Shape memory polymer based on chemically cross-linked poly(vinyl alcohol) containing a small number of water molecules

Starch-based shape memory sponge for rapid hemostasis in penetrating wounds

Death caused by excessive blood loss has always been a global concern. Timely control of bleeding in incompressible penetrated wounds remains a great challenge. Here, we developed a shape memory sponge (SQG) based on modified starch and gelatin (Gel) to control the hemorrhage of penetrating wounds. The porous structure of SQG greatly enhanced the absorption of blood, and the adhesion of erythrocytes and platelets. The water absorption rate of SQG reached 1178.72 ± 12.18% in 10 s. SQG quickly recovered its shape in water (∼3 s) and exhibited high mechanical strength (∼38 kPa), acting as a physically packed barrier to facilitate hemostasis. Furthermore, the positively charged sponges were conducive to activating platelets and promoting the release of coagulation factors. SQG sponges possessed the lowest blood coagulation index (BCI) of 21.32 ± 0.19%, and presented good biocompatibility and obvious inhibitory effect on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Moreover, SQG sponges controlled complete bleeding in 69 ± 20 s and a bleeding loss of 334 ± 138 mg was observed, nearly 50% lower than that of gelatin sponge in rabbit liver penetrating wounds. Overall, SQG possesses a combination of potent shape recovery, rapid hemostasis, and excellent antibacterial and degradation ability, enabling promising applications for hemostasis in non-compressible penetrating wounds.

Experimental and computational analysis of a pharmaceutical-grade shape memory polymer applied to the development of gastroretentive drug delivery systems

The present paper aims at developing an integrated experimental/computational approach towards the design of shape memory devices fabricated by hot-processing with potential for use as gastroretentive drug delivery systems (DDSs) and for personalized therapy if 4D printing is involved. The approach was tested on a plasticized poly(vinyl alcohol) (PVA) of pharmaceutical grade, with a glass transition temperature close to that of the human body (i.e., 37 °C). A comprehensive experimental analysis was conducted in order to fully characterize the PVA thermo-mechanical response as well as to provide the necessary data to calibrate and validate the numerical predictions, based on a thermo-viscoelastic constitutive model, implemented within a finite element framework. Particularly, a thorough thermal, mechanical, and shape memory characterization under different testing conditions and on different sample geometries was first performed. Then, a prototype consisting of an S-shaped device was fabricated, deformed in a temporary compact configuration and tested. Simulation results were compared with the results obtained from shape memory experiments carried out on the prototype. The proposed approach provided useful results and recommendations for the design of PVA-based shape memory DDSs.

Shape Memory Polymers Based on Supramolecular Interactions

Shape memory polymers (SMPs), with the capability to change from one or more temporary shapes to predetermined shapes in response to an external stimulus, have attracted much interest from both academia and industries. When introducing supramolecular interactions that have been featured as dynamic and reversible into the design of novel SMPs, intriguing and unique functionalities have been engendered and thereby broaden the potential applications of the SMPs to new territories. In this review, we summarize recent progress made in SMPs based on supramolecular interactions, provide insight into the material design and shape memory mechanism, elucidate and evaluate their properties and performance, and point out opportunities and applications of SMPs.

Calcium sulfate hemihydrate whisker reinforced polyvinyl alcohol with improved shape memory effect

A novel shape memory composite is synthesized by introducing calcium sulfate hemihydrate whisker to reinforce polyvinyl alcohol.

Thermo- and water-induced shape memory poly(vinyl alcohol) supramolecular networks crosslinked by self-complementary quadruple hydrogen bonding

Poly(vinyl alcohol) (PVA) supramolecular networks cross-linked by ureido-pyrimidinone (UPy) dimers via strong quadruple hydrogen bonding in donor–donor–acceptor–acceptor (DDAA) arrays have been synthesized for the first time.

Moving-window two-dimensional correlation infrared spectroscopic study on the dissolution process of poly(vinyl alcohol)

In this paper, the dissolution process of fully hydrolyzed polyvinyl alcohol (PVA) was investigated by temperature-dependent Fourier transform infrared spectroscopy (FTIR) combined with moving-window two-dimensional (MW2D) correlation infrared spectroscopy (IR). The results show that the FTIR spectra of PVA in OH stretching and bending regions exceed the measuring range of the spectrometer because of the presence of abundant water. The OH stretching and bending peaks reveal that the water mainly diffuses into amorphous region below 45 °C, and water molecules mainly diffuse into crystalline region above 45 °C. The peak at 1141 cm(-1) has ever been thought as the indication of crystallinity of PVA in solid state, but in solution, the peak does not decrease with the dissolution of crystalline region and finally increases when PVA is dissolved completely. The hydrogen bonds between hydroxyl groups in PVA chains are broken by water molecules but abundant new hydrogen bonds between hydroxyl groups in PVA chains and water molecules are formed during the dissolving process. In the 2D correlation analysis of the FTIR spectra, only the correlation movements of hydroxyl groups, including stretching and bending mode, can be observed. The correlation range and intensity are larger than that of PVA in solid state because the dissolution is the interaction process of water molecules diffusing into PVA chains.

Preparation and characterization of Kraft lignin-based moisture-responsive films with reversible shape-change capability

Preparation of moisture-responsive Kraft lignin-based materials by electrospinning blends of Kraft lignin fractions with different physical properties is presented. The differences in thermal mobility between lignin fractions are shown to influence the degree of interfiber fusion occurring during oxidative thermostabilization of electrospun nonwoven fabrics, resulting in different material morphologies including submicrometer fibers, bonded nonwovens, porous films, and smooth films. The relative amount of different lignin fractions and degree of fiber flow and fiber fusion is shown to influence the tendency for the electrospun materials to be transformed into moisture-responsive materials capable of reversible changes in shape. Material characterization by scanning electron microscopy and atomic force microscopy as well characterization of the chemical and physical properties of Kraft lignin fractions by dynamic rheology, 1H and 13C NMR, and gel permeation chromatography combined with multiangle laser light scattering are presented. A proposed mechanism underlying moisture-responsiveness, shape change, and shape recovery is discussed based on the differences in chemical structure and physical properties of Kraft lignin fractions.

Moving-window two-dimensional correlation infrared spectroscopy study on structural variations of partially hydrolyzed poly(vinyl alcohol)

In the present study, the molecular chain changes and structural transitions of partially hydrolyzed poly(vinyl alcohol) (PVA) having a 12 mol% acetate unit were analyzed by moving-window two-dimensional (MW2D) correlation infrared spectroscopy combined with differential scanning calorimetry and thermogravimetric analysis. The results show the glass-transition temperature (T(g)) of PVA is clearly distinguished by MW2D correlation infrared spectroscopy, and the acetate groups start to be eliminated around the melting temperature, whereas the free water molecules in PVA are eliminated above T(g). The correlation movements of the O-H stretching modes, including the free hydroxyl groups and the hydrogen bonds, are clearly determined using MW2D correlation infrared spectroscopy. The spectral variations in the C=O stretching region caused by the elimination of the acetate unit from polymer chains are also discussed on the basis of the results of the MW2D correlation analysis. Such results cannot be obtained by traditional infrared spectroscopy owing to the complex overlapping peaks.