Biodegradable magnesium-based biomaterials: An overview of challenges and opportunities

Bone cells influence the degradation interface of pure Mg and WE43 materials: Insights from multimodal in vitro analysis

In this study, the interaction of pure Mg and WE43 alloy under the presence of osteoblast (OB) and osteoclast (OC) cells and their influence on the degradation of materials have been deeply analyzed. Since OB and OC interaction has an important role in bone remodeling, we examined the surface morphology and dynamic changes in the chemical composition and thickness of the corrosion layers formed on pure Mg and WE43 alloy by direct monoculture and coculture of pre-differentiated OB and OC cells in vitro. Electrochemical techniques examined the corrosion performance. The corrosion products were characterized using a combination of the focused ion beam (FIB), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Cell viability and morphology were assessed by fluorescent microscopy and SEM. Our findings demonstrate cell spread and attachment variations, which differ depending on the Mg substrates. It was clearly shown that cell culture groups delayed degradation processes with the lowest corrosion rate observed in the presence of OBOC coculture for the WE43 substrate. Ca-P enrichment was observed in the outer-middle region of the corrosion layer but only after 7 days of OBOC coculture on WE43 and after 14 days on the pure Mg specimens. STATEMENT OF SIGNIFICANCE: Magnesium metallic materials that can degrade over time provide distinct opportunities for orthopedic application. However, there is still a lack, especially in elucidating cell-material interface characterization. This study investigated the influence of osteoblast-osteoclast coculture in direct Mg-material contact. Our findings demonstrated that pre-differentiated osteoblasts and osteoclasts cocultured on Mg substrates influenced the chemistry of the corrosion layers. The cell spread and attachment were Mg substrate-dependent. The findings of coculturing bone cells directly on Mg materials within an in vitro model provide an effective approach for studying the dynamic degradation processes of Mg alloys while also elucidating cell behavior and their potential contribution to the degradation of these alloys.

The effect of Silver addition and deformation parameters on mechanostructure, biodegradation, antimicrobial and mechanical properties of Zn-based biodegradable alloys

Although low mechanical properties, Zinc (Zn) alloy systems with Copper (Cu) and Silver (Ag) as alloying elements have strong biocompatibility and biodegradability characteristics. This study examined the effects of rolling parameters and Ag alloying on the mechanical, biodegradable, and final structure of an alloy based on Zn. Comparing treated and untreated specimens, the addition of Ag led to a considerable improvement in both hardness and compressive strength. The produced alloys with varying amounts of Ag (between 1 and 4 wt%) were cold rolled at 400-800 r/min and friction coefficients between 0.3 and 0.5. The alloys' ultimate strength rose with an increase in rolling speed for Zn1Cu4Ag, and hardness and compressive strengths rose to 80HV and 470 MPa, respectively. It was demonstrated that rolling force rose somewhat with Ag concentration but significantly increased with rolling speed and friction. E. Coli and S. aureus were used to assess the biodegradable alloys' antibacterial properties. For the Zn-1Cu-2Ag alloy, the inclusion of Ag resulted in a considerable (50%) rise in antibacterial activity that exceeded the effects seen in other alloy systems.

Nanoparticle-Enabled Zn-0.1Mg Alloy with Long-Term Stability, Refined Degradation, and Favorable Biocompatibility for Biodegradable Implant Devices

Zinc-based alloys, specifically Zn-Mg, have garnered considerable attention as promising materials for biodegradable implants due to their favorable mechanical strength, appropriate corrosion rate, and biocompatibility. Nevertheless, the alloy's lack of mechanical stability and integrity, resulting from ductility loss induced by age hardening at room temperature, hampers its practical bioapplication. In this study, ceramic nanoparticles have been successfully incorporated into the Zn-Mg alloy system, leading to a significant improvement in long-term stability as well as mechanical strength and ductility. In addition, this study represents the first investigation of Zn-based nanocomposites both in vitro and in vivo to comprehend the influence of nanoparticles on the degradation behavior and biocompatibility of the Zn system. The findings indicate that the incorporation of WC nanoparticles effectively refines and stabilizes the degradation behavior of Zn-Mg without negatively impacting the cytocompatibility of the alloy. The subcutaneous implantation and femoral implantation further prove the benefits of nanoparticle incorporation and found no negative effects. Collectively, Zn-Mg-WC nanocomposites yield great potential for implant usage.

A novel biodegradable magnesium skin staple: A safety and functional evaluation

BACKGROUND

The potential of biodegradable magnesium (Mg) skin staple has recently garnered widespread attention due to their biodegradability and biocompatibility rather than traditional stainless steel staples, the most commonly used in current clinical practice. The aim of this study is to evaluate the safety and mechanical properties of a novel biodegradable Mg skin staple.

METHODS

A prototype of Mg skin staple was designed using a novel ZK60 Mg alloy. The mechanical properties of the staple were evaluated using a universal testing machine. The cytotoxicity of the staple was examined in vitro and the efficacy of the staple in wound closure was assessed in New Zealand rabbits for one and three weeks, respectively.

RESULTS

The tensile strength of this Mg alloy is 258.4 MPa with 6.9% elongation. The treatment of HaCaT and L929 cells with the staple extract resulted in over 95% cell viability, indicating no cytotoxicity. In vivo, no tissue irritation was observed. No difference was found in wound healing between the Mg skin staple and the stainless steel staple after one and three weeks in the cutting wound on the back of rabbits. Some Mg skin staples spontaneously dislodged from the skin within three weeks, while others were easily removed.

CONCLUSION

Our results confirm the safety, biocompatibility, and functionality of the novel Mg skin staple in wound closure. The efficacy of the staple in wound closure was demonstrated to be as effectively as conventional staples, with the added benefit of decreased long-term retention of skin staples in the wounds.

Antibacterial, Antibiofilm, and Tooth Color Preservation Capacity of Magnesium Oxide Nanoparticles Varnish (in vitro Study)

Purpose

Antibacterial and antibiofilm properties of magnesium oxide nanoparticles (MgONPs) mixture assessed against Streptococcus mutans (S. mutans), in addition to examining MgONPs varnish impact on the preservation of the tooth color and inhibition of methylene blue diffusion to the enamel.

Methods

MgONPs mixture was prepared in deionized water (DW), absolute ethanol (E), and rosin with ethanol (RE), named varnish. The antibacterial and antibiofilm capacities of MgONPs mixtures were tested by agar well diffusion, colony-forming unit (CFU), and biofilm inhibition microtiter methods in triplicate and compared to sodium fluoride varnish (NaF) and chlorhexidine mouthwash (ChX). A spectrophotometer was used to record basic tooth color. The artificial demineralization was initiated for 96 h. Then, experimental materials were applied to the corresponding group, and 10-day pH cycles proceeded. Then, the color was recorded in the same ambient environment. The methylene blue diffusion was evaluated by staining the samples for 24 h. After that, the diffusion test was calculated by a digital camera attached to the stereomicroscope.

Results

The agar well diffusion test expressed a significant inhibition zone with all MgONPs mixtures (p = 0.000), and maximum inhibition zone diameter associated with MgONPs-RE. The same finding was observed in the CFU test. Additionally, 2.5%, 5%, and 10% MgONPs-RE varnish showed strong biofilm inhibition capacity (p = 0.039) compared to NaF and ChX groups that inhibit biofilm formation moderately (p = 0.003). The study shows that the 5% MgONPs-RE varnish maintains basic tooth color with minimal methylene blue diffusion compared to NaF varnish (p = 0.00).

Conclusion

Evaluating MgONPs as a mixture revealed antibacterial and antibiofilm capacity against S. mutans with a higher effect of MgONPs-RE varnish. Also, examining the topical effect of MgONPs-RE varnish on the preservation of the tooth color after pH cycle challenges and methylene blue diffusion to enamel confirmed the high performance of MgONPs-RE varnish at 5%.

Challenges and Pitfalls of Research Designs Involving Magnesium-Based Biomaterials: An Overview

Magnesium-based biomaterials hold remarkable promise for various clinical applications, offering advantages such as reduced stress-shielding and enhanced bone strengthening and vascular remodeling compared to traditional materials. However, ensuring the quality of preclinical research is crucial for the development of these implants. To achieve implant success, an understanding of the cellular responses post-implantation, proper model selection, and good study design are crucial. There are several challenges to reaching a safe and effective translation of laboratory findings into clinical practice. The utilization of Mg-based biomedical devices eliminates the need for biomaterial removal surgery post-healing and mitigates adverse effects associated with permanent biomaterial implantation. However, the high corrosion rate of Mg-based implants poses challenges such as unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. The biocompatibility and degradability of materials based on magnesium have been studied by many researchers in vitro; however, evaluations addressing the impact of the material in vivo still need to be improved. Several animal models, including rats, rabbits, dogs, and pigs, have been explored to assess the potential of magnesium-based materials. Moreover, strategies such as alloying and coating have been identified to enhance the degradation rate of magnesium-based materials in vivo to transform these challenges into opportunities. This review aims to explore the utilization of Mg implants across various biomedical applications within cellular (in vitro) and animal (in vivo) models.

In vitro corrosion and cytocompatibility of Mg-Zn-Ca alloys coated with FHA

In the field of orthopedics, it's crucial to effectively slow down the degradation rate of Mg alloys. This study aims to improve the degradation behavior of Mg-Zn-Ca alloys by electrodepositing fluorohydroxyapatite (FHA). We investigated the microstructure and bond strength of the deposition, as well as degradation and cellular reactions. After 15-30 days of degradation in Hanks solution, FHA deposited alloys showed enhanced stability and less pH change. The strong interfacial bond between FHA and the Mg-Zn-Ca substrate was verified through scratch tests (Critical loads: 10.73 ± 0.014 N in Mg-Zn-0.5Ca alloys). Cellular studies demonstrated that FHA-coated alloys exhibited good cytocompatibility and promoted the growth of MC3T3-E1 cells. Further tests showed FHA-coated alloys owed improved early bone mineralization and osteogenic properties, especially in Mg-Zn-0.5Ca. This research highlighted the potential of FHA-coated Mg-Zn-0.5Ca alloys in orthopedics applications.

Dual-Protection Inorganic-Protein Coating on Mg-Based Biomaterials through Tooth-Enamel-Inspired Biomineralization

Biocompatible magnesium alloys represent revolutionary implantable materials in dentistry and orthopedics but face challenges due to rapid biocorrosion, necessitating protective coatings to mitigate dysfunction. Directly integrating durable protective coatings onto Mg surfaces is challenging because of intrinsic low coating compactness. Herein, inspired by tooth enamel, a novel highly compact dual-protection inorganic-protein (inorganicPro) coating is in situ constructed on Mg surfaces through bovine serum albumin (BSA) protein-boosted reaction between sodium fluoride (NaF) and Mg substrates. The association of Mg ions and BSA establishes a local hydrophobic domain that lowers the formation enthalpy of NaMgF3 nanoparticles. This process generates finer nanoparticles that function as "bricks," facilitating denser packing, consequently reducing voidage inside coatings by over 50% and reinforcing mechanical durability. Moreover, the incorporation of BSA in and on the coatings plays two synergistic roles: 1) acting as "mortar" to seal residual cracks within coatings, thereby promoting coating compactness and tripling anticorrosion performance, and 2) mitigating fouling-accelerated biocorrosion in complex biosystems via tenfold resistance against biofoulant attachments, including biofluids, proteins, and metabolites. This innovative strategy, leveraging proteins to alter inorganic reactions, benefits the future coating design for Mg-based and other metallic materials with tailored anticorrosion and antifouling performances.

Design and Development of Transient Sensing Devices for Healthcare Applications

With the ever-growing requirements in the healthcare sector aimed at personalized diagnostics and treatment, continuous and real-time monitoring of relevant parameters is gaining significant traction. In many applications, health status monitoring may be carried out by dedicated wearable or implantable sensing devices only within a defined period and followed by sensor removal without additional risks for the patient. At the same time, disposal of the increasing number of conventional portable electronic devices with short life cycles raises serious environmental concerns due to the dangerous accumulation of electronic and chemical waste. An attractive solution to address these complex and contradictory demands is offered by biodegradable sensing devices. Such devices may be able to perform required tests within a programmed period and then disappear by safe resorption in the body or harmless degradation in the environment. This work critically assesses the design and development concepts related to biodegradable and bioresorbable sensors for healthcare applications. Different aspects are comprehensively addressed, from fundamental material properties and sensing principles to application-tailored designs, fabrication techniques, and device implementations. The emerging approaches spanning the last 5 years are emphasized and a broad insight into the most important challenges and future perspectives of biodegradable sensors in healthcare are provided.

The Characterization of a Biodegradable Mg Alloy after Powder Bed Fusion with Laser Beam/Metal Processing for Custom Shaped Implants

A new Mg-Zn-Zr-Ca alloy in a powder state, intended to be used for custom shaped implants, was obtained via a mechanical alloying method from pure elemental powder. Further, the obtained powder alloy was processed by a PBF-LB/M (powder bed fusion with laser beam/of metal) procedure to obtain additive manufactured samples for small biodegradable implants. A series of microstructural, mechanical and corrosion analyses were performed. The SEM (scanning electron microscopy) analysis of the powder alloy revealed a good dimensional homogeneity, with a uniform colour, no agglutination and almost rounded particles, suitable for the powder bed fusion procedure. Further, the PBF-LB/M samples revealed a robust and unbreakable morphology, with a suitable porosity (that can reproduce that of cortical bone) and without an undesirable balling effect. The tested Young's modulus of the PBF-LB/M samples, which was 42 GPa, is close to that of cortical bone, 30 GPa. The corrosion tests that were performed in PBS (Phosphate-buffered saline) solution, with three different pH values, show that the corrosion parameters have a satisfactory evolution comparative to the commercial ZK 60 alloy.

Magnesium-lithium thin films for neurological applications-An in vitro investigation of glial cytocompatibility and neuroinflammatory response

Lithium (Li), a widely used drug for bipolar disorder management, is associated with many side effects due to systemic exposure. The localized delivery of lithium through implants could be an approach to overcome this challenge, for which biodegradable magnesium (Mg)-based materials are a promising choice. In this study, we focus on Mg-Li thin film alloys as potential Li-releasing implants. Therefore, we investigated the in vitro short-term corrosion behavior and cytocompatibility of two alloys, Mg-1.6wt%Li and Mg-9.5wt%Li. As glial cells are the key players of foreign body responses to implants, we used human glial cell lines for cytocompatibility studies, and a murine brain slice model for a more holistic view at the neuroinflammatory response. We found that Mg-1.6wt%Li corrodes approximately six times slower than Mg-9.5wt%Li. Microscopic analysis showed that the material surface (Mg-1.6wt%Li) is suitable for cell adhesion. The cytocompatibility test with Mg-1.6wt%Li and Mg-9.5wt%Li alloy extracts revealed that both cell types proliferated well up to 10 mM Mg concentration, irrespective of the Li concentration. In the murine brain slice model, Mg-1.6wt%Li and Mg-9.5wt%Li alloy extracts did not provoke a significant upregulation of glial inflammatory/ reactivity markers (IL-1β, IL-6, FN1, TNC) after 24 h of exposure. Furthermore, the gene expression of IL-1β (up to 3-fold) and IL-6 (up to 16-fold) were significantly downregulated after 96 h, and IL-6 downregulation showed a Li concentration dependency. Together, these results indicate the acute cytocompatibility of two Mg-Li thin film alloys and provide basis for future studies to explore promising applications of the material. STATEMENT OF SIGNIFICANCE: We propose the idea of lithium delivery to the brain via biodegradable implants to reduce systemic side effects of lithium for bipolar disorder therapy and other neurological applications. This is the first in vitro study investigating Mg-xLi thin film degradation under physiological conditions and its influence on cellular responses such as proliferation, viability, morphology and inflammation. Utilizing human brain-derived cell lines, we showed that the material surface of such a thin film alloy is suitable for normal cell attachment. Using murine brain slices, which comprise a multicellular network, we demonstrated that the material extracts did not elicit a pro-inflammatory response. These results substantiate that degradable Mg-Li materials are biocompatible and support the further investigation of their potential as neurological implants.

Influence of Magnesium Degradation on Schwannoma Cell Responses to Nerve Injury Using an In Vitro Injury Model

Nerve guidance conduits for peripheral nerve injuries can be improved using bioactive materials such as magnesium (Mg) and its alloys, which could provide both structural and trophic support. Therefore, we investigated whether exposure to Mg and Mg-1.6wt%Li thin films (Mg/Mg-1.6Li) would alter acute Schwann cell responses to injury. Using the RT4-D6P2T Schwannoma cell line (SCs), we tested extracts from freeze-killed cells (FKC) and nerves (FKN) as in vitro injury stimulants. Both FKC and FKN induced SC release of the macrophage chemoattractant protein 1 (MCP-1), a marker of the repair SC phenotype after injury. Next, FKC-stimulated cells exposed to Mg/Mg-1.6Li reduced MCP-1 release by 30%, suggesting that these materials could have anti-inflammatory effects. Exposing FKC-treated cells to Mg/Mg-1.6Li reduced the gene expression of the nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), and myelin protein zero (MPZ), but not the p75 neurotrophin receptor. In the absence of FKC, Mg/Mg-1.6Li treatment increased the expression of NGF, p75, and MPZ, which can be beneficial to nerve regeneration. Thus, the presence of Mg can differentially alter SCs, depending on the microenvironment. These results demonstrate the applicability of this in vitro nerve injury model, and that Mg has wide-ranging effects on the repair SC phenotype.

Comparison of Time-Zero Primary Stability Between a Biodegradable Magnesium Bone Staple and Metal Bone Staples for Knee Ligament Fixation: A Biomechanical Study in a Porcine Model

Background

Bone staples have been shown previously to be a viable modality for cortical tendon graft fixation in ligament knee surgery. However, soft tissue reactions have been reported, making implant removal necessary. Magnesium alloys are a promising material for biodegradable orthopaedic implants, with mechanical properties closely resembling those of human bone.

Purpose

To compare the primary stability of a biodegradable bone staple prototype made from magnesium to bone staples made from metal in the cortical fixation of tendon grafts during knee surgery.

Study Design

Controlled laboratory study.

Methods

Primary stability of peripheral tendon graft fixation was assessed in a porcine model of medial collateral ligament reconstruction. Two commercially available metal bone staples (Richards fixation staple with spikes [Me1] and spiked ligament staple [Me2]) were compared with a magnesium bone staple prototype for soft tissue fixation. Primary stability was assessed using a uniaxial materials testing machine. Cyclic loading at 50 and 100 N was applied for 500 cycles each, followed by load-to-failure testing.

Results

After 500 cycles at 50 N, elongation was 1.5 ± 0.5 mm in the Me1 group, 1.9 ± 0.5 mm in the Me2 group, and 1.8 ± 0.4 mm in the magnesium group. After 1000 cycles of loading (500 cycles at 50 N and 500 at 100 N), elongation was 3.6 ± 0.9 mm in the Me1 group, 3.5 ± 0.6 mm in the Me2 group, and 4.1 ± 1.0 mm in the magnesium group. No significant differences regarding elongation were found between the groups. Load to failure was 352 ± 115 N in the Me1 group, 373 ± 77 N in the Me2 group, and 449 ± 92 N in the magnesium group, with no significant difference between the groups.

Conclusion

In this study, the magnesium bone staples provided appropriate time-zero biomechanical primary stability in comparison with metal bone staples and may therefore be a feasible alternative for cortical fixation of tendon grafts in knee surgery.

Clinical Relevance

The biodegradability of magnesium bone staples would eliminate the need for later implant removal.

Parametric investigation of W-EDM factors for machining AM60B conductive biomaterial

Wire-electrical discharge machining (W-EDM) is a precise and efficient non-traditional technology employed to cut intricate shapes in conductive biomaterials. These biomaterials are challenging to machine using traditional methods. This present study delves into the impact of various process parameters, namely discharge duration (Ddur), spark gap time (Stime), discharge voltage (Dvolt), and wire advance rate rate (Wadv). This research evaluates the impact of several factors on response variables, namely the machining rate (MR) and surface irregularity (SR), during the machining process of the AM60B magnesium alloy. The confirmation of the material used in the machining process is achieved via the utilisation of a scanning electron microscopy (SEM) image in conjunction with an energy dispersive spectroscopic (EDS) image. The experiment is designed as L9 orthogonal array by using Taguchi's approach, taking into account 4 factors with 3 levels. The objective of this experiment is to ascertain the most favourable values for machining parameters while working with AM60B magnesium alloy using brass wire. Through analysis of variance (ANOVA), the study confirms that wire advance rate (43.10%) is the most influencing parameter for machining rate and surface irregularity followed by spark gap time (33.91%) and discharge duration (11.48%). Additionally, The TOPSIS-CRITIC and the desirability approach were used in order to determine the optimum parameter combinations that provide the most favourable combined output. Confirmatory testing is used to evaluate the efficiency of the stated ideal conditions. The maximum improvement in Desirability approach is obtained at 4.56% and 4.193% for MR and SR respectively. The maximum improvement in TOPSIS approach is obtained at 1.77% and 2.78% for MR and SR respectively.

Multilevel Reset Dependent Set of a Biodegradable Memristor with Physically Transient

The electronic device, with its biocompatibility, biodegradability, and ease of fabrication process, shows great potential to embed into health monitoring and hardware data security systems. Herein, polyvinylpyrrolidone (PVP) biopolymer is presented as an active layer, electrochemically active magnesium (Mg) as a metal electrode, and chitosan-based substrate (CHS) to fabricate biocompatible and biodegradable physically transient neuromorphic device (W/Mg/PVP/Mg/CHS). The I-V curve of device is non-volatile bipolar in nature and shows a unique compliance-induced multilevel RESET-dependent-SET behavior while sweeping the compliance current from a few microamperes to milliamperes. Non-volatile and stable switching properties are demonstrated with a long endurance test (100 sweeps) and retention time of over 104  s. The physically transient memristor (PTM) has remarkably high dynamic RON /ROFF (ON/OFF state resistance) ratio (106 Ω), and when placed in deionized (DI) water, the device is observed to completely dissolve within 10 min. The pulse transient measurements demonstrate the neuromorphic computation capabilities of the device in the form of excitatory post synaptic current (EPSC), potentiation, depression, and learning behavior, which resemble the biological function of neurons. The results demonstrate the potential of W/Mg/PVP/Mg/CHS device for use in future healthcare and physically transient electronics.

Effect of coating time on the formation of coating layer and degradation behavior of hydroxyapatite coated ZK60 alloy

OBJECTIVES

This study aims to investigate the effect of coating time on the formation of hydroxyapatite (HA) coating layer on ZK60 substrate and understand the biodegradation behavior of the coated alloy for biodegradable implant applications.

METHODS

Biodegradable ZK60 alloy was coated by HA layer for different times of 0.5, 1, 2, and 4 h by chemical conversion method. After coating, all the coated specimens were used for immersion test in Hanks' solution to understand the effect of coating time on the degradation behavior of the alloy. The degradation rate of the coated alloy was evaluated by Mg2+ ion quantification and pH change during immersion test. The microstructure of the coating layer was examined by scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS) before and after immersion to understand the degradation behavior of the coated alloy.

RESULTS

HA coating layers were formed successfully on surface of ZK60 specimens after 0.5, 1, 2, and 4 h with different microstructure. Optimal coating quality was observed at 1 or 2 h, characterized by well-formed and uniform HA layers. However, extending the coating duration to 4 h led to the formation of cracks within the HA layer, accompanied by Mg(OH)2. Specimens coated for 1 and 2 h exhibited the lowest degradation rates, while specimens coated for 0.5 and 4 h showed the highest degradation rates. Furthermore, analysis of degradation products revealed the predominance of calcium phosphates formed on the surface of specimens coated for 1 and 2 h. Conversely, specimens coated for 0.5 and 4 h exhibited Mg(OH)2 as the primary degradation product, suggesting a less effective corrosion barrier under these conditions.

CONCLUSION

The HA layer formed after 2 h demonstrated as the most effective coating layer for enhancing the corrosion resistance of the ZK60 alloy for biomedical applications.

Synthesis Technology of Magnesium-Doped Nanometer Hydroxyapatite: A Review

Ion substitution techniques for nanoparticles have become an important neighborhood of biomedical engineering and have led to the development of innovative bioactive materials for health systems. Magnesium-doped nanohydroxyapatite (Mg-nHA) has good bone conductivity, biological activity, flexural strength, and fracture toughness due to particle doping technology, making it an ideal candidate material for biomedical applications. In this Review, we have systematically presented the synthesis methods of Mg-nHA and their application in the field of biomedical science and highlighted the pros and cons of each method. Finally, some future prospects for this important neighborhood are proposed. The purpose of this Review is to provide readers with an understanding of this new field of research on bioactive materials with innovative functions and systematically introduce the latest technologies for obtaining uniform, continuous, and morphologically diverse Mg-nHA.

Incorporation of Controlled Release Systems Improves the Functionality of Biodegradable 3D Printed Cardiovascular Implants

New horizons in cardiovascular research are opened by using 3D printing for biodegradable implants. This additive manufacturing approach allows the design and fabrication of complex structures according to the patient's imaging data in an accurate, reproducible, cost-effective, and quick manner. Acellular cardiovascular implants produced from biodegradable materials have the potential to provide enough support for in situ tissue regeneration while gradually being replaced by neo-autologous tissue. Subsequently, they have the potential to prevent long-term complications. In this Review, we discuss the current status of 3D printing applications in the development of biodegradable cardiovascular implants with a focus on design, biomaterial selection, fabrication methods, and advantages of implantable controlled release systems. Moreover, we delve into the intricate challenges that accompany the clinical translation of these groundbreaking innovations, presenting a glimpse of potential solutions poised to enable the realization of these technologies in the realm of cardiovascular medicine.

Interference screws manufactured from magnesium display similar primary stability for soft tissue anterior cruciate ligament graft fixation compared to a biocomposite material - a biomechanical study

PURPOSE

Biodegradable interference screws (IFS) can be manufactured from different biomaterials. Magnesium was previously shown to possess osteoinductive properties, making it a promising material to promote graft-bone healing in anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to compare IFS made from magnesium to a contemporary biocomposite IFS.

METHODS

In a porcine model of ACL reconstruction, deep porcine flexor tendons were trimmed to a diameter of 8 mm, sutured in Krackow technique, and fixed with either 8 × 30 mm biocomposite IFS (Bc-IFS) or 8 × 30 mm magnesium IFS (Mg-IFS) in an 8 mm diameter bone tunnel in porcine tibiae. Cyclic loading for 1000 cycles from 0 to 250 N was applied, followed by load to failure testing. Elongation, load to failure and stiffness of the tested constructs was determined.

RESULTS

After 1000 cycles at 250 N, elongation was 4.8 mm ± 1.5 in the Bc-IFS group, and 4.9 mm ± 1.5 in the Mg-IFS group. Load to failure was 649.5 N ± 174.3 in the Bc-IFS group, and 683.8 N ± 116.5 in the Mg-IFS group. Stiffness was 125.3 N/mm ± 21.9 in the Bc-IFS group, and 122.5 N/mm ± 20.3 in the Mg-IFS group. No significant differences regarding elongation, load to failure and stiffness between Bc-IFS and Mg-IFS were observed.

CONCLUSION

Magnesium IFS show comparable biomechanical primary stability in comparison to biocomposite IFS and may therefore be an alternative to contemporary biodegradable IFS.

In vitro and in vivo degradation behavior of Mg-0.45Zn-0.45Ca (ZX00) screws for orthopedic applications

Magnesium (Mg) alloys have become a potential material for orthopedic implants due to their unnecessary implant removal, biocompatibility, and mechanical integrity until fracture healing. This study examined the in vitro and in vivo degradation of an Mg fixation screw composed of Mg-0.45Zn-0.45Ca (ZX00, in wt.%). With ZX00 human-sized implants, in vitro immersion tests up to 28 days under physiological conditions, along with electrochemical measurements were performed for the first time. In addition, ZX00 screws were implanted in the diaphysis of sheep for 6, 12, and 24 weeks to assess the degradation and biocompatibility of the screws in vivo. Using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), micro-computed tomography (μCT), X-ray photoelectron spectroscopy (XPS), and histology, the surface and cross-sectional morphologies of the corrosion layers formed, as well as the bone-corrosion-layer-implant interfaces, were analyzed. Our findings from in vivo testing demonstrated that ZX00 alloy promotes bone healing and the formation of new bone in direct contact with the corrosion products. In addition, the same elemental composition of corrosion products was observed for in vitro and in vivo experiments; however, their elemental distribution and thicknesses differ depending on the implant location. Our findings suggest that the corrosion resistance was microstructure-dependent. The head zone was the least corrosion-resistant, indicating that the production procedure could impact the corrosion performance of the implant. In spite of this, the formation of new bone and no adverse effects on the surrounding tissues demonstrated that the ZX00 is a suitable Mg-based alloy for temporary bone implants.

An Overview of Scaffolds and Biomaterials for Skin Expansion and Soft Tissue Regeneration: Insights on Zinc and Magnesium as New Potential Key Elements

The utilization of materials in medical implants, serving as substitutes for non-functional biological structures, supporting damaged tissues, or reinforcing active organs, holds significant importance in modern healthcare, positively impacting the quality of life for millions of individuals worldwide. However, certain implants may only be required temporarily to aid in the healing process of diseased or injured tissues and tissue expansion. Biodegradable metals, including zinc (Zn), magnesium (Mg), iron, and others, present a new paradigm in the realm of implant materials. Ongoing research focuses on developing optimized materials that meet medical standards, encompassing controllable corrosion rates, sustained mechanical stability, and favorable biocompatibility. Achieving these objectives involves refining alloy compositions and tailoring processing techniques to carefully control microstructures and mechanical properties. Among the materials under investigation, Mg- and Zn-based biodegradable materials and their alloys demonstrate the ability to provide necessary support during tissue regeneration while gradually degrading over time. Furthermore, as essential elements in the human body, Mg and Zn offer additional benefits, including promoting wound healing, facilitating cell growth, and participating in gene generation while interacting with various vital biological functions. This review provides an overview of the physiological function and significance for human health of Mg and Zn and their usage as implants in tissue regeneration using tissue scaffolds. The scaffold qualities, such as biodegradation, mechanical characteristics, and biocompatibility, are also discussed.

Biological Performance of Duplex PEO + CNT/PCL Coating on AZ31B Mg Alloy for Orthopedic and Dental Applications

To regulate the degradation rate and improve the surface biocompatibility of the AZ31B magnesium alloy, three different coating systems were produced via plasma electrolytic oxidation (PEO): simple PEO, PEO incorporating multi-walled carbon nanotubes (PEO + CNT), and a duplex coating that included a polycaprolactone top layer (PEO + CNT/PCL). Surfaces were characterized by chemical content, roughness, topography, and wettability. Biological properties analysis included cell metabolism and adhesion. PEO ± CNT resulted in an augmented surface roughness compared with the base material (BM), while PCL deposition produced the smoothest surface. All surfaces had a contact angle below 90°. The exposure of gFib-TERT and bmMSC to culture media collected after 3 or 24 h did not affect their metabolism. A decrease in metabolic activity of 9% and 14% for bmMSC and of 14% and 29% for gFib-TERT was observed after 3 and 7 days, respectively. All cells died after 7 days of exposure to BM and after 15 days of exposure to coated surfaces. Saos-2 and gFib-TERT adhered poorly to BM, in contrast to bmMSC. All cells on PEO anchored into the pores with filopodia, exhibited tiny adhesion protrusions on PEO + CNT, and presented a web-like spreading with lamellipodia on PEO + CNT/PCL. The smooth and homogenous surface of the duplex PEO + CNT/PCL coating decreased magnesium corrosion and led to better biological functionality.

Detailing the influence of PEO-coated biodegradable Mg-based implants on the lacuno-canalicular network in sheep bone: A pilot study

An increasing prevalence of bone-related injuries and aging geriatric populations continue to drive the orthopaedic implant market. A hierarchical analysis of bone remodelling after material implantation is necessary to better understand the relationship between implant and bone. Osteocytes, which are housed and communicate through the lacuno-canalicular network (LCN), are integral to bone health and remodelling processes. Therefore, it is essential to examine the framework of the LCN in response to implant materials or surface treatments. Biodegradable materials offer an alternative solution to permanent implants, which may require revision or removal surgeries. Magnesium alloys have resurfaced as promising materials due to their bone-like properties and safe degradation in vivo. To further tailor their degradation capabilities, surface treatments such as plasma electrolytic oxidation (PEO) have demonstrated to slow degradation. For the first time, the influence of a biodegradable material on the LCN is investigated by means of non-destructive 3D imaging. In this pilot study, we hypothesize noticeable variations in the LCN caused by altered chemical stimuli introduced by the PEO-coating. Utilising synchrotron-based transmission X-ray microscopy, we have characterised morphological LCN differences around uncoated and PEO-coated WE43 screws implanted into sheep bone. Bone specimens were explanted after 4, 8, and 12 weeks and regions near the implant surface were prepared for imaging. Findings from this investigation indicate that the slower degradation of PEO-coated WE43 induces healthier lacunar shapes within the LCN. However, the stimuli perceived by the uncoated material with higher degradation rates induces a greater connected LCN better prepared for bone disturbance.

Facile bioactive transformation of magnesium alloy surfaces for surgical implant applications

The market for orthopedic implant alloys has seen significant growth in recent years, and efforts to reduce the carbon footprint of medical treatment (i.e., green medicine) have prompted extensive research on biodegradable magnesium-based alloys. Magnesium alloys provide the mechanical strength and biocompatibility required of medical implants; however, they are highly prone to corrosion. In this study, Mg-9Li alloy was immersed in cell culture medium to simulate degradation in the human body, while monitoring the corresponding effects of the reaction products on cells. Variations in pH revealed the generation of hydroxyl groups, which led to cell death. At day-5 of the reaction, a coating of MgCO3 (H2O)3, HA, and α -TCP appeared on sample surfaces. The coating presented three-dimensional surface structures (at nanometer to submicron scales), anti-corrosion effects, and an altered surface micro-environment conducive to the adhesion of osteoblasts. This analysis based on bio-simulation immersion has important implications for the clinical use of Mg alloys to secure regenerated periodontal tissue.

Characterization and Biocompatibility Assessment of Boron Nitride Magnesium Nanocomposites for Orthopedic Applications

Magnesium (Mg) has been intensively studied as a promising alternative material to inert metallic alloys for orthopedic fixation devices due to its biodegradable nature inside the body and its favorable biocompatibility. However, the low mechanical strength and rapid corrosion of Mg in physiological environments represent the main challenges for the development of Mg-based devices for orthopedic applications. A possible solution to these limitations is the incorporation of a small content of biocompatible nanoparticles into the Mg matrix to increase strength and possibly corrosion resistance of the resulting nanocomposites. In this work, the effect of adding boron nitride (BN) nanoparticles (0.5 and 1.5 vol.%) on the mechanical properties, corrosion behavior, and biocompatibility of Mg-based nanocomposites was investigated. The properties of the nanocomposites fabricated using powder metallurgy methods were assessed using microstructure analyses, microhardness, compression tests, in vitro corrosion, contact angle, and cytotoxicity tests. A significant increase in the microhardness, strength, and corrosion rates of Mg-BN nanocomposites was detected compared with those of pure Mg (0% BN). Crystalline surface post-corrosion byproducts were detected and identified via SEM, EDX, and XRD. Biocompatibility assessments showed that the incorporation of BN nanoparticles had no significant impact on the cytotoxicity of Mg and samples were hydrophilic based on the contact angle results. These results confirm that the addition of BN nanoparticles to the Mg matrix can increase strength and corrosion resistance without influencing cytotoxicity in vitro. Further investigation into the chemical behavior of nanocomposites in physiological environments is needed to determine the potential impact of corrosive byproducts. Surface treatments and formulation methods that would increase the viability of these materials in vivo are also needed.

Refixation of a Large Osteochondral Fragment with Magnesium Compression Screws-A Case Report

INTRODUCTION

Osteochondrosis dissecans (OCD) is a disease affecting the subchondral bone and the overlying articular cartilage. The etiology is most likely a combination of biological and mechanical factors. The incidence is highest in children >12 years old and it predominantly affects the knee. In high-grade OCD lesions, free osteochondral fragments usually are refixed via titanium screws or biodegradable screws or pins. In this case, headless compression screws made from magnesium were used for refixation.

CASE REPORT

A thirteen-year-old female patient with a two-year history of knee pain was diagnosed with an OCD lesion of the medial femoral condyle. After initial conservative treatment, displacement of the osteochondral fragment occurred. Refixation was performed using two headless magnesium compression screws. At the 6 months follow up, the patient was pain free, and the fragment showed progressive healing while the implants were biodegrading.

DISCUSSION

Existing implants for refixation of OCD lesions either require subsequent removal or show less stability and possible inflammatory reactions. The new generation of magnesium screws used in this case did not lead to a gas release, as described for previous magnesium implants, while maintaining stability during continuous biodegradation.

CONCLUSIONS

The data available to date on magnesium implants for the treatment of OCD are promising. However, the evidence on the magnesium implants in refixation surgery of OCD lesions is still limited. Further research needs to be conducted to provide data on outcomes and possible complications.

Ion elemental-optimized layered double hydroxide nanoparticles promote chondrogenic differentiation and intervertebral disc regeneration of mesenchymal stem cells through focal adhesion signaling pathway

Chronic low back pain and dyskinesia caused by intervertebral disc degeneration (IDD) are seriously aggravated and become more prevalent with age. Current clinical treatments do not restore the biological structure and inherent function of the disc. The emergence of tissue engineering and regenerative medicine has provided new insights into the treatment of IDD. We synthesized biocompatible layered double hydroxide (LDH) nanoparticles and optimized their ion elemental compositions to promote chondrogenic differentiation of human umbilical cord mesenchymal stem cells (hUC-MSCs). The chondrogenic differentiation of LDH-treated MSCs was validated using Alcian blue staining, qPCR, and immunofluorescence analyses. LDH-pretreated hUC-MSCs were differentiated prior to transplantation into the degenerative site of a needle puncture IDD rat model. Repair and regeneration evaluated using X-ray, magnetic resonance imaging, and tissue immunostaining 4–12 weeks after transplantation showed recovery of the disc space height and integrated tissue structure. Transcriptome sequencing revealed significant regulatory roles of the extracellular matrix (ECM) and integrin receptors of focal adhesion signaling pathway in enhancing chondrogenic differentiation and thus prompting tissue regeneration. The construction of ion-specific LDH nanomaterials for in situ intervertebral disc regeneration through the focal adhesion signaling pathway provides theoretical basis for clinical transformation in IDD treatment.

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LDH nanoparticles with different elemental compositions are constructed to optimize the chondrogenic differentiation of hUC-MSCs.

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Optimized-LDH pretreated hUC-MSCs transplantation show recovery of disc space height and integrated tissue structure.

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ECM and focal adhesion signaling pathway play significant roles in LDH-promoted cell differentiation and tissue regeneration.

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Ion-specific optimizing LDH provides theoretical basis for clinical transformation on IDD treatment.

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.

Study on Material Design and Corrosion Resistance Based on Multi-Principal Component Alloying Theory

This study mainly attempts to develop Mg-based alloy materials with excellent corrosion resistance by means of multi-principal alloying. The alloy elements are determined based on the multi-principal alloy elements and the performance requirements of the components of biomaterials. Mg30Zn30Sn30Sr5Bi5 alloy was successfully prepared by vacuum magnetic levitation melting. Through the electrochemical corrosion test with m-SBF solution (pH7.4) as the electrolyte, the corrosion rate of alloy Mg30Zn30Sn30Sr5Bi5 alloy decreased to 20% of pure Mg. It could also be seen from the polarization curve that when the self-corrosion current density is low, the alloy shows superior corrosion resistance. Nevertheless, with the increase in self-corrosion current density, although the anodic corrosion performance of the alloy is obviously better than that of pure Mg, the cathode shows the opposite situation. The Nyquist diagram shows that the self-corrosion potential of the alloy is much higher than that of pure Mg. In general, under the condition of low self-corrosion current density, the alloy materials display excellent corrosion resistance. It is proved that the multi-principal alloying method is of positive significance for improving the corrosion resistance of Mg alloys.

Advances in Multifunctional Bioactive Coatings for Metallic Bone Implants

To fix the bone in orthopedics, it is almost always necessary to use implants. Metals provide the needed physical and mechanical properties for load-bearing applications. Although widely used as biomedical materials for the replacement of hard tissue, metallic implants still confront challenges, among which the foremost is their low biocompatibility. Some of them also suffer from excessive wear, low corrosion resistance, infections and shielding stress. To address these issues, various coatings have been applied to enhance their in vitro and in vivo performance. When merged with the beneficial properties of various bio-ceramic or polymer coatings remarkable bioactive, osteogenic, antibacterial, or biodegradable composite implants can be created. In this review, bioactive and high-performance coatings for metallic bone implants are systematically reviewed and their biocompatibility is discussed. Updates in coating materials and formulations for metallic implants, as well as their production routes, have been provided. The ways of improving the bioactive coating performance by incorporating bioactive moieties such as growth factors, osteogenic factors, immunomodulatory factors, antibiotics, or other drugs that are locally released in a controlled manner have also been addressed.

Immune response differences in degradable and non-degradable alloy implants

Alloy based implants have made a great impact in the clinic and in preclinical research. Immune responses are one of the major causes of failure of these implants in the clinic. Although the immune responses toward non-degradable alloy implants are well documented, there is a poor understanding of the immune responses against degradable alloy implants. Recently, there have been several reports suggesting that degradable implants may develop substantial immune responses. This phenomenon needs to be further studied in detail to make the case for the degradable implants to be utilized in clinics. Herein, we review these new recent reports suggesting the role of innate and potentially adaptive immune cells in inducing immune responses against degradable implants. First, we discussed immune responses to allergen components of non-degradable implants to give a better overview on differences in the immune response between non-degradable and degradable implants. Furthermore, we also provide potential areas of research that can be undertaken that may shed light on the local and global immune responses that are generated in response to degradable implants.

Enhanced abrasive-mixed-µ-EDM performance towards improved surface characteristics of biodegradable Mg AZ31B alloy

The non-degradable metallic implants, such as bone screws, often act as the source of dysfunction and harmful corrosion products in the aqueous environment inside the human body. Many of these implants are fixed either temporarily or permanently into the human body, and therefore, both need to match tight tolerances with a remarkably finished surface to eradicate burrs or striations. In this regard, the new generation of degradable magnesium (Mg) alloy implants with excellent osseointegration and low elasticity (like that of human bone), minimizing stress shielding, have been identified as potential candidates to challenge surgical procedures reintervention. However, the biological response of an implant toward the cells in vivo can be predominantly regulated by modifying the surface chemistry, morphology, and corrosion characteristics. Powder or abrasive-mixed-micro-electric discharge machining (A-M-µ-EDM) is gaining attention for executing precision machining and achieving a simultaneous surface modification on micro-manufactured surfaces, suitable for clinical applications. Therefore, the present research aimed at improving the surface characteristics of Mg AZ31B alloy via an augmented performance of A-M-µ-EDM by adopting copper and brass-micro-electrodes (C-µ-E and B-µ-E) in association with distinct abrasive particle concentrations (APCs: 0, 1.5, 3, 4.5, and 6 g/l) of bioactive zinc abrasives. To enhance the A-M-µ-EDM capabilities, the experiments were designed with a one-variable-at-a-time (OVAT) strategy, and the trial runs were conducted using different combinations of µ-electrodes and APCs. The superior performance of A-M-µ-EDM was noticed with the fusion of C-µ-E and 3 g/l APC in terms of minimum machining time (MT) and dimensional deviation (DD). The additional outcomes of this work reported favorable improvements in surface morphology, chemistry, topography, wettability, microhardness, and corrosion resistance on the A-M-µ-EDMed sample of interest.

The Mechanical, Thermal, and Chemical Properties of PLA-Mg Filaments Produced via a Colloidal Route for Fused-Filament Fabrication

The effect of Mg particles on the thermal, chemical, physical, and primarily mechanical properties of 3D-printed PLA/Mg composites is studied in this paper. Recently, new colloidal processing has been proposed to introduce Mg particles into the PLA matrix, which ensures good dispersion of the particles and better thermal properties, allowing for thermal processing routes such as extrusion or 3D printing via fused-filament fabrication. The thermal and physical properties are here studied in 1D single-filament-printed PLA/Mg composites with 0 to 10 wt.% of Mg particles by Differential Scanning Calorimetry (DSC); we analyse the PLA chain modifications produced, the crystallinity fraction, and the different crystalline forms of the PLA after thermal processing. Fourier Transform Infrared Spectroscopy (FTIR) is used to confirm the influence of the PLA/Mg colloidal processing after printing. The mechanical properties are measured with a universal tensile test machine on the 1D single-printed filaments via fused-filament fabrication (FFF); the filaments were naturally aged to stable conditions. Filaments with and without a notch are studied to obtain the materials' tensile strength, elastic modulus, and fracture toughness. Different analytical models to explain the results of the PLA-Mg were studied, in which the minimum values for the interface strength of the PLA-Mg composites were calculated.

Additive Manufactured Magnesium-Based Scaffolds for Tissue Engineering

Additive manufacturing (AM) is an important technology that led to a high evolution in the manufacture of personalized implants adapted to the anatomical requirements of patients. Due to a worldwide graft shortage, synthetic scaffolds must be developed. Regarding this aspect, biodegradable materials such as magnesium and its alloys are a possible solution because the second surgery for implant removal is eliminated. Magnesium (Mg) exhibits mechanical properties, which are similar to human bone, biodegradability in human fluids, high biocompatibility, and increased ability to stimulate new bone formation. A current research trend consists of Mg-based scaffold design and manufacture using AM technologies. This review presents the importance of biodegradable implants in treating bone defects, the most used AM methods to produce Mg scaffolds based on powder metallurgy, AM-manufactured implants properties, and in vitro and in vivo analysis. Scaffold properties such as biodegradation, densification, mechanical properties, microstructure, and biocompatibility are presented with examples extracted from the recent literature. The challenges for AM-produced Mg implants by taking into account the available literature are also discussed.

Performance of PEO/Polymer Coatings on the Biodegradability, Antibacterial Effect and Biocompatibility of Mg-Based Materials

Magnesium (Mg) alloys have recently attracted attention in biomedicine as biodegradable materials with non-toxic degradable products. Such compounds have become a frontier in the study of biodegradable materials because of their remarkable biomechanical compatibility and superior biocompatibility. The use of Mg-based implants reduces the negative consequences of permanent biological implants by eliminating the necessity for biomaterial surgery following the healing process. However, the quick deterioration, formation of considerable gas of hydrogen volumes and a rise in the body environment pH are obstacles in the application of Mg as an implant material. Hence, compelling advances for erosion resistance and biocompatibility of magnesium and its alloys are noteworthy. Surface modification may be a practical approach because it improves the erosion resistance compared with extensive preparation of a treated surface for progressed bone recovery and cell attachment. Coating produced by plasma electrolytic oxidation (PEO) seems a compelling method in order to enhance magnesium and the properties of its alloys. PEO-formed coatings cannot provide long-term protection in the physiological environment due to their porous nature. Thus, a polymer coating is applied on the porous PEO-formed coating, which is steadily applied on the surface. Polymer coatings improve the biocompatibility properties of Mg and its alloys and increase corrosion resistance. In this article, the most recent advancements in PEO/polymer composite coatings are reviewed, and the biocompatibility of such coatings is examined.

Advancing intestinal organoid technology to decipher nano-intestine interactions and treat intestinal disease

With research burgeoning in nanoscience and nanotechnology, there is an urgent need to develop new biological models that can simulate native structure, function, and genetic properties of tissues to evaluate the adverse or beneficial effects of nanomaterials on a host. Among the current biological models, three-dimensional (3D) organoids have developed as powerful tools in the study of nanomaterial-biology (nano-bio) interactions, since these models can overcome many of the limitations of cell and animal models. A deep understanding of organoid techniques will facilitate the development of more efficient nanomedicines and further the fields of tissue engineering and personalized medicine. Herein, we summarize the recent progress in intestinal organoids culture systems with a focus on our understanding of the nature and influencing factors of intestinal organoid growth. We also discuss biomimetic extracellular matrices (ECMs) coupled with nanotechnology. In particular, we analyze the application prospects for intestinal organoids in investigating nano-intestine interactions. By integrating nanotechnology and organoid technology, this recently developed model will fill the gaps left due to the deficiencies of traditional cell and animal models, thus accelerating both our understanding of intestine-related nanotoxicity and the development of nanomedicines.

Bone Remodeling Interaction with Magnesium Alloy Implants Studied by SEM and EDX

The development direction of bioresorbable fixing structures is currently very relevant because it corresponds to the priority areas in worldwide biotechnology development. Magnesium (Mg)-based alloys are gaining high levels of attention due to their promising potential use as the basis for fixating structures. These alloys can be an alternative to non-degradable metal implants in orthopedics, maxillofacial surgery, neurosurgery, and veterinary medicine. In our study, we formulated a Mg-2Zn-2Ga alloy, prepared pins, and analyzed their biodegradation level based on SEM (scanning electron microscopy) and EDX (energy-dispersive X-ray analysis) after carrying out an experimental study on rats. We assessed the resorption parameters 1, 3, and 6 months after surgery. In general, the biodegradation process was characterized by the systematic development of newly formed bone tissue. Our results showed that Mg-2Zn-2Ga magnesium alloys are suitable for clinical applications.

Advanced Light Source Analytical Techniques for Exploring the Biological Behavior and Fate of Nanomedicines

Exploration of the biological behavior and fate of nanoparticles, as affected by the nanomaterial-biology (nano-bio) interaction, has become progressively critical for guiding the rational design and optimization of nanomedicines to minimize adverse effects, support clinical translation, and aid in evaluation by regulatory agencies. Because of the complexity of the biological environment and the dynamic variations in the bioactivity of nanomedicines, in-situ, label-free analysis of the transport and transformation of nanomedicines has remained a challenge. Recent improvements in optics, detectors, and light sources have allowed the expansion of advanced light source (ALS) analytical technologies to dig into the underexplored behavior and fate of nanomedicines in vivo. It is increasingly important to further develop ALS-based analytical technologies with higher spatial and temporal resolution, multimodal data fusion, and intelligent prediction abilities to fully unlock the potential of nanomedicines. In this Outlook, we focus on several selected ALS analytical technologies, including imaging and spectroscopy, and provide an overview of the emerging opportunities for their applications in the exploration of the biological behavior and fate of nanomedicines. We also discuss the challenges and limitations faced by current approaches and tools and the expectations for the future development of advanced light sources and technologies. Improved ALS imaging and spectroscopy techniques will accelerate a profound understanding of the biological behavior of new nanomedicines. Such advancements are expected to inspire new insights into nanomedicine research and promote the development of ALS capabilities and methods more suitable for nanomedicine evaluation with the goal of clinical translation.

A review on magnesium alloys for biomedical applications

Magnesium (Mg) and Mg alloys are considered as potential candidates for biomedical applications because of their high specific strength, low density, and elastic modulus, degradability, good biocompatibility and biomechanical compatibility. However, the rapid corrosion rate of Mg alloys results in premature loss of mechanical integrity, limiting their clinical application in load-bearing parts. Besides, the low strength of Mg alloys restricts their further application. Thus, it is essential to understand the characteristics and influencing factors of mechanical and corrosion behavior, as well as the methods to improve the mechanical performances and corrosion resistance of Mg alloys. This paper reviews the recent progress in elucidating the corrosion mechanism, optimizing the composition, and microstructure, enhancing the mechanical performances, and controlling the degradation rate of Mg alloys. In particular, the research progress of surface modification technology of Mg alloys is emphasized. Finally, the development direction of biomedical Mg alloys in the future is prospected.

Comparative Osteogenesis and Degradation Behavior of Magnesium Implant in Epiphysis and Diaphysis of the Long Bone in the Rat Model

Magnesium (Mg), as a biodegradable material, is a promising candidate for orthopedic surgery. Long-bone fractures usually occur in cancellous-bone-rich epiphysis at each end or the cortical-rich diaphysis in the center, with different bone healing processes. Little is known about the differences in results between the two regions when applying Mg implants. Therefore, this study aimed to compare the biodegradation and osteogenesis of Mg implants in a rat model's epiphysis and diaphysis of the long bone. Twelve male Sprague Dawley rats underwent Mg rod implantation in the distal femoral epiphyses and tibial diaphyses. Every three weeks for up to twelve weeks, degradation behavior, gas evolution, and new bone formation were measured by micro CT. Histomorphology was analyzed by Hematoxylin and Eosin, Villanueva bone staining, and TRAP staining for osteoclastogenesis evaluations. Micro-CT analysis showed statistically significant higher new bone formation in the epiphysis group than in the diaphysis group, which correlated with a lower gas volume. Histological analysis showed higher osseointegration of Mg implants in the epiphyseal region than in the diaphyseal region. The magnesium implant's osteoclastogenesis-inhibiting properties were shown in the surrounding areas in both the cortical bone of the diaphysis and the cancellous bone of the epiphysis. Our findings show the differences in the magnesium implant's osteogenesis and biodegradation in the epiphysis and the diaphysis. These dissimilarities indicate a better response of the epiphyseal region to the Mg implants, a promising biomaterial for orthopedic surgery applications.

γ-Fe2 O3 Loading Mitoxantrone and Glucose Oxidase for pH-Responsive Chemo/Chemodynamic/Photothermal Synergistic Cancer Therapy

Traditional cancer therapy is limited by poor prognosis and risk of recurrence. Emerging therapies offer alternatives to these problems. In addition, synergistic therapy can combine the advantages of multiple therapies to eliminate cancer cells while attenuating damage to normal tissues. Herein, a theranostic nanoplatform based on the chemotherapeutic drug mitoxantrone (MTO) and glucose oxidase (GOx) co-loaded γ-Fe₂ O₃ nanoparticles (MTO-GOx@γ-Fe₂ O₃ NPs) is designed and prepared to realize photoacoustic imaging-guided chemo/chemodynamic/photothermal (CT/CDT/PTT) synergistic cancer therapy. With a particle size of about 86.2 nm, the synthesized MTO-GOx@γ-Fe₂ O₃ NPs can selectively accumulate at tumor sites by enhanced permeability and retention (EPR) effects. After entering cancer cells by endocytosis, MTO-GOx@γ-Fe₂ O₃ NPs decompose into Fe³⁺ ions and release cargo because of their pH-responsive characteristic. As a Food and Drug Administration (FDA)-approved chemotherapy drug, MTO shows strong DNA disruption ability and satisfying photothermal conversion ability under laser irradiation for photothermal therapy. Simultaneously, GOx catalyzes the decomposition of glucose and generates hydrogen peroxide (H₂ O₂ ) to enhance the chemodynamic therapy efficiency. In vitro and in vivo experiments reveal that MTO-GOx@γ-Fe₂ O₃ NPs possess a significant synergistic therapeutic effect in cancer treatment.

Recent Advancements in Materials and Coatings for Biomedical Implants

Metallic materials such as stainless steel (SS), titanium (Ti), magnesium (Mg) alloys, and cobalt-chromium (Co-Cr) alloys are widely used as biomaterials for implant applications. Metallic implants sometimes fail in surgeries due to inadequate biocompatibility, faster degradation rate (Mg-based alloys), inflammatory response, infections, inertness (SS, Ti, and Co-Cr alloys), lower corrosion resistance, elastic modulus mismatch, excessive wear, and shielding stress. Therefore, to address this problem, it is necessary to develop a method to improve the biofunctionalization of metallic implant surfaces by changing the materials' surface and morphology without altering the mechanical properties of metallic implants. Among various methods, surface modification on metallic surfaces by applying coatings is an effective way to improve implant material performance. In this review, we discuss the recent developments in ceramics, polymers, and metallic materials used for implant applications. Their biocompatibility is also discussed. The recent trends in coatings for biomedical implants, applications, and their future directions were also discussed in detail.

Protective Effect of Iron Oxide Nanoparticles on Periodontal Injury in Rats by Inhibiting Collagenase-1 and Alkaline Phosphatase Expression

This study intends to assess whether iron oxide nanoparticles affect periodontal injury and collagenase-1 (COL-1), and alkaline phosphatase (ALP) in rats. In this study, the ALP activity and Col-1 concentration in rats with periodontal injury were determined.We detected the periodontal histopathological changes and expression of periodontal pocket depth (PD) and attachment loss (AL) by Hematoxylin and eosin (HE) staining.We also detected Col-1 and ALP proteins in periodontal tissues by Western blot. Real-time reverse transcription-polymerase chain reaction (RT-PCR) detected Col-1 and ALP mRNA level in periodontal tissues of rats in each group, while ALP activity and Col-1 concentration in gingival crevicular fluid in model group increased compared to sham group (P < 0.05). After intervention by iron oxide nanoparticles, ALP activity and Col-1 concentration in the gingival crevicular fluid of model rats decreased greatly (P < 0.05). The gingival atrophy was more serious in model group, and many inflammatory cells infiltrated into the tissue and destroyed the alveolar tissue. Meanwhile, the periodontal tissue from rats in intervention group was greatly improved, and the degree of alveolar bone destruction was also significantly reduced, while the PD and AL periodontal indexes were significantly inhibited (P < 0.05). The protein and relative expression showed that the protein and mRNA expressions of ALP and Col-1 in periodontal tissue from model group were lower than those in sham group (P < 0.05). After intervention by iron oxide nanoparticles, the protein and mRNA expressions of ALP and Col-1 in the periodontal tissues in intervention group increased (P < 0.05). Iron oxide nanoparticles can thus inhibit the expression of ALP and COL-1 in periodontal injury rats, and improve the periodontal injury tissue.

The Biodegradability and in Vitro Cytological Study on the Composite of PLGA Combined With Magnesium Metal

The main goal of this study was to develop a novel poly (lactic-co-glycolic acid) (PLGA) composite biodegradable material with magnesium (Mg) metal to overcome the acidic degradation of PLGA and to investigate the cytocompatibility and osteogenesis of the novel material. PLGA composites with 5 and 10 wt% Mg were prepared. The samples were initially cut into 10 mm × 10 mm films, which were used to detect the pH value to evaluate the self-neutralized ability. Murine embryo osteoblast precursor (MC3T3-E1) cells were used for in vitro experiments to evaluate the cytotoxicity, apoptosis, adhesion, and osteogenic differentiation effect of the composite biodegradable material. pH monitoring showed that the average value of PLGA with 10 wt% Mg group was closer to the normal physiological environment than that of other groups. Cell proliferation and adhesion assays indicated no significant difference between the groups, and all the samples showed no toxicity to cells. As for cell apoptosis detection, the rate of early apoptotic cells was proportional to the ratio of Mg. However, the ratios of the experimental groups were lower than those of the control group. Alkaline phosphatase activity staining demonstrated that PLGA with 10 wt% Mg could effectively improve the osteogenic differentiation of MC3T3-E1 cells. In summary, PLGA with 10 wt% Mg possessed effective osteogenic properties and cytocompatibility and therefore could provide a wide range of applications in bone defect repair and scaffold-based tissue engineering in clinical practice.

Biodegradable Magnesium Biomaterials-Road to the Clinic

In recent decades, we have witnessed radical changes in the use of permanent biomaterials. The intrinsic ability of magnesium (Mg) and its alloys to degrade without releasing toxic degradation products has led to a vast range of applications in the biomedical field, including cardiovascular stents, musculoskeletal, and orthopedic applications. With the use of biodegradable Mg biomaterials, patients would not suffer second surgery and surgical pain anymore. Be that as it may, the main drawbacks of these biomaterials are the high corrosion rate and unexpected degradation in physiological environments. Since biodegradable Mg-based implants are expected to show controllable degradation and match the requirements of specific applications, various techniques, such as designing a magnesium alloy and modifying the surface characteristics, are employed to tailor the degradation rate. In this paper, some fundamentals and particular aspects of magnesium degradation in physiological environments are summarized, and approaches to control the degradation behavior of Mg-based biomaterials are presented.

Research on Orientation of Basic Fibroblast Growth Factor with Magnetic Nanoparticles (MNPs) on Regeneration and Recovery of Rats' Dampened Skeletal Muscle and Expressed Level of Matrix Metalloproteinase

The basic fibroblast growth factor (bFGF) has a special role in improving proliferation and differentiation of fiber cells in growth of muscle. The function of bFGF with magnetic nanoparticles (MNPs) on regeneration and recovery of rats' dampened skeletal muscle and expression of MMPS were studied in our research. The MNPs packed with bFGF were prepared and 95 experimental rats were selected. These 30 rats were equally divided into control group, model group (self-healing without obstruction after model was established), bFGF group (disposed with bFGF packaged with MNP). The contractility and stress relaxation of rats' skeletal muscle were observed at the 48th h, 10th, 17th, 24th and 30th days after damage. The remaining 65 rats were divided randomly into control group (5 rats) and experimental group (60 rats intervened with MNPs packaged with bFGF). The groups were randomly divided into 0.5 h, 1 h, 3 h, 6 h, 12 h, 1 d, 2 d, 3 d, 4 d, 7 d, 10 d and 14 d according to different executed time. The levels of bFGF and MMPS were detected by HE staining method and immunohistochemical staining. There was a significant declining tendency of shrinkage stress of muscle in the model, sham-operation, BSA and bFGF groups compared with control group in the second day. The contractility after contusion wound in the regeneration and recovery of rats' skeletal muscle was effectively alleviated with MNPs packaged with bFGF.

Biodegradable magnesium-based biomaterials: An overview of challenges and opportunities

As promising biodegradable materials with nontoxic degradation products, magnesium (Mg) and its alloys have received more and more attention in the biomedical field very recently. Having excellent biocompatibility and unique mechanical properties, magnesium-based alloys currently cover a broad range of applications in the biomedical field. The use of Mg-based biomedical devices eliminates the need for biomaterial removal surgery after the healing process and reduces adverse effects induced by the implantation of permanent biomaterials. However, the high corrosion rate of Mg-based implants leads to unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. To overcome these limitations, alloying Mg with suitable alloying elements and surface treatment come highly recommended. In this area, open questions remain on the behavior of Mg-based biomaterials in the human body and the effects of different factors that have resulted in these challenges. In addition to that, many techniques are yet to be verified to turn these challenges into opportunities. Accordingly, this article aims to review major challenges and opportunities for Mg-based biomaterials to minimize the challenges for the development of novel biomaterials made of Mg and its alloys.