Development of composite cultured oral mucosa utilizing collagen sponge matrix and contracted collagen gel: a preliminary study for clinical applications

Full-Thickness Oral Mucoperiosteal Defects: Challenges and Opportunities

Regenerative engineering strategies for the oral mucoperiosteum, as may be needed following surgeries, such as cleft palate repair and tumor resection, are underdeveloped compared with those for maxillofacial bone. However, critical-size tissue defects left to heal by secondary intention can lead to complications, such as infection, fistula formation, scarring, and midface hypoplasia. This review describes current clinical practice for replacing mucoperiosteal tissue, including autografts and allografts. Potentially paradigm-shifting experimental regenerative engineering strategies for mucoperiosteal wound healing, such as hybrid grafts and engineered matrices, are also discussed. Throughout the review, the advantages and disadvantages of each replacement or regeneration strategy are outlined in the context of clinical outcomes, quality of life for the patient, availability of materials, and cost of care. Finally, future directions for research and development in the area of mucoperiosteum repair are proposed, with an emphasis on identifying globally available and affordable solutions for promoting mucoperiosteal regeneration. Impact statement Unassisted oral mucoperiosteal wound healing can lead to severe complications such as infection, fistulae, scarring, and developmental abnormalities. Thus, strategies for promoting wound healing must be considered when mucoperiosteal defects are incident to oral surgery, as in palatoplasty or tumor resection. Emerging mucoperiosteal tissue engineering strategies, described in this study, have the potential to overcome the limitations of current standard-of-care donor tissue grafts. For example, the use of engineered mucoperiosteal biomaterials could circumvent concerns about tissue availability and immunogenicity. Moreover, employment of tissue engineering strategies may improve the equity of oral wound care by increasing global affordability and accessibility of materials.

Protective effect of inactivated blastoconidia in keratinocytes and human reconstituted epithelium against C. albicans infection

Candida albicans is commensal yeast that colonizes skin and mucosa; however, it can become an opportunist pathogen by changing from blastoconidia (commensal form) into hypha (pathogenic form). Each form activates a different cytokines response in epithelial cells. Little is known about the commensal role of C. albicans in the innate immunity. This work studied whether stimulation with C. albicans blastoconidia induces protection in keratinocytes and/or in a reconstituted human epithelium (RHE) infected with C. albicans. For this, inactivated C. albicans blastoconidia was used to stimulate keratinocytes and RHE prior to infection with C. albicans. Blastoconidia induced different cytokine expression profiles; in the case of RHE it decreased interleukin (IL)-1β and IL-10 and increased IL-8, tumor necrosis factor α (TNF-α), and interferon γ (IFN-γ). A significant increase in the expression of human β-defensins (HBD) 2 and HBD3 was observed in blastoconidia stimulated keratinocytes and RHE, associated with impaired growth and viability of C. albicans. Additionally, blastoconidia stimulation decreased the expression of virulence factors in C. albicans that are associated with filamentation (EFG1, CPH1 and NRG1), adhesion (ALS5), and invasion (SAP2). Blastoconidia stimulated RHE was significantly less damaged by C. albicans invasion. These results show that the commensal form of C. albicans would exert a protective effect against self-infection.

Treatment of intractable oral ulceration with an oral mucosa equivalent

The current use of steroids or pharmacological immunomodulators for the treatment of intractable oral ulceration is ineffective, necessitating newer cell-based therapeutic approaches. We examined the potential efficacy of an oral mucosa equivalent developed in this study in an in vivo model of repeat major oral ulceration mimicking the intractable oral ulceration observed clinically. Oral mucosal samples and plasma fibrin were obtained from Sprague-Dawley rats. The oral mucosa equivalents were prepared with cultured mucosal keratinocytes and plasma fibrin mixed with cultured fibroblasts. Ulcers were chemically induced on the rat buccal mucosa thrice in 3 weeks and covered with or without mucosa equivalents. Gross and microscopic findings and mRNA expression levels were compared between the ulcer control and mucosa equivalent groups. Oral mucosal keratinocytes and fibroblasts were cultured in vitro to achieve high viability and colony-forming efficiency. The equivalents showed epithelial and subepithelial structures similar to those of oral mucosa and exhibited high p63 positivity. In the in vivo study, ulceration was resolved earlier without significant granulation or scarring in the equivalent group than in control group (p < 0.05). Microscopic examinations revealed rapid re-epithelialization and less fibrosis in the equivalent group than in the control group (p < 0.05). Mucosa equivalent-covered ulcers showed histological characteristics similar to those of the normal buccal mucosa and exhibited lower expression of TGFB1, ACTA2, and FN1 mRNAs than the control group. The in vitro-engineered oral mucosa equivalent promotes ulcer healing without scarring and functional deficits. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1779-1785, 2019.

Use of a pre-vascularised oral mucosal cell sheet for promoting cutaneous burn wound healing

Pre-vascularised cell sheets have been used to promote early angiogenesis and graft survival. However, the use of pre-vascularised mucosal cell sheets for burn wounds has been rarely evaluated. Therefore, we examined the applicability of an oral pre-vascularised mucosal cell sheet that we had previously developed for the treatment of cutaneous burn wounds.

Methods: Mucosal keratinocytes, fibroblasts, and endothelial progenitor cells were isolated from the oral mucosa and peripheral blood and were expanded in vitro. Mucosal cell sheets were generated by seeding cultured keratinocytes onto a mixture of fibroblasts, endothelial cells, and fibrin. Third-degree burn wounds were created on the backs of rats and were covered with the cell sheets, skin grafts, or silastic sheets as a control. Gross and microscopic findings and gene expression profiles of wounds were compared among the groups.

Results: CD31-positive microvessels were observed in the fibrin-matrix layer of the cell sheet. In the cutaneous burn wound model, the cell sheets promoted wound healing, with accelerated wound closure and less scarring than with silastic sheets and skin grafts. The cell sheets had more microvessels and proliferating cells and less neutrophil infiltration and fibrotic features than the controls or skin grafts. The cell sheet induced higher mRNA expression of KRT14, VEGFA, IL10, and AQP3 and lower mRNA expression of TGFB1, IL6, ICAM1, ACTA2, and FN1 than did the controls or skin grafts.

Conclusions: The pre-vascularised mucosal cell sheet promotes cutaneous burn wound healing.

Oral mucosa-on-a-chip to assess layer-specific responses to bacteria and dental materials

The human oral mucosa hosts a diverse microbiome and is exposed to potentially toxic biomaterials from dental restoratives. Mucosal health is partly determined by cell and tissue responses to challenges such as dental materials and pathogenic bacteria. An in vitro model to rapidly determine potential layer-specific responses would lead to a better understanding of mucosal homeostasis and pathology. Therefore, this study aimed to develop a co-cultured microfluidic mucosal model on-a-chip to rapidly assess mucosal remodeling and the responses of epithelial and subepithelial layers to challenges typically found in the oral environment. A gingival fibroblast-laden collagen hydrogel was assembled in the central channel of a three-channel microfluidic chamber with interconnecting pores, followed by a keratinocyte layer attached to the collagen exposed in the pores. This configuration produced apical and subepithelial side channels capable of sustaining flow. Keratinocyte, fibroblast, and collagen densities were optimized to create a co-culture tissue-like construct stable over one week. Cells were stained and imaged with epifluorescence microscopy to confirm layer characteristics. As proof-of-concept, the mucosal construct was exposed separately to a dental monomer, 2-hydroxylethyl methacrylate (HEMA), and the oral bacteria Streptococcus mutans. Exposure to HEMA lowered mucosal cell viability, while exposure to the bacteria lowered trans-epithelial electrical resistance. These findings suggest that the oral mucosa-on-a-chip is useful for studying oral mucosal interactions with bacteria and biomaterials with a histology-like view of the tissue layers.

Plasticity of oral mucosal cell sheets for accelerated and scarless skin wound healing

OBJECTIVES

Wound healing is generally faster and associated with less scarring in the oral mucosa than in the skin. Although rarely studied, oral mucosa equivalents may contribute to rapid, scarless cutaneous wound healing. Therefore, we examined the potential utility of our newly developed oral mucosal cell sheet in skin wound healing.

MATERIALS AND METHODS

Oral mucosa and skin samples were obtained from surgical patients and Sprague-Dawley rats. Keratinocytes and fibroblasts were primarily cultured for in vitro cell expansion. Mucosa and skin equivalents were produced with a mixture of cultured fibroblasts and autologous fibrin from plasma and seeding keratinocytes. Mucosal and skin cell sheets were transplanted in full-thickness excisional wounds of rat skin with control wounds. Gross, histological, and molecular characteristics of wound healing according to different postsurgical days were compared in control and cell sheet-covered wounds.

RESULTS

Keratinocytes and fibroblasts derived from the oral mucosa were cultured faster than those derived from the skin. The in vitro-engineered oral mucosa and skin equivalents were successfully produced using complete autologous mucosa or skin and plasma fibrin, showing similarity to the histological characteristics of the skin or mucosa. In the in vivo rat model, the oral mucosal and skin cell sheet promoted wound healing with early wound closure and less scarring. The cell sheet-treated wounds showed lower TGF-β1, α-smooth muscle actin, and fibronectin mRNA expression than the control wounds.

CONCLUSIONS

The oral mucosal cell sheet demonstrated in vivo tissue plasticity through good adaptation to skin wounds, contributing to accelerated and scarless healing.

Use of oral mucosal cell sheets for accelerated oral surgical wound healing

BACKGROUND

We developed a highly efficient in vitro-engineered mucosa equivalent using completely autologous mucosa and blood and investigated its feasibility and efficacy for oral surgical wound healing.

METHODS

Small oral mucosa samples were obtained from surgical patients, and keratinocytes and fibroblasts were primarily grown in media without animal products for generating 3D cell sheets.

RESULTS

Morphological characteristics of the cell sheets were comparable to those of human mucosa, although p63-positive cells were more numerous in cell sheets. In addition, cell sheets were flexible, expandable, and easy to handle or transfer. In further in vivo rat experiments with deep wounding of the buccal mucosa and soft tissues, controls had significantly thinner epithelium and thicker collagen densities than those with cell sheets.

CONCLUSION

Autologous cell sheets can be engineered in vitro from oral keratinocytes, fibroblasts, and fibrin, and can be used clinically to accelerate healing of oral soft tissue defects.

Impact of Implant Surface Micropatterns on Epithelial Cell Behavior

PURPOSE

This study investigated the effect of topography on cell behavior by screening polydimethylsiloxane (PDMS) molds with different nanoscale micropatterns to determine the ideal surface characteristics for attachment of human epithelial cells.

MATERIALS AND METHODS

A soft PDMS mold with regular dot arrays was fabricated based on an aluminum oxide template with ordered nanotube arrays and used as a substrate for cell culture. Cell proliferation, spread, and morphology, as well as features of the extracellular matrix and the actin cytoskeleton were assessed.

DISCUSSION

Cells grown on 100-nm regular dot arrays had the highest proliferation rate and spread, with the longest pseudopodia; they showed robust actin distribution relative to the control group.

CONCLUSION

Three-dimensional PDMS microstructures with 100 nm regular dot arrays were the most effective surface for epithelial cell attachment. These findings can aid in the manufacture of superior materials for use in implants to better integrate into recipient tissue.

Effects of photochemical riboflavin-mediated crosslinks on the physical properties of collagen constructs and fibrils

The use of collagen scaffold in tissue engineering is on the rise, as modifications to mechanical properties are becoming more effective in strengthening constructs whilst preserving the natural biocompatibility. The combined technique of plastic compression and cross-linking is known to increase the mechanical strength of the collagen construct. Here, a modified protocol for engineering these collagen constructs is used to bring together a plastic compression method, combined with controlled photochemical crosslinking using riboflavin as a photoinitiator. In order to ascertain the effects of the photochemical crosslinking approach and the impact of the crosslinks created upon the properties of the engineered collagen constructs, the constructs were characterized both at the macroscale and at the fibrillar level. The resulting constructs were found to have a 2.5 fold increase in their Young's modulus, reaching a value of 650 ± 73 kPa when compared to non-crosslinked control collagen constructs. This value is not yet comparable to that of native tendon, but it proves that combining a crosslinking methodology to collagen tissue engineering may offer a new approach to create stronger, biomimetic constructs. A notable outcome of crosslinking collagen with riboflavin is the collagen's greater affinity for water; it was demonstrated that riboflavin crosslinked collagen retains water for a longer period of time compared to non-cross-linked control samples. The affinity of the cross-linked collagen to water also resulted in an increase of individual collagen fibrils' cross-sectional area as function of the crosslinking. These changes in water affinity and fibril morphology induced by the process of crosslinking could indicate that the crosslinked chains created during the photochemical crosslinking process may act as intermolecular hydrophilic nanosprings. These intermolecular nanosprings would be responsible for a change in the fibril morphology to accommodate variable volume of water within the fibril.

Collagen--emerging collagen based therapies hit the patient

The choice of biomaterials available for regenerative medicine continues to grow rapidly, with new materials often claiming advantages over the short-comings of those already in existence. Going back to nature, collagen is one of the most abundant proteins in mammals and its role is essential to our way of life. It can therefore be obtained from many sources including porcine, bovine, equine or human and offer a great promise as a biomimetic scaffold for regenerative medicine. Using naturally derived collagen, extracellular matrices (ECMs), as surgical materials have become established practice for a number of years. For clinical use the goal has been to preserve as much of the composition and structure of the ECM as possible without adverse effects to the recipient. This review will therefore cover in-depth both naturally and synthetically produced collagen matrices. Furthermore the production of more sophisticated three dimensional collagen scaffolds that provide cues at nano-, micro- and meso-scale for molecules, cells, proteins and bulk fluids by inducing fibrils alignments, embossing and layered configuration through the application of plastic compression technology will be discussed in details. This review will also shed light on both naturally and synthetically derived collagen products that have been available in the market for several purposes including neural repair, as cosmetic for the treatment of dermatologic defects, haemostatic agents, mucosal wound dressing and guided bone regeneration membrane. There are other several potential applications of collagen still under investigations and they are also covered in this review.

In vitro engineering of complete autologous oral mucosa equivalents: characterization of a novel scaffold

BACKGROUND AND OBJECTIVE

Restoration of oral mucosa defects by means of in vitro-cultured equivalents has become a valid alternative in the field of oral and periodontics surgery. Although different techniques have been described, none has been able to provide an equivalent with an autologous scaffold for the epithelium. The purpose of this study was to obtain complete autologous oral mucosa equivalents (CAOME) using the patient's own fibroblasts and plasma and to characterize these equivalents both morphologically and immunohistochemically.

MATERIAL AND METHODS

We acquired cell types (keratinocytes and fibroblasts) from the same mucosal samples, which were taken from healthy patients who underwent oral surgery. To construct the CAOME, a small sample of blood was obtained from the patient and subsequently processed to obtain a fibrin glue scaffold. All CAOME thus obtained were stained using the standard hematoxylin and eosin method to study their morphological characteristics. To establish the type of cells in the epithelial layer, CAOME were stained with pancytokeratin AE1/AE3, cytokeratins 5/6 and 13, p-63 and Ki-67. Finally, laminin 5 and collagen IV were used to reveal the presence of a basal membrane.

RESULTS

The CAOME featured a monolayer of cube-shaped epithelial cells similar to that found on the basal layer of the oral mucosa. Close to the epithelial layer lay the fibrin and fibroblasts-embedded scaffold. The CAOME was positive to pancytokeratin AE1/AE3, cytokeratin 5/6 and p-63. No reaction was found to cytokeratin 13 and Ki-67. There was staining to laminin 5 but not to collagen IV.

CONCLUSIONS

It is possible to engineer a CAOME with an epithelium of basal-like and immature keratinocytes, which could potentially reconstruct in vivo loss of tissue.

Development, optimization and characterization of a full-thickness tissue engineered human oral mucosal model for biological assessment of dental biomaterials

Restorative dental materials and oral health care products come into direct contact with oral mucosa and can cause adverse reactions. In order to obtain an accurate risk assessment, the in vitro test model must reflect the clinical situation as closely as possible. The aim of this study was to develop and optimize a three-dimensional full-thickness engineered human oral mucosal model, which can be used for biological assessment of dental materials. In this study human oral fibroblasts and keratinocytes were isolated from patients and seeded onto a number of collagen-based and synthetic scaffolds using a variety of cell seeding techniques and grown at the air/liquid interface to construct human oral mucosa equivalents. Suitability of 10 different scaffolds for engineering human oral mucosa was evaluated in terms of biocompatibility, biostability, porosity, and the ability to mimic normal human oral mucosa morphology. Finally an optimized full-thickness engineered human oral mucosa was developed and characterized using transmission electron microscopy and immunostaining. The oral mucosa reconstruct resembled native human oral mucosa and it has the potential to be used as an accurate and reproducible test model in mucotoxicity and biocompatibility evaluation of dental materials.

Controlled microchannelling in dense collagen scaffolds by soluble phosphate glass fibers

A problem with tissue engineering scaffolds is maintaining seeded cell viability and function due to limitations of oxygen and nutrient transfer. An approach to maintain suitable oxygen concentrations throughout the scaffold would be to controllably incorporate microchannelling within these scaffolds. This study investigated the incorporation of unidirectionally aligned soluble phosphate based glass fibers (PGF) into dense collagen scaffolds. PGF are degradable, and their degradation can be controlled through their chemistry and dimensions. Plastic compression was used to produce composite scaffolds at three different weight percentage while maintaining greater than 80% resident cell viability. PGF-collagen scaffold composition was quantified through thermogravimetric analysis as well as being morphologically and mechanically characterized. PGF degradation was measured through ion chromatography, and channel formation was verified with ultrasound imaging and SEM. The free movement of coated microbubble agents confirmed the channels to be continuous in nature and of 30-40 microm diameter. These microchannels in dense native collagen matrices could play an important role in hypoxia/perfusion limitations and also in the transportation of nutrients and potentially forming blood vessels through dense implants.

Tissue-engineered oral mucosa: a review of the scientific literature

Tissue-engineered oral mucosal equivalents have been developed for clinical applications and also for in vitro studies of biocompatibility, mucosal irritation, disease, and other basic oral biology phenomena. This paper reviews different tissue-engineering strategies used for the production of human oral mucosal equivalents, their relative advantages and drawbacks, and their applications. Techniques used for skin tissue engineering that may possibly be used for in vitro reconstruction of human oral mucosa are also discussed.

Cultured mucosal cell sheet with a double layer of keratinocytes and fibroblasts on a collagen membrane

The aim of this study was to develop a novel cultured mucosal membrane that was facile to prepare and easy to handle, and that could be applied to mucosal defects in the oral cavity. Human oral keratinocytes and fibroblasts were prepared from the oral mucosa. We made the following two types of cultured mucosal cell sheets: a monolayer sheet of keratinocytes cultured on a collagen membrane (K-S) and a double-layered sheet of keratinocytes and fibroblasts on a collagen membrane (KF-S). A collagen membrane was used as a control. Each type of sheet was transplanted onto dorsal skin defects of nude mice. The wound area was measured for the assessment of wound contraction and a specimen was harvested for histologic evaluation 1 week and 4 weeks after grafting. Wound contraction was minimal with KF-S grafts. Although histologic examination showed normal differentiation of the epithelium in all graft types, the involucrin expression pattern of KFS was most similar to that of normal epithelium. These results indicate that a double-layered sheet of keratinocytes and fibroblasts cultured on a collagen membrane may facilitate epithelial healing and prevent wound contraction.

Properties of engineered vascular constructs made from collagen, fibrin, and collagen–fibrin mixtures

Vascular constructs were formed by embedding rat aortic smooth muscle cells in three-dimensional matrices of Type I collagen, fibrin, or a mixture of collagen and fibrin in a 1:1 ratio, at total matrix protein concentrations of 2 and 4 mg/ml. Morphological and mechanical properties were evaluated after 6 days in culture, and the effect of cyclic mechanical strain on collagen-fibrin mixture constructs was also studied. Constructs made with the lower protein concentration compacted to the greatest degree, and fibrin was found to enhance gel compaction. Each matrix type exhibited a characteristic stress-strain profile. Pure collagen had the highest linear modulus and pure fibrin had the lowest. The ultimate tensile stress was strongly dependent on the degree of gel compaction, and collagen-fibrin mixtures at 2mg/ml total protein content exhibited the highest values. Application of cyclic mechanical strain to collagen-fibrin mixture constructs caused a significant increase in gel compaction and a decrease in cell proliferation. The linear modulus, ultimate tensile stress and toughness of the constructs were all augmented by mechanical strain. These results demonstrate that the properties of engineered vascular tissues can be modulated by the combination of selected extracellular matrix components, and the application of mechanical stimulation.

Effects of bacterial toxins on air-exposed cultured human respiratory sinus epithelium

The present study was designed to investigate the effects of the bacterial toxins lipopolysaccharide (LPS) and lipoteichoic acid (LTA) on air-exposed cultured human respiratory sinus epithelium. The morphological changes, proliferation, and differentiation of sphenoid sinus mucosa were examined after incubation with different LPS or LTA concentrations. Air-exposed cultured sinus mucosa differentiated from pseudostratified respiratory epithelium to squamous ciliated epithelium with few goblet cells. High concentrations of bacterial toxins induced a significant increase in mucus production and a decrease in ciliated cells. Ki67 immunostaining showed an increased cell proliferation after incubation with moderate levels of LPS or LTA. High concentrations of bacterial toxins, on the other hand, induced a decreased proliferation. Involucrin expression was clearly altered by incubation with high levels of bacterial toxins, indicating an increased degree of terminal differentiation. These results indicate that the bacterial toxins LPS and LTA both induce comparable dose-dependent morphological changes in sinus epithelium.