Biological evaluation of porous nanocomposite scaffolds based on strontium substituted β-TCP and bioactive glass: An in vitro and in vivo study

Reconstructing Critical-Sized Mandibular Defects in a Rabbit Model: Enhancing Angiogenesis and Facilitating Bone Regeneration via a Cell-Loaded 3D-Printed Hydrogel-Ceramic Scaffold Application

In this study, we propose a spatially patterned 3D-printed nanohydroxyapatite (nHA)/beta-tricalcium phosphate (β-TCP)/collagen composite scaffold incorporating human dental pulp-derived mesenchymal stem cells (hDP-MSCs) for bone regeneration in critical-sized defects. We investigated angiogenesis and osteogenesis in a rabbit critical-sized mandibular defect model treated with this engineered construct. The critical and synergistic role of collagen coating and incorporation of stem cells in the regeneration process was confirmed by including a cell-free uncoated 3D-printed nHA/β-TCP scaffold, a stem cell-loaded 3D-printed nHA/β-TCP scaffold, and a cell-free collagen-coated 3D-printed nHA/β-TCP scaffold in the experimental design, in addition to an empty defect. Posteuthanasia evaluations through X-ray analysis, histological assessments, immunohistochemistry staining, histomorphometry, and reverse transcription-polymerase chain reaction (RT-PCR) suggest the formation of substantial woven and lamellar bone in the cell-loaded collagen-coated 3D-printed nHA/β-TCP scaffolds. Histomorphometric analysis demonstrated a significant increase in osteoblasts, osteocytes, osteoclasts, bone area, and vascularization compared to that observed in the control group. Conversely, a significant decrease in fibroblasts/fibrocytes and connective tissue was observed in this group compared to that in the control group. RT-PCR indicated a significant upregulation in the expression of osteogenesis-related genes, including BMP2, ALPL, SOX9, Runx2, and SPP1. The findings suggest that the hDP-MSC-loaded 3D-printed nHA/β-TCP/collagen composite scaffold is promising for bone regeneration in critical-sized defects.

Regulation of the antibiotic elution profile from tricalcium phosphate bone cement by addition of bioactive glass

This work aimed at tailoring of different properties of antibacterial drug delivery Ca-phosphate cements by incorporation of bioactive glass (BG). The cements were prepared from beta-tricalcium phosphate cement (β-TCP) and BG based on 50 SiO2-20 CaO-15 Na2O-7 B2O3-4 P2O5-4 Al2O3 wt% with different percentages of BG [5, 10, 15, and 20% (w/w)]. The composite cements were characterized by XRD, FTIR, and TEM. Moreover, in vitro bioactivity and biodegradation were evaluated in the simulated body fluid (SBF) at 37 °C. In addition, physical properties and mechanical strength were determined. Also, the effect of glass addition on the drug release profile was examined using gentamicin. Finally, the antimicrobial activity was studied against Staphylococcus aureus, Pseudomonas aeruginosa, and Klebsiella pneumonia bacteria, one unicellular fungal strain (Candida albicans), and one multicellular fungal strain (Mucor racemosus). The results showed that after soaking in SBF, the compression strength values ranged from 14 to 36 MPa, the bulk densities and porosities were within 1.35 to 1.49 g/cm3 and 51.3 to 44.71%, respectively. Furthermore, gentamicin was released in a sustained manner, and BG decreased the released drug amount from ~ 80% (in pure β-TCP) to 47-53% in the composite cements. A drug release profile that is sustained by all samples was achieved. The antimicrobial test showed good activity of gentamicin-conjugated cements against bacteria and fungi used in this study. Additionally, cytotoxicity results proved that all samples were safe on MG-63 cells up to 50 µg/mL with no more than 7-12% dead cells. From the view of the physico-mechanical properties, bioactivity, biodegradation, and drug release rate, 20BG/β-TCP sample was nominated for practical bone grafting material, where it showed appropriate setting time and a relatively high mechanical strength suitable for cancellous bone.

Effect of strontium substitution on functional activity of phosphate-based glass

Phosphate-based glass (PBG) is a bioactive agent, composed of a glass network with phosphate as the primary component and can be substituted with various therapeutic ions for functional enhancement. Strontium (Sr) has been shown to stimulate osteogenic activity and inhibit pro-inflammatory responses. Despite this potential, there are limited studies that focus on the proportion of Sr substituted and its impact on the functional activity of resulting Sr-substituted PBG (PSr). In this study, focusing on the cellular biological response we synthesized and investigated the functional activity of PSr by characterizing its properties and comparing the effect of Sr substitution on cellular bioactivity. Moreover, we benchmarked the optimal composition against 45S5 bioactive glass (BG). Our results showed that PSr groups exhibited a glass structure and phosphate network like that of PBG. The release of Sr and P was most stable for PSr6, which showed favorable cell viability. Furthermore, PSr6 elicited excellent early osteogenic marker expression and inhibition of pro-inflammatory cytokine expression, which was significant compared to BG. In addition, compared to BG, PSr6 had markedly higher expression of osteopontin in immunocytochemistry, higher ALP expression in osteogenic media, and denser alizarin red staining in vitro. We also observed a comparable in vivo regenerative response in a 4-week rabbit calvaria defect model. Therefore, based on the results of this study, PSr6 could be identified as the functionally optimized composition with the potential to be applied as a valuable bioactive component of existing biomaterials used for bone regeneration.

Kaempferol-loaded bioactive glass-based scaffold for bone tissue engineering: in vitro and in vivo evaluation

Due to the increasing prevalence of bone disorders among people especially in average age, the future of treatments for osseous abnormalities has been illuminated by scaffold-based bone tissue engineering. In this study, in vitro and in vivo properties of 58S bioactive glass-based scaffolds for bone tissue engineering (bare (B.SC), Zein-coated (C.SC), and Zein-coated containing Kaempferol (KC.SC)) were evaluated. This is a follow-up study on our previously published paper, where we synthesized 58S bioactive glass-based scaffolds coated with Kaempferol-loaded Zein biopolymer, and characterized from mostly engineering points of view to find the optimum composition. For this aim, in vitro assessments were done to evaluate the osteogenic capacity and biological features of the scaffolds. In the in vivo section, all types of scaffolds with/without bone marrow-derived stem cells (BMSC) were implanted into rat calvaria bone defects, and potential of bone healing was assessed using imaging, staining, and histomorphometric analyses. It was shown that, Zein-coating covered surface cracks leading to better mechanical properties without negative effect on bioactivity and cell attachment. Also, BMSC differentiation proved that the presence of Kaempferol caused higher calcium deposition, increased alkaline phosphatase activity, bone-specific gene upregulation in vitro. Further, in vivo study confirmed positive effect of BMSC-loaded KC.SC on significant new bone formation resulting in complete bone regeneration. Combining physical properties of coated scaffolds with the osteogenic effect of Kaempferol and BMSCs could represent a new strategy for bone regeneration and provide a more effective approach to repairing critical-sized bone defects.

3D-Printing for Critical Sized Bone Defects: Current Concepts and Future Directions

The management and definitive treatment of segmental bone defects in the setting of acute trauma, fracture non-union, revision joint arthroplasty, and tumor surgery are challenging clinical problems with no consistently satisfactory solution. Orthopaedic surgeons are developing novel strategies to treat these problems, including three-dimensional (3D) printing combined with growth factors and/or cells. This article reviews the current strategies for management of segmental bone loss in orthopaedic surgery, including graft selection, bone graft substitutes, and operative techniques. Furthermore, we highlight 3D printing as a technology that may serve a major role in the management of segmental defects. The optimization of a 3D-printed scaffold design through printing technique, material selection, and scaffold geometry, as well as biologic additives to enhance bone regeneration and incorporation could change the treatment paradigm for these difficult bone repair problems.

Enhanced ectopic bone formation by strontium-substituted calcium phosphate ceramics through regulation of osteoclastogenesis and osteoblastogenesis

To explore how strontium influences osteoclastogenesis and osteoblastogenesis during material-induced ectopic bone formation, porous strontium-substituted biphasic calcium phosphate (Sr-BCP) and BCP ceramics with equivalent pore structures and comparable grain size and porosity were prepared. In vitro results showed that compared with BCP, Sr-BCP inhibited the osteoclastic differentiation of osteoclast precursors by delaying cell fusion, down-regulating the expression of osteoclast marker genes, and reducing the activity of osteoclast specific proteins, possibly due to the activated ERK signaling pathway but the suppressed p38, JNK and AKT signaling pathways. Meanwhile, Sr-BCP promoted the osteogenic differentiation of mesenchymal stem cells (MSCs) by up-regulating the osteogenic gene expression. Sr-BCP also mediated the expression of important osteoblast-osteoclast coupling factors, as evidenced by the increased Opg/Rankl ratio in mMSCs, and the reduced Rank expression and enhanced EphrinB2 expression in osteoclast precursors. Similar results were observed in an in vivo study based on a murine intramuscular implantation model. The sign of ectopic bone formation was only seen in Sr-BCP at 8 weeks. Compared to BCP, Sr-BCP obviously hindered the formation of TRAP- and CTSK-positive multinucleated osteoclast-like cells during the early implantation time up to 6 weeks, which is consistent with the in vivo PCR results. This suggested that Sr-BCP could clearly accelerate the ectopic bone formation by promoting osteogenesis but suppressing osteoclastogenesis, which might be closely related to the expression of osteoblast-osteoclast coupling factors regulated by Sr²⁺. These findings may help in the design and fabrication of smart bone substitutes with the desired potential for bone regeneration through modulating both osteoclastic resorption and osteoblastic synthesis.

Degradation-Kinetics-Controllable and Tissue-Regeneration-Matchable Photocross-linked Alginate Hydrogels for Bone Repair

Photocross-linked alginate hydrogels, due to their biodegradability, biocompatibility, strong control for gelling kinetics in space and time, and admirable adaptability for in situ polymerization with a minimally invasive approach in surgical procedures, have created great expectations in bone regeneration. However, hydrogels with suitable degradation kinetics that can match the tissue regeneration process have not been designed, which limits their further application in bone tissue engineering. Herein, we finely developed an oxidation strategy for alginate to obtain hydrogels with more suitable degradation rates and comprehensively explored their physical and biological performances in vitro and in vivo to further advance the clinical application for the hydrogels in bone repair. The physical properties of the gels can be tuned via tailoring the degree of alginate oxidation. In particular, in vivo degradation studies showed that the degradation rates of the gels were significantly increased by oxidizing alginate. The activity, proliferation, initial adhesion, and osteogenic differentiation of rat and rabbit bone marrow stromal cells (BMSCs) cultured with/in the hydrogels were explored, and the results demonstrated that the gels possessed excellent biocompatibility and that the encapsulated BMSCs were capable of osteogenic differentiation. Furthermore, in vivo implantation of rabbit BMSC-loaded gels into tibial plateau defects of rabbits demonstrated the feasibility of hydrogels with appropriate degradation rates for bone repair. This study indicated that hydrogels with increasingly controllable and matchable degradation kinetics and satisfactory bioproperties demonstrate great clinical potential in bone tissue engineering and regenerative medicine and could also provide references for drug/growth-factor delivery therapeutic strategies for diseases requiring specific drug/growth-factor durations of action.

Effect of Doping Element and Electrolyte’s pH on the Properties of Hydroxyapatite Coatings Obtained by Pulsed Galvanostatic Technique

Hydroxyapatite (HAp) is the most widely used calcium phosphate as a coating on metal implants due to its biocompatibility and bioactivity. The aim of this research is to evaluate the effect of the pH’s electrolyte and doping element on the morphology, roughness, chemical, and phasic composition of hydroxyapatite-based coatings obtained by pulsed galvanostatic electrochemical deposition. As doping elements, both Sr and Ag were selected due to their good osseoinductive character and antibacterial effect, respectively. The electrolytes were prepared at pH 4 and 5, in which specific concentrations of Sr, Ag, and Sr + Ag were added. In terms of morphology, all coatings consist in ribbon-like crystals, which at pH 5 appear to be a little larger. Addition of Sr did not affect the morphology of HAp, while Ag addition has led to the formation of flower-like crystals agglomeration. When both doping elements were added, the flowers like agglomerations caused by the Ag have diminished, indicating the competition between Sr and Ag. X-Ray Diffraction analysis has highlighted that Sr and/or Ag have successfully substituted the Ca in the HAp structure. Moreover, at higher pH, the crystallinity of all HAp coatings was enhanced. Thus, it can be said that the electrolyte’s pH enhances to some extent the properties of HAp-based coatings, while the addition of Sr and/or Ag does not negatively impact the obtained features of HAp, indicating that by using pulsed galvanostatic electrochemical deposition, materials with tunable features dictated by the function of the coated medical device can be designed.

Applying extrusion-based 3D printing technique accelerates fabricating complex biphasic calcium phosphate-based scaffolds for bone tissue regeneration

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Biphasic calcium phosphates offer a chemically similar biomaterial to the natural bone, which can significantly accelerate bone formation and reconstruction.

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Robocasting is a suitable technique to produce porous scaffolds supporting cell viability, proliferation, and differentiation.

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This review discusses materials and methods utilized for BCP robocasting, considering recent advancements and existing challenges in using additives for bioink preparation.

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Commercialization and marketing approach, in-vitro and in-vivo evaluations, biologic responses, and post-processing steps are also investigated.

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Possible strategies and opportunities for the use of BCP toward injured bone regeneration along with clinical applications are discussed.

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The study proposes that BCP possesses an acceptable level of bone substituting, considering its challenges and struggles.

Background

Aim of review

Key scientific concepts of review

Transforming the Degradation Rate of β-tricalcium Phosphate Bone Replacement Using 3-Dimensional Printing

BACKGROUND

β-Tricalcium phosphate (β-TCP) is one of the most common synthetic bone grafting materials utilized in craniofacial reconstruction; however, it is limited by a slow degradation rate. The aim of this study was to leverage 3-dimensional (3D) printing in an effort to accelerate the degradation kinetics of β-TCP.

METHODS

Twenty-two 1-month-old New Zealand white rabbits underwent creation of calvarial and alveolar defects, repaired with 3D-printed β-TCP scaffolds coated with 1000 μM of osteogenic agent dipyridamole. Rabbits were euthanized after 2, 6, and 18 months after surgical intervention. Bone regeneration, scaffold degradation, and bone mechanical properties were quantified.

RESULTS

Histological analysis confirmed the generation of vascularized and organized bone. Microcomputed tomography analysis from 2 to 18 months demonstrated decreased scaffold volume within calvarial (23.6% ± 2.5%, 5.1% ± 2.2%; P < 0.001) and alveolar (21.5% ± 2.2%, 0.2% ± 1.9%; P < 0.001) defects, with degradation rates of 54.6%/year and 90.5%/year, respectively. Scaffold-inducted bone generation within the defect was volumetrically similar to native bone in the calvarium (55.7% ± 6.9% vs 46.7% ± 6.8%; P = 0.064) and alveolus (31.4% ± 7.1% vs 33.8% ± 3.7%; P = 0.337). Mechanical properties between regenerated and native bone were similar.

CONCLUSIONS

Our study demonstrates an improved degradation profile and replacement of absorbed β-TCP with vascularized, organized bone through 3D printing and addition of an osteogenic agent. This novel additive manufacturing and tissue engineering protocol has implications to the future of craniofacial skeletal reconstruction as a safe and efficacious bone tissue engineering method.

Strontium mineralized silk fibroin porous microcarriers with enhanced osteogenesis as injectable bone tissue engineering vehicles

In this paper, silk fibroin (SF) porous microcarriers containing strontium were constructed as injectable bone tissue engineering vehicles. The effects of SF concentration and strontium content on micromorphology, element distribution, strontium ion release and cellular behavior of the constructed microcarriers were investigated. The microcarriers with an open interconnected pore can be fabricated by controlling the concentration of SF. The strontium functionalized SF microcarriers showed the sustained release of strontium ion and allowed bone mesenchymal stem cells (BMSCs) to attach, proliferate and secrete extracellular matrix. Furthermore, the strontium functionalized SF microcarriers improved the osteogenic capability of BMSCs in vitro compared with those microcarriers without sustained release of strontium ion. This study presents a valuable approach to fabricate polymeric microcarriers with the capability of sustained release of strontium ion that show potential in bone tissue engineering applications.

Fabrication of three dimensional bioactive Sr2+ substituted apatite scaffolds by gel-casting technique for hard tissue regeneration

This study aimed to fabricate three-dimensional (3D) bioactive Sr²⁺ -substituted apatite (Sr-HAP) scaffolds prepared by gel-casting with polymer sponge infiltration technique. 3D Sr-HAP scaffolds were prepared as engineering constructs with interconnected porous structure with a pore size of 200-600 μm ranging from a 10 × 10 × 6 mm size was designed. The characterization of X-ray diffraction, field emission scanning electron microscopy, and energy dispersion spectroscopy was utilized in order to evaluate the crystalline phase, structure, and morphology in the interconnected porous of the synthesized Sr-HAP scaffold. The bioactive and biocompatible of the resultant Sr-HAP scaffolds were analyzed by using simulated body fluid solution. Furthermore, the cytotoxicity and proliferation of MG-63 cell lines on the scaffolds were examined in 24 h culture. Furthermore, in vivo experiments demonstrated that the tibia bone defect with 4 mm diameter in rabbits was successfully healed by Sr-HAP porous scaffold after 45 days implantation. The histological images indicated the improved cell proliferation and new bone formation occurred in the porous scaffold treated group. The results indicated that the fabricated Sr-HAP scaffold is a promising capacity to infuse bone regeneration and promote in vivo tissue repair.

Osteogenic capability of strontium and icariin-loaded TiO2 nanotube coatings in vitro and in osteoporotic rats

Titanium (Ti) and Ti alloys are widely used biomaterials, but they lack osteogenic capability for rapid bone integration. To improve osseointegration of Ti implants, TiO2 nanotubes were prepared using the anodizing oxidation technique, and strontium (Sr) combined with icariin (ICA) was loaded on TiO2 nanotube coatings. Cell adhesion and proliferation of MC3T3-E1 cells, alkaline phosphatase (ALP) activity, mineralization of extracellular matrix, and bone formation around titanium implants in ovariectomized rats, were examined separately. The results showed that compared with pure Ti, TiO2 and Sr-loaded TiO2 coatings, the coatings loaded with both Sr and ICA showed better effect on cell adhesion and proliferation, higher ALP activity and more red-stained mineralized nodules. Furthermore, more bone was formed around implants loaded with both Sr and ICA in osteoporotic rats. Therefore, coating with Sr and ICA is valuable for clinical application to strengthen the osseointegration of titanium implants, especially in osteoporotic patients.

In vivo behavior of bioactive glass-based composites in animal models for bone regeneration

This review presents the recent advances and the current state-of-the-art of bioactive glass-based composite biomaterials intended for bone regeneration. Composite materials comprise two (or more) constituents at the nanometre scale, in which typically, one constituent is organic and functions as the matrix phase and the other constituent is inorganic and behaves as the reinforcing phase. Such materials, thereby, more closely resemble natural bio-nanocomposites such as bone. Various glass compositions in combination with a wide range of natural and synthetic polymers have been evaluated in vivo under experimental conditions ranging from unloaded critical-sized defects to mechanically-loaded, weight-bearing sites with highly favourable outcomes. Additional possibilities include controlled release of anti-osteoporotic drugs, ions, antibiotics, pro-angiogenic substances and pro-osteogenic substances. Histological and morphological evaluations suggest the formation of new, highly vascularised bone that displays signs of remodelling over time. With the possibility to tailor the mechanical and chemical properties through careful selection of individual components, as well as the overall geometry (from mesoporous particles and micro-/nanospheres to 3D scaffolds and coatings) through innovative manufacturing processes, such biomaterials present exciting new avenues for bone repair and regeneration.

Aspirin modified strontium-doped β-tricalcium phosphate can accelerate the healing of femoral metaphyseal defects in ovariectomized rats

The purpose was to observe whether local administration Strontium (Sr) and Aspirin (Asp) can enhance the efficacy of β-Tricalcium phosphate(β-TCP) in the treatment of osteoporotic bone defect. The MC3T3-E1 cells were co-cultured with β-TCP, Sr/β-TCP, Asp-Sr/β-TCP scaffold and induced to osteogenesis, and the cell viability, mineralization ability were observed by MTT, Alizarin Red staining(ARS) and Western blotting(WB). Then this scaffolds were implanted into the femoral epiphysis bone defect model of ovariectomized(OVX) rats for 8 weeks. X-ray, Micro-CT, histology and Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis were used to observe the therapeutic effect and explore the possible mechanism. MTT, ARS results show that the cell mineralization and viability of Asp-Sr/β-TCP group is significantly higher than Control group, β-TCP group and Sr/β-TCP group. Protein expression show that the osteogenic protein expression such as ALP、OP、RUNX-2、OC and COL-1 of Asp-Sr/β-TCP group is significantly higher than Control group, β-TCP group and Sr/β-TCP group. X-ray images, Micro-CT and Histological analysis evaluation show that, group Asp-Sr/β-TCP presented the strongest effect on bone regeneration and bone mineralization, when compared with β-TCP group and Sr/β-TCP group. RT-qPCR analysis show that Asp-Sr/β-TCP, β-TCP group and Sr/β-TCP group showed increased BMP2, Smad1, OPG than the OVX group(p < 0.05), while Asp-Sr/β-TCP exhibited decreased TNF-α、IFN-γ and RANKL than the OVX group(p < 0.05). Our current study demonstrated that Asp-Sr/ β-TCP is a scheme for rapid repair of femoral condylar defects, and these effects may be achieved by inhibiting local inflammation and through BMP-2/Smad1 and OPG/RANKL signaling pathway.

Effect of Bone Morphogenic Protein-2-Loaded Mesoporous Strontium Substitution Calcium Silicate/Recycled Fish Gelatin 3D Cell-Laden Scaffold for Bone Tissue Engineering

Bone has a complex hierarchical structure with the capability of self-regeneration. In the case of critical-sized defects, the regeneration capabilities of normal bones are severely impaired, thus causing non-union healing of bones. Therefore, bone tissue engineering has since emerged to solve problems relating to critical-sized bone defects. Amongst the many biomaterials available on the market, calcium silicate-based (CS) cements have garnered huge interest due to their versatility and good bioactivity. In the recent decade, scientists have attempted to modify or functionalize CS cement in order to enhance the bioactivity of CS. Reports have been made that the addition of mesoporous nanoparticles onto scaffolds could enhance the bone regenerative capabilities of scaffolds. For this study, the main objective was to reuse gelatin from fish wastes and use it to combine with bone morphogenetic protein (BMP)-2 and Sr-doped CS scaffolds to create a novel BMP-2-loaded, hydrogel-based mesoporous SrCS scaffold (FGSrB) and to evaluate for its composition and mechanical strength. From this study, it was shown that such a novel scaffold could be fabricated without affecting the structural properties of FGSr. In addition, it was proven that FGSrB could be used for drug delivery to allow stable localized drug release. Such modifications were found to enhance cellular proliferation, thus leading to enhanced secretion of alkaline phosphatase and calcium. The above results showed that such a modification could be used as a potential alternative for future bone tissue engineering research.

Enhanced Proliferation and Differentiation of Human Mesenchymal Stem Cell-laden Recycled Fish Gelatin/Strontium Substitution Calcium Silicate 3D Scaffolds

Cell-encapsulated bioscaffold is a promising and novel method to allow fabrication of live functional organs for tissue engineering and regenerative medicine. However, traditional fabrication methods of 3D scaffolds and cell-laden hydrogels still face many difficulties and challenges. This study uses a newer 3D fabrication technique and the concept of recycling of an unutilized resource to fabricate a novel scaffold for bone tissue engineering. In this study, fish-extracted gelatin was incorporated with bioactive ceramic for bone tissue engineering, and with this we successfully fabricated a novel fish gelatin methacrylate (FG) polymer hydrogel mixed with strontium-doped calcium silicate powder (FGSr) 3D scaffold via photo-crosslinking. Our results indicated that the tensile strength of FGSr was almost 2.5-fold higher as compared to FG thus making it a better candidate for future clinical applications. The in-vitro assays illustrated that the FGSr scaffolds showed good biocompatibility with human Wharton jelly-derived mesenchymal stem cells (WJMSC), as well as enhancing the osteogenesis differentiation of WJMSC. The WJMSC-laden FGSr 3D scaffolds expressed a higher degree of alkaline phosphatase activity than those on cell-laden FG 3D scaffolds and this result was further proven with the subsequent calcium deposition results. Therefore, these results showed that 3D-printed cell-laden FGSr scaffolds had enhanced mechanical property and osteogenic-related behavior that made for a more suitable candidate for future clinical applications.