Biological evaluation and finite-element modeling of porous poly(para-phenylene) for orthopaedic implants

Comparison of three frailty evaluation tools in predicting postoperative adverse events in older patients undergoing lumbar fusion surgery: a prospective cohort study of 240 patients

PURPOSE

To compare the utility of the frailty phenotype (FP), the FRAIL scale, and 5-item modified Frailty Index (mFI-5) in predicting postoperative adverse events after enhanced recovery after lumbar fusion surgery in older patients.

METHODS

This study prospectively included older patients (> 75 years) who underwent transforaminal lumbar interbody fusion from June 2019 to August 2021. Frailty status was evaluated using FP, the FRAIL scale, and mFI-5. The study investigated the associations between these three frailty tools and total adverse events, complications, and secondary outcomes. Multivariable logistic regression analysis was performed to identify predictors of total adverse events, complications, and secondary outcomes.

RESULTS

Correlation analysis demonstrated that frailty assessed by the FP was significantly associated with an increased incidence of complications (55.7% vs. 41.5%, p =.028) and prolonged hospital stays (29.5% vs. 16.9%, p =.021). Frailty identified using the FRAIL scale was significantly linked to prolonged hospital stays (33.7% vs. 16.2%, p =.002). Additionally, frailty assessed by the mFI-5 was associated with higher rates of 30-day readmission (18.5% vs. 6.3%, p =.003) and 30-day reoperation (7.4% vs. 0.6%, p =.007). Multivariate logistic regression revealed that an FP score of ≥ 3 was an independent risk factor for total adverse events, complications, and secondary outcomes, while a FRAIL score of ≥ 3 was an independent risk factor for secondary outcomes.

CONCLUSION

Frailty as defined by the FP is an independent risk factor for total adverse events, complications, and secondary outcomes. Frailty as defined by the FRAIL scale is an independent risk factor for secondary outcomes. The mFI-5 has not been demonstrated to be an independent risk factor for any postoperative adverse events.

Laser powder bed fusion printed poly-ether-ether-ketone/bioactive glass composite scaffolds with dual-scale pores for enhanced osseointegration and bone ingrowth

Although poly-ether-ether-ketone (PEEK) implants hold significant medical promise, their bioinert nature presents challenges in osseointegration and bone ingrowth within clinical contexts. To mitigate these challenges, the present study introduces Diamond PEEK/bioactive glass (BG) composite scaffolds, characterized by macro/micro dual-porous structures, precisely fabricated via laser powder bed fusion (LPBF) technology. The findings indicate that an increase in BG content within these scaffolds significantly augments their hydrophilicity and hydroxyapatite formation capacities. Stress-strain curve analysis demonstrates reliable load-bearing stability across all scaffold types. In vitro assessments confirmed the non-cytotoxicity of PEEK/BG samples and demonstrated improved osteogenic differentiation and mineralization with increased BG incorporation. Further, in vivo experiments illustrated that the Diamond porous structure of these scaffolds facilitated bone growth, an effect notably amplified with higher BG content. Particularly in groups with 15 wt.% and 25 wt.% BG scaffolds, new bone formation was observed not only within the macropores of the Diamond structure but also within the micropores inside the scaffold rod, suggesting an almost seamless fusion with the new bone. This demonstrates the scaffolds' effective osteointegration and bone ingrowth properties. This study conclusively established the effectiveness of Diamond-structured PEEK/BG composite scaffolds, fabricated via LPBF, in bone repair. It highlights the crucial role of BG in enhancing osteogenic potential through interaction with the macro/micro pores of the scaffold. STATEMENT OF SIGNIFICANCE: This study addresses the bioinert nature of PEEK implants by developing Diamond-structured PEEK/bioactive glass (BG) composite scaffolds by laser powder bed fusion. The dual-porous macro/microstructure enhances hydrophilicity and hydroxyapatite formation, vital for bone regeneration. By adjusting the BG content, we controlled the melt viscosity and sintering rate, leading to the formation of beneficial microscale pores. These pores resolve the issue of ineffective bioactive fillers in previous LPBF-fabricated scaffolds, enhancing the osteogenic potential of BG and inducing superior bone ingrowth and osseointegration. In vitro and in vivo analyses show enhanced osteogenic differentiation, mineralization, and bone growth, underscoring the clinical potential of these scaffolds for bone repair.

A Surface-Mediated Biomimetic Porous Polyether-Ether-Ketone Scaffold for Regulating Immunity and Promoting Osteogenesis

The repair of critical-sized bone defects remains a major challenge for clinical orthopedic surgery. Here, we develop a surface biofunctionalized three-dimensional (3D) porous polyether-ether-ketone (PEEK) scaffold that can simultaneously promote osteogenesis and regulate macrophage polarization. The scaffold is created using polydopamine (PDA)-assisted immobilization of silk fibroin (SF) and the electrostatic self-assembly of nanocrystalline hydroxyapatite (nano-HA) on a 3D-printed porous PEEK scaffold. The SF/nano-HA functionalized surface provides a bone-like microenvironment for osteoblastic cells' adhesion, proliferation, mineralization and osteogenic differentiation. Moreover, the biofunctionalized surface can effectively drive macrophages polarization from the pro-inflammatory M1 phenotype to the anti-inflammatory M2 phenotype. Integrin β1-specific cell-matrix binding and the activation of Ca2+ receptor-mediated signaling pathway play critical roles in the regulation of macrophage polarization. Compared with the as-printed scaffold, the SF/nano-HA functionalized porous PEEK scaffold induces minimal inflammatory response, enhanced angiogenesis, and substantial new bone formation, resulting in improved osseointegration in vivo. This study not only develops a promising candidate for bone repair but also demonstrates a facile surface biofunctionalization strategy for orthopedic implants to improve osseointegration by stimulating osteogenesis and regulating immunity.

The Formation Process and Mechanism of the 3D Porous Network on the Sulfonated PEEK Surface

A three-dimensional (3D) porous network can be prepared on the PEEK surface by sulfonation with enhanced osseointegration and antibacterial properties. However, few studies have been conducted on the formation mechanism of a 3D porous network. In this work, the surface and cross-sectional morphologies, chemical compositions, functional groups, surface wettability, and crystalline states of sulfonated PEEK were investigated at different sulfonation times and coagulant concentrations. The results show that the number of nodular structures and broken fibers on the sulfonated PEEK surface as well as the size of macrovoids in the cross sections increase with increasing sulfonation times when water is used as a coagulant. In contrast, dilute sulfuric acid as a coagulant can inhibit the formation of surface porous structures and macrovoids in the cross sections. Moreover, all of the sulfonated PEEK samples have the same chemical compositions but exhibit better hydrophilicity as the number of microsized pores decreases. It is proposed that non-solvent-induced phase separation (NIPS) occurs during the sulfonation process, and the formation mechanism of surface and cross-sectional morphologies is discussed. Furthermore, it is assumed that the air is trapped in the microsized pores, leaving the surface of the 3D porous network in the Cassie-wetting state. All of these preliminary results throw light on the nature of the sulfonation process and may guide further modification of the structures of sulfonated PEEK.

Research progress of vascularization strategies of tissue-engineered bone

The bone defect caused by fracture, bone tumor, infection, and other causes is not only a problematic point in clinical treatment but also one of the hot issues in current research. The development of bone tissue engineering provides a new way to repair bone defects. Many animal experimental and rising clinical application studies have shown their excellent application prospects. The construction of rapid vascularization of tissue-engineered bone is the main bottleneck and critical factor in repairing bone defects. The rapid establishment of vascular networks early after biomaterial implantation can provide sufficient nutrients and transport metabolites. If the slow formation of the local vascular network results in a lack of blood supply, the osteogenesis process will be delayed or even unable to form new bone. The researchers modified the scaffold material by changing the physical and chemical properties of the scaffold material, loading the growth factor sustained release system, and combining it with trace elements so that it can promote early angiogenesis in the process of induced bone regeneration, which is beneficial to the whole process of bone regeneration. This article reviews the local vascular microenvironment in the process of bone defect repair and the current methods of improving scaffold materials and promoting vascularization.

Design and manufacturing of biomimetic scaffolds for bone repair inspired by bone trabeculae

Porous scaffold (PorS) implants, particularly those that mimic the structural features of natural cancellous bone (NCanB), are increasingly essential for the treatment of large-area bone defects. However, the mechanical properties of NCanB-based bionic bone scaffold (BioS) and its performance as a bone repair material have not been fully explored. This study investigates the effect of bionic structure parameters on the mechanical properties and bone reconstruction performance of BioS. Using laser powder bed fusion (L-PBF) technology, different BioS with various structural parameters were created and evaluated using Micro-CT, compression testing, Finite Element (FE) Simulation, and computational fluid dynamics (CFD), and compared to commonly used clinical PorS. Assess the capacity of the BioS scaffold to support and enhance bone reconstruction following implantation through the evaluation of its mechanical properties, permeability, and fluid shear stress (FSS). BioS-85-90 and BioS-80-50 showed suitable mechanical properties, performed well in FE simulation of implantation, demonstrated outstanding abilities for osteoinductive ingrowth and bone tissue differentiation, and proved to be reliable materials for the reconstruction of bone defects. Therefore, BioS shows significant potential for clinical application as a bone reconstruction material, providing a solid foundation for the integration of tissue engineering and bionic design.

Bio-Activated PEEK: Promising Platforms for Improving Osteogenesis through Modulating Macrophage Polarization

The attention on orthopedic biomaterials has shifted from their direct osteogenic properties to their osteoimmunomodulation, especially the modulation of macrophage polarization. Presently, advanced technologies endow polyetheretherketone (PEEK) with good osteoimmunomodulation by modifying PEEK surface characteristics or incorporating bioactive substances with regulating macrophage polarization. Recent studies have demonstrated that the fabrication of a hydrophilic surface and the incorporation of bioactive substances into PEEK (e.g., zinc, calcium, and phosphate) are good strategies to promote osteogenesis by enhancing the polarization of M2 macrophages. Furthermore, the modification by other osteoimmunomodulatory composites (e.g., lncRNA-MM2P, IL-4, IL-10, and chitosan) and their controlled and desired release may make PEEK an optimal bio-activated implant for regulating and balancing the osteogenic system and immune system. The purpose of this review is to comprehensively evaluate the potential of bio-activated PEEK in polarizing macrophages into M2 phenotype to improve osteogenesis. For this objective, we retrieved and discussed different kinds of bio-activated PEEK regarding improving osteogenesis through modulating macrophage polarization. Meanwhile, the relevant challenges and outlook were presented. We hope that this review can shed light on the development of bio-activated PEEK with more favorable osteoimmunomodulation.

Additively-manufactured PEEK/HA porous scaffolds with highly-controllable mechanical properties and excellent biocompatibility

Polyetheretherketone (PEEK) was widely applied into fabricating of orthopaedic implants, benefitting its excellent biocompatibility and similar mechanical properties to native bones. However, the inertness of PEEK hinders its integration with the surrounding bone tissue. Here PEEK scaffolds with a series of hydroxyapatite (HA) contents in gradient were manufactured via fused filament fabrication (FFF) 3D printing techniques. The influence of the pore size, HA content and printing direction on the mechanical properties of the PEEK/HA scaffolds was systematically evaluated. By adjusting the pore size and HA contents, the elastic modulus of the PEEK/HA scaffolds can be widely tuned in the range of 624.7-50.6 MPa, similar to the variation range of natural cancellous bone. Meanwhile, the scaffolds exhibited higher Young's modulus and lower compressive strength along Z printing direction. The mapping relationship among geometric parameters, HA content, printing direction and mechanical properties was established, which gave more accurate predictions and controllability of the modulus and strength of scaffolds. The PEEK/HA scaffolds with the micro-structured surface could promote cell attachment and mineralization in vitro. Therefore, the FFF-printed PEEK/HA composites scaffolds can be a good candidate for bone grafting and tissue engineering.

A novel surgical model for the preclinical assessment of the osseointegration of dental implants: a surgical protocol and pilot study results

BACKGROUND

Dental implants are considered the gold standard replacement for missing natural teeth. The successful clinical performance of dental implants is due to their ability to osseointegrate with the surrounding bone. Most dental implants are manufactured from Titanium and it alloys. Titanium does however have some shortcomings so alternative materials are frequently being investigated. Effective preclinical studies are essential to transfer the innovations from the benchtop to the patients. Many preclinical studies are carried out in the extra-oral bones of small animal models to assess the osseointegration of the newly developed materials. This does not simulate the oral environment where the dental implants are subjected to several factors that influence osseointegration; therefore, they can have limited clinical value.

AIM

This study aimed to develop an appropriate in-vivo model for dental implant research that mimic the clinical setting. The study evaluated the applicability of the new model and investigated the impact of the surgical procedure on animal welfare.

MATERIALS AND METHODS

The model was developed in male New Zealand white rabbits. The implants were inserted in the extraction sockets of the secondary incisors in the maxilla. The model allows a split-mouth comparative analysis. The implants' osseointegration was assessed clinically, radiographically using micro-computed tomography (µ-CT), and histologically. A randomised, controlled split-mouth design was conducted in 6 rabbits. A total of twelve implants were inserted. In each rabbit, two implants; one experimental implant on one side, and one control implant on the other side were applied. Screw-shaped implants were used with a length of 8 mm and a diameter of 2 mm.

RESULTS

All the rabbits tolerated the surgical procedure well. The osseointegration was confirmed clinically, histologically and radiographically. Quantitative assessment of bone volume and mineral density was measured in the peri-implant bone tissues. The findings suggest that the new preclinical model is excellent, facilitating a comprehensive evaluation of osseointegration of dental implants in translational research pertaining to the human application.

CONCLUSION

The presented model proved to be safe, reproducible and required basic surgical skills to perform.

The State of Starch/Hydroxyapatite Composite Scaffold in Bone Tissue Engineering with Consideration for Dielectric Measurement as an Alternative Characterization Technique

Hydroxyapatite (HA) has been widely used as a scaffold in tissue engineering. HA possesses high mechanical stress and exhibits particularly excellent biocompatibility owing to its similarity to natural bone. Nonetheless, this ceramic scaffold has limited applications due to its apparent brittleness. Therefore, this had presented some difficulties when shaping implants out of HA and for sustaining a high mechanical load. Fortunately, these drawbacks can be improved by combining HA with other biomaterials. Starch was heavily considered for biomedical device applications in favor of its low cost, wide availability, and biocompatibility properties that complement HA. This review provides an insight into starch/HA composites used in the fabrication of bone tissue scaffolds and numerous factors that influence the scaffold properties. Moreover, an alternative characterization of scaffolds via dielectric and free space measurement as a potential contactless and nondestructive measurement method is also highlighted.

Effects of printing path and material components on mechanical properties of 3D-printed polyether-ether-ketone/hydroxyapatite composites

Polyether-ether-ketone (PEEK) exhibits excellent mechanical properties and biocompatibility. Three-dimensional (3D) printing of PEEK bone substitutes has been widely used in clinical application. However, the inertness of pure PEEK hinders its integration with the surrounding bone tissue. In this study, for the first time, PEEK/hydroxyapatite (HA) composite specimens were fabricated using fused filament fabrication (FFF) technology. PEEK/HA filaments with HA contents of 0-30 wt% were fabricated via mechanical mixing and extrusion. The HA distributions inside the composite matrix and the surface morphology characteristics of the PEEK/HA composites were examined. The effects of the printing path and HA content on the mechanics of the PEEK/HA composites were systematically investigated. The results indicated that the HA particles were uniformly distributed on the composite matrix. With an increase in the HA content, the modulus of the PEEK/HA composite increased, while the strength and failure strain concomitantly decreased. When the HA content increased to 30 wt%, the tensile modulus of the composite increased by 68.6% compared with that of pure PEEK printed along the horizontal 90° path, while the tensile strength decreased by 48.2% compared with that of pure PEEK printed along the vertical 90° path. The fracture elongation of the printed specimens with different HA contents decreased in the following order: horizontal 0° > horizontal 90° > vertical 90°. The best comprehensive mechanical properties were achieved for pure PEEK fabricated along the horizontal 0° path. The results indicate that FFF technology is applicable for additive manufacturing of PEEK/HA composites with controllable compositions. Printed PEEK/HA composites have potential for applications in the design and manufacturing of personalized bone substitutes.

Desktop-Stereolithography 3D Printing of a Polyporous Extracellular Matrix Bioink for Bone Defect Regeneration

Introduction

Decellularized tendon extracellular matrix (tECM) perfectly provides the natural environment and holds great potential for bone regeneration in Bone tissue engineering (BTE) area. However, its densifying fiber structure leads to reduced cell permeability. Our study aimed to combine tECM with polyethylene glycol diacrylate (PEGDA) to form a biological scaffold with appropriate porosity and strength using stereolithography (SLA) technology for bone defect repair.

Methods

The tECM was produced and evaluated. Mesenchymal stem cell (MSC) was used to evaluate the biocompatibility of PEGDA/tECM bioink in vitro. Mineralization ability of the bioink was also evaluated in vitro. After preparing 3D printed polyporous PEGDA/tECM scaffolds (3D-pPES) via SLA, the calvarial defect generation capacity of 3D-pPES was assessed.

Results

The tECM was obtained and the decellularized effect was confirmed. The tECM increased the swelling ratio and porosity of PEGDA bioink, both cellular proliferation and biomineralization in vitro of the bioink were significantly optimized. The 3D-pPES was fabricated. Compared to the control group, increased cell migration efficiency, up-regulation of osteogenic differentiation RNA level, and better calvarial defect repair in rat of the 3D-pPES group were observed.

Conclusion

This study demonstrates that the 3D-pPES may be a promising strategy for bone defect treatment.

Gaseous sulfur trioxide induced controllable sulfonation promoting biomineralization and osseointegration of polyetheretherketone implants

Fabricating a desired porous structure on the surface of biomedical polyetheretherketone (PEEK) implants for enhancing biological functions is crucial and difficult due to its inherent chemical inertness. In this study, a porous surface of PEEK implants was fabricated by controllable sulfonation using gaseous sulfur trioxide (SO₃) for different time (5, 15, 30, 60 and 90 min). Micro-topological structure was generated on the surface of sulfonated PEEK implants preserving original mechanical properties. The protein absorption capacity and apatite forming ability was thus improved by the morphological and elemental change with higher degree of sulfonation. In combination of the appropriate micromorphology and bioactive sulfonate components, the cell adhesion, migration, proliferation and extracellular matrix secretion were obviously enhanced by the SPEEK-15 samples which were sulfonated for 15 min. Finding from this study revealed that controllable sulfonation by gaseous SO₃ would be an extraordinarily strategy for improving osseointegration of PEEK implants by adjusting the microstructure and chemical composition while maintaining excellent mechanical properties.

Early osteointegration evaluation of porous Ti6Al4V scaffolds designed based on triply periodic minimal surface models

BACKGROUND

The graded porous structures were designed using triply periodic minimal surfaces models to mimic the biomechanical properties of bone. The mechanical properties and bone formation ability were evaluated to explore the feasibility of the design method in bone tissue engineering.

METHODS

The scaffolds were designed using a P-surface with different pore sizes. All materials were fabricated using 3D printing technology and the mechanical properties were tested by an electronic universal testing device. The biomechanical properties were then analyzed by finite element method, while the ontogenesis of the material in vivo was examined by implanting the scaffolds for five weeks in pigs.

RESULTS

According to the obtained results, the pore size ranged between 100 μm to about 700 μm and porosity were around 49.54%. The graded porous architectures can decrease the stiffness of implants and reduce the stress shielding effect. In addition, these porous structures can stimulate bone ingrowth and achieve a stable interface between implants and surrounding bone tissues after 5 weeks' implantation. The micro-CT results also demonstrated the obviously bone formation around all the porous structures.

CONCLUSION

To sum up, the triply periodic minimal surfaces based graded porous structure is effective in decreasing the stress shielding effect, promoting early osteogenesis and osteointegration. This is the first research to explore the effect of this kind of porous structures on bone formation in vivo where the obtained results supported the previous theoretical research on the application potential in bone tissue engineering.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Porous architecture designed using triply periodic minimal surface models can achieve gradually changed pore size and appropriate porosity for bone regeneration. This kind of structure can mimic the Young's modulus of natural bone tissue, improve the stress transmission capability and dismiss the stress shielding effect. It also can stimulate the early bone integration in vivo and enhance the binding force between bone and implants, which may bring a new design method for orthopaedic implants and their surface structure.