Magnesium (Mg)-based biomaterials have attracted increasing attention in biomedical applications, such as orthopaedic, cardiovascular, urological, and neural applications because of the biocompatibility, biodegradability, antibacterial properties, and excellent mechanical properties. However, rapid degradation of Mg is the major concern for many clinical applications. Alloying Mg with other elements and engineering proper surfaces are the two approaches to control the degradation of Mg-based biomaterials. Our lab has investigated several classes of Mg-based biodegradable alloys and various surface treatment methods for medical implant and device applications. This mini-review highlights key research progress on Mg-based biomaterials and suggests future directions for Mg-based biomaterials.

The ability to interface electronic materials with the peripheral nervous system is required for stimulation and monitoring of neural signals. Thus, the design and engineering of robust neural interfaces that maintain material-tissue contact in the presence of material or tissue micromotion offer the potential to conduct novel measurements and develop future therapies that require chronic interface with the peripheral nervous system. However, such remains an open challenge given the constraints of existing materials sets and manufacturing approaches for design and fabrication of neural interfaces. Here, we investigated the potential to leverage a rapid prototyping approach for the design and fabrication of nerve cuffs that contain supporting features to mechanically stabilize the interaction between cuff electrodes and peripheral nerve. A hybrid 3D printing and robotic-embedding (i.e., pick-and-place) system was used to design and fabricate silicone nerve cuffs (800 µm diameter) containing conforming platinum (Pt) electrodes. We demonstrate that the electrical impedance of the cuff electrodes can be reduced by deposition of the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on cuff electrodes via a post-processing electropolymerization technique. The computer-aided design and manufacturing approach was also used to design and integrate supporting features to the cuff that mechanically stabilize the interface between the cuff electrodes and the peripheral nerve. Both ‘self-locking’ and suture-assisted locking mechanisms are demonstrated based on the principle of making geometric alterations to the cuff opening via 3D printing. Ultimately, this work shows 3D printing offers considerable opportunity to integrate supporting features, and potentially even novel electronic materials, into nerve cuffs that can support the design and engineering of next generation neural interfaces.

Polymer composites of Polylactic acid (PLA) and poly-ε-caprolactone (PCL), containing small amounts of titanium oxide (TiO2) were developed for biomedical applications. These composite materials were prepared, and then printed using Fused Deposition Modeling (FDM). 3D printed structures were characterized to determine their mechanical properties and biocompatibility. DSC analysis yielded useful information regarding the immiscibility of the different polymers, and it was observed that the particles of TiO2 improved the stability of the polymers. The ultimate tensile strength and the fracture strain increased by adding TiO2 as a filler, resulting in values of approximately 45 MPa and 5.5 % elongation. The printed composites show excellent in vitro biocompatibility including cell proliferation and adhesion, and are therefore promising candidates to be used in the biomedical field for bone replacement procedures, due to their properties similar to those of cancellous bone.

A kinetic model for ECM decellularization with Trypsin and Deoxycholic Acid as reactants in a batch system has been developed. The decellularization mechanism has been analysed by solving a series of ordinary differential equations relating heterogeneous reaction kinetics at the solid/liquid interface to mass transfer of reactant and products. In order to remove the Deoxyribonucleic acid (DNA) of porcine, special emphasis has been given to the surface area for regulating the depth and amount of the penetration of the reagent, the numerical analysis thereof, and the corresponding experiment were carried out. The effect of chemical reaction order, rate constants and mass transfer coefficients on the overall decellularization rate has been analysed and discussed.

Magnesium (Mg) and its alloys have showed a promising potential for medical implant applications due to their attractive biocompatibility and mechanical strength. Despite these promising properties, the critical challenge with Mg-based implants is rapid degradation in physiological environment that results in early loss of mechanical strength and hydrogen gas accumulation at the local site. Hydroxyapatite (HA) coatings provide a sound solution for controlling Mg degradation at the bone interface. In this paper, HA coatings with different particle sizes, namely, microHA (mHA) and nanoHA (nHA), were deposited on Mg plates and rods with two different pressures using N2 Biomedical’s proprietary deposition process called IonTiteTM. Surface characterization of the deposited layers showed mHA coated Mg prepared at high pressure had more homogeneous HA particles distribution with less defects.

Extracellular Matrix (ECM), a natural biomaterials, have recently garnered attention in tissue engineering for their high degree of cell proliferative capacity, biocompatibility, biodegradability, and tenability in the body. Decellularization process offers a unique approach for fabricating ECM-based natural scaffold for tissue engineering application by removing intracellular contents in a tissue that could cause any adverse host responses. The effects of Supercritical carbon dioxide (Sc-CO2) treatment on the histological and biochemical properties of the decellularized extracellular matrix (de-ECM) were evaluated and compared with de-ECM from conventional decellularization process to see if it offers significantly reduced treatment times, complete decellularization, and well preserved extracellular matrix structure. The study has shown that a novel method of using supercritical fluid extraction system indeed removed all unnecessary residues and only leaving ECM. The potential of Sc-CO2 de-ECM progressed as a promising approach in tissue repair and regeneration.

Alginate is a hydrogel polymer commonly used in multiple drug delivery and cellular tissue transplantation applications. Tunability, gel formation, and stabilization properties of this biopolymer contributes to a better controlled and prolonged release of encapsulated drugs as well as the ability to provide immunoisolation to transplanted cells. One commonly used application of this biopolymer is pancreatic islet transplantation, as a promising approach of providing insulin to type 1 diabetics. The encapsulant alginate provides passage to nutrients, glucose and oxygen and allows the insulin to diffuse while blocking immunoglobulins. In this study, a hydrogel encapsulator is designed and used to fabricate spherical alginate microcapsules. These capsules are then incubated in either a calcium chloride solution typical used to polymerize alginate or a physiological media formulated to mimic in vivo conditions. The diffusion of different molecular weight particles tagged with spectrally distinct fluorescent molecules into the microspheres is observed using confocal laser microscopy. We characterize changes in diffusional characteristics of these molecules within alginate spheres as a function of incubation duration. We estimate diffusion coefficients (D) from fluorescence image series and observe a notable increase in capsule permeability once incubated in physiological media. Our strategy can serve as quantitative method to analyze structural changes in hydrogels.

The proximity of minerals found in human hard tissues may influence cell phenotype. Since cells respond to a range of environmental cues, this study sought to identify the influence of two apatite-based microparticles, hydroxyapatite (HA) and fluoroapatite (FA), upon dental and bone cells. After bone marrow stromal cells (BMSCs), 7F2 osteoblasts and dental pulp stem cells (DPSCs) were plated into media with or without HA or FA particles, the cells were analyzed for alkaline phosphatase (ALP) production, collagen I production, osteocalcin production, and mineralization for two weeks. The BMSCs and DPSCs in media without any microparticles produced more ALP compared to those with microparticles from Day 5 forward. In addition, the collagen I and osteocalcin production in cultures without microparticles was higher than in cultures containing either HA or FA particles. While some studies have shown increased osteogeonic differentiation in the presence of mineral particles, those studies used nanoparticles that were able to be internalized by the cells and were smaller than the microparticles used in this study.