Biomimetic porous Mg with tunable mechanical properties and biodegradation rates for bone regeneration

Analysis of the CPZ/Wnt4 osteogenic pathway for high-bonding-strength composite-coated magnesium scaffolds through transcriptomics

Magnesium (Mg)-based scaffolds are garnering increasing attention as bone repair materials owing to their biodegradability and mechanical resemblance to natural bone. Their effectiveness can be augmented by incorporating surface coatings to meet clinical needs. However, the limited bonding strength and unclear mechanisms of these coatings have impeded the clinical utility of scaffolds. To address these issues, this study introduces a composite coating of high-bonding-strength polydopamine-microarc oxidation (PDA-MHA) on Mg-based scaffolds. The results showed that the PDA-MHA coating achieved a bonding strength of 40.56 ± 1.426 MPa with the Mg scaffold surface, effectively enhancing hydrophilicity and controlling degradation rates. Furthermore, the scaffold facilitated bone regeneration by influencing osteogenic markers such as RUNX-2, OPN, OCN, and VEGF. Transcriptomic analyses further demonstrated that the PDA-MHA/Mg scaffold upregulated carboxypeptidase Z expression and activated the Wnt-4/β-catenin signaling pathway, thereby promoting bone regeneration. Overall, this study demonstrated that PDA can synergistically enhance bone repair with Mg scaffold, broadening the application scenarios of Mg and PDA in the field of biomaterials. Moreover, this study provides a theoretical underpinning for the application and clinical translation of Mg-based scaffolds in bone tissue engineering endeavors.

Mimicking the mechanical properties of cortical bone with an additively manufactured biodegradable Zn-3Mg alloy

Additively manufactured (AM) biodegradable zinc (Zn) alloys have recently emerged as promising porous bone-substituting materials, due to their moderate degradation rates, good biocompatibility, geometrically ordered microarchitectures, and bone-mimicking mechanical properties. While AM Zn alloy porous scaffolds mimicking the mechanical properties of trabecular bone have been previously reported, mimicking the mechanical properties of cortical bone remains a formidable challenge. To overcome this challenge, we developed the AM Zn-3Mg alloy. We used laser powder bed fusion to process Zn-3Mg and compared it with pure Zn. The AM Zn-3Mg alloy exhibited significantly refined grains and a unique microstructure with interlaced α-Zn/Mg2Zn11 phases. The compressive properties of the solid Zn-3Mg specimens greatly exceeded their tensile properties, with a compressive yield strength of up to 601 MPa and an ultimate strain of >60 %. We then designed and fabricated functionally graded porous structures with a solid core and achieved cortical bone-mimicking mechanical properties, including a compressive yield strength of >120 MPa and an elastic modulus of ≈20 GPa. The biodegradation rates of the Zn-3Mg specimens were lower than those of pure Zn and could be adjusted by tuning the AM process parameters. The Zn-3Mg specimens also exhibited improved biocompatibility as compared to pure Zn, including higher metabolic activity and enhanced osteogenic behavior of MC3T3 cells cultured with the extracts from the Zn-3Mg alloy specimens. Altogether, these results marked major progress in developing AM porous biodegradable metallic bone substitutes, which paved the way toward clinical adoption of Zn-based scaffolds for the treatment of load-bearing bony defects. STATEMENT OF SIGNIFICANCE: Our study presents a significant advancement in the realm of biodegradable metallic bone substitutes through the development of an additively manufactured Zn-3Mg alloy. This novel alloy showcases refined grains and a distinctive microstructure, enabling the fabrication of functionally graded porous structures with mechanical properties resembling cortical bone. The achieved compressive yield strength and elastic modulus signify a critical leap toward mimicking the mechanical behavior of load-bearing bone. Moreover, our findings reveal tunable biodegradation rates and enhanced biocompatibility compared to pure Zn, emphasizing the potential clinical utility of Zn-based scaffolds for treating load-bearing bony defects. This breakthrough opens doors for the wider adoption of zinc-based materials in regenerative orthopedics.

Exploration of microstructural characteristics, mechanical properties, andin vitrobiocompatibility of biodegradable porous magnesium scaffolds for orthopaedic implants

In this study, porous magnesium (Mg) scaffolds were investigated with varying strontium (Sr) and constant zinc (Zn) concentrations through the powder metallurgy process. All samples were examined at room temperature to evaluate their microstructure, mechanical andin-vitrodegradation behaviour and biological properties. Results indicated that adding Sr was associated with fine average grain size, increased mechanical strength, and a decreased corrosion rate. All samples show tiny isolated and open interconnected pores (porosities: 18%-30%, pores: 127-279 µm) with a suitable surface roughness of less than 0.5 µm. All the provided samples possess mechanical and hemocompatible properties that closely resemble natural bone. Mg-4Zn-2Sr has the highest hardness (102.61 ± 15.1 HV) and compressive strength (24.80 MPa) than Mg-4Zn-0.5Sr (85 ± 8.5 HV, 22.14 MPa) and Mg-4Zn-1Sr (97.71 ± 11.2 HV, 18.06 MPa). Immersion results revealed that samples in phosphate-buffered saline solutions have excellent degradability properties, which makes them a promising biodegradable material for orthopaedic applications. The scaffold with the highest Sr concentration shows the best optimised mechanical and degradation behaviour out of the three porous scaffolds, with a 2.7% hemolysis rate.

A strategy for enhancing bioactivity and osseointegration with antibacterial effect by incorporating magnesium in polylactic acid based biodegradable orthopedic implant

Biodegradable orthopedic implants are essential for restoring the physiological structure and function of bone tissue while ensuring complete degradation after recovery. Polylactic acid (PLA), a biodegradable polymer, is considered a promising material due to its considerable mechanical properties and biocompatibility. However, further improvements are necessary to enhance the mechanical strength and bioactivity of PLA for reliable load-bearing orthopedic applications. In this study, a multifunctional PLA-based composite was fabricated by incorporating tricalcium phosphate (TCP) microspheres and magnesium (Mg) particles homogenously at a volume fraction of 40 %. This approach aims to enhance mechanical strength, accelerate pore generation, and improve biological and antibacterial performance. Mg content was incorporated into the composite at varying values of 1, 3, and 5 vol% (referred to as PLA/TCP-1 Mg, PLA/TCP-3 Mg, and PLA/TCP-5 Mg, respectively). The compressive strength and stiffness were significantly enhanced in all composites, reaching 87.7, 85.9, and 84.1 MPa, and 2.7, 3.0, and 3.1 GPa, respectively. The degradation test indicated faster elimination of the reinforcers as the Mg content increased, resulting in accelerated pore generation to induce enhanced osseointegration. Because PLA/TCP-3 Mg and PLA/TCP-5 Mg exhibited cracks in the PLA matrix due to rapid corrosion of Mg forming corrosion byproducts, to optimize the Mg particle content, PLA/TCP-1 Mg was selected for further evaluation. As determined by in vitro biological and antibacterial testing, PLA/TCP-1 Mg showed enhanced bioactivity with pre-osteoblast cells and exhibited antibacterial properties by suppressing bacterial colonization. Overall, the multifunctional PLA/TCP-Mg composite showed improved mechanobiological performance, making it a promising material for biodegradable orthopedic implants.

Antibacterial PLA/Mg composite with enhanced mechanical and biological performance for biodegradable orthopedic implants

Biodegradability, bone-healing rate, and prevention of bacterial infection are critical factors for orthopedic implants. Polylactic acid (PLA) is a good candidate biodegradable material; however, it has insufficient mechanical strength and bioactivity for orthopedic implants. Magnesium (Mg), has good bioactivity, biodegradability, and sufficient mechanical properties, similar to that of bone. Moreover, Mg has an inherent antibacterial property via a photothermal effect, which generates localized heat, thus preventing bacterial infection. Therefore, Mg is a good candidate material for PLA composites, to improve their mechanical and biological performance and add an antibacterial property. Herein, we fabricated an antibacterial PLA/Mg composite for enhanced mechanical and biological performance with an antibacterial property for application as biodegradable orthopedic implants. The composite was fabricated with 15 and 30 vol% of Mg homogeneously dispersed in PLA without the generation of a defect using a high-shear mixer. The composites exhibited an enhanced compressive strength of 107.3 and 93.2 MPa, and stiffness of 2.3 and 2.5 GPa, respectively, compared with those of pure PLA which were 68.8 MPa and 1.6 GPa, respectively. Moreover, the PLA/Mg composite at 15 vol% Mg exhibited significant improvement of biological performance in terms of enhanced initial cell attachment and cell proliferation, whereas the composite at 30 vol% Mg showed deteriorated cell proliferation and differentiation because of the rapid degradation of the Mg particles. In turn, the PLA/Mg composites exerted an antibacterial effect based on the inherent antibacterial property of Mg as well as the photothermal effect induced by near-infrared (NIR) treatment, which can minimize infection after implantation surgery. Therefore, antibacterial PLA/Mg composites with enhanced mechanical and biological performance may be a candidate material with great potential for biodegradable orthopedic implants.

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.

3D-Printed Functional Hydrogel by DNA-Induced Biomineralization for Accelerated Diabetic Wound Healing

Chronic wounds in diabetic patients are challenging because their prolonged inflammation makes healing difficult, thus burdening patients, society, and health care systems. Customized dressing materials are needed to effectively treat such wounds that vary in shape and depth. The continuous development of 3D-printing technology along with artificial intelligence has increased the precision, versatility, and compatibility of various materials, thus providing the considerable potential to meet the abovementioned needs. Herein, functional 3D-printing inks comprising DNA from salmon sperm and DNA-induced biosilica inspired by marine sponges, are developed for the machine learning-based 3D-printing of wound dressings. The DNA and biomineralized silica are incorporated into hydrogel inks in a fast, facile manner. The 3D-printed wound dressing thus generates provided appropriate porosity, characterized by effective exudate and blood absorption at wound sites, and mechanical tunability indicated by good shape fidelity and printability during optimized 3D printing. Moreover, the DNA and biomineralized silica act as nanotherapeutics, enhancing the biological activity of the dressings in terms of reactive oxygen species scavenging, angiogenesis, and anti-inflammation activity, thereby accelerating acute and diabetic wound healing. These bioinspired 3D-printed hydrogels produce using a DNA-induced biomineralization strategy are an excellent functional platform for clinical applications in acute and chronic wound repair.

Incorporation of Magnesium and Zinc Metallic Particles in PLGA Bi-layered Membranes with Sequential Ion Release for Guided Bone Regeneration

Guided bone regeneration (GBR) membranes are commonly used for periodontal tissue regeneration. Due to the complications of existing GBR membranes, the design of bioactive membranes is still relevant. GBR membranes with an asymmetric structure can accommodate the functional requirements of different interfacial tissues. Here, poly(lactic acid-glycolic acid) (PLGA) was selected as the matrix for preparing a bi-layered membrane with both dense and porous structure. The dense layer for blocking soft tissues was incorporated with zinc (Zn) particles, while the porous layer for promoting bone regeneration was co-incorporated with magnesium (Mg) and Zn particles. Mg/Zn-embedded PLGA membranes exhibited 166% higher mechanical strength in comparison with pure PLGA membranes and showed suitable degradation properties with a sequential ion release behavior of Mg²⁺ first and continuously Zn²⁺. More importantly, the release of Zn²⁺ from bi-layered PLGA endowed GBR membranes with excellent antibacterial activity (antibacterial rate > 69.3%) as well as good cytocompatibility with MC3T3-E1 (mouse calvaria pre-osteoblastic cells) and HGF-1 (human gingival fibroblast cells). Thus, the asymmetric bi-layered PLGA membranes embedded with Mg and Zn particles provide a simple and effective strategy to not only reinforce the PLGA membrane but also endow membranes with osteogenic and antibacterial activity due to the continuous ion release profile, which serves as a promising candidate for use in GBR therapy.

AZ63/Ti/Zr Nanocomposite for Bone-Related Biomedical Applications

Considering the unique properties of magnesium and its alloy, it has a vast demand in biomedical applications, particularly the implant material in tissue engineering due to its biodegradability. But the fixing spares must hold such implants till the end of the biodegradation of implant material. The composite technology will offer the added benefits of altering the material properties to match the requirements of the desired applications. Hence, this experimental investigation is aimed at developing a composite material for manufacturing fixing spares like a screw for implants in biomedical applications. The matrix of AZ63 magnesium alloy is reinforced with nanoparticles of zirconium (Zr) and titanium (Ti) through the stir casting-type synthesis method. The samples were prepared with equal contributions of zirconium (Zr) and titanium (Ti) nanoparticles in the total reinforcement percentage (3%, 6%, 9%, and 12%). The corrosive and tribological studies were done. In the corrosive study, the process parameters like NaCl concentration, pH value, and exposure time were varied at three levels. In the wear study, the applied Load, speed of sliding, and the distance of the slide were considered at four levels. Taguchi analysis was employed in this investigation to optimize the reinforcement and independent factors to minimize the wear and corrosive losses. The minimum wear rate was achieved in the 12% reinforced sample with the input factor levels of 60 N of load on the pin, 1 m/s of disc speed at a sliding distance was 1500 m, and the 12% reinforce samples also recorded a minimum corrosive rate of 0.0076 mm/year at the operating environment of 5% NaCl-concentrated solution with the pH value of 9 for 24 hrs of exposure. The prediction model was developed based on the experimental results.

Fabrication and characterization of biodegradable Zn scaffold by vacuum heating-press sintering for bone repair

Bone repair materials with excellent mechanical properties are highly desirable, especially in load-bearing sits. However, the currently used ceramic- and polymer-based ones mainly show poor mechanical properties. Recently, biodegradable metals have attracted extensive attention due to their reliable mechanical strength and degradability. As biodegradable metals, zinc-based materials are promising due to their suitable degradation rate and good biocompatibility. Here, we fabricated biodegradable porous Zn scaffolds with relatively high mechanical properties by vacuum heating-press sintering using NaCl particles as space holders. The microstructure, actual porosity, compressive mechanical properties, in vitro degradation behavior and the vitality of osteoblasts of porous Zn scaffolds were tested and investigated. The results show the porosities of the prepared porous Zn scaffolds are ranging from 11.3 % to 63.3 %, and the pore sizes are similar to the size range of the screened NaCl particles (200-500 μm). Compressive yield strength of 14.2-73.7 MPa and compressive elastic modulus of 1.9-6.7 GPa are shown on porous Zn scaffolds, some of which approach to that of cancellous bone (2-12 MPa and 0.1-5 GPa). Compared to bulk Zn, although the porous structures cause a partial loss of strength, the reliable mechanical properties are still retained. In addition, the porous structures not only greatly increase the degradation rate, but also promote the proliferation of osteoblasts. Based on these results, biodegradable porous Zn scaffolds (porosity in the 40 %-50 %) fabricated by vacuum heating-press sintering method show high application potential for clinical bone repair.

A facile way to construct Sr-doped apatite coating on the surface of 3D printed scaffolds to improve osteogenic effect

Bone-like apatite coating fabricated by biomineralization process is a facile way for surface modification of porous scaffolds to improve interfacial behaviors and thus facilitate cell attachment, proliferation, and differentiation for bone tissue engineering. In this study, a Sr-containing calcium phosphate solution was made and used to construct a thick layer of Sr-doped bone-like apatite on the surface of 3D printed scaffolds via biomineralization process. Importantly, Sr-doped bone-like apatite could form and fully cover the 3D printed scaffolds surface in hours. The characterization results indicated that Sr2+ ions successfully replaced Ca2+ ions in bone-like apatite and the molar ratio of Sr/(Ca+Sr) was up to 8.2%. Furthermore, the Sr-doped apatite coating increased the compressive strength and Young’s modulus of composite scaffolds. The compatibility and bioactivity of mineralized scaffolds were evaluated by cell attachment, proliferation, and differentiation of MC3T3-E1 cells. It was found that Sr-doped apatite coating could gradually release Sr2+ ions and further promote cell attachment, proliferation rate, and the expression of alkaline phosphatase activity and osteogenic related genes, such as collagen type I (Col I), Runt-related transcription factor 2 (Runx-2), osteopontin, and osterix. Therefore, the Sr-doped apatite coating fabricated by this facile and rapid biomineralization process offers a new strategy to modify 3D printed porous scaffolds with significantly improved mechanical and biological properties for bone tissue engineering applications.

Strategies to Control In Vitro Degradation of Mg Scaffolds Processed by Powder Metallurgy

Magnesium scaffolds are biodegradable, biocompatible, bioactive porous scaffolds, which find applications within tissue engineering. The presence of porosity increases surface area and enhances cell proliferation and tissue ingrowth. These characteristics make Mg scaffolds key materials to enhance the healing processes of tissues such as cartilage and bone. However, along with the increment of porosity, the corrosion of magnesium within a physiological environment occurs faster. It is, therefore, necessary to control the degradation rate of Mg scaffolds in order to maintain their mechanical properties during the healing process. Several studies have been performed to increase Mg scaffolds’ corrosion resistance. The different approaches include the modification of the Mg surface by conversion coatings or deposited coatings. The nature of the coatings varies from ceramics such as hydroxyapatite and calcium phosphates to polymers such as polycaprolactone or gelatin. In this work, we propose a novel approach to generating a protective bilayer coating on the Mg scaffold surface composed of a first layer of naturally occurring Mg corrosion products (hydroxide and phosphates) and a second layer of a homogeneous and biocompatible coating of polylactic acid. The Mg scaffolds were fabricated from Mg powder by means of powder metallurgy using ammonium bicarbonate as a space holder. The size and amount of porosity were controlled using different size distributions of space holders. We addressed the influence of scaffold pore size on the conversion and deposition processes and how the coating process influences the in vitro degradation of the scaffolds.

Extrusion-based 3D printed magnesium scaffolds with multifunctional MgF2 and MgF2-CaP coatings

Additively manufactured (AM) biodegradable magnesium (Mg) scaffolds with precisely controlled and fully interconnected porous structures offer unprecedented potential as temporary bone substitutes and for bone regeneration in critical-sized bone defects. However, current attempts to apply AM techniques, mainly powder bed fusion AM, for the preparation of Mg scaffolds, have encountered some crucial difficulties related to safety in AM operations and severe oxidation during AM processes. To avoid these difficulties, extrusion-based 3D printing has been recently developed to prepare porous Mg scaffolds with highly interconnected structures. However, limited bioactivity and a too high rate of biodegradation remain the major challenges that need to be addressed. Here, we present a new generation of extrusion-based 3D printed porous Mg scaffolds that are coated with MgF₂ and MgF₂-CaP to improve their corrosion resistance and biocompatibility, thereby bringing the AM scaffolds closer to meeting the clinical requirements for bone substitutes. The mechanical properties, in vitro biodegradation behavior, electrochemical response, and biocompatibility of the 3D printed Mg scaffolds with a macroporosity of 55% and a strut density of 92% were evaluated. Furthermore, comparisons were made between the bare scaffolds and the scaffolds with coatings. The coating not only covered the struts but also infiltrated the struts through micropores, resulting in decreases in both macro- and micro-porosity. The bare Mg scaffolds exhibited poor corrosion resistance due to the highly interconnected porous structure, while the MgF₂-CaP coatings remarkably improved the corrosion resistance, lowering the biodegradation rate of the scaffolds down to 0.2 mm y^-1. The compressive mechanical properties of the bare and coated Mg scaffolds before and during in vitro immersion tests for up to 7 days were both in the range of the values reported for the trabecular bone. Moreover, direct culture of MC3T3-E1 preosteoblasts on the coated Mg scaffolds confirmed their good biocompatibility. Overall, this study clearly demonstrated the great potential of MgF₂-CaP coated porous Mg prepared by extrusion-based 3D printing for further development as a bone substitute.

Novel Inorganic Nanomaterial-Based Therapy for Bone Tissue Regeneration

Extensive bone defect repair remains a clinical challenge, since ideal implantable scaffolds require the integration of excellent biocompatibility, sufficient mechanical strength and high biological activity to support bone regeneration. The inorganic nanomaterial-based therapy is of great significance due to their excellent mechanical properties, adjustable biological interface and diversified functions. Calcium-phosphorus compounds, silica and metal-based materials are the most common categories of inorganic nanomaterials for bone defect repairing. Nano hydroxyapatites, similar to natural bone apatite minerals in terms of physiochemical and biological activities, are the most widely studied in the field of biomineralization. Nano silica could realize the bone-like hierarchical structure through biosilica mineralization process, and biomimetic silicifications could stimulate osteoblast activity for bone formation and also inhibit osteoclast differentiation. Novel metallic nanomaterials, including Ti, Mg, Zn and alloys, possess remarkable strength and stress absorption capacity, which could overcome the drawbacks of low mechanical properties of polymer-based materials and the brittleness of bioceramics. Moreover, the biodegradability, antibacterial activity and stem cell inducibility of metal nanomaterials can promote bone regeneration. In this review, the advantages of the novel inorganic nanomaterial-based therapy are summarized, laying the foundation for the development of novel bone regeneration strategies in future.

Powder based additive manufacturing for biomedical application of titanium and its alloys: a review

Powder based additive manufacturing (AM) technology of Ti and its alloys has received great attention in biomedical applications owing to its advantages such as customized fabrication, potential to be cost-, time-, and resource-saving. The performance of additive manufactured implants or scaffolds strongly depends on various kinds of AM technique and the quality of Ti and its alloy powders. This paper has specifically covered the process of commonly used powder-based AM technique and the powder production of Ti and its alloy. The selected techniques include laser-based powder bed fusion of metals (PBF-LB/M), electron beam powder bed fusion of metals (PBF-EB/M), and directed energy deposition utilized in the production of the biomaterials are discussed as well as the powder fed system of binder jetting. Moreover, titanium based powder production methods such as gas atomization, plasma atomization, and plasma rotating electrode process are also discussed.

Construction of tantalum/poly(ether imide) coatings on magnesium implants with both corrosion protection and osseointegration properties

Poly(ether imide) (PEI) has shown satisfactory corrosion protection capability with good adhesion strength as a coating for magnesium (Mg), a potential candidate of biodegradable orthopedic implant material. However, its innate hydrophobic property causes insufficient osteoblast affinity and a lack of osseointegration. Herein, we modify the physical and chemical properties of a PEI-coated Mg implant. A plasma immersion ion implantation technique is combined with direct current (DC) magnetron sputtering to introduce biologically compatible tantalum (Ta) onto the surface of the PEI coating. The PEI-coating layer is not damaged during this process owing to the extremely short processing time (30 s), retaining its high corrosion protection property and adhesion stability. The Ta-implanted layer (roughly 10-nm-thick) on the topmost PEI surface generates long-term surface hydrophilicity and favorable surface conditions for pre-osteoblasts to adhere, proliferate, and differentiate. Furthermore, in a rabbit femur study, the Ta/PEI-coated Mg implant demonstrates significantly enhanced bone tissue affinity and osseointegration capability. These results indicate that Ta/PEI-coated Mg is promising for achieving early mechanical fixation and long-term success in biodegradable orthopedic implant applications.

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PEI coating with subsequent Ta ion implantation was prepared on WE43 Mg alloy implant.

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The corrosion resistance of Mg alloy implant was improved by Ta embedded PEI coating.

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The wettability of PEI coating layer was enhanced by embedded Ta on its top-surface.

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Ta embedded PEI coating significantly improved in vitro and in vivo responses.

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Ta embedded PEI-coated Mg is highly suitable as a biodegradable orthopedic implant material.

Enhanced Bioactivity of Micropatterned Hydroxyapatite Embedded Poly(L-lactic) Acid for a Load-Bearing Implant

Poly(L-lactic) acid (PLLA) is among the most promising polymers for bone fixation, repair, and tissue engineering due to its biodegradability and relatively good mechanical strength. Despite these beneficial characteristics, its poor bioactivity often requires incorporation of bioactive ceramic materials. A bioresorbable composite made of PLLA and hydroxyapatite (HA) may improve biocompatibility but typically causes deterioration in mechanical properties, and bioactive coatings inevitably carry a risk of coating delamination. Therefore, in this study, we embedded micropatterned HA on the surface of PLLA to improve bioactivity while eliminating the risk of HA delamination. An HA pattern was successfully embedded in a PLLA matrix without degeneration of the matrix’s mechanical properties, thanks to a transfer technique involving conversion of Mg to HA. Furthermore, patterned HA/PLLA’s biological response outperformed that of pure PLLA. These results confirm patterned HA/PLLA as a candidate for wide acceptance in biodegradable load-bearing implant applications.

Additively manufactured biodegradable porous metals

Partially due to the unavailability of ideal bone substitutes, the treatment of large bony defects remains one of the most important challenges of orthopedic surgery. Additively manufactured (AM) biodegradable porous metals that have emerged since 2018 provide unprecedented opportunities for fulfilling the requirements of an ideal bone implant. First, the multi-scale geometry of these implants can be customized to mimic the human bone in terms of both micro-architecture and mechanical properties. Second, a porous structure with interconnected pores possesses a large surface area, which is favorable for the adhesion and proliferation of cells and, thus, bony ingrowth. Finally, the freeform geometrical design of such biomaterials could be exploited to adjust their biodegradation behavior so as to maintain the structural integrity of the implant during the healing process while ensuring that the implant disappears afterwards, paving the way for full bone regeneration. While the AM biodegradable porous metals that have been studied so far have shown many unique properties as compared to their solid counterparts, the unprecedented degree of flexibility in their geometrical design has not yet been fully exploited to optimize their properties and performance. In order to develop the ideal bone implants, it is important to take advantage of the full potential of AM biodegradable porous metals through detailed and systematic study on their biodegradation behavior, mechanical properties, biocompatibility, and bone regeneration performance. This review paper presents the state of the art in AM biodegradable porous metals and is focused on the effects of material type, processing, geometrical design, and post-AM treatments on the mechanical properties, biodegradation behavior, in vitro biocompatibility, and in vivo bone regeneration performance of AM porous Mg, Fe, and Zn as well as their alloys. We also identify a number of knowledge gaps and the challenges encountered in adopting AM biodegradable porous metals for orthopedic applications and suggest some promising areas for future research.

Surface Modifications of Biodegradable Metallic Foams for Medical Applications

Significant progress was achieved presently in the development of metallic foam-like materials improved by biocompatible coatings. Material properties of the iron, magnesium, zinc, and their alloys are promising for their uses in medical applications, especially for orthopedic and bone tissue purposes. Current processing technologies and a variety of modifications of the surface and composition facilitate the design of adjusted medical devices with desirable mechanical, morphological, and functional properties. This article reviews the recent progress in the design of advanced degradable metallic biomaterials perfected by different coatings: polymer, inorganic ceramic, and metallic. Appropriate coating of metallic foams could improve the biocompatibility, osteogenesis, and bone tissue-bonding properties. In this paper, a comprehensive review of different coating types used for the enhancement of one or several properties of biodegradable porous implants is given. An outline of the conventional preparation methods of metallic foams and a brief overview of different alloys for medical applications are also provided. In addition, current challenges and future research directions of processing and surface modifications of biodegradable metallic foams for medical applications are suggested.

Silicate bioceramics: from soft tissue regeneration to tumor therapy

Great efforts have been devoted to exploiting silicate bioceramics for various applications in soft tissue regeneration, owing to their excellent bioactivity. Based on the inherent ability of silicate bioceramics to repair tissue, bioactive ions are easily incorporated into silicate bioceramics to endow them with extra biological properties, such as enhanced angiogenesis, antibiosis, enhanced osteogenesis, and antitumor effect, which significantly expands the application of multifunctional silicate bioceramics. Furthermore, silicate nanobioceramics with unique structures have been widely employed for tumor therapy. In recent years, the novel applications of silicate bioceramics for both tissue regeneration and tumor therapy have substantially grown. Eliminating the skin tumors first and then repairing the skin wounds has been widely investigated by our groups, which might shed some light on treating other soft tissue tumor or tumor-induced defects. This review first describes the recent advances made in the development of silicate bioceramics as therapeutic platforms for soft tissue regeneration. We then highlight the major silicate nanobioceramics used for tumor therapy. Silicate bioceramics for both soft tissue regeneration and tumor therapy are further emphasized. Finally, challenges and future directions of silicate bioceramics stepping into the clinics are discussed. This review will inspire researchers to create the efficient and functional silicate bioceramics needed for regeneration and tumor therapy of other tissues.

Preparation and Application of Magnetic Responsive Materials in Bone Tissue Engineering

At present, many kinds of materials are used for bone tissue engineering, such as polymer materials, metals, etc., which in general have good biocompatibility and mechanical properties. However, these materials cannot be controlled artificially after implantation, which may result in poor repair performance. The appearance of the magnetic response material enables the scaffolds to have the corresponding ability to the external magnetic field. Within the magnetic field, the magnetic response material can achieve the targeted release of the drug, improve the performance of the scaffold, and further have a positive impact on bone formation. This paper first reviewed the preparation methods of magnetic responsive materials such as magnetic nanoparticles, magnetic polymers, magnetic bioceramic materials and magnetic alloys in recent years, and then introduced its main applications in the field of bone tissue engineering, including promoting osteogenic differentiation, targets release, bioimaging, cell patterning, etc. Finally, the mechanism of magnetic response materials to promote bone regeneration was introduced. The combination of magnetic field treatment methods will bring significant progress to regenerative medicine and help to improve the treatment of bone defects and promote bone tissue repair.

Chemoreactive Nanotherapeutics by Metal Peroxide Based Nanomedicine

The advances of nanobiotechnology and nanomedicine enable the triggering of in situ chemical reactions in disease microenvironment for achieving disease-specific nanotherapeutics with both intriguing therapeutic efficacy and mitigated side effects. Metal peroxide based nanoparticles, as one of the important but generally ignored categories of metal-involved nanosystems, can function as the solid precursors to produce oxygen (O2) and hydrogen peroxide (H2O2) through simple chemical reactions, both of which are the important chemical species for enhancing the therapeutic outcome of versatile modalities, accompanied with the unique bioactivity of metal ion based components. This progress report summarizes and discusses the most representative paradigms of metal peroxides in chemoreactive nanomedicine, including copper peroxide (CuO2), calcium peroxide (CaO2), magnesium peroxide (MgO2), zinc peroxide (ZnO2), barium peroxide (BaO2), and titanium peroxide (TiOx) nanosystems. Their reactions and corresponding products have been broadly explored in versatile disease treatments, including catalytic nanotherapeutics, photodynamic therapy, radiation therapy, antibacterial infection, tissue regeneration, and some synergistically therapeutic applications. This progress report particularly focuses on the underlying reaction mechanisms on enhancing the therapeutic efficacy of these modalities, accompanied with the discussion on their biological effects and biosafety. The existing gap between fundamental research and clinical translation of these metal peroxide based nanotherapeutic technologies is finally discussed in depth.

Bioinspired surface modification of orthopedic implants for bone tissue engineering

Biomedical implants have been widely used in various orthopedic treatments, including total hip arthroplasty, joint arthrodesis, fracture fixation, non-union, dental repair, etc. The modern research and development of orthopedic implants have gradually shifted from traditional mechanical support to a bioactive graft in order to endow them with better osteoinduction and osteoconduction. Inspired by structural and mechanical properties of natural bone, this review provides a panorama of current biological surface modifications for facilitating the interaction between medical implants and bone tissue and gives a future outlook for fabricating the next-generation multifunctional and smart implants by systematically biomimicking the physiological processes involved in formation and functioning of bones.

Degradable magnesium-based alloys for biomedical applications: The role of critical alloying elements

Magnesium-based alloys exhibit biodegradable, biocompatible and excellent mechanical properties which enable them to serve as ideal candidate biomedical materials. In particular, their biodegradable ability helps patients to avoid a second surgery. The corrosion rate, however, is too rapid to sustain the healing process. Alloying is an effective method to slow down the corrosion rate. However, currently magnesium alloys used as biomaterials are mostly commercial alloys without considering cytotoxicity from the perspective of biosafety. This article comprehensively reviews the status of various existing and newly developed degradable magnesium-based alloys specially designed for biomedical application. The effects of critical alloying elements, compositions, heat treatment and processing technology on the microstructure, mechanical properties and corrosion resistance of magnesium alloys are discussed in detail. This article covers Mg-Ca based, Mg-Zn based, Mg-Sr based, Mg-RE based and Mg-Cu-based alloy systems. The novel methods of fabricating Mg-based biomaterials and surface treatment on Mg based alloys for potential biomedical applications are summarized.