Longitudinally centered embossed structure in the locking compression plate for biodegradable bone implant plate: a finite element analysis

Design improvements to enhance mechanical performance of a locking compression plate as a biodegradable implant plate: a finite element analysis

Mg alloy is one of the most suitable biodegradable materials for making modern LCP. This is due to the osseointegration property, low elastic modulus, the presence in the human bone, and the excellent biodegradable nature. But it lacks much-needed strength compared to conventional (Ti, SS alloys) implants due to low strength of biodegradable (Mg, Zn alloys) materials. The problem can be solved by either biodegradable material development or by design improvement of existing LCP. Improving the design is a better way to improve the LCP. This paper aims to improve the design of existing LCP through the addition of features and their implications by analysing the stress distribution across the plates for improved biodegradable implant mechanical performance. Various designs have been developed and each has certain advantages over conventional LCP which ACT and 4PBT have been demonstrated via the FEM. They are best suited for femur bone fracture treatment replacing conventional metal alloys LCP. The CTLCP, SLCP, and SELCP have improved performance at stress concentration regions while STLCP especially has 36.74% less stress generation than conventional LCP along with excellent biodegradable performance. The designs are discussed in detail to analyse the effect of added features in conventional LCP.

Material synthesis and design optimization of biomaterials for biomedical implant applications

Introduction

In the modern era, the use of biomaterials in orthopaedics has revolutionised the healthcare sector. Traditionally, some non-biodegradable materials such as titanium and stainless steel are used as biomaterials. However, issues such as toxicity, poor tissue adhesion, and stress-shielding effect can occur with non-biodegradable materials for bone fracture fixation. Several biodegradable materials have been developed to resolve these issues but have not yet been appropriately industrialized for implant applications. These substances can be classified into metals, ceramics, and polymers, which can be blended to create composites that enhance biocompatibility and biomechanical characteristics.

Methods

This study began by contrasting the biocompatibility and mechanical compatibility among various alloys: biodegradable low entropy (BLE) alloys, biodegradable medium entropy (BME) alloys, biodegradable high entropy (BHE) alloys, and non-biodegradable medium entropy (NBME) alloys. Additionally, the design morphology of bio-implants like plates, screws, and others was inspected. Moreover, a meta-analysis was conducted to optimize the design of biomaterials, ensuring appropriate biocompatibility and degradation rate. A subsequent statistical analysis was executed to determine the optimal material concentration for bio-implant alloy creation.

Results

Initially, in this paper, the advantages of biodegradable materials over conventional non-biodegradable materials are discussed and bibliometric analysis is done to show recent research contributions in the field of biomedical implant application. Then compared biocompatibility and mechanical compatibility among BLE alloys, BME alloys, BHE alloys, NBME alloys. Furthermore, investigated the design morphology of bio-implants such as plates and screws. Also presented a meta-analysis for design optimization of biomaterials to meet suitable biocompatibility and biodegradation rates and presented a statistical analysis among them, which helps to select the appropriate material concentration for bio-implant alloy formation.

Conclusion

It was observed that in biodegradable materials, tensile strength is in the pattern of NBME > BHE > BME > BLE, and the degradation rate is in the pattern of BME > NBME > BHE > BLE. This study suggests that biodegradable materials (BLE and BME) are a much better choice than non-biodegradable materials in orthopaedic applications. It was also observed that a Biodegradable locking compression plate (BLCP) can provide the necessary strength and performance. Further, the systematic meta-analysis presented herein furnishes crucial data to researchers, guiding them in enhancing the efficiency of diverse biomaterials and optimizing their designs.

Finite element method-based simulation on bone fracture fixation configuration factors for biodegradable embossed locking compression plate

As an evolution, biodegradable implants need to maximize mechanical performance thereby may lead to confusion in selection of the biodegradable material and implant design to the fracture site. This requires selecting a unique fixation configuration to fit within the fractured bone, factors of which can be bone-plate clearance, interfragmentary gap, alteration in screw fixation position and variation in the number of screws whose configuration optimization can re-maximize the mechanical performance of the biodegradable implant. Therefore, these factors have been optimized based on the induced minimum stress using the finite element method-based simulation for which biodegradable embossed locking plates (BELCP) via screws made of Mg-alloy have been fitted over two fragments of femur body (as hollow cylindrical cortical bone). An average human weight of 62 kg is applied to one segment of the femur for all different configurations of each factor, where another segment is assumed to be fixed. By this simulation, the most optimal fixation configuration was found at a minimum induced stress value of 41.96 MPa which is approximately 85%, 18%, 6% and 48% respectively less than all maximum stress induced configurations in each of the factor. This optimized configuration was at the minimum clearance between bone and plate with a 3 mm interfragmentary gap using 8 screws where the locking screw begins to apply from the center of the BELCP. Overall, BELCP may be a better biodegradable implant plate for bone fracture fixation with these optimized fixation configurations as the improved mechanical performance after experimental validation.

Biomechanical analysis of titanium-alloy and biodegradable implants in dual plate osteosynthesis for AO/ASIF type 33-C2 fractures

Background and objective

Treating geriatric osteoporotic distal femur fractures has always presented challenges, but developing biodegradable materials has brought new opportunities for therapeutic intervention. Despite this progress, there currently needs to be more evidence-based biomechanical guidelines for using dual plate fixation and biodegradable materials in treating osteoporotic comminuted distal femoral fractures.In this study, finite element analysis was conducted to evaluate the mechanical effectiveness of different implant materials (titanium alloys, biodegradable materials, and combinations of both) in the fixation of physiological and osteoporotic distal femoral fractures.

Methods

We constructed finite element models of 33-C2 fractures and three types of plates: the Lateral Less Invasive Stabilization System (LISS) plate, the titanium-alloy medial plate (TAP), and the biodegradable plate (BP). To evaluate the biomechanical advantages in both physiological femur (PF) and osteoporotic femur (OF) conditions, three scenarios were developed: LISS + TAP, LISS + BP, and double biodegradable plates (DBPs). Five loading conditions were applied to measure structural stiffness, fracture micromotion, and implant stress: medio-lateral four-point bending, antero-posterior four-point bending, axial loading, torsional loading, and sideways falling. Several parameters were examined, including peak Von Mises Stress (VMS) of the femur and lateral plate, maximum displacement, bending angle, torsional angle of fracture, and risk of fracture.

Results

In four-point bending tests, the lateral plate of the DBPs group exhibited a slightly lower peak VMS compared to the LISS + TAP and LISS + BP groups. When subjected to axial loading, the stiffness values of the LISS + TAP (OF) were 1.42 times and 1.86 times higher than LISS + BP (OF) and DBPs (OF) groups, and the peak VMS of lateral plate of DBPs (OF) construct was approximately 2% and 16% lower than that of the LISS + TAP (OF) and LISS + BP (OF) constructs. Under torsional loading, DBPs (OF) demonstrated rotational stiffness that was respectively 2% and 52% greater than that of LISS + TAP (OF) and LISS + BP (OF). Regarding the peak VMS of femur, the values of DBPs (OF) were almost 8% and 15% lower than those of LISS + TAP (OF) and LISS + BP (OF).

Conclusions

The use of DBPs at 11.33 GPa facilitated early mobilization of load-bearing joints but exhibited limited ability to support full weight-bearing activities. Though LISS + TAP met practical strength requirements, one should consider the potential biological irritation and stress shielding. Thus, employing a combination of biodegradable and metal internal fixation is a valid approach to effectively treat weight-bearing joint fractures in clinical practice.

Biomechanical evaluation on a novel design of biodegradable embossed locking compression plate for orthopaedic applications using finite element analysis

In orthopaedics, conventional implant plates such as locking compression plate (LCP) made from non-biodegradable materials play a vital role in the fixation to support bone fractures, but also create a complication such as stress shielding. These again require a painful surgery to remove/replace after they have healed as it does not degrade into the physiological environment (PE). Currently, there has already been enough discovery of biodegradable materials that, despite being mechanically inefficient compared to non-biodegradable materials, can completely be biodegraded in PE during and after healing to avoid such problems. While there has been insufficient research on the design of biodegradable implant plates, the implementation of which may help achieve the goal with an effort of high mechanical strength. A novel design of biodegradable embossed locking compression plate (BELCP) is designed for biodegradable materials to approach superior mechanical performance and complete degradation over time, considering all such parameters and factors. For biomechanical evaluation, four-point bending test (4PBT), axial compressive and tensile test (ACTT) and torsion test (TT) have been performed on LCP, BELCP and its continuously degraded forms made of biodegradable material (Mg-alloy) using finite element method. BELCP has found 50%, 100% and 100% higher mechanical performance and safer in 4PBT, ACTT and TT, respectively, than LCP. Moreover, BELCP has also observed safe during continuous degradation up to 6 months after implantation under these three tests, considering an approximate sustained degradation rate of about 4 mm/year. Even Mg-alloy made BELCP can be sufficient and safer to support fractured bone than SS-alloy made LCP, but not Ti-alloy made LCP. BELCP can be a successful biodegradable bone implant plate after human/animal trials in the future.

Effectiveness of non-uniform thickness on a locking compression plate used as a biodegradable bone implant plate

Conventional locking compression plate (LCP) made of non-biodegradable materials are well-known bone implants for internal fracture fixation because of their proven experimental success. LCP, however, is mechanically underpowered when made up of biodegradable materials (even with Mg-alloy). The biodegradable implant plate should not only exhibit adequate mechanical performance during implantation but also perform well after fracture, at least until complete healing of the fractured bone. With the aim of achieving enhanced mechanical performance, the design of the LCP has been modified to the design of Biodegradable Locking Compression Plate (BLCP) by adding a suitable thickness in the middle (only 4.6% of the total volume of the LCP), which may help retain some additional strength during implantation and after degradation. Both BLCP and LCP have been comparatively analyzed via FEM with the aid of axial compression and four-point bending tests. BLCP has a better mechanical capability of withstanding loads in its degraded form than in its non-degradable form. Furthermore, BLCP is up to 15.83% mechanically better in the non-degraded form as compared to LCP, which again becomes up to 100% more mechanically adequate in the degraded forms of BLCP than in LCP. BLCP is found safe for degradation up to 2 mm or 6 months with an estimated degradation rate of 4 mm/year, which may allow it to support fractured bone for at least the standard healing time. BLCP can be considered as a superior biodegradable bone implant plate after experimental assurance with the physiological environment and may replace LCP.