Free-standing copolymer network samples with two types of crystallizable domains are capable of a fully reversible bidirectional shape-memory effect. One set of crystallizable domains determines the shape-shifting geometry while the other provides the thermally controlled actuation capability.

A reversible triple‐shape effect is achieved for multi‐phase polymer networks based on two different crystallizable segments. The reversibility of the two shape‐changes is based on crystallization induced elongation (CIE) occurring during cooling and melting‐induced contraction (MIC) during heating under constant stress.

Thermo‐sensitive triple‐shape polymers can perform two consecutive shape changes in response to heat. These shape changes correspond to the recovery of two different deformations in reverse order, which were programmed previously at elevated temperature levels (Tmid and Thigh) by the application of external stress. Recently, an AB copolymer network was described, which surprisingly exhibited a triple‐shape effect despite being programmed with only one deformation at Thigh. Here it is explored whether a copolymer network system can be designed that enables a one‐step deformation process at ambient temperature (cold drawing) as a novel, gentle, and easy‐to‐handle triple‐shape‐creation procedure, in addition to the procedures reported to date, which generally involve deformation(s) at elevated temperature(s). A copolymer‐network system with two crystallizable polyester segments is synthesized and characterized, fulfilling two crucial criteria. These materials can be deformed at ambient temperature by cold drawing and show, even at Thigh, which is above the melting points of both switching domains, elongation at break of up to 250%. Copolymer networks with PCL contents of 75 and 50 wt% show a triple‐shape effect after cold drawing with shape‐fixity ratios between 65% and 80% and a total‐shape‐recovery ratio above 97%. Furthermore, in these copolymer networks, the triple‐shape effect can be obtained after a one‐step deformation at Thigh. Independent of the temperature at which the deformation is applied (ambient temperature or Thigh), copolymer networks that have the same compositions show similar switching temperatures and proportioning of the recovery in two steps. The two‐step programming procedure enables a triple‐shape effect in copolymer networks for an even broader range of compositions. This versatile triple‐shape‐material system based on tailored building blocks is an interesting candidate material for applications in fixation systems or disassembling systems.

Biodegradable shape-memory polymers have attracted tremendous interest as potential implant materials for minimally invasive surgery. Here, the precise control of the material's functions, for example, the switching temperature T(sw), is a particular challenge. T(sw) should be either between room and body temperature for automatically inducing the shape change upon implantation or slightly above body temperature for on demand activation. We explored whether T(sw) of amorphous polymer networks from star-shaped rac-dilactide-based macrotetrols and a diisocyanate can be controlled systematically by incorporation of p-dioxanone, diglycolide, or epsilon-caprolactone as comonomer. Thermomechanical experiments resulted that T(sw) could be adjusted between 14 and 56 degrees C by selection of comonomer type and ratio without affecting the advantageous elastic properties of the polymer networks. Furthermore, the hydrolytic degradation rate could be varied in a wide range by the content of easily hydrolyzable ester bonds, the material's hydrophilicity, and its molecular mobility.

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Biodegradable polymers are versatile polymeric materials that have a high potential in biomedical applications avoiding subsequent surgeries to remove, for example, an implanted device. In the past decade, significant advances have been achieved with poly(lactide acid) (PLA)-based materials, as they can be equipped with an additional functionality, that is, a shape-memory effect (SME). Shape-memory polymers (SMPs) can switch their shape in a predefined manner upon application of a specific external stimulus. Accordingly, SMPs have a high potential for applications ranging from electronic engineering, textiles, aerospace, and energy to biomedical and drug delivery fields based on the perspectives of new capabilities arising with such materials in biomedicine. This study summarizes the progress in SMPs with a particular focus on PLA, illustrates the design of suitable homo- and copolymer structures as well as the link between the (co)polymer structure and switching functionality, and describes recent advantages in the implementation of novel switching phenomena into SMP technology.

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