Comparison of two methods of fatigue testing bone cement

Two different methods have been used to fatigue test four bone cements. Each method has been used previously, but the results have not been compared. The ISO 527-based method tests a minimum of 10 samples over a single stress range in tension only and uses Weibull analysis to calculate the median number of cycles to failure and the Weibull modulus. The ASTM F2118 test regime uses fewer specimens at various stress levels tested in fully reversed tension–compression, and generates a stress vs. number of cycles to failure (S–N) or Wöhler curve. Data from specimens with pores greater than 1 mm across is rejected. The ISO 527-based test while quicker to perform, provides only tensile fatigue data, but the material tested includes pores, thus the cement is closer to cement in clinical application. The ASTM regime uses tension and compression loading and multiple stress levels, thus is closer to physiological loading, but excludes specimens with defects obviously greater than 1 mm, so is less representative of cement in vivo. The fatigue lives between the cements were up to a factor 15 different for the single stress level tension only tests, while they were only a factor of 2 different in the fully reversed tension–compression testing. The ISO 527-based results are more sensitive to surface flaws, thus the differences found using ASTM F2118 are more indicative of differences in the fatigue lives. However, ISO 527-based tests are quicker, so are useful for initial screening

The effect of annealing on the elastoplastic and viscoelastic responses of isotactic polypropylene

Observations are reported on isotactic polypropylene (i) in a series of tensile tests with a constant strain rate on specimens annealed for 24 h at various temperatures in the range from 110 to 150 C and (ii) in two series of creep tests in the sub-yield region of deformation on samples not subjected to thermal treatment and on specimens annealed at 140 C. A model is developed for the elastoplastic and nonlinear viscoelastic responses of semicrystalline polymers. A polymer is treated an equivalent transient network of macromolecules bridged by junctions (physical cross-links, entanglements and lamellar blocks). The network is assumed to be highly heterogeneous, and it is thought of as an ensemble of meso-regions with different activation energies for separation of strands from temporary nodes. The elastoplastic behavior is modelled as sliding of meso-domains with respect to each other driven by mechanical factors. The viscoelastic response is attributed to detachment of active strands from temporary junctions and attachment of dangling chains to the network. Constitutive equations for isothermal uniaxial deformation are derived by using the laws of thermodynamics. Adjustable parameters in the stress-strain relations are found by fitting the experimental data.Comment: 29 pages, 14 figure

Biomimetic potential of some methacrylate-based copolymers: A comparative study

Preparation of new biocompatible materials for bone recovery has consistently gained interest in the last few decades. Special attention was given to polymers that contain negatively charged groups, such as phosphate, carboxyl, and sulfonic groups toward calcification. This present paper work demonstrates that other functional groups present also potential application in bone pathology. New copolymers of 2-hydroxyethyl methacrylate with diallyldimethylammonium chloride (DADMAC), glycidyl methacrylate (GlyMA), methacrylic acid (MAA), 2-methacryloyloxymethyl acetoacetate (MOEAA), 2-methacryloyloxyethyltriethylammonium chloride (MOETAC), and tetrahydrofurfuryl methacrylate (THFMA) were obtained. The copolymers were characterized by FTIR, swelling potential, and they were submitted to in vitro tests for calcification and cytotoxicity evaluation. GlyMA and MOETAC-containing copolymers show promising results for further in vivo mineralization tests, as a potential alternative to the classical bone grafts, in bone tissue engineering

Fabrication and Clinical Evaluation of a Novel 3D printed Hydroxyapatite/Polycaprolactone Composite (Novel 3DP HA/ PCL) for Maxillary Sinus Augmentation: A Preliminary Study

Objective: To fabricate a 3DP hydroxyapatite/polycaprolactone composite graft material and assess its clinical efficacy in maxillary sinus augmentation through a preliminary assessment of bone density changes over a one-year period, compared to deproteinized bovine bone mineral graft. Methods: A 3DP hydroxyapatite/polycaprolactone (HA/PCL) composite was fabricated using 3D printing of calcium sulfate-based material, followed by phase transformation and PCL infiltration. The composite was characterized through SEM, XRD, micro-CT, and compression testing. In a clinical study, 3DP HA/PCL composite material was compared with deproteinized bovine bone graft in sinus augmentation procedures. Cone-beam computed tomography (CBCT) was used to measure bone density at baseline, 6 months, and 1-year post-operation. Results: SEM and micro-CT analyses revealed that the 3DP HA/PCL composite exhibited a highly porous, three-dimensional architecture with HA crystals combined with PCL. The microstructure was characterized by a mixture of spherical and irregular-shaped particles with 60.67% porosity. Compression testing demonstrated that the 3DP HA/PCL composite granules had a compressive load resistance of 7.55 ± 1.71 N. The calculated compressive strength of the granule was approximately 2.4 MPa. CBCT analysis of bone density changes revealed distinct patterns between the two groups. Significant differences in graft bone density were observed in the control group at all time points (P < 0.05) , while the 3DP HA/PCL group demonstrated no significant changes (P < 0.3831). However, between 6 months to 1 year, the 3DP HA/PCL group exhibited an increased bone density gain trend similar to the rate observed in the xenograft group. At 1 year, the increase in bone density from T1 to T3 was significant in both the control and test groups., These findings indicate that while 3DP HA/PCL grafts initially increase bone density more slowly than xenografts, they demonstrate a more pronounced gain in the later phase compared to the early phase. Conclusion: Based on the promising preliminary results from the sinus augmentation study, 3DP HA/PCL composite demonstrates potential as an alternative bone graft material to deproteinized bovine bone mineral

Three-dimensional printing of porous load-bearing bioceramic scaffolds

This article reports on the use of the binder jetting three-dimensional printing process combined with sintering to process bioceramic materials to form micro- and macroporous three-dimensional structures. Three different glass-ceramic formulations, apatite–wollastonite and two silicate-based glasses, have been processed using this route to create porous structures which have Young’s modulus equivalent to cortical bone and average bending strengths in the range 24–36 MPa. It is demonstrated that a range of macroporous geometries can be created with accuracies of ±0.25 mm over length scales up to 40 mm. Hot-stage microscopy is a valuable tool in the definition of processing parameters for the sintering step of the process. Overall, it is concluded that binder jetting followed by sintering offers a versatile process for the manufacture of load-bearing bioceramic components for bone replacement applications

Development of Antibiotics Impregnated Nanosized Silver Phosphate-Doped Hydroxyapatite Bone Graft

Nanosized Ag3PO4 loaded hydroxyapatite which was prepared by a novel low temperature phosphorization of 3D printed calcium sulfate dihydrate at the nominal silver concentration of 0.001 M and 0.005 M was impregnated by two antibiotics including gentamicin and vancomycin. Phase composition, microstructure, antibiotics loading, silver content, antimicrobial performance, and cytotoxic potential of the prepared samples were characterized. It was found that the fabricated sample consisted of hydroxyapatite as a main phase and spherical-shaped silver phosphate nanoparticles distributing within the cluster of hydroxyapatite crystals. Antibacterial activity of the samples against two bacterial strains (gram negative P. aeruginosa and gram positive S. aureus) was carried out. It was found that the combination of antibiotics and nanosized Ag3PO4 in hydroxyapatite could enhance the antibacterial performance of the samples by increasing the duration in which the materials exhibited antibacterial property and the size of the inhibition zone depending on the type of antibiotics and bacterial strains compared to those contained antibiotics or nanosilver phosphate alone. Cytotoxic potential against osteoblasts of antibiotics impregnated nanosilver phosphate hydroxyapatite was found to depend on the combination of antibiotics content, type of antibiotics, and nanosilver phosphate content

Manufacturing of Porous Polyethylene Ocular Implant by Three Dimensional Printing

In enucleation and evisceration, porous polyethylene ocular implants have been used to replace eyes of patients to restore function or aesthetic appearance effectively since they permit fibrovascularization and direct suturing of extraocular muscles. Traditionally, they are produced by sintering the particles below their melting temperature in a mould to create a porous structure. In this study, the feasibility of using new mould-less three dimensional printing process to manufacture high porosity and large pore size ocular implants was investigated and compared its properties with the traditionally manufactured sampl

An experimental investigation into the dimensional error of powder-binder three-dimensional printing

This paper is an experimental investigation into the dimensional error of the rapid prototyping additive process of powder-binder three-dimensional printing. Ten replicates of a purpose-designed part were produced using a three-dimensional printer, and measurements of the internal and external features of all surfaces were made using a general purpose coordinate measuring machine. The results reveal that the bases of all replicates (nominally flat) have a concave curvature, producing a flatness error of the primary datum. This is in contrast to findings regarding other three-dimensional printing processes, widely reported in the literature, where a convex curvature was observed. All external surfaces investigated in this study showed positive deviation from nominal values, especially in the z-axis. The z-axis error consisted of a consistent positive cumulative error and a different constant error in different replicates. By compensating for datum surface error, the average total height error of the test parts can be reduced by 25.52 %. All the dimensional errors are hypothesised to be explained by expansion and the subsequent distortion caused by layer interaction during and after the printing process

Tissue Integrated 3D Printed Porous Polyethylene Implant

Synthetic polymers are widely used in biomedical applications due to their advantages compared to other materials including low cost and ease of processability, good corrosion resistance and high properties to weight ratio. Among several polymeric biomaterials, polyethylene is a biocompatible polymer which has a long history of being utilized in many biomedical applications ranging from simple components to advanced implants. Although dense polyethylene is known to be a bioinert material which does not interact with host tissue, polyethylene in its appropriate porous form has been shown to be able to integrate well with surrounding host tissues and could widen its uses as bioactive implants. Porous polyethylene structure which was fabricated by three dimensional printing (3DP) is demonstrated. Its manufacturing technique, properties and clinical applications as tissue integrated implants which permitted soft or hard tissue ingrowth in tissue regeneration and replacement is discussed.</jats:p