Human in vitro bone models can create the possibility for investigation of physiological bone remodeling while addressing the principle of replacement, reduction and refinement of animal experiments (3R). Current in vitro models lack cell-matrix interactions and their spatiotemporal complexity. To facilitate these analyses, a bone-mimetic template is developed in this study, inspired by bone's extracellular matrix composition and organization. Silk fibroin (SF) is used as an organic matrix, poly-aspartic acid (pAsp) is used to mimic the functionality of noncollagenous proteins, and 10× simulated body fluid serves as mineralization solution. By using pAsp in the mineralization solution, minerals are guided toward the SF material resulting in mineralization inside and as a coating on top of the SF. After cytocompatibility testing, remodeling experiments are performed in which mineralized scaffold remodeling by osteoclasts and osteoblasts is tracked with nondestructive microcomputed tomography and medium analyses over a period of 42 d. The mineralized scaffolds support osteoclastic resorption and osteoblastic mineralization, in the physiological bone remodeling specific sequence. This model could therefore facilitate the investigation of cell-matrix interactions and may thus reduce animal experiments and advance in vitro drug testing for bone remodeling pathologies like osteoporosis, where cell-matrix interactions need to be targeted.

The extracellular microenvironment is an important regulator of cell functions. Numerous structural cues present in the cellular microenvironment, such as ligand distribution and substrate topography, have been shown to influence cell behavior. However, the roles of these cues are often studied individually using simplified, single-cue platforms that lack the complexity of the three-dimensional, multi-cue environment cells encounter in vivo. Developing ways to bridge this gap, while still allowing mechanistic investigation into the cellular response, represents a critical step to advance the field. Here, we present a new approach to address this need by combining optics-based protein patterning and lithography-based substrate microfabrication, which enables high-throughput investigation of complex cellular environments. Using a contactless and maskless UV-projection system, we created patterns of extracellular proteins (resembling contact-guidance cues) on a two-and-a-half-dimensional (2.5D) cell culture chip containing a library of well-defined microstructures (resembling topographical cues). As a first step, we optimized experimental parameters of the patterning protocol for the patterning of protein matrixes on planar and non-planar (2.5D cell culture chip) substrates and tested the technique with adherent cells (human bone marrow stromal cells). Next, we fine-tuned protein incubation conditions for two different vascular-derived human cell types (myofibroblasts and umbilical vein endothelial cells) and quantified the orientation response of these cells on the 2.5D, physiologically relevant multi-cue environments. On concave, patterned structures (curvatures between κ = 1/2500 and κ = 1/125 μm–1), both cell types predominantly oriented in the direction of the contact-guidance pattern. In contrast, for human myofibroblasts on micropatterned convex substrates with higher curvatures (κ ≥ 1/1000 μm–1), the majority of cells aligned along the longitudinal direction of the 2.5D features, indicating that these cells followed the structural cues from the substrate curvature instead. These findings exemplify the potential of this approach for systematic investigation of cellular responses to multiple microenvironmental cues.

Surface-initiated controlled radical polymerization is a popular technique for the modification of biomaterials with, for example, antifouling polymers. Here, we report on the functionalization of a supramolecular biomaterial with zwitterionic poly(sulfobetaine methacrylate) via atom transfer radical polymerization from a macroinitiator additive, which is embedded in the hard phase of the ureido-pyrimidinone-based material. Poly(sulfobetaine methacrylate) was successfully polymerized from these surfaces, and the polymerized sulfobetaine content, with corresponding antifouling properties, depended on both the macroinitiator additive concentration and polymerization time. Furthermore, the polymerization from the macroinitiator additive was successfully translated to functional electrospun scaffolds, showing the potential for this functionalization strategy in supramolecular material systems.

Human in vitro bone models can create the possibility for investigation of physiological bone remodeling while addressing the principle of replacement, reduction and refinement of animal experiments (3R). Current in vitro models lack cell-matrix interactions and their spatiotemporal complexity. To facilitate these analyses, a bone-mimetic template was developed in this study, inspired by bone extracellular matrix composition and organization. Silk fibroin (SF) was used as an organic matrix, poly-aspartic acid (pAsp) was used to mimic the functionality of non-collagenous proteins, and 10x simulated body fluid served as mineralization solution. By using pAsp in the mineralization solution, minerals were guided towards the SF material resulting in mineralization inside and as a coating on top of the SF. After cytocompatibility testing, remodeling experiments were performed in which mineralized scaffold remodeling by osteoclasts and osteoblasts was tracked with non-destructive micro-computed tomography and medium analyses over a period of 42 days. The mineralized scaffolds supported osteoclastic resorption and osteoblastic mineralization, in the physiological bone remodeling specific sequence. This model could therefore facilitate the investigation of cell-matrix interactions and may thus reduce animal experiments and advance in vitro drug testing for bone remodeling pathologies like osteoporosis, where cell-matrix interactions need to be targeted.

Titanium implants are widely used in medicine but have a risk of biomaterial-associated infection (BAI), of which traditional antibiotic-based treatment is affected by resistance. Antimicrobial peptides (AMPs) are used to successfully kill antibiotic-resistant bacteria. Herein, a supramolecular coating for titanium implants is developed which presents the synthetic antimicrobial and antibiofilm peptide SAAP-148 via supramolecular interactions using ureido-pyrimidinone supramolecular units (UPy-SAAP-148GG). Material characterization of dropcast coatings shows the presence of UPy-SAAP-148GG at the surface. The supramolecular immobilized peptide remains antimicrobially active in dropcast polymer films and can successfully kill (antibiotic-resistant) Staphylococcus aureus, Acinetobacter baumannii, and Escherichia coli. Minor toxicity for human dermal fibroblasts is observed, with a reduced cell attachment after 24 h. Subsequently, a dipcoat coating on titanium implants is developed and tested in vivo in a subcutaneous implant infection mouse model with S. aureus administered locally on the implant before implantation to mimic contamination during surgery. The supramolecular coating containing 5 mol% of UPy-SAAP-148GG significantly prevents colonization of the implant surface as well as of the surrounding tissue, with no signs of toxicity. This shows that supramolecular AMP coatings on titanium are eminently suitable to prevent BAI.

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