Phenomenological modeling of the stress-free two-way shape-memory effect in semi-crystalline networks: Formulation, numerical simulation, and experimental validation

Polymers exhibiting the stress-free two-way shape-memory effect (SME) represent an appealing solution to achieve self-standing reversible actuation that is a fundamental feature required by numerous applications. The present paper proposes a one-dimensional continuum phenomenological framework to model single-component semi-crystalline polymer networks exhibiting both the one-way SME and the two-way SME under stress and stress-free conditions. A comprehensive experimental campaign is first performed on semi-crystalline networks based on poly(ε-caprolactone) (PCL) to characterize the mechanical and thermal properties as well as the one-way and two-way shape memory behavior of the material under different thermo-mechanical conditions. The results guide the formulation of the model, elucidating the selection of the control and phase variables and motivating the choice of their evolution laws. Model capabilities are then demonstrated against experimental data. All the phenomena that influence the stress-free two-way SME, including the actuation temperature, heating/cooling rates, applied stress/strain, and the amount of skeleton and actuation phase, are analyzed and discussed, giving new important insight for application developme

3D Printed Shape Memory Polymers for Biomedical Applications

3D Printed Shape Memory Polymers for Biomedical Applications3D Printed Shape Memory Polymers for Biomedical Application

PLA/PCL-based foams as scaffolds for tissue engineering applications

In this paper a novel procedure to produce rigid polymeric foams, with well interconnected open pores and with potential application as scaffolds for tissue engineering, is presented. The materials were prepared starting from a precursor obtained by melt blending a poly(L-lactic acid) (PLLA)/poly(caprolactone) (PCL) blend with a superabsorbent polymer (SAP), consisting of crosslinked particles of sodium polyacrylate. Immersion in water allowed the SAP particles to swell and leach from the matrix, giving rise to a foam structure, easily and safely obtained without the need of organic solvents or chemical foaming agents. The achievement of a proper property profile and foamed structure was investigated through thermal, mechanical and morphological analyses on the prepared systems, comparing properties and structure before and after SAP particles leaching. SEM analysis evidenced the precursor structure formed by a PLLA matrix embedding PCL particles (average diameter: 6 μm) and SAP particles (30-50 μm), and the achievement of a porous structure after water immersion. The effectiveness of the SAP particles leaching was ensured by the weak particles-matrix adhesion, as suggested by mechanical tests. A preliminary biological investigation showed that the chemical composition allowed good cell adhesion on neat and foamed PLA/PCL blends, and highlighted the role of the interconnected porous morphology in significantly increasing cell proliferation

PLA/PCL-based foams as scaffolds for tissue engineering applications

In this paper a novel procedure to produce rigid polymeric foams, with well interconnected open pores and with potential application as scaffolds for tissue engineering, is presented. The materials were prepared starting from a precursor obtained by melt blending a poly(L-lactic acid) (PLLA)/poly(caprolactone) (PCL) blend with a superabsorbent polymer (SAP), consisting of crosslinked particles of sodium polyacrylate. Immersion in water allowed the SAP particles to swell and leach from the matrix, giving rise to a foam structure, easily and safely obtained without the need of organic solvents or chemical foaming agents. The achievement of a proper property profile and foamed structure was investigated through thermal, mechanical and morphological analyses on the prepared systems, comparing properties and structure before and after SAP particles leaching. SEM analysis evidenced the precursor structure formed by a PLLA matrix embedding PCL particles (average diameter: 6 μm) and SAP particles (30-50 μm), and the achievement of a porous structure after water immersion. The effectiveness of the SAP particles leaching was ensured by the weak particles-matrix adhesion, as suggested by mechanical tests. A preliminary biological investigation showed that the chemical composition allowed good cell adhesion on neat and foamed PLA/PCL blends, and highlighted the role of the interconnected porous morphology in significantly increasing cell proliferation

PLA/PCL-based foams as scaffolds for tissue engineering applications

In this paper a novel procedure to produce rigid polymeric foams, with well interconnected open pores and with potential application as scaffolds for tissue engineering, is presented. The materials were prepared starting from a precursor obtained by melt blending a poly(L-lactic acid) (PLLA)/poly(caprolactone) (PCL) blend with a superabsorbent polymer (SAP), consisting of crosslinked particles of sodium polyacrylate. Immersion in water allowed the SAP particles to swell and leach from the matrix, giving rise to a foam structure, easily and safely obtained without the need of organic solvents or chemical foaming agents. The achievement of a proper property profile and foamed structure was investigated through thermal, mechanical and morphological analyses on the prepared systems, comparing properties and structure before and after SAP particles leaching. SEM analysis evidenced the precursor structure formed by a PLLA matrix embedding PCL particles (average diameter: 6 μm) and SAP particles (30-50 μm), and the achievement of a porous structure after water immersion. The effectiveness of the SAP particles leaching was ensured by the weak particles-matrix adhesion, as suggested by mechanical tests. A preliminary biological investigation showed that the chemical composition allowed good cell adhesion on neat and foamed PLA/PCL blends, and highlighted the role of the interconnected porous morphology in significantly increasing cell proliferation

Temperature-memory effect in 3D printed photopolymers with broad glass transition

The recent efforts towards the realization of shape memory polymer-based structures through additive manufacturing techniques (3D-printing) are often referred with the name 4D-printing (the 4th dimension representing the time-dependent shape evolution of the printed element) and aim at providing systems capable of complex shape changes and sequential motions. In this paper the shape memory capabilities of commercial photopolymer systems printed by stereolithography were investigated, allowing to describe the recovery process as a function of temperature. Particular attention was reserved towards the effect of the deformation temperature, which in presence of a broad glass transition region allows to achieve the so called "temperature memory effect", i.e. the possibility to modify the thermal trigger of the shape memory effect through the deformation temperature. The temperature memory features of the printed materials were quantified and a sequential thermally activated deployment was attempted

Expandable Drug Delivery Systems Based on Shape Memory Polymers: Impact of Film Coating on Mechanical Properties and Release and Recovery Performance

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