Tailored Polyelectrolyte Multilayer Systems by Variation of Polyelectrolyte Composition and EDC/NHS Cross-Linking: Physicochemical Characterization and In Vitro Evaluation.

The layer-by-layer (LbL) self-assembly technique is an effective method to immobilize components of the extracellular matrix (ECM) such as collagen and heparin onto, e.g., implant surfaces/medical devices with the aim of forming polyelectrolyte multilayers (PEMs). Increasing evidence even suggests that cross-linking influences the physicochemical character of PEM films since mechanical cues inherent to the substrate may be as important as its chemical nature to influence the cellular behavior. In this study, for the first-time different collagen/heparin films have been prepared and cross-linked with EDC/NHS chemistry. Quartz crystal microbalance, zeta potential analyzer, diffuse reflectance Fourier transform infrared spectroscopy, atomic force microscopy and ellipsometry were used to characterize film growth, stiffness, and topography of different film systems. The analysis of all data proves a nearly linear film growth for all PEM systems, the efficacy of cross-linking and the corresponding changes in the film rigidity after cross-linking and an appropriate surface topography. Furthermore, preliminary cell culture experiments illustrated those cellular processes correlate roughly with the quantity of newly created covalent amide bonds. This allows a precise adjustment of the physicochemical properties of the selected film architecture regarding the desired application and target cells. It could be shown that collagen improves the biocompatibility of heparin containing PEMs and due to their ECM-analogue nature both molecules are ideal candidates intended to be used for any biomedical application with a certain preference to improve the performance of bone implants or bone augmentation strategies.

Poly-Alanine-ε-Caprolacton-Methacrylate as Scaffold Material with Tuneable Biomechanical Properties for Osteochondral Implants.

An aging population and injury-related damage of the bone substance lead to an increasing need of innovative materials for the regeneration of osteochondral defects. Biodegradable polymers form the basis for suitable artificial implants intended for bone replacement or bone augmentation. The great advantage of these structures is the site-specific implant design, which leads to a considerable improvement in patient outcomes and significantly reduced post-operative regeneration times. Thus, biomechanical and biochemical parameters as well as the rate of degradation can be set by the selection of the polymer system and the processing technology. Within this study, we developed a polymer platform based on the amino acid Alanine and ε-Caprolacton for use as raw material for osteochondral implants. The biomechanical and degradation properties of these Poly-(Alanine-co-ε-Caprolacton)-Methacrylate (ACM) copolymers can be adjusted by changing the ratio of the monomers. Fabrication of artificial structures for musculo-skeletal tissue engineering was done by Two-Photon-Polymerization (2PP), which represents an innovative technique for generating defined scaffolds with tailor-made mechanical and structural properties. Here we show the synthesis, physicochemical characterization, as well as first results for structuring ACM using 2PP technology. The data demonstrate the high potential of ACM copolymers as precursors for the fabrication of biomimetic implants for bone-cartilage reconstruction.

Porous 3D Scaffolds Enhance MSC Vitality and Reduce Osteoclast Activity.

In the context of an aging population, unhealthy Western lifestyle, and the lack of an optimal surgical treatment, deep osteochondral defects pose a great challenge for the public health system. Biodegradable, biomimetic scaffolds seem to be a promising solution. In this study we investigated the biocompatibility of porous poly-((D,L)-lactide-ε-caprolactone)dimethacrylate (LCM) scaffolds in contrast to compact LCM scaffolds and blank cell culture plastic. Thus, morphology, cytotoxicity and metabolic activity of human mesenchymal stromal cells (MSC) seeded directly on the materials were analyzed after three and six days of culturing. Further, osteoclastogenesis and osteoclastic activity were assessed using reverse-transcriptase real-time PCR of osteoclast-specific genes, EIA and morphologic aspects after four, eight, and twelve days. LCM scaffolds did not display cytotoxic effects on MSC. After three days, metabolic activity of MSC was enhanced on 3D porous scaffolds (PS) compared to 2D compact scaffolds (CS). Osteoclast activity seemed to be reduced at PS compared to cell culture plastic at all time points, while no differences in osteoclastogenesis were detectable between the materials. These results indicate a good cytocompatibility of LCM scaffolds. Interestingly, porous 3D structure induced higher metabolic activity of MSC as well as reduced osteoclast activity.

Biomimetic Designer Scaffolds Made of D,L-Lactide-ɛ-Caprolactone Polymers by 2-Photon Polymerization.

IMPACT STATEMENT: In tissue engineering (TE), the establishment of cell targeting materials, which mimic the conditions of the physiological extracellular matrix (ECM), seems to be a mission impossible without advanced materials and fabrication techniques. With this in mind we established a toolbox based on (D,L)-lactide-ɛ-caprolactone methacrylate (LCM) copolymers in combination with a nano-micromaskless lithography technique, the two-photon polymerization (2-PP) to mimic the hierarchical structured and complex milieu of the natural ECM. To demonstrate the versatility of this toolbox, we choose two completely different application scenarios in bone and tumor TE to show the high potential of this concept in therapeutic and diagnostic application.

Ni(II)-NTA modified poly(ethylene imine) glycopolymers: physicochemical properties and first in vitro study of polyplexes formed with HIV-derived peptides.

Alternative delivery entities are desirable in immunotherapies in which polyplexes are widely formed by electrostatic interactions to induce cellular uptake processes for bioactive molecules. In our study, biocompatible Ni(II)-nitrilo(triacetic acid)-modified poly(ethylene imine)-maltose (Ni-NTA-DG) is realized and evaluated as complexation agent against His-tagged peptides using fluorescence polarization and dynamic light scattering. The polyplexes are stable until a pH of 6.5-6.0, and also up to 50 mM of imidazole. A first uptake approach shows that polyplexes lead to an increase in peptide uptake in monocyte-derived immature dendritic cells. In summary, Ni-NTA-DG represents a promising (delivery) platform for forthcoming in vitro applications.

Synthesis of hetero-polymer functionalized nanocarriers by combining surface-initiated ATRP and RAFT polymerization.

Smart nanocarriers are created based on a bi-functional hetero-initiator for RAFT and ATRP technique, bi-functionalizing mesoporous silica nanoparticles with two polymer types. The pH-dependent behavior of PDEAEMA as the gatekeeper polymer is verified by electrokinetic measurements and a controlled release behavior is demonstrated using doxorubicin as the drug.