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Development of Biodegradable Mg-based alloys with controlled degradation rate for temporary implant applications
Development of Biodegradable Mg-based alloys with controlled degradation rate for temporary implant applications
Biomaterials have a vital role to play in uplifting the overall lifestyle and longevity of human life and thus attracting a great deal of attention in today’s era. Over the last few decades, concurrent with the enormous improvement in the field of medical sciences, the life expectancy and average life span of an individual have increased globally, leading to an increase in the elderly population throughout the world. The ever-rising demand for orthopedic implants necessitates an acceleration in research and developmental work concentrated over finding suitable orthopedic implant materials.
Permanent implants are ideally meant to stay inside our body until lifetime as a replacement of natural bone. However, there are instances which require only temporary support for the bone or tissue to heal until the fracture repairs and then the implants can degrade inside our body, thus eliminating the requirement of the cumbersome secondary implant removal surgery associated with permanent implants. These temporary implants commonly include screws, nuts, micro-clips, stents etc.
Radiographs comparing the conventional stainless-steel screws and Mg-based RESOMET® screws for fixation of radius fracture. The Mg screw gets dissolved progressively within 12 months with appreciable bone regeneration and fracture healing
Figure Reference: J.W. Lee et al./, Proc. Natl. Acad. Sci. 113 (2016) 716–721.
Amongst the several available alternatives suitable for fabricating temporary implants, the Mg-based alloys are gaining immense popularity due to the unique combination of desirable properties they offer, for instance, their natural degradability in body-fluid, appreciable biocompatibility, osteogenic property and most importantly their close resemblance with natural bone in terms of density and elastic modulus.
Despite possessing several desirable properties, the commercialization of Mg-based devices as temporary implants is still limited due to their uncontrollable degradation rate in the physiological environment. The presence of a high concentration of chloride ions (~96-106 mEq/L) in bodily fluid and a pH of around 7.4 - 7.6 , makes the Mg-based implants to degrade much more aggressively compared to the typical aqueous solution. Moreover, the rapid rate of formation of gas bubbles has a negative impact on the patient’s health. In this degradation process, the implants lose adequate mechanical integrity to bear the load and become highly prone to sudden untimely failure. Therefore, the development of Mg-based implants with a controlled degradation rate to sustain the required period of the bone healing process (~24-32 weeks) still stands as a challenge, and it compels the researchers and scientists to put more efforts in modifying bio-corrosion properties of Mg alloys by suitable means.
Based on the state of art in the field, the following research problem has been formulated.
Figure references:
D. Zhao et al., Biomaterials 112 (2017) 287-302
C.E. Baker et al., Clinic Rev Bone Miner Metabol. (2018) 16:142–158
Research Problem:
Research Problem:
The capability of Mg-based alloys to degrade naturally in the physiological environment advocates their use as a suitable temporary implant material. Since the last two decades, the Mg-based alloys have been subjected to continuous and progressive modifications in terms of alloy composition and surface coatings to meet the target degradation rate in order to eliminate the existing mismatch between bone-healing and alloy degradation period. However, the commercialization of Mg-based devices as temporary implants is still limited due to their uncontrollable degradation rate in the physiological environment.
Therefore, the requirement is to develope an alloy system with high biocompatibility, sufficient mechanical strength, and most importantly adequate bio-corrosion resistance.
Key Research Objectives:
Key Research Objectives:
Alloy Designing and development of the alloy
Establishing suitable heat-treatment and plastic deformation schedule to gain favorable properties required for target application
Understanding the effect of thermo-mechanical processing on mechanical, bio-corrosion properties (in SBF) and cytotoxicity
improvement of corrosion resistance of the material by formation of appropriate surface coatings
Some potential future applications of the alloy
Some potential future applications of the alloy
Figure reference: Yongjun Chen et al., Acta Biomaterialia, 10 (2014) 4561-4573
Highlights of the Progress done so far:
Highlights of the Progress done so far:
Alloy composition has been selected based on comprehensive literature survey.
Alloy has been developed through conventional casting route.
Preliminary characterization of the developed as-cast alloy is done.
Based on the parameters obtained from characterization of as-cast alloy, along with the help of thermodynamic calculations (using FactSage database) and kinetic diffusion modelling (of alloying elements), the homogenization schedule of the alloy was designed to attain target properties.
Thereafter, based on the modelling results, the experimental works concerned to the homogenization treatment of the alloy has been carried out and the experimental results have been thoroughly characterized.
The mechanical properties (in terms of tensile strength, microhardness etc.) of the heat-treated alloys have been checked to understand the structure-property correlation, and to find out the optimum condition to carry out the further thermomechanical processing treatments.
The corrosion set-up is being customized in our lab for carrying out the bio-corrosion experiments.
The in-vitro degradation behavior of the homogenized alloys have been carried out under simulated body environment of the selected specimens.
The hot deformation (using Hard Plate Hot Forging) process has been carried out on selected specimens at varied temperatures.
The mechanical properties of the specimens are characterized and slip system activity is elucidated using VPSC simulation
The in-vitro degradation behaviour of the deformed alloys have been characterized to understand their corrosion susceptibility.
Biological properties like in-vitro cytotoxicity, antimicrobial properties are examined to understand the applicability of the alloy in practical applications.
Recently, we are trying to develop a biodegradable coating on a selected specimen to further improve its degradation behaviour.
Potential future application of the developed alloy:
Achieving the target properties would make this alloy applicable to practical applications like forming a ‘screw’ or a ‘plate’ that can be used as a temporary implant in near-future.
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