Dental tissue repair: novel models for tissue regeneration strategies

The Ethical Implications of Tissue Engineering for Regenerative Purposes: A Systematic Review

Tissue Engineering (TE) is a branch of Regenerative Medicine (RM) that combines stem cells and biomaterial scaffolds to create living tissue constructs to restore patients' organs after injury or disease. Over the last decade, emerging technologies such as 3D bioprinting, biofabrication, supramolecular materials, induced pluripotent stem cells, and organoids have entered the field. While this rapidly evolving field is expected to have great therapeutic potential, its development from bench to bedside presents several ethical and societal challenges. To make sure TE will reach its ultimate goal of improving patient welfare, these challenges should be mapped out and evaluated. Therefore, we performed a systematic review of the ethical implications of the development and application of TE for regenerative purposes, as mentioned in the academic literature. A search query in PubMed, Embase, Scopus, and PhilPapers yielded 2451 unique articles. After systematic screening, 237 relevant ethical and biomedical articles published between 2008 and 2021 were included in our review. We identified a broad range of ethical implications that could be categorized under 10 themes. Seven themes trace the development from bench to bedside: (1) animal experimentation, (2) handling human tissue, (3) informed consent, (4) therapeutic potential, (5) risk and safety, (6) clinical translation, and (7) societal impact. Three themes represent ethical safeguards relevant to all developmental phases: (8) scientific integrity, (9) regulation, and (10) patient and public involvement. This review reveals that since 2008 a significant body of literature has emerged on how to design clinical trials for TE in a responsible manner. However, several topics remain in need of more attention. These include the acceptability of alternative translational pathways outside clinical trials, soft impacts on society and questions of ownership over engineered tissues. Overall, this overview of the ethical and societal implications of the field will help promote responsible development of new interventions in TE and RM. It can also serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. Impact statement To our knowledge, this is the first time that the ethical implications of Tissue Engineering (TE) have been reviewed systematically. By gathering existing scholarly work and identifying knowledge gaps, this review facilitates further research into the ethical and societal implications of TE and Regenerative Medicine (RM) and other emerging biomedical technologies. Moreover, it will serve as a valuable resource and educational tool for scientists, engineers, and clinicians in the field by providing an overview of the ethical considerations relevant to their work. As such, our review may promote successful and responsible development of new strategies in TE and RM.

Effect of tea root-derived proanthocyanidin fractions on protection of dentin collagen

Objectives

Proanthocyanidins (PAs) have been widely used as effective agents for dentin collagen cross-linking to enhance the biomechanics and biostability of dentin in vitro. However, the effects and protective mechanisms of various tea root-derived PA components on dentin remain undefined. This study evaluated the effects of these tea root-derived PA components on dentin biomechanics and biostability.

Methods

In this study, ethyl acetate and n-butyl alcohol were used to extract PAs with different degrees of polymerization from tea roots; the effects of these PA extracts on dentin were evaluated.

Results

Dentin was treated with glutaraldehyde, ethyl acetate, n-butyl alcohol, or water. PAs with a high degree of polymerization, extracted using n-butyl alcohol, were able to more effectively improve dentin collagen cross-linking, increase resistance to bacterial collagenase digestion, and enhance dentin elasticity, relative to treatment with glutaraldehyde or PAs with a low degree of polymerization (extracted using ethyl acetate). Additionally, treatment with aqueous extract of tea roots was detrimental to dentin stability and function.

Conclusions

PAs with a high degree of polymerization were effective for dentin protection and restoration in vitro, suggesting clinical treatment potential for tea root-derived PAs.

BMP-2 and type I collagen preservation in human deciduous teeth after demineralization

BACKGROUND

Great interest has recently been focused on tooth and tooth derivatives as suitable substrates for the treatment of alveolar bone defects. Here, we propose the use of demineralized baby teeth (BT) as potential grafting materials for bone augmentation procedures.

METHODS

Particles of human BT (Ø < 1 mm) were demineralized by means of a chemical/thermal treatment. Demineralized BT particles were thoroughly characterized by scanning electron microscopy/energy dispersive X-ray analyses to evaluate the effects of the demineralization on BT topography and mineral phase composition, and by enzyme-linked immunosorbent assays (ELISA) to quantify collagen and bone morphogenetic protein-2 (BMP-2) protein contents. The response of SAOS-2 cells to exogenous BMP-2 stimulation was evaluated to identify the minimum BMP-2 concentration able to induce osteodifferentiation in vitro (alkaline phosphatase (ALP) activity).

RESULTS

The demineralization treatment led to a dramatic decrease in relative Ca and P content (%) of ≈75% with respect to the native BT particles, while preserving native protein conformation and activity. Interestingly, the demineralization process led to a rise in the bioavailability of BMP-2 in BT particles, as compared to the untreated counterparts. The BMP-2 content found in demineralized BT was also proved to be very effective in enhancing ALP activity, thus in the osteodifferentiation of SAOS-2 cells in vitro, as confirmed by cell experiments performed upon exogenously added BMP-2.

CONCLUSIONS

In this study we demonstrate that the BMP-2 content found in demineralized BT is very effective in inducing cell osteodifferentiation, and strengthens the idea that BTs are very attractive bioactive materials for bone-grafting procedures.

Demineralized dentin and enamel matrices as suitable substrates for bone regeneration

Background

In recent decades, tooth derivatives such as dentin (D) and enamel (E) have been considered as potential graft biomaterials to treat bone defects. This study aimed to investigate the effects of demineralization on the physical-chemical and biological behavior of D and E.

Methods

Human D and E were minced into particles (Ø<1 mm), demineralized and sterilized. Thorough physical-chemical and biochemical characterizations of native and demineralized materials were performed by SEM and EDS analysis and ELISA kits to determine mineral, collagen type I and BMP-2 contents. In addition, MG63 and SAOS-2 cells were seeded on tooth-derived materials and Bio-Oss®, and a comparison of cell responses in terms of adhesion and proliferation was carried out.

Results

The sterilization process, as a combination of chemical and thermal treatments, was found to be effective for all materials. On the other hand, D demineralization allowed preserving the collagen content, while increasing BMP-2 bioavailability. D and demineralized D (dD) displayed excellent biocompatibility, even greater than Bio-Oss®. Conversely, the high mineral content displayed by E, as confirmed by EDS analysis, inhibited cell proliferation. Of note, even though the demineralization process was somehow less effective in E than in D, demineralized E (dE) displayed increased BMP-2 bioavailability and improved performance in vitro compared with native E.

Conclusions

Our results substantiate the idea that the demineralization process lead to an increase of BMP-2 bioavailability, thus paving the way toward development of more effective, osteoinductive tooth-derived materials for bone regeneration and replacement.

Correlation between Fibrillin-1 Degradation and mRNA Downregulation and Myofibroblast Differentiation in Cultured Human Dental Pulp Tissue

Myofibroblasts and extracellular matrix are important components in wound healing. Alpha-smooth muscle actin (α-SMA) is a marker of myofibroblasts. Fibrillin-1 is a major constituent of microfibrils and an extracellular-regulator of TGF-β1, an important cytokine in the transdifferentiation of resident fibroblasts into myofibroblasts. To study the correlation between changes in fibrillin-1 expression and myofibroblast differentiation, we examined alterations in fibrillin-1 and α-SMA expression in organotypic cultures of dental pulp in vitro. Extracted healthy human teeth were cut to 1-mm-thick slices and cultured for 7 days. In intact dental pulp, fibrillin-1 was broadly distributed, and α-SMA was observed in pericytes and vascular smooth muscle cells. After 7 days of culture, immunostaining for fibrillin-1 became faint concomitant with a downregulation in its mRNA levels. Furthermore, fibroblasts, odontoblasts and Schwann cells were immunoreactive for α-SMA with a significant increase in α-SMA mRNA expression. Double immunofluorescence staining was positive for pSmad2/3, central mediators of TGF-β signaling, and α-SMA. The administration of inhibitors for extracellular matrix proteases recovered fibrillin-1 immunostaining; moreover, fibroblasts lost their immunoreactivity for α-SMA along with a downregulation in α-SMA mRNA. These findings suggest that the expression of α-SMA is TGF-β1 dependent, and fibrillin-1 degradation and downregulation might be implicated in the differentiation of myofibroblasts in dental pulp wound healing.

Engineered collagen hydrogels for the sustained release of biomolecules and imaging agents: promoting the growth of human gingival cells

We present here the in vitro release profiles of either fluorescently labeled biomolecules or computed tomography contrast nanoagents from engineered collagen hydrogels under physiological conditions. The collagen constructs were designed as potential biocompatible inserts into wounded human gingiva. The collagen hydrogels were fabricated under a variety of conditions in order to optimize the release profile of biomolecules and nanoparticles for the desired duration and amount. The collagen constructs containing biomolecules/nanoconstructs were incubated under physiological conditions (ie, 37°C and 5% CO2) for 24 hours, and the release profile was tuned from 20% to 70% of initially loaded materials by varying the gelation conditions of the collagen constructs. The amounts of released biomolecules and nanoparticles were quantified respectively by measuring the intensity of fluorescence and X-ray scattering. The collagen hydrogel we fabricated may serve as an efficient platform for the controlled release of biomolecules and imaging agents in human gingiva to facilitate the regeneration of oral tissues.