Oral mucositis on a chip: modeling induction by chemo- and radiation treatments and recovery

Recombinant Human Keratinocyte Growth Factor Ameliorates Cancer Treatment-Induced Oral Mucositis on a Chip

Oral mucositis (OM) is a severe complication of cancer therapies caused by off-target cytotoxicity. Palifermin, which is recombinant human keratinocyte growth factor (KGF), is currently the only mitigating treatment available to a subset of OM patients. This study used a previously established model of oral mucositis on a chip (OM-OC) comprised of a confluent human gingival keratinocytes (GIE) layer attached to a basement membrane-lined subepithelial layer consisting of human gingival fibroblasts (HGF) and human dermal microvascular endothelial cells (HMEC) on a stable collagen I gel. Cisplatin, radiation, and combined treatments are followed by a recovery period in the OM-OC to determine possible cellular and molecular mechanisms of OM under effects of KGF. Cancer treatments affected the keratinocyte layer, causing death and epithelial barrier loss. Both keratinocytes and subepithelial cells died rapidly, as evidenced by propidium iodide staining. In response to radiation exposure, cell death occurred in the apical epithelial layer, predominantly, within 24h. Cisplatin exposure predominantly promoted death of basal epithelial cells within 32-36h. Presence of KGF in OM-OC protected tissues from damage caused by cancer treatments in a dose-dependent manner, being more effective at 10 ng/mL. As verified by F-actin staining and the Alamar Blue assay, KGF contributed to epithelial survival and induced proliferation of GIE and HGF as well as HMEC within 120h. When the expression of eighty inflammatory cytokines is evaluated at OM induction (Day 12) and resolution (Day 18) stages in OM-OC, some cytokines are identified as potential novel therapeutic targets. In comparison with chemoradiation exposure, KGF treatment showed a trend to decrease IL-8 and TNF-a expression at Day 12 and 18, and TGF-β1 at Day 18 in OM-OC. Taken together, these findings support the utility of OM-OC as a platform to model epithelial damage and evaluate molecular mechanisms following OM treatment.

Tiny Organs, Big Impact: How Microfluidic Organ-on-Chip Technology Is Revolutionizing Mucosal Tissues and Vasculature

Organ-on-chip (OOC) technology has gained importance for biomedical studies and drug development. This technology involves microfluidic devices that mimic the structure and function of specific human organs or tissues. OOCs are a promising alternative to traditional cell-based models and animals, as they provide a more representative experimental model of human physiology. By creating a microenvironment that closely resembles in vivo conditions, OOC platforms enable the study of intricate interactions between different cells as well as a better understanding of the underlying mechanisms pertaining to diseases. OOCs can be integrated with other technologies, such as sensors and imaging systems to monitor real-time responses and gather extensive data on tissue behavior. Despite these advances, OOCs for many organs are in their initial stages of development, with several challenges yet to be overcome. These include improving the complexity and maturity of these cellular models, enhancing their reproducibility, standardization, and scaling them up for high-throughput uses. Nonetheless, OOCs hold great promise in advancing biomedical research, drug discovery, and personalized medicine, benefiting human health and well-being. Here, we review several recent OOCs that attempt to overcome some of these challenges. These OOCs with unique applications can be engineered to model organ systems such as the stomach, cornea, blood vessels, and mouth, allowing for analyses and investigations under more realistic conditions. With this, these models can lead to the discovery of potential therapeutic interventions. In this review, we express the significance of the relationship between mucosal tissues and vasculature in organ-on-chip (OOC) systems. This interconnection mirrors the intricate physiological interactions observed in the human body, making it crucial for achieving accurate and meaningful representations of biological processes within OOC models. Vasculature delivers essential nutrients and oxygen to mucosal tissues, ensuring their proper function and survival. This exchange is critical for maintaining the health and integrity of mucosal barriers. This review will discuss the OOCs used to represent the mucosal architecture and vasculature, and it can encourage us to think of ways in which the integration of both can better mimic the complexities of biological systems and gain deeper insights into various physiological and pathological processes. This will help to facilitate the development of more accurate predictive models, which are invaluable for advancing our understanding of disease mechanisms and developing novel therapeutic interventions.

Biological Evaluation of Oral Care Products Using 3D Tissue-Engineered In Vitro Models of Plaque-Induced Gingivitis

BACKGROUND

The aim of this study was to investigate and visualize the anti-inflammatory and anti-bacterial effects of different oral care products using an infected and inflamed 3D tissue-engineered gingival mucosal model.

METHODS

A 3D full-thickness oral mucosal model was engineered inside tissue culture inserts using collagen hydrogels populated with human gingival fibroblasts and THP-1 monocytes and layered with oral epithelial cell lines. Oral saliva bacteria were cultured and added to the surface of the models and inflammation was further simulated with lipopolysaccharide (LPS) of Escherichia coli. The 3D models were exposed to three different types of toothpastes, a chlorhexidine antiseptic mouthwash, different antibiotics, and a mechanical rinse with phosphate-buffered saline (PBS) prior to biological evaluation using the PrestoBlue tissue viability assay, histology, optical coherence tomography (OCT), confocal microscopy, and measurement of the release of the inflammatory markers IL-1β, IL-6, and IL-8 with ELISA.

RESULTS

Multiple-endpoint analyses of the infected oral mucosal models treated with different anti-bacterial agents showed consistent outcomes in terms of tissue viability, histology, OCT, and confocal microscopy findings. In terms of anti-inflammatory testings, the positive control group showed the highest level of inflammation compared with all other groups. Depending on the anti-bacterial and anti-inflammatory potential of the test groups, different levels of inflammation were observed in the test groups.

CONCLUSIONS

The inflamed 3D oral mucosal model developed in this study has the potential to be used as a suitable in vitro model for testing the biocompatibility, anti-inflammatory, and anti-bacterial properties of oral care products including mouthwashes and toothpastes. The results of this study indicate that the chlorhexidine mouthwash has both anti-bacterial and cytotoxic effects on the 3D oral mucosal model. Hyaluronic-acid-containing toothpaste has significant anti-bacterial and anti-inflammatory effects on the 3D oral mucosal model.

Microphysiological Modeling of Gingival Tissues and Host-Material Interactions Using Gingiva-on-Chip

Gingiva plays a crucial barrier role at the interface of teeth, tooth-supporting structures, microbiome, and external agents. To mimic this complex microenvironment, an in vitro microphysiological platform and biofabricated full-thickness gingival equivalents (gingiva-on-chip) within a vertically stacked microfluidic device is developed. This design allowed long-term and air-liquid interface culture, and host-material interactions under flow conditions. Compared to static cultures, dynamic cultures on-chip enabled the biofabrication of gingival equivalents with stable mucosal matrix, improved epithelial morphogenesis, and barrier features. Additionally, a diseased state with disrupted barrier function representative of gingival/oral mucosal ulcers is modeled. The apical flow feature is utilized to emulate the mechanical action of mouth rinse and integrate the assessment of host-material interactions and transmucosal permeation of oral-care formulations in both healthy and diseased states. Although the gingiva-on-chip cultures have thicker and more mature epithelium, the flow of oral-care formulations induced increased tissue disruption and cytotoxic features compared to static conditions. The realistic emulation of mouth rinsing action facilitated a more physiological assessment of mucosal irritation potential. Overall, this microphysiological system enables biofabrication of human gingiva equivalents in intact and ulcerated states, providing a miniaturized and integrated platform for downstream host-material and host-microbiome applications in gingival and oral mucosa research.

Slow hydrogel matrix degradation enhances salivary gland mimetic phenotype

We recently developed a salivary gland tissue mimetic (SGm), comprised of salivary gland cells encapsulated in matrix metalloproteinase (MMP)-degradable poly(ethylene glycol) hydrogels within arrays of ∼320 µm diameter spherical cavities molded in PDMS. The SGm provides a functional and physiologically relevant platform well-suited to high-throughput drug screening for radioprotective compounds. However, the utility of the SGm would benefit from improved retention of acinar cell phenotype and function. We hypothesized that tuning biochemical cues presented within the PEG hydrogel matrix would improve maintenance of acinar cell phenotype and function by mimicking the natural extracellular matrix microenvironment of the intact gland. Hydrogels formed using slower-degrading MMP-sensitive peptide crosslinkers showed >2-fold increase in sphere number formed at 48 h, increased expression of acinar cell markers, and more robust response to calcium stimulation by the secretory agonist, carbachol, with reduced SGm tissue cluster disruption and outgrowth during prolonged culture. The incorporation of adhesive peptides containing RGD or IKVAV improved calcium flux response to secretory agonists at 14 days of culture. Tuning the hydrogel matrix improved cell aggregation, and promoted acinar cell phenotype, and stability of the SGm over 14 days of culture. Furthermore, combining this matrix with optimized media conditions synergistically prolonged the retention of the acinar cell phenotype in SGm. STATEMENT OF SIGNIFICANCE: Salivary gland (SG) dysfunction occurs due to off-target radiation due to head and neck cancer treatments. Progress in understanding gland dysfunction and developing therapeutic strategies for the SG are hampered by the lack of in vitro models, as salivary gland cells rapidly lose critical secretory function within 24 hours in vitro. Herein, we identify properties of poly(ethylene glycol) hydrogel matrices that enhance the secretory phenotype of SG tissue mimetics within the previously-described SG-microbubble tissue chip environment. Combining slow-degrading hydrogels with media conditions optimized for secretory marker expression further enhanced functional secretory response and secretory marker expression.

Gut-on-a-Chip Research for Drug Development: Implications of Chip Design on Preclinical Oral Bioavailability or Intestinal Disease Studies

The gut plays a key role in drug absorption and metabolism of orally ingested drugs. Additionally, the characterization of intestinal disease processes is increasingly gaining more attention, as gut health is an important contributor to our overall health. The most recent innovation to study intestinal processes in vitro is the development of gut-on-a-chip (GOC) systems. Compared to conventional in vitro models, they offer more translational value, and many different GOC models have been presented over the past years. Herein, we reflect on the almost unlimited choices in designing and selecting a GOC for preclinical drug (or food) development research. Four components that largely influence the GOC design are highlighted, namely (1) the biological research questions, (2) chip fabrication and materials, (3) tissue engineering, and (4) the environmental and biochemical cues to add or measure in the GOC. Examples of GOC studies in the two major areas of preclinical intestinal research are presented: (1) intestinal absorption and metabolism to study the oral bioavailability of compounds, and (2) treatment-orientated research for intestinal diseases. The last section of this review presents an outlook on the limitations to overcome in order to accelerate preclinical GOC research.

Programmable Physical Properties of Freestanding Chitosan Membranes Electrofabricated in Microfluidics

Microfluidic-integrated freestanding membranes with suitable biocompatibility and tunable physicochemical properties are in high demand for a wide range of life science and biological studies. However, there is a lack of facile and rapid methods to integrate such versatile membranes into microfluidics. A recently invented interfacial electrofabrication of chitosan membranes offers an in-situ membrane integration strategy that is flexible, controllable, simple, and biologically friendly. In this follow-up study, we explored the ability to program the physical properties of these chitosan membranes by varying the electrofabrication conditions (e.g., applied voltage and pH of alginate). We found a strong association between membrane growth rate, properties, and fabrication parameters: high electrical stimuli and pH of alginate resulted in high optical retardance and low permeability, and vice versa. This suggests that the molecular alignment and density of electrofabricated chitosan membranes could be actively tailored according to application needs. Lastly, we demonstrated that this interfacial electrofabrication could easily be expanded to produce chitosan membrane arrays with higher uniformity than the previously well-established flow assembly method. This study demonstrates the tunability of the electrofabricated membranes' properties and functionality, thus expanding the utility of such membranes for broader applications in the future.

Modeling Crevicular Fluid Flow and Host-Oral Microbiome Interactions in a Gingival Crevice-on-Chip

Gingival crevice and gingival crevicular fluid (GCF) flow play a crucial role at the gingiva-oral microbiome interface which contributes toward maintaining the balance between gingival health and periodontal disease. Interstitial flow of GCF strongly impacts the host-microbiome interactions and tissue responses. However, currently available in vitro preclinical models largely disregard the dynamic nature of gingival crevicular microenvironment, thus limiting the progress in the development of periodontal therapeutics. Here, a proof-of-principle "gingival crevice-on-chip" microfluidic platform to culture gingival connective tissue equivalent (CTE) under dynamic interstitial fluid flow mimicking the GCF is described. On-chip co-culture using oral symbiont (Streptococcus oralis) shows the potential to recapitulate microbial colonization, formation of biofilm-like structures at the tissue-microbiome interface, long-term co-culture, and bacterial clearance secondary to simulated GCF (s-GCF) flow. Further, on-chip exposure of the gingival CTEs to the toll-like receptor-2 (TLR-2) agonist or periodontal pathogen Fusobacterium nucleatum demonstrates the potential to mimic early gingival inflammation. In contrast to direct exposure, the induction of s-GCF flow toward the bacterial front attenuates the secretion of inflammatory mediators demonstrating the protective effect of GCF flow. This proposed in vitro platform offers the potential to study complex host-microbe interactions in periodontal disease and the development of periodontal therapeutics under near-microphysiological conditions.