3D Printed Composite Scaffolds in Bone Tissue Engineering: A Systematic Review.

OBJECTIVE: This study aimed to analyze the effect of fabrication factors on both biological and physico-chemical features of 3-dimensional (3D) printed composite scaffolds. METHOD: Electronic search was done according to the PRISMA guideline in PubMed and Scopus databases limited to English articles published until May 2021. Studies in which composite scaffolds were fabricated through computer-aided design and computer-aided manufacturing (CADCAM)- based methods were included. Articles regarding the features of the scaffolds fabricated through indirect techniques were excluded. RESULTS: Full text of 121 studies were reviewed, and 69 met the inclusion criteria. According to analyzed studies, PCL and HA were the most commonly used polymer and ceramic, respectively. Besides, the solvent-based technique was the most commonly used composition technique, which enabled preparing blends with high concentrations of ceramic materials. The most common fabrication method used in the included studies was Fused Deposition Modeling (FDM). The addition of bio-ceramics enhanced the mechanical features and the biological behaviors of the printed scaffolds in a ratio-dependent manner. However, studies that analyzed the effect of ceramic weight ratio showed that scaffolds with the highest ceramic content did not necessarily possess the optimal biological and non-biological features. CONCLUSION: The biological and physico-chemical behaviors of the scaffold can be affected by pre-printing factors, including utilized materials, composition techniques, and fabrication methods. Fabricating scaffolds with high mineral content as of the natural bone may not provide the optimal condition for bone formation. Therefore, it is recommended that future studies compare the efficiency of different kinds of biomaterials rather than different weight ratios of one type.

Periodontal Ligament Stem Cell Isolation Protocol: A Systematic Review.

Despite the plethora of literature regarding isolation and characterization of periodontal ligament stem cells (PDLSCs), due to the existence of controversies in the results, in this comprehensive review, we aimed to summarize and compare the effect of isolation methods on PDLSC properties, including clonogenicity, viability/proliferation, markers expression, cell morphology, differentiation, and regeneration. Moreover, the outcomes of included studies, considering various parameters, such as teeth developmental stages, donor age, periodontal ligament health status, and part of the teeth root from which PDLSCs were derived, have been systematically discussed. It has been shown that from included studies, PDLSCs can be isolated from teeth at any developmental stages, health status condition, and donor age. Furthermore, a non-enzymatic digestion method, named as an explant or outgrowth technique, is a suitable protocol for PDLSCs isolation.

Identification Osteogenic Signaling Pathways Following Mechanical Stimulation: A Systematic Review.

INTRODUCTION: It has been shown that mechanical forces can induce or promote osteogenic differentiation as well as remodeling of the new created bone tissues. To apply this characteristic in bone tissue engineering, it is important to know which mechanical stimuli through which signaling pathway has a more significant impact on osteogenesis. METHODS: In this systematic study, an electronic search was conducted using PubMed and Google Scholar databases. This study has been prepared and organized according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Included studies were first categorized according to the in vivo and in vitro studies. RESULTS: Six types of mechanical stresses were used in these articles and the most commonly used mechanical force and cell source were tension and bone marrow-derived mesenchymal stem cells (BMMSCs), respectively. These forces were able to trigger twelve signaling pathways in which Wnt pathway was so prominent. CONCLUSION: 1) Although specific signaling pathways are induced through specific mechanical forces, Wnt signaling pathways are predominantly activated by almost all types of force/stimulation, 2) All signaling pathways regulate expression of RUNX2, which is known as a master regulator of osteogenesis, 3) In Tension force, the mode of force administration, i.e, continuous or noncontinuous tension is more important than the percentage of elongation.

Effect of metformin on the behavior of dental pulp stem cells cultured on freeze-dried bone allografts.

BACKGROUND: Considering the complications associated with autogenous bone grafting, the use of freezedried bone allograft (FDBA) granules may be considered as an alternative treatment plan. OBJECTIVES: The aim of this study was to evaluate the effect of metformin on both the proliferation and osteogenic capability of dental pulp stem cells (DPSCs) cultured on FDBA granules. MATERIAL AND METHODS: First, a pilot study was conducted only on DPSCs to confirm cellular viability and the osteoinducing effect of 100 µmol/L metformin. Next, the cells were loaded on FDBA granules and treated with and without metformin. Finally, the following analyses were performed: scanning electron microscopy (SEM) (cell attachment); the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay (proliferation); and alkaline phosphatase (ALP) activity analysis (osteogenic differentiation). RESULTS: The SEM images revealed that metformin enhanced the adhesion of DPSCs on FDBA granules. In addition, metformin was shown to increase cell proliferation/viability from day 1 to day 7. Compared to the control, a significant difference was observed after 7 days of treatment. Metformin enhanced the osteogenic capability of FDBA in both standard and osteoinducing conditions. An increase in ALP activity was significant after 7 days of treatment. The positive effect of metformin on differentiation was significant in osteoinducing conditions. CONCLUSIONS: Metformin can be applied as an additional osteoinductive factor in bone regeneration treatment. Moreover, scaffolds with controlled release of metformin can be considered a proper osteoinductive bone substitute that may lessen the complications related to applying allograft scaffolds alone.

Improved bone regeneration through amniotic membrane loaded with buccal fat pad-derived MSCs as an adjuvant in maxillomandibular reconstruction.

BACKGROUND: Human amniotic membranes (HAMs), as a biological membrane with healing, osteogenic, and cell therapy potential, has been in the spotlight to enhance the outcomes of treating bone defects. Present study aims to clinically assess the potential of HAM loaded with buccal fat pad-derived stem cells (BFSCs) as an osteogenic coverage for onlay bone grafts to maxillomandibular bone defects. MATERIALS AND METHODS: Nine patients with jaw bone defects were enrolled in the present study. The patients were allocated to two study groups: Iliac crest bone graft with HAM coverage (n = 5), and Iliac bone grafts covered with HAM loaded with BFSCs (n = 4). Five months following the grafting and prior to implant placement, cone beam computed tomography was performed for radiomorphometric analysis. RESULTS: The mean increase in bone width was found to be significantly greater in the HAM + BFSCs group (4.42 ± 1.03 mm versus 3.07 ± 0.73 mm, p < 0.05). Further, the changes in vertical dimension were greater in the HAM + BFSCs group (4.66 ± 1.06 mm versus 4.14 ± 1.03 mm, p > 0.05). CONCLUSION: Combined use of HAM with mesenchymal stem cells may enhance bone regeneration specifically in the horizontal dimension. Moreover, this methodology reduces the amount of harvested autogenous bone and diminish secondary bone resorption.

Buccal Fat Pad-Derived Stem Cells in Three-Dimensional Rehabilitation of Large Alveolar Defects: A Report of Two Cases.

This case report seeks to describe efficient clinical application of adipose-derived stem cells (AdSCs) originated from buccal fat pad (BFP) in combination with conventional guided bone regeneration as protected healing space for reconstruction of large alveolar defects after extraction of multiple impacted teeth. The first case was a 19-year-old woman with several impacted teeth in the maxillary and mandibular regions, which could not be forced to erupt and were recommended for surgical extraction by the orthodontist. After this procedure, a large bone defect was created, and this space was filled by AdSC loaded natural bovine bone mineral (NBBM), which was protected with lateral ramus cortical plates, microscrews, and collagen membrane. After 6 months of post-guided bone regeneration, the patient received 6 and 7 implant placements, respectively, in the maxilla and mandible. At 10 months postoperatively, radiographic evaluation revealed thorough survival of implants. The second case was a 22-year-old man with the same complaint and large bony defects created after his teeth were extracted. After 6 months of post-guided bone regeneration, he received 4 dental implants in his maxilla and 7 implants in the mandible. At 48 months postoperatively, radiographs showed complete survival of implants. This approach represented a considerable amount of 3-dimensional bone formation in both cases, which enabled us to use dental implant therapy for rehabilitation of the whole dentition. The application of AdSCs isolated from BFP in combination with NBBM can be considered an efficient treatment for bone regeneration in large alveolar bone defects.

Antibody Administration for Bone Tissue Engineering: A Systematic Review.

BACKGROUND: Currently, antibodies are progressively applied in medicine for different purposes, including diagnostic and therapeutic indications. Over twenty monoclonal antibodies utilized for many therapeutic reasons from therapy of cancers, immune disorders, and osteoporosis to localized bony defects. In addition, therapeutic antibodies represented various findings in bone tissue engineering. OBJECTIVES: The current study aims to systematically review the available literature on antibody assisted bone regeneration in animal models. METHODS: A through electronic search was conducted from January 1992 to June 2017 limited to English language publications on administrations of antibodies for bone regeneration. Data extraction was ere performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. RESULTS: Twenty studies were selected and analyzed in this systematic review. Among these studies, six articles reported in vitro results in addition to in vivo evaluations. The data is tabulated according to the route of administrations as locally administrated antibody which includes anti-bone morphogenetic protein 2 (anti-BMP2) and systemic administrated antibodies, which include anti-sclerostin and anti- Dickkopf-1 (DKK1). Data are summarized and reported by the following variables: Type of study, types of cells for in vitro investigations, types of animal models and defects characteristics, types of scaffolds used in the defect site, duration of follow-ups; and outcomes of assessments. CONCLUSIONS: A novel approach of administration of antibodies demonstrated promising results for bone tissue engineering. However, more investigations, particularly in larger animals, are required for their further possible clinical administration.

Application of Bioreactors to Improve Functionality of Bone Tissue Engineering Constructs: A Systematic Review.

BACKGROUND: Traditional attempts to grow bone grafts in vitro have been based on culturing cell-scaffold constructs under static culture conditions. However, limitations associated with this approach have led to the development of various types of technologies and equipments. One of these is a bioreactor acting as an intermediate between static (in vitro) and dynamic (in vivo) conditions, which can mimic physiological and mechanical body conditions. OBJECTIVE: The aim of this study was to systematically review the available literature on application of different types of bioreactors in bone tissue engineering. METHODS: A thorough search in PubMed and Google Scholar databases from January 2011 to December 2016 was performed. All in vitro and in vivo studies about bioreactor applications in bone tissue engineering were included and categorized according to bioreactor types. CONCLUSION: A comprehensive systematic review of all the studies from the past five years yielded several findings: (1) combined bioreactors seem effective in bone tissue engineering; (2) 1- 2 ml/min is an appropriate flow rate range; (3) a cylinder is an appropriative scaffold shape; and (4) incubation of the scaffold with cells prior to transfer to the bioreactor followed by administration of osteogenic medium in the bioreactor seems an efficient approach to help cells properly attach and differentiate.

Polymeric scaffolds in tissue engineering: a literature review.

The tissue engineering scaffold acts as an extracellular matrix that interacts to the cells prior to forming new tissues. The chemical and structural characteristics of scaffolds are major concerns in fabricating of ideal three-dimensional structure for tissue engineering applications. The polymer scaffolds used for tissue engineering should possess proper architecture and mechanical properties in addition to supporting cell adhesion, proliferation, and differentiation. Much research has been done on the topic of polymeric scaffold properties such as surface topographic features (roughness and hydrophilicity) and scaffold microstructures (pore size, porosity, pore interconnectivity, and pore and fiber architectures) that influence the cell-scaffold interactions. In this review, efforts were given to evaluate the effect of both chemical and structural characteristics of scaffolds on cell behaviors such as adhesion, proliferation, migration, and differentiation. This review would provide the fundamental information which would be beneficial for scaffold design in future. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 431-459, 2017.

Polymeric vs hydroxyapatite-based scaffolds on dental pulp stem cell proliferation and differentiation.

AIM: To evaluate adhesion, proliferation and differentiation of human dental pulp stem cells (hDPSCs) on four commercially available scaffold biomaterials. METHODS: hDPSCs were isolated from human dental pulp tissues of extracted wisdom teeth and established in stem cell growth medium. hDPSCs at passage 3-5 were seeded on four commercially available scaffold biomaterials, SureOss (Allograft), Cerabone (Xenograft), PLLA (Synthetic), and OSTEON II Collagen (Composite), for 7 and 14 d in osteogenic medium. Cell adhesion and morphology to the scaffolds were evaluated by scanning electron microscopy (SEM). Cell proliferation and differentiation into osteogenic lineage were evaluated using DNA counting and alkaline phosphatase (ALP) activity assay, respectively. RESULTS: All scaffold biomaterials except SureOss (Allograft) supported hDPSC adhesion, proliferation and differentiation. hDPSCs seeded on PLLA (Synthetic) scaffold showed the highest cell proliferation and attachment as indicated with both SEM and DNA counting assay. Evaluating the osteogenic differentiation capability of hDPSCs on different scaffold biomaterials with ALP activity assay showed high level of ALP activity on cells cultured on PLLA (Synthetic) and OSTEON II Collagen (Composite) scaffolds. SEM micrographs also showed that in the presence of Cerabone (Xenograft) and OSTEON II Collagen (Composite) scaffolds, the hDPSCs demonstrated the fibroblastic phenotype with several cytoplasmic extension, while the cells on PLLA scaffold showed the osteoblastic-like morphology, round-like shape. CONCLUSION: PLLA scaffold supports adhesion, proliferation and osteogenic differentiation of hDPSCs. Hence, it may be useful in combination with hDPSCs for cell-based reconstructive therapy.

Expression of bone morphogenetic protein-6 in dental follicle stem cells and its effect on osteogenic differentiation.

The dental follicle (DF) plays an essential role in tooth eruption via regulation of bone resorption and bone formation. Bone morphogenetic protein-6 (BMP6) expression in the DF is coincident with bone growth in the tooth crypt. DF stem cells (DFSCs) have been shown to possess strong osteogenic capability. This study aims to determine the expression of BMP6 in DFSCs and to elucidate the role of BMP6 in the osteogenesis of DFSCs. DFSCs and their non-stem cell counterpart, DF cells (DFCs), were obtained from the DFs of rat pups. We showed that expression of BMP6 was significantly higher in the DFSCs than in the DFCs. DFSCs lost osteogenic capability during in vitro expansion, and DFSCs in late passages had reduced BMP6 expression as compared to early passages of DFSCs when they were subjected to osteogenic induction. Addition of exogenous human recombinant BMP6 (hrBMP6) to the osteogenic medium dramatically enhanced the osteogenesis of the late-passage DFSCs. Knockdown of BMP6 by short interfering RNA in the DFSCs in early passages resulted in a decrease in osteogenesis, which could be restored by addition of hrBMP6. We concluded that DFSCs need to express high levels of BMP6 to maintain their osteogenesis capability. Increased BMP6 expression seen in vivo in the DF may reflect the activation of DFSCs for osteogenic differentiation for bone growth during tooth eruption.