3D printed magnesium-doped β-TCP gyroid scaffold with osteogenesis, angiogenesis, immunomodulation properties and bone regeneration capability in vivo

Bioactive ceramic-based materials: beneficial properties and potential applications in dental repair and regeneration

Bioactive ceramics, primarily consisting of bioactive glasses, glass-ceramics, calcium orthophosphate ceramics, calcium silicate ceramics and calcium carbonate ceramics, have received great attention in the past decades given their biocompatible nature and excellent bioactivity in stimulating cell proliferation, differentiation and tissue regeneration. Recent studies have tried to combine bioactive ceramics with bioactive ions, polymers, bioactive proteins and other chemicals to improve their mechanical and biological properties, thus rendering them more valid in tissue engineering scaffolds. This review presents the beneficial properties and potential applications of bioactive ceramic-based materials in dentistry, particularly in the repair and regeneration of dental hard tissue, pulp-dentin complex, periodontal tissue and bone tissue. Moreover, greater insights into the mechanisms of bioactive ceramics and the development of ceramic-based materials are provided.

In Vivo Osteogenic and Angiogenic Properties of a 3D-Printed Isosorbide-Based Gyroid Scaffold Manufactured via Digital Light Processing

INTRODUCTION

Osteogenic and angiogenic properties of synthetic bone grafts play a crucial role in the restoration of bone defects. Angiogenesis is recognised for its support in bone regeneration, particularly in larger defects. The objective of this study is to evaluate the new bone formation and neovascularisation of a 3D-printed isosorbide-based novel CSMA-2 polymer in biomimetic gyroid structures.

METHODS

The gyroid scaffolds were fabricated by 3D printing CSMA-2 polymers with different hydroxyapatite (HA) filler concentrations using the digital light processing (DLP) method. A small animal subcutaneous model and a rat calvaria critical-size defect model were performed to analyse tissue compatibility, angiogenesis, and new bone formation.

RESULTS

The in vivo results showed good biocompatibility of the 3D-printed gyroid scaffolds with no visible prolonged inflammatory reaction. Blood vessels were found to infiltrate the pores from day 7 of the implantation. New bone formation was confirmed with positive MT staining and BMP-2 expression, particularly on scaffolds with 10% HA. Bone volume was significantly higher in the CSMA-2 10HA group compared to the sham control group.

DISCUSSION AND CONCLUSIONS

The results of the subcutaneous model demonstrated a favourable tissue response, including angiogenesis and fibrous tissue, indicative of the early wound healing process. The results from the critical-size defect model showcased new bone formation, as confirmed by micro-CT imaging and immunohistochemistry. The combination of CSMA-2 as the 3D printing material and the gyroid as the 3D structure was found to support essential events in bone healing, specifically angiogenesis and osteogenesis.

Magnesium-containing bioceramics stimulate exosomal miR-196a-5p secretion to promote senescent osteogenesis through targeting Hoxa7/MAPK signaling axis

Stem cell senescence is characterized by progressive functional dysfunction and secretory phenotypic changes including decreased proliferation, dysfunction of osteogenic and angiogenic differentiation, increased secretion of the senescence-associated secretory phenotype (SASP), which bring difficulties for bone repair. Rescuing or delaying senescence of aged bone marrow mesenchymal stem cells (O-BMSCs) was considered as effective strategy for bone regeneration in aging microenvironment. Magnesium (Mg) ion released from bioceramics was reported to facilitate bone regeneration via enhancing osteogenesis and alleviating senescence. In this study, Akermanite biocreamics (Akt) containing Mg ion as a model was demonstrated to promote osteogenesis and angiogenesis effects of O-BMSCs by activating the MAPK signaling pathway in vitro. Moreover, the enhanced osteogenesis effects might be attributed to enhanced Mg-containing Akt-mediated exosomal miR-196a-5p cargo targeting Hoxa7 and activation of MAPK signaling pathway. Furthermore, the in vivo study confirmed that 3D-printed porous Mg-containing Akt scaffolds effectively increased bone regeneration in cranial defects of aged rats. The current results indicated that the exosomal-miR-196a-5p/Hoxa7/MAPK signaling axis might be the potential mechanism underlying Akt-mediated osteogenesis. The exosome-meditaed therapy stimulated by the released Mg ion contained in Akt biocreamics or other biomaterials might serve as a candidate strategy for bone repair in aged individuals.

Use of Biomaterials in 3D Printing as a Solution to Microbial Infections in Arthroplasty and Osseous Reconstruction

The incidence of microbial infections in orthopedic prosthetic surgeries is a perennial problem that increases morbidity and mortality, representing one of the major complications of such medical interventions. The emergence of novel technologies, especially 3D printing, represents a promising avenue of development for reducing the risk of such eventualities. There are already a host of biomaterials, suitable for 3D printing, that are being tested for antimicrobial properties when they are coated with bioactive compounds, such as antibiotics, or combined with hydrogels with antimicrobial and antioxidant properties, such as chitosan and metal nanoparticles, among others. The materials discussed in the context of this paper comprise beta-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP), hydroxyapatite, lithium disilicate glass, polyetheretherketone (PEEK), poly(propylene fumarate) (PPF), poly(trimethylene carbonate) (PTMC), and zirconia. While the recent research results are promising, further development is required to address the increasing antibiotic resistance exhibited by several common pathogens, the potential for fungal infections, and the potential toxicity of some metal nanoparticles. Other solutions, like the incorporation of phytochemicals, should also be explored. Incorporating artificial intelligence (AI) in the development of certain orthopedic implants and the potential use of AI against bacterial infections might represent viable solutions to these problems. Finally, there are some legal considerations associated with the use of biomaterials and the widespread use of 3D printing, which must be taken into account.

Biomaterials Adapted to Vat Photopolymerization in 3D Printing: Characteristics and Medical Applications

Along with the rapid and extensive advancements in the 3D printing field, a diverse range of uses for 3D printing have appeared in the spectrum of medical applications. Vat photopolymerization (VPP) stands out as one of the most extensively researched methods of 3D printing, with its main advantages being a high printing speed and the ability to produce high-resolution structures. A major challenge in using VPP 3D-printed materials in medicine is the general incompatibility of standard VPP resin mixtures with the requirements of biocompatibility and biofunctionality. Instead of developing completely new materials, an alternate approach to solving this problem involves adapting existing biomaterials. These materials are incompatible with VPP 3D printing in their pure form but can be adapted to the VPP chemistry and general process through the use of innovative mixtures and the addition of specific pre- and post-printing steps. This review's primary objective is to highlight biofunctional and biocompatible materials that have been adapted to VPP. We present and compare the suitability of these adapted materials to different medical applications and propose other biomaterials that could be further adapted to the VPP 3D printing process in order to fulfill patient-specific medical requirements.

Osseointegration of functionally graded Ti6Al4V porous implants: Histology of the pore network

The additive manufacturing of titanium into porous geometries offers a means to generate low-stiffness endosseous implants with a greater surface area available for osseointegration. In this work, selective laser melting was used to produce gyroid-based scaffolds with a uniform pore size of 300 μm or functionally graded pore size from 600 μm to 300 μm. Initial in vitro assessment with Saos-2 cells showed favourable cell proliferation at pore sizes of 300 and 600 μm. Following implantation into rabbit tibiae, early histological observations at four weeks indicated some residual inflammation alongside neovessel infiltration into the scaffold interior and some early apposition of mineralized bone tissue. At twelve weeks, both scaffolds were filled with a mixture of adipocyte-rich marrow, micro-capillaries, and mineralized bone tissue. X-ray microcomputed tomography showed a higher bone volume fraction (BV/TV) and percentage of bone-implant contact (BIC) in the implants with 300 μm pores than in the functionally graded specimens. In functionally graded specimens, localized BV/TV measurement was observed to be higher in the innermost region containing smaller pores (estimated at 300-400 μm) than in larger pores at the implant exterior. The unit cell topology of the porous implant was also observed to guide the direction of bone ingrowth by conducting along the implant struts. These results suggest that in vivo experimentation is necessary alongside parametric optimization of functionally graded porous implants to predict short-term and long-term bone apposition.

Polysaccharide-bioceramic composites for bone tissue engineering: A review

Limitations associated with conventional bone substitutes such as autografts, increasing demand for bone grafts, and growing elderly population worldwide necessitate development of unique materials as bone graft substitutes. Bone tissue engineering (BTE) would ensure therapy advancement, efficiency, and cost-effective treatment modalities of bone defects. One way of engineering bone tissue scaffolds by mimicking natural bone tissue composed of organic and inorganic phases is to utilize polysaccharide-bioceramic hybrid composites. Polysaccharides are abundant in nature, and present in human body. Biominerals, like hydroxyapatite are present in natural bone and some of them possess osteoconductive and osteoinductive properties. Ion doped bioceramics could substitute protein-based biosignal molecules to achieve osteogenesis, vasculogenesis, angiogenesis, and stress shielding. This review is a systemic summary on properties, advantages, and limitations of polysaccharide-bioceramic/ion doped bioceramic composites along with their recent advancements in BTE.

Influence of Ag and/or Sr Dopants on the Mechanical Properties and In Vitro Degradation of β-Tricalcium Phosphate-Based Ceramics

β-tricalcium phosphate has good biodegradability and biocompatibility; it is widely perceived as a good material for treating bone deficiency. In this research, different contents of strontium (Sr) and silver (Ag) ion-doped β-tricalcium phosphate powders were prepared using the sol-gel method. After obtaining the best ratio of pore-forming agent and binder, the as-synthesized powders were sintered in a muffle for 5 h at 1000 °C to obtain the samples. Then, these samples were degraded in vitro in simulated body fluids. The samples were tested using a series of characterization methods before and after degradation. Results showed that the amount of Sr and/or Ag doping had an effect on the crystallinity and structural parameters of the samples. After degradation, though the compressive strength of these samples decreased overall, the compressive strength of the undoped samples was higher than that of the doped samples. Notably, apatite-like materials were observed on the surface of the samples. All the results indicate that Sr and/or Ag β-TCP has good osteogenesis and proper mechanical properties; it will be applied as a prospective biomaterial in the area of bone repair.

Superiority of Triply Periodic Minimal Surface Gyroid Structure to Strut-Based Grid Structure in Both Strength and Bone Regeneration

The aging population has rapidly driven the demand for bone regeneration. The pore structure of a scaffold is a critical factor that affects its mechanical strength and bone regeneration. Triply periodic minimal surface gyroid structures similar to the trabecular bone structure are considered superior to strut-based lattice structures (e.g., grids) in terms of bone regeneration. However, at this stage, this is only a hypothesis and is not supported by evidence. In this study, we experimentally validated this hypothesis by comparing gyroid and grid scaffolds composed of carbonate apatite. The gyroid scaffolds possessed compressive strength approximately 1.6-fold higher than that of the grid scaffolds because the gyroid structure prevented stress concentration, whereas the grid structure could not. The porosity of gyroid scaffolds was higher than that of the grid scaffolds; however, porosity and compressive strength generally have a trade-off relationship. Moreover, the gyroid scaffolds formed more than twice the amount of bone as grid scaffolds in a critical-sized bone defect in rabbit femur condyles. This favorable bone regeneration using gyroid scaffolds was attributed to the high permeability (i.e., larger volume of macropores or porosity) and curvature profile of the gyroid structure. Thus, this study validated the conventional hypothesis using in vivo experiments and revealed factors that led to this hypothetical outcome. The findings of this study are expected to contribute to the development of scaffolds that can achieve early bone regeneration without sacrificing the mechanical strength.

Additive manufacturing of barium-doped calcium silicate/poly-ε-caprolactone scaffolds to activate CaSR and AKT signalling and osteogenic differentiation of mesenchymal stem cells

3D-printed scaffolds are suitable for patient-specific implant preparation for bone regeneration in large-scale critical bone defects. In addition, these scaffolds should have mechanical and biological properties similar to those of natural bone tissue. In this study, 3D-printed barium-doped calcium silicate (BaCS)/poly-ε-caprolactone (PCL) composite scaffolds were fabricated as an alternative strategy for bone tissue engineering to achieve appropriate physicochemical characteristics and stimulate osteogenesis. Scaffolds containing 10% Ba (Ba10) showed optimal mechanical properties, preventing premature scaffold degradation during immersion while enabling ion release in a sustained manner to achieve the desired therapeutic goals. In addition, Wharton's jelly mesenchymal stem cells (WJMSCs) were used to assess biocompatibility and osteogenic differentiation behaviour. WJMSCs were cultured on the scaffold and permeabilised via ICP to analyse the presence of Si and Ba ions in the medium and cell lysates, suggesting that the ions released by the scaffold could effectively enter the cells. The protein expression of CaSR, PI3K, Akt, and JNK confirmed that CaSR could activate cells cultured in Ba10, thereby affecting the subsequent PI3k/Akt and JNK pathways and further promoting osteogenic differentiation. The in vivo performance of the proposed scaffolds was assessed using micro-CT and histological slices, which revealed that the BaCS scaffolds could further enhance bone regeneration, compared with bare scaffolds. These results suggest the potential use of 3D-printed BaCS/PCL scaffolds as next-generation substitutes for bone regeneration.

The combined effect of zinc and calcium on the biodegradation of ultrahigh-purity magnesium implants

Magnesium (Mg)-based implants are promising candidates for orthopedic interventions, because of their biocompatibility, good mechanical features, and ability to degrade completely in the body, eliminating the need for an additional removal surgery. In the present study, we synthesized and investigated two Mg-based materials, ultrahigh-purity ZX00 (Mg-Zn-Ca; <0.5 wt% Zn and <0.5 wt% Ca, in wt%; Fe-content <1 ppm) and ultrahigh-purity Mg (XHP-Mg, >99.999 wt% Mg; Fe-content <1 ppm), in vitro and in vivo in juvenile healthy rats to clarify the effect of the alloying elements Zn and Ca on mechanical properties, microstructure, cytocompatibility and degradation rate. Potential differences in bone formation and bone in-growth were also assessed and compared with state-of-the-art non-degradable titanium (Ti)-implanted, sham-operated, and control (non-intervention) groups, using micro-computed tomography, histology and scanning electron microscopy. At 6 and 24 weeks after implantation, serum alkaline phosphatase (ALP), calcium (Ca), and Mg level were measured and bone marrow stromal cells (BMSCs) were isolated for real-time PCR analysis. Results show that ZX00 implants have smaller grain size and superior mechanical properties than XHP-Mg, and that both reveal good biocompatibility in cytocompatibilty tests. ZX00 homogenously degraded with an increased gas accumulation 12 and 24 weeks after implantation, whereas XHP-Mg exhibited higher gas accumulation already at 2 weeks. Serum ALP, Ca, and Mg levels were comparable among all groups and both Mg-based implants led to similar relative expression levels of Alp, Runx2, and Bmp-2 genes at weeks 6 and 24. Histologically, Mg-based implants are superior for new bone tissue formation and bone in-growth compared to Ti implants. Furthermore, by tracking the sequence of multicolor fluorochrome labels, we observed higher mineral apposition rate at week 2 in both Mg-based implants compared to the control groups. Our findings suggest that (i) ZX00 and XHP-Mg support bone formation and remodeling, (ii) both Mg-based implants are superior to Ti implants in terms of new bone tissue formation and osseointegration, and (iii) ZX00 is more favorable due to its lower degradation rate and moderate gas accumulation.

Synergistic Effect of Static Magnetic Fields and 3D-Printed Iron-Oxide-Nanoparticle-Containing Calcium Silicate/Poly-ε-Caprolactone Scaffolds for Bone Tissue Engineering

In scaffold-regulated bone regeneration, most three-dimensional (3D)-printed scaffolds do not provide physical stimulation to stem cells. In this study, a magnetic scaffold was fabricated using fused deposition modeling with calcium silicate (CS), iron oxide nanoparticles (Fe₃O₄), and poly-ε-caprolactone (PCL) as the matrix for internal magnetic sources. A static magnetic field was used as an external magnetic source. It was observed that 5% Fe₃O₄ provided a favorable combination of compressive strength (9.6 ± 0.9 MPa) and degradation rate (21.6 ± 1.9% for four weeks). Furthermore, the Fe₃O₄-containing scaffold increased in vitro bioactivity and Wharton's jelly mesenchymal stem cells' (WJMSCs) adhesion. Moreover, it was shown that the Fe₃O₄-containing scaffold enhanced WJMSCs' proliferation, alkaline phosphatase activity, and the osteogenic-related proteins of the scaffold. Under the synergistic effect of the static magnetic field, the CS scaffold containing Fe₃O₄ can not only enhance cell activity but also stimulate the simultaneous secretion of collagen I and osteocalcin. Overall, our results demonstrated that Fe₃O₄-containing CS/PCL scaffolds could be fabricated three dimensionally and combined with a static magnetic field to affect cell behaviors, potentially increasing the likelihood of clinical applications for bone tissue engineering.

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.