New prebiotic chemistry inspired filter media for stormwater/greywater disinfection

Greywater and stormwater have received significant attention due to increasing water scarcity. Passive filtration such as biofiltration has been a popular treatment method with its low energy input and environmental friendliness. However, pathogen removal capacity needs improvement to achieve safe water quality. In this study, a prebiotic chemistry inspired copolymer based on aminomalononitrile and 3,4,5-trihydroxybenzaldehyde (AMNT30) was introduced to develop antimicrobial media for passive filtration. The AMNT30 polymer provided an adhesive coating on zeolite substrates following a spontaneous polymerisation process at room temperature. AMNT30 coated media were investigated for metal loading capacity, surface morphology, E. coli removal and metal leaching after filtration of different water sources (i.e. stormwater, greywater, and deionised water) at low/high conductivity. The coating enhanced metal ion loading on the surface and demonstrated that >8 log reduction of E. coli can be achieved for silver loaded materials compared to a 1 log reduction for copper loaded materials. The coating also increased the stability of the metals on the media irrespective of inflow characteristics. This study provided the first example using AMNT30 to create antimicrobial water purification media. It is expected that this technology will find applications in the water treatment industry.

Biological responses of human osteoblasts and osteoclasts to flame-sprayed coatings of hydroxyapatite and fluorapatite blends

The aim of this study was to determine how the activities of human osteoblastic cells and osteoclasts respond to substrates of thermal-sprayed mechanical blends of hydroxyapatite and fluorapatite with a view of determining an optimal blend ratio for osseointegration. Human osteoblastic cells and osteoclasts were grown on titanium alloy discs coated with blends of hydroxyapatite and fluorapatite, with concentrations ranging from 0 to 100% fluorapatite. Human osteoblastic cells attached in greater numbers and proliferated at a greater rate on blends containing 40% fluorapatite. Human osteoblastic cells grown on blends containing 40% fluorapatite for 7 days also expressed the highest levels of mRNA for several proteins involved with regulating bone metabolism (osteoprotegerin and receptor activator nuclear factor kappa B ligand), and bone formation (osteopontin, osteonectin and bone sialoprotein 1). Osteoclasts resorbed the dentine but poorly resorbed the hydroxyapatite-fluorapatite blends, particularly at high levels of fluorapatite. This in vitro study demonstrates that thermal-sprayed hydroxyapatitecoatings containing 40% fluorapatite may promote optimal bone growth and improve osseointegration of implants.

Patterned and switchable surfaces for biomolecular manipulation

The interactions of biomolecules and cells with solid interfaces play a pivotal role in a range of biomedical applications and have therefore been studied in great detail. An improved understanding of these interactions results in the ability to manipulate DNA, proteins and other biomolecules, as well as cells, spatially and temporally at surfaces with high precision. This in turn engenders the development of advanced devices, such as biosensors, bioelectronic components, smart biomaterials and microarrays. Spatial control can be achieved by the production of patterned surface chemistries using modern high-resolution patterning technologies based on lithography, microprinting or microfluidics, whilst temporal control is accessible through the application of switchable surface architectures. The combination of these two surface properties offers unprecedented control over the behaviour of biomolecules and cells at the solid-liquid interface. This review discusses the behaviour of biomolecules and cells at solid interfaces and highlights fundamental and applied research exploring patterned and switchable surfaces.

Synthetic biodegradable microparticles for articular cartilage tissue engineering

Articular cartilage tissue engineering procedures require the transplantation of chondrocytes that have been expanded in vitro. The expansion is carried out for a considerable time and can lead to a modulation of cell phenotype. However, microcarrier cultures have been shown to allow cell expansion while maintaining the phenotype. Here, we have used the biodegradable polyester poly(lactide-co-glycolide) (PLGA) in the form of microspheres and irregular shaped microparticles with a diameter between 47 and 210 microm. Surface modification of particles was carried out by ammonia plasma treatment and subsequent adsorption of collagen. Alternatively, particles were modified by partial hydrolysis and subsequent immobilization of an amine-terminated dendrimer. Each surface modification step was characterized by X-ray photoelectron spectroscopy. The effectiveness of the surface modification procedures was demonstrated by in vitro cell culture experiments using sheep articular cartilage chondrocytes. A significant influence of both the particle shape and the surface chemistry on the proliferation rate was observed while the phenotype was maintained independent of the surface chemistry or particle shape. Chondrocytes cultured on PLGA microspheres were further assessed for cartilage tissue formation in collagen type I gels in nude mice. The tissue that were formed showed the appearance of a hyaline-like cartilage and the presence of the microspheres substantially reduced the degree of collagen gel contraction over 1-2 months.

The control of Staphylococcus epidermidis biofilm formation and in vivo infection rates by covalently bound furanones

In order to overcome the continuing infection rate associated with biomaterials, the use of covalently bound furanones as an antibiofilm coating for biomaterials has been investigated. Furanones have previously been shown to inhibit growth of Gram-positive and Gram-negative bacteria. The aim of these studies were to covalently bind furanones to polymers and to test their efficacy for inhibiting biofilm formation of Staphylococcus epidermidis and in vivo infection rate. Two methods of covalent attachment of furanones were used. The first, a co-polymerisation with a styrene polymer, and second, a plasma-1-ethyl-3-(dimethylaminopropyl) carbodiimide (EDC) reaction to produce furanone-coated catheters. Biofilm formation by S. epidermidis in vitro was inhibited by 89% for polystryene-furanone disks and by 78% by furanone-coated catheters (p<0.01). In an in vivo sheep model we found furanones were effective at controlling infection for up to 65 days. Furanones have potential to be used as a coating for biomaterials to control infection caused by S. epidermidis.

High density binding of proteins and peptides to poly(D,L-lactide) grafted with polyacrylic acid

The use of graft polymers for the functionalisation of biomaterial surfaces is already widespread. We investigated the adsorptive and covalent binding of a variety of proteins and peptides to poly(D,L-lactide) grafted with polyacrylic acid. Covalent attachment was achieved through coupling of amino groups of the protein/peptide to the carboxyl groups of the graft polymer by using a water-soluble carbodiimide and N-hydroxysuccinimide. Binding densities were determined by automated amino acid analysis after acid hydrolysis of both the poly(D,L-lactide) and the adsorbed and covalently bound proteins. Experiments in the absence and presence of the coupling reagents allow to discriminate between adsorptive and covalent binding. Although the adsorptivc binding is quite substantial in absolute terms, the amount of adsorbed protein is relatively low as compared to the total amount of bound protein. Total binding densities of 20-30 microg/cm2 can easily be achieved. Depending on the concentration and on the properties of the proteins and peptides, between 5% and 80% of the totally bound protein may be physically adsorbed. Densities expressed in molecules/10 nm2 vary from 0.5 molecule fibronectin to 2,000 laminin-peptide molecules: their binding densities clearly correlate with their respective molecular masses. Obviously, the binding densities are governed by their individual three-dimensional space requirements rather than the density of the available carboxyl groups. From the number of carboxyl groups/10 nm2 (18,000-30,000 COOH/10 nm2) the average length of the acrylic acid graft polymer molecules was estimated. Based on the assumption that about 10 copolymer chains can be accommodated on 10 nm2, the average length of the polymer chains, which corresponds to the thickness of the graft phase, is estimated to be 0.5-1 microm. The organisation of the proteins and peptides within the polyacrylic acid phase was further investigated by experiments in which a protein (BSA) and a peptide (Val-Lys) were allowed to react in either a singular, a consecutive or a simultaneous way. Together with XPS and IR-ATR surface characterisation experiments a three-dimensional picture of the arrangement of the immobilised proteins and peptides within the graft polymer phase emerges.

Development of a new biodegradable intravascular polymer stent with simultaneous incorporation of bioactive substances

OBJECTIVE

Due to the thrombogenicity and permanent implant nature of metallic stents, bioresorable synthetic polymers have been proposed for stents and local drug delivery systems. Bioresorbable polyesters like poly(D,L-lactide) demonstrated excellent biocompatibility in various tissues. This paper describes a novel method for the molding of these polymers. The specific CESP-process (Controlled Expansion of Saturated Polymers) is characterised by the use of the plasticizer carbon dioxide and allows the incorporation of bioactive substances at physiologic temperatures into the polymer bulk and the production of complex designed implants.

METHODS

The CESP-process is characterised by the exposure of an amorphous polymer to an inert gas at high pressure with a significant lower glass transition point. The plasticizing effect makes it possible to process polylactides at a temperature close to room temperature. The low process temperature constitutes a key advantage for thermally sensitive polymers and allows the incorporation of thermally sensitive pharmaceutical additives. To obtain some preliminary information on the biocompatibility, in vitro cell toxicity testing as well as drug release assessment was performed.

RESULTS

Different polymer sheets were produced using the CESP-process. Cytotoxicity was not observed in any molded polymer material. According to the mechanical and biocompatibility results Poly(D,L-lactide) (P-DL-LA) was investigated in the CESP-process. Finite element analysis was used to test the possible geometry of an adequate stent. A helical design was chosen and a stent-prototype was produced using the CESP-process. Peroxidase activity as an incorporated marker enzyme could be measured over 6 weeks. Different drug release profiles were obtained due to various pore sizes of the polymer.

CONCLUSIONS

The new CESP-process can be used to process biodegradable polymers and to mold different stent geometries without inducing cytotoxic effects to the material. Furthermore, this procedure permits the simultaneous incorporation of bioactive substances during the molding process. Drug release kinetics can be regulated by different pore sizes of the material.

Biocompatibility, cell adhesion, and degradation of surface-modified biodegradable polymers designed for the upper urinary tract

OBJECTIVES

The aim of this study was to develop a short bioresorbable ureteric stent and to characterize polymers and their surface modifications with respect to biocompatibility, degradation kinetics, cell adhesion properties, and incorporation of biologically active substances. Poly(D,L-lactide) PDLLA, poly(D,L-lactide-co-glycolide) PDLLA-co-GLY, and poly(D,L-lactide-co-trimethylenecarbonate) PDLLA-co-TMC were chosen as basic polymers. Surface modification was performed by plasma-induced graft polymerization and included grafting with hydroxyethylmethacrylate (HEMA), oligo(ethyleneoxide)-monomethacrylate (OEOMA), and acrylic acid (AAC). Biocompatibility of the polymers was assessed in vitro applying parameters of cell morphology, proliferative activity, and cell adhesion. All polymers were biocompatible and exerted no toxic effect on urothelial cell lines and on primary human urothelial cell cultures. A markedly reduced cell adhesion could be achieved in polymers grafted with HEMA, OEOMA, and AAC. Our results indicate that surface modification of bioresorbable polymers by grafting with HEMA, OEOMA, or AAC is an efficient approach to improve surface properties with respect to biocompatibility and cell adhesion properties.

Development of a biodegradable ureteric stent: surface modification and in vitro assessment

The aim of the present study was to develop a short bioresorbable ureteric stent and to characterize the chosen polymers with respect to surface modification, biocompatibility, and loading of a biologically active compound. As materials for the stent, poly(D,L-lactide) and poly(D,L-lactide-co-glycolide) were chosen. Degradation experiments were carried out and analytical data were obtained by contact angle measurement, X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy in the attenuated reflection mode (FTIR-ATR). Gas loading technology was used to incorporate biologically active compounds, and biocompatibility of the polymers was assessed by in vitro cellular assays, applying measures such as cell morphology, proliferative activity, and membrane integrity. Our results indicate that surface modification of bioresorbable polymers is a suitable and efficient approach to improve the surface properties. Incorporation of biologically active compounds was possible without loss of activity, and in vitro assessment of cellular responses demonstrated the biocompatibility of the chosen polymers and modifications.