Fabrication of a biodegradable and cytocompatible magnesium/nanohydroxyapatite/fluorapatite composite by upward friction stir processing for biomedical applications

Investigation of Friction Stir Welding of Additively Manufactured Biocompatible Thermoplastics Using Stationary Shoulder and Assisted Heating

Additive manufacturing (AM), also known as 3D printing, offers many advantages and, particularly in the medical field, it has stood out for its potential for the manufacture of patient-specific implantable devices. Thus, the unique properties of 3D-printed biocompatible polymers such as Polylactic Acid (PLA) and Polyetheretherketone (PEEK) have made these materials the focus of recent research where new post-processing and joining techniques need to be investigated. This study investigates the weldability of PLA and PEEK 3D-printed plates through stationary shoulder friction stir welding (SS-FSW) with assisted heating. An SS-FSW apparatus was developed to address the challenges of rotating shoulder FSW of thermoplastics, with assisted heating either through the shoulder or through the backing plate, thus minimizing material removal defects in the welds. Successful welds revealed that SS-FSW improves surface quality in both PLA and PEEK welds compared to rotating shoulder tools. Process parameters for PLA welds are investigated using the Taguchi method, emphasizing the importance of lower travel speeds to achieve higher joint efficiencies. In PEEK welds, the heated backing plate proved effective in increasing process heat input and reducing cooldown rates which were associated with higher crystallinity PEEK. Despite these findings, further research is needed to improve the weld strength of SS-FSW with these materials considering aspects like tool design, process stability, and 3D printing parameters. This investigation emphasizes the potential of SS-FSW in the assembly of thermoplastic materials, offering insights into the weldability of additively manufactured biocompatible polymers like PLA and PEEK.

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Advances in Biodegradable Polymers and Biomaterials for Medical Applications-A Review

The introduction of new materials for the production of various types of constructs that can connect directly to tissues has enabled the development of such fields of science as medicine, tissue, and regenerative engineering. The implementation of these types of materials, called biomaterials, has contributed to a significant improvement in the quality of human life in terms of health. This is due to the constantly growing availability of new implants, prostheses, tools, and surgical equipment, which, thanks to their specific features such as biocompatibility, appropriate mechanical properties, ease of sterilization, and high porosity, ensure an improvement of living. Biodegradation ensures, among other things, the ideal rate of development for regenerated tissue. Current tissue engineering and regenerative medicine strategies aim to restore the function of damaged tissues. The current gold standard is autografts (using the patient's tissue to accelerate healing), but limitations such as limited procurement of certain tissues, long operative time, and donor site morbidity have warranted the search for alternative options. The use of biomaterials for this purpose is an attractive option and the number of biomaterials being developed and tested is growing rapidly.

An investigation on the fabrication and characterization of friction stir processed nano-HAp reinforced AZ91D magnesium matrix surface composite for bio-implants

In the present research, friction stir processed (FSPed) nano-hydroxyapatite reinforced AZ91D magnesium matrix surface composite has been developed with improved ultimate tensile strength (UTS) and biological performance, which are needed for the bio-implants. Nano-hydroxyapatite reinforcement with varying proportions (5.8%, 8.3%, and 12.5%) was introduced into the AZ91-D parent material (PM) by the grooving method with different grooves of 0.5, 1 & 1.5 mm of width and 2 mm depth machined on the surface of the PM. Taguchi's L-9 orthogonal array was employed to optimize the processing variables for enhancing the UTS of the developed composite material. The optimum parameters were discovered to be the tool rotational speed of 1000 rpm, transverse speed of 50 mm/min, and 12.5% reinforcement concentration. The results revealed that the tool rotational speed contributes the highest effect (43.69%) on UTS, followed by the reinforcement percentage (37.49%) and transverse speed (18.31%). The FSPed samples at the optimized parameter setting confirmed the enhancement of 30.17% and 31.86% in UTS and micro-hardness, respectively, compared to the PM. Cytotoxicity of the optimized sample was also found superior compared to the other FSPed samples. The optimized FSPed composite's grain size was 6.88 times smaller than the AZ91D parent matrix material. The improved mechanical and biological performances of the composites are attributed to the significant grain refinement and proper dispersion of the nHAp reinforcement in the matrix.

Enhancement of Scaffold In Vivo Biodegradability for Bone Regeneration Using P28 Peptide Formulations

The field of bone tissue engineering has shown a great variety of bone graft substitute materials under development to date, with the aim to reconstruct new bone tissue while maintaining characteristics close to the native bone. Currently, insufficient scaffold degradation remains the critical limitation for the success of tailoring the bone formation turnover rate. This study examines novel scaffold formulations to improve the degradation rate in vivo, utilising chitosan (CS), hydroxyapatite (HAp) and fluorapatite (FAp) at different ratios. Previously, the P28 peptide was reported to present similar, if not better performance in new bone production to its native protein, bone morphogenetic protein-2 (BMP-2), in promoting osteogenesis in vivo. Therefore, various P28 concentrations were incorporated into the CS/HAp/FAp scaffolds for implantation in vivo. H&E staining shows minimal scaffold traces in most of the defects induced after eight weeks, showing the enhanced biodegradability of the scaffolds in vivo. The HE stain highlighted the thickened periosteum indicating a new bone formation in the scaffolds, where CS/HAp/FAp/P28 75 µg and CS/HAp/FAp/P28 150 µg showed the cortical and trabecular thickening. CS/HAp/FAp 1:1 P28 150 µg scaffolds showed a higher intensity of calcein green label with the absence of xylenol orange label, which indicates that mineralisation and remodelling was not ongoing four days prior to sacrifice. Conversely, double labelling was observed in the CS/HAp/FAp 1:1 P28 25 µg and CS/HAp/FAp/P28 75 µg, which indicates continued mineralisation at days ten and four prior to sacrifice. Based on the HE and fluorochrome label, CS/HAp/FAp 1:1 with P28 peptides presented a consistent positive osteoinduction following the implantation in the femoral condyle defects. These results show the ability of this tailored formulation to improve the scaffold degradation for bone regeneration and present a cost-effective alternative to BMP-2.

Mechanical performance and bioactivation of 3D-printed PEEK for high-performance implant manufacture: a review

Polyetheretherketone (PEEK) has stood out as the leading high-performance thermoplastic for the replacement of metals in orthopaedic, trauma and spinal implant applications due to its high biocompatibility and mechanical properties. Despite its potential for custom-made medical devices, 3D-printed PEEK's mechanical performance depends on processing parameters and its bioinertness may hinder bone opposition to the implant. Concerning these challenges, this review focuses on the available literature addressing the improvement of the mechanical performance of PEEK processed through "fused filament fabrication" (FFF) along with literature on bioactivation of PEEK for improved osseointegration. The reviewed research suggests that improvements can be achieved in mechanical performance of 3D-printed PEEK with adequate FFF parametrization while different bioactivation techniques can be used to improve the bioperformance of 3D-printed PEEK. The adequate approaches towards these procedures can increase PEEK's potential for the manufacture of high-performance custom-made implantable devices that display improved bone-implant integration and prevent stress shielding of the treated bone.

Hydrothermal Synthesis of Fluorapatite Coatings over Titanium Implants for Enhanced Osseointegration-An In Vivo Study in the Rabbit

This work aims at the development and characterization of fluorapatite coatings, innovatively prepared by the hydrothermal method, aiming for enhanced osseointegration of titanium implants. Fluoride-containing coatings were prepared and characterized by scanning and transmission electron microscopy, Fourier-transform infrared spectroscopy-attenuated total reflectance, and X-ray photoelectron spectroscopy. The biological response was characterized by microtomographic evaluation and histomorphometric analysis upon orthotopic implantation in a translational rabbit experimental model. Physic-chemical analysis revealed the inclusion of fluoride in the apatite lattice with fluorapatite formation, associated with the presence of citrate species. The in vivo biological assessment of coated implants revealed an enhanced bone formation process-with increased bone-to-implant contact and bone volume. The attained enhancement of the osteogenic process may be attributable to the conjoined modulatory activity of selected fluoride and citrate levels within the produced coatings. In this regard, the production of fluorapatite coatings with citrate, through the hydrothermal method, entails a promising approach for enhanced osseointegration in implant dentistry and orthopedic applications.

Bioresorbable Chitosan-Based Bone Regeneration Scaffold Using Various Bioceramics and the Alteration of Photoinitiator Concentration in an Extended UV Photocrosslinking Reaction

Bone tissue engineering (BTE) is an ongoing field of research based on clinical needs to treat delayed and non-union long bone fractures. An ideal tissue engineering scaffold should have a biodegradability property matching the rate of new bone turnover, be non-toxic, have good mechanical properties, and mimic the natural extracellular matrix to induce bone regeneration. In this study, biodegradable chitosan (CS) scaffolds were prepared with combinations of bioactive ceramics, namely hydroxyapatite (HAp), tricalcium phosphate-α (TCP- α), and fluorapatite (FAp), with a fixed concentration of benzophenone photoinitiator (50 µL of 0.1% (w/v)) and crosslinked using a UV curing system. The efficacy of the one-step crosslinking reaction was assessed using swelling and compression testing, SEM and FTIR analysis, and biodegradation studies in simulated body fluid. Results indicate that the scaffolds had comparable mechanical properties, which were: 13.69 ± 1.06 (CS/HAp), 12.82 ± 4.10 (CS/TCP-α), 13.87 ± 2.9 (CS/HAp/TCP-α), and 15.55 ± 0.56 (CS/FAp). Consequently, various benzophenone concentrations were added to CS/HAp formulations to determine their effect on the degradation rate. Based on the mechanical properties and degradation profile of CS/HAp, it was found that 5 µL of 0.1% (w/v) benzophenone resulted in the highest degradation rate at eight weeks (54.48% degraded), while maintaining compressive strength between (4.04 ± 1.49 to 10.17 ± 4.78 MPa) during degradation testing. These results indicate that incorporating bioceramics with a suitable photoinitiator concentration can tailor the biodegradability and load-bearing capacity of the scaffolds.