Mesoporous silica nanoparticle-functionalized poly(methyl methacrylate)-based bone cement for effective antibiotics delivery

Poly(methyl methacrylate)-based bone cements are functionalized with mesoporous silica nanoparticles (MSN) to enable a highly efficient and sustained release of antibiotics to reduce the risk of post-operative joint infection. To overcome the limited drug release of 5% for only 1 day with the current commercial-grade bone cements, a 8 wt% MSN-formulated bone cement is able to increase the drug release efficiency by 14-fold and sustain the release for up to 80 days. The loaded MSN is suggested to build up an effective network of rod-shaped silica particles with uniformly arranged nanoporous channels, which is responsible for the effective drug diffusion and extend time-release to the external surfaces. MSN has no detrimental effect on the critical weight-bearing bending modulus and compression strength of bone cement. In vitro assay test results show a much sustained antibacterial effect and low cytotoxicity of MSN demonstrating the potential applicability of MSN-formulated bone cement.     

Mechanical behaviour of poly(methyl methacrylate)

A series of tensile and three-point bending studies was conducted at various temperatures and loading rates using a commercial poly(methyl methacrylate) (PMMA). Tensile properties and fracture toughness data were obtained for the various conditions. In general, both tensile strength and fracture toughness increase with increasing loading rate and decreasing temperatur E. However, when the temperature reaches the glass transition region, the relationships between fracture toughness, loading rate, and temperature become very complex. This behaviour is due to the simultaneous interaction of viscoelasticity and localized plastic deformation. In the glass transition region, the fracture mechanism changes from a brittle to a ductile mode of failure. A failure envelope constructed from tensile tests suggests that the maximum elongation that the glassy PMMA can withstand without failure is about 130%. The calculated apparent activation energies suggest that the failure process of thermoplastic polymers (at least PMMA) follows a viscoelastic process, either glass or transition. The former is the case if crack initiation is required.Deceased.     

Preparation of hydroxyapatite/poly(methyl methacrylate) and calcium silicate/poly(methyl methacrylate) interpenetrating hybrid composites

Hydroxyapatite/poly(methyl methacrylate) (HAp/PMMA) and calcium silicate/poly(methyl methacrylate) (CS/PMMA) composites were prepared by interpenetrating bulk polymerization of methyl methacrylate (MMA) monomer in porous structures of HAp and CS. The porous HAp and CS templates were prepared by mixing their calcined powders with poly(vinyl alcohol) (PVA) solution, shaping by uniaxial pressing and then firing at 1,100 °C for HAp and 900 °C for CS. The templates were soaked in the solution mixture of MMA monomer and 0.1 mol% of benzoyl peroxide (BPO) for 24 h. The pre-composites were then bulk polymerized at 85 °C for 24 h under nitrogen atmosphere. The microstructures of the composites showed the interpenetrating of PMMA into the porous HAp and CS structures. Thermogravimetric analysis indicated that the PMMA content in the HAp/PMMA and CS/PMMA composites were 13 and 26 wt%, respectively. Weight average molecular weights ( ) of PMMA were about 491,000 for HAp/PMMA composites and about 348,000 for CS/PMMA composites. Compressive strengths of these composites were about 90–131 MPa in which they were significantly higher than their starting porous templates.     

Hot compaction of poly(methyl methacrylate) composites based on fiber shrinkage results

Uniaxial self-reinforced composite poly(methyl methacrylate) (SRC-PMMA) is being investigated as a pre-coat material for the femoral component of total hip replacements. Hot compaction of self-reinforced composites is largely an empirical process which varies the processing parameters of time, temperature and pressure until the desired properties are obtained. Previous work has shown that PMMA fibers have unique thermal relaxation properties dependent upon the retained molecular orientation in them. This work processed composites at times and temperatures that span the relaxation process for a single fiber. It was found that molecular orientation, as measured by birefringence, was lost in composites processed at times greater than relaxation times for single fibers. Flexural properties were also found to vary with processing conditions, with the highest values of 165 ± 15 MPa and 168 ± 3 MPa found at high and low processing times, respectively. These are significantly stronger than unreinforced PMMA which has a flexural strength of 127 ± 14 MPa. It is hypothesized that diffusion between fibers occurs much more quickly than the loss of molecular orientation and it was seen that SRC-PMMA processing conditions can be predicted from the relaxation times and temperatures from single fibers.     

Environmentally-affected indentation fracture in poly(ethersulphone) and poly(methyl methacrylate)

The effect of plasticization on the ductile-to-brittle fracture transitions (DBFT) in the ball indentation of poly (ethersulphone) (PES) and poly(methyl methacrylate) (PMMA) has been studied. The DBFT in various organic liquids are governed by a size effect related to the indenter radius, in accordance with the Puttick theory of fracture transitions. In addition, abrasive wear rates of the polymers in these liquids are shown to correlate with the critical indenter radius needed to produce a fracture transition, owing to the connection with fracture toughness.     

Blends of poly(methyl methacrylate) and polyamides

The morphology of PMMA blends with different polyamides (PA-6, 6/9 and 12) was investigated by transmission electron microscopy, recognizing PA-6/PMMA as the most miscible pair. Blends of these polymers were prepared from solutions in m-cresol and formic acid and the morphology was highly dependent on the solvent. The morphology and the segregation degree of extruded PA-6/PMMA blends was investigated by scanning electron microscopy and dynamic-mechanical analysis. The compatibilization succeeded by the introduction of a block copolymer of polyamide and poly(ethylene oxide).     

Electrospun poly(methyl methacrylate) nanofibers and microparticles

Electrospinning at relatively low polymer concentrations results in particles rather than fibers. This particle-formation process can be termed as electrospray. So electrospinning/electrospray is a highly versatile method to process fibers and particles with different morphologies. In this work, poly(methyl methacrylate) (PMMA) micro- and nanostructures with different morphologies (fibers, spheres, cup-like, and ring-like) have been produced by a facile electrospinning/electrospray method. PMMA was electrospun into various morphologies from only DMF without any other solvents. Field emission scanning electron microscope (FESEM) images demonstrate the different morphologies and prove this technique to be an effective method for obtaining morphology-controllable polymer materials by changing the processing parameters. These micro- and nanostructured polymer materials may find applications in drug delivery and filtration media.     

Thermal degradation behaviors of poly (dimethylsiloxane)-urethane-graft-poly (methyl methacrylate) copolymers based on various diisocyanates

The thermal decomposition behaviors of slightly crosslinked poly(dimethylsiloxane)-urethane-graft-poly(methyl methacrylate) (PDMS-urethane-g-PMMA) copolymers based on two diisocyanates: 2,4-toluene diisocyanate (2,4-TDI) and m-xylene diisocyanate (m-XDI) are discussed. By analyzing the residues of the decomposed copolymers and thermal degradation behaviors of copolymers, it was proposed that poly(dimethylsiloxane) (PDMS) in the copolymers traps free radicals generated from the thermal decomposition of the copolymer and reduces the rate of thermal decomposition. In addition, the crosslinking structure of PDMS can also reduce the evaporation of volatiles from the thermal decomposition process.     

Wettability of poly(methyl methacrylate) surfaces in dental use

Poly(methyl methacrylate) is widely used in dentistry. In contact with water, there is an increase in the polar surface free energy from 9.5 to 21 mJ m^–2. Various other surface modification treatments have been examined (chemical treatment, gold deposition and flaming), which also bring about a surface polar component increase and thus produce a better wettability in contact with water or saliva. The water modification seems to be the best treatment.     

Fatigue failure of poly(methyl methacrylate) in alcohol environments

Fatigue tests of poly(methyl methacrylate) were conducted in environments of methanol, 1-butanol, and 1-octanol at room temperature under cyclic tensile loading at 10 Hz. The fatigue lifetime increased as the molar volume of the environmental alcohol increased, and indicated no correlation with the solubility parameter. The scanning electron micrographs of the fracture surfaces reveal that crazes strongly participate in the fatigue fracture, and suggest that a great increase in the fatigue lifetime in methanol brought about by pre-soaking the specimen in methanol for a period below 100 h, which has been previously reported, is caused by the combined effects both of the case II diffusion of methanol producing the softened matter and the internal compressive stress in the swollen surface layer and of a cooperative work of crazing, shear flow and/or shear cracking taking place under cyclic tensile loading.     

Strength of poly(methyl methacrylate) with indentation flaws

Controlled flaws were introduced into poly(methyl methacrylate) samples in the presence of liquid acetone using a Vickers indenter over a range of indentation loads from 100 to 1400 N. Due to the large plastic zone underneath the indenter, the radial crack formed by indentation consisted of two halves, known as Palmqvist cracks, instead of a single semicircular crack. The strengths of the samples were measured in air either immediately following indentation or after a stress-relief anneal. The strength of the as-indented samples was about 6% less than that of the annealed samples; however, the dependence of strength on indentation load was similar for both sets of samples. These results were interpreted in terms of an indentation fracture mechanics model. The analysis is consistent with poly(methyl methacrylate) having a rising fracture toughness with increasing crack size.     

Craze initiation in poly(methyl methacrylate) exposed to n-alkanes

The critical stresses for craze initiation were measured on poly(methyl methacrylate) exposed to n-alkanes both under static torsion and under static tension at room temperature. Crazes are observed even under torsion where the dilatational stress is absent, as the authors previously pointed out. The critical stresses for craze initiation under both types of loading increase with increasing liquid molar volume, and decrease with increasing loading time. The ratio of the critical crazing stress under torsion to that under tension is almost constant irrespective of the kind of liquid and the loading time. In contrast with the critical crazing strain measured by the use of the elliptical bending device, the critical crazing stresses do not show a lower limiting value even under long-time (200 min) loading, and are correlated with neither the solubility parameter nor the equilibrium solubility of the liquid predicted from the solution theory.     

Some recent results on crack healing of poly(methyl methacrylate)

The solvent healing and void growth of poly(methyl methacrylate) (PMMA) at elevated temperatures were studied. In addition to entanglement between two or more broken polymeric chains, the chemical bonds between two polymeric broken chains were produced during healing in methanol or d₁-methanol. Cracks in PMMA were induced either by Nd-YAG laser irradiation or by acetone immersion. The solvents occupied the voids enclosed by polymeric chains. The chemical bonds and structure were analyzed with FTIR and NMR spectroscopy. The results show that in addition to mechanical lock of broken chains, hydrogen bond increases with uptake of solvent which enhances the crack healing. The cylindrical crack in PMMA was healed at temperatures 110-160 °C and spherical void was grown at temperatures 170-190 °C. This suggests that annealing above the glass transition temperature of polymer is a necessary condition for thermal healing, but not for the sufficient condition.     

Tensile behaviour of blends of poly(vinylidene fluoride) with poly(methyl methacrylate)

Blends of poly(vinylidene fluoride) (PVF₂) and poly(methyl methacrylate) (PMMA) were prepared over a wide concentration range and tested in tension at the same relative temperature below the glass transition. Testing was performed at strain rates ranging from 10 to 0.01 min^–1 at test temperatures fromT _g-40 toT _g-10. By normalizing the test temperature to fixed increments belowT _g, blends and homopolymers can be compared on the basis of PVF₂ and PMMA composition and crystallinity. In nearly all blends, under conditions favouring disentanglement, (decrease in strain rate, or increase in test temperature), the yield stress and drawing stress decreased while the breaking strain increased. For materials with about the same degree of crystallinity, those with a higher proportion of amorphous PVF₂ exhibited brittle-like behaviour as a result of interlamellar tie molecules. In the semicrystalline blends, yield stress remains high as the test temperature approachesT _g, whereas in the amorphous blends the yield stress falls to zero nearT _g. Results of physical ageing support the role of interlamellar ties which cause semicrystalline blends to exhibit ageing at temperatures aboveT _g.     

Feasibility study of friction spot welding of dissimilar single-lap joint between poly(methyl methacrylate) and poly(methyl methacrylate)-SiO2 nanocomposite

In this work, the feasibility of friction spot welding (FSpW) of a commercial poly(methyl methacrylate) (PMMA) GS grade and a PMMA 6 N/2 wt% silica (SiO₂) nanocomposite was investigated. Single-lap joints welded at rotational speeds of 1000, 2000 and 3000 rpm were produced. The analysis of the joint microstructure and material flow pattern indicated that joints could be produced using all of the tested welding conditions. However, the joint produced at 1000 rpm displayed sharp weld lines (weak links), indicating insufficient heat input, while the welds produced at 3000 rpm displayed excessive plastic deformation (bulging of the bottom plate), volumetric defects and a lack of material mixing in the welded area, associated with higher heat input. The weld produced at a rotational speed of 2000 rpm resulted in improved material mixing, which was indicated by the absence of weld lines and volumetric defects due to the more correct heat input. This welding condition was selected for further mechanical testing. Lap shear testing of PMMA GS/PMMA 6 N/2 wt% SiO₂ nanocomposite single lap joints welded at 2000 rpm resulted in an average ultimate lap shear strength of 3.9 ± 0.05 MPa. These weld strength values are equal to or better than those obtained using state-of-the-art welding techniques for PMMA materials, thereby demonstrating the potential of friction spot welding for thermoplastic nanocomposites.     

Mechanical properties of blends of poly(methyl methacrylate) and poly(vinylidene fluoride)

The mechanical properties of blends of the crystallizable polymer poly(vinylidene fluoride) and the amorphous material poly(methyl methacrylate) have been investigated as a function of composition both for glassy amorphous materials and for partially crystalline materials. The data obtained were interpreted in terms of the molecular and super-molecular structure of the blends and in terms of their dynamic properties.The main conclusions were that the mechanical properties are not strongly dependent on details of the distribution of the two components in the material nor on the crystal modifications present. The mechanical properties were found to depend primarily on the location of the glass transition temperature relative to the elongation temperature and on the presence or absence of crystalline regions. The degree of crystallinity was found to play an important role in determining the properties only at lower values of this quantity. The advantage of these blends is that the important parameters, namely, the degree of crystallinity and the location of the glass transition temperature, can be adjusted at will by varying the composition appropriately. This allows well-defined variations of the mechanical properties to be achieved.     

Cadmium sulfide photoluminescence in poly(methyl methacrylate)-matrix composites

Poly(methyl methacrylate)-matrix composites containing cadmium, lead, and zinc sulfides and also mixed (cadmium lead and cadmium zinc) sulfides were prepared by reacting metal salts with thioacetamide. The transmission of the composites in the range λ > 500 nm is 92% at absorbing layer thicknesses of ≤5 mm. The photoluminescence (PL) of the composites in the wavelength range 500–820 nm is due to the cadmium sulfide, and that in the wavelength range 300–550 nm arises from the zinc sulfide. It results from radiative recombination at levels of extrinsic structural defects in CdS and ZnS, respectively. The PL excitation spectra contain excitonic absorption bands of cadmium sulfide and zinc sulfide quantum dots. The PL of the cadmium sulfide in the composites is influenced by the presence of lead(II) and zinc(II) ions and the complexation of cations on the surface of the particles.     

PMMA基凝胶聚合物电解质研究进展

综述了聚甲基丙烯酸甲酯(PMMA)基凝胶聚合物电解质(GPE)的研究进展,提出了PMMA基凝胶电解质目前主要存在的问题,着重讨论了采用共聚共混、交联和添加无机填料等对PMMA进行改性的方法,以及PMMA基GPE的三种制备方法.