Choy Sin Lee

Metal–organic frameworks (MOFs) are crystalline materials formed by linking organic linkers with metal ions or clusters. MOFs are highly porous materials with tunable structures that have numerous applications from environmental remediation to energy storage. Oleochemicals have gained attention as biodegradable building blocks for MOF synthesis, reflecting a growing interest in sustainable feedstocks for advanced materials. Their incorporation into MOFs enhances structural diversity and expands the functions of MOFs through their unique physicochemical properties. This review presents the oleochemicals employed as building blocks and modulators in MOFs with their properties and the resulting framework characteristics. Oleochemical‐derived dicarboxylic acids function as structural linkers or as co‐linkers with pendant groups, while fatty acids serve as modulators for defect engineering to regulate particle size, surface area, and porosity. However, the application of oleochemicals in MOFs synthesis is hindered by critical knowledge gaps regarding how the impurities in dicarboxylic acids could disrupt crystallization and how the inherent flexibility and hydrophilicity of these aliphatic diacids chain compromise stability. It outlines the challenges that will be critical in optimising the design, synthesis, stability, and application of oleochemical‐derived precursors for MOFs, paving the way for high‐performance sustainable materials.

Stimulus‐responsive metal–organic frameworks (MOFs) are a subclass of MOFs that undergo physicochemical changes in response to external stimuli. The large surface area, tunable properties, and high porosity of MOFs and their dynamic nature of stimulus‐responsiveness, making them highly effective for sensing applications. The luminescence properties of MOF‐based sensors enable optical detection, making them cost‐effective compared with conventional sensing techniques. MOFs can response to various stimuli; however, the practical application of these stimulus‐responsive MOFs is limited by challenges such as poor processability and stability, requiring further advancements to enhance their real‐world viability. Recently, the integration of stimulus‐responsive MOFs into hydrogels has been extensively explored to improve their performance as sensors. This review highlights the utilization of stimulus‐responsive MOF–hydrogel composites as sensors. The types of stimuli, preparation methods, and the distinct roles of both MOF and hydrogel components are discussed. The applications covered include biosensing, environmental remediation, and agricultural food safety monitoring, with target analytes spanning across heavy metals, toxic anions, volatile organic compounds, pesticides, biomolecules, and mycotoxins. Furthermore, the challenges and future prospects of stimulus‐responsive MOF–hydrogel composites are evaluated, with rational design strategies proposed to guide future development.

A review of recent advances of NIR-light induced photothermal-responsive shape memory polyurethane for industrial and medical applications. It covers the classes of photothermal agents, responsive mechanism, synthesis, advantages, and challenges.

A UV‐ and thermo‐responsive polyurethane‐acrylate prepolymer was synthesized from palm olein (PO_o) via a non‐isocyanate route. The process included epoxidation of PO_o, carbonation of epoxidized palm olein (EPO_o) into polycyclic carbonate in a solvent‐free and mild condition (100°C, 1 atm), followed by reacting with ethylene diamine and acrylic acid. The chemical structure of the non‐isocyanate polyurethane‐acrylate (NIPUA) prepolymer was elucidated by ¹H and ¹³C nuclear magnetic resonance (NMR) and Fourier transform‐infrared spectroscopy (FTIR), while weight average molecular weight of NIPUA was determined by gel permeation chromatography (GPC). The NIPUA (0–20 wt%) was incorporated with thermoplastic elastomer (TPE) as a plasticizer and cured under UV light and thermal stimulations. The cured NIPUA/TPE films were characterized by FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile strength test. Under UV and thermal stimulations, the NIPUA/TPE demonstrated enhanced tensile properties (elongation at break >1280%, Young's modulus ~25 MPa), thermal properties (lower T_g), lower water contact angle, and shortened curing time as compared with the blank TPE. The 20 wt% NIPUA/TPE films exhibited susceptibility to enzymatic biodegradation and noncytotoxic to HEK 293 cells in vitro, demonstrated it's potential as a UV‐ and thermo‐responsive plasticizer for TPE in manufacturing of medical devices.

A pH responsive non‐isocyanate polyurethane‐acrylate (NIPUA) is synthesized through utilizing palm olein and sunflower oil as feedstock. The unsaturated acyl chains of both vegetable oils are converted into epoxy rings through epoxidation and subjected to carbonation with binary catalytic system under a solventless and mild condition to produce the cyclic carbonates. The cyclic carbonates were reacted with 1,4‐butanediamine and itaconic acid to produce the NIPUA. The intermediates and product were characterized by FTIR spectroscopy, NMR spectroscopy and gel permeation chromatography. The NIPUA was incorporated with poly(vinyl pyrrolidone) (PVP) to form a polymer carrier system loaded with a hydrophobic model drug, lovastatin (LOV). All NIPUA/PVP preformulations demonstrated pH responsiveness, with 1 to 2‐folds enhanced solubility at pH 7.4 compared to pH 2.0. NIPUA/PVP exhibited solubility enhancer effect by significantly enhanced solubility (2–4 times) compared to pure LOV, LOV‐loaded PVP, and Medostatin tablets at both pH levels. LOV‐loaded NIPUA/PVP exhibited lower enthalpy energy in DSC thermogram than LOV‐loaded PVP, indicating disruption of LOV's crystalline structure. In MTT assay, IC₅₀ values were 30.76 μg mL⁻¹ for pure LOV and 273.53 μg mL⁻¹ for NIPUA/PVP, demonstrating the potential of NIPUA as an environmentally friendly, pH responsive drug carrier for controlled release of poorly water‐soluble drugs.

Metal–organic frameworks (MOFs) have attracted chemical and material research interests in recent years due to their incredibly prominent properties and unique structures. Although MOFs have many unique characteristics, including tunable pore structures and functionality, their application performances are hindered by their powdered crystalline state, intrinsic fragility, poor processability, and stability. Recent studies have shown that the incorporation of MOFs into hydrogel outperforms the MOFs in their crystalline state. This article presents the current development of stimulus-responsive MOF–hydrogel composites in terms of synthesis of MOF and preparation of MOF–hydrogel, characterization, and advancement of stimulus-responsive MOF–hydrogel composite in drug delivery and wound management. The article also discusses prospective study directions, delineating potential avenues for further exploration and innovation in this dynamic field.

Stimuli responsiveness has been an attractive feature of smart material design, wherein the chemical and physical properties of the material can be varied in response to small environmental change. Polyurethane (PU), a widely used synthetic polymer can be upgraded into a light-responsive smart polymer by introducing a light-sensitive moiety into the polymer matrix. For instance, azobenzene, spiropyran, and coumarin result in reversible light-induced reactions, while o-nitrobenzyl can result in irreversible light-induced reactions. These variations of light-stimulus properties endow PU with wide ranges of physical, mechanical, and chemical changes upon exposure to different wavelengths of light. PU responsiveness has rarely been reviewed even though it is known to be one of the most versatile polymers with diverse ranges of applications in household, automotive, electronic, construction, medical, and biomedical industries. This review focuses on the classes of light-responsive moieties used in PU systems, their synthesis, and the response mechanism of light-responsive PU-based materials, which also include dual- or multi-responsive light-responsive PU systems. The advantages and limitations of light-responsive PU are reviewed and challenges in the development of light-responsive PU are discussed.

Due to the specific physiological pH throughout the human body, pH-responsive polymers have been considered for aiding drug delivery systems. Depending on the surrounding pH conditions, the polymers can undergo swelling or contraction behaviors, and a degradation mechanism can release incorporated substances. Additionally, polyurethane, a highly versatile polymer, has been reported for its biocompatibility properties, in which it demonstrates good biological response and sustainability in biomedical applications. In this review, we focus on summarizing the applications of pH-responsive polyurethane in the biomedical and drug delivery fields in recent years. In recent studies, there have been great developments in pH-responsive polyurethanes used as controlled drug delivery systems for oral administration, intravaginal administration, and targeted drug delivery systems for chemotherapy treatment. Other applications such as surface biomaterials, sensors, and optical imaging probes are also discussed in this review.

There has been increasing concern over the toxic effects of microplastics (MP), nanoplastics (NP), and copper (Cu) on microalgae. However, the combined toxicity of the metal in the presence of polystyrene (PS) MP/NP on microalgae has not been well studied, particularly after long-term exposure (i.e., longer than 4 days). The primary aim of the present study was to investigate the effect of PS MP and NP on Cu toxicity on two freshwater microalgae, namely Chlorella sp. TJ6-5 and Pseudokirchneriella subcapitata NIES-35 after acute exposure for 4 days and up to 16 days. The results showed that both microalgae were sensitive to Cu, but tolerant to MP/NP. However, MP/NP increased the toxicity of Cu at EC₅₀ in both microalgae, which was only noticeable in chronic exposure. Single and combined treatment of MP/NP and Cu induced higher oxidative stress and caused morphological and ultrastructural changes in both microalgae. The adsorption of Cu to MP and NP was low (0.23–14.9%), with most of the Cu present in free ionic form (81.6–105.8%). The findings on different sensitivity of microalgae to Cu in the presence of MP/NP may have significant implication as microalgae are likely to be exposed to a mixture of both MP/NP and Cu in the environment. For example, in air-blasting technology, MP and NP are used as abrasive medium to remove Cu-containing antifouling paints on hulls of ship and submerged surfaces. Wastewater treatment plants receive household wastes containing MP and NP, as well as stormwater runoffs and industrial wastes contaminated with heavy metals.