The Prospects of Zinc as a Structural Material for Biodegradable Implants—A Review Paper

In the last decade, iron and magnesium, both pure and alloyed, have been extensively studied as potential biodegradable metals for medical applications. However, broad experience with these material systems has uncovered critical limitations in terms of their suitability for clinical applications. Recently, zinc and zinc-based alloys have been proposed as new additions to the list of degradable metals and as promising alternatives to magnesium and iron. The main byproduct of zinc metal corrosion, Zn2+, is highly regulated within physiological systems and plays a critical role in numerous fundamental cellular processes. Zn2+ released from an implant may suppress harmful smooth muscle cells and restenosis in arteries, while stimulating beneficial osteogenesis in bone. An important limitation of pure zinc as a potential biodegradable structural support, however, lies in its low strength (σUTS ~ 30 MPa) and plasticity (ε \u3c 0.25%) that are insufficient for most medical device applications. Developing high strength and ductility zinc with sufficient hardness, while retaining its biocompatibility, is one of the main goals of metallurgical engineering. This paper will review and compare the biocompatibility, corrosion behavior and mechanical properties of pure zinc, as well as currently researched zinc alloys

Albumin-enriched Fibrin Hydrogel Embedded in Active Ferromagnetic Networks Improves Osteoblast Differentiation and Vascular Self-organisation

Porous coatings on prosthetic implants encourage implant fixation. Enhanced fixation may be achieved using a magneto-active porous coating that can deform elastically in vivo on application of an external magnetic field, straining in-growing bone. Such coating, made of 444 ferritic stainless steel fibres, was previously characterised in terms of its mechanical and cellular responses. In this work, co-cultures of human osteoblasts and endothelial cells were seeded into a novel fibrin-based hydrogel embedded in a 444 ferritic stainless steel fibre network. Albumin was successfully incorporated into fibrin hydrogels improving the specific permeability and the diffusion of fluorescently-tagged dextrans without affecting their Young’s modulus. The beneficial effect of albumin was demonstrated by the upregulation of osteogenic and angiogenic gene expression. Furthermore, mineralisation, extracellular matrix production and formation of vessel-like structures were enhanced in albumin-enriched fibrin hydrogels compared to fibrin hydrogels. Collectively, the results indicate that the albumin-enriched fibrin hydrogel is a promising bio-matrix for bone tissue engineering and orthopaedic applications.EPSRC (EP/R511675/1) Blavatnik Family Foundation. Reuben Foundation. WD Armstrong Studentship Isaac Newton Trust Rosetrees Trust (M787)

The Effect of Microstructural Imperfections on Corrosion Fatigue of Additively Manufactured ER70S-6 Alloy Produced by Wire Arc Deposition

This study aims at evaluating the effect of microstructure imperfections on the corrosion fatigue performance of an ER70S-6 alloy produced by wire arc additive manufacturing (WAAM) process, in a 3.5% NaCl solution. For reference, a regular ST-37 alloy with relatively similar chemical composition was considered as a counterpart alloy. This was justified by the fact that the ER70S-6 alloy is usually used for conventional welding of ST-37 steel. The results obtained indicated that while the ST-37 alloy exhibited fatigue strength of 240 MPa in the corrosive solution, the additively manufactured ER70S-6 alloy showed fatigue strength of only 140 MPa. These differences were related to microstructural imperfections that are inherently produced during the WAAM process.</jats:p

Functionalisation of a heat-derived and bio-inert albumin hydrogel with extracellular matrix by air plasma treatment

Funder: Cambridge Commonwealth, European and International Trust; doi: https://doi.org/10.13039/501100003343Funder: Trinity College, University of Cambridge; doi: https://doi.org/10.13039/501100000727Funder: Blavatnik Family Foundation; doi: https://doi.org/10.13039/100011643Funder: Reuben FoundationFunder: Worshipful Council of EngineersFunder: Isaac Newton Trust; doi: https://doi.org/10.13039/501100004815Abstract: Albumin-based hydrogels are increasingly attractive in tissue engineering because they provide a xeno-free, biocompatible and potentially patient-specific platform for tissue engineering and drug delivery. The majority of research on albumin hydrogels has focused on bovine serum albumin (BSA), leaving human serum albumin (HSA) comparatively understudied. Different gelation methods are usually employed for HSA and BSA, and variations in the amino acid sequences of HSA and BSA exist; these account for differences in the hydrogel properties. Heat-induced gelation of aqueous HSA is the easiest method of synthesizing HSA hydrogels however hydrogel opacity and poor cell attachment limit their usefulness in downstream applications. Here, a solution to this problem is presented. Stable and translucent HSA hydrogels were created by controlled thermal gelation and the addition of sodium chloride. The resulting bio-inert hydrogel was then subjected to air plasma treatment which functionalised its surface, enabling the attachment of basement membrane matrix (Geltrex). In vitro survival and proliferation studies of foetal human osteoblasts subsequently demonstrated good biocompatibility of functionalised albumin hydrogels compared to untreated samples. Thus, air plasma treatment enables functionalisation of inert heat-derived HSA hydrogels with extracellular matrix proteins and these may be used as a xeno-free platform for biomedical research or cell therapy

The Prospects of Zinc as a Structural Material for Biodegradable Implants—A Review Paper

In the last decade, iron and magnesium, both pure and alloyed, have been extensively studied as potential biodegradable metals for medical applications. However, broad experience with these material systems has uncovered critical limitations in terms of their suitability for clinical applications. Recently, zinc and zinc-based alloys have been proposed as new additions to the list of degradable metals and as promising alternatives to magnesium and iron. The main byproduct of zinc metal corrosion, Zn2+, is highly regulated within physiological systems and plays a critical role in numerous fundamental cellular processes. Zn2+ released from an implant may suppress harmful smooth muscle cells and restenosis in arteries, while stimulating beneficial osteogenesis in bone. An important limitation of pure zinc as a potential biodegradable structural support, however, lies in its low strength (σUTS ~ 30 MPa) and plasticity (ε &lt; 0.25%) that are insufficient for most medical device applications. Developing high strength and ductility zinc with sufficient hardness, while retaining its biocompatibility, is one of the main goals of metallurgical engineering. This paper will review and compare the biocompatibility, corrosion behavior and mechanical properties of pure zinc, as well as currently researched zinc alloys

Functionalisation of a heat-derived and bio-inert albumin hydrogel with extracellular matrix by air plasma treatment

Funder: Cambridge Commonwealth, European and International Trust; doi: https://doi.org/10.13039/501100003343Funder: Trinity College, University of Cambridge; doi: https://doi.org/10.13039/501100000727Funder: Blavatnik Family Foundation; doi: https://doi.org/10.13039/100011643Funder: Reuben FoundationFunder: Worshipful Council of EngineersFunder: Isaac Newton Trust; doi: https://doi.org/10.13039/501100004815Abstract: Albumin-based hydrogels are increasingly attractive in tissue engineering because they provide a xeno-free, biocompatible and potentially patient-specific platform for tissue engineering and drug delivery. The majority of research on albumin hydrogels has focused on bovine serum albumin (BSA), leaving human serum albumin (HSA) comparatively understudied. Different gelation methods are usually employed for HSA and BSA, and variations in the amino acid sequences of HSA and BSA exist; these account for differences in the hydrogel properties. Heat-induced gelation of aqueous HSA is the easiest method of synthesizing HSA hydrogels however hydrogel opacity and poor cell attachment limit their usefulness in downstream applications. Here, a solution to this problem is presented. Stable and translucent HSA hydrogels were created by controlled thermal gelation and the addition of sodium chloride. The resulting bio-inert hydrogel was then subjected to air plasma treatment which functionalised its surface, enabling the attachment of basement membrane matrix (Geltrex). In vitro survival and proliferation studies of foetal human osteoblasts subsequently demonstrated good biocompatibility of functionalised albumin hydrogels compared to untreated samples. Thus, air plasma treatment enables functionalisation of inert heat-derived HSA hydrogels with extracellular matrix proteins and these may be used as a xeno-free platform for biomedical research or cell therapy

Cytotoxic characteristics of biodegradable EW10X04 Mg alloy after Nd coating and subsequent heat treatment

© 2016 Elsevier B.V. All rights reserved. Porous Mg scaffolds are considered as potential bone growth promoting materials. Unfortunately, the high rate of biocorrosion inherent to Mg alloys may cause a premature loss of mechanical strength, excessive evolution of hydrogen gas, and a rapidly shifting surface topography, all of which may hinder the ability of native cells to attach and grow on the implant surface. Here we investigated the cell cytotoxicity effects during corrosion of a novel magnesium alloy, EW10X04 (Mg-1.2%Nd-0.5%Y-0.5%Zr-0.4%Ca), following diffusion coating (DC) and heat treatment to reduce the corrosion rate. Cells were exposed either to corrosion products or to the corroding scaffold surface, in vitro. The microstructure characterization of the scaffold surface was carried out by scanning electron microscopy (SEM) equipped with a Noran energy dispersive spectrometer (EDS). Phase analyses were obtained by X-ray diffraction (XRD). We found that cell viability, growth, and adhesion were all improved when cultured on the EW10X04 + DC surface or under corrosion product extracts due to lower corrosion rates relative to the EW10X04 control samples. It is therefore believed that the tested alloy after Nd coating and heat treatment may introduce a good balance between its biodegradation characteristics and cytotoxic effects towards cells

The Effect of Microstructural Imperfections on Corrosion Fatigue of Additively Manufactured ER70S-6 Alloy Produced by Wire Arc Deposition

This study aims at evaluating the effect of microstructure imperfections on the corrosion fatigue performance of an ER70S-6 alloy produced by wire arc additive manufacturing (WAAM) process, in a 3.5% NaCl solution. For reference, a regular ST-37 alloy with relatively similar chemical composition was considered as a counterpart alloy. This was justified by the fact that the ER70S-6 alloy is usually used for conventional welding of ST-37 steel. The results obtained indicated that while the ST-37 alloy exhibited fatigue strength of 240 MPa in the corrosive solution, the additively manufactured ER70S-6 alloy showed fatigue strength of only 140 MPa. These differences were related to microstructural imperfections that are inherently produced during the WAAM process

Environmental Behavior of Low Carbon Steel Produced by a Wire Arc Additive Manufacturing Process

Current additive manufacturing (AM) processes are mainly focused on powder bed technologies, such as electron beam melting (EBM) and selective laser melting (SLM). However, the main disadvantages of such techniques are related to the high cost of metal powder, the degree of energy consumption, and the sizes of the components, that are limited by the size of the printing cell. The aim of the present study was to evaluate the environmental behavior of low carbon steel (ER70S-6) produced by a relatively inexpensive AM process using wire feed arc welding. The mechanical properties were examined by tension testing and hardness measurements, while microstructure was assessed by scanning electron microscopy and X-ray diffraction analysis. General corrosion performance was evaluated by salt spray testing, immersion testing, potentiodynamic polarization analysis, and electrochemical impedance spectroscopy. Stress corrosion performance was characterized in terms of slow strain rate testing (SSRT). All corrosion tests were carried out in 3.5% NaCl solution at room temperature. The results indicated that the general corrosion resistance of wire arc additive manufacturing (WAAM) samples were quite similar to those of the counterpart ST-37 steel and the stress corrosion resistance of both alloys was adequate. Altogether, it was clearly evident that the WAAM process did not encounter any deterioration in corrosion performance compared to its conventional wrought alloy counterpart

Patient-specific Ti-6Al-4V lattice implants for critical-sized load-bearing bone defects reconstruction

The advancement in additive manufacturing in recent years opened a new era for bone reconstruction methods, allowing for the design of customized implants that perfectly match clinical needs. This challenge is even more prominent in critical-sized bone defects, where the bone cannot heal independently. Here we present a novel workflow for such cases. First, a multidisciplinary team conducted the surgical plan, including the design of an intraoperative patient-specific instrument. Then, a Ti-6Al-4V implant was created to exactly fit the resected tumor's bone gap. An ambitious bone regenerative approach was taken in designing the implants with a porous-lattice body acting as a scaffold for new bone formation, reinforced with standard orthopedic instruments for adequate mechanical support. To prevent future failure of the implant, a finite element analysis was used to evaluate stress distribution simulation according to the multi-axis forces and moments applied on the bone during walking. Our results demonstrate the potential for Ti-6Al-4V implants to become the best practice for reconstructing significant bone defects. This proof-of-concept may enhance clinical care and catalyze new frontiers in patient-specific medicine. To the best of our knowledge, this is the first study to describe in detail the design and fabrication of this method