The effect of pores and connections geometries on bone ingrowth into titanium scaffolds: an assessment based on 3D microCT images

In order to support bone tissue regeneration, porous biomaterial implants (scaffolds) must offer chemical and mechanical properties, besides favorable fluid transport. Titanium implants provide these requirements, and depending on their microstructural parameters, the osteointegration process can be stimulated. The pore structure of scaffolds plays an essential role in this process, guiding fluid transport for neo-bone regeneration. The objective of this work was to analyze geometric and morphologic parameters of the porous microstructure of implants and analyze their influences in the bone regeneration process, and then discuss which parameters are the most fundamental. Bone ingrowths into two different sorts of porous titanium implants were analyzed after 7, 14, 21, 28, and 35 incubation days in experimental animal models. Measurements were accomplished with x-ray microtomography image analysis from rabbit tibiae, applying a pore-network technique. Taking into account the most favorable pore sizes for neo-bone regeneration, a novel approach was employed to assess the influence of the pore structure on this process: the analyses were carried out considering minimum pore and connection sizes. With this technique, pores and connections were analyzed separately and the influence of connectivity was deeply evaluated. This investigation showed a considerable influence of the size of connections on the permeability parameter and consequently on the neo-bone regeneration. The results indicate that the processing of porous scaffolds must be focused on deliver pore connections that stimulate the transport of fluids throughout the implant to be applied as a bone replacer.

Chick Embryo Model for Homing and Host Interactions of Tissue Engineering-Purposed Human Dental Stem Cells

Human dental stem cells (hDSC) have a potential for regenerative therapies and could differentiate in vitro into many tissues, such as dentin, nerve, and vascular endothelium. Gallus gallus domesticus developing fertilized egg or chick embryo is an experimental model absent of xenografts rejection, largely employed in replacement of mammal species in scientific research and preclinical studies to evaluate angiogenesis and vasculogenesis, tissue differentiation, and embryonic development. This multiscale research deals with the homing and cell signaling effects of a standardized hDSC toward the receptor tissues of G. gallus domesticus in ovo. The hDSC were obtained from the explantation from third molars, characterized by cell cytometry, and employed without any further purification procedure. Four experimental groups were studied, according to the kind of cell tracing strategy, named: Control, mCherry-labeled hDSC, QTracker-labeled hDSC, and QTracker-exposed controls. The eggs were kept in an incubator temperature of 37.6°C and humidity 86%, and the embryos were euthanized after 10 days of incubation. In vivo fluorescence and histological analysis were conducted. The fluorescence of the embryos inoculated with mCherry hDSC or the QTracker hDSC was associated with the bones and the beak tooth, and labeled cell islands could be localized in part of the samples. The inoculation of the QTracker probe resulted in proliferating bone tissue labeling. The hDSC inoculated groups presented cartilage plate hypertrophy and atypical morphology, meanwhile Control eggs were negative. The results demonstrated that hDSC can migrate to the cartilaginous tissues of the chick embryos, survive in this environment, implant, and interfere with the growth of developing bone.

Tooth Tissue Engineering: The Importance of Blood Products as a Supplement in Tissue Culture Medium for Human Pulp Dental Stem Cells

One of the goals in using cells for tissue engineering (TE) and cell therapy consists of optimizing the medium for cell culture. The present study compares three different blood product supplements for improved cell proliferation and protection against DNA damage in cultured human dental pulp stem cells for tooth TE applications. Human cells from dental pulp were first characterized as adult stem cells (ectomesenchymal mixed origin) by flow cytometry. Next, four different cell culture conditions were tested: I, supplement-free; II, supplemented with fetal bovine serum; III, allogeneic human serum; and IV, autologous human serum. Cultured cells were then characterized for cell proliferation, mineralized nodule formation, and colony-forming units (CFU) capability. After 28 days in culture, the comet assay was performed to assess possible damage in cellular DNA. Our results revealed that Protocol IV achieved higher cell proliferation than Protocol I (p = 0.0112). Protocols II and III resulted in higher cell proliferation than Protocol I, but no statistical differences were found relative to Protocol IV. The comet assay revealed less cell damage in cells cultured using Protocol IV as compared to Protocols II and III. The damage percentage observed on Protocol II was significantly higher than all other protocols. CFUs capability was highest using Protocol IV (p = 0.0018) and III, respectively, and the highest degree of mineralization was observed using Protocol IV as compared to Protocols II and III. Protocol IV resulted in significantly improved cell proliferation, and no cell damage was observed. These results demonstrate that human blood product supplements can be used as feasible supplements for culturing adult human dental stem cells.

Tooth tissue engineering: tooth decellularization for natural scaffold

AIM

Tissue engineering is a multidisciplinary science that aims to produce replacement organs and biological substitutes. One of the techniques involves decellularizing a biological organ without altering its structure. One challenge is how to demonstrate which method would be better for this process.

METHODOLOGY

Fifty premolar teeth were divided into five groups: G1 (control): solution of 10% formaldehyde; G2: phosphate buffer saline (PBS), 28 g of tetrasodium ethylenediaminetetraacetic (EDTA), sodium hypochlorite 2.5% (SH); G3: PBS, EDTA and 40v hydrogen peroxide (HP); G4: PBS, EDTA, SH, enzymatic detergent (ED); and G5: PBS, EDTA, HP, ED. Each group was analyzed by scanning electron microscopy (SEM), x-ray, measured weights and color and received statistical analysis.

CONCLUSION

This study demonstrated that G5 was the most appropriate method to obtain a natural scaffold.

Tooth tissue engineering: the influence of hydrophilic surface on nanocrystalline diamond films for human dental stem cells

New techniques for tissue engineering (TE) are rapidly emerging. The basic concept of autologous TE is to isolate cells from small biopsy specimens, and to expand these cells in culture for subsequent seeding onto biodegradable scaffolds. Nanocrystalline diamond films have attracted the attention of researchers from a variety of different areas in recent years, due to their unique and exceptional properties. In this approach, human dental stem cells (hDSCs) were characterized by flow cytometry and grown on diamond films with hydrogen (H)-terminated and oxygen (O)-terminated surfaces for 28 days, and then removed by lysis and washing with distilled water. Energy dispersive spectroscopy analysis was performed, showing that the regions with O-terminated surfaces contained much higher levels of deposited calcium, oxygen, and phosphorus. These results suggest that the extracellular matrix was considerably more developed in the O-terminated regions, as compared with the H-terminated regions. In addition, optical microscopy of hDSCs cultured on the diamond substrate with H- and O-terminated surfaces, before washing with distilled water, showed preferential directions of the cells arrangement, where orthogonal lines suggest that the cells appeared to be following the O-terminated regions or hydrophilic surface. These findings suggest that O-terminated diamond surfaces prepared on biodegradable scaffolds can be useful for mineralized dental tissue formation.

Cytogenetic instability of dental pulp stem cell lines

Human adult stem cells (hASCs) offer a potentially renewable source of cell types that are easily isolated and rapidly expanded for use in regenerative medicine and cell therapies without the complicating ethical problems that are associated with embryonic stem cells. However, the eventual therapeutic use of hASCs requires that these cells and their derivatives maintain their genomic stability. There is currently a lack of systematic studies that are aimed at characterising aberrant chromosomal changes in cultured ASCs over time. However, the presence of mosaicism and accumulation of karyotypic abnormalities within cultured cell subpopulations have been reported. To investigate cytogenetic integrity of cultured human dental stem cell (hDSC) lines, we analysed four expanded hDSC cultures using classical G banding and fluorescent in situ hybridisation (FISH) with X chromosome specific probe. Our preliminary results revealed that about 70% of the cells exhibited karyotypic abnormalities including polyploidy, aneuploidy and ring chromosomes. The heterogeneous spectrum of abnormalities indicates a high frequency of chromosomal mutations that continuously arise upon extended culture. These findings emphasise the need for the careful analysis of the cytogenetic stability of cultured hDSCs before they can be used in clinical therapies.

Tooth tissue engineering: optimal dental stem cell harvest based on tooth development

Our long-term objective is to devise reliable methods to generate biological replacement teeth exhibiting the physical properties and functions of naturally formed human teeth. Previously, we demonstrated the successful use of tissue engineering approaches to generate small, bioengineered tooth crowns from harvested pig and rat postnatal dental stem cells (DSCs). To facilitate characterizations of human DSCs, we have developed a novel radiographic staging system to accurately correlate human third molar tooth developmental stage with anticipated harvested DSC yield. Our results demonstrated that DSC yields were higher in less developed teeth (Stages 1 and 2), and lower in more developed teeth (Stages 3, 4, and 5). The greatest cell yields and colony-forming units (CFUs) capability was obtained from Stages 1 and 2 tooth dental pulp. We conclude that radiographic developmental staging can be used to accurately assess the utility of harvested human teeth for future dental tissue engineering applications.

Bioengineered dental tissues grown in the rat jaw

Our long-term objective is to develop methods to form, in the jaw, bioengineered replacement teeth that exhibit physical properties and functions similar to those of natural teeth. Our results show that cultured rat tooth bud cells, seeded onto biodegradable scaffolds, implanted into the jaws of adult rat hosts and grown for 12 weeks, formed small, organized, bioengineered tooth crowns, containing dentin, enamel, pulp, and periodontal ligament tissues, similar to identical cell-seeded scaffolds implanted and grown in the omentum. Radiographic, histological, and immunohistochemical analyses showed that bioengineered teeth consisted of organized dentin, enamel, and pulp tissues. This study advances practical applications for dental tissue engineering by demonstrating that bioengineered tooth tissues can be regenerated at the site of previously lost teeth, and supports the use of tissue engineering strategies in humans, to regenerate previously lost and/or missing teeth. The results presented in this report support the feasibility of bioengineered replacement tooth formation in the jaw.

Bioengineered teeth from cultured rat tooth bud cells

The recent bioengineering of complex tooth structures from pig tooth bud tissues suggests the potential for the regeneration of mammalian dental tissues. We have improved tooth bioengineering methods by comparing the utility of cultured rat tooth bud cells obtained from three- to seven-day post-natal (dpn) rats for tooth-tissue-engineering applications. Cell-seeded biodegradable scaffolds were grown in the omenta of adult rat hosts for 12 wks, then harvested. Analyses of 12-week implant tissues demonstrated that dissociated 4-dpn rat tooth bud cells seeded for 1 hr onto PGA or PLGA scaffolds generated bioengineered tooth tissues most reliably. We conclude that tooth-tissue-engineering methods can be used to generate both pig and rat tooth tissues. Furthermore, our ability to bioengineer tooth structures from cultured tooth bud cells suggests that dental epithelial and mesenchymal stem cells can be maintained in vitro for at least 6 days.