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Chemical functionalization of poly(epsilon-caprolactone) (PCL) enables a molecular integration of additional function. Here, we report an approach to incorporate reactive alkynyl side-groups by synthesizing a chain-extended PCL, where the reactive site is introduced through the covalently functionalizable chain extender 3 (prop-2-yn-1-yloxy)propane-1,2-diol (YPD). Chain-extended PCL with M-w of 101 to 385 kg.mol(-1) were successfully synthesized in a one-pot reaction from PCL-diols with various molar masses, L-lysine ethyl ester diisocyanate (LDI) or trimethyl(hexamethylene)diisocyanate (TMDI), and YPD, in which the density of functionalizable groups and spacing between them can be controlled by the composition of the polymer. The employed diisocyanate compounds and YPD possess an asymmetric structure and form a non-crystallizable segment leaving the PCL crystallites to dominate the material's mechanical properties. The mixed glass transition temperature T-g = - 60 to - 46 degrees C of the PCL/polyurethane amorphous phase maintains the synthesized materials in a highly elastic state at ambient and physiological conditions. Reaction conditions for covalent attachment in copper(I)-catalyzed azide-alkyne-cycloaddition reactions (CuAAC) in solution were optimized in a series of model reactions between the alkyne moieties of the chain-extended PCL and benzyl azide, reaching conversions over 95% of the alkyne moieties and with yields of up to 94% for the purified functionalized PCL. This methodology was applied for reaction with the azide-functionalized cell adhesion peptide GRGDS. The required modification of the peptide provides selectivity in the coupling reactions. The obtained results suggest that YPD could potentially be employed as versatile molecular unit for the creation of a variety of functionalizable polyesters as well as polyurethanes and polycarbonates offering efficient and selective click-reactions.
Tissue reconstruction has an unmet need for soft active scaffolds that enable gentle loading with regeneration-directing bioactive components by soaking up but also provide macroscopic dimensional stability. Here microporous hydrogels capable of an inverse shape-memory effect (iSME) are described, which in contrast to classical shape-memory polymers (SMPs) recover their permanent shape upon cooling. These hydrogels are designed as covalently photo cross-linked polymer networks with oligo(ethylene glycol)-oligo(propylene glycol)-oligo(ethylene glycol) (OEG-OPG-OEG) segments. When heated after deformation, the OEG-OPG-OEG segments form micelles fixing the temporary shape. Upon cooling, the micelles dissociate again, the deformation is reversed and the permanent shape is obtained. Applicability of this iSME is demonstrated by the gentle loading of platelet-rich plasma (PRP) without causing any platelet activation during this process. PRP is highly bioactive and is widely acknowledged for its regenerative effects. Hence, the microporous inverse shape-memory hydrogel (iSMH) with a cooling induced pore-size effect represents a promising candidate scaffold for tissue regeneration for potential usage in minimally invasive surgery applications.
The degradation of polymers is described by mathematical models based on bond cleavage statistics including the decreasing probability of chain cuts with decreasing average chain length. We derive equations for the degradation of chains under a random chain cut and a chain end cut mechanism, which are compared to existing models. The results are used to predict the influence of internal molecular parameters. It is shown that both chain cut mechanisms lead to a similar shape of the mass or molecular mass loss curve. A characteristic time is derived, which can be used to extract the maximum length of soluble fragments l of the polymer. We show that the complete description is needed to extract the degradation rate constant k from the molecular mass loss curve and that l can be used to design polymers that lose less mechanical stability before entering the mass loss phase.
Copolyesterurethanes (PDLCLs) based on oligo(epsilon-caprolactone) (OCL) and oligo(omega-pentadecalactone) (OPDL) segments are biodegradable thermoplastic temperature-memory polymers. The temperature-memory capability in these polymers with crystallizable control units is implemented by a thermomechanical programming process causing alterations in the crystallite arrangement and chain organization. These morphological changes can potentially affect degradation. Initial observations on the macroscopic level inspire the hypothesis that switching of the controlling units causes an accelerated degradation of the material, resulting in programmable degradation by sequential coupling of functions. Hence, detailed degradation studies on Langmuir films of a PDLCL with 40 wt% OPDL content are carried out under enzymatic catalysis. The temperature-memory creation procedure is mimicked by compression at different temperatures. The evolution of the chain organization and mechanical properties during the degradation process is investigated by means of polarization-modulated infrared reflection absorption spectroscopy, interfacial rheology and to some extend by X-ray reflectivity. The experiments on PDLCL Langmuir films imply that degradability is not enhanced by thermal switching, as the former depends on the temperature during cold programming. Nevertheless, the thin film experiments show that the leaching of OCL segments does not induce further crystallization of the OPDL segments, which is beneficial for a controlled and predictable degradation.
The Venus flytrap is a fascinating plant with a finely tuned mechanical bi-stable system, which can switch between mono- and bi-stability. Here, we combine geometrical design of compliant mechanics and the function of shape-memory polymers to enable switching between bi- and mono-stable states. Digital design and modelling using the Chained Beam Constraint Model forecasted two geometries, which were experimentally realized as structured films of cross-linked poly[ethylene-co-(vinyl acetate)] supported by digital manufacturing. Mechanical evaluation confirmed our predicted features. We demonstrated that a shape-memory effect could switch between bi- and mono-stability for the same construct, effectively imitating the Venus flytrap.
Maximizing the efficiency of nanocarrier-mediated co-delivery of genes for co-expression in the same cell is critical for many applications. Strategies to maximize co-delivery of nucleic acids (NA) focused largely on carrier systems, with little attention towards payload composition itself. Here, we investigated the effects of different payload designs: co-delivery of two individual "monocistronic" NAs versus a single bicistronic NA comprising two genes separated by a 2A self-cleavage site. Unexpectedly, co-delivery via the monocistronic design resulted in a higher percentage of co-expressing cells, while predictive co-expression via the bicistronic design remained elusive. Our results will aid the application-dependent selection of the optimal methodology for co-delivery of genes.
Complexes from catalysts and initiator can be used to insert a specific number of additional chemical functional groups in (co)polymers prepared by ring-opening polymerization (ROP) of lactones. We report on the synthesis of cooligomers from sec-butyl-morpholine-2,5-dione (SBMD) and para-dioxanone (PDX) by ROP with varied feed ratios in the bulk using the catalyst complex SnOct(2)/2-hydroxyethyl sulfide. M-n of the cooligomers (determined by GPC) decreased with decreasing SBMD feed ratio from 4200 +/- 420 to 800 +/- 80 g mol(-1). When the feed ratio was reduced from 80 to 50 mol% the molar ratio of SBMD of the cooligomers (determined by H-1-NMR) remained nearly unchanged between 81 and 86 mol% and was attributed to a higher reactivity of SBMD. This assumption was confirmed by fractionation of GPC, in which an increase of SBMD with increasing molecular weight was observed. The catalyst/initiator system provides a high potential to create orthogonal building blocks by cleavage of the sulfide bond.
Crystallization and degradation behaviour of multiblock copolyester blends in Langmuir monolayers
(2021)
Supporting the wound healing of soft tissues requires fixation devices becoming more elastic while degrading. To address this unmet need, we designed a blend of degradable multiblock copolymers, which is cross-linked by PLA stereocomplexation combining two soft segments differing substantially in their hydrolytic degradation rate. The degradation path and concomitant structural changes are predicted by Langmuir monolayer technique. The fast hydrolysis of one soft segment leads to a decrease of the total polymer mass at constant physical cross-linking density. The corresponding increase of the average spacing between the network nodes suggests the targeted increase of the blend's flexibility.
The potential of using crystallinity as morphological parameter to control polyester degradation in acidic environments is explored in ultrathin films by Langmuir technique. Films of hydroxy or methacrylate end-capped oligo(epsilon-caprolactone) (OCL) are prepared at the air-water interface as a function of mean molecular area (MMA). The obtained amorphous, partially crystalline or highly crystalline ultrathin films of OCL are hydrolytically degraded at pH similar to 1.2 on water surface or on silicon surface as-transferred films. A high crystallinity reduces the hydrolytic degradation rate of the films on both water and solid surfaces. Different acceleration rates of hydrolytic degradation of semi-crystalline films are achieved either by crystals complete melting, partially melting, or by heating them below their melting temperatures. Semi-crystalline OCL films transferred via water onto a solid surface retain their crystalline morphology, degrade in a controlled manner, and are of interest as thermoswitchable coatings for cell substrates and medical devices.
Soft actuator performance can be tuned by chemistry or mechanical manipulation, but this adjustability is limited especially in view of their growing technological relevance. Inspired from textile engineering, we designed and fabricated fiber mesh actuators and introduced new features like anisotropic behavior and soft-tissue like elastic deformability. Design criteria for the meshes are the formation of fiber bundles, the angle between fiber bundles in different stacked layers and covalent crosslinks forming within and between fibers at their interfacial contact areas. Through crosslinking the interfiber bond strength increased from a bond transmitting neither axial nor rotational loads (pin joint) to a bond strength capable of both (welded joint). For non-linear elastic stiffening, stacked fiber bundles with four embracing fibers were created forming microstructural rhombus shapes. Loading the rhombus diagonally allowed generation of “soft tissue”-like mechanics. By adjustment of stacking angles, the point of strong increase in stress is tuned. While the highest stresses are observed in aligned and crosslinked fiber mats along the direction of the fiber, the strongest shape-memory actuation behavior is found in randomly oriented fiber mats. Fiber mesh actuators controlled by temperature are of high significance as soft robot skins and as for active patches supporting tissue regeneration.