In vitro effect of mineralized and demineralized bone allografts on proliferation and differentiation of MG-63 osteoblast-like cells

Bioengineering from the laboratory to clinical translation in oral and maxillofacial reconstruction

Background

Conventional techniques used in oral and maxillofacial reconstruction focus mainly on utilizing autologous tissues that have unquestionably improved function and esthetics for many patients, worldwide. However, the success depends on countless factors such as: donor and recipient sites conditions, patient's medical history, surgeon's experience, restricted availability of high-quality autogenous tissues or stem cells, and increased surgical cost and time.

Materials and Methods

Lately, teaming researchers, scientists, surgeons, and engineers, to address these limitations, have allowed tremendous progress in recombinant protein therapy, cell-based therapy, and gene therapy.

Results

Over the past few years, biomedical engineering has been evolving from the laboratory to clinical applications, for replacement of damaged body tissues due to trauma, cancer, congenital or acquired disorders.

Conclusions

This review provides an outlook on the content, benefits, recent advances, limitations, and future expectations of biomedical engineering for salivary glands, oral mucosa, dental structures, and maxillofacial reconstruction.

Cellular Behaviors of Periodontal Ligament Stem Cells in the Presence of Bone Grafting Biomaterials, In-Vitro Study

Periodontal regeneration through the employment of bone substitutes has become a feasible strategy in animal and clinical studies. In this regard, we aimed to compare the periodontal ligament stem cell behavior in the vicinity of various bone grafting substitutes. Three types of popular bone substitutes, including allografts (Regen), xenografts (Cerabone), and alloplasts (Osteon) were studied in this experimental survey. The cellular attachment was assessed after four hours using the MTS assay and SEM imaging. In addition, cellular proliferation was investigated after 1, 3, 5, and 7 days through MTS assay. Osteogenesis was studied after 21 days of cell culture in a differentiation medium (DM+) and a normal medium (DM-), by employing real-time PCR and alizarin red staining. The highest cellular attachment was seen in the xenograft group with a significant difference in comparison to the other grafting materials. Despite the relatively low primary attachment of cells to allografts, the allograft group showed the highest total proliferation rate, while the lowest proliferation capacity was found in the alloplast group. Osteogenesis fount to be accelerated mostly by xenografts in both mediums (DM+ and DM-) after 3 weeks, while alloplasts showed the lowest osteogenesis. This study revealed that the type of bone substitutes used in regenerative treatments can affect cellular behavior and as a whole allografts and xenografts showed better results.

Clinical and Radiologic Outcome of First Metatarsophalangeal Joint Arthrodesis Using a Human Allogeneic Cortical Bone Screw

Background:

Different fixation techniques are established for first metatarsophalangeal joint (MTPJ) arthrodesis, including compression screws, plates, Kirschner wires, metal- and bioabsorbable screws as well as staples. The purpose of this study was to investigate and present first clinical and radiologic results using a novel human, allogeneic cortical bone screw for arthrodesis of the first MTPJ.

Methods:

Arthrodesis of the first MTPJ was performed in 31 patients with hallux rigidus. Percentage union and time to union were the first outcomes; visual analog scale for pain, hallux valgus angle (HVA), intermetatarsal angle, and American Orthopaedic Foot & Ankle Society (AOFAS) hallux score were secondary outcomes.

Results:

Median time to union was 89 days, and union was observed in all patients. There were 4 complications (2 osteolysis margin, 1 cystic brightening, and 1 severe swelling at the first follow-up) all of that resolved at last follow-up. Pain significantly decreased from visual analog scale 8.0 to 0.2 points ( P < .0001). The HVA decreased from 30.4 to 10.2 degrees in the patient group with deformities. The total AOFAS score increased significantly from 48 to 87 ( P < .0001).

Conclusion:

Primary and revision arthrodesis of hallux rigidus with the human, allogeneic cortical bone screw reveals satisfying results similar to clinical and radiologic outcomes of other surgical techniques. Within 1 year, the human, allogeneic cortical bone screw is fully remodeled to host bone.

Level of Evidence:

Level IV, retrospective case series without control group.

The role of cortical perforations in allogeneic block grafting for lateral augmentation in maxilla: A randomized clinical trial

BACKGROUND

The need of decortication on the recipient site remains unclear for bone regeneration. To our knowledge, there are no human clinical trials that studied the influence of decortication on cancellous allogeneic block grafting.

PURPOSE

The aim of the present study is to evaluate the influence of perforating the cortex of the recipient site on cancellous allogeneic block graft integration and revascularization in the maxilla.

MATERIAL AND METHODS

Twenty-six patients referred for lateral bone augmentation were included in this clinical trial. Patients received freeze-dried bone allograft cancellous blocks obtained from the iliac crest; cortical perforations of the recipient bed were performed in the test group while in the control group it was left intact. After a 4-month healing period another surgery was performed to place dental implants, and a bone biopsy was collected using a trephine. All samples underwent micro-CT scans, and were processed for histomorphometric and immunohistochemical analysis. Implant survival comparisons were made using a repeated measures analysis of variance (ANOVA) while all other variables were compared using the analysis of covariance (ANCOVA).

RESULTS

One hundred and nineteen implants were placed into 110 augmented sites. One hundred percent implant survival rate was reported during 24 months follow-up period. No differences were reported in bleeding on probing at 1 (5.6 vs 9%) and 2 years (13.2 vs 12.1%), probing pocket depth at 1 (3.4 ± 0.95 vs 3.6 ± 1.12 mm) and 2 years (3.8 ± 1.02 vs 4.1 ± 1.46 mm), and marginal bone loss at 1 (0.2 ± 0.52 vs 0.3 ± 0.57 mm) and 2 years (0.6 ± 0.91 vs 0.5 ± 0.87 mm). No statistically significant differences were found in the micro-CT and histomorphometric analysis in terms of newly formed bone (25.7 ± 11.2% vs 22.3 ± 9.7%), soft tissue (33.0 ± 14.7% vs 36.5 ± 15.7%), remnant allograft (39.3 ± 20.4% vs 41.2 ± 22.7%), and bone mineralization (57.2 ± 10.6% vs 53.8 ± 8.7%). Perforating the cortex of the recipient site had no significant effect on angiogenesis as shown by immunohistochemical analysis of CD34 positive blood vessels (39.21 ± 10.53/mm² vs 34.16 ± 12.67/mm² ).

CONCLUSION

Cancellous allogeneic bone block grafts are a clinically acceptable alternative for horizontal bone augmentation. Cortical perforations of the recipient site in the maxilla did not improve angiogenesis nor bone formation within the block graft.

Biological and mechanical evaluation of mineralized-hydrogel scaffolds for tissue engineering applications

Chitosan and gelatin have been extensively used in tissue engineering for a wide range of different applications, such as wound healing or bone regeneration, due to their advantages: excellent biocompatibility (promoting cell adhesion and proliferation), low price and biodegradability. Nonetheless, their main drawback is that they have poor mechanical properties, consequently restricting their use in bone tissue engineering. In previous studies, both materials were cross-linked, with added calcium minerals, which led to an improvement in both mechanical and biological properties. Therefore, this study carries out a mechanical and biological characterization of mineral-hydrogel scaffolds in order to find the best compositions. Different proportions of calcium compounds (CaCO₃ and CaHPO₄) are used to make up between 20% and 30% of the minerals used in a mineral-hydrogel mix. This addition of minerals enhances not only the mechanical properties, but also the biological ones. On the one hand, the higher the amount of minerals added to the composition, the better the mechanical properties obtained. Additionally, as the proportion of CaCO₃ in comparison with CaHPO₄ rises, the mechanical properties improve. On the other hand, both cell proliferation and mineralization are improved with the addition of calcium minerals.

Biomimetic trace metals improve bone regenerative properties of calcium phosphate bioceramics

The bone regenerative capacity of synthetic calcium phosphates (CaPs) can be enhanced through the enrichment with selected metal trace ions. However, defining the optimal elemental composition required for bone formation is challenging due to many possible concentrations and combinations of these elements. We hypothesized that the ideal elemental composition exists in the inorganic phase of the bone extracellular matrix (ECM). To study our hypothesis, we first obtained natural hydroxyapatite through the calcination of bovine bone, which was then investigated its reactivity with acidic phosphates to produce CaP cements. Bioceramic scaffolds fabricated using these cements were assessed for their composition, properties, and in vivo regenerative performance and compared with controls. We found that natural hydroxyapatite could react with phosphoric acid to produce CaP cements with biomimetic trace metals. These cements present significantly superior in vivo bone regenerative performance compared with cements prepared using synthetic apatite. In summary, this study opens new avenues for further advancements in the field of CaP bone biomaterials by introducing a simple approach to develop biomimetic CaPs. This work also sheds light on the role of the inorganic phase of bone and its composition in defining the regenerative properties of natural bone xenografts.

The effect of embryonic origin on the osteoinductive potential of bone allografts

STATEMENT OF PROBLEM

Allografts with osteoinduction potential are widely used to augment bone in surgical and prosthetic rehabilitations. However, osteoinduction potential varies among commercially available allografts. Donor bones are derived from different embryonic origins, either the neural crest or mesoderm. Whether the origin of the bones affects the osteoinductivity of allograftsis is unclear.

PURPOSE

The purpose of this ex vivo study was to investigate the osteoinduction potential of allografts derived from bones with distinct embryonic origins.

MATERIAL AND METHODS

Allografts were obtained from human frontal and parietal bones at 2 different ages (fetal and adult). The specimens were divided into 4 groups: adult frontal (n=5), adult parietal (n=5), fetal frontal (n=10), and fetal parietal (n=10). Two investigations were conducted to assess the osteoinductive potential of these allografts. First, the osteogenesis of human osteoblasts exposed to these allografts were evaluated by analyzing the expression of runt-related transcription factor 2 (RUNX2), collagen type 1 alpha 2 chain (COL1A2), and bone gamma-carboxyglutamate protein (BGLAP) genes using quantitative real-time polymerase chain reaction (qRT-PCR). Second, the protein content of the adult frontal and parietal bone matrices was analyzed using liquid chromatography tandem mass spectrometry (LC-MS/MS). One-way ANOVA and the t test were used for statistical analyses of the gene and protein expression of the groups (α=.05).

RESULTS

No difference was found in the gene expression of the cells exposed to frontal or parietal bones. However, all 3 genes were significantly overexpressed in cells treated with fetal bones compared with adult bones. No difference was found in protein expression between adult frontal and adult parietal bones.

CONCLUSIONS

No difference was found in the osteoinductive capacity of frontal and parietal bones used as allografts. However, the osteoinductivity of fetal bones can be higher than that of adult bones. Further microanalyses are needed to determine the protein content of fetal bones.

Allogenic vs. synthetic granules for bone tissue engineering: an in vitro study

The aim of this study was to compare human dental pulp stem cells' (DPSCs) attachment, proliferation and osteogenic differentiation on allogenic and synthetic biphasic bone granules. In this in vitro study, two types of bone granules were used: allograft [freeze-dried bone allograft (FDBA)] and biphasic granules [hydroxyapatite/beta-tricalcium phosphate (HA/β-TCP)]. By isolation of DPSCs, their attachment to bone granules was observed by scanning electron microscope (SEM) at day 1 and 7 of cultivation. Vital cells were measured by MTT assay at 1, 3, and 7 days of cell culture. Comparison of vital cells at different time points was considered as cell proliferation. Finally, differentiation of DPSCs was evaluated by measurement of alkaline phosphatase (ALP) activity 3, 7, 14, and 21 days after cell seeding in standard and osteogenic media. Data were analyzed using two-way ANOVA with a significant level of 0.05. Attachment of DPSCs on FDBA granules seemed relatively stronger. The number of cells (based on MTT values) and ALP activity of the cells cultured on both study groups increased between time points (p ≤ 0.001). FDBA granules had more cells compared to HA/β-TCP granules (p < 0.001). There was no significant difference between ALP activity of two study groups cultured in the standard medium (p = 0.347) and they were both higher than the control group (p < 0.05). In the osteogenic medium, FDBA group had significantly higher ALP activity compared to HA/β-TCP (p = 0.035) and control (p = 0.001) groups while there was no significant difference between ALP activity of HA/β-TCP and control groups (p = 0.645). In conclusion, current in vitro study revealed that FDBA granules have more potential in supporting DPSCs attachment and proliferation and inducing their ALP activity compared to HA/β-TCP granules. Therefore, FDBA could serve as a proper bone substitute material.

* Extracellular Matrices for Bone Regeneration: A Literature Review

The gold standard material for bone regeneration is still autologous bone, a mesenchymal tissue that consists mainly of extracellular matrix (ECM) (90% v/v) and little cellular content (10% v/v). However, the fact that decellularized allogenic bone grafts often present a clinical performance comparable to autologous bone grafts demonstrates the crucial role of ECM in bone regeneration. For long, the mechanism by which bone allografts function was not clear, but recent research has unveiled many unique characteristics of ECM that seem to play a key role in tissue regeneration. This is further confirmed by the fact that synthetic biomaterials with composition and properties resembling bone ECM present excellent bone regeneration properties. In this context, ECM molecules such as glycosaminoglycans (GAGs) and self-assembly peptides (SAPs) can improve the performance of bone regeneration biomaterials. Moreover, decellularized ECM derived either from native tissues such as bone, cartilage, skin, and tooth germs or from cells such as osteoblasts, chondrocytes, and stem cells has shown promising results in bone regeneration applications. Understanding the role of ECM in bone regeneration is crucial for the development of the next generation of biomaterials for bone tissue engineering. In this sense, this review addresses the state-of-the-art on this subject matter.

In vitro comparison of the efficacy of TGF-β1 and PDGF-BB in combination with freeze-dried bone allografts for induction of osteogenic differentiation in MG-63 osteoblast-like cells

Predictable regeneration of alveolar bone defects has always been a challenge in implant dentistry. Bone allografts are widely used bone substitutes with controversial osteoinductive activity. This in vitro study aimed to assess the osteogenic potential of some commercially available freeze-dried bone allografts supplemented with human recombinant platelet-derived growth factor-BB and transforming growth factor beta-1. Cell viability, mineralization, and osteogenic gene expression of MG-63 osteoblast-like cells were compared among the allograft alone, allograft/platelet-derived growth factor-BB, allograft/transforming growth factor beta-1, and allograft/platelet-derived growth factor-BB/transforming growth factor beta-1 groups. The methyl thiazol tetrazolium assay, real-time quantitative reverse transcription polymerase chain reaction and alizarin red staining were performed, respectively, for assessment of cell viability, differentiation, and mineralization at 24-72 h post treatment. The allograft with greater cytotoxic effect on MG-63 cells caused the lowest differentiation among the groups. In comparison with allograft alone, allograft/transforming growth factor beta-1, and allograft/transforming growth factor beta-1/platelet-derived growth factor-BB caused significant upregulation of bone sialoprotein and osteocalcin osteogenic mid-late marker genes, and resulted in significantly higher amounts of calcified nodules especially in mineralized non-cytotoxic allograft group. Supplementation of platelet-derived growth factor-BB alone in 5 ng/mL concentration had no significant effect on differentiation or mineralization markers. According to the results, transforming growth factor beta-1 acts synergistically with bone allografts to enhance the osteogenic differentiation potential. Therefore, this combination may be useful for rapid transformation of undifferentiated cells into bone-forming cells for bone regeneration. However, platelet-derived growth factor-BB supplementation did not support this synergistic ability to enhance osteogenic differentiation and thus, further investigations are required.