Synthesis and characterisation of styrene butadiene styrene-g-acrylic acid for potential use in biomedical applications

The work undertaken investigates the mechanical and thermal properties of styrene butadiene styrene (SBS) grafted with acrylic acid (AA) for use as a potential biomedical material. SBS-g-AA was synthesised by UV polymerisation and analytical techniques such as differential scanning calorimetry (DSC), attenuated total reflectance infrared Fourier transform spectrometry (ATR-FTIR), dynamic mechanical thermal analysis (DMTA) and tensile tests were used to characterise the grafted copolymers. From the DSC analysis, the glass transitions of polystyrene (PS) and polybutadiene (PB) domains present in the SBS copolymer were detected at 67 °C and ? 90 °C respectively. ATR-FTIR spectral analysis was used in conjunction with the DSC thermographs to analyse the grafted copolymers. The peak (1711 cm^? 1 ) associated with CO stretching in poly acrylic acid was located at 1725 cm^? 1 on the grafted SBS-g-AA copolymer which confirmed grafting took place. Mechanical testing was carried out to analyse the physical attributes of the grafted copolymers. It was found that a decrease in Young's modulus and stress at break occurred for SBS-g-AA copolymers which were soxhlet extracted using chloroform (washed). It was evident from the DMTA results that the glass transition values for each of the washed grafted samples increased, thus establishing that grafting had occurred onto the various butadiene segments along the SBS backbone. The results showed that the hydrophilic monomer was successfully grafted onto a hydrophobic polymer and the mechanical and thermal properties were in the useful range for biomedical applications.     

The synthesis and characterisation of grafted random styrene butadiene for biomedical applications

The work undertaken investigates the spectral, thermal and surface characteristics of a random styrene butadiene rubber (SBR) with monomeric graft(s) of acrylic acid (AA), N-vinyl-2-pyrrolidinone (NVP) or N-isopropylacrylamide (NIPAAm) synthesised using UV polymerisation. The grafted materials were characterised by differential scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), attenuated total reflectance infrared Fourier transform spectrometry (ATR-FTIR) and atomic force microscopy (AFM). Thermograph analysis has shown an endothermic transition occurring at ~75 °C for all random SB-g-NVP copolymers, whereas the T _g value for random SB copolymer was found at 60 °C, thus suggesting that a chemical reaction between styrene and NVP had occurred. Similar thermal profiles to that of random SB-g-NVP copolymers were evident when random SB was UV polymerised with AA. When NIPAAm was grafted onto random SB, a notable exothermic transition was evident in all samples tested using DSC. It was established using MDSC that this exothermic transition was caused by the breakdown of crosslinks as a result of UV polymerisation.

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Synthesis and characterisation of styrene butadiene styrene-g-<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide via UV polymerisation for potential use in biomedical applications

The work undertaken investigates the mechanical and thermal properties of a styrene butadiene styrene (SBS) grafted with N-isopropylacrylamide (NIPAAm) for potential use in the field of biomaterials. SBS-g-NIPAAm was synthesised using UV polymerisation and analytical techniques such as differential scanning calorimetry (DSC), attenuated total reflectance Fourier transform spectrometry (ATR-FTIR), dynamic mechanical thermal analysis (DMTA) and tensile tests were used to characterise the grafted copolymers. The ATR-FTIR spectrum for NIPAAm illustrates bands corresponding to C=O stretching and NH bending for secondary amides at 1655 and 1544 cm⁻¹, respectively. These bands are represented as shoulders in SBS-g-NIPAAm copolymers. In relation to the thermal analysis, the butadiene domain present in the SBS and the grafted SBS copolymers were analysed using DSC. It was evident that all of the grafted samples have a broad thermal transition when compared to the PB domain present in SBS, suggesting that grafting had occurred within each of the SBS-g-NIPAAm copolymers. This was confirmed by the use of DMTA, where the results showed an increase in T _g values from −92 to −74 °C for SBS-g-NIPAAm copolymers.     

Synthesis and characterisation of nanobioactive glass for biomedical applications

In recent years, bioactive materials have become important in applications such as implantation, bone regeneration, scaffold, oral implantation and antioxidant materials because of their excellent bioactivity, biocompatibility, osteoconductivity and osteoinductive properties. When exposed to simulated body fluid, bioactive glasses have the ability to bond with both hard and soft tissues through the formation of a hydroxyapatite layer. Nowadays, nanotechnology is emerging as a nascent technology in all disciplines because of its high surface-to-volume ratio and unique properties at nanoscale length. The impact of nanotechnology in biomaterials is of interest because of the enhancement in their biocompatibility and bioactivity. In this investigation, the preparation of nanobioactive glasses by using different methods (such as sol-gel, hydrothermal and sonochemical) is discussed in detail. The structural and morphological characterisation of the prepared samples was made.     

Synthesis and characterisation of sol gel derived bioactive glass for biomedical applications

Bioactive glasses have been used successfully as bone-filling materials in orthopaedic and dental surgery, but their poor mechanical strength limits their applications in load-bearing positions. Approaches to strengthen materials decrease their bioactivity. In order to realize the optimal matching between mechanical and biological properties, the sol-gel-self propagating method is adopted to prepare gel-derived bioglass bulk: 58S in the system SiO₂–CaO–P₂O₅. The obtained glass was analysed for its composition, crystalinity and morphology through FT-IR, Raman, XRD, STEM and X-ray microanalysis.     

Synthesis of hydroxyapatite nanotubes for biomedical applications

Single phase, stoichiometrically pure, hollow nanotubes of hydroxyapatite have been synthesized and single-particle analysis has been performed to successfully prove the sole formation of Ca₁₀(PO₄)₆(OH)₂ phase. The facile synthesis involves a sol–gel process under neutral conditions in the presence of a sacrifical anodic alumina template. The structures formed are hollow nanotubes that have been characterized by XRD, SEM, TEM, SAED, EELS, EDS and BET measurements. The diameter of the resulting tubes is in the range of 140–350 nm, length is on the order of a few microns and the wall thickness of the tubes was found to be ca. 30 nm. Moreover these tubes had a large BET surface area of 115 m²/g and were found to be biocompatible. They displayed inertness in the presence of NIH 3T3 mouse fibroblast cells as dictated by an MTT assay.     

Physical and mechanical characterisation of 3D-printed porous titanium for biomedical applications

The elastic modulus of metallic orthopaedic implants is typically 6–12 times greater than cortical bone, causing stress shielding: over time, bone atrophies through decreased mechanical strain, which can lead to fracture at the implantation site. Introducing pores into an implant will lower the modulus significantly. Three dimensional printing (3DP) is capable of producing parts with dual porosity features: micropores by process (residual pores from binder burnout) and macropores by design via a computer aided design model. Titanium was chosen due to its excellent biocompatibility, superior corrosion resistance, durability, osteointegration capability, relatively low elastic modulus, and high strength to weight ratio. The mechanical and physical properties of 3DP titanium were studied and compared to the properties of bone. The mechanical and physical properties were tailored by varying the binder (polyvinyl alcohol) content and the sintering temperature of the titanium samples. The fabricated titanium samples had a porosity of 32.2–53.4 % and a compressive modulus of 0.86–2.48 GPa, within the range of cancellous bone modulus. Other physical and mechanical properties were investigated including fracture strength, density, fracture toughness, hardness and surface roughness. The correlation between the porous 3DP titanium-bulk modulus ratio and porosity was also quantified.     

Evaluation of an elastomer for biomedical use in load-bearing applications

The fatigue behaviour of a medical-grade thermoplastic polyolefin (TPO) was investigated with the objective of using TPOs for endoprosthetical aims in dental and orthopaedic applications. For this purpose, a TPO was subjected to the combined action of shear and compression fatigue while in contact with Hanks' solution. Cyclic loading between 150 and 1500 kPa shear stress and a number of cycles up to 9×10⁶ was applied. The potential fatigue damage was assessed by in-fatigue-recording of the mechanical hysteresis curves and, after fatigue, by swelling tests in acetic acid solutions, dynamic mechanical thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The combined and critical application of these techniques allowed us to conclude that this material exhibits a very satisfactory fatigue behaviour under the loads investigated, making this material potentially useful for endoprostheses. Moreover, biomedical prescreening tests (according to USP Class VI) were all negative, stimulating continued research on this type of material.     

Synthesis and sintering of biomimetic hydroxyapatite nanoparticles for biomedical applications

Synthesis of monodisperse nanoparticles with uniform morphology and narrow size distribution as achieved by nature is a challenge to materials scientists. Mimicking the process of biomineralization has led to the development of biomolecules mediated synthesis of nanoparticles that overcomes many of the problems associated with nanoparticle synthesis. Termed as biomimetics this paradigm shift in the philosophy of synthesis of materials is very advantageous for the design-based synthesis of nanoparticles. The effect of concentration of a protein named bovine serum albumin on particle size, morphology and degree of crystallinity of biomimetically synthesized hydroxyapatite particles, has been studied. Results establish 0.5% protein as the required concentration to produce 30–40 nm sized hydroxyapatite particles with an optimum degree of crystallinity as required for biomedical applications. These particles synthesized under certain stringent conditions are found to have stoichiometric calcium:phosphorus ratio of 1.67 and exhibit restricted grain growth during sintering.     

Synthesis and physical characterization of magnetite nanoparticles for biomedical applications

Iron oxide nanoparticles for biomedical applications in the size range of 15–130 nm were prepared by either oxidative hydrolysis of ferrous sulfate with KOH or precipitation from ferrous/ferric chloride solutions. The magnetite particle size is controlled by variation of pH and temperature. The synthesized magnetite nanoparticles are partially oxidized as signaled by ferrous concentrations of below 24 wt% Fe²⁺ and lattice parameters of a₀ ≤ 8.39 Å which are smaller compared to 8.39 Å for stoichiometric magnetite. The extend of oxidation increases with decreasing particle size. Heating at 150–350 °C topotactically transforms the magnetite nanoparticles into stoichiometric tetragonal maghemite (ferrous ion concentration c_Fe²⁺=0 and a₀ = 8.34 Å) without significant particle growth. The magnetite–maghemite transformation is studied with thermal analysis, XRD and IR spectroscopy. The saturation magnetizations of the magnetite and maghemite particles decrease with decreasing particle size. The variation of M_s with particle size is interpreted using a magnetic core–shell particle model. Magnetite particles with d ≤ 16 nm show superparamagnetic behavior at room temperature whereas particles with diameter >16 nm display hysteresis behavior. These particles are candidates for biomedical applications, e.g. controlled drug release or hyperthermia.     

Preparation and characterisation of calcium-phosphate porous microspheres with a uniform size for biomedical applications

In the present work, a novel route for the preparation of porous ceramic microspheres is described. Two ceramic powders, calcium-titanium-phosphate (CTP) and hydroxyapatite (HAp), were mixed with a sodium alginate solution that enabled the preparation of spherical particles, using the droplet extrusion method combined with ionotropic gelation in the presence of Ca²⁺. The spherical particles were subsequently sintered, to burn-off the polymer and obtain calcium-phosphate microspheres with a uniform size and an interconnected porous network. CTP microspheres with diameters ranging from 513 ± 24 μm to 792 ± 35 μm and with pores of approximately 40 μm were obtained. HAp microspheres presented diameters of 429 ± 46 μm and 632 ± 40 μm and pores of ca. 2 μm. Depending on the formulations tested, the structure of both calcium phosphates may become altered during the sintering process, suggesting that the ratio between the ceramic phase and the polymer solution is a critical parameter. Porous microspheres prepared using the described methodology are promising candidates as bone defect fillers and scaffolds for bone tissue regeneration.     

Investigations on the addition of styrene butadiene rubber in natural rubber and dichlorocarbene modified styrene butadiene rubber blends

This paper focuses on the use of styrene butadiene rubber (SBR) as a viscosity modifier in novel blends of natural rubber (NR) and dichlorocarbene modified styrene butadiene rubber (DCSBR). The processing characteristics, vulcanisation kinetics, stress-strain behaviour, mechanical properties and low temperature transition of the blends have been examined in order to analyse the influence of SBR in the blends. The change in cross-link density values from stress strain behaviour and equilibrium swelling data has been correlated with the technological properties of the blends. The excellent mechanical properties and the increased cross-link density in blends in the presence of 5—10 phr of styrene butadiene rubber reveals the viscosity modifying action of SBR in NR/DCSBR blends. The variation in viscosities of these blends with the addition of SBR is reflected in the DSC thermograms. The resulting blends show very high resistance to thermal ageing as compared to those without SBR.     

Emerging 2D nanomaterials for biomedical applications

Two-dimensional (2D) nanomaterials are an emerging class of biomaterials with remarkable potential for biomedical applications. The planar topography of these nanomaterials confers unique physical, chemical, electronic and optical properties, making them attractive candidates for therapeutic delivery, biosensing, bioimaging, regenerative medicine, and additive manufacturing strategies. The high surface-to-volume ratio of 2D nanomaterials promotes enhanced interactions with biomolecules and cells. A range of 2D nanomaterials, including transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), layered silicates (nanoclays), 2D metal carbides and nitrides (MXenes), metal–organic framework (MOFs), covalent organic frameworks (COFs) and polymer nanosheets have been investigated for their potential in biomedical applications. Here, we will critically evaluate recent advances of 2D nanomaterial strategies in biomedical engineering and discuss emerging approaches and current limitations associated with these nanomaterials. Due to their unique physical, chemical, and biological properties, this new class of nanomaterials has the potential to become a platform technology in regenerative medicine and other biomedical applications.     

Synthesis and characterisation of nanostructured hardystonite coating on stainless steel for biomedical application

Here, nanostructured hardystonite bioceramic (Ca₂ ZnSi₂ O₇) was synthesised from tetraethyl orthosilicate, zinc nitrate hexahydrate, and calcium nitrate tetrahydrate via sol–gel method, dried at 60–120°C, and finally calcinated at 1300°C. X‐ray diffraction (XRD) analysis confirmed the formation of hardystonite bioceramic. Afterwards, electrophoretic method was utilised to coat the hardystonite ceramic on 316L stainless steel (SS). Methanol solution was used as suspension solvent. The best deposition procedure was carried out by electrophoretic device in the voltage of 50 V for 5 min. XRD analysis was employed for phase characterisation and scanning electron microscopy was utilised for microstructural and morphological characterisations of the coatings. Chemical composition of the coating was evaluated by energy‐dispersive X‐ray spectroscopy. The hardystonite coating improved the corrosion resistance of the substrate, so the corrosion current density in the coated samples was less than the uncoated ones (nine times). In order to assess the bioactivity of the coating, simulated body fluid was used. The main results of the coated sample bioactivity demonstrated that the nanostructured hardystonite coating could amend the in vitro SS bioactivity. Therefore, SS coated with nanostructured hardystonite may be a promising candidate to be applied as bioactive hard tissue implants.Inspec keywords: bioceramics, stainless steel, X‐ray diffraction, corrosion protective coatings, X‐ray chemical analysis, sol‐gel processing, calcium compounds, current density, nanofabrication, zinc compounds, scanning electron microscopy, corrosion resistance, calcination, crystal microstructure, nanostructured materials, prosthetics, nanomedicine, electrophoretic coatings, electrophoretic coating techniquesOther keywords: X‐ray diffraction analysis, electrophoretic method, XRD analysis, phase characterisation, microstructural characterisations, morphological characterisations, energy‐dispersive X‐ray spectroscopy, coated sample bioactivity, nanostructured hardystonite coating, zinc nitrate hexahydrate, sol–gel method, 316L stainless steel, tetraethyl orthosilicate, calcium nitrate tetrahydrate, suspension solvent, deposition procedure, scanning electron microscopy, chemical composition, corrosion resistance, corrosion current density, bioactive hard tissue implants, temperature 1300.0 degC, voltage 50.0 V, time 5.0 min, temperature 60 degC to 120 degC, Ca₂ ZnSi₂ O₇      

Processing,characterisation, and biocompatibility of zinc modified metaphosphate based glasses for biomedical applications

Bulk and structural properties of zinc oxide (0 up to 20 mol%) containing phosphate glasses, developed for biomedical applications, were investigated throughout this study using differential thermal analysis (DTA), differential scanning calorimetry, X-ray powder diffraction and 31P and 23Na MAS NMR. Surface wettability and MG63 viability were also considered for surface characterisation of these glasses. The results indicated that incorporation of zinc oxide as a dopant into phosphate glasses produced a significant increase in density; however, the thermal properties presented in glass transition, and melting temperatures were reduced. NaZn(PO3)3 was detected in the X-Ray Powder Diffraction Analysis (XRD) trace of zinc containing glasses, and the proportion of this phase increased with increasing zinc oxide content. NaCa(PO3)3 as a second main phase and CaP2O6 in minor amounts were also detected. The 31P and 23Na MAS NMR results suggested that the relative abundances of the Q1 and Q2 phosphorus sites, and the local sodium environment were unaffected as CaO was replaced by ZnO in this system. The replacement of CaO with ZnO did seem to have the effect of increasing the local disorder of the Q2 metaphosphate chains, but less so for the Q1 chain-terminating sites which were already relatively disordered due to the proximity of modifying cations. Glasses with zinc oxide less than 5 mol% showed higher surface wettability, while those with 5 up to 20 mol% showed comparable wettability as zinc oxide free glasses. Regardless of the high hydrophilicity and surface reactivity of these zinc oxide containing glasses, they had lower biocompatibility, in particular 10-20 mol% ZnO, compared to both zinc free glasses and Thermanox. This may be associated with the release of significant amount of Zn2+ enough to be toxic to MG63.     

Synthesis of core-shell nanoclusters with high magnetic moment for biomedical applications

Biocompatible magnetic nanoparticles have been found to be promising in several biomedical applications for tagging, imaging, sensing, and separation in recent years. Most magnetic particles or beads currently used in biomedical applications are based on ferromagnetic iron oxides with very low specific magnetic moments of about 20-30 emu/g. Here, we report a new approach to synthesize monodispersive core-shell nanostructured clusters with high specific magnetic moments above 200 emu/g. The Fe nanoclusters, ranging in size from 2 to 100 nm, are produced from a newly developed cluster source and go to a deposition chamber, where a chemical reaction starts, and the nanoclusters are coated with Fe oxides. High-resolution transmission electron microscopy images show the coatings are very uniform. The core-shell nanoclusters are superparamagnetic at room temperature for sizes less than 12 nm, and have the coercivity of about 1.5 kOe at low temperature (5 K).     

Synthesis of a disulfide cross-linked polygalacturonic acid hydrogel for biomedical applications

Polygalacturonic acid (PGA) hydrogel cross-linked via disulfide bonds was synthesized using a thiol oxidation reaction. PGA was grafted with cysteine to yield thiolated PGA (denoted PGA_cys). Per gram, PGA-conjugated cysteine was 725 ± 77 μmol, and the degree of modification was 16.24 %. A PGA_cys hydrogel film was fabricated under physiological conditions, with gel content 91.6 % and water content 43.3 %. The PGA_cys hydrogel was used as a drug carrier for rosmarinic acid (RA) (denoted PGA_cys/RA) and to prevent postsurgical adhesion. The in vitro dynamic release behavior of RA from the PGA_cys hydrogel was analyzed. The profiles showed that 80 % of the total RA was released from the hydrogel within 15 min, followed by zero-order kinetic release. Animal implant studies showed that PGA_cys and PGA_cys/RA hydrogel films reduced adhesion incidence by over 90 %, significantly higher than did Hyaluronate/Carboxymethylcellulose (analogous Seprafilm?) (42 %). The PGA_cys/RA hydrogel film also reduced the early inflammatory reaction.     

Synthesis and characterization of manganese containing mesoporous bioactive glass nanoparticles for biomedical applications

Mesoporous bioactive glass (BG) nanoparticles based in the system: SiO₂–P₂O₅–CaO–MnO were synthesized via a modified Stöber process at various concentrations of Mn (0–7 mol %). The synthesized manganese-doped BG nanoparticles were characterized in terms of morphology, composition, in vitro bioactivity and antibacterial activity. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis confirmed that the particles had spherical morphology (mean particle size: 110?nm) with disordered mesoporous structure. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Mn, Ca, Si and P in the synthesized Mn-doped BG particles. Moreover, X-ray diffraction (XRD) analysis showed that Mn has been incorporated in the amorphous silica network (bioactive glass). Moreover, it was found that manganese-doped BG particles form apatite crystals upon immersion in simulated body fluid (SBF). Inductively coupled plasma atomic emission spectroscopy (ICP-OES) measurements confirmed that Mn is released in a sustained manner, which provided antibacterial effect against Bacillus subtilis, Pseudomonas aeruginosa and Staphylococcus aureus. The results indicate that the incorporation of Mn in the bioactive glass network is an effective strategy to develop novel multifunctional BG nanoparticles for bone tissue engineering.     

Carbon-based nanozymes for biomedical applications

Nanozymes are nanomaterials with enzyme-like properties that have attracted significant interest owing to their capability to address the limitations of traditional enzymes such as fragility,high cost,and impossible mass production.Over the past decade,a broad variety of nanomaterials have been found to mimic the enzyme-like activity by engineering the active centers of natural enzymes or developing multivalent elements within nanostructures.Carbon nanomaterials with well-defined electronic and geometric structures have served as favorable surrogates of traditional enzymes by mimicking the highly evolved catalytic center of natural enzymes.In particular,by combining the unique electronic,optical,thermal,and mechanical properties,carbon nanomaterials-based nanozymes can offer a variety of multifunctional platforms for biomedical applications.In this review,we will introduce the enzymatic characteristics and recent advances of carbon nanozymes,and summarize their significant applications in biomedicine.