Synthesis and in-vitro characterization of biodegradable porous magnesium-based scaffolds containing silver for bone tissue engineering

Infection is a major potential complication in the clinical treatment of bone injuries. Magnesium (Mg)-based composites are biodegradable and antibacterial biomaterials that have been employed to reduce infection following surgical implants. The aim of present study was to synthesize and in-vitro characterize Mg-based scaffolds containing silver for bone tissue engineering. Porous Mg-based scaffolds with four silver concentrations (i.e., 0, 0.5 wt.%, 1 wt.%, and 2 wt.%), denoted by Mg?Ca?Mn-Zn-xAg (MCMZ?xAg)(where x is the silver concentration), were fabricated by the space holder technique. The effects of silver concentration on pore architecture, mechanical properties, bioactivity, and zone of bacterial inhibition were investigated in-vitro. X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence microscopy were utilized to characterize the obtained scaffolds. In-vitro corrosion test results indicated that the MCMZ scaffolds with lower silver content were more resistant to corrosion than those enriched with higher amounts of silver. Examination of the antibacterial activity showed that the MCMZ?Ag scaffolds exhibited superb potential with respect to suppressing the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), in the inhibition zone around the MCMZ?Ag scaffolds, with increasing in the amount of incorporated silver;however, higher amounts of silver increased the cytotoxicity. Taken together, the results of this study demonstrate that the porous 0.5 wt.% Ag-containing scaffolds with interconnected pores, adequate mechanical properties, antibacterial activity, and cell adhesion are promising with respect to the repair and substitution of damaged and diseased bones.

Printabilitye-A key issue in extrusion-based bioprinting

Three-dimensional(3D)extrusion-based bioprinting is widely used in tissue engineering and regenerative medicine to create cell-incorporated constructs or scaffolds based on the extrusion technique.One critical issue in 3D extrusion-based bioprinting is printability or the capability to form and maintain reproducible 3D scaffolds from bioink(a mixture of biomaterials and cells).Research shows that printability can be affected by many factors or parameters,including those associated with the bioink,printing process,and scaffold design,but these are far from certain.This review highlights recent developments in the printability assessment of extrusion-based bioprinting with a focus on the definition of printability,printability measurements and characterization,and printability-affecting factors.Key issues and challenges related to printability are also identified and discussed,along with approaches or strategies for improving printability in extrusion-based bioprinting.

Additive manufacturing of biodegradable magnesium-based materials:Design strategies,properties,and biomedical applications

Magnesium(Mg)-based materials are a new generation of alloys with the exclusive ability to be biodegradable within the human/animal body.In addition to biodegradability,their inherent biocompatibility and similar-to-bone density make Mg-based alloys good candidates for fabricating surgical bioimplants for use in orthopedic and traumatology treatments.To this end,nowadays additive manufacturing(AM)along with three-dimensional(3D)printing represents a promising manufacturing technique as it allows for the integration of bioimplant design and manufacturing processes specific to given applications.Meanwhile,this technique also faces many new challenges associated with the properties of Mg-based alloys,including high chemical reactivity,potential for combustion,and low vaporization temperature.In this review article,various AM processes to fabricate biomedical implants from Mg-based alloys,along with their metallic microstructure,mechanical properties,biodegradability,biocompatibility,and antibacterial properties,as well as various post-AM treatments were critically reviewed.Also,the challenges and issues involved in AM processes from the perspectives of bioimplant design,properties,and applications were identified;the possibilities and potential scope of the Mg-based scaffolds/implants are discussed and highlighted.

3D biofabrication of vascular networks for tissue regeneration:A report on recent advances

Rapid progress in tissue engineering research in past decades has opened up vast possibilities to tackle the challenges of generating tissues or organs that mimic native structures. The success of tissue engineered constructs largely depends on the incorporation of a stable vascular network that eventually anastomoses with the host vasculature to support the various biological functions of embedded cells. In recent years, significant progress has been achieved with respect to extrusion, laser, micro-molding, and electrospinning-based techniques that allow the fabrication of any geometry in a layer-by-layer fashion. Moreover, decellularized matrix, self-assembled structures, and cell sheets have been explored to replace the biopolymers needed for scaffold fabrication. While the techniques have evolved to create specific tissues or organs with outstanding geometric precision, formation of interconnected, functional, and perfused vascular networks remains a challenge. This article briefly reviews recent progress in 3D fabrication approaches used to fabricate vascular networks with incorporated cells, angiogenic factors, proteins, and/or peptides. The influence of the fabricated network on blood vessel formation, and the various features, merits, and shortcomings of the various fabrication techniques are discussed and summarized.

Bioprinting and in vitro characterization of alginate dialdehyde-gelatin hydrogel bio‑ink

Cell-laden cardiac patches have recently been emerging to renew cellular sources for myocardial infarction(MI,commonly know as a heart attack)repair.However,the fabrication of cell-laden patches with porous structure remains challenging due to the limitations of currently available hydrogels and existing processing techniques.The present study utilized a bioprinting technique to fabricate hydrogel patches and characterize them in terms of printability,mechanical and biological properties.Cell-laden hydrogel(or bio-ink)was formulated from alginate dialdehyde(ADA)and gelatin(GEL)to improve the printability,degradability as well as bioactivity.Five groups of hydrogel compositions were designed to investigate the influence of the oxidation degree of ADA and hydrogels concentration on the properties of printed scaffolds.ADA-GEL hydrogels have generally shown favorable for living cells(EA.hy926 cells and hybrid human umbilical vein endothelial cell line).The hydrogel with an oxidation degree of 10%and a concentration ratio of 70/30(or 10%ADA70-GEL30)demonstrated the best printability among the groups examined.Formulated hydrogels were also bioprinted with the living cells(EA.hy926),and the scaffolds printed were then subject to the cell culture for 7 days.Our results illustrate that the scaffolds bioprinted from 10%ADA70–GEL30 hydrogels had the best homogenous cell distribution and also the highest cell viability.Taken together,in the present study we synthesized a newly formulated bio-ink from ADA and GEL and for the fist time,used them to bioprint cardiac patches,which have the potential to be used in MI repair.

A Survey of Modeling and Control of Piezoelectric Actuators

Piezoelectric actuators (PEAs) have been widely used in micro- and nanopositioning applications due to their fine resolution, fast responses, and large actuating forces. However, the existence of nonlinearities such as hysteresis makes modeling and control of PEAs challenging. This paper reviews the recent achievements in modeling and control of piezoelectric actuators. Specifically, various methods for modeling linear and nonlinear behaviors of PEAs, including vibration dynamics, hysteresis, and creep, are examined;and the issues involved are identified. In the control of PEAs as applied to positioning, a review of various control schemes of both model-based and non-model-based is presented along with their limitations. The challenges associated with the control problem are also discussed. This paper is concluded with the emerging issues identified in modeling and control of PEAs for future research.

Modeling of Piezoelectric Actuators Based on a New Rate-Independent Hysteresis Model

Accurate model representatives of piezoelectric actuators (PEAs) are important for both understanding the dynamic behaviors of PEAs and control scheme development. However, among the existing models, the most widely used classical Preisach hysteresis model are incapable of representing the commonly-encountered one-sided (non-negative voltage input range) hysteresis behaviors of PEAs. To solve this problem, a new rate-independent hysteresis model was developed for the one-sided hysteresis and then integrated with the models representative of creep and dynamics to form a single model for the PEAs. Experiments were carried out to validate the developed models.