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Abstract Intracranial aneurysms (ICAs) are focal dilations in the brain's arteries. When left untreated, ICAs can grow to the point of rupture, accounting for 50–80% of subarachnoid hemorrhage cases. Current treatments include surgical clipping and endovascular coil embolization to block circulation into the aneurysmal space for preventing aneurysm rupture. As for endovascular embolization, patients could experience aneurysm recurrence due to an incomplete coil filling or compaction over time. The use of shape memory polymers (SMPs) in place of conventional platinum coils could provide more control and predictability for mitigating these complications. This study was focused on characterization of an aliphatic urethane-based SMP to evaluate its potential as a novel biomaterial for endovascular embolization. Twelve compositions of the SMP were synthesized and their thermomechanical properties together with the shape recovery behavior were comprehensively investigated. Our results showed that the SMPs experienced a significant decrease in storage and loss moduli as heated above their glass transition temperatures (32.3–83.2 °C), and that all SMPs were thermally stable up to 265 °C. Moreover, the SMPs exhibited both composition-dependent stress relaxation and a decrease in elastic modulus during cyclic loading. The shape recovery time was less than 11 s for all SMP compositions, which is sufficiently short for shape changing during embolization procedures. Several candidate compositions were identified, which possess a glass transition temperature above body temperature (37 °C) and below the threshold of causing tissue damage (45 °C). They also exhibit high material strength and low stress relaxation behavior, suggesting their potential applicability to endovascular embolization of ICAs. Graphical abstract fx1 Highlights • A detailed experimental procedure has been developed for the synthesis of aliphatic urethane-based shape memory polymers. • Comprehensive thermomechanical characterizations on a variety of SMP compositions have been performed. • Investigations of the polymer's working temperature, thermal stability and their mechanical behavior have been made. • Recovery tests has demonstrated superb shape recovery of the SMPs desirable for the endovascular embolization procedure. • SMP compositions that meet our criteria have been identified with their great potential for individualized ICA treatment. [ABSTRACT FROM AUTHOR]

Abstract Finite element models of biomedical applications increasingly use anisotropic hyperelastic material formulations. Appropriate material parameters are essential for a reliable outcome of these simulations, which is why planar biaxial testing of soft biological tissues is gaining importance. However, much is still to be learned regarding the ideal methodology for performing this type of test and the subsequent parameter fitting procedure. This paper focuses on the effect of an unknown sample orientation or a mistake in the sample orientation in a planar biaxial test using rakes. To this end, finite element simulations were conducted with various degrees of misalignment. Variations to the test method and subsequent fitting procedures are compared and evaluated. For a perfectly aligned sample and for a slightly misaligned sample, the parameters of the Gasser-Ogden-Holzapfel model can be found to a reasonable accuracy using a planar biaxial test with rakes and a parameter fitting procedure that takes into account the boundary conditions. However, after a certain threshold of misalignment, reliable parameters can no longer be found. The level of this threshold seems to be material dependent. For a sample with unknown sample orientation, material parameters could theoretically be obtained by increasing the degrees of freedom along which test data is obtained, e.g. by adding the data of a rail shear test. However, in the situation and the material model studied here, the inhomogeneous boundary conditions of the test set-ups render it impossible to obtain the correct parameters, even when using the parameter fitting method that takes into account boundary conditions. To conclude, it is always important to carefully track the sample orientation during harvesting and preparation and to minimize the misalignment during mounting. For transversely isotropic samples with an unknown orientation, we advise against parameter fitting based on a planar biaxial test, even when combined with a rail shear test. [ABSTRACT FROM AUTHOR]

Abstract In this research, a new metal matrix nanocomposite with enhanced capability for biomedical applications was fabricated by incorporation of nano-sized hydroxyapatite (HA) particles within the titanium substrate using multi-pass friction-stir processing (FSP). These n-HA particles were dispersed effectively within the titanium matrix. Titanium metal-matrix was processed without introducing the HA nanoparticles, as well, for the aim of comparison. The results showed the formation of different regions with various microstructural features and mechanical property across the processed materials. A thin layer with ultra-fine grain structure and indentation hardness value of up to ~400 HV was formed on the surface after FSP modification of coarse-grained titanium substrate. This was due to severe shear deformation induced by the rotating shoulder as well as the surface absorption of N and O elements from the atmosphere inside the layer. Incorporation of nanoparticles and subsequent grain structural refinement owing to operative dynamic recrystallization mechanisms leads to a maximum hardness improvement of up to ~250 HV in the lower regions (as compared to the average hardness value of base metal ~150 HV). The FSP modified pure titanium exhibited a good combination of strength and ductility by refining the grain structure with a well-developed dimple-like structure on the fracture surface. For the nanocomposite specimen, the trend of the tensile property was found deteriorative showing the impaired features on the fracture surface. This is attributed to the complex structure of HA compound and low quality of interfacial bonding between the nanoparticles and titanium matrix. [ABSTRACT FROM AUTHOR]

Abstract Considering that micromotions generated at the bone-implant interface under physiological loading introduce mechanical strain on the tissue and surface of the implant and that strain can be introduced during processing of the biomedical device, we elucidate here the interplay between mechanically-induced nanoscale twinning in austenitic stainless steel on osteoblast functions. Mechanically-induced nanoscale twinning significantly impacted cell attachment, cell-substrate interactions, proliferation, and subsequent synthesis of prominent proteins (fibronectin, actin, and vinculin). Twinning was beneficial in favorably modulating cellular activity and contributed to small differences in hydrophilicity and nanoscale roughness in relation to the untwinned surface. [ABSTRACT FROM AUTHOR]

In this study, chitosan-poly(methacrylic acid-co- N -isopropylacrylamide) [chitosan-p(MAA-co-NIPAM)] hydrogels were synthesized by emulsion polymerization. In order to be used as a carrier for drug delivery systems, the hydrogels had to be biocompatible, biodegradable and multi-responsive. The polymerization was performed by copolymerize MAA and NIPAM with chitosan polymer to produce a chitosan-based hydrogel. Due to instability during synthesis and complexity of components to produce the hydrogel, further study at different times of reaction is important to observe the synthesis process, the effect of end product on swelling behaviour and the most important is to find the best way to control the hydrogel synthesis in order to have an optimal swelling behaviour for drug release application. Studied by using Fourier transform infra-red (FTIR) spectroscopy found that, the synthesized was successfully produced stable chitosan-based hydrogel with PNIPAM continuously covered the outer surface of hydrogel which influenced much on the stability during synthesis. The chitosan and PMAA increased the zeta potential of the hydrogel and the chitosan capable to control shrinkage above human body temperature. The chitosan-p(MAA-co-NIPAM) hydrogels also responses to pH and temperature thus improved the ability to performance as a drug carrier. [ABSTRACT FROM AUTHOR]

Porous structures, manufactured of a biocompatible metal, mimicking human bone structure are the future of orthopedic implantology. Fully porous materials, however, suffer from certain drawbacks. To overcome these, gradient in structure can be prepared. With gradient in porosity mechanical properties can be optimized to an appropriate value, implant can be attributed a similar gradient macrostructure as bone, tissue adhesion may be promoted and also various modification with organic or inorganic substances are possible. In this study, additive technology selective laser melting (SLM) was used to produce three types of gradient porosity model specimens of titanium alloy Ti-6Al-4V. As this technology has the potential to prepare complex structures in the near-net form, to control porosity, pore size and shape, it represents a promising option. The first part of the research work was focused on the characterization of the material itself in the as-produced state, only with heat treatment applied. The second part dealt with the influence of porosity on mechanical properties. The study has shown SLM brings significant changes in the surface chemistry. Despite this finding, titanium alloy retained its cytocompatibility, as it was outlined by in vitro tests with U-2 OS cells. With introduced porosity yield strength, ultimate strength and stiffness showed linear decrease, both in tension and compression. With respect to the future use in the form of orthopedic implant, especially reduction in Young's modulus down to the human bone value (30.5±2 GPa) is very appreciated as the stress-shielding effect followed by possible implant loosening is limited. [ABSTRACT FROM AUTHOR]

Abstract: Biomanufacturing integrates life science and engineering fundamentals to produce biocompatible products enhancing the quality of life. The state-of-the-art of this rapidly evolving manufacturing sector is presented and discussed, in particular the additive electrical, chemical and physical processes currently being applied to produce synthetic and biological parts. This fabrication strategy is strongly material-dependent, so the main classes of biomaterials are detailed. It is explained the potential to process composite materials combining synthetic and biological materials, such as cells, proteins and growth factors, as well the interdependences between materials and processes. The techniques commonly used to increase the bioactivity of clinical implants and improve the interface characteristics between biological tissues and implants are also presented. [Copyright &y& Elsevier]