Retentive drug delivery systems (DDSs) are intended for prolonged residence and release inside hollow muscular organs, to achieve either local or systemic therapeutic goals. Recently, formulations based on shape memory polymers (SMPs) have gained attention in view of their special ability to recover a shape with greater spatial encumbrance at the target organ (e.g., urinary bladder or stomach), triggered by contact with biological fluids at body temperature. In this work, poly(vinyl alcohol) (PVA), a pharmaceutical-grade SMP previously shown to be an interesting 4D printing candidate, was employed to fabricate expandable organ-retentive prototypes by hot melt extrusion. With the aim of improving the mechanical resistance of the expandable DDS and slowing down relevant drug release, the application of insoluble permeable coatings based on either Eudragit^® RS/RL or Eudragit^® NE was evaluated using simple I-shaped specimens. The impact of the composition and thickness of the coating on the shape memory, swelling, and release behavior as well as on the mechanical properties of these specimens was thoroughly investigated and the effectiveness of the proposed strategy was demonstrated by the results obtained.

4D printing is an innovative manufacturing approach that combines 3D printing and stimuli- responsive abilities to produce objects with complex geometry and capable of shapeshifting over time (the fourth dimension). To pursue such an approach this paper proposes to develop re-entrant honeycomb auxetic grids with tunable shape reconfigurable behavior. Particularly, the work combines 3D printing and a photopolymer exhibiting the so-called temperature memory effect (TME), a peculiar shape memory behavior expressing the capability of the material to remember not only the original shape but also the deformation temperature. A thorough experimental activity was carried out on single auxetic unit cells, chosen as representative of the whole auxetic grid, to properly highlight and assess their response upon heating after single-step and multiple-step deformation histories and to describe the recovery process as a function of time and temperature. Results demonstrate the possibility to achieve an easily controlled TME and to successfully exploit it for autonomous, complex hierarchical transformations over a large range of temperatures. As a proof-of-concept, the study of the sequential recovery of an entire auxetic grid subjected to double-step programming allowed highlighting a decoupled in-plane elongation and out-of-plane bending. The behavior of the 4D-printed auxetic structures was simulated by means of finite element (FE) analysis, using a thermoviscoelastic model of the photopolymer and viscoelastic experimental data obtained by time-temperature superposition analysis applied to multifrequency dynamic mechanical tests and to isothermal recovery tests. A good correspondence between experiments and simulations was obtained for all shape memory tests, demonstrating that the proposed FE approach is a suitable tool to support the design of these structures. The combination of 3D printing and TME opens new perspectives to achieve dynamic tunability in mechanical metamaterials, that is a key ingredient in several application fields.

The occurrence of periprosthetic joint infections (PJI) after total joint replacement constitutes a great burden for the patients and the healthcare system. Antibiotic‐loaded polymethylmethacrylate (PMMA) bone cement is often used in temporary spacers during antibiotic treatment. PMMA is not a load‐bearing solution and needs to be replaced by a functional implant. Elution from the ultrahigh molecular weight polyethylene (UHMWPE) bearing surface for drug delivery can combine functionality with the release of clinically relevant doses of antibiotics. In this study, the feasibility of incorporating a range of antibiotics into UHMWPE is investigated. Drug stability is assessed by thermo‐gravimetric analysis and nuclear magnetic resonance spectroscopy. Drug‐loaded UHMWPEs are prepared by compression molding, using eight antibiotics at different loading. The predicted intra‐articular concentrations of drugs eluted from UHMWPE are above minimum inhibitory concentration for at least 3 weeks against Staphylococci, which are the major causative bacteria for PJI. The antibacterial efficacy is confirmed for samples covering 2% of a representative knee implant in vitro over 72 h, showing that a small fraction of the implant surface loaded with antibiotics may be sufficient against Staphylococci.

Two-way shape memory polymers are stimulus-responsive materials capable of changing their shape between two configurations based on an on/off thermal stimulus. While the traditional effect has been studied under the application of an external mechanical load, it was demonstrated also in the absence of an external load. Such a response only relies on a carefully tailored macromolecular architecture of the polymer combined with a specific thermo-mechanical protocol. In particular, semicrystalline networks, either consisting of a multi-phase copolymer network or a homopolymer based network with broad phase transitions, have been proposed to this aim under ad hoc thermo-mechanical histories. In this work, the two-way shape memory behavior is studied on a poly(ϵ-caprolactone)-based network, crosslinked by means of a sol–gel approach and tailored on the selection of the molecular weight of the precursor polymer. Changing the prepolymer precursor allowed to tune the melting/crystallization regions of the networks, thus the thermal region of the reversible shape memory effect. The application of properly designed thermo-mechanical cycles allowed to study the two-way shape memory effect without the application of an external load under tensile conditions. Given a specific network, the stress-free actuation of the reversible elongation-contraction cycle under tensile conditions was induced across its specific melting/crystallization region. The extent of the effect was found to depend on the crystalline fraction remaining for the given actuation temperature and on the tensile stretched state imposed on the materials during the training step. The results were compared with the response achieved under the traditional two-way shape memory protocol under stress. The stress-free two-way shape memory effect was also successfully demonstrated and emphasized, under flexural conditions, which suggests the potential of these materials as intrinsically reversible actuators, promising for applications in the biomedical field and/or for soft robotics.