Optimisation and feature selection of poly-beta-amino-ester as a drug delivery system for cartilage

Drug localisation is still one of the main challenges in treating pathologies affecting cartilage; poly-beta-amino-esters (PBAEs) drug conjugates are a possible solution; however, their efficacy highly depends on the polymer structure hence the full potential of this delivery system is still unknown. For the purpose of optimising the delivery system design, a large library of PBAEs was synthesised and dexamethasone (DEX) uptake in cartilage was determined. All three components of PBAE (amine, acrylate and end-capping) impacted the outcome. The most effective PBAE identified enhanced DEX uptake by 8 folds compared to an equivalent dose of the commercial formulation and also prevented, through delivery of DEX, the cartilage degradation caused by IL-1α (interleukine1α). A chemometrics based predictive model was constructed and PBAEs properties most affecting the performance of the drug delivery systems were identified. This model will allow further computer based PBAEs optimisation and fast track the bench to market process for this delivery system

An injectable hydrogel as bone graft material with added antimicrobial properties

Currently, the technique which provides the best chances for a successful bone graft, is the use of bone tissue from the same patient receiving it (autograft); the main limitations are the limited availability and the risks involved in removing living bone tissue, for example, explant site pain and morbidity. Allografts and xenografts may overcome these limitations; however, they increase the risk of rejection. For all these reasons the development of an artificial bone graft material is particularly important and hydrogels are a promising alternative for bone regeneration. Gels were prepared using 1,4-butanediol diacrylate as crosslinker and alpha tricalciumphosphate; ZnCl2 and SrCl2 were added to the aqueous phase. MTT results demonstrated that the addition of strontium had a beneficial effect on the osteoblast cells density on hydrogels, and zinc instead did not increase osteoblast proliferation. The amount of calcium produced by the osteoblast cells quantified through the Alizarin Red protocol revealed that both strontium and zinc positively influenced the formation of calcium; furthermore, their effect was synergistic. Rheology properties were used to mechanically characterize the hydrogels and especially the influence of crosslinker's concentration on them, showing the hydrogels presented had extremely good mechanical properties. Furthermore, the antimicrobial activity of strontium and zinc in the hydrogels against methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis was determine

Lethal photosensitisation of bacteria using Silica-TBO nanoconjugates

Pathogenic microorganisms are gradually becoming resistant to antibiotics, thereby novel antimicrobial technologies are urgently needed. Photodynamic therapy (PDT) is a process that employs the energy of photons to generate reactive oxygen species through a class a chemicals known as photosensitisers. PDT has shown antimicrobial activity as the oxygen reactive species can inactivate microorganisms, at the same time, the doses required to provide antimicrobial actions are not lethal to mammalian cells. We covalently bound Toluidine blue O (TBO), a very common and safe photosensitiser, to silica nanoparticles. The conjugates exhibited antimicrobial activity against MRSA, S. epidermidis and E. coli when irradiated with laser light at 630 nm. Using a light source with a power of 500 mW the bacterial reduction exhibited a dose-response behaviour and it was 2 log10 for S. epidermidis and E. coli after 2 and 3 min, respectively. No antimicrobial activity was exhibited by the unconjugated nanoparticles or by the laser light alone. The release of TBO from the nanoparticles was pH dependent with higher amounts of photosensitisers detected at pH = 4 than pH = 7 consistent with the formation of amide bonds between nanoparticles and TBO. The light activated nanoparticles developed in this work offer a platform for the controlled delivery of TBO through a pH responsive mechanism for antimicrobial applications

Poly-beta-amino-esters nano-vehicles based drug delivery system for cartilage

The efficient delivery of therapeutic molecules to the cartilage of joints is major obstacle in developing useful therapeutic interventions; hence, a targeted drug delivery system for this tissue is critical. We have overcome the challenge by developing a system that employs electrostatic attraction between the negatively charged constituents of cartilage and a positively charged polymer, poly-beta amino esters (PBAEs). We have demonstrated cartilage uptake of dexamethasone (DEX) covalently bound to the PBAE was doubled and retention in tissues prolonged compared to the equivalent dose of the commercial drug formulation. Moreover, no adverse effects on chondrocytes were found. Our data also show that PBAEs can bind not only healthy cartilage tissues but also enzymatically treated cartilage mimicking early stages of OA. Our PBAEs-prodrug technology's advantages are fourfold; the specificity and efficacy of its targeting mechanism for cartilage, the ease of its production and the low-cost nature of the delivery system

Risk equations for prosthetic joint infections (PJIs) in UK: a retrospective study using the Clinical Practice Research Datalink (CPRD) AURUM and GOLD databases

Background: Prosthetic joint infections (PJIs) are a serious negative outcome of arthroplasty with incidence of about 1%. Risk of PJI could depend on local treatment policies and guidelines; no UK-specific risk scoring is currently available. Objective: To determine a risk quantification model for the development of PJI using electronic health records. Design: Records in Clinical Practice Research Datalink (CPRD) GOLD and AURUM of patients undergoing hip or knee arthroplasty between January 2007 and December 2014, with linkage to Hospital Episode Statistics and Office of National Statistics, were obtained. Cohorts’ characteristics and risk equations through parametric models were developed and compared between the two databases. Pooled cohort risk equations were determined for the UK population and simplified through stepwise selection. Results: After applying the inclusion/exclusion criteria, 174 905 joints (1021 developed PJI) were identified in CPRD AURUM and 48 419 joints (228 developed PJI) in CPRD GOLD. Patients undergoing hip or knee arthroplasty in both databases exhibited different sociodemographic characteristics and medical/drug history. However, the quantification of the impact of such covariates (coefficients of parametric models fitted to the survival curves) on the risk of PJI between the two cohorts was not statistically significant. The log-normal model fitted to the pooled cohorts after stepwise selection had a C-statistic >0.7. Conclusions: The risk prediction tool developed here could help prevent PJI through identifying modifiable risk factors pre-surgery and identifying the patients most likely to benefit from close monitoring/preventive actions. As derived from the UK population, such tool will help the National Health Service reduce the impact of PJI on its resources and patient lives

Feasibility and application of machine learning enabled fast screening of poly-beta-amino-esters for cartilage therapies

Despite the large prevalence of diseases affecting cartilage (e.g. knee osteoarthritis affecting 16% of population globally), no curative treatments are available because of the limited capacity of drugs to localise in such tissue caused by low vascularisation and electrostatic repulsion. While an effective delivery system is sought, the only option is using high drug doses that can lead to systemic side effects. We introduced poly-beta-amino-esters (PBAEs) to effectively deliver drugs into cartilage tissues. PBAEs are copolymer of amines and di-acrylates further end-capped with other amine; therefore encompassing a very large research space for the identification of optimal candidates. In order to accelerate the screening of all possible PBAEs, the results of a small pool of polymers (n = 90) were used to train a variety of machine learning (ML) methods using only polymers properties available in public libraries or estimated from the chemical structure. Bagged multivariate adaptive regression splines (MARS) returned the best predictive performance and was used on the remaining (n = 3915) possible PBAEs resulting in the recognition of pivotal features; a further round of screening was carried out on PBAEs (n = 150) with small variations of structure of the main candidates from the first round. The refinements of such characteristics enabled the identification of a leading candidate predicted to improve drug uptake > 20 folds over conventional clinical treatment; this uptake improvement was also experimentally confirmed. This work highlights the potential of ML to accelerate biomaterials development by efficiently extracting information from a limited experimental dataset thus allowing patients to benefit earlier from a new technology and at a lower price. Such roadmap could also be applied for other drug/materials development where optimisation would normally be approached through combinatorial chemistry

Rheometer enabled study of cartilage frequency-dependent properties

Despite the well-established dependence of cartilage mechanical properties on the frequency of the applied load, most research in the field is carried out in either load-free or constant load conditions because of the complexity of the equipment required for the determination of time-dependent properties. These simpler analyses provide a limited representation of cartilage properties thus greatly reducing the impact of the information gathered hindering the understanding of the mechanisms involved in this tissue replacement, development and pathology. More complex techniques could represent better investigative methods, but their uptake in cartilage research is limited by the highly specialised training required and cost of the equipment. There is, therefore, a clear need for alternative experimental approaches to cartilage testing to be deployed in research and clinical settings using more user-friendly and financial accessible devices. Frequency dependent material properties can be determined through rheometry that is an easy to use requiring a relatively inexpensive device; we present how a commercial rheometer can be adapted to determine the viscoelastic properties of articular cartilage. Frequency-sweep tests were run at various applied normal loads on immature, mature and trypsinased (as model of osteoarthritis) cartilage samples to determine the dynamic shear moduli (G*, G′ G″) of the tissues. Moduli increased with increasing frequency and applied load; mature cartilage had generally the highest moduli and GAG depleted samples the lowest. Hydraulic permeability (KH) was estimated from the rheological data and decreased with applied load; GAG depleted cartilage exhibited higher hydraulic permeability than either immature or mature tissues. The rheometer-based methodology developed was validated by the close comparison of the rheometer-obtained cartilage characteristics (G*, G′, G″, KH) with results obtained with more complex testing techniques available in literature. Rheometry is relatively simpler and does not require highly capital intensive machinery and staff training is more accessible; thus the use of a rheometer would represent a cost-effective approach for the determination of frequency-dependent properties of cartilage for more comprehensive and impactful results for both healthcare professional and R&D

Multi-asperity elliptical JKR model for adhesion of a surface with non-axially symmetric asperities

Surfaces can present high levels of topographic asymmetry and, therefore, theories based on the assumption of symmetry cannot be effectively employed. A new multi-asperity adhesion model that assumes that asperities are not perfectly hemispherical is presented here, this model is based on the elliptical JKR model for a single asperity. The adhesion between a soft tissue with asperities greatly asymmetric and a polymer was modelled, the predicted adhesion forces were successfully validated against experimentally obtained data. Moreover, simulations with a simpler model, which assumes symmetrical asperities, have been also carried out; these results were significantly different from those obtained, using both the newly developed model and those determined experimentally. This highlights the importance of the model presented in this work

Boron mass transfer during seeded microfiltration.

Seeded microfiltration combines the processes of microfiltration and sorption of a solute onto a solid particle, including ion exchange. The process can be performed for investigations in simple stirred cells, for laboratory mass transfer analysis, and for process-scale applications in crossflow filtration systems. Seeded microfiltration of boron at feed concentrations of up to 4 ppm using a N-glucamine type ion exchange resin showed that the process was dependent on the internal diffusion of boron inside the resin particle, with an effective particle diffusivity of 5.5 x 10−10m2 s−1. The kinetics of the process were modelled by a coupled mass transfer model, based on a well mixed stirred system, aqueous film diffusion, particle diffusion and a Langmuir type isotherm for the equilibrium conditions. The modelling suggests that a resin particle diameter of 50μm would provide improved boron extraction performance, whilst easily being retained within the microfiltration process. A comparison of the analysis of mass transfer between a conventional batch stirred cell and the continuously fed seeded microfiltration system shows that the continuously fed system has many advantages for the laboratory investigation of mass transfer parameters

Detachment of Listeria innocua and Pantoea agglomerans from cylinders of agar and potato tissue under conditions of Couette flow

Cylinders of raw potato or agar were contacted with suspensions of Listeria innocua and Pantoea agglomerans and then used as replacement rotors in a rheometer in order to investigate detachment under the influence of known shear forces. These shear forces were functions solely of the rotational speed of the rotor and the fluid (glycerol) in which the cylinders were caused to rotate. With this system surface shear forces ranging from 1.3 to 125 Pa could be generated corresponding to rotational speeds of 12.5 to 775 rpm. Under these conditions detachment phenomena were quite rapid with in most cases complete detachment being achieved over timescales of the order of 30 s. In general, lower shear forces were required to detach L. innocua from both agar and potato. For agar cylinders an applied shear force of only 1.3 Pa was sufficient to achieve 98 % detachment of L. innocua after 20 s. By contrast, relatively high shear forces were required to detach P. agglomerans particularly from potato; under an applied shear force of 2.8 Pa only 9.5 % detachment was achieved after 30 s. The results obtained at the highest shear forces studied here (125 Pa) with potato cylinders were suggestive of mass transfer into glycerol of one or more constituents present in potatoes that caused detached cells to aggregate causing an apparent decrease in percentage detachment. The data obtained could be used as a basis for the rational design of washing processes for fresh ready to eat food products