Moisture-Activated Rheological Structuring of Nonaqueous Poloxamine–Poly(Acrylic Acid) Systems Designed as Novel Biomedical Implants

This study reports the formulation/characterisation of novel polymeric platforms designed to behave as low-viscosity systems in the nonaqueous state, however, following uptake of aqueous ?uids, exhibit rheological structuring and mucoadhesion. The rheological/mechanical and mucoadhesive properties of platforms containing poly(acrylic acid) (PAA, 1%, 3%, 5%, w/w) and poloxamines (Tetronic 904, 901, 704, 701, 304), both in the absence and presence of phosphate buffered saline (PBS, pH 7.4) are described. With the exception of Tetronic 904, all formulations exhibited Newtonian ?ow in the nonaqueous state, whereas, all aqueous formulations displayed pseudoplastic ?ow. The consistency and viscoelastic properties were dependent on the concentrations of PAA and PBS and Tetronic grade. PBS signi?cantly increased the consistency, viscoelasticity and mucoadhesion, reaching a maximum at a de?ned concentration of PBS that was dependent on PAA concentration and Tetronic grade. Formulations containing Tetronic 904 exhibited greatest consistency and elasticity both prior to and after dilution with PBS. Increasing PAA concentration enhanced the mucoadhesive properties. Prolonged drug release of metronidazole was observed from formulations containing 10% (w/w) PBS, 3% and, particularly, 5% (w/w) PAA. It is suggested that the physicochemical properties of formulations containing 3% or 5% (w/w) PAA and Tetronic 904, would render them suitable platforms for administration to body cavities.

Evaluation of cement stresses in finite element analyses of cemented orthopaedic implants

Stress analysis of the cement fixation of orthopaedic implants to bone is frequently? carried out using finite element analysis. However, the stress distribution in the cement laver is usually intricate, and it is difficult to report it in a way that facilitates comparison of implants for pre-clinical testing. To study this problem, and make recommendations for stress reporting, a finite element analysis of a hip prosthesis implanted into a synthetic composite femur is developed. Three cases are analyzed: a fully bonded implant, a debonded implant, and a debonded implant where the cement is removed distal to the stein tip. In addition to peak stresses, and contour and vector plots, a stressed volume and probability-of-failure analysis is reported. It is predicted that the peak stress is highest for the debonded stem, and that removal of the distal cement more than halves this peak stress. This would suggest that omission of the distal cement is good for polished prostheses (as practiced for the Exeter design). However; if the percentage of cement stressed above a certain threshold (say 3 MPa) is considered, then the removal of distal cement is shown to be disadvantageous because a higher volume of cement is stressed to above the threshold. Vector plots clearly demonstrate the different load transfer for bonded and debonded prostheses: A bonded stein generates maximum tensile stresses in the longitudinal direction, whereas a debonded stem generates most tensile stresses in the hoop direction, except near the tip where tensile longitudinal stresses occur due to subsidence of the stein. Removal of the cement distal to the tip allows greater subsidence but alleviates these large stresses at the tip, albeit at the expense of increased hoop stresses throughout the mantle. It is concluded that a thorough analysis of cemented implants should not report peak stress, which can be misleading, but rather stressed volume, and that vector plots should be reported if a precise analysis of the load transfer mechanism is required.

An examination of the thermorheological and drug release properties of zinc tetraphenylporphyrin-containing thermoresponsive hydrogels, designed as light activated antimicrobial implants

This study describes the thermorheological, mechanical and drug release properties of novel, light-activated antimicrobial implants. Hydrogels, based on N-isopropylacrylamide (NIPAA) and hydroxyethyl methacryl ate (HEMA) and either devoid of or containing zinc tetraphenylporphyrin, were prepared by free radical polymerisation and characterised using oscillatory rheometry and texture profile analysis. Drug release was studied at both 20 and 37 degrees C. Hydrogels containing NIPAA exhibited a sol-gel temperature (Tin), which increased as the proportion of HEMA increased and was

A review on the use of corneal implants for the treatment of presbyopia

In recent years there has seen an increased interest in refractive surgery for the correction of presbyopia. This can be attributed to a number of factors such as the increased demand from patients to have perfect vision without the need for glasses, spurred on by the success of high street refractive laser surgery. Also the World Health Organisation (WHO) estimated in 2005 that over a 1.04 billion people worldwide are affected by presbyopia (Holden et al. 2008). This vast number of people is valued as a potential market and is a huge enticement to the ophthalmic industry to try and develop devices and products to treat this condition. Recent advances in technology have renewed interest in the implantation of corneal inlays for surgical treatment of presbyopia. Dexl et al. (2011) suggest that the reason for this is the further development of biomaterial technology, advances in femtosecond laser and the need for a reversible presbyopic treatment.

Solvent induced phase inversion-based in situ forming controlled release drug delivery implants

In situ forming (ISF) drug delivery implants have gained tremendous levels of interest over the last few decades. This is due to their wide range of biomedical applications such as in tissue engineering, cell encapsulation, microfluidics, bioengineering and drug delivery. Drug delivery implants forming upon injection has shown a range of advantages which include localized drug delivery, easy and less invasive application, sustained drug action, ability to tailor drug delivery, reduction in side effects associated with systemic delivery and also improved patient compliance and comfort. Different factors such as temperature, pH, ions, and exchange of solvents are involved in in situ implant formation. This review especially focuses on ISF implants that are formed through solvent induced phase inversion (SPI) technique. The article critically reviews and compares a wide range of polymers, solvents, and co-solvents that have been used in SPI implant preparation for control release of a range of drug molecules. Major drawback of SPI systems has been their high burst release. In this regard, the article exhaustively discusses factors that affect the burst release and different modification strategies that has been utilised to reduce the burst effect from these implants. Performance and controversial issues associated with the use of different biocompatible solvents in SPI systems is also discussed. Biodegradation, formulation stability, methods of characterisation and sterilisation techniques of SPI systems is comprehensively reviewed. Furthermore, the review also examines current SPI-based marketed products, their therapeutic application and associated clinical data. It also exemplifies the interest of multi-billion dollar pharma companies worldwide for further developments of SPI systems to a range of therapeutic applications. The authors believe that this will be the first review article that extensively investigate and discusses studies done to date on SPI systems. In so doing, this article will undoubtedly serve as an enlightening tool for the scientists working in the concerned area.

Influence of concrete composition on anchorage bond behavior of prestressing reinforcement

An experimental research addressing the effects of concrete composition and strength on anchorage bond behavior of prestressing reinforcement is presented to clarify the effect of material properties that have appeared contradictory in previous literature. Bond stresses and anchorage lengths have been obtained in twelve concrete mixes made up of different cement contents (C) – 350 to 500 kg/m3 – and water/cement (w/c) ratios – 0.3 to 0.5 – with compressive strength at 24 h ranging from 24 to 55 MPa. A testing technique based on measuring the prestressing force in specimens with different embedment lengths has been used. The results show that anchorage length increases when w/c increases, more significantly when C is higher; the effect of C reveals different trends based on w/c. The obtained anchorage bond stresses are greater for higher concrete compressive strength, and their average ratio of 1.45 with respect to transmission bond stresses implies a potential bond capacity.

Slip distribution model along the anchorage length of prestressing strands

An analytical model to predict strand slips within both transmission and anchorage lengths in pretensioned prestressed concrete members is presented. This model has been derived from an experimental research work by analysing the bond behavior and determining the transmission and anchorage lengths of seven-wire prestressing steel strands in different concrete mixes. A testing technique based on measuring the prestressing strand force in specimens with different embedment lengths has been used. The testing technique allows measurement of free end slip as well as indirect determination of the strand slip at different cross sections of a member without interfering with bond phenomena. The experimental results and the proposed model for strand slip distribution have been compared with theoretical predictions according to different equations in the literature and with experimental results obtained by other researchers. © 2013 Elsevier Ltd.