations.

Cellular considerations for optimizing bone cell culture and remodeling in a lab-on-a-chip platform

Our lab has developed a lab-on-a-chip platform for bone remodeling that enables long-term culturing of bone cells out to 7 weeks and serves as a foundation toward a multicellular organ-on-a-chip system. Here, we optimized culturing protocols for osteoblasts, osteoclasts and osteocytes within the lab-on-a-chip and performed functional activity assays for quantifying bone formation and resorption. We analyzed cell seeding densities, feeding schedules and time in culture as a basis for optimizing culturing protocols. Further, we addressed concerns of sterility, cytotoxicity and leakage during the extended culture period within the polydimethylsiloxane chip. This system provides a method for quantifying the soluble effects of mechanically stimulated osteocytes on bone remodeling (formation/resorption).

Anticancer efficacies of arsenic disulfide through apoptosis induction, cell cycle arrest, and pro-survival signal inhibition in human breast cancer cells

Arsenic disulfide, a major effective component of realgar, has been investigated for its anti-cancer potential and shown to have therapeutic efficacies in hematological and some solid tumors. However, its effect against breast cancer is rarely reported. In this study, we investigated the anti-cancer effects of As₂S₂ in human breast cancer cell lines MCF-7 and MDA-MB-231, and further elucidated its underlying mechanisms. As₂S₂ significantly inhibited cell viabilities, induced apoptosis, and led to cell cycle arrest in both cell lines with a dose- and time-dependent manner. As₂S₂ upregulated pro-apoptotic proteins like p53 and PARP in MCF-7 cells. Besides, As₂S₂ downregulated anti-apoptotic proteins like Bcl-2 and Mcl-1, as well as cell cycle-related proteins cyclin A2 and cyclin D1 in both cell lines. Of note, the expression level of cyclin B1 was downregulated in MCF-7 cells, whereas, upregulated in MDA-MB-231 cells. Moreover, As₂S₂ significantly inhibited the pro-survival signals in PI3K/Akt pathway in both cell lines. In conclusion, As₂S₂ inhibited cell viabilities, induced apoptosis and cell cycle arrest in both MCF-7 and MDA-MB-231 cell lines by regulating the expression of key proteins involved in related pathways. These results provide fundamental insights into the clinical application of As₂S₂ for treatment of patients with breast cancer.

A multiscale fluidic device for the study of dendrite-mediated cell to cell communication

Many cell types communicate by means of dendritic extensions via a multi-tiered set of geometric and chemical cues. Until recently, mimicking the compartmentalized in vivo cellular environment of dendrite-expressing cells such as osteocytes and motor neurons in a spatially and temporally controllable manner was limited by the challenges of in vitro device fabrication at submicron scales. Utilizing the improved resolution of current fabrication technology, we have designed a multiscale device, the Macro-micro-nano system, or Mμn, composed of two distinct cell-seeding and interrogation compartments separated by a nanochannel array. The array enables dendrite ingrowth, while providing a mechanism for fluidic sequestration and/or temporally-mediated diffusible signaling between cell populations. Modeling of the Mμn system predicted the ability to isolate diffusible signals, namely ATP. Empirical diffusion studies verified computational modeling. In addition, cell viability, dendrite interaction with the nanoarray, and cellular purinergic response to heat shock were experimentally evaluated within the device for both osteocytes and motor neurons. Our results describe a novel in vitro system in which dendrite-expressing cell types can be studied within nano-environments that mimic in vivo conditions. In particular, the Mμn system enables real-time observation of cell to cell communication between cell populations in distinct, but fluidically coupled regions.