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Biodegradable zinc (Zn) alloys are promising implant materials to restore bone defects in orthopedics. Adding silver (Ag) to Zn not only enhances its mechanical properties but also improves its antibacterial properties. However, the regular pattern of Ag composition on the properties of Zn-xAg alloys remains unclear. In this paper, Zn-Ag alloys with different Ag contents ranging from 0.5 to 6.0% were prepared by casting process and were systematically investigated both in vitro and in vivo. Mechanical tests suggest that the increase of Ag content enhanced the yield strength (YS), ultimate tensile strength (UTS), Vickers hardness, and elongation. Compared with pure Zn, the maximum YS, UTS, Vickers hardness, and elongation were achieved at Zn-6Ag, which were increased by 267%, 295%, 115%, and 172%, respectively. The degradation rate increased and the antibacterial properties were enhanced accordingly. All 25% and most 50% extracts of Zn-Ag alloys significantly promoted the proliferation of MC3T3-E1 cells, except for 50% Zn-6Ag extracts showing cytotoxicity. In the rat femoral condyle model, Zn-2Ag and Zn-4Ag alloys exhibited enhanced osteogenic performance at the early stage of implantation compared with pure Zn. Zn-Ag alloys (especially Zn-2Ag and Zn-4Ag) are identified as promising bone repair materials.

Existing research suggested 300∼600 μm as the optimal pore size range for metallic bone implants. The human bones, however, have numerous pores smaller than 300 μm for bone ingrowth, cell growth and migration, fluid flow, and so forth. The bone implant with such small-sized pores has been rarely manufactured and its property is unclear. In the paper, biodegradable Fe scaffolds of different pore sizes (50 μm, 100 μm, 150 μm, 200 μm, and 300 μm) were fabricated by direct ink writing (DIW) with subsequent sintering. The interconnected pores of all scaffolds are highly precise and have no residual powders. The in-vitro degradation and compression tests were conducted on the scaffolds to evaluate the effect of pore size on degradation and mechanical behaviors, respectively. The results indicate that a decrease in pore size leads to an increase in degradation rate, from 0.0423 ± 0.0014 to 0.0433 ± 0.0035 mm/year, with the exception of the 50 μm scaffolds which exhibit the lowest value of 0.0052 ± 0.0018 mm/year due to clogging by degradation products; meanwhile, both elastic modulus and yield strength rise from 344.8 ± 18.6 MPa to 625.0 ± 52.5 MPa and from 9.5 ± 0.9 MPa to 15.1 ± 0.8 MPa, respectively. The pore size of 100 μm shows the most significant potential for use in Fe bone implants regarding its good degradation and mechanical behaviors. Our work provides new insight into the preferable pore size of metallic bone implants produced by additive manufacturing.

Astragalus residue powder (ARP)/thermoplastic starch (TPS)/poly(lactic acid) (PLA) biocomposites were prepared by fused-deposition modeling (FDM) 3D-printing technology for the first time in this paper, and certain physico-mechanical properties and soil-burial-biodegradation behaviors of the biocomposites were investigated. The results showed that after raising the dosage of ARP, the tensile and flexural strengths, the elongation at break and the thermal stability of the sample decreased, while the tensile and flexural moduli increased; after raising the dosage of TPS, the tensile and flexural strengths, the elongation at break and the thermal stability all decreased. Among all of the samples, sample C—which was composed of 11 wt.% ARP, 10 wt.% TPS and 79 wt.% PLA—was the cheapest and also the most easily degraded in water. The soil-degradation-behavior analysis of sample C showed that, after being buried in soil, the surfaces of the samples became grey at first, then darkened, after which the smooth surfaces became rough and certain components were found to detach from the samples. After soil burial for 180 days, there was weight loss of 21.40%, and the flexural strength and modulus, as well as the storage modulus, reduced from 82.1 MPa, 11,922.16 MPa and 2395.3 MPa to 47.6 MPa, 6653.92 MPa and 1476.5 MPa, respectively. Soil burial had little effect on the glass transition, cold crystallization or melting temperatures, while it reduced the crystallinity of the samples. It is concluded that the FDM 3D-printed ARP/TPS/PLA biocomposites are easy to degrade in soil conditions. This study developed a new kind of thoroughly degradable biocomposite for FDM 3D printing. [ABSTRACT FROM AUTHOR]

• Mg-Zn-Ca alloy scaffold with spherical/cubic hybrid pores was prepared. • The structure–property relationships were evaluated by experiments and theoretical analysis. • The Mg alloy scaffold was adaptive to the cancellous bone in terms of mechanical properties. • A flowing-assisted chemical conversion treatment was introduced for surface modification. Biodegradable Mg-based scaffolds are regarded as potential bone tissue engineering materials for a promising approach to bone repair. In this work, the spherical/cubic hybrid pore-forming agents were introduced to prepare a porous Mg-based alloy scaffold by the negative salt pattern molding method. The porous Mg-Zn-Ca alloy scaffold containing spherical/cubic hybrid pores exhibited a porosity of about 68.60 % and a surface area ratio of about 7.88 cm2/cm3. The compressive elastic modulus was about 0.32 GPa and the compressive strength was about 4.22 MPa, close to cancellous bone. However, the rapid degradation of Mg alloy scaffold was inadaptive to orthopedic repair. Thus, a calcium phytate coating was prepared on the Mg-based scaffold for surface modification to retard rapid corrosion. [ABSTRACT FROM AUTHOR]

The repair of segmental bone defects caused by traumatic injury or pathological diseases remains a substantial challenge in clinic. Poly-l-lactic acid (PLLA) is recognized as one potential bone substitute material due to its natural biodegradability and excellent biocompatibility. Nevertheless, it still faces several fundamental puzzles including insufficient mechanical properties, slow degradation and poor osteogenic activity. To address these issues, the corresponding strategies were thoroughly explored in this review. Regulation of molecular weight and crystallization, as well as the control of crack propagation were the mainstream methods to improve the mechanical properties of PLLA, whereas surface medication and polymer blending was commonly adopted to regulate the degradation behavior. To achieve desirable tissue regeneration ability, the combination of physical stimulation (electric and magnetic) brings about a new and attractive solution, since it is able to mimic the electro-magnetic microenvironment of human body. Furthermore, future research directions are proposed from the prospects of fabrication process, dynamic degradation and multifunctional application. This review aims to offer deep insights and meaningful guidelines for future study of PLLA as implants.

Microstructure, degradation behavior in vitro and mechanical property of as-extruded Mg-2Zn-0.2Zr-xSc (x = 0, 0.2, 0.4, 0.6, 0.8, wt.%) alloys was investigated. Fine rod-like Mg(Zn,Sc,Zr) phase in as-extruded ZK-(0.4–0.8)Sc alloys inhibits recrystallized grains growth, resulting in grain refinement. The addition of Sc decreases the degradation rate in vitro and improves the mechanical property of ZK20 alloy. All tested alloys had no cytotoxicity effect on HUVEC and MC3T3-E1 cells. This work provides a better understanding on adding Sc as alloying element for biomedical Mg alloys with superior mechanical property, slower degradation rate and good biocompatibility.

Mg-based porous materials, as potential bone tissue engineering scaffolds, are considered an attractive strategy for bone repair owing to favorable biodegradability, good biocompatibility and suitable mechanical properties. In this work, 3D-cubic interconnected porous Mg–xZn–0.3Ca (x = 0,3,6) scaffolds were prepared to obtain desirable pore structures with a mean porosity up to 73% and main pore size of 400–500 µm, which pore structures were close to the human cancellous bone. The structure–property relationships in the present scaffolds were analyzed by experiments and theoretical models of generalized method of cells (GMC). Mg–xZn–0.3Ca scaffolds exhibited good compression properties with a maximum above 5 MPa in yield strength and about 0.4 GPa in elastic modulus. This was attributed to not only the alloy strengthening but also the large minimum solid area. On the other hand, the scaffolds showed undesirable and relatively serious degradation behavior in Hank's solution, resulting from Zn addition in Mg-based scaffolds and the high surface area ratio in the pore structure. Therefore, surface modifications are worth studying for controlled degradation in the future. In conclusion, this research would explore a novel attempt to introduce 3D-cubic pore structure for Mg-based scaffolds, and provide new insights into the preparations of Mg-based scaffolds with good service performances for bone repair.

Zinc (Zn)-based composites have received extensive attention as promising biodegradable materials due to their unique combination of moderate biodegradability, biocompatibility, and functionality. Nevertheless, the low mechanical strength of as-cast Zn-based composites impedes their practical clinical application. Here we reported the mechanical properties, corrosion behavior, wear properties, and cytotoxicity of in situ synthesized biodegradable Zn–xMg 2 Ge (x = 1, 3, and 5 wt.%) composites for bone-implant applications. The mechanical properties of Zn–xMg 2 Ge composites were effectively improved by alloying and hot-rolling due to particle reinforcement of the Mg 2 Ge intermetallic phase and dynamic recrystallization. The hot-rolled (HR) Zn–3Mg 2 Ge composite exhibited the best mechanical properties, including a yield strength of 162.3 MPa, an ultimate tensile strength of 264.3 MPa, an elongation of 10.9%, and a Brinell hardness of 83.9 HB. With an increase in Mg 2 Ge content, the corrosion and degradation rates of the HR Zn–xMg 2 Ge composites gradually increased, while their wear rate decreased and then increased in Hanks' solution. The diluted extract (12.5% concentration) of the HR Zn–3Mg 2 Ge composite showed the highest cell viability compared to the other HR composites and their as-cast pure Zn counterparts. Overall, the HR Zn–3Mg 2 Ge composite can be considered a promising biodegradable Zn-based composite for bone-implant applications. This paper reports the mechanical properties, corrosion behavior, wear properties, and cytotoxicity of in situ synthesized biodegradable Zn–xMg 2 Ge (x = 1, 3, and 5 wt.%) composites for bone-implant applications. Our findings demonstrated that the mechanical properties of Zn–xMg 2 Ge composites were effectively improved by alloying and hot-rolling due to Mg 2 Ge particle reinforcement and dynamic recrystallization. The hot-rolled Zn–3Mg 2 Ge composite showed superior cytocompatibility, satisfying corrosion and degradation rates, and the best mechanical properties including a yield strength of 162.3 MPa, an ultimate tensile strength of 264.3 MPa, and an elongation of 10.9%. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present work, the biomedical as-cast pure Mg, Mg–1Ca and Mg–2Sr alloys were processed with equal channel angular pressing (ECAP) technique to develop ultrafine microstructure within the materials, and their microstructures, mechanical properties, degradation behavior, cytocompatibility in vitro and biocompatibility in vivo were studied comprehensively. Finer-gained microstructures and improved mechanical properties of these three materials after ECAP were confirmed compared to their as-cast counterparts. Moreover, after ECAP the degradation rate of pure Mg was increased while that of Mg–1Ca or Mg–2Sr alloys decreased compared to the as-cast counterparts. Additionally, good in vitro cytocompatibility and in vivo biocompatibility of these three materials were revealed by cell cultural tests using osteoblastic MC3T3-E1 and human mesenchymal stem cells (hMSC) and in vivo animal tests at the lateral epicondyle of SD-rats’ femur. This study offers an alternative powerful avenue to achieve good comprehensive properties of magnesium-based biodegradable metals. It might also help to extend the applied range of magnesium-based biodegradable metals in orthopedic field.

• PBSTs with different chain segments were synthesized by adjusting ratio of aromatic and aliphatic units. • Effect of aromatic content on foam shrinkage behavior of PBST was analyzed. • Biodegradability and mechanical properties of PBST foams can be adjusted by changing aromatic content. • A careful balance should be considered between good biodegradability and favorable mechanical properties in PBST foams. Poly (butylene succinate-butylene terephthalate) (PBST) with different chain segments was synthesized by in-situ polycondensation, and foams were prepared by supercritical CO 2 foaming. The crystallinity and tensile modulus of PBST increases with the aromatic content, slowing down the diffusion of CO 2 and enhancing the dimensional stability of PBST foam. The rheological analysis reveals that a higher temperature of PBST modulus platform is correlated with a higher aromatic content, which is more conducive to the cell stability. The foaming temperature window is 60 - 80 °C at 30% aromatic content, which moves to 160 - 175 °C at 70% aromatic content, and the maximum expansion ratio of PBST foam decreases from 40.7 to 9.8. With the increase of aromatic content from 30% to 70%, there is an obvious improvement in the compressive modulus of PBST foam, from 0.92 MPa to 6.65 MPa, accompanied by a reduction in the weight loss rate of degradation decreased from 10.78% to 3.04% in 10 days. Hence, there is a careful balance between degradability and foamability of PBST foams. Introducing a suitable aromatic content obtained higher strength to improve the cell stability on the premise that the strong degradability can be maintained, which provides an effective strategy to prepare PBST foams with good degradability and favorable mechanical properties. [ABSTRACT FROM AUTHOR]

Mg-based porous materials, as potential bone tissue engineering scaffolds, are considered an attractive strategy for bone repair owing to favorable biodegradability, good biocompatibility and suitable mechanical properties. In this work, 3D-cubic interconnected porous Mg–xZn–0.3Ca (x = 0,3,6) scaffolds were prepared to obtain desirable pore structures with a mean porosity up to 73% and main pore size of 400–500 µm, which pore structures were close to the human cancellous bone. The structure–property relationships in the present scaffolds were analyzed by experiments and theoretical models of generalized method of cells (GMC). Mg–xZn–0.3Ca scaffolds exhibited good compression properties with a maximum above 5 MPa in yield strength and about 0.4 GPa in elastic modulus. This was attributed to not only the alloy strengthening but also the large minimum solid area. On the other hand, the scaffolds showed undesirable and relatively serious degradation behavior in Hank's solution, resulting from Zn addition in Mg-based scaffolds and the high surface area ratio in the pore structure. Therefore, surface modifications are worth studying for controlled degradation in the future. In conclusion, this research would explore a novel attempt to introduce 3D-cubic pore structure for Mg-based scaffolds, and provide new insights into the preparations of Mg-based scaffolds with good service performances for bone repair. [ABSTRACT FROM AUTHOR]

Al2O3f/SiO2 composites were fabricated efficiently using sol‐gel process. The degradation behavior exposed to Na2SO4 environment at 1100℃ and MMH/N2O4 bipropellants test were investigated and compared. The results showed that the strength of Al2O3f/SiO2 composites gradually decreased as the ratio of Na2SO4:water increased; the strength of the composites was only 23.56 MPa at 20% (Na2SO4:water), which suggested that the composites maintained lower strength. Cracks began to appear in SiO2 matrix, and the structure of Al2O3f/SiO2 composites could be corroded which would corrode the SiO2 matrix, leaving naked fibers. Developing a protective layer with higher stability for Al2O3f/SiO2 composites would be considered for long time use. The composites showed higher ablation resistance to MMH/N2O4 bipropellant test; the flexural strength was (77.15 ± 4.56) MPa and the retention ratio was 98.7%. The degradation of Al2O3f/SiO2 composites was promoted owing to the thermal‐mechanical and chemical factors. SiO2 matrix became weak and fragile at elevated temperature; some SiO2 matrix became loosened and porous after being washed away through the shearing of MMH/N2O4 bipropellants, which prevented cracks from penetrating Al2O3 fibers. With ongoing test, the fibers were worsened by thermal‐mechanical corrosion. [ABSTRACT FROM AUTHOR]

Calcium silicate can be used as an excellent material for biodegradable bone scaffolds because it can provide bioactive ions to promote bone regeneration. However, the brittleness and rapid degradation of calcium silicate scaffolds have significantly limited their clinical application. In this work, the calcium silicate scaffolds printed by DLP technology were immersed in a gelatin solution under high vacuum condition to obtain calcium silicate/gelatin composite scaffolds with good mechanical and biological properties. Then, genipin was used as a cross-linker for gelatin to control the degradation properties of the composite scaffolds. The initial compressive strength and toughness of the composite scaffolds were 5.0 times and one order of magnitude higher than those of the pure calcium silicate scaffolds, respectively. The gelatin on the surface of the scaffolds could effectively act as a protective layer to regulate the degradation behaviors of the calcium silicate substrate through controlling the crosslinking degree of the gelatin. After degrading for 14 days, the composite scaffolds at 1.0 % genipin concentration exhibited the highest compressive strength of 8.6 ± 0.8 MPa, much higher than that of the pure ceramic scaffold (1.5 ± 0.3 MPa). It can be found that the toughness of the composite scaffolds were almost over 13.2 times higher than that of the pure ceramic scaffold during degradation, despite the higher toughness loss for the former. Furthermore, the composite scaffolds showed enhanced cell biocompatibility and viability. These results demonstrate that the calcium silicate/gelatin composite scaffolds can be a promising candidate in bone tissue regeneration. [ABSTRACT FROM AUTHOR]

Coronary artery disease (CAD) is the leading killer of humans worldwide. Bioresorbable polymeric stents have attracted a great deal of interest because they can treat CAD without producing long-term complications. Bioresorbable polymeric stents (BMSs) have undergone a sustainable revolution in terms of material processing, mechanical performance, biodegradability and manufacture techniques. Biodegradable polymers and copolymers have been widely studied as potential material candidates for bioresorbable stents. It is a great challenge to find a reasonable balance between the mechanical properties and degradation behavior of bioresorbable polymeric stents. Surface modification and drug-coating methods are generally used to improve biocompatibility and drug loading performance, which are decisive factors for the safety and efficacy of bioresorbable stents. Traditional stent manufacture techniques include etching, micro-electro discharge machining, electroforming, die-casting and laser cutting. The rapid development of 3D printing has brought continuous innovation and the wide application of biodegradable materials, which provides a novel technique for the additive manufacture of bioresorbable stents. This review aims to describe the problems regarding and the achievements of biodegradable stents from their birth to the present and discuss potential difficulties and challenges in the future.

Objectives: As promising alternative to current metallic biomaterials, the porous Mg scaffold with a 3‐D open‐pore framework has drawn much attention in recent years due to its suitable biodegradation, biocompatibility, and mechanical properties for human bones. This experiment's aim is to study the mechanical properties, biosafety, and osteogenesis of porous Mg‐Zn alloy. Methods: A porous Mg‐2Zn‐0.3Ca (wt%) alloy was successfully prepared by infiltration casting, and the size of NaCl particles was detected by a laser particle size analyzer. The microstructure of the Mg‐2Zn‐0.3Ca alloy was characterized by the stereoscopic microscope and Sirion Field emission scanning electron microscope. X‐ray computerized tomography scanning (x‐CT) was used to create the 3‐D image. The degradation rate was measured using the mass loss method and the pH values were determined together. The engineering stress–strain curve, compressive modulus, and yield strength were tested next. The bone marrow stromal cells (BMSC) were cultured in vitro. The CCK‐8 method was used to detect the proliferation of the BMSC. Alkaline phosphatase (ALP) and alizarin red staining were used to reflect the differentiation effects. After co‐culturing, cell growth on the material's surface was observed by scanning electron microscope (SEM). The cell adhesion was tested by confocal microscopy. Results: The obtained results showed that by using near‐spherical NaCl filling particles, the porous Mg alloy formed complete open‐cell foam with a very uniform size of pores in the range of 500–600 μm. Benefitting from the small size and uniform distribution of pores, the present porous alloy exhibited a very high porosity, up to 80%, and compressive yield strength up to 6.5 MPa. The degradation test showed that both the pH and the mass loss rate had similar change tendency, with a rapid rise in the early stage for 1–2 day's immersion and subsequently remaining smooth after 3 days. In vitro cytocompatibility trials demonstrated that in comparison with Ti, the porous alloy accelerated proliferation in 1, 3, 5, and 7 days (P < 0.001), and the osteogenic differentiation test showed that the ALP activity in the experimental group was significantly higher (P = 0.017) and has more osteogenesis nodules. Cell adhesion testing showed good osteoconductivity by more BMSC adhesion around the holes. The confocal microscopy results showed that cells in porous Mg‐based alloy had better cytoskeletal morphology and were larger in number than in titanium. Conclusions: These results indicated that this porous Mg‐based alloy fabricated by infiltration casting shows great mechanical properties and biocompatibilities, and it has potential as an ideal bone tissue engineering scaffold material for bone regeneration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design degradable Mg-2Zn-0.2Zr- x Sc (ZK- x Sc, x = 0, 0.2, 0.4, 0.6, 0.8, wt.%) alloys as potential implants. • Investigate the effect of alloying element (Sc) on microstructure, degradation behavior and mechanical property of as-extruded ZK alloy. • The addition of Sc in ZK alloy decreases the degradation rate and improves the ultimate tensile strength. • Provide a better understanding on Sc as alloying elements for biomedical Mg alloys with superior mechanical property, slower degradation rate and good biocompatibility. Microstructure, degradation behavior in vitro and mechanical property of as-extruded Mg-2Zn-0.2Zr- x Sc (x = 0, 0.2, 0.4, 0.6, 0.8, wt.%) alloys was investigated. Fine rod-like Mg(Zn,Sc,Zr) phase in as-extruded ZK-(0.4–0.8)Sc alloys inhibits recrystallized grains growth, resulting in grain refinement. The addition of Sc decreases the degradation rate in vitro and improves the mechanical property of ZK20 alloy. All tested alloys had no cytotoxicity effect on HUVEC and MC3T3-E1 cells. This work provides a better understanding on adding Sc as alloying element for biomedical Mg alloys with superior mechanical property, slower degradation rate and good biocompatibility. [ABSTRACT FROM AUTHOR]

Coronary artery disease (CAD) is the leading killer of humans worldwide. Bioresorbable polymeric stents have attracted a great deal of interest because they can treat CAD without producing long-term complications. Bioresorbable polymeric stents (BMSs) have undergone a sustainable revolution in terms of material processing, mechanical performance, biodegradability and manufacture techniques. Biodegradable polymers and copolymers have been widely studied as potential material candidates for bioresorbable stents. It is a great challenge to find a reasonable balance between the mechanical properties and degradation behavior of bioresorbable polymeric stents. Surface modification and drug-coating methods are generally used to improve biocompatibility and drug loading performance, which are decisive factors for the safety and efficacy of bioresorbable stents. Traditional stent manufacture techniques include etching, micro-electro discharge machining, electroforming, die-casting and laser cutting. The rapid development of 3D printing has brought continuous innovation and the wide application of biodegradable materials, which provides a novel technique for the additive manufacture of bioresorbable stents. This review aims to describe the problems regarding and the achievements of biodegradable stents from their birth to the present and discuss potential difficulties and challenges in the future. [ABSTRACT FROM AUTHOR]