Omar Khalid
The brain's ability to adapt and change in response to its environment is known as neuroplasticity or brain plasticity. It was once believed that neuroplasticity only occurred during childhood, but it is now understood that the brain can alter and grow throughout adulthood as well. Synaptic plasticity, or the ability of synapses to strengthen or weaken over time, is a key component of neuroplasticity and is closely linked to memory formation and storage. The concept of synaptic plasticity and its role in memory is known as the synaptic plasticity and memory (SPM) hypothesis. This hypothesis suggests that changes in synaptic connections are a fundamental mechanism of learning and memory retention. While there is substantial evidence supporting this theory, a conclusive link between synapses and memory storage has not yet been established. Nonetheless, real-life examples of brain plasticity, such as improvements in cognitive abilities and behavioural changes following brain training or injuries, showcase the brain's remarkable ability to adapt and reorganise its functions.
| Characteristics | Values |
|---|---|
| Definition | Shape-memory polymers (SMPs) are polymeric smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape when induced by an external stimulus (trigger). |
| External Stimulus | Temperature change, electric or magnetic field, light, or solution. |
| Advantages over SMAs | Higher capacity for elastic deformation, lower cost, lower density, broader range of application temperatures, easier processing, potential biocompatibility and biodegradability, and superior mechanical properties. |
| Applications | Robotics, smart fabrics, self-deployable sun sails in spacecraft, intelligent medical devices, and self-disassembling mobile phones. |
| Types of SMPs | Polyurethanes, polyurethanes with ionic or mesogenic components, block copolymers (e.g., PET and PEO), polytetrafluoroethylene (PFTE), polylactide (PLA), and ethylene-vinyl acetate (EVA). |
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What You'll Learn
Shape-memory polymers (SMPs)
SMPs have a semi-crystalline structure, allowing them to exist in two states: a crystalline state, which is uniform and rigid, and an amorphous state, where polymer subunits are randomly scattered and flexible. The transition between these states occurs at a specific temperature, usually room temperature, known as the "glass transition temperature" (Tg). At Tg, the polymer changes from a rigid crystalline state to a flexible amorphous state.
SMPs have a high capacity for elastic deformation, up to 200% in most cases, and can double in size, allowing for more complex geometries in various applications. They also have a softer, rubbery feel, which makes them ideal for biomedical devices as they are less likely to damage surrounding tissue. Additionally, SMPs have a much lower cost, lower density, and are easy to process compared to SMAs. They can be classified as shape-memory blocks, foams, fibres, and films, and can exhibit one-way, two-way reversible, or multiple-shape memory effects.
The external stimuli that trigger the shape memory effect in SMPs include temperature change, electric or magnetic fields, light or specific wavelengths of light, irradiation with infrared light, immersion in water, and chemical compounds. SMPs can be used in a wide range of applications, including smart fabrics, self-deployable sun sails in spacecraft, intelligent medical devices, self-disassembling mobile phones, robotics, photonics, sensors, aerospace, and biomedicine. In photonics, for example, SMPs enable the production of functional and responsive photonic gratings, allowing for the reprogramming of the lattice parameter and tuning of diffractive behaviour. In the medical field, biodegradable SMPs (BSMPs) are used for minimally invasive procedures, such as smart medical implants, tissue scaffolds, and self-expanding stents.
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Polymer chains
The two states of a polymer are a crystalline state and an amorphous state. In the crystalline state, the polymer is uniformly organised and becomes a rigid, relatively strong structure. In the amorphous state, the polymer subunits are randomly scattered and are relatively soft and flexible, moving around with ease. The transition between these states is achieved when the polymer reaches its glass transition temperature (Tg). At Tg, the polymer changes from a crystalline state to an amorphous state.
The glass transition temperature is not the only temperature that affects SMPs. The melting temperature (Tm) also plays a role. When the SMP exceeds its transition temperature (Ttrans) while remaining below its permanent temperature (Tperm), the material is activated to switch back to its original form. Below Ttrans, the flexibility of the segments is limited. If Tm is chosen for programming the SMP, strain-induced crystallization can be initiated when stretched above Tm and subsequently cooled below Tm.
The polymer chains in SMPs can become entangled with their neighbours. If a force is applied for a short time, this entanglement prevents the large movement of the chain, and the sample recovers its original conformation when the force is removed. However, if the force is applied for a longer period, a relaxation process occurs, leading to plastic and irreversible deformation due to the slipping and disentangling of the polymer chains. Cross-linking, both chemical and physical, can be employed to prevent this slipping and flow.
SMPs have a wide range of applications due to their unique properties. They have a high capacity for elastic deformation, low cost, low density, easy processability, potential biocompatibility and biodegradability, and superior mechanical properties compared to shape-memory alloys (SMAs). SMPs are being used in robotics, biomedical devices, and automotive components, with potential future applications in smart fabrics, spacecraft, intelligent medical devices, and electronics.
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External stimuli
Shape-memory polymers (SMPs) are polymeric smart materials that can return to their original shape after being deformed. This ability is known as the shape memory effect (SME). SMPs can be deformed into a temporary shape and will remain in this form until they are triggered by an external stimulus to return to their original, permanent shape.
SMPs differ from shape-memory alloys (SMAs) in that they exhibit a glass transition or melting transition from a hard to a soft phase, which is responsible for the shape-memory effect. SMAs, on the other hand, exhibit martensitic/austenitic transitions. SMPs have several advantages over SMAs, including a high capacity for elastic deformation, lower cost, lower density, a broad range of application temperatures, easy processing, potential biocompatibility and biodegradability, and superior mechanical properties.
There are numerous external stimuli that can be used to trigger the shape memory effect in SMPs. One of the most common stimuli is temperature change. SMPs can be heated above their glass-transition or melting temperature to resume their original shape. This property has been studied for use in the automatic disassembly of electronic products to aid recycling. For example, SMPs can be used as actuator snap fasteners that hold or release components during the product's use and can then be triggered by heat to release for easy disassembly. Temperature change can also be used in medical applications, such as SMP-based catheters that soften at body temperature, reducing the risk of soft tissue damage during surgical delivery.
Light is another external stimulus that can be used to trigger the shape memory effect. Light-activated shape-memory polymers (LASMPs) use processes of photo-crosslinking and photo-cleaving to change the cross-linking density within the material. For example, polymers containing cinnamic groups can be fixed into predetermined shapes by UV light illumination and then recover their original shape when exposed to UV light of a different wavelength.
Other external stimuli that can trigger the shape memory effect in SMPs include irradiation with infrared light, immersion in water, and the application of electric or magnetic fields.
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Smart materials
One example of smart materials in action is sportswear with ventilation valves that react to temperature and humidity. The valves open when the wearer sweats and close when the body cools down. Smart materials can also be used in buildings to adapt to weather conditions such as wind, heat, or rain. Additionally, they have potential applications in the medical field, such as in the creation of intelligent medical devices and drugs that can be released into the bloodstream when an infection is detected.
Shape-memory polymers (SMPs) are a type of smart material with the ability to return to their original shape after being deformed. This shape memory effect can be triggered by external stimuli such as heat, light, electric or magnetic fields, or immersion in water. SMPs have a wide range of properties, from stable to biodegradable, soft to hard, and elastic to rigid. They also have a much lower cost, lower density, and are easier to process than shape memory alloys.
Other types of smart materials include piezoelectric materials, which produce a voltage when stress is applied, and dielectric elastomers (DEs), which produce large strains under the influence of an external electric field. Magnetic shape memory alloys change their shape in response to changes in the magnetic field, while pH-sensitive polymers alter their volume when the pH of the surrounding medium changes. Thermoelectric materials are used to convert temperature differences into electricity and vice versa.
The development of smart materials is an exciting area of research, with new discoveries being made and applications being explored. Smart materials have the potential to revolutionise various sectors, including design, medicine, architecture, and food. With the advent of 4D printing, it is now possible to print smart materials, opening up even more possibilities for their use.
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Biomedical applications
Shape-memory polymers (SMPs) are smart materials that can return to their original shape from a deformed state when triggered by external stimuli such as heat, electricity, magnetic fields, light, or solutions. This ability, known as the shape memory effect (SME), has a wide range of potential applications, including in the biomedical field.
In the biomedical field, SMPs have been investigated for their potential use in medical devices, implants, and drug delivery systems. For example, SMP-based catheters can soften at body temperature, reducing the risk of soft tissue damage during surgical procedures. SMPs can also be used as biodegradable stitches, self-expanding stents, implants for treating obesity, self-fitting vascular and coronary grafts, and customised orthopaedic devices.
The use of SMPs in medicine could lead to less invasive procedures and smarter medical implants. SMPs can also be used as structural components that repair themselves, such as car parts that can be repaired by applying temperature.
Additionally, SMPs can be used in combination with other materials to create composite structures. For example, SMP composites (SMCs) filled with conductive or magnetic fillers can be used to trigger shape recovery or provide alternative methods of triggering shape memory.
The development of SMPs for biomedical applications is an active area of research, with ongoing investigations into their safety and effectiveness for in vivo use.
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Frequently asked questions
Plastic memory is the ability of certain materials to return to their original shape after being deformed. These materials are known as shape-memory polymers (SMPs).
SMPs have a semi-crystalline structure, allowing them to exist in two states at the same time within a specific temperature range, usually room temperature. When an external stimulus, such as temperature change, is applied, the SMP transitions between its temporary deformed state and its permanent original state.
SMPs have a wide range of applications, including smart fabrics, self-deployable sun sails in spacecraft, intelligent medical devices, and self-disassembling mobile phones. In medicine, SMPs can be used for medical implants, and doctors use SMP wires that expand into a mesh when heated by body temperature.
SMPs offer several advantages over traditional materials. They have a high capacity for elastic deformation, are cost-effective, have low density, are easy to process, and exhibit superior mechanical properties. Additionally, SMPs can be tailored to have specific properties, such as biodegradability, rigidity, or elasticity, making them versatile for various applications.
