This article provides an overview of various patterning methodologies, and it is organized into three major sections: generation of patterns, replication of patterns, and three‐dimensional patterning. Generation of patterns from scratch is usually accomplished by serial techniques that are able to provide arbitrary features. The writing process can be carried out in many different ways. It can be achieved using a rigid stylus; or a focused beam of photons, electrons, and other energetic particles. It can also be accomplished using an electrical or magnetic field; or through localized add‐on of materials such as a liquid‐like ink from an external source. In addition, some ordered but relatively simple patterns can be formed by means of self‐assembly. In replication of patterns, structural information from a mask, master, or stamp is transferred to multiple copies with the use of an appropriate material. The patterned features on a mask are mainly used to direct a flux of radiation or physical matter from a source onto a substrate, whereas a master/stamp serves as the original for replication based on embossing, molding, or printing. The last section of this article deals with three‐dimensional patterning, where both vertical and lateral dimensions of a structure need to be precisely controlled to generate well‐defined shapes and profiles. The article is illustrated with various examples derived from recent developments in this field.

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.

Semi-interpenetrating polymer network (semi-IPN) hydrogel was prepared to recognize hemoglobin, by molecularly imprinted method, in the mild aqueous media of chitosan and acrylamide in the presence of N,N'-methylenebisacrylamide as the cross-linking agent. The hydrogel obtained has been investigated by using thermal analysis, X-ray diffraction, differential scanning calorimetry (DSC), and environmental scanning electron microscope (ESEM). Langmuir analysis showed that an equal class of adsorption was formed in the hydrogel, and the adsorption equilibrium constant and the maximum adsorption capacity were evaluated to be 4.27 g/mL and 36.53 mg/g wet hydrogel, respectively. The imprinted semi-IPN hydrogel has a much higher adsorption capacity for hemoglobin than the nonimprinted hydrogel with the same chemical composition and also has a higher selectivity for the imprinted molecule.

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This work reports the formation of thermoresponsive poly(N-isopropylacrylamide-co-styrene) (PNIPAAmSt) microgel films and their use for cell growth and detachment via temperature stimuli. Thermoresponsive surface films can be conveniently produced by spin-coating or drop-coating of PNIPAAmSt microgel dispersions onto substrates such as glass coverslips, cell culture plates, and flasks, making this technique widely accessible. The thickness, stability, and reversibility of the PNIPAAmSt films coated on silicon wafers with respect to temperature switching were examined by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM). The results unraveled the direct link between thermoreversibility and changes in film thickness and surface morphology, showing reversible hydration and dehydration. Under different coating conditions, well-packed microgel monolayers could be utilized for effective cell recovery and harvesting. Furthermore, cell adhesion and detachment processes were reversible and there was no sign of loss of cell viability during repeated surface attachment, growth, and detachment, showing a mild interaction between cells and thermoresponsive surface. More importantly, there was little deterioration of the packing of the thermoresponsive films or any major loss of microgel particles during reuse, indicating their robustness. These PNIPAAmSt microgel films thus open up a convenient interfacial platform for cell and cell sheet harvesting while avoiding the damage of enzymatic cleavage.