Biodegradable materials for bone defect repair

Compared with non-degradable materials,biodegradable biomaterials play an increasingly important role in the repairing of severe bone defects,and have attracted extensive attention from researchers.In the treatment of bone defects,scaffolds made of biodegradable materials can provide a crawling bridge for new bone tissue in the gap and a platform for cells and growth factors to play a physiological role,which will eventually be degraded and absorbed in the body and be replaced by the new bone tissue.Traditional biodegradable materials include polymers,ceramics and metals,which have been used in bone defect repairing for many years.Although these materials have more or fewer shortcomings,they are still the cornerstone of our development of a new generation of degradable materials.With the rapid development of modern science and technology,in the 21 st century,more and more kinds of new biodegradable materials emerge in endlessly,such as new intelligent micro-nano materials and cell-based products.At the same time,there are many new fabrication technologies of improving biodegradable materials,such as modular fabrication,3 D and 4 D printing,interface reinforcement and nanotechnology.This review will introduce various kinds of biodegradable materials commonly used in bone defect repairing,especially the newly emerging materials and their fabrication technology in recent years,and look forward to the future research direction,hoping to provide researchers in the field with some inspiration and reference.

Biodegradable materials as binders for IVth generation moulding sands

This paper focuses on the possibility of using the biodegradable materials as binders(or parts of binders' compositions) for foundry moulding and core sands. Results showed that there is a great possibility of using available biodegradable materials as foundry moulding sand binders. Using biodegradable materials as partial content of new binders, or additives to moulding sands may not only decrease the toxicity and increase reclamation ability of tested moulding sands, but also accelerate the biodegradation rate of used binders, and the new biodegradable additive(PCL) did not decrease the strength and thermal properties. In addition, using polycaprolactone(PCL) as a biodegradable material may improve the flexibility of moulding sands with polymeric binder and reduce toxicity.

A review on biodegradable materials for cardiovascular stent application

A stent is a medical device designed to serve as a temporary or permanent internal scaffold to maintain or increase the lumen of a body conduit. The researcher;~ and engineers diverted to investigate biodegradable materials due to the limitation of metallic materials in stent application such as stent restenosis which requires prolonged anti platelet therapy, often result in smaller lumen after implantation and obstruct re-stenting treatments. Biomedical implants with temporary function for the vascular intervention are extensively studied in recent years. The rationale for biodegradable stent is to provide the support for the vessel in predicted period of time and then degrading into biocompatible constituent. The degradation of stent makes the re-stenting possible after several months and also ameliorates the vessel wall quality. The present article focuses on the biodegradable materials for the cardiovascular stent. The objective of this review is to describe the possible biodegradable materials for stent and their properties such as design criteria, degradation behavior, drawbacks and advantages with their recent clinical and preclinical trials.

Recent progress on biodegradable materials and transient electronics

Transient electronics(or biodegradable electronics)is an emerging technology whose key characteristic is an ability to dissolve,resorb,or physically disappear in physiological environments in a controlled manner.Potential applications include eco-friendly sensors,temporary biomedical implants,and datasecure hardware.Biodegradable electronics built with water-soluble,biocompatible active and passive materials can provide multifunctional operations for diagnostic and therapeutic purposes,such as monitoring intracranial pressure,identifying neural networks,assisting wound healing process,etc.This review summarizes the up-to-date materials strategies,manufacturing schemes,and device layouts for biodegradable electronics,and the outlook is discussed at the end.It is expected that the translation of these materials and technologies into clinical settings could potentially provide vital tools that are beneficial for human healthcare.

Antibacterial mechanism with consequent cytotoxicity of different reinforcements in biodegradable magnesium and zinc alloys: A review

Benefits achieved by the biodegradable magnesium(Mg) and zinc(Zn) implants could be suppressed due to the invasion of infectious microbial, common bacteria, and fungi. Postoperative medications and the antibacterial properties of pure Mg and Zn are insufficient against biofilm and antibiotic-resistant bacteria, bringing osteomyelitis, necrosis, and even death. This study evaluates the antibacterial performance of biodegradable Mg and Zn alloys of different reinforcements, including silver(Ag), copper(Cu), lithium(Li), and gallium(Ga). Copper ions(Cu^(2+)) can eradicate biofilms and antibiotic-resistant bacteria by extracting electrons from the cellular structure. Silver ion(Ag^(+)) kills bacteria by creating bonds with the thiol group. Gallium ion(Ga^(3+)) inhibits ferric ion(Fe^(3+)) absorption, leading to nutrient deficiency and bacterial death. Nanoparticles and reactive oxygen species(ROS) can penetrate bacteria cell walls directly, develop bonds with receptors, and damage nucleotides. Antibacterial action depends on the alkali nature of metal ions and their degradation rate, which often causes cytotoxicity in living cells. Therefore, this review emphasizes the insight into degradation rate, antibacterial mechanism, and their consequent cytotoxicity and observes the correlation between antibacterial performance and oxidation number of metal ions.

Magnesium as Biodegradable Implant Material

Drawbacks associated with permanent metallic implants lead to the search for degradable metallic biomaterials. Magnesium alloys have been highly considered as Mg has a high biocorrosion potential and is essential to bodies. In this study, corrosion behaviour of pure magnesium and magnesium alloy AZ31 in both static and dynamic physiological conditions (Hank's solution) has been investigated. It is found that the materials degrade fast at beginning, then stabilize after 5 days of immersion. High purity in the materials reduces the corrosion rate while the dynamic condition accelerates the degradation process. In order to slow down the degradation process to meet the requirement for their bio-applications, an anodized coating is applied and is proved as effective in controlling the biodegradation rate.

A review on in vitro corrosion performance test of biodegradable metallic materials

Extensive in vitro corrosion test systems have been carried out to simulate the in vivo corrosion behavior of biodegradable metallic materials. Various methods have their own unique benefits and limitations. The corrosion mechanism of biodegradable alloys and in vitro corrosion test systems on biodegradable metallic materials are reviewed, to build a reasonable simulated in vitro test system for mimicking the in vivo animal test from the aspects of electrolyte solution selection, surface roughness influence, test methods and evaluation methodology of corrosion rate. Buffered simulated body fluid containing similar components to human blood plasma should be applied as electrolyte solution, such as simulated body fluid （SBF） and culture medium with serum. Surface roughness of samples and ratio of solution volume to sample surface area should be adopted based on the real implant situation, and the dynamic corrosion is preferred. As to the evaluation methodology of corrosion rate, different methods may complement one another.

Structural and corrosion characterization of biodegradable Mg-RE (RE=Gd, Y, Nd) alloys

Binary Mg-Gd （up to 5% Gd in mass fraction）, Mg-Nd （up to 9% Nd in mass fraction） and ternary Mg-Gd-Y （up to 5% Gd, 1% Y） alloys with precisely determined contents of cathodic impurities （Fe, Ni, Cu, Co） were studied. The alloys were studied in the as-cast state （cooling rate of 500 K/min） and after solution heat treatment （T4）. Structures were investigated by optical and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and glow discharge spectrometry. Structural investigation was completed by Vickers hardness measurements. Corrosion behavior in the simulated physiological solution （9 g/L NaCl） was assessed by immersion tests and potentiodynamic measurements. It was found that the structures of the as-cast alloys were dominated by fine a-Mg dendrites and eutectic Mg-RE phases. The dendrites exhibited RE-concentration gradients which were most pronounced in the Mg-Gd alloys. For this reason, the T4 heat treatment of the Mg-Gd alloy led to the formation of a new cuboidal Mg5Gd phase. The corrosion resistance was significantly improved by Gd. The effect of Nd was weak and the addition of Y to Mg-Gd alloys had harmful effect on the corrosion resistance. The T4 heat treatment strongly accelerated the corrosion of Mg-Gd alloys. Its effect on the corrosion of Mg-Nd alloys was not significant. The observed corrosion behavior of the alloys was discussed in relation to their structural states and contents of cathodic impurities.

Fabrication of a Knitted Biodegradable Stents for Tracheal Regeneration

Endoluminal stents for reinforcement and regeneration of human trachea have been developed by weft-knitting method on a small-diameter circular knitting machine. The constituent materials of the stent are Polyglactin, Polypropylene and Chitosan with Polyglactin and Polypropylene plate-stitched fabric acting as backbone while chitosan as matrix, respectively. The fabrication procedures including knitting and coating are described in this paper. Mechanical and animal tests have been carried out to evaluate the mechanical properties of the stents.

Characterization of Potential Cellulose from Hylocereus Polyrhizus(Dragon Fruit)peel:A Study on Physicochemical and Thermal Properties

The strict environmental regulations to overcome the drawbacks of consumption and disposal of non-renewable synthetic materials have motivated this investigation.The physical,chemical,morphological,and thermal properties of Hylocereus Polyrhizus peel(HPP)powder obtained from the raw materials were examined in this study.The physical properties analyzes of Hylocereus Polyrhizus peel(HPP)powder discovered that the moisture content,density,and water holding capacity were 9.70%,0.45 g/cm^(3),and 98.60%,respectively.Meanwhile,the chemical composition analysis of Hylocereus Polyrhizus peel(HPP)powder revealed that the powder was significantly high in cellulose contents(34.35%)from other bio-peel wastes.The crystallinity index of Hylocereus Polyrhizus peel(HPP)powder was 32.76%,according to further X-ray diffraction(XRD)analysis.The thermal stability of Hylocereus Polyrhizus peel(HPP)powder was examined using thermogravimetric analysis(TGA)and found thermally stable at 204℃.The morphological study via scanning electron microscopy(SEM)showed a shriveled and irregular geometry surface.Hylocereus Polyrhizus peel(HPP)powder demonstrated the peak in the range representing the major functional groups responsible for pectin’s properties.Thus,the findings revealed that the Hylocereus Polyrhizus peel(HPP)powder has the potential for the development of biodegradable and renewable materials.

Recent advances in immobilized enzymes on nanocarriers

Recent progress in nanotechnology has provided high-performance nanomaterials for enzyme immobilization.Nanobiocatalysts combining enzymes and nanocarriers are drawing increasing attention because of their high catalytic performance,enhanced stabilities,improved enzyme-substrate affinities,and reusabilities.Many studies have been performed to investigate the efficient use of cellulose nanocrystals,polydopamine-based nanomaterials,and synthetic polymer nanogels for enzyme immobilization.Various nanobiocatalysts are highlighted in this review,with the emphasis on the design,preparation,properties,and potential applications of nanoscale enzyme carriers and nanobiocatalysts.

Opportunities and challenges for the biodegradable magnesium alloys as next-generation biomaterials

In recent years,biodegradable magnesium alloys emerge as a new class of biomaterials for tissue engineering and medical devices.Deploying biodegradable magnesium-based materials not only avoids a second surgical intervention for implant removal but also circumvents the long-term foreign body effect of permanent implants.However,these materials are often subjected to an uncontrolled and fast degradation,acute toxic responses and rapid structural failure presumably due to a localized,too rapid corrosion process.The patented Mg-Nd-Zn-based alloys(JiaoDa BioMg[JDBM])have been developed in Shanghai Jiao Tong University in recent years.The alloy series exhibit lower biodegradation rate and homogeneous nanophasic degradation patterns as compared with other biodegradable Mg alloys.The in vitro cytotoxicity tests using various types of cells indicate excellent biocompatibility of JDBM.Finally,bone implants using JDBM-1 alloy and cardiovascular stents using JDBM-2 alloy have been successfully fabricated and in vivo long-term assessment via implantation in animal model have been performed.The results confirmed the reduced degradation rate in vivo,excellent tissue compatibility and long-term structural and mechanical durability.Thus,this novel Mg-alloy series with highly uniform nanophasic biodegradation represent a major breakthrough in the field and a promising candidate for manufacturing the next generation biodegradable implants.

Experimental Study on the Mechanical Properties of Novel Plate-knitted Composite Tracheal Stents

A new knitted composite artificial tracheal stent made of polyglactin(PGLA) and polypropylene (PP) filaments for reinforcement and regeneration of human trachea has been developed by plated-knitting technique on a small-diameter circular knitting machine.Both tensile and compressive tests were carried out to determine the Young's modulus and the critical pressure corresponding to crushing of the stent.The experimental results confirmed that the new type of knitted composite artificial stent is mechanically feasible.

RING-OPENING POLYMERIZATION OF ε-CAPROLACTONE BY LANTHANOCENE CATALYSIS

Ring-opening polymerization of ε-caprolactone (CL) catalyzed bylanthanocenes, O(C_2H_4C_5H_3CH_3)_2YCl (Cat-YCl) and Me_2Si[(CH_3)_3SiC_5H_3]_2NdCl(Cat-NdCl) has been carried out for the first time. It has been found that both yttroceneand neodymocene are very efficient to catalyze the polymerization of CL, giving high molec-ular weight poly (ε-caprolactone) (PCL ). The effects of [cat] / [ε- CL] molar ratio, polymeriza-tion temperature and time, as well as solvents were investigated and polymerization tem-perature is found to be the most important factor affecting the polymerization. The bulkpolymerization gives higher molecular weight PCL and higher conversion than that in solu-tion polymerization. NaBPh_4 was found to promote the polymerization of ε-caprolactone,and thus to increase both the polymerization conversion and MW of poly (ε- caprolactone ).

Improvement of Plant Growing Techniques in Drying up and Water Scarcity Conditions

Due to its specificity, seasonality and location of large areas, the crops are exposed to the greatest degree of risks posed by climate change. To maintain stability and increase yields, it is imperative to implement an innovative approach by which to optimize certain processes such as tillage, sowing and irrigation. The main tasks of innovative solutions are proposed to increase the soil water holding capacities in the root layer over a prolonged period of time, and improve the accuracy of the drilling process for row crops and vegetables by using biodegradable materials, and on this basis to optimize the irrigation by use of specialized software products to determine irrigation scheduling and irrigation requirements.

Investigation of Mg–Zn–Y–Nd alloy for potential application of biodegradable esophageal stent material

In recent years,due to unhealthy dietary habits and other reasons,advanced esophageal cancer patients are on the rise,threatening human health and life safety at all times.Stents implantation as an important complementary or alternative method for chemotherapy has been widely applied in clinics.However,the adhesion and proliferation of pathological cells,such as tumor cells,fibroblasts and epithelial cells,may interfere the efficacy of stents.Further multiple implantation due to restenosis may also bring pain to patients.In this contribution,we preferred a biodegradable material Mg–Zn–Y–Nd alloy for potential application of esophageal stent.The hardness testing showed that Mg–Zn–Y–Nd alloy owned less mechanical properties compared with the commercial esophageal stents material,317L stainless steel(317L SS),while Mg–Zn–Y–Nd displayed significantly better biodegradation than 317L SS.Cell apoptosis assay indicated Mg–Zn–Y–Nd inhibited adhesion and proliferation of tumor cells,fibroblasts and epithelial cells.Our research suggested potential application of Mg–Zn–Y–Nd alloy as a novel material for biodegradable esophageal stent.

Effects of external stress on biodegradable orthopedic materials: A review

Biodegradable orthopedic materials(BOMs)are used in rehabilitation and reconstruction of fractured tissues.The response of BOMs to the combined action of physiological stress and corrosion is an important issue in vivo since stress-assisted degradation and cracking are common.Although the degradation behavior and kinetics of BOMs have been investigated under static conditions,stress effects can be very serious and even fatal in the dynamic physiological environment.Since stress is unavoidable in biomedical applications of BOMs,recent work has focused on the evaluation and prediction of the properties of BOMs under stress in corrosive media.This article reviews recent progress in this important area focusing on biodegradable metals,polymers,and ceramics.

On the material dependency of peri-implant morphology and stability in healing bone

The microstructural architecture of remodeled bone in the peri-implant region of screw implants plays a vital role in the distribution of strain energy and implant stability.We present a study in which screw implants made from titanium,polyetheretherketone and biodegradable magnesium-gadolinium alloys were implanted into rat tibia and subjected to a push-out test four,eight and twelve weeks after implantation.Screws were 4 mm in length and with an M2 thread.The loading experiment was accompanied by simultaneous three-dimensional imaging using synchrotron-radiation microcomputed tomography at 5μm resolution.Bone deformation and strains were tracked by applying optical flow-based digital volume correlation to the recorded image sequences.Implant stabilities measured for screws of biodegradable alloys were comparable to pins whereas non-degradable biomaterials experienced additional mechanical stabilization.Peri-implant bone morphology and strain transfer from the loaded implant site depended heavily on the biomaterial utilized.Titanium implants stimulated rapid callus formation displaying a consistent monomodal strain profile whereas the bone volume fraction in the vicinity of magnesium-gadolinium alloys exhibited a minimum close to the interface of the implant and less ordered strain transfer.Correlations in our data suggest that implant stability benefits from disparate bone morphological properties depending on the biomaterial utilized.This leaves the choice of biomaterial as situational depending on local tissue properties.

Biomaterials for spinal cord repair

Spinal cord injury （SCI） results in permanent loss of function leading to often devastating personal, economic and social problems. A contributing factor to the permanence of SCI is that damaged axons do not regenerate, which prevents the re-establishment of axonal circuits involved in function. Many groups are working to develop treatments that address the lack of axon regeneration after SCI. The emergence of biomaterials for regeneration and increased collaboration between engineers, basic and translational scientists, and clinicians hold promise for the development of effective therapies for SCI. A plethora of biomaterials is available and has been tested in various models of SCI. Considering the clinical relevance of contusion injuries, we primarily focus on polymers that meet the specific criteria for addressing this type of injury. Biomaterials may provide structural support and/or serve as a delivery vehicle for factors to arrest growth inhibition and promote axonal growth. Designing materials to address the specific needs of the damaged central nervous system is crucial and possible with current technology. Here, we review the most prominent materials, their optimal characteristics, and their potential roles in repairing and regenerating damaged axons following SCI.

In Vitro Study on Mg-Sn-Mn Alloy as Biodegradable Metals

The mechanical properties, chemical properties and biocompatibility of Mg-3Sn-0.5Mn alloy were tested. A series of in vitro evaluations such as tensile test, static and dynamic immersion test, hemocompatibility test as well as cytotoxicity test were presented, with commercial magnesium alloy WE43 as the control. Mg-3Sn-0.5Mn alloy possesses suitable strength and superior ductility compared with WE43 and AZ31. Static immersion and dynamic degradation tests showed more uniform degradation with a more moderate rate for Mg-3Sn-0.5Mn alloy （0.34 mm/y in static condition and 0.25 mm/y in dynamic condition） compared with WE43 alloy （0.42 mm/y in static condition and 0.33 mm/y in dynamic condition） in Hank＇s solution. Blood compatibility evaluation suggested that Mg-3Sn-0.5Mn alloy had no destructive effect on erythrocyte and showed excellent anti-thrombogenicity to blood system. Besides, Mg-3Sn-0.5Mn alloy showed no inhibition effect to L929 metabolic activity and mild toxicity to vascular smooth muscle cell （VSMC） in preliminary cell viability assessment. By considering its excellent mechanical strength, corrosion resistance, low ion release rate and good biocompatibility, Mg-3Sn-0.5Mn alloy may be a promising economical candidate as biomedical implant material for load-bearing clinical applications in the future.