Papers by Author: Andreas Lendlein

Abstract: Biodegradable polymers are applied in temporary implants, such as surgical sutures and controlled drug delivery systems. They are also of relevance in biomaterial-based Regenerative Therapies, where they provide a temporary substitute of the extra-cellular matrix. A major limitation of established degradable implant materials is the fact, that their degradation behavior can not be reliably predicted applying existing experimental methodologies. Therefore a knowledge-based approach is clearly needed to overcome this problem and to enable the tailored design of biodegradable polymers. Here we describe two methods, which can be applied in this approach: molecular modeling combining atomistic bulk and interface models with quantum chemical studies and experimental investigations of macromolecule degradation in Langmuir monolayers. The polymers utilized to exemplarily illustrate the concepts are aliphatic (co)polyesters [e.g. poly(-caprolactone) (PCL), polyglycolide (PGA), poly(rac-lactide) (PDLLA), poly[(rac-lactide)-co-glycolide] (PLGA)] and copoly(ether)esteruretanes as multiblock copolymers. The molecular modeling approach permits to efficiently investigate the influence of micro-structural properties like free volume distribution, cohesive energy density and concentration of polar functional groups on the bulk water uptake as one constituent part of hydrolytic degradation. The Langmuir monolayer investigations on polymer degradation on the other hand yield the dynamics of bond splitting during degradation within hours separately from time consuming diffusion processes, which may take months in bulk samples.

Abstract: Most polymers used in clinical applications today are materials that have been developed originally for application areas other than biomedicine. On the other side, different biomedical applications are demanding different combinations of material properties and functionalities. Compared to the intrinsic material properties, a functionality is not given by nature but result from the combination of the polymer architecture and a suitable process. Examples for functionalities that play a prominent role in the development of multifunctional polymers for medical applications are biofunctionality (e.g. cell or tissue specificity), degradability, or shape-memory functionality. In this sense, an important aim for developing multifunctional polymers is tailoring of biomaterials for specific biomedical applications. Here the traditional approach, which is designing a single new homo- or copolymer, reaches its limits. The strategy, that is applied here, is the development of polymer systems whose macroscopic properties can be tailored over a wide range by variation of molecular parameters. The Shape-memory capability of a material is its ability to trigger a predefined shape change by exposure to an external stimulus. A change in shape initiated by heat is called thermally-induced shape-memory effect. Thermally, light-, and magnetically induced shape-memory polymers will be presented, that were developed especially for minimally invasive surgery and other biomedical applications. Furthermore triple-shape polymers will be introduced, that have the capability to perform two subsequent shape changes. Thus enabling more complex movements of a polymeric material.