No-Observed-Effect Level of Silver Phosphate in Carbonate Apatite Artificial Bone on Initial Bone Regeneration

Ant-nest type porous scaffold with micro-struts consisting of carbonate apatite for promoting bone formation and scaffold resorption

Scaffolds having appropriate mechanical strength and providing a proper microenvironment for osteogenesis are expected to be effective alternatives to autografts for bone regeneration. In this study, ant-nest type porous (ANP) scaffolds consisting of CO3 Ap were fabricated using calcium carbonate powder or slurry and two types of polyurethane foam through a dissolution-precipitation reaction. ANP-type, three-dimensional, interconnected porous CO3 Ap scaffolds were fabricated by burning out the struts of polyurethane foams embedded in CaCO3 , followed by compositional transformation from CaCO3 to CO3 Ap. The types of polyurethane foam and impregnation methods of CaCO3 into polyurethane form affected the geometry of the resulting ANP structures. Mechanical and in vivo biological performances of these scaffolds relied on the geometry of the ANP structures. The ANP structures displayed had a clear structural advantage in bone regeneration, owing to the promotion of cell and tissue migration throughout the scaffolds. In particular, ANP-structured scaffolds, which had highest porosity, interconnectivity, and smallest strut thickness, had a mechanical strength comparable to cancellous bone, formed more new bone, were highly resorbed, resulting in cancellous bone-like bone tissue regeneration at 12 weeks of healing. The results suggest that bone regeneration after the migration of cell and tissue into the entire scaffolds is affected by strut thickness preferentially over porosity and interconnectivity. ANP-structured CO3 Ap scaffolds are attractive for bone regeneration.

Electrochemical Deposition of Copper on Bioactive Porous Titanium Dioxide Layer: Antibacterial and Pro-Osteogenic Activities

Ti surfaces must exhibit antibacterial activity without cytotoxicity to promote bone reconstruction and prevent infection simultaneously. In this study, we employed a two-step electrochemical treatment process, namely, microarc oxidation (MAO) and cathodic electrochemical deposition (CED), to modify Ti surfaces. During the MAO step, a porous TiO2 (pTiO2) layer with a surface roughness of approximately 2.0 μm was generated on the Ti surface, and in the CED step, Cu was deposited onto the pTiO2 layer on the Ti surface, forming Cu@pTiO2. Cu@pTiO2 exhibited a similar structure, adhesion strength, and crystal phase to pTiO2. Moreover, X-ray photoelectron spectroscopy (XPS) confirmed the presence of Cu in Cu@pTiO2 at an approximate concentration of 1.0 atom %. Cu@pTiO2 demonstrated a sustained release of Cu ions for a minimum of 28 days in a simulated in vivo environment. In vitro experiments revealed that Cu@pTiO2 effectively eradicated approximately 99% of Staphylococcus aureus and Escherichia coli and inhibited biofilm formation, in contrast to the Ti and pTiO2 surfaces. Moreover, Cu@pTiO2 supported the proliferation of osteoblast-like cells at a rate comparable to that observed on the Ti and pTiO2 surfaces. Similar to pTiO2, Cu@pTiO2 promoted the calcification of osteoblast-like cells compared with Ti. In summary, we successfully conferred antibacterial and pro-osteogenic activities to Ti surfaces without inducing cytotoxic effects or structural and mechanical alterations in pTiO2 through the application of MAO and CED processes. Moreover, we found that the pTiO2 layer promoted bacterial growth and biofilm formation more effectively than the Ti surface, highlighting the potential drawbacks of rough and porous surfaces. Our findings provide fundamental insights into the surface design of Ti-based medical devices for bone reconstruction and infection prevention.

Fabrication and histological evaluation of ant-nest type porous carbonate apatite artificial bone using polyurethane foam as a porogen

The composition of carbonate apatite (CO₃ Ap) aids bone regeneration. Other features, such as porosity and pore interconnectivity of artificial bone, also govern bone regeneration. In general, a trade-off exists between the porosity and mechanical strength of artificial bone. Therefore, this suggests that the interconnected pores in the ant-nest-type porous (ANP) structure of artificial bone accelerate bone regeneration by minimizing the sacrifice of mechanical strength. The unique structure of polyurethane foam has the potential to endow CO₃ Ap with an ANP structure without forming excess pores. This study investigated the efficacy of polyurethane foam as a porogen in providing ANP structure to CO₃ Ap artificial bone. The polyurethane foam was completely decomposed by sintering and the resulting CO₃ Ap displayed ANP structure with a compressive strength of approximately 15 MPa. Furthermore, in vivo experiments revealed that the migration of cells and tissues into the interior of CO₃ Ap through the interconnected pores accelerated bone regeneration in the ANP-structured CO₃ Ap. Thus, this indicates that using polyurethane foam as a porogen endows the CO₃ Ap artificial bone with an ANP structure that accelerates bone regeneration.

Is Silver the New Gold? A Systematic Review of the Preclinical Evidence of Its Use in Bone Substitutes as Antiseptic

Antibiotic-laden bone substitutes represent a viable option in the treatment of bone and joint infections with bone defects. In particular, the addition of silver ions or silver nanoparticles to bone substitutes to achieve local antiseptic activity could represent a further contribution, also helping to prevent bacterial resistance to antibiotics. An in-depth search of the main scientific databases was performed regarding the use of silver compounds for bone substitution. The available evidence is still limited to the preclinical level: 22 laboratory studies, 2 animal models, and 3 studies, with both in vitro and in vivo analysis, were found on the topic. Numerous biomaterials have been evaluated. In vitro studies confirmed that silver in bone substitutes retains the antibacterial activity already demonstrated in coatings materials. Cytotoxicity was generally found to be low and only related to silver concentrations higher than those sufficient to achieve antibacterial activity. Instead, there are only a few in vivo studies, which appear to confirm antibacterial efficacy, although there is insufficient evidence on the pharmacokinetics and safety profile of the compounds investigated. In conclusion, research on bone substitutes doped with silver is in its early stages, but the preliminary findings seem promising.

A Review on the Recent Advancements on Therapeutic Effects of Ions in the Physiological Environments

This review focuses on the therapeutic effects of ions when released in physiological environments. Recent studies have shown that metallic ions like Ag+, Sr2+, Mg2+, Mn2+, Cu2+, Ca2+, P+5, etc., have shown promising results in drug delivery systems and regenerative medicine. These metallic ions can be loaded in nanoparticles, mesoporous bioactive glass nanoparticles (MBGNs), hydroxyapatite (HA), calcium phosphates, polymeric coatings, and salt solutions. The metallic ions can exhibit different functions in the physiological environment such as antibacterial, antiviral, anticancer, bioactive, biocompatible, and angiogenic effects. Furthermore, the metals/metalloid ions can be loaded into scaffolds to improve osteoblast proliferation, differentiation, bone development, fibroblast growth, and improved wound healing efficacy. Moreover, different ions possess different therapeutic limits. Therefore, further mechanisms need to be developed for the highly controlled and sustained release of these ions. This review paper summarizes the recent progress in the use of metallic/metalloid ions in regenerative medicine and encourages further study of ions as a solution to cure diseases.

Surface functionalization with copper endows carbonate apatite honeycomb scaffold with antibacterial, proangiogenic, and pro-osteogenic activities

Osteomyelitis is a potentially devastating inflammatory bone disease that leads to bone destruction and loss. Treatment of osteomyelitis requires the removal of residual bacteria as well as osteogenesis with angiogenesis at the site of treatment. Use of an appropriate amount of copper (Cu) in treatment scaffolds may achieve these goals without the risk of toxicity. In this study, the surface of the carbonate apatite honeycomb scaffold was functionalized with Cu through a dissolution-precipitation reaction. The resulting scaffolds retained the honeycomb structure after immersion in CuCl₂ solution, and Cu was precipitated on the surface as libethenite [Cu₂(OH)PO₄]. The surface Cu concentration was controlled by the concentration of the CuCl₂ solution. Scaffolds with a surface Cu concentration of 23.8 wt% exhibited antibacterial and cytotoxic effects, whereas those with concentrations of ≤4.6 wt% exerted antibacterial effects without negatively affecting the cellular adhesion, proliferation, differentiation, and calcification of osteoblast-like cells. Furthermore, scaffolds with a surface Cu concentration of 4.6 wt% Cu inhibited bacterial growth for at least 28 days and displayed proangiogenic and pro-osteogenic activities in vivo. These data confirm the success in functionalizing scaffolds with Cu that may be utilized as an innovative osteomyelitis therapy.

ATR inhibitor AZD6738 increases the sensitivity of colorectal cancer cells to 5‑fluorouracil by inhibiting repair of DNA damage

The repair of DNA damage caused by chemotherapy in cancer cells occurs mainly at two cell cycle checkpoints (G₁ and G₂) and is a factor contributing to chemoresistance. Most colorectal cancers harbor mutations in p53, the main pathway involved in the G₁ checkpoint, and thus, are particularly dependent on the G₂ checkpoint for DNA repair. The present study examined the effect of AZD6738, a specific inhibitor of ataxia telangiectasia mutated and rad3-related (ATR) involved in the G₂ checkpoint, combined with 5-fluorouracil (5-FU), a central chemotherapeutic agent, on colorectal cancer cells. Since 5-FU has a DNA-damaging effect, its combination with AZD6738 is likely to enhance the therapeutic effect. The effects of the AZD6738/5-FU combination were evaluated in various colorectal cancer cells (HT29, SW480, HCT116 and DLD-1 cells) by flow cytometry (HT29 cells), western blotting (HT29 cells) and water-soluble tetrazolium 1 assays (HT29, SW480, HCT116 and DLD-1 cells), as well as in an experimental animal model (HT29 cells). In vitro, the AZD6738/5-FU combination increased the number of mitotic cells according to flow cytometry, decreased the checkpoint kinase 1 phosphorylation levels and increased cleaved caspase-3 and phosphorylated form of H2A.X variant histone levels according to western blotting, and decreased the proliferation rate of four colon cancer cell lines according to cell viability experiments. In vivo, xenografted colorectal cancer cells treated with the AZD6738/5-FU combination exhibited a marked decrease in proliferation compared with the 5-FU alone group. The present results suggested that AZD6738 enhanced the effect of 5-FU in p53-mutated colorectal cancer.

Effects of Pore Interconnectivity on Bone Regeneration in Carbonate Apatite Blocks

Porous architecture in bone substitutes, notably the interconnectivity of pores, is a critical factor for bone ingrowth. However, controlling the pore interconnectivity while maintaining the microarchitecture has not yet been achieved using conventional methods, such as sintering. Herein, we fabricated a porous block using the crystal growth of calcium sulfate dihydrate, and controlled the pore interconnectivity by limiting the region of crystal growth. The calcium sulfate dihydrate blocks were transformed to bone apatite, carbonate apatite (CO₃Ap) through dissolution–precipitation reactions. Thus, CO₃Ap blocks with 15% and 30% interconnected pore volumes were obtained while maintaining the microarchitecture: they were designated as CO₃Ap-15 and CO₃Ap-30, respectively. At 4 weeks after implantation in a rabbit femur defect, new bone formed throughout CO₃Ap-30, whereas little bone was formed in the center region of CO₃Ap-15. At 12 weeks after implantation, a large portion of CO₃Ap-30 was replaced with new bone and the boundary with the host bone became blurred. In contrast, CO₃Ap-15 remained in the defect and the boundary with the host bone was still clear. Thus, the interconnected pores promote bone ingrowth, followed by replacement of the material with new bone. These findings provide a useful guide for designing bone substitutes for rapid bone regeneration.

Antibacterial Honeycomb Scaffolds for Achieving Infection Prevention and Bone Regeneration

Surgical site infection (SSI) is a severe complication associated with orthopedic bone reconstruction. For both infection prevention and bone regeneration, the framework surface of osteoconductive and bioresorbable scaffolds must be locally modified by minimum antibacterial substances, without sacrificing the osteoconductivity of the scaffold framework. In this study, we fabricated antibacterial honeycomb scaffolds by replacing carbonate apatite, which is the main component of the scaffold, with silver phosphate locally on the scaffold surface via dissolution-precipitation reactions. When the silver content was 9.9 × 10^-4 wt %, the honeycomb scaffolds showed antibacterial activity without cytotoxicity and allowed cell proliferation, differentiation, and mineralization. Furthermore, the antibacterial honeycomb scaffolds perfectly prevented bacterial infection in vivo in the presence of methicillin-resistant Staphylococcus aureus, formed new bone at 2 weeks after surgery, and were gradually replaced with a new bone. Thus, the antibacterial honeycomb scaffolds achieved both infection prevention and bone regeneration. In contrast, severe infection symptoms, including abscess formation, osteolytic lesions, and inflammation, occurred 2 weeks after surgery when honeycomb scaffolds without silver phosphate modification were implanted. Nevertheless, the unmodified honeycomb scaffolds eliminated bacteria and necrotic bone through their scaffold channels, resulting in symptom improvement and bone formation. These results suggest that the honeycomb structure is inherently effective in hindering bacterial growth. This novel insight may contribute to the development of antibacterial scaffolds. Moreover, our modification method is useful for providing antibacterial activity to various biomaterials.