Fuel Cells II

Abstract

New insights in cell and developmental biology are expected to pave the way for new therapies for a number of severe diseases by exploiting mechanisms to reactivate the cellular potential of regeneration. However, the utilization of molecular switches controlling cellular fate decisions for new therapies very often depends on the availability of biomimetic materials. As (bio)macromolecules are the base of a vast majority of dedicated functions of living organisms it is quite obvious that polymer science has the chance to play a key role in the advent of regenerative therapies. In turn, the challenge of developing biomimetic structures can be expected to substantially influence the field of polymer science as the bidirectional exchange of concepts and technologies with the dynamically evolving disciplines of the life science creates new transdisciplinary areas. Altogether, unraveling and mimicking structures and functions of biopolymers by synthetic architectures will more and more enable the rational design of bioactive materials going beyond the simple imitation of living matter. The contributions collected in this special volume were selected to mirror the status of research on biomimeticmaterials in an exciting transition period: a wealth of different strategies has been pioneered and the field is about to further branch out in lively subdisciplines. A well-established strategy of tissue engineering concerns the use of biodegradable polymers for the generation of cell scaffolds. Among those, natural polyesters from the group of polyhydroxyalkanoates (PHAs) have emerged as particularly promisingmaterials for various applications. Thomas Freier comprehensively describes the characteristics of promising biopolyesters, together with strategies that can be used to adjust the material properties to the clinical requirements and presents examples of potential applications. Biopolymers of the extracellular matrix (ECM) mark the other edge of the spectrum of the currently used materials. Artificial matrices based on biopolymers isolated fromnaturewere successfullyutilized to prepare a variety of bioactive materials capable of supporting desired cell fate transitions to enhance the integration and performance of engineered tissues. Along that line, the review of Tilo Pompe, Katrin Salchert and myself emphasizes recent research to modulate the functionality of ECM biopolymers through their combination with synthetic polymeric materials. The contribution of ShyniVarghese and JenniferH. Elisseeff reviews natural and synthetic hydrogels and their use in musculoskeletal tissue engineering. Themost appealing feature of hydrogels as scaffoldingmaterials is their structural similarity to ECM and their easy processability under mild conditions. The primary developments in this field comprise formulation of biomimetic hydrogels incorporating specific biochemical and biophysical cues so as to mimic the natural ECM, design strategies for cell-mediated degradation of scaffolds, techniques for achieving in situ gelation which allow a minimally invasive administration of cell-laden hydrogels into the defect site, scaffoldmediated differentiation of adult and embryonic stem cells, and finally, the integration of tissue-engineered “biological implants” with the native tissue. A promising approach to the generation of biofunctional nanomaterials that may become particularly useful for in vivo tissue engineering strategies concerns the assembly of amphiphilic peptide systems. Xiaojun Zhao and ShuguangZhang review thecurrent status inthisfieldreferringto a classification scheme of the peptide molecules according to their net charge. Recent work dedicated to the formation of nanofibers, bionanotubes and vesicles based on this principle is discussed. A key aspect of either variant of polymer scaffold is the control of cell adhesion as it is crucial to cellular and host responses to implanted devices, and biotechnological cell culture supports. Emphasizing this aspect the review by Andres J. Garcia focuses on interfaces controlling cell adhesive interactions, highlighting surfaces that control protein adsorption, biomimetic substrates presenting bioadhesivemotifs, andmicropatterned surfaces. These approaches represent promising strategies to engineer cell-material biomolecular interactions in order to elicit specific cellular responses and enhance the biological performance of materials in a variety of biomedical and biotechnological applications. Another, similarly important aspect of bioactive materials for regenerative therapies concerns the use of growth factors to promote regeneration of lost or compromised tissues and organs. Claudia Fischbach and David J. Mooney survey the state of the technology to supply growth factors by polymeric systems in a well-controlled, localized, and sustained manner. Design attributes for polymeric systems for VEGF delivery are discussed, and subsequently illustrated in the context of three specific applications: therapeutic angiogenesis, bone regeneration, and nerve regeneration. We would be extremely delighted if our collection of reviews is of interest to a wide readership and fosters more activity in polymer science dedicated to the development of biomimetic structures. However, by its very nature, the selection involved arbitrariness and I would like to apologize to all those who possibly find their priorities underestimated. I am deeply obliged to the authors of the following reviews who undertook considerable efforts to summarize a very dynamic field. Beyond that, I would like to thank all colleagues who – although not represented by a review in this issue – significantly contributed to the recent progress in biomimetic polymers and, thus, provided the basis for this survey.