Design approaches and challenges for biodegradable bone implants: a review

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.

Patient-specific implants made of 3D printed bioresorbable polymers at the point-of-care: material, technology, and scope of surgical application

BACKGROUND

Bioresorbable patient-specific additive-manufactured bone grafts, meshes, and plates are emerging as a promising alternative that can overcome the challenges associated with conventional off-the-shelf implants. The fabrication of patient-specific implants (PSIs) directly at the point-of-care (POC), such as hospitals, clinics, and surgical centers, allows for more flexible, faster, and more efficient processes, reducing the need for outsourcing to external manufacturers. We want to emphasize the potential advantages of producing bioresorbable polymer implants for cranio-maxillofacial surgery at the POC by highlighting its surgical applications, benefits, and limitations.

METHODS

This study describes the workflow of designing and fabricating degradable polymeric PSIs using three-dimensional (3D) printing technology. The cortical bone was segmented from the patient's computed tomography data using Materialise Mimics software, and the PSIs were designed created using Geomagic Freeform and nTopology software. The implants were finally printed via Arburg Plastic Freeforming (APF) of medical-grade poly (L-lactide-co-D, L-lactide) with 30% β-tricalcium phosphate and evaluated for fit.

RESULTS

3D printed implants using APF technology showed surfaces with highly uniform and well-connected droplets with minimal gap formation between the printed paths. For the plates and meshes, a wall thickness down to 0.8 mm could be achieved. In this study, we successfully printed plates for osteosynthesis, implants for orbital floor fractures, meshes for alveolar bone regeneration, and bone scaffolds with interconnected channels.

CONCLUSIONS

This study shows the feasibility of using 3D printing to create degradable polymeric PSIs seamlessly integrated into virtual surgical planning workflows. Implementing POC 3D printing of biodegradable PSI can potentially improve therapeutic outcomes, but regulatory compliance must be addressed.

Biomaterial composed of chitosan, riboflavin, and hydroxyapatite for bone tissue regeneration

Biomaterial engineering approaches involve using a combination of miscellaneous bioactive molecules which may promote cell proliferation and, thus, form a scaffold with the environment that favors the regeneration process. Chitosan, a naturally occurring biodegradable polymer, possess some essential features, i.e., biodegradability, biocompatibility, and in the solid phase good porosity, which may contribute to promote cell adhesion. Moreover, doping of the materials with other biocompounds will create a unique and multifunctional scaffold that will be useful in regenerative medicine. This study is focused on the manufacturing and characterization of composite materials based on chitosan, hydroxyapatite, and riboflavin. The resulting films were fabricated by the casting/solvent evaporation method. Morphological and spectroscopy analyses of the films revealed a porous structure and an interconnection between chitosan and apatite. The composite material showed an inhibitory effect on Staphylococcus aureus and exhibited higher antioxidant activity compared to pure chitosan. In vitro studies on riboflavin showed increased cell proliferation and migration of fibroblasts and osteosarcoma cells, thus demonstrating their potential for bone tissue engineering applications.

Biocompatibility Assessment of Zinc Alloys as a New Potential Material for Bioabsorbable Implants for Osteosynthesis

In the last several years, zinc and its alloys have come into focus as bioabsorbable materials by qualifying themselves with an excellent corrosion rate, mechanical properties, anti-bacterial effects. and considerable biocompatibility. In this study, the biocompatibility of zinc-silver alloys containing 3.3 wt% silver (ZnAg3) was assessed by evaluating their cell viability, the proliferation rate, and the cell toxicity. Two alloys were investigated in which one was phosphated and the other was non-phosphated. The alloys were tested on human osteoblasts (hOb), which are, to a large extent, responsible for bone formation and healing processes. The performance of the phosphated alloy did not differ significantly from the non-phosphated alloy. The results showed a promising biocompatibility with hOb for both alloys equally in all conducted assays, qualifying ZnAg3 for further investigations such as in vivo studies.

Biomimetic Remineralized Three-Dimensional Collagen Bone Matrices with an Enhanced Osteostimulating Effect

Bone grafts with a high potential for osseointegration, capable of providing a complete and effective regeneration of bone tissue, remain an urgent and unresolved issue. The presented work proposes an approach to develop composite biomimetic bone material for reconstructive surgery by deposition (remineralization) on the surface of high-purity, demineralized bone collagen matrix calcium phosphate layers. Histological and elemental analysis have shown reproduction of the bone tissue matrix architectonics, and a high-purity degree of the obtained collagen scaffolds; the cell culture and confocal microscopy have demonstrated a high biocompatibility of the materials obtained. Adsorption spectroscopy, scanning electron microscopy, microcomputed tomography (microCT) and infrared spectroscopy, and X-ray diffraction have proven the efficiency of the deposition of calcium phosphates on the surface of bone collagen scaffolds. Cell culture and confocal microscopy methods have shown high biocompatibility of both demineralized and remineralized bone matrices. In the model of heterotopic implantation in rats, at the term of seven weeks, an intensive intratrabecular infiltration of calcium phosphate precipitates, and a pronounced synthetic activity of osteoblast remodeling and rebuilding implanted materials, were revealed in remineralized bone collagen matrices in contrast to demineralized ones. Thus, remineralization of highly purified demineralized bone matrices significantly enhanced their osteostimulating ability. The data obtained are of interest for the creation of new highly effective osteoplastic materials for bone tissue regeneration and augmentation.

Ceria-based coatings on magnesium alloys for biomedical applications: a literature review

Magnesium alloys are being studied for use in temporary orthopedic implants because of their mechanical properties, which are similar to those of human bone, and their good biocompatibility. However, their application is limited due to their rapid degradation, and early loss of their mechanical properties, decreasing the stability of the implant and its proper synchronization with tissue regeneration. In this regard, various surface coatings have been used to improve their biological, physico-chemical and biodegradation properties. Currently, one of the most explored strategies is using smart coatings because of their self-healing properties that can slow down the corrosion process of Mg and its alloys. Ceria-based materials show promise as coatings for these alloys. Their unique redox capacity not only provides Mg alloys with good self-healing properties but also interesting biological properties, which are described in this paper. Despite this, some problems and challenges related to the biocompatibility and application of these materials in coatings remain unsolved. In this article, a critical review is presented summarizing the most representative literature on ceria-based coatings on Mg alloys for their potential use as biomaterials. The results show that ceria is a versatile material that may be used in industrial and biomedical applications.

Microstructure, Mechanical, In Vitro Biodegradation, and Antimicrobial Behavior of a Mg-Zn-Ca-Sr/ZrO2 Composite Prepared Using Powder Metallurgy

Biodegradable materials, especially Mg alloys, have an exceptional advantage over nonbiodegradable materials in orthopedic applications, such as avoiding second surgery for removal/replacement, stress shielding, but not enough mechanical strength, and so forth. By further improving the Mg alloy to get all the remaining required properties, it can be used for better biodegradable implants, which depend adequately on material optimization, processing, and so forth. A Mg-Zn-Ca-Sr/ZrO₂ composite has been prepared using powder metallurgy by adding 0, 1, 2, and 3 wt % of ZrO₂, which also contains Zn, Ca, and Sr as nutrient elements. Microstructure characterization, as well as mechanical and in vitro biodegradation, have been investigated by hardness, compression, and immersion tests. The highest compressive strength, contraction, and hardness of about 185.6 MPa, 9.5%, and 65.2 HRB are observed in the 2% ZrO₂-containing composite, respectively, whereas a minimum biodegradation rate of 2.76 mm/year is observed on the same. The antibiotic sensitivity observations against Staphylococcus aureus suggest that the alloy C3 has superior biological activity against the pathogen which ranks this alloy on top in merit. Overall, Mg-Zn-Ca-Sr/ZrO₂ exhibits impressive potential for use as a biodegradable and antibiotic material for orthopedic applications.

Functionally graded additive manufacturing for orthopedic applications

Background

Additive Manufacturing due to its benefits in developing parts with complex geometries and shapes, has evolved as an alternate manufacturing process to develop implants with desired properties. The structure of human bones being anisotropic in nature is biologically functionally graded i,e. The structure possesses different properties in different directions. Therefore, various orthopedic implants such as knee, hip and other bone plates, if functionally graded can perform better. In this context, the development of functionally graded (FG) parts for orthopedic application with tailored anisotropic properties has become easier through the use of additive manufacturing (AM).

Objectives

and Rationale: The current paper aims to study the various aspects of additively manufactured FG parts for orthopedic applications. It presents the details of various orthopedic implants such as knee, hip and other bone plates in a structured manner. A systematic literature review is conducted to study the various material and functional aspects of functionally graded parts for orthopedic applications. A section is also dedicated to discuss the mechanical properties of functionally graded parts.

Conclusion

The literature revealed that additive manufacturing can provide lot of opportunities for development of functionally graded orthopedic implants with improved properties and durability. Further, the effect of various FG parameters on the mechanical behavior of these implants needs to be studied in detail. Also, with the advent of various AM technologies, the functional grading can be achieved by various means e.g. density, porosity, microstructure, composition, etc. By varying the AM parameters. However, the current limitations of cost and material biocompatibility prevent the widespread exploitation of AM technologies for various orthopedic applications.

Evaluation of the Biocompatibility and Osteogenic Properties of Metal Oxide Coatings Applied by Magnetron Sputtering as Potential Biofunctional Surface Modifications for Orthopedic Implants

Biomaterials with adequate properties to direct a biological response are essential for orthopedic and dental implants. The surface properties are responsible for the biological response; thus, coatings with biologically relevant properties such as osteoinduction are exciting options to tailor the surface of different bulk materials. Metal oxide coatings such as TiO₂, ZrO₂, Nb₂O₅ and Ta₂O₅ have been suggested as promising for orthopedic and dental implants. However, a comparative study among them is still missing to select the most promising for bone-growth-related applications. In this work, using magnetron sputtering, TiO₂, ZrO₂, Ta₂O₅, and Nb₂O₅ thin films were deposited on Si (100) substrates. The coatings were characterized by Optical Profilometry, Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, X-ray Photoelectron Spectroscopy, X-ray Diffraction, Water Contact Angle measurements, and Surface Free Energy calculations. The cell adhesion, viability, proliferation, and differentiation toward the osteoblastic phenotype of mesenchymal stem cells plated on the coatings were measured to define the biological response. Results confirmed that all coatings were biocompatible. However, a more significant number of cells and proliferative cells were observed on Nb₂O₅ and Ta₂O₅ compared to TiO₂ and ZrO_2. Nevertheless, Nb₂O₅ and Ta₂O₅ seemed to induce cell differentiation toward the osteoblastic phenotype in a longer cell culture time than TiO₂ and ZrO₂.

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.

Effectiveness of laddered embossed structure in a locking compression plate for biodegradable orthopaedic implants

Locking compression plate (LCP) has conventionally been the most extensively employed plate in internal fixation bone implants used in orthopaedic applications. LCP is usually made up of non-biodegradable materials that have a higher mechanical capability. Biodegradable materials, by and large, have less mechanical strength at the point of implantation and lose strength even more after a few months of continuous degradation in the physiological environment. To attain the adequate mechanical capability of a biodegradable bone implant plate, LCP has been modified by adding laddered - type semicircular filleted embossed structure. This improved design may be named as laddered embossed locking compression plate (LELCP). It is likely to provide additional mechanical strength with the most eligible biodegradable material, namely, Mg-alloy, even after continuous degradation that results in diminished thickness. For mechanical validation and comparison of LELCP made up of Mg-alloy, four-point bending test (4PBT) and axial compressive test (ACT) have been performed on LELCP, LCP and continuously degraded LELCP (CD-LELCP) with the aid of finite element method (FEM) for the assembly of bone segments, plate and screw segments. LELCP, when subjected to the above mentioned two tests, has been observed to provide 26% and 10.4% lower equivalent stress, respectively, than LCP without degradation. It is also observed mechanically safe and capable of up to 2 and 6 months of continuous degradation (uniform reduction in thickness) for 4PBT and ACT, respectively. These results have also been found reasonably accurate through real-time surgical simulations by approaching the most optimal mesh. According to these improved mechanical performance parameters, LELCP may be used or considered as a viable biodegradable implant plate option in the future after real life or in vivo validation.

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

In the current revolution of internal fixation implant in orthopaedics, a biodegradable implant is the most awaited and exceptional medical device where biodegradable material has paid more attention to the success of a biodegradable implant than the design of a biodegradable bone implant plate. By far, LCP is the most traditionally used implant plate (using non-biodegradable material) because of its experimental success, but not with qualified biodegradable material (Mg-alloy). This lack of mechanical performance is a major drawback that can be rectified by better structural design. This will help avoid few other problems as well. Therefore, with proper consideration, the LCP has been added to a semicircular filleted longitudinally centered embossed (LCE) structure to enhance overall mechanical performance that can help emphasize mechanical support even after continuous degradation when applied in a physiological environment. For mechanical verification of this advanced design of biodegradable bone implant plate, four-point bending test (4PBT) and axial compression test (ACT) have been performed using FEM on LCELCP, LCP, continuously degraded (CD)-LCELCP, and CD-LCP. LCELCP showed reduced stress of about 22% and 10% in 4PBT and ACT, respectively, compared to LCP. CD-LCELCP is safe during ACT over 6 months of continuous degradation when the degradation rate is assumed to be 4 mm/year. These results also ensured accuracy using mesh convergence and also mesh checked for quality assurance. Overall, LCELCP can be considered as a biodegradable bone implant plate because of its superior performance, if its ultimate validation is carried out through animal/human trials as future work.