Particle Size of Hydroxyapatite Granules Calcified from Red Algae Affects the Osteogenic Potential of Human Mesenchymal Stem Cells in vitro

Improved visualisation of ACP-engineered osteoblastic spheroids: a comparative study of contrast-enhanced micro-CT and traditional imaging techniques

This study investigates osteoblastic cell spheroid cultivation methods, exploring flat-bottom, U-bottom, and rotary flask techniques with and without amorphous calcium phosphate (ACP) supplementation to replicate the 3D bone tissue microenvironment. ACP particles derived from eggshell waste exhibit enhanced osteogenic activity in 3D models. However, representative imaging of intricate 3D tissue-engineered constructs poses challenges in conventional imaging techniques due to notable scattering and absorption effects in light microscopy, and hence limited penetration depth. We investigated contrast-enhanced micro-CT as a methodological approach for comprehensive morphological 3D-analysis of thein-vitromodel and compared the technique with confocal laser scanning microscopy, scanning electron microscopy and classical histology. Phosphotungstic acid and iodine-based contrast agents were employed for micro-CT imaging in laboratory and synchrotron micro-CT imaging. Results revealed spheroid shape variations and structural integrity influenced by cultivation methods and ACP particles. The study underscores the advantage of 3D spheroid models over traditional 2D cultures in mimicking bone tissue architecture and cellular interactions, emphasising the growing demand for novel imaging techniques to visualise 3D tissue-engineered models. Contrast-enhanced micro-CT emerges as a promising non-invasive imaging method for tissue-engineered constructs containing ACP particles, offering insights into sample morphology, enabling virtual histology before further analysis.

Osteogenic differentiation and proliferation potentials of human bone marrow and umbilical cord-derived mesenchymal stem cells on the 3D-printed hydroxyapatite scaffolds

Mesenchymal stem cells (MSCs) are a promising candidate for bone repair. However, the maintenance of MSCs injected into the bone injury site remains inefficient. A potential approach is to develop a bone-liked platform that incorporates MSCs into a biocompatible 3D scaffold to facilitate bone grafting into the desired location. Bone tissue engineering is a multistep process that requires optimizing several variables, including the source of cells, osteogenic stimulation factors, and scaffold properties. This study aims to evaluate the proliferation and osteogenic differentiation potentials of MSCs cultured on 2 types of 3D-printed hydroxyapatite, including a 3D-printed HA and biomimetic calcium phosphate-coated 3D-printed HA. MSCs from bone marrow (BM-MSCs) and umbilical cord (UC-MSCs) were cultured on the 3D-printed HA and coated 3D-printed HA. Scanning electron microscopy and immunofluorescence staining were used to examine the characteristics and the attachment of MSCs to the scaffolds. Additionally, the cell proliferation was monitored, and the ability of cells to differentiate into osteoblast was assessed using alkaline phosphatase (ALP) activity and osteogenic gene expression. The BM-MSCs and UC-MSCs attached to a plastic culture plate with a spindle-shaped morphology exhibited an immunophenotype consistent with the characteristics of MSCs. Both MSC types could attach and survive on the 3D-printed HA and coated 3D-printed HA scaffolds. The MSCs cultured on these scaffolds displayed sufficient osteoblastic differentiation capacity, as evidenced by increased ALP activity and the expression of osteogenic genes and proteins compared to the control. Interestingly, MSCs grown on coated 3D-printed HA exhibited a higher ALP activity and osteogenic gene expression than those cultured on the 3D-printed HA. The finding indicated that BM-MSCs and UC-MSCs cultured on the 3D-printed HA and coated 3D-printed HA scaffolds could proliferate and differentiate into osteoblasts. Thus, the HA scaffolds could provide a suitable and favorable environment for the 3D culture of MSCs in bone tissue engineering. Additionally, biomimetic coating with octacalcium phosphate may improve the biocompatibility of the bone regeneration scaffold.

The Osteoinductivity of Calcium Phosphate-Based Biomaterials: A Tight Interaction With Bone Healing

Calcium phosphate (CaP)-based bioceramics are the most widely used synthetic biomaterials for reconstructing damaged bone. Accompanied by bone healing process, implanted materials are gradually degraded while bone ultimately returns to its original geometry and function. In this progress report, we reviewed the complex and tight relationship between the bone healing response and CaP-based biomaterials, with the emphasis on the in vivo degradation mechanisms of such material and their osteoinductive properties mediated by immune responses, osteoclastogenesis and osteoblasts. A deep understanding of the interaction between biological healing process and biomaterials will optimize the design of CaP-based biomaterials, and further translate into effective strategies for biomaterials customization.

Comparison between hydroxyapatite and polycaprolactone in inducing osteogenic differentiation and augmenting maxillary bone regeneration in rats

Background

The selection of appropriate scaffold plays an important role in ensuring the success of bone regeneration. The use of scaffolds with different materials and their effect on the osteogenic performance of cells is not well studied and this can affect the selection of suitable scaffolds for transplantation. Hence, this study aimed to investigate the comparative ability of two different synthetic scaffolds, mainly hydroxyapatite (HA) and polycaprolactone (PCL) scaffolds in promoting in vitro and in vivo bone regeneration.

Method

In vitro cell viability, morphology, and alkaline phosphatase (ALP) activity of MC3T3-E1 cells on HA and PCL scaffolds were determined in comparison to the accepted model outlined for two-dimensional systems. An in vivo study involving the transplantation of MC3T3-E1 cells with scaffolds into an artificial bone defect of 4 mm length and 1.5 mm depth in the rat's left maxilla was conducted. Three-dimensional analysis using micro-computed tomography (micro-CT), hematoxylin and eosin (H&E), and immunohistochemistry analyses evaluation were performed after six weeks of transplantation.

Results

MC3T3-E1 cells on the HA scaffold showed the highest cell viability. The cell viability on both scaffolds decreased after 14 days of culture, which reflects the dominant occurrence of osteoblast differentiation. An early sign of osteoblast differentiation can be detected on the PCL scaffold. However, cells on the HA scaffold showed more prominent results with intense mineralized nodules and significantly (p < 0.05) high levels of ALP activity with prolonged osteoblast induction. Micro-CT and H&E analyses confirmed the in vitro results with bone formation were significantly (p < 0.05) greater in HA scaffold and was supported by IHC analysis which confirmed stronger expression of osteogenic markers ALP and osteocalcin.

Conclusion

Different scaffold materials of HA and PCL might have influenced the bone regeneration ability of MC3T3-E1. Regardless, in vitro and in vivo bone regeneration was better in the HA scaffold which indicates its great potential for application in bone regeneration.

Signaling Pathway and Transcriptional Regulation in Osteoblasts during Bone Healing: Direct Involvement of Hydroxyapatite as a Biomaterial

Bone defects and periodontal disease are pathological conditions that may become neglected diseases if not treated properly. Hydroxyapatite (HA), along with tricalcium phosphate and bioglass ceramic, is a biomaterial widely applied to orthopedic and dental uses. The in vivo performance of HA is determined by the interaction between HA particles with bone cells, particularly the bone mineralizing cells osteoblasts. It has been reported that HA-induced osteoblastic differentiation by increasing the expression of osteogenic transcription factors. However, the pathway involved and the events that occur in the cell membrane have not been well understood and remain controversial. Advances in gene editing and the discovery of pharmacologic inhibitors assist researchers to better understand osteoblastic differentiation. This review summarizes the involvement of extracellular signal-regulated kinase (ERK), p38, Wnt, and bone morphogenetic protein 2 (BMP2) in osteoblastic cellular regulation induced by HA. These advances enhance the current understanding of the molecular mechanism of HA as a biomaterial. Moreover, they provide a better strategy for the design of HA to be utilized in bone engineering.

In vivo evaluation of shark teeth-derived bioapatites

OBJECTIVE

The present work proposes the shark teeth as a new source of bioapatites for bone filler applications in maxillary sinus elevation, periodontal regeneration or implants placement. This abundant fishing by-product provides an improved hydroxyapatite (HA) with fluorine contributions. The in vivo evaluation of osteointegration and bone mineral density levels promoted by these marine bioapatites was the main objective.

MATERIALS AND METHODS

Marine bioapatite granules of two sizes (1 mm, <20 μm) were obtained and characterized (XRD, SEM, ICP-OES) to determine morphology and composition. In vivo evaluation was performed, after bioapatites implantation in critical defects of parietal bone of 25 rats, for 3 weeks. Commercial synthetic HA/βTCP (60/40%) material and unfilled defects were used as controls. Radiology, micro-CT, histology and quantification of bone mineral density are presented.

RESULTS

These marine bioapatites presented a globular porous morphology. A biphasic composition ~70% apatitic (HA, apatite-CaF, fluorapatite) and ~30% non-apatitic phase (whitlockite, tricalcium bis(orthophosphate)), with contributions of F (1.0 ± 0.5%wt), Na (0.9 ± 0.2%wt) and Mg (0.65 ± 0.04%wt) was confirmed. After implantation period, higher osteointegration of 1-mm marine bioapatites than commercial synthetic granules was observed, together with bone formation from the defect surroundings but also at central area (potential osteoinductive properties). New bone cells penetrated inside pores and inter-granular cavities. Higher bone mineral density, in both 1-mm and <20-μm granules, than on commercial synthetic graft was determined, being significant in 1-mm bioapatites (a P < 0.05).

CONCLUSION

Shark teeth bioapatites were successfully validated as new functionally efficient bone filler in rat model, promoting significantly increased bone mineral density than synthetic control.

Small-sized granules of biphasic bone substitutes support fast implant bed vascularization

The present study investigated the influence of granule size of 2 biphasic bone substitutes (BoneCeramic® 400–700 μm and 500–1000 μm) on the induction of multinucleated giant cells (MNGCs) and implant bed vascularization in a subcutaneous implantation model in rats. Furthermore, degradation mechanisms and particle phagocytosis of both materials were examined by transmission electron microscopy (TEM). Both granule types induced tissue reactions involving primarily mononuclear cells and only small numbers of MNGCs. Higher numbers of MNGCs were detected in the group with small granules starting on day 30, while higher vascularization was observed only at day 10 in this group. TEM analysis revealed that both mono- and multinucleated cells were involved in the phagocytosis of the materials. Additionally, the results allowed recognition of the MNGCs as the foreign body giant cell phenotype. Histomorphometrical analysis of the size of phagocytosed particles showed no differences between the 2 granule types. The results indicate that granule size seems to have impact on early implant bed vascularization and also on the induction of MNGCs in the late phase of the tissue reaction. Furthermore, the results revealed that a synthetic bone substitute material can induce tissue reactions similar to those of some xenogeneic materials, thus pointing to a need to elucidate their “ideal” physical characteristics. The results also show that granule size in the range studied did not alter phagocytosis by mononuclear cells. Finally, the investigation substantiates the differentiation of material-induced MNGCs, which are of the foreign body giant cell type.

Enhanced bone regeneration by silicon-substituted hydroxyapatite derived from cuttlefish bone

OBJECTIVE

There is growing interest in the use of cuttlefish bone (CB) as a bone graft material. Silicon (Si) plays an important role in bone formation and calcification. This study aimed to prepare Si-substituted CB-derived hydroxyapatite (Si-CB-HAp) using a natural CB to improve the bioactivity for bone formation.

MATERIALS AND METHODS

We prepared Si-HAp from CB (Si-CB-HAp) using a hydrothermal and solvothermal method. The microstructure and chemical composition were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersive X-ray spectrometer (EDS). The bioactivity of the Si-CB-HAp was evaluated using human mesenchymal stem cells. Furthermore, the in vivo bone regeneration efficiency was evaluated using a rabbit calvarial defect model.

RESULTS

Our results show that the Si content was 0.77 wt% in Si-CB-HAp, and its original microstructure was conserved. The presence of Si was shown to enhance cell proliferation and early cellular attachment of human mesenchymal stem cells. Additionally, results of alkaline phosphatase activity and real-time PCR for osteoblast marker genes show that Si substitution into CB-HAp enhanced osteoblast differentiation. In addition, in vivo bone defect healing experiments show that the formation of bone with Si-CB-HAp is higher than that with CB-HAp.

CONCLUSION

These results indicate that Si-CB-HAp may potentially be used as a bone graft material to enhance bone healing.

Comparison of in vitro and in vivo bioactivity: cuttlefish-bone-derived hydroxyapatite and synthetic hydroxyapatite granules as a bone graft substitute

Bone reconstruction in clinical settings often requires bone substitutes. Hydroxyapatite (HAp) is a widely used bone substitute due to its osteoconductive properties and bone bonding ability. The aim of this study was to evaluate HAp granules derived from cuttlefish bone (CB-HAp) as a substitute biomaterial for bone grafts. In this study, HAp granules were prepared from raw CB by using a hydrothermal reaction. The formation of HAp from CB was confirmed by scanning electron microscopy and x-ray diffraction analysis. The bioactivity of the CB-HAp granules was evaluated both in vitro and in vivo. Our results show that CB-HAp is non-toxic and that CB-HAp granules supported improved cell adhesion, proliferation and differentiation compared to stoichiometric synthetic HAp granules. Furthermore, in vivo bone defect healing experiments show that the formation of bone with CB-HAp is higher than that with pure HAp. These results show that CB-HAp granules have excellent potential for use as a bone graft material.

The effect of particle size on the osteointegration of injectable silicate-substituted calcium phosphate bone substitute materials

Calcium phosphate (CaP) particles as a carrier in an injectable bone filler allows less invasive treatment of bony defects. The effect of changing granule size within a poloxamer filler on the osteointegration of silicate-substituted calcium phosphate (SiCaP) bone substitute materials was investigated in an ovine critical-sized femoral condyle defect model. Treatment group (TG) 1 consisted of SiCaP granules sized 1000-2000 μm in diameter (100 vol %). TG2 investigated a granule size of 250-500 μm (75 vol %), TG3 a granule size of 90-125 μm (75 vol %) and TG4 a granule size of 90-125 μm (50 vol %). Following a 4 and 8 week in vivo period, bone area, bone-implant contact, and remaining implant area were quantified within each defect. At 4 weeks, significantly increased bone formation was measured in TG2 (13.32% ± 1.38%) when compared with all other groups (p = 0.021 in all cases). Bone in contact with the bone substitute surface was also significantly higher in TG2. At 8 weeks most new bone was associated within defects containing the smallest granule size investigated (at the lower volume) (TG4) (42.78 ± 3.36%) however this group was also associated with higher amounts of fragmented SiCaP. These smaller particles were phagocytosed by macrophages and did not appear to have a negative influence on healing. In conclusion, SiCaP granules of 250-500 μm in size may be a more suitable scaffold when used as an injectable bone filler and may be a convenient method for treating bony defects.

Synthesis methods for nanosized hydroxyapatite with diverse structures

Hydroxyapatite (HAp) is the major mineral constituent of vertebrate bones and teeth. It has been well documented that HAp nanoparticles can significantly increase the biocompatibility and bioactivity of man-made biomaterials. Over the past decade, HAp nanoparticles have therefore increasingly been in demand, and extensive efforts have been devoted to develop many synthetic routes, involving both scientifically and economically new features. Several investigations have also been made to determine how critical properties of HAp can be effectively controlled by varying the processing parameters. With such a wide variety of methods for the preparation of HAp nanoparticles, choosing a specific procedure to synthesize a well-defined powder can be laborious; accordingly, in the present review, we have summarized all the available information on the preparation methodologies of HAp, and highlighted the inherent advantages and disadvantages involved in each method. This article is focused on nanosized HAp, although recent articles on microsized particles, especially those assembled from nanoparticles and/or nanocrystals, have also been reviewed for comparison. We have also provided several scientific figures and discussed a number of critical issues and challenges which require further research and development.

Comparative evaluation of biocompatibility of dense nanostructured and microstructured Hydroxyapatite/Titania composites

This work deals with the biocompatibility of dense nano- and micro-structured Hydroxyapatite/Titania composites prepared by two step and conventional sintering, respectively. By application of two step sintering, it was shown that the final grain size of HA-15 wt.% TiO2 is maintained lower than 100 nm while by the application of conventional sintering it reaches higher than 100 nm. Biocompatibility of the dense bulks was evaluated by cell attachment and proliferation experiments. Cell morphology, and viability on each nano- and micro-structured Hydroxyapatite/Titania composites were examined at different time points. The nanostructured HA/Titania dense bulk exhibited higher cell viability than a microstructured one. In addition, the effects of ionic products from nano- and micro-structured bulk dissolution on osteoblasts were studied. The MTT test confirmed that the products from nanostructured HA/Titania dense bulk significantly promoted osteoblast proliferation within a certain concentration range.

Comparison of mesenchymal stem cell proliferation and differentiation between biomimetic and electrochemical coatings on different topographic surfaces

The hypothesis for this study was that there is no difference in mesenchymal stem cells (MSCs) proliferation and osteogenic differentiation between calcium-phosphate (CaP) coatings with different crystal size deposited on different topographic surfaces of metal discs. Polished (P) and sand-blasted (SB) tantalum and TiAl6V4 discs were CaP coated by three methods-biomimetic (BioM), electrochemical at 20 mA/cm(2) and at 6.5 mA/cm(2)-and cultured with MSCs. At days 4, 7 and 14, cell proliferation-alamarBlue(®) activity and DNA quantification-and differentiation down the osteogenic lineage-ALP activity normalised per amount of DNA and SEM (morphology)-were analysed. Results showed that MSCs proliferated more when cultured on the nano-sized BioM coatings compared to uncoated and electrochemically coated discs. MSCs also proliferated more on P surfaces than on SB and or electrochemical coatings. All the coatings induced osteogenic differentiation, which was greater on electrochemical coatings and SB discs.

Effects of Dicalcium Silicate Coating Ionic Dissolution Products on Human Mesenchymal Stem-Cell Proliferation and Osteogenic Differentiation

This study investigated the effects of ionic dissolution products released from dicalcium silicate (DS) coatings on human mesenchymal stem cells (hMSC), cultured in the presence or absence of the dissolution products, with or without osteogenic supplements (OS). DS+ medium promoted cell proliferation during the first 4 days, but then inhibited proliferation. DS+OS− medium increased alkaline phosphatase (ALP) activity on day 14, and upregulated runt-related transcription factor 2 and osteonectin mRNA on days 7 and 14, respectively. The addition of osteogenic supplements (DS+OS+) led to a significant increase in ALP activity from days 7 to 21, upregulation of osteogenic markers on day 14, and formation of more mineralized nodules on day 28. The results demonstrated that the ionic dissolution products from DS coating alone can partly induce osteogenic differentiation of hMSC, and that the addition of osteogenic supplements further enhances osteoblast-specific gene expression and mineralization in hMSC.

In vitro effects of nanophase hydroxyapatite particles on proliferation and osteogenic differentiation of bone marrow-derived mesenchymal stem cells

Coculturing scaffolds with seeded cells in vitro is an indispensable process for construction of engineered tissues. It is essential to understand effects of the constituent particles of scaffold on seeded cells. In this study, we investigated the influence of nano-sized hydroxyapatite (nHAP) particles on the proliferation and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (MSCs). nHAP particles were cocultured with MSCs separated from rabbit. Cellular effects of particles were determined by cell counts, Vonkossa stains, and reverse transcription-polymerase chain reaction (RT-PCR) examinations. Results showed that nHAP particles could promote the MSCs growth when particle concentrations were lower than 20 microg/10(4) cells. This effect disappeared when the particles and the cells were cocultured in serum-free media. Higher particle concentrations could significantly inhibit the cell growth. Under the standard culture condition, the only effect of nHAP particles on osteogenic differentiation of MSCs was to enhance the expression of collagen I. Under the osteogenic-inductive culture condition, nHAP particles could inhibit mineralization of cells but promote their osteogenic differentiation. These cellular effects of particles still existed when the particles and the cells were cultured in indirect coculture system. nHAP particles could decrease calcium and phosphate concentrations of culture media, which possibly contributed to the cellular effects of nHAP particles.

Bone graft materials

This article examines each class of bone grafting material based on some of the studies in each of the following categories: safety, animal research, periodontal and maxillofacial applications, skeletal grafting, and attempts to qualify the efficacy of each class of material. The article also examines some of the research being done in "tissue engineering" to get a sense of the future of bone grafting.

Effects of granule size on the osteoconductivity of bovine and synthetic hydroxyapatite: a histologic and histometric study in dogs

Two bovine hydroxyapatites (BHAs), one with granule size of 150 to 200 microm and one with granule size of 300 to 329 micro, and 2 synthetic hydroxyapatites (SHAs), with granule size of 150 and 300 microm, respectively, were compared for effectiveness in repairing circumferential bone defects in dogs. The hydroxyapatites (HAs) were characterized through powder x-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Three trephined bone defects (5.0 mm wide x 4 mm long) were created in the humeruses of 8 dogs. In a random manner, the defects on each side were treated with either BHA with small granules (BHA[s]), BHA with large granules (BHA[L]), SHA with small granules (SHA[s]), SHA with large granules (SHA[L]), or left to heal unaided (bilateral control). Four dogs were sacrificed after 6 and 12 postoperative weeks, respectively. Ground sections of each defect were submitted to histologic and histomorphometric analysis (percentage of area occupied by bone, bone marrow, and biomaterial). As a rule, the HA granules exhibited direct bone contact, regardless of the origin and the size of the granules. Control sites were related and had an increased amount of connective tissue infiltration. At 12 weeks, BHA(s) exhibited improved bone formation compared with SHA(s) and SHA(L). The SHA(s) delivered reduced amounts of bone compared with the remaining groups (control included). The area of bone measured in BHA(s) sites was significantly higher at 12 weeks than 6 weeks. The XRD revealed the tested HA samples to be highly crystalline, while BHA appeared with rougher surface at SEM analysis. The BHA(s) performed better than the SHA(s) and SHA(L), as assessed by the amount of bone measured in both implantation sites at 12 weeks. The BHA's material characteristic itself rather than granules size accounted for the distinctive biological behavior. The increased roughness of the BHAs' surface, as assessed through SEM, seemed to benefit the osteoconduction process.