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.

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.

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.

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.

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.

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.

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.

Vascular restoration therapy and bioresorbable vascular scaffold

This article describes the evolution of minimally invasive intervention technologies for vascular restoration therapy from early-stage balloon angioplasty in 1970s,metallic bare metal stent and metallic drug-eluting stent technologies in 1990s and 2000s,to bioresorbable vascular scaffold(BVS)technology in large-scale development in recent years.The history,the current stage,the challenges and the future of BVS development are discussed in detail as the best available approach for vascular restoration therapy.The criteria of materials selection,design and processing principles of BVS,and the corresponding clinical trial results are also summarized in this article.

Biodegradation of Mg-14Li alloy in simulated body fluid: A proof-of-concept study

High corrosion kinetics and localised corrosion progress are the primary concerns arising from the clinical implementation of magnesium(Mg)based implantable devices.In this study,a binary Mglithium(Li)alloy consisting a record high Li content of 14%(in weight)was employed as model material aiming to yield homogenous and slow corrosion behaviour in a simulated body fluid,i.e.minimum essential medium(MEM),in comparison to that of generic Mg alloy AZ31 and biocompatible Mg-0.5Zn-0.5Ca counterparts.Scanning electron microscopy examination reveals single-phase microstructural characteristics of Mg-14Li(b-Li),whilst the presence of insoluble phases,cathodic to a-Mg matrix,in AZ31 and Mg-0.5Zn-0.5Ca.Though slight differences exist in the corrosion kinetics of all the specimens over a short-term time scale(no longer than 60 min),as indicated by potentiodynamic polarisation and electrochemical impedance spectroscopy,profound variations are apparent in terms of immersion tests,i.e.mass loss and hydrogen evolution measurements(up to 7 days).Cross-sectional micrographs unveil severe pitting corrosion in AZ31 and Mg-0.5Zn-0.5Ca,but not the case for Mg-14Li.X-ray diffraction patterns and X-ray photoelectron spectroscopy confirm that a compact film(25 mm in thickness)consisting of lithium carbonate(Li2CO3)and calcium hydroxide was generated on the surface of Mg-14Li in MEM,which contributes greatly to its low corrosion rate.It is proposed therefore that the single-phase structure and formation of protective and defect-free Li2CO3 film give rise to the controlled and homogenous corrosion behaviour of Mg-14Li in MEM,providing new insights for the exploration of biodegradable Mg materials.

Engineering nanoparticles to overcome immunological barriers for enhanced drug delivery

Nanotechnology has recently gained traction in the medical field as a method of targeted delivery and timed release of therapeutic drugs.As interest in this field grows,design considerations of the selected nanotechnology and extensive knowledge of the human immune system are necessary to design an effective system for drug delivery.Suppression and control of an immune response has become an achievable outcome to ensure efficient treatment of target tissues through careful selection of materials and immune antagonists.This review outlines the immune system,the challenges created by its inherent functions,biocompatible materials that are presently being used to construct nanoparticles,and molecules and techniques used to manipulate the immune response to nanoparticles.