Swelling-Activated, Soft Mechanochemistry in Polymer Materials

Development and application of a protocol for extractables profiling from central venous catheters in neonates

Peripherally inserted central catheters (PICC-lines) used in neonatology are made of thermoplastic polyurethane (TPU) or silicone. These materials usually contain substances that may leach into drug vehicles or blood. In this extractables study, we determined the optimal extraction conditions using TPU films containing defined amounts of butylhydroxytoluene (BHT) and then applied them on unused and explanted PICC-lines. Maceration and sonication tests were carried out with hexane, acetone and water as the extraction solvents. The analyses were performed using gas and liquid chromatography coupled with mass spectrometry detectors, as well as inductive coupled plasma optical emission spectroscopy to detect a wide range of extractables. We selected a limited list of substances to be sought from the usual adjuvants and monomers, related to their carcinogenic, mutagenic or reprotoxic properties and/or existence in endocrine disruptors lists. The TPU-film experiments showed that acetone was slightly better than hexane, and maceration better than sonication. When applied to PICC-lines, the extraction methods were almost similar but acetone was clearly better than hexane for TPU. From the 48 peaks initially observed in GC-MS, we ended up with 37 peaks to follow in TPU PICC-lines, among which were those of BHT and 4,4'-Methylenebis(cyclohexyl isocyanate) isomers. For silicone PICC-lines, out of 41 peaks initially observed in GC-MS, we followed 20 peaks, most of them being identified as cyclosiloxanes. Barium was the main inorganic element extracted for both PICC-lines. For TPU PICC-lines, the inter-batch variability was higher than for intra-batch, but in silicone devices both were similar. When compared to new PICC-lines, explanted TPU PICC-lines extracted peaks had a lower area under the curve (AUC), while the AUCs of the peaks were higher for the majority of silicone PICC-lines extract compounds. No identified substances were detected above their toxicological threshold, but isocyanates and cyclosiloxanes toxicity was mostly studied for other exposition routes than intravenous. The methods defined in this study were efficient in producing extractable profiles from both PICC-lines.

Advancing Dynamic Polymer Mechanochemistry through Synergetic Conformational Gearing

Harnessing mechanical force to modulate material properties and enhance biomechanical functions is essential for advancing smart materials and bioengineering. Polymer mechanochemistry provides an emerging toolkit for exploring unconventional chemical transformations and modulating molecular structures through mechanical force. One of the key challenges is developing innovative force-sensing mechanisms for precise and in situ force detection. This study introduces mDPAC, a dynamic and sensitive mechanophore, demonstrating its mechanochromic properties through synergetic conformational gearing. Its unique mechanoresponsive mechanism is based on the simultaneous conformational synergy between its phenazine and phenyl moieties, facilitated by a worm-gear-like structure. We confirm mDPAC's complex mechanochemical response and elucidate its mechanotransduction mechanism through our experimental data and comprehensive simulations. The compatibility of mDPAC with hydrogels is particularly notable, highlighting its potential for applications in aqueous biological environments as a dynamic force sensor. Moreover, mDPAC's multicolored mechanochromic responses facilitate direct force sensing and visual detection, paving the way for precise and real-time mechanical force sensing in bulk materials.

Mechanochemical Approaches to Fundamental Studies in Soft-Matter Physics

Stretching a segment of a polymer beyond its contour length makes its (primarily backbone) bonds more dissociatively labile, which enables polymer mechanochemistry. Integrating some backbone bonds into suitably designed molecular moieties yields mechanistically and kinetically diverse chemistry, which is becoming increasingly exploitable. Examples include, most prominently, attempts to improve mechanical properties of bulk polymers, as well as prospective applications in drug delivery and synthesis. This review aims to highlight an emerging effort to apply the concepts and experimental tools of mechanochemistry to fundamental physical questions in soft matter. A succinct summary of the state-of-the-knowledge of the field, with emphasis on foundational concepts and generalizable observations, is followed by analysis of 3 recent examples of mechanochemistry yielding molecular-level details of elastomer failure, macromolecular chain dynamics in elongational flows and kinetic allostery. We conclude with reasons to assume that the highlighted approaches are generalizable to a broader range of physical problems than considered to date.

Co-delivery of VEGF and amoxicillin using LP-coated co-axial electrospun fibres for the potential treatment of diabetic wounds

Diabetic complications present throughout a wide range of body tissues, however one of the most widely recognised complications remains to be chronic diabetic wounds. Current treatment options largely rely on standard wound treatment routines which provide no promotion of wound healing mechanisms at different physiological stages of repair. Recently materials produced using novel additive manufacturing techniques have been receiving attention for applications in wound care and tissue repair. Additive manufacturing techniques have recently been used in the interest of targeted drug delivery and production of novel materials resembling characteristics of native tissues. The potential to exploit these highly tailorable manufacturing techniques for the design of novel wound care remedies is highly desirable. In the present study two additive manufacturing techniques are combined to produce a scaffold for the treatment of diabetic wounds. The combination of microfluidic manufacturing of an antimicrobial liposome (LP) formulation and a coaxial electrospinning method incorporating both antimicrobial and proangiogenic factors allowed dual delivery of therapeutics to target both infection and lack of vascularisation at wound sites. The coaxial fibres comprised of a polyvinyl alcohol (PVA) core containing vascular endothelial growth factor (VEGF) and a poly (l-lactide-co-ε-caprolactone) (PLCL) shell blended with amoxicillin (Amox). Additionally, a liposomal formulation was produced to incorporate Amox and adhered to the surface of fibres loaded with Amox and VEGF. The liposomal loading provided the potential to deliver a much higher, more clinically relevant dose of Amox without detrimentally changing the mechanical properties of the material. The growth factor release was sustained up to 7-days in vitro. The therapeutic effect of the antibiotic loading was analysed using a disk diffusion method with a significant increase in zone diameter following LP adhesion, proving the full scaffold system had improved efficacy against both Gram-positive and Gram-negative strains. Additionally, the dual-loaded scaffolds show enhanced potential for supporting vascular growth in vitro, as demonstrated via a viability assay and tubule formation studies. Results showed a significant increase in the average total number of tubes from 10 in control samples to 77 in samples fully-loaded with Amox and VEGF.

Synthesis of Raspberry-like Nanoparticles via Surface Grafting of Positively Charged Polyelectrolyte Brushes: Colloidal Stability and Surface Properties

A method to synthesize stable, raspberry-like nanoparticles (NPs), using surface grafting of poly(glycidyl methacrylate) (PGMA) brushes on a polystyrene (PS) core with varying grafting densities, is reported. A two-step functionalization reaction of PGMA epoxide groups comprising an amination step first using ethylene diamine and then followed by a quaternization using glycidyltrimethylammonium chloride generates permanently and positively charged polyelectrolyte brushes, which result in both steric and electrostatic stabilization. The dispersion stability of the brush-bearing NPs is dramatically improved compared to that of the pristine PS core in salt solutions at ambient (25 °C) and elevated temperatures (60 °C). Additionally, the grafted polyelectrolyte chains undergo a reversible swelling in the presence of different ionic strength (IS) salts, which modulate the surface properties, including roughness, stiffness, and adhesion. An atomic force microscope under both dry and wet conditions was used to image conformational changes of the polyelectrolyte chains during the swelling and deswelling transitions as well as to probe the nanomechanical properties by analyzing the corresponding force-sample separation curves. The quaternized polyelectrolyte brushes undergo a conformational transition from a collapsed state to a swelled state in the osmotic brush (OB) regime triggered by the osmotic gradient of mobile ions to the interior of the polymer chain. At IS ∼ 1 M, the brushes contract and the globules reform (salted brush state) as evidenced by an increase in the surface roughness and a reduction in the adhesion of the brushes. Beyond IS ∼ 1 M, quartz crystal microbalance with dissipation monitoring measurements show that salt uptake continues to take place predominantly on the exterior surface of the brush since salt adsorption is not accompanied by a size increase as measured by dynamic light scattering. The study adds new insights into our understanding of the behavior of NPs bearing salt-responsive polyelectrolyte brushes with adaptive swelling thresholds that can ultimately modulate surface properties.

Morphology and Mechanics of Star Copolymer Ultrathin Films Probed by Atomic Force Microscopy in the Air and in Liquid

Star copolymer films were produced by using spin-coating, drop-casting, and casting deposition techniques, thus obtaining ultrathin and thick films, respectively. The morphology is generally flat, but it becomes substrate-dependent for ultrathin films where the planarization effect of films is not efficient. The indentation hardness of films was investigated by Force Volume Maps in both the air and liquid. In the air, ultrathin films are in the substrate-dominated zone and, thus, the elastic modulus E is overestimated, while E reaches its bulk value for drop-casted ultrathin and thick films. In liquid (water), E follows an exponential decay for all films with a minimum soaked time t0 of 0.37 and 2.65 h for ultrathin and drop-casted ultrathin and thick films, respectively. After this time, E saturates to a value on average 92% smaller than that measured in the air due to film swelling. Such results support the role of film morphology in the antimicrobial activity envisaged in the literature, suggesting also an additional role of film hardness.

Probing the Solubility of Imine-Based Covalent Adaptable Networks

Covalent adaptable networks (CANs) are polymer materials that are covalently cross-linked via dynamic covalent bonds. The cross-linked polymer network is generally expected to be insoluble, as is seen for traditional thermosets. However, in recent years, it has become apparent that-under certain conditions-both dissociative and associative CANs can be dissolved in a good solvent. For some applications (e.g., those that require long-term (chemical) stability), the solubility of CANs can be problematic. However, many forget that (selective) solubility of CANs can also be applied advantageously, for example, in recycling or modification of the materials. In this work, we provide results and insights related to the tunable solubility of imine-based CANs. We observed that selected CANs could be fully dissolved in a good solvent without observing dissociation of imines. Only in an acidic environment (partial) dissociation of imines was observed, which could be reverted to the associated state by addition of a base. By adjusting the network composition, we were able to either facilitate or hamper solubility as well as control the size of the dissolved particles. DLS showed that the size of dissolved polymer particles decreased at lower concentrations. Similarly, decreasing cross-linking density resulted in smaller particles. Last, we showed that we could use the solubility of the CANs as a means for chemical recycling and postpolymerization modification. The combination of our studies with existing literature provides a better understanding of the solubility of CANs and their applications as recyclable thermosets.

Swelling-Induced Chromotropism of Bionanocomposite Hydrogel Beads

Monodispersed gelatin hydrogel beads containing smectite with adsorbed cyanine dye exhibit chromotropic responses to compression and swelling/deswelling by solvent. Photoluminescence color of the beads changes by swelling in water (blue) and deswelling in ethanol (purple) reversibly. The forces generated by swelling/deswelling are thought to induce the transition between the J-aggregate and the monomer of cyanine dye adsorbed on smectite, giving the photoluminescent color changes.

Hydrogel based soft tissue expanders for orodental reconstruction

Tension-free flap closure to prevent soft tissue dehiscence is a prerequisite for successful bone augmentation in orodental reconstructive surgery. Since soft tissue contour follows the underlying jaw bony architecture, resorption of alveolar (jaw) bone limits the availability of soft tissue for wound closure following major bone reconstruction, required to facilitate oral rehabilitation with endosseous dental implants following tooth loss. Although there are several clinical procedures to increase soft tissue volume, these techniques are complicated and technically demanding. Soft tissue expansion, an established technique in reconstructive surgery, is an ideal alternative to generate surplus soft tissue prior to bone augmentation and dental implant placement. Increase in tissue volume can be achieved by using soft tissue expanders (STEs). Contemporary STEs have evolved from silicone balloons to osmotically inflating hydrogel-based systems. Here, we provide an overview of STEs in clinical oral surgery, outline the current research in STEs, and an update on recent clinical trials as well as the associated complications. Also, the mechanism governing soft tissue expansion and the critical factors that control the expansion process are covered. Design considerations for STEs for intraoral applications are given particular attention. Finally, we present our perspectives on utilization of minimally invasive methods to administer STEs for orodental applications. STATEMENT OF SIGNIFICANCE: Soft tissue expansion is required for a range of reconstructive applications and more notably in regenerative dentistry for vertical bone augmentation. This review describes the commercially available soft tissue expanders along with the latest systems being currently developed. This review insightfully discusses the biological and physical mechanisms leading to soft tissue expansion and critically assesses the design criteria of soft tissue expanders. A particular focus is given on the development of a new generation of hydrogel-based soft tissue expanders; their chemistry and required physical properties for tissue expansion is described and the obstacles towards clinical translations are identified. Finally, the review elaborates on promising minimally invasive injectable hydrogel-based tissue expanders and highlights the beneficial features of these systems.

Multifaceted Shape Memory Polymer Technology for Biomedical Application: Combining Self-Softening and Stretchability Properties

Thiol-ene polymers are a promising class of biomaterials with a wide range of potential applications, including organs-on-a-chip, microfluidics, drug delivery, and wound healing. These polymers offer flexibility, softening, and shape memory properties. However, they often lack the inherent stretchability required for wearable or implantable devices. This study investigated the incorporation of di-acrylate chain extenders to improve the stretchability and conformability of those flexible thiol-ene polymers. Thiol-ene/acrylate polymers were synthesized using 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), Trimethylolpropanetris (3-mercaptopropionate) (TMTMP), and Polyethylene Glycol Diacrylate (PEGDA) with different molecular weights (Mn 250 and Mn 575). Fourier Transform Infrared (FTIR) spectroscopy confirmed the complete reaction among the monomers. Uniaxial tensile testing demonstrated the softening and stretching capability of the polymers. The Young's Modulus dropped from 1.12 GPa to 260 MPa upon adding 5 wt% PEGDA 575, indicating that the polymer softened. The Young's Modulus was further reduced to 15 MPa under physiologic conditions. The fracture strain, a measure of stretchability, increased from 55% to 92% with the addition of 5 wt% PEGDA 575. A thermomechanical analysis further confirmed that PEGDA could be used to tune the polymer's glass transition temperature (Tg). Moreover, our polymer exhibited shape memory properties. Our results suggested that thiol-ene/acrylate polymers are a promising new class of materials for biomedical applications requiring flexibility, stretchability, and shape memory properties.

Solvent Swelling-Induced Halogenation of Butyl Rubber Using Polychlorinated N-Alkanes: Structure and Properties

Traditional butyl rubber halogenation technology involves the halogenation of IIR using molecular chlorine or bromine in a solution. However, this method is technologically complex. This study investigated a novel method for the halogenation of butyl rubber to enhance its stability and resistance to thermal oxidation and aggressive media. The butyl rubber was modified through mechanochemical modification, induced by solvent swelling in a polychlorinated n-alkane solution. During the modification, samples were obtained with chlorine content ranging from 3 to 15%. After extraction, the halogen content was quantitatively determined with the oxygen flask combustion method and X-ray photoelectron spectroscopy. It was shown that for samples with total chlorine content of up to 6%, there was almost no leaching of chlorine from the samples. The chemical structure of the extracted rubbers was ascertained using FT-IR and 1H NMR spectroscopy, and it was demonstrated that all samples showed absorption peaks and signals typical for chlorobutyl rubbers. It was observed that modification with polychlorinated n-alkanes improved the thermal and oxidative stability (the oxygen absorption rate decreased by 40%) and chemical resistance, estimated by the degree of swelling, which decreased with the increase in the chlorine content. This technology allows the production of a chlorinated rubber solution that can be directly used by rubber goods manufacturers and suppliers.

Rheological Study of the Formation of Pullulan Hydrogels and Their Use as Carvacrol-Loaded Nanoemulsion Delivery Systems

Hydrogels have been extensively studied as delivery systems for lipophilic compounds. Pullulan hydrogels were prepared, and their gelation kinetics were studied over time. Pullulan exhibited a relatively slow gelling reaction in basic medium (KOH) using trisodium metaphosphate (STMP) as a cross-linking agent, so capsules cannot be obtained by dripping as easily as in the case of alginate and chitosan. The kinetics of pullulan gelation were studied through rheological analysis over time. An optimal [Pullulan]/[KOH] ratio was found for a fixed [Pullulan]/[STMP] ratio. For this given relationship, gelling time measurements indicated that when the concentration of pullulan increased, the gelation time decreased from 60 min for 6% w/w pullulan to 10 min for 10% w/w. After the gel point, a hardening of the hydrogel was observed over the next 5 h. The formed hydrogels presented high degrees of swelling (up to 1800%). Freeze-dried gels were capable of being rehydrated, obtaining gels with rheological characteristics and visual appearance similar to fresh gels, which makes them ideal to be freeze-dried for storage and rehydrated when needed. The behavior of the hydrogels obtained as active ingredient release systems was studied. In this case, the chosen molecule was carvacrol (the main component of oregano oil). As carvacrol is hydrophobic, it was incorporated into the droplets of an oil-in-water nanoemulsion, and the nanoemulsion was incorporated into the hydrogel. The release of the oil was studied at different pHs. It was observed that as the pH increased (from pH 2 to pH 7), the released amount of carvacrol for the gel with pullulan 10% w/w reached 100%; for the other cases, the cumulative release amount was lower. It was attributed to two opposite phenomena in the porous structure of the hydrogel, where more porosity implied a faster release of carvacrol but also a higher degree of swelling that promoted a higher entry of water flow in the opposite direction. This flow of water prevented the active principle from spreading to the release medium.

Stability Studies, Biodegradation Tests, and Mechanical Properties of Sodium Alginate and Gellan Gum Beads Containing Surfactant

The excessive presence of single-use plastics is rapidly degrading our natural environment on a global scale due to their inherent resistance to decomposition. Wet wipes used for personal or household purposes contribute significantly to the accumulation of plastic waste. One potential solution to address this problem involves developing eco-friendly materials that possess the ability to degrade naturally while retaining their washing capabilities. For this purpose, the beads from sodium alginate, gellan gum, and a mixture of these natural polymers containing surfactant were produced using the ionotropic gelation method. Stability studies of the beads by observing their appearance and diameter were performed after incubation in solutions of different pH values. The images showed that macroparticles were reduced in size in an acidic medium and swelled in solution of pH-neutral phosphate-buffered saline. Moreover, all the beads first swelled and then degraded in alkaline conditions. The beads based on gellan gum and combining both polymers were the least sensitive to pH changes. The compression tests revealed that the stiffness of all macroparticles decreased with the increasing pH of the solutions in which they were immersed. The studied beads were more rigid in an acidic solution than in alkaline conditions. The biodegradation of macroparticles was assessed using a respirometric method in soil and seawater. It is important to note that the macroparticles degraded more rapidly in soil than in seawater.