Human triple cell co-culture for evaluation of bone implant materials

Proteolytically degradable PEG hydrogel matrix mimicking tumor immune microenvironment for 3D co-culture of lung adenocarcinoma cells and macrophages

Tumor-associated macrophages and monocytes are the major stromal cell types found in the tumor immune microenvironment (TIME), which modulates tumor progression, invasion, and chemoresistance. To address the need for an in vitro three-dimensional tumor model for understanding the complex cellular interactions within the TIME, we propose a TIME-mimetic co-culture matrix composed of photo-crosslinked poly(ethylene glycol) hydrogels mimicking the characteristics of the tumor and stroma. Desmoplasia-mimetic microgels encapsulating lung adenocarcinoma cells (A549) were embedded with monocyte- or macrophage-type U937 cells in normal stroma-mimetic hydrogel, increasing the proximity between the two cell types. By modulating the proteolytic degradability of the hydrogels, we could separate different cell types with high purities for use in orthogonal assays. In addition, we demonstrated that U937 cells had distinct influences on A549 cell death depending on their activation states (i.e. monocyte, M0, or M1 phenotype). M1 macrophages suppressed tumor growth and increased the susceptibility of A549 cells to cisplatin. In contrast, monocytes upregulated cancer stem cell markers (OCT4, SOX2, and SHH) of A549 cells, showing M2-like features, such as downregulated expression of proinflammatory markers (IL6 and TNFα). These findings suggest that this co-culture system is potentially used for investigation of heterotypic cellular interactions in the TIME.

Bone Regeneration and Oxidative Stress: An Updated Overview

Bone tissue engineering is a complex domain that requires further investigation and benefits from data obtained over past decades. The models are increasing in complexity as they reveal new data from co-culturing and microfluidics applications. The in vitro models now focus on the 3D medium co-culturing of osteoblasts, osteoclasts, and osteocytes utilizing collagen for separation; this type of research allows for controlled medium and in-depth data analysis. Oxidative stress takes a toll on the domain, being beneficial as well as destructive. Reactive oxygen species (ROS) are molecules that influence the differentiation of osteoclasts, but over time their increasing presence can affect patients and aid the appearance of diseases such as osteoporosis. Oxidative stress can be limited by using antioxidants such as vitamin K and N-acetyl cysteine (NAC). Scaffolds and biocompatible coatings such as hydroxyapatite and bioactive glass are required to isolate the implant, protect the zone from the metallic, ionic exchange, and enhance the bone regeneration by mimicking the composition and structure of the body, thus enhancing cell proliferation. The materials can be further functionalized with growth factors that create a better response and higher chances of success for clinical use. This review highlights the vast majority of newly obtained information regarding bone tissue engineering, such as new co-culturing models, implant coatings, scaffolds, biomolecules, and the techniques utilized to obtain them.

In Vivo Efficacy of Neutrophil-Mediated Bone Regeneration Using a Rabbit Calvarial Defect Model

Reconstruction of bone due to surgical removal or disease-related bony defects is a clinical challenge. It is known that the immune system exerts positive immunomodulatory effects on tissue repair and regeneration. In this study, we evaluated the in vivo efficacy of autologous neutrophils on bone regeneration using a rabbit calvarial defect model. Methods: Twelve rabbits, each with two surgically created calvarial bone defects (10 mm diameter), were randomly divided into two groups; (i) single application of neutrophils (SA-NP) vs. SA-NP control, and (ii) repetitive application of neutrophils (RA-NP) vs. RA-NP control. The animals were euthanized at 4 and 8 weeks post-operatively and the treatment outcomes were evaluated by micro-computed tomography, histology, and histomorphometric analyses. Results: The micro-CT analysis showed a significantly higher bone volume fraction (bone volume/total volume) in the neutrophil-treated groups, i.e., median interquartile range (IQR) SA-NP (18) and RA-NP (24), compared with the untreated controls, i.e., SA-NP (7) and RA-NP (14) at 4 weeks (p < 0.05). Similarly, new bone area fraction (bone area/total area) was significantly higher in neutrophil-treated groups at 4 weeks (p < 0.05). Both SA-NP and RA-NP had a considerably higher bone volume and bone area at 8 weeks, although the difference was not statistically significant. In addition, immunohistochemical analysis at 8 weeks revealed a higher expression of osteocalcin in both SA-NP and RA-NP groups. Conclusions: The present study provides first hand evidence that autologous neutrophils may have a positive effect on promoting new bone formation. Future studies should be performed with a larger sample size in non-human primate models. If proven feasible, this new promising strategy could bring clinical benefits for bone defects to the field of oral and maxillofacial surgery.

Triple Culture of Primary Human Osteoblasts, Osteoclasts and Osteocytes as an In Vitro Bone Model

In vitro evaluation of bone graft materials is generally performed by analyzing the interaction with osteoblasts or osteoblast precursors. In vitro bone models comprising different cell species can give specific first information on the performance of those materials. In the present study, a 3D co-culture model was established comprising primary human osteoblasts, osteoclasts and osteocytes. Osteocytes were differentiated from osteoblasts embedded in collagen gels and were cultivated with osteoblast and osteoclasts seeded in patterns on a porous membrane. This experimental setup allowed paracrine signaling as well as separation of the different cell types for final analysis. After 7 days of co-culture, the three cell species showed their typical morphology and gene expression of typical markers like ALPL, BSPII, BLGAP, E11, PHEX, MEPE, RANKL, ACP5, CAII and CTSK. Furthermore, relevant enzyme activities for osteoblasts (ALP) and osteoclasts (TRAP, CTSK, CAII) were detected. Osteoclasts in triple culture showed downregulated TRAP (ACP5) and CAII expression and decreased TRAP activity. ALP and BSPII expression of osteoblasts in triple culture were upregulated. The expression of the osteocyte marker E11 (PDPN) was unchanged; however, osteocalcin (BGLAP) expression was considerably downregulated both in osteoblasts and osteocytes in triple cultures compared to the respective single cultures.

Native-mimicking in vitro microenvironment: an elusive and seductive future for tumor modeling and tissue engineering

Human connective tissues are complex physiological microenvironments favorable for optimal survival, function, growth, proliferation, differentiation, migration, and death of tissue cells. Mimicking native tissue microenvironment using various three-dimensional (3D) tissue culture systems in vitro has been explored for decades, with great advances being achieved recently at material, design and application levels. These achievements are based on improved understandings about the functionalities of various tissue cells, the biocompatibility and biodegradability of scaffolding materials, the biologically functional factors within native tissues, and the pathophysiological conditions of native tissue microenvironments. Here we discuss these continuously evolving physical aspects of tissue microenvironment important for human disease modeling, with a focus on tumors, as well as for tissue repair and regeneration. The combined information about human tissue spaces reflects the necessities of considerations when configuring spatial microenvironments in vitro with native fidelity to culture cells and regenerate tissues that are beyond the formats of 2D and 3D cultures. It is important to associate tissue-specific cells with specific tissues and microenvironments therein for a better understanding of human biology and disease conditions and for the development of novel approaches to treat human diseases.

Cell based advanced therapeutic medicinal products for bone repair: Keep it simple?

The development of cell based advanced therapeutic medicinal products (ATMPs) for bone repair has been expected to revolutionize the health care system for the clinical treatment of bone defects. Despite this great promise, the clinical outcomes of the few cell based ATMPs that have been translated into clinical treatments have been far from impressive. In part, the clinical outcomes have been hampered because of the simplicity of the first wave of products. In response the field has set-out and amassed a plethora of complexities to alleviate the simplicity induced limitations. Many of these potential second wave products have remained "stuck" in the development pipeline. This is due to a number of reasons including the lack of a regulatory framework that has been evolving in the last years and the shortage of enabling technologies for industrial manufacturing to deal with these novel complexities. In this review, we reflect on the current ATMPs and give special attention to novel approaches that are able to provide complexity to ATMPs in a straightforward manner. Moreover, we discuss the potential tools able to produce or predict 'goldilocks' ATMPs, which are neither too simple nor too complex.

Superparamagnetic plasmonic nanoshells for improved imaging, separation and seeding of co-cultured cells

Multifunctional superparamagnetic nanoshells were applied for improved 2D and 3D two-photon luminescence imaging, separation and seeding of co-cultured cells.

Biomaterials in co-culture systems: towards optimizing tissue integration and cell signaling within scaffolds

Most natural tissues consist of multi-cellular systems made up of two or more cell types. However, some of these tissues may not regenerate themselves following tissue injury or disease without some form of intervention, such as from the use of tissue engineered constructs. Recent studies have increasingly used co-cultures in tissue engineering applications as these systems better model the natural tissues, both physically and biologically. This review aims to identify the challenges of using co-culture systems and to highlight different approaches with respect to the use of biomaterials in the use of such systems. The application of co-culture systems to stimulate a desired biological response and examples of studies within particular tissue engineering disciplines are summarized. A description of different analytical co-culture systems is also discussed and the role of biomaterials in the future of co-culture research are elaborated on. Understanding the complex cell-cell and cell-biomaterial interactions involved in co-culture systems will ultimately lead the field towards biomaterial concepts and designs with specific biochemical, electrical, and mechanical characteristics that are tailored towards the needs of distinct co-culture systems.

Synergistic effects of nanotopography and co-culture with endothelial cells on osteogenesis of mesenchymal stem cells

Inspired by the aligned nanostructures and co-existence of vascular cells and stem cells in human cancellous bone, we quantitatively investigated the relative contributions of nanotopography and co-culture with human umbilical endothelial cells (HUVECs) to the osteogenesis of human mesenchymal stem cells (hMSCs). Although both nanotopography and co-culture independently enhanced the osteogenesis of hMSCs, osteogenesis was further enhanced by the two factors in combination, indicating the importance of synergistic cues in stem cell engineering. Interestingly, nanotopography provided a larger relative contribution to the osteogenesis of hMSCs than did co-culture with HUVECs. Furthermore, the osteogenesis of hMSCs was also affected by the density of parallel nanogrooves, exhibiting a maximum at a 1:3 spacing ratio, as defined as the ratio of ridge width to groove width. Analysis of (i) biochemical soluble factors, (ii) hMSC-substrate interaction and (iii) hMSC-HUVEC interaction suggests that (ii) and (iii) play a crucial role in mediating osteogenic phenotypes.