Effects of porogen morphology on the architecture, permeability, and mechanical properties of hydroxyapatite whisker reinforced polyetheretherketone scaffolds

Construction of multileveled and oriented micro/nano channels in Mg doped hydroxyapitite bioceramics and their effect on mimicking mechanical property of cortical bone and biological performance of cancellous bone

Drawing on the structure and components of natural bone, this study developed Mg-doped hydroxyapatite (Mg-HA) bioceramics, characterized by multileveled and oriented micro/nano channels. These channels play a critical role in ensuring both mechanical and biological properties, making bioceramics suitable for various bone defects, particularly those bearing loads. Bioceramics feature uniformly distributed nanogrooves along the microchannels. The compressive strength or fracture toughness of the Mg-HA bioceramics with micro/nano channels formed by single carbon nanotube/carbon fiber (CNT/CF) (Mg-HA(05-CNT/CF)) are comparable to those of cortical bone, attributed to a combination of strengthened compact walls and microchannels, along with a toughening mechanism involving crack pinning and deflection at nanogroove intersections. The introduction of uniform nanogrooves also enhanced the porosity by 35.4 %, while maintaining high permeability owing to the capillary action in the oriented channels. This leads to superior degradation properties, protein adsorption, and in vivo osteogenesis compared with bioceramics with only microchannels. Mg-HA(05-CNT/CF) exhibited not only high strength and toughness comparable to cortical bone, but also permeability similar to cancellous bone, enhanced cell activity, and excellent osteogenic properties. This study presents a novel approach to address the global challenge of applying HA-based bioceramics to load-bearing bone defects, potentially revolutionizing their application in tissue engineering.

Polyether-Ether-Ketone (PEEK) and Its 3D-Printed Quantitate Assessment in Cranial Reconstruction

Three-dimensional (3D) printing, medical imaging, and implant design have all advanced significantly in recent years, and these developments may change how modern craniomaxillofacial surgeons use patient data to create tailored treatments. Polyether-ether-ketone (PEEK) is often seen as an attractive option over metal biomaterials in medical uses, but a solid PEEK implant often leads to poor osseointegration and clinical failure. Therefore, the objective of this study is to demonstrate the quantitative assessment of a custom porous PEEK implant for cranial reconstruction and to evaluate its fitting accuracy. The research proposes an efficient process for designing, fabricating, simulating, and inspecting a customized porous PEEK implant. In this study, a CT scan is utilized in conjunction with a mirrored reconstruction technique to produce a skull implant. In order to foster cell proliferation, the implant is modified into a porous structure. The implant's strength and stability are examined using finite element analysis. Fused filament fabrication (FFF) is utilized to fabricate the porous PEEK implants, and 3D scanning is used to test its fitting accuracy. The results of the biomechanical analysis indicate that the highest stress observed was approximately 61.92 MPa, which is comparatively low when compared with the yield strength and tensile strength of the material. The implant fitting analysis demonstrates that the implant's variance from the normal skull is less than 0.4436 mm, which is rather low given the delicate anatomy of the area. The results of the study demonstrate the implant's endurance while also increasing the patient's cosmetic value.

Impact of surface roughness and bulk porosity on spinal interbody implants

Spinal fusion surgeries are performed to treat a multitude of cervical and lumbar diseases that lead to pain and disability. Spinal interbody fusion involves inserting a cage between the spinal vertebrae, and is often utilized for indirect neurologic decompression, correction of spinal alignment, anterior column stability, and increased fusion rate. The long-term success of interbody fusion relies on complete osseointegration between the implant surface and vertebral end plates. Titanium (Ti)-based alloys and polyetheretherketone (PEEK) interbody cages represent the most commonly utilized materials and provide sufficient mechanics and biocompatibility to assist in fusion. However, modification to the surface and bulk characteristics of these materials has been shown to maximize osseointegration and long-term stability. Specifically, the introduction of intrinsic porosity and surface roughness has been shown to affect spinal interbody mechanics, vascularization, osteoblast attachment, and ingrowth potential. This narrative review synthesizes the mechanical, in vitro, in vivo, and clinical effects on fusion efficacy associated with introduction of porosity in Ti (neat and alloy) and PEEK intervertebral implants.

Friction and wear characteristics of synthetic diamond and graphene-filled polyether ether ketone composites

Modifying tribo films using filler particles is a significant area of research in developing polymer-based tribo components to minimize material loss during the sliding process. This study focused on altering the wear characteristics of a polyetheretherketone (PEEK)/graphene high-performance polymer composite to strengthen the tribo film by adding synthetic diamond particles. The hot-pressed PEEK composite reinforced by graphene and diamond particles increased the hardness and thermal stability of the composite. Compared with pure PEEK, composites containing 1% graphene and 1% diamond particles showed an increment of 25% and 23% in hardness and thermal stability, respectively. Fourier-transform infrared spectroscopy and X-ray diffraction analysis verified the compatibility and intactness of the fillers in the PEEK matrix. The tribo properties of PEEK composites were characterized by a pin-on-disc tribometer on a counter steel surface. A PEEK composite containing 0.75 wt% graphene and 0.5 wt% diamond particles exhibited the lowest friction of 0.17 at a pressure of 1.5 MPa. The specific wear rate was low (1.78 × 10−6 mm3/Nm) for the composite containing 1 wt% graphene and 1 wt% diamond particles at a pressure of 1.5 MPa. Varying synthetic diamond and graphene filler concentrations in the PEEK matrix change the wear process by modifying the tribo film characteristics, revealing the lowest friction and wear rate. X-ray photoelectron and Raman spectroscopy show that the polymer film was transferred to the steel countersurface, and the tribo-chemical products of the tribo film contribute to a stable tribo film. The ferric oxide film and the tribo film improve the composite’s self-lubricating properties and load-bearing ability. Hence, the composite containing 0.75% of graphene and 0.5% of a synthetic diamond can be employed in the sliding bearing application of continuous conveyors used in mass production systems.

Modification of polyetheretherketone (PEEK) physical features to improve osteointegration

Polyetheretherketone (PEEK) has been widely applied in orthopedics because of its excellent mechanical properties, radiolucency, and biocompatibility. However, the bioinertness and poor osteointegration of PEEK have greatly limited its further application. Growing evidence proves that physical factors of implants, including their architecture, surface morphology, stiffness, and mechanical stimulation, matter as much as the composition of their surface chemistry. This review focuses on the multiple strategies for the physical modification of PEEK implants through adjusting their architecture, surface morphology, and stiffness. Many research findings show that transforming the architecture and incorporating reinforcing fillers into PEEK can affect both its mechanical strength and cellular responses. Modified PEEK surfaces at the macro scale and micro/nano scale have positive effects on cell-substrate interactions. More investigations are necessary to reach consensus on the optimal design of PEEK implants and to explore the efficiency of various functional implant surfaces. Soft-tissue integration has been ignored, though evidence shows that physical modifications also improve the adhesion of soft tissue. In the future, ideal PEEK implants should have a desirable topological structure with better surface hydrophilicity and optimum surface chemistry.

Fabrication of In Situ Grown Hydroxyapatite Nanoparticles Modified Porous Polyetheretherketone Matrix Composites to Promote Osteointegration and Enhance Bone Repair

The repairment of critical-sized bone defects is a serious problem that stimulates the development of new biomaterials. In this study, nanohydroxyapatite (nHA)-doped porous polyetheretherketone (pPEEK) were successfully fabricated by the thermally induced phase separation method and hydrothermal treatment. Structural analysis was performed by X-ray diffraction. The water contact angles and scanning electron microscopy were measured to assess physical properties of surfaces. The mechanical strength of the composites is also determined. Microcomputed tomography is used to characterize the nHA content of the composites. The in vitro bioactivity of the composites with or without nHA was investigated by using murine pre-osteoblasts MC3T3-E1, and the results of cytotoxicity and cell proliferation assays revealed that the cytocompatibility of all specimens was good. Adherence assays were employed to examine the adhesion and morphology of cells on different materials. However, nHA-doped composites induced cell attachment and cell spreading more significantly. Osteogenic differentiation was investigated using alkaline phosphatase activity and alizarin red staining, and these in vitro results demonstrated that composites containing nHA particles enhanced osteoblast differentiation. Its effectiveness for promoting osteogenesis was also confirmed in an in vivo animal experiment using a tibial defective rat model. After 8 weeks of implantation, compared to the pure PEEK and pPEEK without nHA groups, the nHA-pPEEK group showed better osteogenic activity. The results indicate that the nHA-pPEEK composites are possibly a well-designed bone substitute for critical-sized bone defects by promoting bone regeneration and osteointegration successfully.

Reconstructing Nanohydroxyapatite Prosthesis Based on CT-Scanning Data and Its Application in Spinal Injury

This study investigated the nanohydroxyapatite (nHA) prosthesis application effect based on CT-scanning data in spinal injury. This study chose 26 spinal injury patients treated in our hospital from September 2017 to September 2018, who were randomly divided into two groups. nHA prosthesis based on CT-scanning data was implanted in the nHA group, whereas titanium mesh was implanted in the titanium mesh group. Consequently, osteoblasts were cultured to test the biological activity of nHA and titanium alloy. In cell tests, we found osteoblasts could better adhere to nHA, and proliferation and activity were higher when planted on nHA material. After surgical treatment, all patients' spinal symptoms (VAS score, JOA score, and Cobb angle) had improved and did not cause obvious inflammatory foreign body reactions. During a two-year follow-up, the fusion time and support settlement in the nHA group was lower, and the vertebral fusion rate and ASIA score were higher than those in the titanium mesh group. Thus, CT-scanning data could further improve the vertebral fusion rate in the nHA group. Consequentially, nHA prosthesis based on CT-scanning data is a better choice for spinal injury therapy.

3D printed PEEK/HA composites for bone tissue engineering applications: Effect of material formulation on mechanical performance and bioactive potential

Polyetheretherketone (PEEK) is a biocompatible polymer widely used for biomedical applications. Because it is biologically inert, bioactive phases, such as nano-hydroxyapatite (HA), have been added to PEEK in order to improve its bioactivity. 3D printing (3DP) technologies are being increasingly used today to manufacture patient specific devices and implants. However, processing of PEEK is challenging due to its high melting point which is above 340 °C. In this study, PEEK-based filaments containing 10 wt% of pure nano-HA, strontium (Sr)- doped nano-HA and Zinc (Zn)-doped nano-HA were produced via hot-melt extrusion and subsequently 3D printed via fused deposition modelling (FDM), following an initial optimization process. The raw materials, extruded filaments and 3D printed samples were characterized in terms of physicochemical, thermal and morphological analysis. Moreover, the mechanical performance of 3D printed specimens was assessed via tensile tensing. Although an increase in the melting point and a reduction in crystallization temperature was observed with the addition of HA and doped HA to pure PEEK, there was no noticeable increase in the degree of crystallinity. Regarding the mechanical behavior, no significant differences were detected following the addition of the inorganic phases to the polymeric matrix, although a small reduction in the ultimate tensile strength (~14%) and Young's modulus (~5%) in PEEK/HA was observed in comparison to pure PEEK. Moreover, in vitro bioactivity of 3D printed samples was evaluated via a simulated body fluid immersion test for up to 28 days; the formation of apatite was observed on the surfaces of sample surfaces containing HA, SrHA and ZnHA. These results indicate the potential to produce bioactive, 3DP PEEK composites for challenging applications such as in craniofacial bone repair.

Bioinspired Modifications of PEEK Implants for Bone Tissue Engineering

In recent years, polyetheretherketone (PEEK) has been increasingly employed as an implant material in clinical applications. Although PEEK is biocompatible, chemically stable, and radiolucent and has an elastic modulus similar to that of natural bone, it suffers from poor integration with surrounding bone tissue after implantation. To improve the bioactivity of PEEK, numerous strategies for functionalizing the PEEK surface and changing the PEEK structure have been proposed. Inspired by the components, structure, and function of bone tissue, this review discusses strategies to enhance the biocompatibility of PEEK implants and provides direction for fabricating multifunctional implants in the future.

Advances in Biodegradable 3D Printed Scaffolds with Carbon-Based Nanomaterials for Bone Regeneration

Bone possesses an inherent capacity to fix itself. However, when a defect larger than a critical size appears, external solutions must be applied. Traditionally, an autograft has been the most used solution in these situations. However, it presents some issues such as donor-site morbidity. In this context, porous biodegradable scaffolds have emerged as an interesting solution. They act as external support for cell growth and degrade when the defect is repaired. For an adequate performance, these scaffolds must meet specific requirements: biocompatibility, interconnected porosity, mechanical properties and biodegradability. To obtain the required porosity, many methods have conventionally been used (e.g., electrospinning, freeze-drying and salt-leaching). However, from the development of additive manufacturing methods a promising solution for this application has been proposed since such methods allow the complete customisation and control of scaffold geometry and porosity. Furthermore, carbon-based nanomaterials present the potential to impart osteoconductivity and antimicrobial properties and reinforce the matrix from a mechanical perspective. These properties make them ideal for use as nanomaterials to improve the properties and performance of scaffolds for bone tissue engineering. This work explores the potential research opportunities and challenges of 3D printed biodegradable composite-based scaffolds containing carbon-based nanomaterials for bone tissue engineering applications.

Hierarchical porosity in additively manufactured bioengineering scaffolds: Fabrication & characterisation

Biomedical scaffolds with a high degree of porosity are known to facilitate the growth of healthy functioning tissues. In this study, scaffolds with hierarchical porosity are manufactured and their mechanical and thermal properties are characterised. Multi-scale porosity is achieved in scaffolds fabricated by Fused Deposition Modelling (FDM) in a novel way. Random intrinsic porosity at micron length scale obtained from particulate leaching is combined with the structured extrinsic porosity at millimeter length scales afforded by controlling the spacing between the struts. Polylactic acid (PLA) is blended with Polyvinyl alcohol (PVA) and an inorganic sacrificial phase, sodium chloride (NaCl), to produce pores at length scales of up to two orders of magnitude smaller than the inter-filament voids within 3D printed lattices. The specific elastic modulus and specific strength are maximised by optimising the polymer blends. The porosity level and pore size distribution of the foamy filaments within lattices are quantified statistically. Compression tests are performed on the porous samples and the observed mechanical response is attributed to the microstructure and density. Simple cellular solid models that possess power law are used to explain the measured trends and the dependence is associated with various mechanisms of elastic deformation of the cell walls. The relationship between pore architecture, pore connectivity, the blend material composition, and mechanical response of produced foams is brought out. Foams obtained using the PLA:PVA:NaCl 42%-18%-40% material blends show relatively high specific elastic modulus, specific strength and strain at failure. A quadratic power law relating the Young's modulus with the relative density is experimentally obtained, which is consistent with theoretical models for open-cell foams. 3D printing with blends, followed by leaching, produces structures with cumulative intrinsic and extrinsic porosity as high as 80%, in addition to good mechanical integrity.