Bavarian Polymer Institute

Achieving precise mechanical control in electrospun fibrous scaffolds remains a critical challenge for tissue engineering, where scaffold stiffness, strength, and extensibility must be tailored to diverse biological environments. Here, we establish a systematic framework for tuning the mechanical behavior of electrospun poly(ε-caprolactone) (PCL) fibers by integrating molecular-weight blending, polymer concentration control, fiber orientation, and environmental exposure within a single study. High-molecular-weight PCL (H-PCL) and blends with low-molecular-weight PCL (L-PCL) were electrospun to produce fibers with controlled diameters, morphologies, and orientations. Fiber alignment emerged as the dominant structural factor governing mechanical performance: oriented fibers exhibited substantially higher stiffness (~ 90–140 MPa) and tensile strength (up to ~ 100 MPa), while randomly deposited fibers showed markedly greater extensibility (up to ~ 1000%). Polymer concentration and resulting fiber diameter further modulated stiffness, with optimal mechanical performance observed at intermediate concentrations (~ 10–12% w/v). Molecular-weight blending provided an additional route to tailor fiber morphology and modulus, with oriented fibers reaching peak stiffness at ~ 50–60% H-PCL. Environmental exposure studies revealed that acidic treatments (formic and acetic acid solutions) reduce stiffness in a concentration- and temperature-dependent manner, whereas physiological soaking in phosphate-buffered saline (PBS, 37 °C) largely preserves scaffold integrity. Collectively, the electrospun scaffolds developed here span a broad mechanical window (~ 5–140 MPa). When positioned against literature-reported electrospun PCL scaffolds for cardiac, bone, and muscle tissue engineering, this range bridges multiple application-relevant stiffness regimes. These results provide a unified structure–property framework for designing mechanically tunable PCL fibrous scaffolds across diverse biomedical applications.

ABSTRACT Predicting the modulus of short fiber‐reinforced composites is complicated by simultaneous variations in fiber length, orientation, and volume fraction during processing. This work refines the classical modified rule of mixtures (MROM) by introducing two concentration‐dependent weighting functions, and , which capture the evolution of effective fiber length, fiber‐fiber interactions, fiber orientation, and loading‐angle effects. A microstructural efficiency coefficient is further incorporated to describe reinforcement degradation from dilute to crowded fiber conditions. The model was validated using ethylene‐vinyl acetate/short carbon fiber composites with fiber volume fractions of 1.37%–16.80%. Young's modulus measured at loading angles of 0°, 45°, and 90° showed excellent agreement with predictions, with the refined formulation outperforming the classical MROM, particularly at higher loading angles. Overall, the refined framework provides a compact and physically grounded framework for accurately predicting stiffness and supports the design and optimization of short fiber‐reinforced polymer systems.

Micellar drug delivery systems have emerged as a versatile platform for improving the solubility, stability, and targeted release of chemo(immuno)therapeutics. This review focuses on micellar formulations that combine two key design principles: the inherent biodegradability of aliphatic poly(carbonate)s and the universal acid-responsive trigger mechanism. These systems are particularly attractive for tumor therapy, where the acidic microenvironment can be exploited for controlled drug release. We differentiate between two major classes: (i) systems employing acid-labile linkages for reversible conjugation of pharmaceutically active compounds, and (ii) systems in which micelle disassembly or polymer backbone degradation is governed by acid-responsive functionalities. Both categories are systematically evaluated according to the chemical motifs enabling acid sensitivity, including oximes, imines, hydrazones, boronate ester, acetals, ketals, and tertiary amines, among others. The review highlights recent advances in synthetic strategies, structure-property relationships, and therapeutic performance, emphasizing how these design elements synergistically enhance drug loading, release kinetics, and biocompatibility. Finally, we discuss current challenges and future directions for translating these smart micellar systems into promising tumor-targeted (immuno-)therapeutics.

Thin films of auto-oxidized dopamine, the so-called polydopamine (PDA), have been introduced as universal bio-inspired “green” adhesion promoter for a variety of applications. This study investigates the effect of different alkaline solutions on PDA films on polyethylene fibers over a time ranging from 1 h to 67 days. On one hand, this supports the application of adhesive PDA films in alkaline media such as cementitious matrices. On the other hand, a controlled chemical decomposition or degradation can be used to reverse adhesion and separate the components of PDA-mediated composite materials for re-use and recycling. The effect of the surface modification and the alkaline treatments was studied using atomic force microscopy, electrokinetic measurements, and spectroscopic techniques. Depending on the composition of the alkaline solution, a progressive dissolution or depolymerization of PDA aggregates was observed. Zeta potential measurements detected, however, acidic groups on the fiber surface even after alkaline treatment for 67 days, indicating that the PDA film was not fully removed. • Alkaline treatment of polydopamine films on polyethylene fibers. • Study of time-dependent degradation over 67 days. • Detachment of polydopamine aggregates in KOH solution. • Depolymerization and dissolution in 3-ionic solution. • Reversal of acid-base properties of residual film.

Natural spider silk fibers are recognized for their outstanding mechanical properties. The production of underlying recombinant spider silk proteins in scalable quantities unlocks their potential for technical and biomedical applications. The recombinant spider silk technology further enables the introduction of new functions via genetic encoding. In the present study, the non-canonical amino acid L-azidohomoalanine is incorporated into the engineered Araneus diadematus fibroin 4, eADF4(C16), at positions explicitly defined by methionine codons in an N-terminal peptide tag. The azido-functionalized eADF4(C16) is processed into particles, films, or electrospun into nanofibers. As functional entities, high molecular weight molecules, such as antibodies, are modified with bio-orthogonal groups suitable for strain-promoted cycloaddition to the exposed azido-groups on the spider silk supports. The antibody-activated spider silk nonwoven meshes exemplarily show their applicability as bio-capturing membranes.

Contractile engineered cardiac patches hold great potential for treating myocardial infarction, serving as biological ventricular assist devices (BioVADs). However, optimal design and attachment of cardiac patches remain insufficiently explored, although both are essential for the mechanical support of damaged hearts. This study presents a platform for personalized macroscale patches with a multi-zonal microarchitecture combining a regenerative zone for cell alignment, a stiff force transmission zone for load transfer, and an elastic attachment zone enabling integration. Based on computational modeling, the design is implemented using a custom G-code generator for melt electrowriting (MEW). Digital image correlation reveals up to a 2.6-fold strain difference between scaffold zones under physiological deformation, confirming zonal interplay. Biaxial testing with preconditioning shows scaffold mechanics replicating native myocardium properties up to 10% strain. For epicardial suture attachment, a reinforced outline enables shape-morphing and increases suture retention 2.16-fold. Dynamic BioVAD cultivation with fibrin-embedded cardiomyocytes significantly (p = 0.01) improves cell alignment versus controls. Finally, in a porcine myocardial infarction model, the BioVAD achieves complete epicardial attachment and vascular ingrowth within 7 days, compared to partial attachment in controls. This study highlights MEW as a versatile platform for tailoring cardiac scaffold mechanics to support tissue integration and cardiac function.

Three-dimensional (3D) models to study human disease mechanisms have demonstrated that the third dimension is an essential component for neuronal maturation and function. However, 3D neuronal cell culture is challenging due to their ultra-soft nature and specific extracellular matrix (ECM) organization. This study presents a microfiber reinforcement approach, combining primary mouse spinal cord neurons (SCNs) in a purpose-adaptable hyaluronic-acid-based matrix with melt electrowritten (MEW) frames to study disease mechanisms. The importance of laminins (LNs) is evaluated, which are vital for neuronal adhesion and maturation. Astrocytes (ACs) are mandatory in brain development and function by secretion of signal molecules, maintaining ion homeostasis, clearing of neurotransmitters, and by actively modulating neuronal activity. Three combinations are compared (i) isolated primary SCN, (ii) SCN with ACs (SCN-AC) and (iii) SCN-AC and LNs (SCN-AC-LN). Multimodal analysis by comparing protein expression, dendrite length, complex mechanical properties, and network functionality via Ca2+-imaging allows validation of structural and functional neuronal network development. The suitability of the 3D model to study pathomechanisms is demonstrated for Stiff Person Syndrome (SPS). For the first time, functional impairment of spinal cord neurons by patient-derived autoantibodies characteristic for SPS is recapitulated in a 3D spinal cord model platform adaptable to other disease types.

Silver nanowires (AgNWs) are extensively reported as 2D conductive composites for their neural metaplasticity mimicking behavior, crucial for next-generation computing. While 2D networks rely on junction-mediated ballistic transport, 3D AgNW bulk composites exhibit diffuse and percolation driven conduction. Comparing these systems could reveal key dimensional effects, though scaling the intricate 2D networks into the bulk remains challenging. We report a highly reproducible 3D metastable powder composite of anisotropic AgNW with poly(vinylpyrrolidone) as a supporting matrix, produced via spray drying. With rapid drying kinetics, affinity-driven anisotropic morphologies are observed with ellipsoidal microstructures bent at flexural angles. First-principles electronic percolation characterization of the compressed composite is determined by a four-point probe (4PP), and the percolative regimes are allotted. 2D AgNW networks reach ∼1-500 S/cm at network densities of ∼0.4-11 μm-2. The 3D composites, on the other hand, span a wider range, from ∼10-8 S/cm at 3 wt % to ∼102 S/cm at ∼90 wt % of AgNW loading. These values reflect the dominant conductive pathways within the interaction volume. Complementary electrochemical impedance spectroscopy confirms pressure-driven extremization in percolation, with conductivity rising by 2 orders of magnitude from ∼10-2 to ∼1 S/cm at applied pressures of 0.3 to 50 MPa even for 10 wt % AgNW, where 4PP measurements show values near 10-5 S/cm. Spray drying was chosen, as scalability was prioritized over nanoscale precision, making it suitable for bulk materials where microstructure control is secondary to throughput. Hence, the morphologically free AgNWs serve as a versatile precursor for industrially relevant down streaming and reprocessing. When the metastable composite was coextruded at high shear with a commercial elastomer, stretching induced alignment of the initially randomly oriented AgNWs was revealed by SEM micrographs.