In vitro degradation and surface bioactivity of iron-matrix composites containing silicate-based bioceramic

The Effectiveness Mechanisms of Carbon Nanotubes (CNTs) as Reinforcements for Magnesium-Based Composites for Biomedical Applications: A Review

As a smart implant, magnesium (Mg) is highly biocompatible and non-toxic. In addition, the elastic modulus of Mg relative to other biodegradable metals (iron and zinc) is close to the elastic modulus of natural bone, making Mg an attractive alternative to hard tissues. However, high corrosion rates and low strength under load relative to bone are some challenges for the widespread use of Mg in orthopedics. Composite fabrication has proven to be an excellent way to improve the mechanical performance and corrosion control of Mg. As a result, their composites emerge as an innovative biodegradable material. Carbon nanotubes (CNTs) have superb properties like low density, high tensile strength, high strength-to-volume ratio, high thermal conductivity, and relatively good antibacterial properties. Therefore, using CNTs as reinforcements for the Mg matrix has been proposed as an essential option. However, the lack of understanding of the mechanisms of effectiveness in mechanical, corrosion, antibacterial, and cellular fields through the presence of CNTs as Mg matrix reinforcements is a challenge for their application. This review focuses on recent findings on Mg/CNT composites fabricated for biological applications. The literature mentions effective mechanisms for mechanical, corrosion, antimicrobial, and cellular domains with the presence of CNTs as reinforcements for Mg-based nanobiocomposites.

A xonotlite nanofiber bioactive 3D-printed hydrogel scaffold based on osteo-/angiogenesis and osteoimmune microenvironment remodeling accelerates vascularized bone regeneration

BACKGROUND

Coordination between osteo-/angiogenesis and the osteoimmune microenvironment is essential for effective bone repair with biomaterials. As a highly personalized and precise biomaterial suitable for repairing complex bone defects in clinical practice, it is essential to endow 3D-printed scaffold the above key capabilities.

RESULTS

Herein, by introducing xonotlite nanofiber (Ca6(Si6O17) (OH)2, CS) into the 3D-printed silk fibroin/gelatin basal scaffold, a novel bone repair system named SGC was fabricated. It was noted that the incorporation of CS could greatly enhance the chemical and mechanical properties of the scaffold to match the needs of bone regeneration. Besides, benefiting from the addition of CS, SGC scaffolds could accelerate osteo-/angiogenic differentiation of bone mesenchymal stem cells (BMSCs) and meanwhile reprogram macrophages to establish a favorable osteoimmune microenvironment. In vivo experiments further demonstrated that SGC scaffolds could efficiently stimulate bone repair and create a regeneration-friendly osteoimmune microenvironment. Mechanistically, we discovered that SGC scaffolds may achieve immune reprogramming in macrophages through a decrease in the expression of Smad6 and Smad7, both of which participate in the transforming growth factor-β (TGF-β) signaling pathway.

CONCLUSION

Overall, this study demonstrated the clinical potential of the SGC scaffold due to its favorable pro-osteo-/angiogenic and osteoimmunomodulatory properties. In addition, it is a promising strategy to develop novel bone repair biomaterials by taking osteoinduction and osteoimmune microenvironment remodeling functions into account.

Iron-Gold Composites for Biodegradable Implants: In Vitro Investigation on Biodegradation and Biomineralization

The biocompatibility and biodegradation of iron (Fe) make it a suitable candidate for developing biodegradable metallic implants. However, the degradation rate of Fe in a physiological environment is extremely slow and needs to be enhanced to a rate compatible with tissue growth. Incorporating noble metals improves the Fe degradation rate by forming galvanic couples. This study incorporated gold (Au) into Fe at very low concentrations of 1.25 and 2.37 μg/g to improve the degradation rate. The electrochemical corrosion test of the samples revealed that the Au-containing samples showed a four-time and nine-time faster degradation rate than pure Fe. Furthermore, the immersion test and long-term electrochemical impedance spectroscopy conducted in simulated body fluid (SBF) revealed that the Au-incorporated samples exhibited increased bioactivity and degraded faster than pure Fe. Integrating nanogold into a Fe matrix increased the in situ formation of hydroxyapatite on the sample's surface and did not cause toxicity to L929-murine fibroblast cells. It is suggested that Fe-Au composites with low concentrations of Au can be used to tailor the biodegradation rate and promote the biomineralization of Fe-based implants in the physiological environment.

A Comprehensive Review of the Current Research Status of Biodegradable Zinc Alloys and Composites for Biomedical Applications

Zinc (Zn)-based biodegradable materials show moderate degradation rates in comparison with other biodegradable materials (Fe and Mg). Biocompatibility and non-toxicity also make them a viable option for implant applications. Furthermore, Pure Zn has poor mechanical behavior, with a tensile strength of around 100-150 MPa and an elongation of 0.3-2%, which is far from reaching the strength required as an orthopedic implant material (tensile strength is more than 300 MPa, elongation more than 15%). Alloy and composite fabrication have proven to be excellent ways to improve the mechanical performance of Zn. Therefore, their alloys and composites have emerged as an innovative category of biodegradable materials. This paper summarizes the most important recent research results on the mechanical and biological characteristics of biodegradable Zn-based implants for orthopedic applications and the most commonly added components in Zn alloys and composites.

Biomaterials as Implants in the Orthopedic Field for Regenerative Medicine: Metal versus Synthetic Polymers

Patients suffering bone fractures in different parts of the body require implants that will enable similar function to that of the natural bone that they are replacing. Joint diseases (rheumatoid arthritis and osteoarthritis) also require surgical intervention with implants such as hip and knee joint replacement. Biomaterial implants are utilized to fix fractures or replace parts of the body. For the majority of these implant cases, either metal or polymer biomaterials are chosen in order to have a similar functional capacity to the original bone material. The biomaterials that are employed most often for implants of bone fracture are metals such as stainless steel and titanium, and polymers such as polyethene and polyetheretherketone (PEEK). This review compared metallic and synthetic polymer implant biomaterials that can be employed to secure load-bearing bone fractures due to their ability to withstand the mechanical stresses and strains of the body, with a focus on their classification, properties, and application.

Fabrication and Properties of Biodegradable Akermanite-Reinforced Fe35Mn Alloys for Temporary Orthopedic Implant Applications

As a representative of the biodegradable iron (Fe)-manganese (Mn) alloys, Fe35Mn has been investigated as a promising biodegradable metal biomaterial for orthopedic applications. However, its slow degradation rate, though better than pure Fe, and poor bioactivity are concerns that retard its clinical applications. Akermanite (Ca₂MgSi₂O₇, Ake) is a silicate-based bioceramic, showing desirable degradability and bioactivity for bone repair. In the present work, Fe35Mn/Ake composites were prepared via a powder metallurgy route. The effect of different contents of Ake (0, 10, 30, 50 vol %) on the microstructure, mechanical properties, degradation, and biocompatibility of the composites was investigated. The ceramic phases were found to be evenly distributed in the metal matrix. The Ake reacted with Fe35Mn and generated CaFeSiO₄ during sintering. The addition of Ake increased the relative density of pure Fe35Mn from ∼90 to ∼94-97%. The compressive yield strength (CYS) and elastic modulus (E_c) increased with increasing Ake, with Fe35Mn/50Ake exhibiting the highest CYS of ∼403 MPa and E_c of ∼18 GPa. However, the ductility decreased at higher Ake concentrations (30 and 50%). Microhardness also showed an increasing trend with the addition of Ake. Electrochemical measurements indicated that higher concentrations of Ake (30 and 50%) could potentially increase the corrosion rate of Fe35Mn from ∼0.25 to ∼0.39 mm/year. However, all of the compositions tested did not show measurable weight loss after immersion in simulated body fluid (SBF) for 4 weeks, attributed to the use of prealloyed raw material, high sintered density of the fabricated composites, and the formation of a dense Ca-, P-, and O-rich layer on the surface. Human osteoblasts on Fe35Mn/Ake composites showed increasing viability with increasing Ake content, indicating improved in vitro biocompatibility. These preliminary results suggest that Fe35Mn/Ake can be a potential material for biodegradable bone implant applications, particularly Fe35Mn/30Ake, if the slow corrosion of the composite can be addressed.

Additive manufacturing of bioactive and biodegradable porous iron-akermanite composites for bone regeneration

Advanced additive manufacturing techniques have been recently used to tackle the two fundamental challenges of biodegradable Fe-based bone-substituting materials, namely low rate of biodegradation and insufficient bioactivity. While additively manufactured porous iron has been somewhat successful in addressing the first challenge, the limited bioactivity of these biomaterials hinder their progress towards clinical application. Herein, we used extrusion-based 3D printing for additive manufacturing of iron-matrix composites containing silicate-based bioceramic particles (akermanite), thereby addressing both of the abovementioned challenges. We developed inks that carried iron and 5, 10, 15, or 20 vol% of akermanite powder mixtures for the 3D printing process and optimized the debinding and sintering steps to produce geometrically-ordered iron-akermanite composites with an open porosity of 69-71%. The composite scaffolds preserved the designed geometry and the original α-Fe and akermanite phases. The in vitro biodegradation rates of the composites were improved as much as 2.6 times the biodegradation rate of geometrically identical pure iron. The yield strengths and elastic moduli of the scaffolds remained within the range of the mechanical properties of the cancellous bone, even after 28 days of biodegradation. The composite scaffolds (10-20 vol% akermanite) demonstrated improved MC3T3-E1 cell adhesion and higher levels of cell proliferation. The cellular secretion of collagen type-1 and the alkaline phosphatase activity on the composite scaffolds (10-20 vol% akermanite) were, respectively higher than and comparable to Ti6Al4V in osteogenic medium. Taken together, these results clearly show the potential of 3D printed porous iron-akermanite composites for further development as promising bone substitutes. STATEMENT OF SIGNIFICANCE: : Porous iron matrix composites containing akermanite particles were produced by means of multi-material additive manufacturing to address the two fundamental challenges associated with biodegradable iron-based biomaterials, namely very low rate of biodegradation and insufficient bioactivity. Our porous iron-akermanite composites exhibited enhanced biodegradability and superior bioactivity compared to porous monolithic iron scaffolds. The murine bone cells proliferated on the composite scaffolds, and secreted the collagen type-1 matrix that stimulated bony-like mineralization. The results show the exceptional potential of the developed porous iron-based composite scaffolds for application as bone substitutes.

Progress in manufacturing and processing of degradable Fe-based implants: a review

Biodegradable metals have gained vast attention as befitting candidates for developing degradable metallic implants. Such implants are primarily employed for temporary applications and are expected to degrade or resorbed after the tissue is healed. Fe-based materials have generated considerable interest as one of the possible biodegradable metals. Like other biometals such as Mg and Zn, Fe exhibits good biocompatibility and biodegradability. The versatility in the mechanical behaviour of Fe-based materials makes them a better choice for load-bearing applications. However, the very low degradation rate of Fe in the physiological environment needs to be improved to make it compatible with tissue growth. Several studies on tailoring the degradation behaviour of Fe in the human body are already reported. Majority of these works include studies on the effect of manufacturing and processing techniques on biocompatibility and biodegradability. This article focuses on a comprehensive review and analysis of the various manufacturing and processing techniques so far reported for developing biodegradable iron-based orthopaedic implants. The current status of research in the field is neatly presented, and a summary of the works is included in the article for the benefit of researchers in the field to contextualise their research and effectively find the lacunae in the existing scholarship.

Osteogenic potential of calcium silicate-doped iron oxide nanoparticles versus calcium silicate for reconstruction of critical-sized mandibular defects: An experimental study in dog model

Objective

To evaluate bioactivity and osteogenic potential of calcium silicate (CS)-doped iron oxide (Fe₂O₃) nanoparticles versus pure CS in the reconstruction of induced critical-sized mandibular defects.

Design

CS-doped Fe₂O₃ was prepared; morphological and microstructure identification of nanoparticles were made. An in vivo randomised design was developed on 24 adult male dogs where four critical-sized mandibular defects were created in each dog. Bone defects were allocated into control, CS, CS-3% Fe₂O₃ and CS-10% Fe₂O₃ group. Dogs were euthanized at 1 and 3 months (12 dog/time) for histopathologic and histomorphometric evaluation.

Results

At three months, bone formation and maturation were evident where mean ± SD percent of mature bone was 2.66 ± 1.8, 9.9 ± 2.5, 22.9 ± 4.9, and 38.6 ± 8.1 in control, CS, CS-3% Fe₂O₃, and CS-10% Fe₂O₃ groups respectively. A high significant (P < 0.001) increase in area percent of mature bone was recorded in CS, CS-3% Fe₂O₃, and CS- 10% Fe₂O₃ groups compared to control group (73%, 88% and 93.3% respectively). Significant increase (P < 0.001) in area of mature bone was recorded in CS-3% Fe₂O₃ and CS-10% Fe₂O₃ groups compared to CS group. A significant increase (P < 0.001) in area of mature bone formation was detected in CS-10% Fe₂O₃ group compared to other groups.

Conclusion

CS-doped Fe₂O₃ has good osteoconductive, biocompatible properties with promoted bone regeneration. Fe₂O₃ has synergistic effect in combination with CS to promote bone formation. Increasing concentration of Fe₂O₃ nanoparticles resulted in improved osteogenesis and maturation. Results suggests that the novel CS-Fe₂O₃ alloplasts could be used for reconstruction of critical-sized bone defects.

Interaction of thin polyethyleneimine layer with the iron surface and its effect on the electrochemical behavior

Polymer-coated metals may act as biodegradable orthopedic implants with adjustable corrosion rates. Metallic surfaces represent a dynamic system with specific interactions occurring after the material is implanted into the human body. An additional layer, in the form of polymeric thin film, changes the nature of this metal-body fluids interface. Moreover, the interaction between polymer and metal itself can differ for various systems. Iron-based material modified with a thin layer of polyethyleneimine (PEI) coating was prepared and studied as potential absorbable implant. Computational methods were employed to study the interaction between the metallic surface and polymer functional monomer units at atomic levels. Various spectroscopical and optical methods (SEM, AFM, Confocal, and Raman spectroscopy) were also used to characterize prepared material. Electrochemical measurements have been chosen to study the polymer adsorption process onto the iron surface and corrosion behavior which is greatly influenced by the PEI presence. The adsorption mechanism of PEI onto iron was proposed alongside the evaluation of Fe and Fe-PEI degradation behavior studied using the impedance method. Bonding via amino -NH₂ group of PEI onto Fe and enhanced corrosion rate of coated samples were observed and confirmed.

Conjunction of gallium doping and calcium silicate mediates osteoblastic and osteoclastic performances of tricalcium phosphate bioceramics

Gallium-containing biomaterials are considered promising for reconstructing osteoporotic bone defects, owing to the potent effect of gallium on restraining osteoclast activities. Nevertheless, the gallium-containing biomaterials were demonstrated to disturb the osteoblast activities. In this study, tricalcium phosphate (TCP) bioceramics were modified by gallium doping in conjunction with incorporation of calcium silicate (CS). The results indicated that the incorporation of CS promoted transition ofβ-TCP toα-TCP, and accelerated densification process, but did not improve the mechanical strength of bioceramics. The silicon released from the composite bioceramics diminished the inhibition effect of released gallium on osteoblast activities, and maintained its effect on restraining osteoclast activities. The TCP-based bioceramics doped with 2.5 mol% gallium and incorporated with 10 mol% CS are considered suitable for treating the bone defects in the osteoporotic environment.

Mechanical Properties and Bioactivity of Poly(Lactic Acid) Composites Containing Poly(Glycolic Acid) Fiber and Hydroxyapatite Particles

To enhance the mechanical strength and bioactivity of poly(lactic acid) (PLA) to the level that can be used as a material for spinal implants, poly(glycolic acid) (PGA) fibers and hydroxyapatite (HA) were introduced as fillers to PLA composites. To improve the poor interface between HA and PLA, HA was grafted by PLA to form HA-g-PLA through coupling reactions, and mixed with PLA. The size of the HA particles in the PLA matrix was observed to be reduced from several micrometers to sub-micrometer by grafting PLA onto HA. The tensile and flexural strength of PLA/HA-g-PLA composites were increased compared with those of PLA/HA, apparently due to the better dispersion of HA and stronger interfacial adhesion between the HA and PLA matrix. We also examined the effects of the length and frequency of grafted PLA chains on the tensile strength of the composites. By the addition of unidirectionally aligned PGA fibers, the flexural strength of the composites was greatly improved to a level comparable with human compact bone. In the bioactivity tests, the growth of apatite on the surface was fastest and most uniform in the PLA/PGA fiber/HA-g-PLA composite.

Synthesis and Modification of Hydroxyapatite Nanofiber for Poly(Lactic Acid) Composites with Enhanced Mechanical Strength and Bioactivity

To enhance the bioactivity of poly(lactic acid) (PLA), a potential bone repair material, without the lowering of mechanical strength, hydroxyapatite (HA) was introduced in the form of nanofibers as the filler for application in spinal implant materials. HA nanofibers (HANF) with aspect ratio as high as ~100 were synthesized by controlling the starting pH of the reaction. While the tensile and flexural strength of PLA/HANF composites were enhanced compared with those of PLA resin, and were higher for the composites with HANF of higher aspect ratio. To further strengthen the composites, HANF was grafted with PLA chain to form HANF-g-PLA, which could improve the interface between the HANF and matrix PLA. PLA/HANF-g-PLA composites showed even higher tensile and flexural strength than PLA/HANF composites, apparently due to the better dispersion and interfacial adhesion. The composite containing 10 wt% HANF-g-PLA showed the flexural strength of 124 MPa, which was 25% higher than that of PLA resin. In the bioactivity test using a simulated body fluid solution, the rate and uniformity of the apatite growth were observed to be higher for the composites with HANF, and were even higher for those with HANF-g-PLA. This study suggested the possibility of using the PLA/HANF-g-PLA composite in the field of spinal implant materials.

Degradation Performance of Open-Cell Biomaterials from Phosphated Carbonyl Iron Powder with PEG Coating

Advances in biomedicine and development of modern technologies in the last century have fostered the improvement in human longevity and well-being. This progress simultaneously initiated the need for novel biomaterials. Recently, degradable metallic biomaterials have attracted serious attention in scientific and clinical research owing to their utilization in some specific applications. This work investigates the effect of the polyethylene glycol (PEG) coating of open-cell iron and phosphorus/iron foams on their microstructure and corrosion properties. The addition of phosphorus causes a slight increase in pore size and the deposition of a polymer coating results in a smoothened surface and a moderate decrease in pore diameter. The PEG coating leads to an increase in corrosion rates in both foams and potentially a more desirable product.

Hydrolytic Expansion Induces Corrosion Propagation for Increased Fe Biodegradation

Fe is regarded as a promising bone implant material due to inherent degradability and high mechanical strength, but its degradation rate is too slow to match the healing rate of bone. In this work, hydrolytic expansion was cleverly exploited to accelerate Fe degradation. Concretely, hydrolyzable Mg2Si was incorporated into Fe matrix through selective laser melting and readily hydrolyzed in a physiological environment, thereby exposing more surface area of Fe matrix to the solution. Moreover, the gaseous hydrolytic products of Mg2Si acted as an expanding agent and cracked the dense degradation product layers of Fe matrix, which offered rapid access for solution invasion and corrosion propagation toward the interior of Fe matrix. This resulted in the breakdown of protective degradation product layers and even the direct peeling off of Fe matrix. Consequently, the degradation rate for Fe/Mg2Si composites (0.33 mm/y) was significantly improved in comparison with that of Fe (0.12 mm/y). Meanwhile, Fe/Mg2Si composites were found to enable the growth and proliferation of MG-63 cells, showing good cytocompatibility. This study indicated that hydrolytic expansion may be an effective strategy to accelerate the degradation of Fe-based implants.

In Vitro Corrosion Behavior of Biodegradable Iron Foams with Polymeric Coating

Research in the field of biodegradable metallic scaffolds has advanced during the last decades. Resorbable implants based on iron have become an attractive alternative to the temporary devices made of inert metals. Overcoming an insufficient corrosion rate of pure iron, though, still remains a problem. In our work, we have prepared iron foams and coated them with three different concentrations of polyethyleneimine (PEI) to increase their corrosion rates. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), Fourier-transform infrared spectroscopy (FT-IR), and Raman spectroscopy were used for characterization of the polymer coating. The corrosion behavior of the powder-metallurgically prepared samples was evaluated electrochemically using an anodic polarization method. A 12 weeks long in vitro degradation study in Hanks’ solution at 37 °C was also performed. Surface morphology, corrosion behavior, and degradation rates of the open-cell foams were studied and discussed. The use of PEI coating led to an increase in the corrosion rates of the cellular material. The sample with the highest concentration of PEI film showed the most rapid corrosion in the environment of simulated body fluids.

Updates on the research and development of absorbable metals for biomedical applications

Absorbable metals, metals that corrode in physiological environment, constitute a new class of biomaterials intended for temporary medical implant applications. The introduction of these metals has shifted the established paradigm of metal implants from preventing corrosion to its direct application. Interest toward absorbable metals has been growing in the past decade. This is proved by the rapid increase in scientific publication, progressive development of standards, and launching the first commercial products. Iron, magnesium, zinc, and their alloys are the current three absorbable metals families. Magnesium-based metals are the most progressing family with a large data set obtained from both basic and translational research. Iron-based metals are still facing a major challenge of low in vivo corrosion rate despite the significant efforts that have been put to overcome its weakness. Zinc-based metals are the new alternative absorbable metals with moderate corrosion rates that fall between those of iron and magnesium. This manuscript provides a brief review on the latest progress in the research and development of absorbable metals, the most important findings, the remaining challenges, and the perspective on the future direction.