Poly(N-isopropylacrylamide) (PNIPAM)-based thermosensitive hydrogels demonstrate great potential in biomedical applications. However, they have inherent drawbacks such as low mechanical strength, limited drug loading capacity and low biodegradability. Formulating PNIPAM with other functional components to form composited hydrogels is an effective strategy to make up for these deficiencies, which can greatly benefit their practical applications. This review seeks to provide a comprehensive observation about the PNIPAM-based composite hydrogels for biomedical applications so as to guide related research. It covers the general principles from the materials choice to the hybridization strategies as well as the performance improvement by focusing on several application areas including drug delivery, tissue engineering and wound dressing. The most effective strategies include incorporation of functional inorganic nanoparticles or self-assembled structures to give composite hydrogels and linking PNIPAM with other polymer blocks of unique properties to produce copolymeric hydrogels, which can improve the properties of the hydrogels by enhancing the mechanical strength, giving higher biocompatibility and biodegradability, introducing multi-stimuli responsibility, enabling higher drug loading capacity as well as controlled release. These aspects will be of great help for promoting the development of PNIPAM-based composite materials for biomedical applications.

DAST nanocrystal dispersion having fixed anisotropy may be enhanced by orientational factors. ExperimentalDAST, lauryl acrylate, and tricyclo[5.2.1.0 2,6 ]decane-4,8-dimethanol diacrylate (TD) were purchased from Aldrich Co. Inc. n-Dodecyltrimethylammonium chloride (DTMAC) and benzoin isopropyl ether (BIPE) were purchased from Tokyo Kasei Co., Ltd. DAST and BIPE were recrystallized twice from methanol and toluene, respectively. The other reagents were used without further purification. An ethanol solution (50 lL) containing DAST (5 mM) and DTMAC (5 mM) was injected into lauryl acrylate (5 mL) containing BIPE (0.1 M) and TD (1 wt.-%) according to the reprecipitation method [2]. The average nanocrystal size was obtained using a DLS-7000 dynamic light scattering analyzer (Otsuka Electronics); the viscosity and refractive index of the dispersion were 4.0 mPa s at 25 C and 1.444 at 20 C, respectively. A sample was positioned between the two poles of an electromagnet (Fluxdial precision electromagnet control system, Applied Magnetics Laboratory Inc.), which can operate at magnetic flux densities of up to 2.5 T, and the absorption spectra of the DAST nanocrystals dispersed in lauryl acrylate solution were measured in both the Faraday and Voigt configurations using a personal computer, the electromagnet, the detectable light from a Xe lamp light source (passed through a polarizer), a JASCO CT-25C monochromator, and a 2023 photodiode detector (New Forcus Inc.). After nitrogen gas had been bubbled through the DAST nanocrystal acrylate dispersion for 20 min, photocuring was performed in the magnetic field by irradiating the sample with UV light from a 500 W high-pressure mercury lamp (UI-501C, USHIO). To fix the anisotropic orientation of the DAST nanocrystal dispersion, we used a superconducting magnet (S15/17/40RT/13 horizontal magnet system, Oxford) having an output of up to 17 T. The optical rotatory dispersion spectra were measured using a JASCO J-820 spectropolarimeter.

Recent research has indicated that polydopamine and synthetic eumelanins are optoelectronic biomaterials in which one-dimensional aggregates composed of ordered-stacking oligomers have been proposed as unique organic semiconductors. However, improving the ordered-stacking of oligomers in polydopamine nanostructures is a big challenge. Herein, we first demonstrate how folic acid molecules influence the morphology and nanostructure of polydopamine via tuning the π-π interactions of oligomers. MALDI-TOF mass spectrometry reveals that porphyrin-like tetramers are characteristic of folic acid-polydopamine (FA-PDA) nanofibers. X-ray diffraction combined with simulation studies indicate that these oligomers favour aggregation into graphite-like ordered nanostructures via strong π-π interactions. High-resolution TEM characterization of carbonized FA-PDA hybrids show that in FA-PDA nanofibers the size of the graphite-like domains is over 100 nm. The addition of folic acid in polydopamine enhances the ordered stacking of oligomers in its nanostructure. Our study steps forward to discover the mystery of the structure-property relationship of FA-PDA hybrids. It paves a way to optimize the properties of PDA through the design and selection of oligomer structures.