In vivo study of porous strontium-doped calcium polyphosphate scaffolds for bone substitute applications

Europium-Doped 3D Dimensional Porous Calcium Phosphate Scaffolds as a Strategy for Facilitating the Comprehensive Regeneration of Bone Tissue: In Vitro and In Vivo

In response to the challenges faced by clinicians treating bone defects caused by various factors, various bone repair materials have been investigated, but the efficiency of bone healing still needs to be improved due to the acting of scaffolds only in a single stage of bone tissue regeneration. We investigated the potential of a novel 3D scaffold to support different stages of bone tissue regeneration, including initial inflammation, proliferation, and remodeling. Eu (0, 0.5, 2, 3.5, 5, and 6.5%) was added to calcium polyphosphate to obtain 3D porous network-doped Eu calcium polyphosphate (EuCPP) scaffolds with ideal mechanical strength and pore size. Both in vitro and in vivo experiments proved that Eu3+ released from 5% EuCPP scaffolds could significantly promote the migration and proliferation of bone marrow stromal cells which effectively promote angiogenesis; 5% EuCPP could significantly upregulate the ratio of OPG/RANKL in MC3T3-E1 and promote the secretion of osteogenic-related growth factors (ALP and OPN) from MC3T3-E1, indicating the potential of the scaffold to inhibit bone resorption and promote bone formation. In conclusion, 5% EuCPP possesses the biological properties of pro-angiogenesis, anti-inflammation, pro-osteogenesis, and inhibiting bone resorption, which may provide a sustained positive effect throughout the process of bone tissue repair.

Enhancing Guided Bone Regeneration with a Novel Carp Collagen Scaffold: Principles and Applications

Bone defects resulting from trauma, surgery, and congenital, infectious, or oncological diseases are a functional and aesthetic burden for patients. Bone regeneration is a demanding procedure, involving a spectrum of molecular processes and requiring the use of various scaffolds and substances, often yielding an unsatisfactory result. Recently, the new collagen sponge and its structural derivatives manufactured from European carp (Cyprinus carpio) were introduced and patented. Due to its fish origin, the novel scaffold poses no risk of allergic reactions or transfer of zoonoses and additionally shows superior biocompatibility, mechanical stability, adjustable degradation rate, and porosity. In this review, we focus on the basic principles of bone regeneration and describe the characteristics of an "ideal" bone scaffold focusing on guided bone regeneration. Moreover, we suggest several possible applications of this novel material in bone regeneration processes, thus opening new horizons for further research.

Repair of a rat calvaria defect with injectable strontium (Sr)-doped polyphosphate dicalcium phosphate dehydrate (P-DCPD) ceramic bone grafts

The trace element strontium (Sr) enhances new bone formation. However, delivering Sr, like other materials, in a sustained manner from a ceramic bone graft substitute (BGS) is difficult. We developed a novel ceramic BGS, polyphosphate dicalcium phosphate dehydrate (P-DCPD), which delivers embedded drugs in a sustained pattern. This study assessed the in vitro and in vivo performance of Sr-doped P-DCPD. In vitro P-DCPD and 10%Sr-P-DCPD were nontoxic and eluents from 10%Sr-P-DCPD significantly enhanced osteoblastic MC3T3 cell differentiation. A sustained, zero-order Sr release was observed from 10%Sr-P-DCPD for up to 70 days. When using this BGS in a rat calvaria defect model, both P-DCPD and 10% Sr-P-DCPD were found to be biocompatible and biodegradable. Histologic data from decalcified and undecalcified tissue showed that 10%Sr-P-DCPD had more extensive new bone formation compared with P-DCPD 12-weeks after surgery and the 10%Sr-P-DCPD had more organized new bone and much less fibrous tissue at the defect margins. The new bone was formed on the surface of the degraded ceramic debris within the bone defect area. P-DCPD represented a promising drug-eluting BGS for repair of critical bone defects.

Tailored Coatings for Enhanced Performance of Zinc-Magnesium Alloys in Absorbable Implants

Absorbable metals exhibit potential for next-generation temporary medical implants, dissolving safely in the body during tissue healing and regeneration. Their commercial incorporation could substantially diminish the need for additional surgeries and complications that are tied to permanent devices. Despite extensive research on magnesium (Mg) and iron (Fe), achieving the optimal combination of mechanical properties, biocompatibility, and controlled degradation rate for absorbable implants remains a challenge. Zinc (Zn) and Zn-based alloys emerged as an attractive alternative for absorbable implants, due to favorable combination of in vivo biocompatibility and degradation behavior. Moreover, the development of suitable coatings can enhance their biological characteristics and tailor their degradation process. In this work, four different biodegradable coatings (based on zinc phosphate (ZnP), collagen (Col), and Ag-doped bioactive glass nanoparticles (AgBGNs)) were synthesized by chemical conversion, spin-coating, or a combination of both on Zn-3Mg substrates. This study assessed the impact of the coatings on in vitro degradation behavior, cytocompatibility, and antibacterial activity. The ZnP-coated samples demonstrated controlled weight loss and a decreased corrosion rate over time, maintaining a physiological pH. Extracts from the uncoated, ZnP-coated, and Col-AgBGN-coated samples showed higher cell viability with increasing concentration. Bacterial viability was significantly impaired in all coated samples, particularly in the Col-AgBGN coating. This study showcases the potential of a strategic material-coating combination to effectively tackle multiple challenges encountered in current medical implant technologies by modifying the properties of absorbable metals to tailor patient treatments.

Facilitated osteogenesis of magnesium implant by coating of strontium incorporated calcium phosphate

This study investigated the corrosion resistance and biocompatibility of magnesium coated with strontium-doped calcium phosphate (Sr-CaP) for dental and orthopedic applications. Sr-CaP was coated on biodegradable magnesium using a chemical dipping method. Magnesium coated with Sr-CaP exhibited better corrosion resistance than pure magnesium. Sr-CaP-coated magnesium showed excellent cell proliferation and differentiation. Additionally, new bone formation was confirmed in vivo. Therefore, Sr-CaP-coated magnesium with reduced degradation and improved biocompatibility can be used for orthopedic and dental implant applications.

3D Printed Osteoblast-Alginate/Collagen Hydrogels Promote Survival, Proliferation and Mineralization at Low Doses of Strontium Calcium Polyphosphate

The generation of biomaterials via 3D printing is an emerging biotechnology with novel methods that seeks to enhance bone regeneration. Alginate and collagen are two commonly used biomaterials for bone tissue engineering and have demonstrated biocompatibility. Strontium (Sr) and Calcium phosphate (CaP) are vital elements of bone and their incorporation in composite materials has shown promising results for skeletal repair. In this study, we investigated strontium calcium polyphosphate (SCPP) doped 3D printed alginate/collagen hydrogels loaded with MC3T3-E1 osteoblasts. These cell-laden scaffolds were crosslinked with different concentrations of 1% SCPP to evaluate the effect of strontium ions on cell behavior and the biomaterial properties of the scaffolds. Through scanning electron microscopy and Raman spectroscopy, we showed that the scaffolds had a granular surface topography with the banding pattern of alginate around 1100 cm^-1 and of collagen around 1430 cm^-1. Our results revealed that 2 mg/mL of SCPP induced the greatest scaffold degradation after 7 days and least amount of swelling after 24 h. Exposure of osteoblasts to SCPP induced severe cytotoxic effects after 1 mg/mL. pH analysis demonstrated acidity in the presence of SCPP at a pH between 2 and 4 at 0.1, 0.3, 0.5, and 1 mg/mL, which can be buffered with cell culture medium. However, when the SCPP was added to the scaffolds, the overall pH increased indicating intrinsic activity of the scaffold to buffer the SCPP. Moreover, cell viability was observed for up to 21 days in scaffolds with early mineralization at 0.3, 0.5, and 1 mg/mL of SCPP. Overall, low doses of SCPP proved to be a potential additive in biomaterial approaches for bone tissue engineering; however, the cytotoxic effects due to its pH must be monitored closely.

Does the incorporation of strontium into calcium phosphate improve bone repair? A meta-analysis

Background

The application of calcium phosphate (CaP)-based bone substitutes plays an important role in periodontal regeneration, implant dentistry and alveolar bone reconstruction. The incorporation of strontium (Sr) into CaP-based bone substitutes appears to improve their biological properties, but the reported in vivo bone repair performance is inconsistent among studies. Herein, we conducted a systematic review and meta-analysis to investigate the in vivo performance of Sr-doped materials.

Methods

We searched PubMed, EMBASE (via OVIDSP), and reference lists to identify relevant animal studies. The search, study selection, and data extraction were performed independently by two investigators. Meta-analyses and sub-group analyses were conducted using Revman version 5.4.1. The heterogeneity between studies were assessed by I². Publication bias was investigated through a funnel plot.

Results

Thirty-five studies were finally enrolled, of which 16 articles that reported on new bone formation (NBF) were included in the meta-analysis, covering 31 comparisons and 445 defects. The overall effect for NBF was 2.25 (95% CI 1.61–2.90, p < 0.00001, I² = 80%). Eight comparisons from 6 studies reported the outcomes of bone volume/tissue volume (BV/TV), with an overall effect of 1.42 (95% CI 0.65–2.18, p = 0.0003, I² = 75%). Fourteen comparisons reported on the material remaining (RM), with the overall effect being -2.26 (95% CI − 4.02 to − 0.50, p = 0.0009, I² = 86%).

Conclusions

Our study revealed that Sr-doped calcium phosphate bone substitutes improved in vivo performance of bone repair. However, more studies are also recommended to further verify this conclusion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02092-7.

Strontium Functionalization of Biomaterials for Bone Tissue Engineering Purposes: A Biological Point of View

Strontium (Sr) is a trace element taken with nutrition and found in bone in close connection to native hydroxyapatite. Sr is involved in a dual mechanism of coupling the stimulation of bone formation with the inhibition of bone resorption, as reported in the literature. Interest in studying Sr has increased in the last decades due to the development of strontium ranelate (SrRan), an orally active agent acting as an anti-osteoporosis drug. However, the use of SrRan was subjected to some limitations starting from 2014 due to its negative side effects on the cardiac safety of patients. In this scenario, an interesting perspective for the administration of Sr is the introduction of Sr ions in biomaterials for bone tissue engineering (BTE) applications. This strategy has attracted attention thanks to its positive effects on bone formation, alongside the reduction of osteoclast activity, proven by in vitro and in vivo studies. The purpose of this review is to go through the classes of biomaterials most commonly used in BTE and functionalized with Sr, i.e., calcium phosphate ceramics, bioactive glasses, metal-based materials, and polymers. The works discussed in this review were selected as representative for each type of the above-mentioned categories, and the biological evaluation in vitro and/or in vivo was the main criterion for selection. The encouraging results collected from the in vitro and in vivo biological evaluations are outlined to highlight the potential applications of materials’ functionalization with Sr as an osteopromoting dopant in BTE.

[In vivo study of strontium-doped calcium phosphate cement for biological properties]

OBJECTIVE

To evaluate the biocompatibility and osteogenic effect of new calcium phosphate cement (CPC) in vivo and to provide experimental basis for its further clinical application.

METHODS

Thirty New Zealand white rabbits were randomly divided into four groups: CPC group, CPC+Bio-Oss group, Bio-Oss group and blank control group. Bone defect models of 6 mm in diameter and 7 mm in depth were made on the lateral condyle of bilateral hind legs of the rabbits. CPC, Bio-Oss and CPC+Bio-Oss mixture were implanted into the bone defect according to the group, and the mass ratio of CPC and Bio-Oss was 4 ∶ 1. The experimental animals were sacrificed the 4th, 12th and 24th week after operation. The tissue around the bone defect was taken for histological evaluation by H&E staining. Bone ingrowth fraction (BIF) was calculated. The expression of BMP-2 and COL-Ⅰ was detected by immunohis- tochemical staining by calculating the mean optical density (MOD) of the positive area the 4th week after operation, and the bone healing of each group was evaluated at different time points. The measurement data were analyzed by one-way ANOVA and LSD test was used for multiple comparison of the differences between the means by SPSS 19.0. P < 0.05 was considered to be statistically significant.

RESULTS

The results of H&E staining showed that the BIF values of CPC group, CPC + Bio-Oss group and Bio-Oss group were significantly higher than those of blank control group at the same time point (P < 0.01). The BIF values of CPC group were lower than those of Bio-Oss group and CPC + Bio-Oss group (P < 0.01). There was no significant difference between CPC + Bio-Oss group and Bio-Oss group. Immunohistochemical staining showed that the MOD values of BMP-2 and COL-Ⅰ in CPC group were higher than those in blank control group, but lower than those in Bio-Oss group and CPC+Bio-Oss group (P < 0.01). There was no significant difference between BMP-2 and COL-Ⅰ in CPC+Bio-Oss group and Bio-Oss group.

CONCLUSION

The new calcium phosphate cement has good biocompatibility and can promote early osteogenesis with stable and long-term effect.

Comparing the physicochemical properties of dicalcium phosphate dihydrate (DCPD) and polymeric DCPD (P-DCPD) cement particles

We developed a new and injectable poly-dicalcium phosphate dihydrate (P-DCPD) forming cement. The key structural difference between P-DCPD and classical DCPD is that P-DCPD is composed of interconnected P-DCPD crystals by interlocking to the polyphosphate chains. In contrast, DCPD is composed of a package of DCPD crystals with weak mutual ionic bonding. The purpose of this continuing study was to compare the physicochemical properties between P-DCPD and DCPD cement particles. Data collected from SEM, X-ray diffraction, and Raman Spectroscopy approaches demonstrated that P-DCPD has a more stable chemical structure than DCPD as evidenced by much less transformation to hydroxyapatite (HA) during setting. Nanoindentation showed a similar hardness while the elastic modulus of P-DCPD is much lower than DCPD that might be due to the much less HA transformation of P-DCPD. P-DCPD has much lower zeta potential and less hydrophilicity than DCPD because of its entangled and interconnected polyphosphate chains. It is expected that superhydrophilic DCPD undergoes faster dissolution than P-DCPD in an aqueous environment. Another interesting finding is that the pH of eluent from P-DCPD is more neutral (6.6-7.1) than DCPD (5.5-6.5). More extensive experiments are currently underway to further evaluate the potential impacts of the different physiochemical performance observed of P-DCPD and DCPD cement particles on the biocompatibility, degradation behavior and bone defect healing efficacy both in vivo and in vitro.

A distinctive release profile of vancomycin and tobramycin from a new and injectable polymeric dicalcium phosphate dehydrate cement (P-DCPD)

A novel injectable polymeric dicalcium phosphate dehydrate (P-DCPD) cement was developed with superior mechanical strength and excellent cohesion. The purpose of this study was to assess the in vitro performance of P-DCPD loaded with vancomycin (VAN-P), tobramycin (TOB-P) and combination of both (VAN/TOB-P) (10%, w/w). There is a distinctive release profile between VAN and TOB. VAN-P showed decreased initial burst (<30% within 3 d) and sustained VAN release (76% in 28 d). In the presence of TOB (VAN/TOB-P), >90% of VAN was released within 3 d (p < 0.05). Slow and limited TOB release was observed both in TOB-P (<5%) and in TOB/VAN-P (<1%) over 28 d. Zone of inhibition (ZOI) of Staphylococcus aureus growth showed that eluents collected from VAN-P had stronger and longer ZOI (28 d) than that from TOB-P (14 d, p < 0.05). Direct contact of VAN-P, TOB-P and VAN/TOB-P cements displayed persistent and strong ZOI for >3 weeks. Interestingly, the cement residues (28 d after drug release) still maintained strong ZOI ability. P-DCPD with or without antibiotics loading were nontoxic and had no inferior impacts on the growth of osteoblastic MC3T3 cells. VAN-P and TOB-P were injectable. No significant influence on setting time was observed in both VAN-P (11.7 ± 1.9 min) and VAN/TOB-P (10.8 ± 1.5 min) as compared to control (12.2 ± 2.6 min). We propose that a distinctive release profile of VAN and TOB observed is mainly due to different distribution pattern of VAN and TOB within P-DCPD matrix. A limited release of TOB might be due to the incorporation of TOB inside the crystalline lattice of P-DCPD crystals. Our data supported that the bactericidal efficacy of antibiotics-loaded P-DCPD is not only depend on the amount and velocity of antibiotics released, but also probably more on the direct contact of attached bacteria on the degrading cement surface.

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.

Sr-HA scaffolds fabricated by SPS technology promote the repair of segmental bone defects

BACKGROUND

Ideal bone defect repair scaffolds should be biodegradable, biocompatible, bioactive, porous, and provide adequate mechanical support. However, it is challenging to fabricate such an ideal bone repair scaffold. Previously, we showed that 5 wt.% strontium-doped hydroxyapatite (Sr-HA) scaffolds prepared by spark plasma sintering (SPS) technology exhibited good biocompatibility. Moreover, unlike pure hydroxyapatite (HA) scaffolds, HA scaffolds containing strontium (Sr) exhibited superior bioactivity, higher proliferation rate of BMSCs and MG-63 osteoblast cells, as well as enhanced BMSCs differentiation.

METHODS

In this study, we prepared pure HA scaffolds and 5 wt.% strontium containing Sr-HA scaffolds by SPS technology without adhesive, ammonium bicarbonate as pore former. Subsequently, scanning electron microscope (SEM) and X-Ray diffraction (XRD) were used to characterize the properties of Sr-HA and HA scaffolds. The ability of the scaffolds to repair bone defects was evaluated using a critical-sized rabbit tibia-bone defect rabbit model. Thirty 3-month-old New Zealand white rabbits were randomly divided into three groups (blank control group, Sr-HA scaffolds implanted group and HA scaffolds implanted group) with 10 rabbits in each group. These rabbits are sacrificed after 8 weeks and 16 weeks of surgery, and the repair effects of each scaffold were evaluated with X-ray, micro-CT, and HE staining. The three-point bending test was employed to assess the mechanical property of repaired bones.

RESULTS

XRD pattern indicated that Sr-HA and HA scaffolds possess a similar crystal structure after sintering, and that incorporation of strontium did not form impure phase. SEM showed that the porosity of Sr-HA and HA scaffolds was about 40 %. Universal Testing Machine tests showed that Sr-HA scaffolds had better compressive strength than HA scaffolds. Bone defect was obvious, and the fibrous tissue was formed in the bone defects of rabbits in the blank control group after 8 weeks of surgery. Sr-HA and HA scaffolds enhanced osteointegration of the host bone, and extensive woven bone was formed on the surface of the Sr-HA scaffolds. After 16 weeks, the bone strump became blunt and a small amount of callus was formed in the blank control group. Comparatively, the scaffolds were substantially degraded in the Sr-HA scaffolds implanted group while scaffolds shadows still were observed in the HA implanted group. Bone remodeling and cavity recanalization were completely developed in the Sr-HA scaffolds group. The compressive strength of repaired bone in the Sr-HA scaffolds implantation group was higher than that of HA scaffolds implantation group after 8 weeks and 16 weeks of surgery.

CONCLUSIONS

Our results show that the Sr-HA composite scaffolds can effectively repair bone defects and have good biodegradable properties.

Effects of Strontium-Doped β-Tricalcium Scaffold on Longitudinal Nuclear Factor-Kappa Beta and Vascular Endothelial Growth Factor Receptor-2 Promoter Activities during Healing in a Murine Critical-Size Bone Defect Model

It was hypothesized that strontium (Sr)-doped β-tricalcium phosphate (TCP)-based scaffolds have a positive effect on the regeneration of large bone defects (LBD). Readouts in our mice models were nuclear factor-kappa beta (NF-κB) activity and vascular endothelial growth factor receptor-2 (VEGFR-2) promoter activity during the healing process. A 2-mm critical-size femoral fracture was performed in transgenic NF-κB- and VEGFR-2-luciferase reporter mice. The fracture was filled with a 3D-printed β-TCP scaffold with or without Sr. A bioluminescence in-vivo imaging system was used to sequentially investigate NF-κB and VEGFR-2 expression for two months. After sacrifice, soft and osseous tissue formation in the fracture sites was histologically examined. NF-κB activity increased in the β-TCP + Sr group in the latter stage (day 40–60). VEGFR-2 activity increased in the + Sr group from days 0–15 but decreased and showed significantly less activity than the β-TCP and non-scaffold groups from days 40–60. The new bone formation and soft tissue formation in the + Sr group were significantly higher than in the β-TCP group, whereas the percentage of osseous tissue formation in the β-TCP group was significantly higher than in the β-TCP + Sr group. We analyzed longitudinal VEGFR-2 promoter activity and NF-κB activity profiles, as respective agents of angiogenesis and inflammation, during LBD healing. The extended inflammation phase and eventually more rapid resorption of scaffold caused by the addition of strontium accelerates temporary bridging of the fracture gaps. This finding has the potential to inform an improved treatment strategy for patients who suffer from osteoporosis.

Recent developments in strontium-based biocomposites for bone regeneration

Recent advances in biomaterial designing techniques offer immense support to tailor biomimetic scaffolds and to engineer the microstructure of biomaterials for triggering bone regeneration in challenging bone defects. The current review presents the different categories of recently explored strontium-integrated biomaterials, including calcium silicate, calcium phosphate, bioglasses and polymer-based synthetic implants along with their in vivo bone formation efficacies and/or in vitro cell responses. The role and significance of controlled drug release scaffold/carrier design in strontium-triggered osteogenesis was also comprehensively described. Furthermore, the effects of stem cells and growth factors on bone remodeling are also elucidated.

Effect of solution condition on hydroxyapatite formation in evaluating bioactivity of B2O3 containing 45S5 bioactive glasses

The effects of testing solutions and conditions on hydroxyapatite (HAp) formation as a means of in vitro bioactivity evaluation of B2O3 containing 45S5 bioactive glasses were systematically investigated. Four glass samples prepared by the traditional melt and quench process, where SiO2 in 45S5 was gradually replaced by B2O3 (up to 30%), were studied. Two solutions: the simulated body fluid (SBF) and K2HPO4 solutions were used as the medium for evaluating in vitro bioactivity through the formation of HAp on glass surface as a function of time. It was found that addition of boron oxide delayed the HAp formation in both SBF and K2HPO4 solutions, while the reaction between glass and the K2HPO4 solution is much faster as compared to SBF. In addition to the composition and medium effects, we also studied whether the solution treatments (e.g., adjusting to maintain a pH of 7.4, refreshing solution at certain time interval, and no disturbance during immersion) affect HAp formation. Fourier transform infrared spectrometer (FTIR) equipped with an attenuated total reflection (ATR) sampling technique and scanning electron microscopy (SEM) were conducted to identify HAp formation on glass powder surfaces and to observe HAp morphologies, respectively. The results show that refreshing solution every 24 h produced the fastest HAp formation for low boron-containing samples when SBF was used as testing solution, while no significant differences were observed when K2HPO4 solution was used. This study thus suggests the testing solutions and conditions play an important role on the in vitro bioactivity testing results and should be carefully considered when study materials with varying bioactivities.

Bioactive glass coatings on metallic implants for biomedical applications

Metallic implant materials possess adequate mechanical properties such as strength, elastic modulus, and ductility for long term support and stability in vivo. Traditional metallic biomaterials, including stainless steels, cobalt-chromium alloys, and titanium and its alloys, have been the gold standards for load-bearing implant materials in hard tissue applications in the past decades. Biodegradable metals including iron, magnesium, and zinc have also emerged as novel biodegradable implant materials with different in vivo degradation rates. However, they do not possess good bioactivity and other biological functions. Bioactive glasses have been widely used as coating materials on the metallic implants to improve their integration with the host tissue and overall biological performances. The present review provides a detailed overview of the benefits and issues of metal alloys when used as biomedical implants and how they are improved by bioactive glass-based coatings for biomedical applications.

Enhanced osteogenesis and angiogenesis by PCL/chitosan/Sr-doped calcium phosphate electrospun nanocomposite membrane for guided bone regeneration

Membranes play pivotal role in guided bone regeneration (GBR) technique for reconstruction alveolar bone. GBR membrane that is able to stimulate both osteogenic and angiogenic differentiation of cells may be more effective in clinic practice. Herein, we fabricated the Sr-doped calcium phosphate/polycaprolactone/chitosan (Sr-CaP/PCL/CS) nanohybrid fibrous membrane by incorporating 20 wt% bioactive Sr-CaP nanoparticles into PCL/CS matrix via one-step electrospinning method, in order to endow the membrane with stimulation of osteogenesis and angiogenesis. The physicochemical properties, mechanical properties, Sr²⁺ release behavior, and the membrane stimulate bone mesenchymal stem cell (BMSCs) differentiation were evaluated in comparison with PCL/CS and CaP/PCL/CS membranes. The SEM images revealed that the nanocomposite membrane mimicked the extracellular matrix structure. The release curve presented a 28-day long continuous release of Sr²⁺ and concentration which was certified in an optimal range for positive biological effects at each timepoint. The in vitro cell culture experiments certified that the Sr-CaP/PCL/CS membrane enjoyed excellent biocompatibility and remarkably promoted rat bone mesenchymal stem cell (BMSCs) adhesion and proliferation. In terms of osteogenic differentiation, BMSCs seeded on the Sr-CaP/PCL/CS membrane showed a higher ALP activity level and a better matrix mineralization. What's more, the synergism of the Sr²⁺ and CaP from the Sr-CaP/PCL/CS membrane enhanced BMSCs angiogenic differentiation, herein resulting in the largest VEGF secretion amount. Consequently, the Sr-CaP/PCL/CS nanohybrid electrospun membrane has promising applications in GBR.

Progress and Applications of Polyphosphate in Bone and Cartilage Regeneration

Patients with bone and cartilage defects due to infection, tumors, and trauma are quite common. Repairing bone and cartilage defects is thus a major problem for clinicians. Autologous and artificial bone transplantations are associated with many challenges, such as limited materials and immune rejection. Bone and cartilage regeneration has become a popular research topic. Inorganic polyphosphate (polyP) is a widely occurring biopolymer with high-energy phosphoanhydride bonds that exists in organisms from bacteria to mammals. Much data indicate that polyP acts as a regulator of gene expression in bone and cartilage tissues and exerts morphogenetic effects on cells involved in bone and cartilage formation. Exposure of these cells to polyP leads to the increase of cytokines that promote the differentiation of mesenchymal stem cells into osteoblasts, accelerates the osteoblast mineralization process, and inhibits the differentiation of osteoclast precursors to functionally active osteoclasts. PolyP-based materials have been widely reported in in vivo and in vitro studies. This paper reviews the current cellular mechanisms and material applications of polyP in bone and cartilage regeneration.

Effect of copper substitution on the local chemical structure and dissolution property of copper-doped β-tricalcium phosphate

Substitution of inorganic ions into β-tricalcium phosphate (β-TCP) is a well-known approach for facilitating biological functions of bioceramics. However, the dissolution mechanism of those β-TCPs is still under intensive debates. In the present study, the effect of copper substitution into β-TCP crystal structure on the local chemical structure and dissolution property of the copper-doped β-TCP (CuTCP) was investigated to clarify the dissolution mechanism of β-TCP. A copper-dependent decrease in the dissolution rate of CuTCP with time was observed. The ¹H → ³¹P nuclear magnetic resonance (NMR) spectra of 10 mol% copper-doped β-TCP after the dissolution test demonstrated an amorphous hydrated layer on the surface of β-TCP core particles, which contained hydroxyapatite and dicalcium phosphate dihydrate and anhydrate. As such, all the dissolution curves could be curve-fitted by a heterogeneous dissolution model composing of fast and slow dissolution components. Overall, dissolution mechanism could be proposed as follows: the CuTCP particles initially dissolved by hydrolysis based on the fast dissolution component. Subsequently, the amorphous hydrated layers were formed on their surface, and caused the diffusion-controlled dissolution. As the result, the slow dissolution component would be dominant, and led to the decreased dissolution rate. STATEMENT OF SIGNIFICANCE: Understanding the dissolution mechanism of copper doped β-tricalcium phosphate (CuTCP) is crucial for designing an angiogenetic controlled copper release CuTCP for therapeutic biomaterials. However, dissolution mechanism of β-TCP or CuTCP is still under intensive debates. This study demonstrated for the first time, that amorphous hydrated layers were formed on the CuTCP particle surface during its dissolution process, which caused a diffusion-controlled dissolution, and decreased the dissolution rate of CuTCP. This work not only provided a novel dissolution mechanism of β-TCP or CuTCP, but also a new finding for designing an angiogenetic controlled copper release CuTCP for therapeutic biomaterials.

Strontium ranelate simultaneously improves the radiopacity and osteogenesis of calcium phosphate cement

In a minimally invasive surgery of osteoporotic fractures, high radiopacity is necessary to monitor the delivery and positioning of injectable cements and good osteogenesis is indispensable. In this work, strontium ranelate (SrR), an agent for treating osteoporosis, is firstly used as a radiopaque agent for calcium phosphate cement (CPC). The addition of SrR does not affect the hydration products of CPC, but prolonged the setting time and decreased the compressive strength. The injectability of the cement was higher than 85% when SrR content is more than 10 wt%. The radiopacity of CPC is significantly improved by SrR and higher than cortical bone when the content of SrR is more than 5 wt%. The concentration of Sr ions released from CPC is increased by the increasing content of SrR, which is among 17-1329 μM. Moreover, CPCs with SrR significantly promote the osteogenic differentiation of mouse bone marrow mesenchymal stem cells and inhibit the osteoclastogenic differentiation of RAW264.7 cells. Based on its good radiopacity and osteogenesis, suppressed osteoclastogenesis and appropriate physicochemical properties, the radiopaque CPC with more than 10 wt% SrR is prospective to be a promising biomaterial for osteoporotic fracture repairing in minimal invasive surgery.

The Role of Strontium Enriched Hydroxyapatite and Tricalcium Phosphate Biomaterials in Osteoporotic Bone Regeneration

Background: Strontium (Sr) enriched biomaterials have been used to improve bone regeneration in vivo. However, most studies provide only two experimental groups. The aim of our study was to compare eleven different bone sample groups from osteoporotic and healthy rabbits’ femoral neck, as it is the most frequent osteoporotic fracture in humans. Methods: Osteoporotic bone defects were filled with hydroxyapatite 30% (HA) and tricalcium phosphate 70% (TCP), 5% Sr-enriched HA30/TCP70, HA70/TCP30, or Sr-HA70/TCP30 granules and were compared with intact leg, sham surgery and healthy non-operated bone. Expression of osteoprotegerin (OPG), nuclear factor kappa beta 105 (NFkB-105), osteocalcin (OC), bone morphogenetic protein 2/4 (BMP-2/4), collagen I (Col-1α), matrix metalloproteinase 2 (MMP-2), tissue inhibitor of matrix metalloproteinase 2 (TIMP-2), interleukin 1 (IL-1) and interleukin 10 (IL-10) was analyzed by histomorphometry and immunohistochemistry. Results: Our study showed that Sr-HA70/TCP30 induced higher expression of all above-mentioned factors compared to intact leg and even higher expression of OC, MMP-2 and NFkB-105 compared to Sr-HA30/TCP70. HA70/TCP30 induced higher level of NFkB-105 and IL-1 compared to HA30/TCP70. Conclusion: Sr-enriched biomaterials improved bone regeneration at molecular level in severe osteoporosis and induced activity of the factors was higher than after pure ceramic, sham or even healthy rabbits.

Potencial of different hydroxyapatites as biomaterials in the bone remodeling

PURPOSE

To analyze the therapeutic potentials of different hydroxyapatites used for the correction of bone defects in rats.

METHODS

Forty rats, male, albino wistar, were distributed in 4 groups. They were submitted to a 3.5 mm defect in tibia. They received low purity hydroxyapatite, Strontium hydroxyapatite and hydroxyapatite doped with gallium, having a seven day evaluation time. Histopathology slides were stained with hematoxylin-eosin, for morphological evaluation. Were analyzed inflammatory processes, necrosis, presence of osteoclasts and osteoblasts, presence of the material, presence of white cells, neovascularization and bone neoformation.

RESULTS

It was observed that the groups HAPSr and HAPGa, presented better results of trabecular bone, hyaline cartilage and bone marrow more organized.

CONCLUSION

There was improvement in the repair of the bone defect produced, showing that these hydroxyapatites are effective osteoinductive, osteoconductive, osteintegrant agents and have biocompatibility, and may be indicated for use in defect repairs.

Marine Collagen/Apatite Composite Scaffolds Envisaging Hard Tissue Applications

The high prevalence of bone defects has become a worldwide problem. Despite the significant amount of research on the subject, the available therapeutic solutions lack efficiency. Autografts, the most commonly used approaches to treat bone defects, have limitations such as donor site morbidity, pain and lack of donor site. Marine resources emerge as an attractive alternative to extract bioactive compounds for further use in bone tissue-engineering approaches. On one hand they can be isolated from by-products, at low cost, creating value from products that are considered waste for the fish transformation industry. One the other hand, religious constraints will be avoided. We isolated two marine origin materials, collagen from shark skin (Prionace glauca) and calcium phosphates from the teeth of two different shark species (Prionace glauca and Isurus oxyrinchus), and further proposed to mix them to produce 3D composite structures for hard tissue applications. Two crosslinking agents, 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride/N-Hydroxysuccinimide (EDC/NHS) and hexamethylene diisocyanate (HMDI), were tested to enhance the scaffolds' properties, with EDC/NHS resulting in better properties. The characterization of the structures showed that the developed composites could support attachment and proliferation of osteoblast-like cells. A promising scaffold for the engineering of bone tissue is thus proposed, based on a strategy of marine by-products valorisation.

Biomimetic mineralized strontium-doped hydroxyapatite on porous poly(l-lactic acid) scaffolds for bone defect repair

Introduction

poly(l-lactic acid) (PLLA) has been approved for clinical use by the US Food and Drug Administration (FDA); however, their stronger hydrophobicity and relatively fast degradation rate restricted their widespread application. In consideration of the composition of bone, the inorganic–organic composite has a great application prospect in bone tissue engineering. Many inorganic–organic composite scaffolds were prepared by directly mixing the active ingredient, but this method is uncontrolled and will lead to lack of homogeneity in the polymer matrix. Strontium (Sr) is an admirable addition to improve the bioactivity and bone induction of hydroxyapatite (HA). To our knowledge, the application of biomimetic mineralized strontium-doped hydroxyapatite on porous poly(l-lactic acid) (Sr-HA/PLLA) scaffolds for bone defect repair has never been reported till date. Biomimetic mineralized Sr-HA/PLLA porous scaffold was developed in this study. The results indicated that the Sr-HA/PLLA porous scaffold could improve the surface hydrophobicity, reduce the acidic environment of the degradation, and enhance the osteoinductivity; moreover, the ability of protein adsorption and the modulus of compression were increased. The results also clearly showed the effectiveness of the Sr-HA/PLLA porous scaffold in promoting cell adhesion, proliferation, and alkaline phosphatase (ALP) activity. The micro computed tomography (micro-CT) results showed that more new bones were formed by Sr-HA/PLLA porous scaffold treatment. The histological results confirmed the osteoinductivity of the Sr-HA/PLLA porous scaffold. The results suggested that the Sr-HA/PLLA porous scaffold has a good application prospect in bone tissue engineering in the future.

Purpose

The purpose of this study was to promote the bone repair.

Materials and methods

Surgical operation of rabbits was carried out in this study.

Results

The results showed that formation of a large number of new bones by the Sr-HA/PLLA porous scaffold treatment is possible.

Conclusion

Biomimetic mineralized Sr-HA/PLLA porous scaffold could effectively promote the restoration of bone defects in vivo.

Effect of microporosity on scaffolds for bone tissue engineering

Microporosity has a critical role in improving the osteogenesis of scaffolds for bone tissue engineering. Although the exact mechanism, by which it promotes new bone formation, is not well recognized yet, the related hypothesis can be found in many previous studies. This review presents those possible mechanisms about how the microporosity enhances the osteogenic-related functions of cells in vitro and the osteogenic activity of scaffolds in vivo. In summary, the increased specific surface areas by microporosity can offer more protein adsorption sites and accelerate the release of degradation products, which facilitate the interactions between scaffolds and cells. Meanwhile, the unique surface properties of microporous scaffolds have a considerable effect on the protein adsorption. Moreover, capillary force generated by the microporosity can improve the attachment of bone-related cells on the scaffolds surface, and even make the cells achieve penetration into the micropores smaller than them. This review also pays attention to the relationship between the biological and mechanical properties of microporous scaffolds. Although lots of achievements have been obtained, there is still a lot of work to do, some of which has been proposed in the conclusions and perspectives part.

The Feasibility and Functional Performance of Ternary Borate-Filled Hydrophilic Bone Cements: Targeting Therapeutic Release Thresholds for Strontium

We examine the feasibility and functionality of hydrophilic modifications to a borate glass reinforced resin composite; with the objective of meeting and maintaining therapeutic thresholds for Sr release over time, as a potential method of incorporating antiosteoporotic therapy into a vertebroplasty material. Fifteen composites were formulated with the hydrophilic agent hydroxyl ethyl methacrylate (HEMA, 15, 22.5, 30, 37.5 or 45 wt% of resin phase) and filled with a borate glass (55, 60 or 65 wt% of total cement) with known Sr release characteristics. Cements were examined with respect to degree of cure, water sorption, Sr release, and biaxial flexural strength over 60 days of incubation in phosphate buffered saline. While water sorption and glass degradation increased with increasing HEMA content, Sr release peaked with the 30% HEMA compositions, scanning electron microscope (SEM) imaging confirmed the surface precipitation of a Sr phosphate compound. Biaxial flexural strengths ranged between 16 and 44 MPa, decreasing with increased HEMA content. Degree of cure increased with HEMA content (42 to 81%), while no significant effect was seen on setting times (209 to 263 s). High HEMA content may provide a method of increasing monomer conversion without effect on setting reaction, providing sustained mechanical strength over 60 days.

* 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 vivo and clinical application of strontium-enriched biomaterials for bone regeneration: A systematic review

OBJECTIVES

This systematic review aimed to assess the in vivo and clinical effect of strontium (Sr)-enriched biomaterials in bone formation and/or remodelling.

METHODS

A systematic search was performed in Pubmed, followed by a two-step selection process. We included in vivo original studies on Sr-containing biomaterials used for bone support or regeneration, comparing at least two groups that only differ in Sr addition in the experimental group.

RESULTS

A total of 572 references were retrieved and 27 were included. Animal models were used in 26 articles, and one article described a human study. Osteoporotic models were included in 11 papers. All articles showed similar or increased effect of Sr in bone formation and/or regeneration, in both healthy and osteoporotic models. No study found a decreased effect. Adverse effects were assessed in 17 articles, 13 on local and four on systemic adverse effects. From these, only one reported a systemic impact from Sr addition. Data on gene and/or protein expression were available from seven studies.

CONCLUSIONS

This review showed the safety and effectiveness of Sr-enriched biomaterials for stimulating bone formation and remodelling in animal models. The effect seems to increase over time and is impacted by the concentration used. However, included studies present a wide range of study methods. Future work should focus on consistent models and guidelines when developing a future clinical application of this element.Cite this article: N. Neves, D. Linhares, G. Costa, C. C. Ribeiro, M. A. Barbosa. In vivo and clinical application of strontium-enriched biomaterials for bone regeneration: A systematic review. Bone Joint Res 2017;6:366-375. DOI: 10.1302/2046-3758.66.BJR-2016-0311.R1.

Strontium doped poly-ε-caprolactone composite scaffolds made by reactive foaming

In the reconstruction and regeneration of bone tissue, a primary goal is to initiate bone growth and to stabilize the surrounding bone. In this regard, a potentially useful component in biomaterials for bone tissue engineering is strontium, which acts as cationic active agent, triggering certain intracellular pathways and acting as so called dual action bone agent which inhibits bone resorption while stimulating bone regeneration. In this study we established a novel processing for the foaming of a polymer (poly-ε-caprolactone) and simultaneous chemical reaction of a mixture of calcium and strontium hydroxides to the respective carbonates using supercritical carbon dioxide. The resultant porous composite scaffold was optimized in composition and strontium content and was characterized via different spectroscopic (infrared and Raman spectroscopy, energy dispersive X-ray spectroscopy), imaging (SEM, μCT), mechanical testing and in vitro methods (fluorescence vital staining, MTT-assay). As a result, the composite scaffold showed good in vitro biocompatibility with partly open pore structure and the expected chemistry. First mechanical testing results indicate sufficient mechanical stability to support future in vivo applications.

Highly controlled coating of strontium-doped hydroxyapatite on electrospun poly(ɛ-caprolactone) fibers

Electrospun fibers show great potential as scaffolds for bone tissue engineering due to their architectural biomimicry to the extracellular matrix (ECM). Cation substitution of strontium for calcium in hydroxyapatite (HAp) positively influences the mechanism of bone remodeling including enhancing bone regeneration and reducing bone resorption. The objective of this study was to attach strontium-doped HAp (SrHAp) to electrospun poly(ɛ-caprolactone) (PCL) fibers for creation of novel composite scaffolds that can not only mimic the architecture and composition of ECM but also affect bone remodeling favorably. We demonstrated for the first time the highly controlled SrHAp coatings on electrospun PCL fibers. We showed the reproducible manufacturing of composite fiber scaffolds with controllable thickness, composition, and morphology of SrHAp coatings. We further showed that the released strontium and calcium cations from coatings could reach effective concentrations within 1 day and endure more than 28 days. Additionally, the Young's modulus of the SrHAp-coated PCL fibers was up to around six times higher than that of raw fibers dependent on the coating thickness and composition. Together, this novel class of composite fiber scaffolds may hold great promise for bone regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 753-763, 2017.

Structural analysis of xSrO-(50 - x)CaO-50P2O5 glasses with x=0, 5, or 10 mol% for potential use in a local delivery system for osteomyelitis treatment

The introduction of ions into a local delivery matrix is one method of managing degradation and subsequent release of the incorporated therapeutic agents. Of interest in this study was whether we could modify the structural nature of calcium polyphosphate (CPP) glass and the subsequent therapeutic potential of this local delivery matrix with inclusion of strontium (Sr). We found that adding 10 mol% Sr significantly increased the density and chain length of the glass. There was no significant impact of Sr doping on the subsequent loading of vancomycin into the matrix, or the matrix porosity. The noted differences in structural stability, ion release, and vancomycin release between the un-doped CPP matrices and 10 mol% Sr-doped CPP matrices in vitro are likely a result of a decrease in glass disorder upon Sr addition to the glass and preferential retention of Sr over Ca during matrix degradation. This study has provided further evidence that Sr incorporation may serve to both manipulate antibiotic release from the amorphous CPP matrix and provide a potential source of therapeutic ions for enhanced bone regeneration.

Osteoinduction of bone grafting materials for bone repair and regeneration

Regeneration of bone defects caused by trauma, infection, tumours or inherent genetic disorders is a clinical challenge that usually necessitates bone grafting materials. Autologous bone or autograft is still considered the clinical "gold standard" and the most effective method for bone regeneration. However, limited bone supply and donor site morbidity are the most important disadvantages of autografting. Improved biomaterials are needed to match the performance of autograft as this is still superior to that of synthetic bone grafts. Osteoinductive materials would be the perfect candidates for achieving this task. The aim of this article is to review the different groups of bone substitutes in terms of their most recently reported osteoinductive properties. The different factors influencing osteoinductivity by biomaterials as well as the mechanisms behind this phenomenon are also presented, showing that it is very limited compared to osteoinductivity shown by bone morphogenetic proteins (BMPs). Therefore, a new term to describe osteoinductivity by biomaterials is proposed. Different strategies for adding osteoinductivity (BMPs, stem cells) to bone substitutes are also discussed. The overall objective of this paper is to gather the current knowledge on osteoinductivity of bone grafting materials for the effective development of new graft substitutes that enhance bone regeneration.

Understanding of dopant-induced osteogenesis and angiogenesis in calcium phosphate ceramics

General trends in synthetic bone grafting materials are shifting towards approaches that can illicit osteoinductive properties. Pharmacologics and biologics have been used in combination with calcium phosphate (CaP) ceramics, however, they have recently become the target of scrutiny over safety. The importance of trace elements in natural bone health is well documented. Ions, for example, lithium, zinc, magnesium, manganese, silicon, strontium, etc., have been shown to increase osteogenesis and neovascularization. Incorporation of dopants (trace metal ions) into CaPs can provide a platform for safe and efficient delivery in clinical applications where increased bone healing is favorable. This review highlights the use of trace elements in CaP biomaterials, and offers an insight into the mechanisms of how metal ions can enhance both osteogenesis and angiogenesis.

Biomimetic preparation of trace element-codoped calcium phosphate for promoting osteoporotic bone defect repair

Specific implants to speedily regenerate critical-sized osteoporotic bone defects (COBDs) are a major clinical need. However, little progress in methods focusing on biological repair has been reported. We developed a biomimetic mineralization method to prepare trace element-codoped calcium phosphate (CaP) particles via hydrothermal treatment of modified simulated body fluid (SBF) with the addition of binary to quaternary trace elements. The morphology, structure, and composition of the particles were characterized by a combination of SEM, TEM, XRD, and FTIR measurements. The quantitative analysis shows that the dopant contents in the solid phase can be regulated by the trace ion concentrations in the aqueous medium. The conditioned cell culture medium from the quaternary Mg/Zn/Sr/Si-co-doped CaP (qCaP) could significantly enhance cell activity and osteogenic differentiation of ovariectomized rat-derived bone marrow mesenchymal stem cells. After injecting the qCaP-loaded chitosan/hyaluronic acid hydrogel into the COBDs, histology and computed tomography scanning revealed that the new bone regeneration was significantly enhanced, and the quantity of mature bone was substantially increased in the rats implanted with qCaP 12 weeks post-operatively in comparison with the defects filled with the CaP obtained from SBF. These results suggest that the biomimetic mineralization of the trace ion-added SBF allows the preparation of highly bioactive trace element-codoped CaP biomaterials and these materials are potential candidates for the biological repair of COBDs.

Application of scaffolds for bone regeneration strategies: current trends and future directions

Scaffolds are extensively used in surgery to replace missing bone and to achieve bony union and fusion. An ideal scaffold should not only maintain, induce, and restore biological functions where cells, extracellular matrix, and growth factors are needed, but also have the right properties with respect to degradation, cell binding, cellular uptake, non-immunogenicity, mechanical strength, and flexibility. Here we examine both the basic science behind the development of scaffolds and comprehensively and systematically review the clinical applications.

Cell-mediated degradation of strontium-doped calcium polyphosphate scaffold for bone tissue engineering

Bio-ceramic porous scaffolds used in bone tissue engineering are incorporated in vivo by a process of cellular in-growth, followed by cell-mediated degradation and replacement of these scaffolds, in which macrophages and osteoclasts play the key role. Calcium polyphosphate (CPP) is an inorganic polymeric bioceramic which has been increasingly studied as a bone graft. The solution-mediated chemical degradation of strontium-substituted calcium polyphosphate (SCPP) scaffolds is well established in vitro, but an in vitro model of cell-mediated SCPP scaffold degradation has not been investigated. Herein, RAW264.7 (a murine monocyte/macrophage cell line) and osteoclasts were cultured on CPP and SCPP scaffolds. The weight loss and release amount of Sr(2+), Ca(2+) and PO(4)(3-) in a degradation medium indicated that macrophages could accelerate the degradation of SCPP. According to the results from MTT assay and scanning electron microscopy, it was found that a low dose of strontium was beneficial to the proliferation of macrophages, while strontium inhibited the activity of osteoclasts. This study will aid in developing SCPP scaffolds for in vivo bone tissue engineering.

Review: development of clinically relevant scaffolds for vascularised bone tissue engineering

Clinical translation of scaffold-based bone tissue engineering (BTE) therapy still faces many challenges despite intense investigations and advancement over the years. To address these clinical barriers, it is important to analyse the current technical challenges in constructing a clinically relevant scaffold and subsequent clinical issues relating to bone repair. This review highlights the key challenges hampering widespread clinical translation of scaffold-based vascularised BTE, with a focus on the repair of large non-union defects. The main limitations of current scaffolds include the lack of sufficient vascularisation, insufficient mechanical strength as well as issues relating to the osseointegration of the bioresorbable scaffold and bone infection management. Critical insights on the current trends of scaffold technologies and future directions for advancing next-generation BTE scaffolds into the clinical realm are discussed. Considerations concerning regulatory approval and the route towards commercialisation of the scaffolds for widespread clinical utility will also be introduced.

Controlling the biological function of calcium phosphate bone substitutes with drugs

There is a growing interest in bone tissue engineering for bone repair after traumatic, surgical or pathological injury, such as osteolytic tumor or osteoporosis. In this regard, calcium phosphate (CaP) bone substitutes have been used extensively as bone-targeting drug-delivery systems. This localized approach improves the osteogenic potential of bone substitutes by delivering bone growth factors, thus extending their biofunctionality to any pathological context, including infection, irradiation, tumor and osteoporosis. This review briefly describes the physical and chemical processes implicated in the preparation of drug-delivering CaPs. It also describes the impact of these processes on the intrinsic properties of CaPs, especially in terms of the drug-release profile. In addition, this review focuses on the potential influence of drugs on the resorption rate of CaPs. Interestingly, by modulating the resorption parameters of CaP biomaterials, it should be possible to control the release of bone-stimulating ions, such as inorganic phosphate, in the vicinity of bone cells. Finally, recent in vitro and in vivo evaluations are extensively reported.

Acceleration of segmental bone regeneration in a rabbit model by strontium-doped calcium polyphosphate scaffold through stimulating VEGF and bFGF secretion from osteoblasts

The development of suitable bioactive three-dimensional scaffold for the promotion of bone regeneration is critical in bone tissue engineering. The purpose of this study was to investigate in vivo osteogenesis of the porous strontium-doped calcium polyphosphate (SCPP) scaffolds for bone repair, as well as the relationship between osteogenic properties of SCPP scaffolds and the secretion of bFGF and VEGF from osteoblasts stimulated by SCPP. Besides, the advantages of scaffolds seeded with mesenchymal stem cells (MSCs) for bone repair were also studied. Firstly, the bone repair evaluation of scaffolds was performed on a rabbit segmental bony defects model over a period of 16 weeks by histology combined with X-ray microradiography. And then, in order to avoid the influence from the other factors such as hypoxia which emerge in vivo study and affect the secretion of VEGF and bFGF from host cells, human osteoblast-like cells (MG63) were seeded to SCPP, CPP and HA scaffolds in vitro to determine the ability of these scaffolds to stimulate the secretion of angiogenic growth factors (VEGF and bFGF) from MG63 and further explore the reason for the better osteogenic properties of SCPP scaffolds. The histological and X-ray microradiographic results showed that the SCPP scaffolds presented better osteogenic potential than CPP and HA scaffolds, when combined with MSCs, the SCPP scaffolds could further accelerate the bone repair. And the amounts of VEGF measured by ELISA assay in SCPP, CPP and HA groups after cultured for 7 days were about 364.989 pg/mL, 244.035 pg/mL and 232.785 pg/mL, respectively. Accordingly, the amounts of bFGF were about 27.085 pg/mL, 15.727 pg/mL and 8.326 pg/mL. The results revealed that the SCPP scaffolds significantly enhanced the bFGF and VEGF secretion compared with other scaffolds. The results presented in vivo and in vitro study demonstrated that the SCPP could accelerate bone formation through stimulating the secretion of VEGF and bFGF from osteoblasts, making it attractive for bone regeneration.

In vitro and in vivo studies on a Mg-Sr binary alloy system developed as a new kind of biodegradable metal

Magnesium alloys have shown potential as biodegradable metallic materials for orthopedic applications due to their degradability, resemblance to cortical bone and biocompatible degradation/corrosion products. However, the fast corrosion rate and the potential toxicity of their alloying element limit the clinical application of Mg alloys. From the viewpoint of both metallurgy and biocompatibility, strontium (Sr) was selected to prepare hot rolled Mg-Sr binary alloys (with a Sr content ranging from 1 to 4 wt.%) in the present study. The optimal Sr content was screened with respect to the mechanical and corrosion properties of Mg-Sr binary alloys and the feasibility of the use of Mg-Sr alloys as orthopedic biodegradable metals was investigated by in vitro cell experiments and intramedullary implantation tests. The mechanical properties and corrosion rates of Mg-Sr alloys were dose dependent with respect to the added Sr content. The as-rolled Mg-2Sr alloy exhibited the highest strength and slowest corrosion rate, suggesting that the optimal Sr content was 2 wt.%. The as-rolled Mg-2Sr alloy showed Grade I cytotoxicity and induced higher alkaline phosphatase activity than the other alloys. During the 4 weeks implantation period we saw gradual degradation of the as-rolled Mg-2Sr alloy within a bone tunnel. Micro-computer tomography and histological analysis showed an enhanced mineral density and thicker cortical bone around the experimental implants. Higher levels of Sr were observed in newly formed peri-implant bone compared with the control. In summary, this study shows that the optimal content of added Sr is 2 wt.% for binary Mg-Sr alloys in the rolled state and that the as-rolled Mg-2Sr alloy in vivo produces an acceptable host response.