# Recent Developments in Materials Science for the Conservation and Restoration of Historic Artifacts
## 6 Smart Materials--A Potential Breakthrough in Heritage Science
### Key Characteristics of Smart Materials  
Considering their potential use in heritage science, some important characteristics of smart materials must be underlined. Smart materials can alter their physical, chemical, or mechanical properties when exposed to specific stimuli. For example, shape-memory alloys can return to their original shape after being deformed when subjected to heat [101]. This property is particularly useful in applications where structural integrity must be maintained under varying conditions. At the same time, many smart materials can detect changes in their surroundings and respond accordingly. This capability allows them to provide real-time information about environmental conditions [102]. For instance, piezoelectric materials generate electrical signals in response to mechanical stress, making them suitable for sensors and actuators [103]. Some smart materials can be programmed to exhibit specific behaviors or responses based on predetermined conditions. This feature enhances their versatility in various applications. Programmable shape-memory polymers can be designed to change shape at specific temperatures or under particular conditions [104]. Certain smart materials possess the ability to repair themselves after damage, which extends their lifespan and reduces maintenance needs. Self-healing polymers can autonomously recover from scratches or cracks when exposed to specific stimuli [105]. Smart materials can also optimize resource use and promote sustainability by adapting their properties based on changing environmental factors. For example, thermochromic materials change color with temperature fluctuations, providing visual indicators for temperature control [106]. In the category of smart materials, several types of materials can be classified, all possessing a range of properties that contribute to their functionality in heritage conservation applications. These properties include the following:  
* Responsiveness to environmental changes
* Thermochromic materials change color in response to temperature variations. They can be used in coatings that indicate temperature fluctuations, providing visual cues for monitoring environmental conditions [107]. This property is particularly useful for artworks sensitive to heat exposure. * Hydrogels can swell or shrink in response to changes in humidity or temperature. These responsive behaviors make them useful for monitoring moisture levels in artifacts [108]. The ability to provide real-time feedback on humidity levels helps prevent damage caused by excessive moisture. * Shape-memory alloys can undergo significant deformation and return to their original shape upon heating. This property is beneficial for applications requiring
flexibility and adaptability. For example, they can be used in structural reinforcements that adjust based on temperature changes [109]. * Many smart materials offer a favorable balance between strength and weight. This characteristic is particularly advantageous for applications where structural integrity is essential without adding excessive weight [110]. Lightweight yet strong materials are crucial for preserving fragile artifacts. - Smart polymers often exhibit high elasticity, allowing them to stretch and conform to various shapes while maintaining strength [6]. This flexibility is a very important aspect for developing applications such as adaptive supports for fragile artifacts. * Smart materials are often engineered for chemical stability under various environmental conditions, ensuring they retain functionality over time without degrading [111]. This property is essential for long-term conservation efforts where exposure to pollutants or moisture is a concern. * The chemical composition of smart materials can be modified to achieve specific properties or functionalities tailored to the needs of particular conservation projects. For instance, the addition of plasticizers can enhance flexibility while maintaining mechanical strength [112].