Prevention of plasticizer leaching from PVC medical devices by using organic–inorganic hybrid coatings

Environmental-friendly extraction of di(2-ethylhexyl) phthalate from poly(vinyl chloride) using liquefied dimethyl ether

Poly(vinyl chloride) (PVC) is one of the most widely used plastics. However, a major challenge in recycling PVC is that there is no economical method to separate and remove its toxic phthalate plasticizers. This research made a breakthrough by extracting PVC with liquefied dimethyl ether (DME) and successfully separating the plasticizer components. Nearly all (97.1 %) of the di(2-ethylhexyl) phthalate plasticizer was extracted within 30 min by passing liquefied DME (285 g) through PVC at 25 °C. The compatibility of PVC with organic solvents, including liquefied DME, was derived theoretically from their Hansen solubility parameters (HSP), and actual dissolution experiments were conducted to determine the optimal PVC solvents. A liquefied DME mixture was used to dissolve PVC, and the extract was diluted with ethanol to precipitate the dissolved PVC. We demonstrated that liquefied DME is a promising method for producing high quality recycled products and that the process retains the fundamental properties of plasticizers and PVC without inducing degradation or depolymerization. Because of its low boiling point, DME can be easily separated from the solute after extraction, allowing for efficient reuse of the solvent, extracted plasticizer, and PVC. DME does not require heat and produces little harmful wastewater, which significantly reduces the energy consumption of the plasticizer additive separation process.

Fluorination of PVC medical devices to prevent plasticizers migration

Medical devices (MD) are often made of plasticized polyvinylchloride (PVC). However, plasticizers may leach out into infused solutions and expose the patients to a toxic risk. The aim of the present work is to fluorinate plasticized PVC tubular MDs to create a barrier layer on their internal surface, and to study the impact of such a chemical treatment on the migration of the plasticizers. Following fluorination by pure molecular fluorine, the physico-chemical characterization of these modified MDs was carried out using various spectroscopic and microscopic techniques or tensile tests, evidencing the formation of covalent C-F bonds on the surface of the treated samples without modification of their mechanical and optical properties. The migration of plasticizers from fluorinated MDs was assessed using gas chromatography coupled with mass spectrometry and was found considerably decreased in comparison with the pristine MDs. After 24 h, the amount of tri-octyltrimellitate plasticizer (TOTM) detected in migrates from fluorinated MDs was even lower than the limit of quantification. Complementary cytotoxicity assays were performed according to the ISO EN 10993-5 standard, showing that the new fluorinated material does not cause a cytotoxic effect on L929 cells.

Sheathed fixation improves BASHTI technique in an anterior cruciate ligament reconstruction

Bone and Site Hold Tendon Inside (BASHTI) technique is an implant-less surgical methodology used for anterior cruciate ligament (ACL) reconstruction. It has some clinical advantages, such as speeding up the healing process. Since the force required to insert the core bone inside the tunnel may damage the core bone and affect the fixation process, the study aims to investigate the strength of fixation of BASHTI technique using proposed sheathed core bones. Experimental tests were performed to evaluate the biomechanical strength of the fixation. Synthetic bone combined with bovine tendons as a graft was used. Polymers were used to create the sheath for mechanical testing. The results showed that fixation strength and stiffness in PTFE sheath with 0.1 mm were 343.86 N and 114.62 N/mm and in PVC sheath with similar thickness, 235.95 N, and 93.36 N/mm. Subsequently, 0.2 mm PTFE sheaths were tested in two different sections: incomplete fixation and complete fixation. The strength and stiffness of the first section were 221.6 N and 66.99 N/mm and for the second section 420.02 N and 126.16 N/mm. Using sheath facilitates the fixation process in BASHTI technique. The 0.1 mm PTFE sheath and 0.2 mm PTFE sheath with complete fixation provide higher fixation strength than other groups. The outcome showed that engaged length has a direct effect on the fixation strength. The BASHTI technique offers an implant-less organic ACL reconstruction method that can improve the fixation method and speed up the healing process.

Bioactive glass-based organic/inorganic hybrids: an analysis of the current trends in polymer design and selection

Bioactive glass-based organic/inorganic hybrids are a family of materials holding great promise in the biomedical field. Developed from bioactive glasses following recent advances in sol-gel and polymer chemistry, they can overcome many limitations of traditional composites typically used in bone repair and orthopedics. Thanks to their unique molecular structure, hybrids are often characterized by synergistic properties that go beyond a mere combination of their two components; it is possible to synthesize materials with a wide variety of mechanical and biological properties. The polymeric component, in particular, can be tailored to prepare tough, load-bearing materials, or rubber-like elastomers. It can also be a key factor in the determination of a wide range of interesting biological properties. In addition, polymers can also be used within hybrids as carriers for therapeutic ions (although this is normally the role of silica). This review offers a brief look into the history of hybrids, from the discovery of bioactive glasses to the latest developments, with a particular emphasis on polymer design and chemistry. First the benefits and limitations of hybrids will be discussed and compared with those of alternative approaches (for instance, nanocomposites). Then, key advances in the field will be presented focusing on the polymeric component: its chemistry, its physicochemical and biological advantages, its drawbacks, and selected applications. Comprehensive tables summarizing all the polymers used to date to fabricate sol-gel hybrids for biomedical applications are also provided, to offer a handbook of all the available candidates for hybrid synthesis. In addition to the current trends, open challenges and possible avenues of future development are proposed.

Modelling and assessment of plasticizer migration and structure changes in hydrophobic starch-based films

The structures of starch and starch-based materials determine additives migration from material matrix. Propionylated starch derived from waxy, normal, G50 and G80 starch were selected as the matrix, the amylose effect on plasticizer (triacetin) migration as well as structural changes in hydrophobic starch-based films were discussed. The constant (k₁) of first-order rate and initial release rate (V₀) of triacetin migration were consistent with the increment of amylose content. Meanwhile, diffusion model disclosed that Fick's second law was apposite to characterize the short-term migration of triacetin, and larger diffusion coefficient (D) values of short- and long-term migration were also found in films with higher amylose content, indicating that amylose-formed structures were in favor of triacetin migration. In comparison of propionylated amylopectin, Van der Waals's interactions between propionylated amylose and triacetin were easier to be weakened with the migration of triacetin, which promoted the decrease of wavenumber of C-O-C, and enlarged the inter-planner spacing of crystalline structures, promoting the formation of amorphous structures and wrinkles and embossments in films with higher amylose content. This work confirmed that regulating the structures of starch were effective to control the migration behavior of additives from starch-based films.

Sustained Calcium(II)-Release to Impart Bioactivity in Hybrid Glass Scaffolds for Bone Tissue Engineering

In this study, we integrated different calcium sources into sol-gel hybrid glass scaffolds with the aim of producing implants with long-lasting calcium release while maintaining mechanical strength of the implant. Calcium(II)-release was used to introduce bioactivity to the material and eventually support implant integration into a bone tissue defect. Tetraethyl orthosilicate (TEOS) derived silica sols were cross-linked with an ethoxysilylated 4-armed macromer, pentaerythritol ethoxylate and processed into macroporous scaffolds with defined pore structure by indirect rapid prototyping. Triethyl phosphate (TEP) was shown to function as silica sol solvent. In a first approach, we investigated the integration of 1 to 10% CaCl2 in order to test the hypothesis that small CaCl2 amounts can be physically entrapped and slowly released from hybrid glass scaffolds. With 5 and 10% CaCl2 we observed an extensive burst release, whereas slightly improved release profiles were found for lower Calcium(II) contents. In contrast, introduction of melt-derived bioactive 45S5 glass microparticles (BG-MP) into the hybrid glass scaffolds as another Calcium(II) source led to an approximately linear release of Calcium(II) in Tris(hydroxymethyl)aminomethane (TRIS) buffer over 12 weeks. pH increase caused by BG-MP could be controlled by their amount integrated into the scaffolds. Compression strength remained unchanged compared to scaffolds without BG-MP. In cell culture medium as well as in simulated body fluid, we observed a rapid formation of a carbonated hydroxyapatite layer on BG-MP containing scaffolds. However, this mineral layer consumed the released Calcium(II) ions and prevented an additional increase in Calcium(II) concentration in the cell culture medium. Cell culture studies on the different scaffolds with osteoblast-like SaOS-2 cells as well as bone marrow derived mesenchymal stem cells (hMSC) did not show any advantages concerning osteogenic differentiation due to the integration of BG-MP into the scaffolds. Nonetheless, via the formation of a hydroxyapatite layer and the ability to control the pH increase, we speculate that implant integration in vivo and bone regeneration may benefit from this concept.

Fast Surface Hydrophilization via Atmospheric Pressure Plasma Polymerization for Biological and Technical Applications

Polymeric surfaces can benefit from functional modifications prior to using them for biological and/or technical applications. Surfaces considered for biocompatibility studies can be modified to gain beneficiary hydrophilic properties. For such modifications, the preparation of highly hydrophilic surfaces by means of plasma polymerization can be a good alternative to classical wet chemistry or plasma activation in simple atomic or molecular gasses. Atmospheric pressure plasma polymerization makes possible rapid, simple, and time-stable hydrophilic surface preparation, regardless of the type and properties of the material whose surface is to be modified. In this work, the surface of polypropylene was coated with a thin nanolayer of plasma-polymer which was prepared from a low-concentration mixture of propane-butane in nitrogen using atmospheric pressure plasma. A deposition time of only 1 second was necessary to achieve satisfactory hydrophilic properties. Highly hydrophilic, stable surfaces were obtained when the deposition time was 10 seconds. The thin layers of the prepared plasma-polymer exhibit highly stable wetting properties, they are smooth, homogeneous, flexible, and have good adhesion to the surface of polypropylene substrates. Moreover, they are constituted from essential elements only (C, H, N, O). This makes the presented modified plasma-polymer surfaces interesting for further studies in biological and/or technical applications.

Cytotoxicity Study of Ionophore-Based Membranes: Toward On-Body and in Vivo Ion Sensing

We present the most complete study to date comprising in vitro cytotoxicity tests of ion-selective membranes (ISMs) in terms of cell viability, proliferation, and adhesion assays with human dermal fibroblasts. ISMs were prepared with different types of plasticizers and ionophores to be tested in combination with assays that focus on the medium-term and long-term leaching of compounds. Furthermore, the ISMs were prepared in different configurations considering (i) inner-filling solution-type electrodes, (ii) all-solid-state electrodes based on a conventional drop-cast of the membrane, (iii) peeling after the preparation of a wearable sensor, and (iv) detachment from a microneedle-based sensor, thus covering a wide range of membrane shapes. One of the aims of this study, other than the demonstration of the biocompatibility of various ISMs and materials tested herein, is to create an awareness in the scientific community surrounding the need to perform biocompatibility assays during the very first steps of any sensor development with an intended biomedical application. This will foster meeting the requirements for subsequent on-body application of the sensor and avoiding further problems during massive validations toward the final in vivo use and commercialization of such devices.

Separation mechanism of polyvinyl chloride and copper components from swollen electric cables by mechanical agitation

In this study, a high-accuracy separation process is proposed for recycling pure polyvinyl chloride (PVC) and Cu from the thin electric cables of electrical, electronic, and automotive wastes by PVC swelling and mechanical agitation in hydrophobic organic solvent mixed with water. The high stirring speed and low blade height combined with proper blade type and reactor tank shape ensure a separation rate of over 98%. By conducting computational fluid dynamic and discrete element model simulations, quantitative force, fluid velocity, and data visualization analyses were performed. The obtained separation rate exhibited strong positive correlations with the resultant, drag, and centripetal forces at various stirring speeds and blade heights. Using the experimental and simulation data, a plausible separation mechanism was suggested. It was found that Cu pieces could slip out from swollen PVC covers under the action of external forces, while the stirring speed should be high enough to apply sufficient external forces to cables via either blade-to-cable collisions or fluid drag. Furthermore, the vertical motion of cables induced by the low blade height was essential because the rotation in the bottom reactor part inhibited the slipping of Cu pieces.

How Green is Your Plasticizer?

Plasticizers are additives that are used to impart flexibility to polymer blends and improve their processability. Plasticizers are typically not covalently bound to the polymers, allowing them to leach out over time, which results in human exposure and environmental contamination. Phthalates, in particular, have been the subject of increasing concern due to their established ubiquity in the environment and their suspected negative health effects, including endocrine disrupting and anti-androgenic effects. As there is mounting pressure to find safe replacement compounds, this review addresses the design and experimental elements that should be considered in order for a new or existing plasticizer to be considered green. Specifically, a multi-disciplinary and holistic approach should be taken which includes toxicity testing (both in vitro and in vivo), biodegradation testing (with attention to metabolites), as well as leaching studies. Special consideration should also be given to the design stages of producing a new molecule and the synthetic and scale-up processes should also be optimized. Only by taking a multi-faceted approach can a plasticizer be considered truly green.

Biodegradable and adjustable sol-gel glass based hybrid scaffolds from multi-armed oligomeric building blocks

Biodegradability is a crucial characteristic to improve the clinical potential of sol-gel-derived glass materials. To this end, a set of degradable organic/inorganic class II hybrids from a tetraethoxysilane(TEOS)-derived silica sol and oligovalent cross-linker oligomers containing oligo(d,l-lactide) domains was developed and characterized. A series of 18 oligomers (Mn: 1100-3200Da) with different degrees of ethoxylation and varying length of oligoester units was established and chemical composition was determined. Applicability of an established indirect rapid prototyping method enabled fabrication of a total of 85 different hybrid scaffold formulations from 3-isocyanatopropyltriethoxysilane-functionalized macromers. In vitro degradation was analyzed over 12months and a continuous linear weight loss (0.2-0.5wt%/d) combined with only moderate material swelling was detected which was controlled by oligo(lactide) content and matrix hydrophilicity. Compressive strength (2-30MPa) and compressive modulus (44-716MPa) were determined and total content, oligo(ethylene oxide) content, oligo(lactide) content and molecular weight of the oligomeric cross-linkers as well as material porosity were identified as the main factors determining hybrid mechanics. Cytocompatibility was assessed by cell culture experiments with human adipose tissue-derived stem cells (hASC). Cell migration into the entire scaffold pore network was indicated and continuous proliferation over 14days was found. ALP activity linearly increased over 2weeks indicating osteogenic differentiation. The presented glass-based hybrid concept with precisely adjustable material properties holds promise for regenerative purposes.

STATEMENT OF SIGNIFICANCE

Adaption of degradation kinetics toward physiological relevance is still an unmet challenge of (bio-)glass engineering. We therefore present a glass-derived hybrid material with adjustable degradation. A flexible design concept based on degradable multi-armed oligomers was combined with an established indirect rapid prototyping method to produce a systematic set of porous sol-gel-derived class II hybrid scaffolds. Mechanical properties in the range of cancellous bone were narrowly controlled by hybrid composition. The oligoester introduction resulted in significantly increased compressive moduli. Cytocompatible hybrids degraded in physiologically relevant time frames and a promising linear and controllable weight loss profile was found. To our knowledge, our degradation study represents the most extensive long-term investigation of sol-gel-derived class II hybrids. Due to the broad adjustability of material properties, our concept offers potential for engineering of biodegradable hybrid materials for versatile applications.

A Strategy for Nonmigrating Highly Plasticized PVC

Nonmigrating highly plasticized PVC was prepared based on a new compound that acts as a plasticizer that was derived from di(2-ethylhexyl) 4-hydrophthalate and chlorinated paraffin-52. The as-prepared PVC has a plasticizing efficiency as high as DOP and its migration is totally suppressed. Unlike other reported methods, this approach increases the interaction between phthalate and PVC to suppress its migration, not simply to enlarge its molecular size (or molecular weight). This methodology is highly versatile for producing the desired non-leaching PVC with a permanent plasticizer effect.

Thiol-functionalized nanogels as reactive plasticizers for crosslinked polymer networks

Significant efforts have been expended to mitigate plasticizer migration from crosslinked methacrylic and poly(vinyl chloride) polymer networks by synthesizing reactive plasticizers that can blend homogenously within the networks to reduce polymer property change, acute toxicity and downstream environmental effects of plasticizer migration with limited and varying amount of success. We hypothesized that appropriate thiol-functionalized nanogels synthesized using the same monomers as the parent network to generate highly compact, crosslinked structures will form thermally stable, homogenous networks and perform as optimal reactive plasticizers. Nanogels were synthesized via a thiol-Michael addition solution polymerization and incorporated at different mass ratios within a polyethylene glycol 400 urethane dimethacrylic monomer to form photo-crosslinked networks. While maintaining the inherent hydrolytic stability, thermal stability and biocompatibility of the parent matrix at ~99% acrylic group conversion, the PEG400 urethane dimethacrylic -nanogel networks retained optical clarity with >90% visible light transmission at 20wt% nanogel concentration within the matrix. The addition of the nanogels also enhanced the elongation of the parent matrix by up to 320%, while a 37°C reduction in glass transition temperature (∆T_g) and ≥50% reduction in modulus was observed. A 52% reduction in the shrinkage stress of the material was also noted. The results indicate that the application of thiol-functionalized nanogels as plasticizers to alter the bulk properties of the parent matrix while mitigating plasticizer migration by covalently crosslinking the nanogels within the polymer matrix provides a simple yet efficient technique to generate network-specific plasticizers with the ability to alter targeted properties within polymers.

Indirect rapid prototyping of sol-gel hybrid glass scaffolds for bone regeneration - Effects of organic crosslinker valence, content and molecular weight on mechanical properties

We present a series of organic/inorganic hybrid sol-gel derived glasses, made from a tetraethoxysilane-derived silica sol (100% SiO2) and oligovalent organic crosslinkers functionalized with 3-isocyanatopropyltriethoxysilane. The material was susceptible to heat sterilization. The hybrids were processed into pore-interconnected scaffolds by an indirect rapid prototyping method, described here for the first time for sol-gel glass materials. A large panel of polyethylene oxide-derived 2- to 4-armed crosslinkers of molecular weights ranging between 170 and 8000Da were incorporated and their effect on scaffold mechanical properties was investigated. By multiple linear regression, 'organic content' and the 'content of ethylene oxide units in the hybrid' were identified as the main factors that determined compressive strength and modulus, respectively. In general, 3- and 4-armed crosslinkers performed better than linear molecules. Compression tests and cell culture experiments with osteoblast-like SaOS-2 cells showed that macroporous scaffolds can be produced with compressive strengths of up to 33±2MPa and with a pore structure that allows cells to grow deep into the scaffolds and form mineral deposits. Compressive moduli between 27±7MPa and 568±98MPa were obtained depending on the hybrid composition and problems associated with the inherent brittleness of sol-gel glass materials could be overcome. SaOS-2 cells showed cytocompatibility on hybrid glass scaffolds and mineral accumulation started as early as day 7. On day 14, we also found mineral accumulation on control hybrid glass scaffolds without cells, indicating a positive effect of the hybrid glass on mineral accumulation.

STATEMENT OF SIGNIFICANCE

We produced a hybrid sol-gel glass material with significantly improved mechanical properties towards an application in bone regeneration and processed the material into macroporous scaffolds of controlled architecture by indirect rapid prototyping. We were able to produce macroporous materials of relevant porosity and pore size with compressive moduli, covering the range reported for cancellous bone while an even higher compressive strength was maintained. By multiple linear regression, we identified crosslinker parameters, namely organic content and the content of ethylene oxide units in the hybrids that predominantly determined the mechanics of the hybrid materials. The scaffolds proved to be cytocompatible and induced mineralization in SaOS-2 cells. This provides new insight on the critical parameters for the design of the organic components of covalent hybrid sol-gel glasses.

Aqueous leaching of di-2-ethylhexyl phthalate and "green" plasticizers from poly(vinyl chloride)

A method was developed to assess leaching of several poly(vinyl chloride) (PVC) plasticizers in aqueous media using gas chromatography (GC), and compared to a gravimetric standard test method (ASTM Method D1239). The GC method was a more direct measurement of plasticizer concentration in the aqueous phase. The leaching of commercial plasticizers, as well as several series of "green" candidate plasticizers, were assessed as a function of their molecular characteristics and compared to the industry standard PVC plasticizer, di-2-ethylhexyl phthalate (DEHP). It was found that plasticizers containing longer alkyl chains or non-polar branching emanating from polar structural units, increased the hydrophobicity of the molecule and reduced its aqueous leaching rate. Several "green" plasticizer candidates were found to minimize aqueous leaching to rates ten times below that of DEHP; notably dioctyl succinate (DOS), dihexyl maleate (DHM), methyl cyclohexyl diester (MCDE), diethylhexyl succinate (DEHS), hexanediol dibenzoate (C6), and the commercially available Hexamoll® DINCH.

Packaging Considerations for Biopreservation

SUMMARY: The packaging system chosen for biopreservation is critical for many reasons. An ideal biopreservation container system must provide for closure integrity, sample stability and ready access to the preserved material. This means the system needs to be hermetically sealed to ensure integrity of the specimen is maintained throughout processing, storage and distribution; the system must remain stable over long periods of time as many biobanked samples may be stored indefinitely; and functionally closed access systems must be used to avoid contamination upon sample withdraw. This study reviews the suitability of a new commercially available vial configuration container utilizing blood bag style closure and access systems that can be hermetically sealed and remain stable through cryopreservation and biobanking procedures. This vial based systems allow for current good manufacturing/tissue practice (cGTP) requirements during processing of samples and may provide the benefit of ease of delivery by a care giver. In this study, the CellSeal® closed system cryovial was evaluated and compared to standard screw cap vials. The CellSeal system was evaluated for durability, closure integrity through transportation and maintenance of functional viability of a cryopreserved mesenchymal stem cell model. The results of this initial proof-of-concept study indicated that the CellSeal vials are highly suitable for biopreservation and biobanking, and provide a suitable container system for clinical and commercial cell therapy products frozen in small volumes.

Metals and the integrity of a biological coating: the cuticle of mussel byssus

The cuticle of mussel byssal threads is a robust natural coating that combines high extensibility with high stiffness and hardness. In this study, fluorescence microscopy and elemental analysis were exploited to show that the 3,4-dihydroxyphenyl-L-alanine (dopa) residues of mussel foot protein-1 colocalize with Fe and Ca distributions in the cuticle of Mytilus galloprovincialis mussel byssal threads. Chelated removal of Fe and Ca from the cuticle of intact threads resulted in a 50% reduction in cuticle hardness, and thin sections subjected to the same treatment showed a disruption of cuticle integrity. Dopa-metal complexes may provide significant interactions for the integrity of composite cuticles deformed under tension.

Organic-inorganic hybrids as transparent coatings for UV and X-ray shielding

This work reports the synthesis of new polymer-titania hybrids, where the organic phase is constituted by polyesters such as poly(-caprolactone), poly(d,l-lactic acid), and poly(l-lactic acid). In these hybrids, very strong interaction between the organic and inorganic domains is obtained through transesterification of ester moieties by titanium atoms, which leads to organotitanium esters. The influence of the structure of the polyester on the mode of its interaction with titania is also investigated. Hybrids with a range of solid-state properties, which depend on the starting polymer characteristics and on the inorganic-phase content, are obtained. Hybrids are applied as coatings on a variety of substrates. They show intrinsic optical transparency and the ability to completely block UV radiation in the range UVB and UV-A2. In particular, when applied to different textiles, the hybrids impart radiopacity to the fabrics, opening new perspectives in the field of personal protective clothing and equipment.

Synthesis of organic–inorganic hybrid compounds based on Bis-GMA and its sol–gel behavior analysis using Taguchi method

OBJECTIVES

The aim of this study was the synthesis of organic-inorganic hybrid compounds based on Bis-GMA and incorporation of them into conventional Bis-GMA/TEGDMA dental resins. This was achieved by the synthesis of Bis-GMA bearing two -Si(OEt)3 reactive groups (a bridged monomer) and subsequent hydrolysis-condensation reactions with TEOS, in TEGDMA media.

METHODS

The structure of the bridged monomer was characterized by using FTIR technique. The sol-gel behavior of the aforementioned hydrolysis-condensation reactions was investigated by using an experimental design based on the Taguchi method. Therefore, amounts of the bridged monomer, TEOS and TEGDMA in the gelation process were optimized in order to achieve the maximum gel content without complete gelation of the mixture.

RESULTS

It was found that the amount of the bridged monomer has the major effect with the amount of TEGDMA having a minor effect. The cross-over effect between the constituents of the mixture was also investigated to be negligible.

SIGNIFICANCE

The organic-inorganic hybrids developed based on Bis-GMA can be combined with commonly used methacrylate light-curable dental resins.