Mechanical and Bioactive Properties of PMMA Bone Cement: A Review

Over the past few decades, poly(methyl methacrylate) (PMMA) based bone cement has been clinically used extensively in orthopedics for arthroplasty and kyphoplasty, due to its biocompatibility and excellent primary fixation to the host bone. In this focused review, we discuss the use of various fillers and secondary chemical moieties to improve the bioactivity and the physicochemical properties. The viscosity of the PMMA blend formulations and working time are crucial to achieving intimate contact with the osseous tissue, which is highly sensitive to organic or inorganic fillers. Hydroxyapatite as a reinforcement resulted in compromised mechanical properties of the modified cement. The possible mechanisms of the additive- or filler-dependent strengthening or weakening of the PMMA blend are critically reviewed. The addition of layered double hydroxides with surface functionalization appears to be a promising approach to enhance the bonding of filler with the PMMA matrix. Such an approach consequently improves the mechanical properties, owing to enhanced dispersion as well as contributions from crack bridging. Finally, the use of emerging alternatives, such as nanoparticles, and the use of natural biomolecules were highlighted to improve bioactivity and antibacterial properties.

Perceptible exciton-to-trion conversion and signature of defect mediated vibronic modes and spin relaxation in nanoscale WS2 exposed to γ-rays

In this work, we report manifested optical, optoelectronic and spin-spin relaxation features of a few layered tungsten disulphide (WS₂) nanosheets subjected to energetic γ-photons (∼1.3 MeV) emitted from a Co⁶⁰ source. Upon intense irradiation (dose = 96 kGy), a slight departure from the pure hexagonal phase was realized with the introduction of the trigonal phase at large. Moreover, in the Raman spectra, as a consequence of the radiation-induced effect, an apparent improvement of the E-to-A mode intensity and a reduction in phonon lifetimes have been realized, with the latter being dependent on the linewidths. The emergence of the new peak (D) maxima observable at ∼406 cm^-1 in the Raman spectra and ∼680 nm in the photoluminescence (PL) spectra can be attributed to the introduction of defect centres owing to realization of sulphur vacancies (V _S) in the irradiated nanoscale WS₂. Additionally, neutral exciton to charged exciton (trion) conversion is anticipated in the overall PL characteristics. The PL decay dynamics, while following bi-exponential trends, have revealed ample improvement in both the fast parameter (0.39 ± 0.01 ns to 1.88 ± 0.03 ns) and the slow parameter (2.36 ± 0.03 ns to 12.1 ± 0.4 ns) after γ-impact. We attribute this to the finite band gap expansion and the incorporation of new localized states within the gap, respectively. A declining exciton annihilation rate is also witnessed. The isotropic nature of the electron paramagnetic resonance spectra as a consequence of γ-exposure would essentially characterize a uniform distribution of the paramagnetic species in the system, while predicting a three-fold improvement of relative spin density at 96 kGy. Exploring defect dynamics and spin dynamics in 2D nanoscale systems does not only strengthen fundamental insight but can also offer ample scope for designing suitable components in the areas of miniaturized optoelectronic and spintronic devices.