In vivo performance of a rare earth free Mg-Zn-Ca alloy manufactured using twin roll casting for potential applications in the cranial and maxillofacial fixation devices

A magnesium alloy containing essential,non-toxic,biodegradable elements such as Ca and Zn has been fabricated using a novel twin-roll casting process(TRC).Microstructure,mechanical properties,in vivo corrosion and biocompatibility have been assessed and compared to the properties of the rare earth(RE)element containing WE43 alloy.TRC Mg-0.5 wt% Zn-0.5 wt% Ca exhibited fine grains with an average grain size ranging from 70 to 150μm.Mechanical properties of a TRC Mg-0.5Zn-0.5Ca alloy showed an ultimate tensile strength of 220 MPa and ductility of 9.3%.The TRC Mg-0.5Zn-0.5Ca alloy showed a degradation rate of 0.51±0.07 mm/y similar to that of the WE43 alloy(0.47±0.09 mm/y)in the rat model after 1 week of implantation.By week 4 the biodegradation rates of both alloys studied were lowered and stabilized with fewer gas pockets around the implant.The histological analysis shows that both WE43 and TRC Mg-0.5Zn-0.5Ca alloy triggered comparable tissue healing responses at respective times of implantation.The presence of more organized scarring tissue around the TRC Mg-0.5Zn-0.5Ca alloys suggests that the biodegradation of the RE-free alloy may be more conducive to the tissue proliferation and remodelling process.

Injectable and thermosensitive hydrogels mediating a universal macromolecular contrast agent with radiopacity for noninvasive imaging of deep tissues

It is very challenging to visualize implantable medical devices made of biodegradable polymers in deep tissues.Herein,we designed a novel macromolecular contrast agent with ultrahigh radiopacity(iodinate content>50%)via polymerizing an iodinated trimethylene carbonate monomer into the two ends of poly(ethylene glycol)(PEG).A set of thermosensitive and biodegradable polyester-PEG-polyester triblock copolymers with varied polyester compositions synthesized by us,which were soluble in water at room temperature and could spontaneously form hydrogels at body temperature,were selected as the demonstration materials.The addition of macromolecular contrast agent did not obviously compromise the injectability and thermogelation properties of polymeric hydrogels,but conferred them with excellent X-ray opacity,enabling visualization of the hydrogels at clinically relevant depths through X-ray fluoroscopy or Micro-CT.In a mouse model,the 3D morphology of the radiopaque hydrogels after injection into different target sites was visible using Micro-CT imaging,and their injection volume could be accurately obtained.Furthermore,the subcutaneous degradation process of a radiopaque hydrogel could be non-invasively monitored in a real-time and quantitative manner.In particular,the corrected degradation curve based on Micro-CT imaging well matched with the degradation profile of virgin polymer hydrogel determined by the gravimetric method.These findings indicate that the macromolecular contrast agent has good universality for the construction of various radiopaque polymer hydrogels,and can nondestructively trace and quantify their degradation in vivo.Meanwhile,the present methodology developed by us affords a platform technology for deep tissue imaging of polymeric materials.