Tailoring crystallinity of electrospun Plla fibres by control of electrospinning parameters

Poly(L-lactic acid) (PLLA) fibers were fabricated by electrospinning. The effects of various electrospinning process parameters on the thermal properties, especially the crystallinity of the electrospun fibers were investigated. Thermal analysis of the fibers revealed that they exhibited degree of crystallinity ranging from 23% to 46% while that for the as-received granules was approximately 37%, suggesting that the crystallinity of electrospun PLLA fibres can be controlled by optimizing the electrospinning process. This finding is very important because crystallinity affects polymer properties such as degradation, stiffness,yield stress, modulus and tensile strength, solubility, optical and electrical properties which will in turn affect the behavior of these materials when they are utilized in energy,environment, defense and security applications. The results presented in this paper show that the degree of crystallinity of the electrospun fibers decreased with increasing the polymer solution concentration. Furthermore, an optimum electrospinning voltage at which maximum degree of crystallinity can be obtained was observed. At voltages higher or lower than the optimum electrospinning voltage, the degree of rystallinity will decrease or increase,respectively. The effect of the needle tip to collector distance (NTCD) on the degree of\ud crystallinity follows no predictable and consistent pattern

Defensin-Like Peptides and Their Antimicrobial Activity in Free-Form and Immobilized on Material Surfaces

Defensins are naturally occurring antimicrobial peptides secreted in the human body. Mammalian defensins are small, cysteine-rich, cationic peptides, generally consisting of 18–45 amino acids. The antimicrobial activity of defensins arises from their unique amino acid sequence, showing activity against both Gram-positive and Gram-negative bacteria, fungi and enveloped viruses. The use of antimicrobial peptides is rising due to their potential to control biofilm formation and kill microorganisms that are highly tolerant to antibiotics. In free-form, defensins are capable of destroying such microorganisms through numerous mechanisms mainly the carpet, the toroidal and the Barrel-Stave models. However, immobilization of antimicrobial peptides (AMPs) on surfaces with the help of coupling agents and spacers can improve the AMPs’ lifespan and stability in the physiological environment leading to applications for medical devices and implants. Fundamental understanding of both free-form and surface-immobilized defensins is important to design more effective antimicrobial peptides and improve their performance in future developments

Functionalisation of Ti6Al4V and hydroxyapatite surfaces with combined peptides based on KKLPDA and EEEEEEEE peptides

Surface modifications are usually performed on titanium alloys to improve osteo-integration and surface bioactivity. Modifications such as alkaline and acid etching, or coating with bioactive materials such as hydroxyapatite, have previously been demonstrated. The aim of this work is to develop a peptide with combined titanium oxide and hydroxyapatite binders in order to achieve a biomimetic hydroxyapatite coating on titanium surfaces. The technology would also be applicable for the functionalisation of titanium and hydroxyapatite surfaces for selective protein adsorption, conjugation of antimicrobial peptides, and adsorption of specialised drugs for drug delivery. In this work, functionalisation of Ti6Al4V and hydroxyapatite surfaces was achieved using combined titanium-hydroxyapatite (Ti-Hap) peptides based on titanium binder (RKLPDA) and hydroxyapatite binder (EEEEEEEE) peptides. Homogeneous peptide coatings on Ti6Al4V surfaces were obtained after surface chemical treatments with a 30 wt % aqueous solution of H2O2 for 24 and 48 hours. The treated titanium surfaces presented an average roughness of Sa=197 nm (24 h) and Sa=128 nm (48 h); an untreated mirror polished sample exhibited an Sa of 13 nm. The advancing water contact angle of the titanium oxide layer after 1 hour of exposure to 30 wt % aqueous solution of H2O2 was around 65°, decreasing gradually with time until it reached 35° after a 48 hour exposure, suggesting that the surface hydrophilicity increased over etching time. The presence of a lysine (L) amino acid in the sequence of the titanium binder resulted in fluorescence intensity roughly 16 % higher compared with the arginine (R) amino acid analogue and therefore the lysine containing titanium binder was used in this work. The Ti-Hap peptide KKLPDAEEEEEEEE (Ti-Hap1) was not adsorbed by the treated Ti6Al4V surfaces and therefore was modified. The modifications involved the inclusion of a glycine spacer between the binding terminals (Ti-Hap2) and the addition of a second titanium binder (KKLPDA) (Ti-Hap3 and Ti-Hap4). The Ti-Hap peptide aptamer which exhibited the strongest intensity after the titanium dip coating was KKLPDAKKLPDAEEEEEEEE (Ti-Hap4). On the other hand, hydroxyapatite surfaces, exhibiting an average roughness of Sa=1.42 µm, showed a higher fluorescence for all peptides compared with titanium surfaces

Nanoclay reinforced glass ionomer cement:in vitro wear evaluation and comparison by two wear test methods

Glass ionomer cement (GIC) represents a major transformation in restorative dentistry. Wear of dental restoratives is a common phenomenon and the determination of the wear resistance of direct-restorative materials is a challenging task. The aim of this paper was to evaluate the wear resistance of novel glass ionomer cement by two wear-test methods and to compare the two wear methods.The wear resistance of a conventional glass ionomer cement (HiFi Advanced Health Care Kent, UK) and cements modified by including various percentages of nanoclays (1, 2 and 4 wt %) was measured by a reciprocating wear test (ball-on-flat) and Oregon Health and Sciences University’s (OHSU) wear simulator. The OHSU wear simulation subjected the cement specimens to three wear mechanisms, namely abrasion, three-body abrasion and attrition using a steatite antagonist. The abrasion wear resulted in material loss from GIC specimen as the steatite antagonist forced through the exposed glass particles when it travelled along the sliding path.The hardness of specimens was measured by the Vickers hardness test. The results of reciprocation wear test showed that HiFi-1 resulted in the lowest wear volume 4.90 (0.60) mm3 (p < 0.05), but there was no significant difference (p > 0.05) in the wear volume in comparison to HiFi, HiFi-2 and HiFi-4. Similarly, the results of OHSU wear simulator showed that the total wear volume of HiFi-4 1.49 (0.24) was higher than HiFi-1 and HiFi-2. However, no significant difference (p > 0.05) was found in the OHSU total wear volume in GICs after nanoclay incorporation. The Vickers hardness (HV) of the nanoclay-reinforced cements was measured between 62 and 89 HV. Nanoclay addition at a higher concentration (4%) resulted in higher wear volume and wear depth. The total wear volumes were less dependent upon abrasion volume and attrition volume. The total wear depths were strongly influenced by attrition depth and to some extent by abrasion depth. The addition of nanoclay in higher wt % to HiFi did not result in significant improvement in wear resistance and hardness. Nonetheless, wear is a very complex phenomenon because it is sensitive to a wide number of factors that do not necessarily act in the same way when compared using different parameters

Selective modification of Ti6Al4V surfaces for biomedical applications

The surface of a medical implant is required to interact favourably with ions, biomolecules and cells in vivo, commonly resulting in the formation of the extracellular matrix. Medical grade Ti6Al4V alloy is widely used in orthopaedic and dental applications for bone replacement due to its advantageous mechanical properties and biocompatibility, which enhances the adhesion between native tissue and the implanted material. In this study, chemical and thermal modification of a medical-grade Ti6Al4V alloy were performed to enhance electrostatic interactions at the alloy surface with a synthetic peptide, suitable for conferring drug release capabilities and antimicrobial properties. The modified surfaces exhibited a range of topographies and chemical compositions depending primarily on the treatment temperature. The surface wetting behaviour was found to be pH-dependent, as were the adhesive properties, evidenced by chemical force titration atomic force microscopy

Effect of Nanoclay Dispersion on the Properties of a Commercial Glass Ionomer Cement

Objective. The reinforcement effect of polymer-grade montmorillonite (PGV and PGN nanoclay) on Fuji-IX glass ionomer cement was investigated. Materials and Method. PGV and PGV nanoclays (2.0 wt%) were dispersed in the liquid portion of Fuji-IX. Fourier-transform infrared (FTIR) spectroscopy and gel permeation chromatography (GPC) were used to quantify acid-base reaction and the liquid portion of GIC. The mechanical properties (CS, DTS, FS, and Ef) of cements (n = 20) were measured at 1 hour, 1 day, and 1 month. The microstructure was examined by cryo-SEM and TEM. Results. FTIR shows that the setting reaction involves the neutralisation of PAA by the glass powder which was linked with the formation of calcium and aluminium salt-complexes. The experimental GICs (C-V and C-N) exhibited mechanical properties in compliance to ISO standard requirement have higher values than Fuji-IX cement. There was no significant correlation of mechanical properties was found between C-V and C-N. The average Mw of Fuji-IX was 15,700 and the refractive index chromatogram peak area was 33,800. TEM observation confirmed that nanoclays were mostly exfoliated and dispersed in the matrix of GIC. Conclusion. The reinforcement of nanoclays in GICs may potentially produce cements with better mechanical properties without compromising the nature of polyacid neutralisation

Polydopamine Linking Substrate for AMPs: Characterisation and Stability on Ti6Al4V

Infections are common complications in joint replacement surgeries. Eradicated infections can lead to implant failure. In this paper, analogues of the peptide KR-12 derived from the human cathelicidin LL-37 were designed, synthesised, and characterised. The designed antimicrobial peptides (AMPs) were attached to the surface of a titanium alloy, Ti6Al4V, by conjugation to a polydopamine linking substrate. The topography of the polydopamine coating was evaluated by electron microscopy and coating thickness measurements were performed with ellipsometry and Atomic Force Microscopy (AFM). The subsequently attached peptide stability was investigated with release profile studies in simulated body fluid, using both fluorescence imaging and High-Performance Liquid Chromatography (HPLC). Finally, the hydrophobicity of the coating was characterised by water contact angle measurements. The designed AMPs were shown to provide long-term bonding to the polydopamine-coated Ti6Al4V surfaces