481 research outputs found
In vitro degradation of a chitosan-based osteochondral construct points to a transient effect on cellular viability
No full textBioresorbable chitosan scaffolds have shown potential for osteochondral repair applications. The in vivo degradation of chitosan, mediated by lysozyme and releasing glucosamine, enables progressive replacement by ingrowing tissue. Here the degradation process of a chitosan-nHA based bioresorbable scaffold was investigated for mass loss, mechanical properties and degradation products released from the scaffold when subjected to clinically relevant enzyme concentrations. The scaffold showed accelerated mass loss during the early stages of degradation but without substantial reduction in mechanical strength or structure deterioration. Although not cytotoxic, the medium in which the scaffold was degraded for over 2 weeks showed a transient decrease in mesenchymal stem cell viability, and the main degradation product (glucosamine) demonstrated a possible adverse effect on viability when added at its peak concentration. This study has implications for the design and biomedical application of chitosan scaffolds, underlining the importance of modelling degradation products to determine suitability for clinical translation
Preclinical biological and physicochemical evaluation of two-photon engineered 3D biomimetic copolymer scaffolds for bone healing
No full textA major challenge in orthopedics is the repair of large non-union bone fractures. A promising therapy for this indication is the use of biodegradable bioinspired biomaterials that stabilize the fracture site, relieve pain and initiate bone formation and healing. This study uses a multidisciplinary evaluation strategy to assess immunogenicity, allergenicity, bone responses and physicochemical properties of a novel biomaterial scaffold. Two-photon stereolithography generated personalized custom-built scaffolds with a repeating 3D structure of Schwarz Primitive minimal surface unit cell with a specific pore size of ∼400 μm from three different methacrylated poly(D,L-lactide-co-ε-caprolactone) copolymers with lactide to caprolactone monomer ratios of 16 : 4, 18 : 2 and 9 : 1. Using in vitro and in vivo assays for bone responses, immunological reactions and degradation dynamics, we found that copolymer composition influenced the scaffold physicochemical and biological properties. The scaffolds with the fastest degradation rate correlated with adverse cellular effects and mechanical stiffness correlated with in vitro osteoblast mineralization. The physicochemical properties also correlated with in vivo bone healing and immune responses. Overall these observations provide compelling support for these scaffolds for bone repair and illustrate the effectiveness of a promising multidisciplinary strategy with great potential for the preclinical evaluation of biomaterials
Manufacture and characterisation of bioresorbable fibre reinforced composite rods and screws for bone fracture fixation applications
No full textBioresorbable implants are an attractive alternative to metallic bone fixation devices and offer potential to eliminate some of the clinical challenges with the latter. This work explores the manufacturing of fully bioresorbable fibre-reinforced composite rods and screws for such applications. Poly lactic acid (PLA) and phosphate glass fibres (PGF) were combined to provide mechanical reinforcement and biocompatibility characteristics. Aligned and randomly reinforced PLA/PGF composites were prepared by compression moulding prior to thermomechanical deformation into rod and screw forms. In vitro degradation and mechanical properties retention were investigated in phosphate buffered saline (PBS) at 37°C. The composite rods and screws exceeded published data for bioresorbable implants in their virgin state and were towards the upper range of cortical bone properties. The properties reduced rapidly in an aqueous medium and this was attributed to matrix plasticisation and fibre/matrix disbonding. The degraded samples maintained strength and stiffness close to the lower limits of the cortical bone. Water uptake and mass loss for composites exceeded equivalent values for PLA alone due to water wicking at the fibre/matrix interface. Ion release tests correlated linearly with mass loss profiles confirming that the dominant degradation mechanism was fibre dissolution. The PLA/PGF composites also exhibited good biocompatibility to human osteosarcoma and human mesenchymal stem cells
Manufacture and characterisation of bioresorbable fibre reinforced composite rods and screws for bone fracture fixation applications
No full textBioresorbable implants are an attractive alternative to metallic bone fixation devices and offer potential to eliminate some of the clinical challenges with the latter. This work explores the manufacturing of fully bioresorbable fibre-reinforced composite rods and screws for such applications. Poly lactic acid (PLA) and phosphate glass fibres (PGF) were combined to provide mechanical reinforcement and biocompatibility characteristics. Aligned and randomly reinforced PLA/PGF composites were prepared by compression moulding prior to thermomechanical deformation into rod and screw forms. In vitro degradation and mechanical properties retention were investigated in phosphate buffered saline (PBS) at 37°C. The composite rods and screws exceeded published data for bioresorbable implants in their virgin state and were towards the upper range of cortical bone properties. The properties reduced rapidly in an aqueous medium and this was attributed to matrix plasticisation and fibre/matrix disbonding. The degraded samples maintained strength and stiffness close to the lower limits of the cortical bone. Water uptake and mass loss for composites exceeded equivalent values for PLA alone due to water wicking at the fibre/matrix interface. Ion release tests correlated linearly with mass loss profiles confirming that the dominant degradation mechanism was fibre dissolution. The PLA/PGF composites also exhibited good biocompatibility to human osteosarcoma and human mesenchymal stem cells.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Functional performance of a bi-layered chitosan-nano-hydroxyapatite osteochondral scaffold: a pre-clinical <i>in vitro</i> tribological study
No full textOsteochondral grafts are used for repair of focal osteochondral lesions. Autologous grafts are the gold standard treatment; however, limited graft availability and donor site morbidity restrict use. Therefore, there is a clinical need for different graft sources/materials which replicate natural cartilage function. Chitosan has been proposed for this application. The aim of this study was to assess the biomechanics and biotribology of a bioresorbable chitosan/chitosan-nano-hydroxyapatite osteochondral construct (OCC), implanted in an in vitro porcine knee experimental simulation model. The OCC implanted in different surgical positions (flush, proud and inverted) was compared to predicate grafts in current clinical use and a positive control consisting of a stainless steel graft implanted proud of the cartilage surface. After 3 h (10 800 cycles) wear simulation under a walking gait, subsidence occurred in all OCC samples irrespective of surgical positioning, but with no apparent loss of material and low meniscus wear. Half the predicate grafts exhibited delamination and scratching of the cartilage surfaces. No graft subsidence occurred in the positive controls but wear and deformation of the meniscus were apparent. Implanting a new chitosan-based OCC either optimally (flush), inverted or proud of the cartilage surface resulted in minimal wear, damage and deformation of the meniscus
What Does It Mean to Say That Procedure Is Political?
No full textProcedure is not the first field of law to face controversy along these lines. Law’s independence from politics, in both its descriptive and normative aspects, is a century long legal challenge.9 This Article aims to clarify what we mean when we characterize procedure as political, as well as to understand some of the harms generated by failing to confront and acknowledge the political. This is a preliminary step in approaching future formulations of procedural rules if they cannot be depoliticized
Multi-regression analysis between stable isotope composition and hydrochemical parameters in karst springs to provide insights into groundwater origin and subsurface processes: regional application to Lebanon
No full textJoint applications of isotope characterization using δ2H, δ18O and geochemical analyses have allowed for a better conceptualization of hydrological systems and helped in the evaluation and management of water resources. Processes of infiltration, and evapotranspiration (ETP), as well as mixing in the unsaturated zone, incur changes in the meteoric δ2H-δ18O signal that is transferred to groundwater during recharge. Previous studies on the isotopic composition of atmospheric precipitation highlight the importance of rainwater differentiation in terms of chemical composition and isotopic signature as a function of topographical and orographic variations as well as natural and anthropogenic impacts and identified altitude gradients for both δ2H and δ18O. In this work, a comparative correlative analysis of stable oxygen and deuterium isotopes was conducted on selected Lebanese springs. At the first stage, a hydrochemical analysis allowed the characterization of the springs and their clustering according to their predominant ionic content and aquifer units. Additionally, a multi-regression analysis reveals a relationship between hydrogen and oxygen isotopes and other easily measured parameters at the spring such as temperature, electrical conductivity, elevation, and easting and northing. The obtained relationship validated on a second campaign was attributed qualitatively to the extent and elevation of the spring catchment, the depth of flow, mixing, the snow effect, and residence time. Moreover, outliers characterized by a very large catchment area or allochthonous recharge could be outlined in the set of investigated springs. The results show that the stable isotopic signature indicative of recharge areas can be inferred based on easily measured spring parameters and can, therefore, help in the identification of protection zones and direct areas of spring recharge from a regional dataset. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature
Tubular Scaffold with Shape Recovery Effect for Cell Guide Applications
No full textTubular scaffolds with aligned polylactic acid (PLA) fibres were fabricated for cell guide applications by immersing rolled PLA fibre mats into a polyvinyl acetate (PVAc) solution to bind the mats. The PVAc solution was also mixed with up to 30 wt % β-tricalcium phosphate (β-TCP) content. Cross-sectional images of the scaffold materials obtained via scanning electron microscopy (SEM) revealed the aligned fibre morphology along with a significant number of voids in between the bundles of fibres. The addition of β-TCP into the scaffolds played an important role in increasing the void content from 17.1% to 25.3% for the 30 wt % β-TCP loading, which was measured via micro-CT (µCT) analysis. Furthermore, µCT analyses revealed the distribution of aggregated β-TCP particles in between the various PLA fibre layers of the scaffold. The compressive modulus properties of the scaffolds increased from 66 MPa to 83 MPa and the compressive strength properties decreased from 67 MPa to 41 MPa for the 30 wt % β-TCP content scaffold. The scaffolds produced were observed to change into a soft and flexible form which demonstrated shape recovery properties after immersion in phosphate buffered saline (PBS) media at 37 °C for 24 h. The cytocompatibility studies (using MG-63 human osteosarcoma cell line) revealed preferential cell proliferation along the longitudinal direction of the fibres as compared to the control tissue culture plastic. The manufacturing process highlighted above reveals a simple process for inducing controlled cell alignment and varying porosity features within tubular scaffolds for potential tissue engineering applications
Lokalne oblasti kot subjekti zagotavljanja javnega reda in miru
No full textPurpose:
This paper deals with the legal regulation of Estonia’s public order from the aspect of local governments. The purpose of the article is to analyse relevant Estonian legislation to help identify problems and make suggestions for improvement. Proposals are intended for the institutions involved in developing legislation in Estonia. Local governments in the country act according to the Constitution of the Republic of Estonia (1992), but still retain enough legal autonomy to decide on local affairs independently of the state government.
Methods:
The paper is based on an analysis of national legislation. In the legal research, the author pays attention to written sources of law, e.g. the Constitution of the Republic of Estonia (1992), and subsequent legal acts regulating public order.
Findings:
The main task of local government is to provide public services and improve the quality of the living environment. In Estonia, the principal provider of internal security is the Police and Border Guard Board. It is the responsibility of local government to assist the national structures in fulfilling their duties. On the other hand, the municipalities are required to ensure public order within their territories. The legal power given by parliament to local governments to carry out such activities is insufficient to ensure the law is enforced.
Practical Implications:
The findings in this paper highlight areas in which the legal regulation could be improved.
Originality/Value:
Although the legal basis for Estonian municipalities’ operations has been studied carefully, it is necessary to examine issues concerning the links between local governments and public order in detail. The continually changing legislation makes the situation complex to handle. It also provides an opportunity for international comparative analysis with other European Union member states.Namen prispevka:
Prispevek prikazuje estonsko pravno podlago zagotavljanja javnega reda in miru z vidika lokalnih oblasti. Namen prispevka je analizirati veljavno zakonodajo, identificirati težave in pripraviti predloge za izboljšave. Predlogi izboljšav so namenjeni institucijam, zadolženim za pripravo estonske zakonodaje. Lokalne oblasti sicer delujejo v skladu z estonsko ustavo, vendar imajo tudi določeno mero pravne avtonomije.
Metode:
Prispevek temelji na analizi nacionalne zakonodaje, predvsem ustave in zakonskih predpisov, ki urejajo področje javnega reda in miru.
Ugotovitve:
Glavna naloga lokalnih oblasti je zagotavljanje javnih storitev in čim večje kakovosti bivalnega okolja. Notranjo varnost v Estoniji zagotavlja policija (angl. Police and Border Guard Board), lokalne oblasti pa sodelujejo pri izpolnjevanju varnostnih nalog državnih organov ter hkrati zagotavljajo javni red in mir na svojem območju. Pooblastila lokalnih oblasti za izvajanje teh dejavnosti niso zadostna.
Praktična uporabnost:
Ugotovitve prispevka lahko pripomorejo k izboljšanju pravne ureditve.
Izvirnost/pomembnost prispevka:
V prispevku je predstavljena pravna podlaga za delovanje lokalnih oblasti na področju zagotavljanja javnega reda in miru, ki je zaradi nenehnih sprememb zakonodaje na tem področju precej zapletena. Prispevek predstavlja tudi osnovo za nadaljnjo primerjalno analizo z drugimi članicami Evropske unije
A review of natural fibres and biopolymer composites : progress, limitations, and enhancement strategies
No full textThe interest in natural fibres and biopolymers for developing bio-composites has greatly increased in recent years, motivated by the need to reduce the environmental impact of traditional synthetic, fossil fuel-derived materials. However, several limitations associated with the use of natural fibres and polymers should be addressed if they are to be seriously considered mainstream fibre reinforcements. These include poor compatibility of natural fibres with polymer matrices, variability, high moisture absorption, and flammability. Various surface treatments have been studied to tackle these drawbacks, such as alkalisation, silane treatment, acetylation, plasma treatment, and polydopamine coating. This review paper considers the classification, properties, and limitations of natural fibres and biopolymers in the context of bio-composite materials. An overview of recent advancements and enhancement strategies to overcome such limitations will also be discussed, with a focus on mechanical performance, moisture absorption behaviour, and flammability of composites. The limitations of natural fibres, biopolymers, and their bio-composites should be carefully addressed to enable the widespread use of bio-composites in various applications, including electronics, automotive, and construction
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