Utilizing osteocyte derived factors to enhance cell viability and osteogenic matrix deposition within IPN hydrogels

Many bone defects arising due to traumatic injury, disease, or surgery are unable to regenerate, requiring intervention. More than four million graft procedures are performed each year to treat these defects making bone the second most commonly transplanted tissue worldwide. However, these types of graft suffer from a limited supply, a second surgical site, donor site morbidity, and pain. Due to the unmet clinical need for new materials to promote skeletal repair, this study aimed to produce novel biomimetic materials to enhance stem/stromal cell osteogenesis and bone repair by recapitulating aspects of the biophysical and biochemical cues found within the bone microenvironment. Utilizing a collagen type I-alginate interpenetrating polymer network we fabricated a material which mirrors the mechanical and structural properties of unmineralized bone, consisting of a porous fibrous matrix with a young's modulus of 64 kPa, both of which have been shown to enhance mesenchymal stromal/stem cell (MSC) osteogenesis. Moreover, by combining this material with biochemical paracrine factors released by statically cultured and mechanically stimulated osteocytes, we further mirrored the biochemical environment of the bone niche, enhancing stromal/stem cell viability, differentiation, and matrix deposition. Therefore, this biomimetic material represents a novel approach to promote skeletal repair

Natural hydrogels for bone tissue engineering

The prevalence of bone defects, their associated morbidity, and socio-economic cost explain the need for skeletal repair and regeneration. Therefore, the selection, design, and processing of hydrogels should be engineered in such a way so that they provide both biochemical and biophysical (substrate stiffness, matrix topography, match between material degradation and extracellular matrix deposition, and mechanical stimulation) cues from the native extracellular matrix inductive for cell attachment, migration, proliferation, and differentiation. A strong emphasis is put on how the biological cues are being mimicked in natural hydrogel materials (alginate, chitosan, collagen, and gelatin) and how this design can be further improved in the future

From chain growth to step growth polymerization of photoreactive poly-epsilon-caprolactone : the network topology of bioresorbable networks as tool in tissue engineering

Control of the network topology by selection of an appropriate cross-linking chemistry is introduced as a new strategy to improve the elasticity and toughness of bioresorbable networks. The development of novel photocross-linkable and bioresorbable oligomers is essential for the application of light-based 3D-printing techniques in the context of tissue engineering. Although light-based 3D-printing techniques are characterized by an increased resolution and manufacturing speed as compared to extrusion-based 3D-printing, their application remains limited. Via chemical modification, poly-epsilon-caprolactone (PCL) is functionalized with photoreactive end groups such as acrylates, alkenes, and alkynes. Based on these precursors, networks with different topologies are designed via chain growth polymerization, step growth polymerization, or a combination thereof. The influence of the network topology and the concomitant cross-linking chemistry on the thermal, mechanical, and biological properties are elucidated together with their applicability in digital light processing (DLP). Photocross-linkable PCL with an elongation at break of 736.3 +/- 47% and an ultimate strength of 21.3 +/- 0.8 MPa is realized, which is approximately tenfold higher compared to the current state-of-the-art. Finally, extremely elastic DLP-printed dog bones are developed which can fully retrieve their initial length upon stress relieve at an elongation of 1000%

Nature-Inspired Dual Purpose Strategy toward Cell-Adhesive PCL Networks: C(-linker-)RGD Incorporation via Thiol-ene Crosslinking

In an attempt to mimic nature’s ability to adhere cells, PCL is often coated with nature-derived polymers or its surface is functionalized with a cell-binding motif. However, said surface modifications are limited to the material’s surface, include multiple steps, and are mediated by harsh conditions. Here, we introduce a single-step strategy toward cell-adhesive polymer networks where thiol-ene chemistry serves a dual purpose. First, alkene-functionalized PCL is crosslinked by means of a multifunctional thiol. Second, by means of a cysteine coupling site, the cell-binding motif C(-linker-)RGD is covalently bound throughout the PCL networks during crosslinking. Moreover, the influence of various linkers (type and length), between the cysteine coupling site and the cell-binding motif RGD, is investigated and the functionalization is assessed by means of static contact angle measurements and X-ray photoelectron spectroscopy. Finally, successful introduction of cell adhesiveness is illustrated for the networks by seeding fibroblasts onto the functionalized PCL networks

Surface contamination and electrical damage by focused ion beam: conditions applicable to the extraction of TEM lamellae from nano-electronic devices

status: publishe

Optimization of hybrid gelatin-polysaccharide bioinks exploiting thiol-norbornene chemistry using a reducing additive

Thiol-norbornene chemistry offers great potential in the field of hydrogel development, given its step growth crosslinking mechanism. However, limitations exist with regard to deposition-based bioprinting of thiol-containing hydrogels, associated with premature crosslinking of thiolated (bio)polymers resulting from disulfide formation in the presence of oxygen. More specifically, disulfide formation can result in an increase in viscosity thereby impeding the printing process. In the present work, hydrogels constituting norbornene-modified dextran (DexNB) combined with thiolated gelatin (GelSH) are selected as case study to explore the potential of incorporating the reducing agent tris(2-carboxyethyl)phosphine (TCEP), to prevent the formation of disulfides. We observed that, in addition to preventing disulfide formation, TCEP also contributed to premature, spontaneous thiol-norbornene crosslinking without the use of UV light as evidenced via 1H-NMR spectroscopy. Herein, an optimal concentration of 25 mol% TCEP with respect to the amount of thiols was found, thereby limiting auto-gelation by both minimizing disulfide formation and spontaneous thiol-norbornene reaction. This concentration results in a constant viscosity during at least 24 hours, a more homogeneous network being formed as evidenced using atomic force microscopy while retaining bioink biocompatibility as evidenced by a cell viability of human foreskin fibroblasts exceeding 70 % according to ISO 10993-6:2016

3D-printed shape memory poly(alkylene terephthalate) scaffolds as cardiovascular stents revealing enhanced endothelialization

Cardiovascular diseases are the leading cause of death and current treatments such as stents still suffer from disadvantages. Balloon expansion causes damage to the arterial wall and limited and delayed endothelialization gives rise to restenosis and thrombosis. New more performing materials that circumvent these disadvantages are required to improve the success rate of interventions. To this end, the use of a novel polymer, poly(hexamethylene terephthalate), is investigated for this application. The synthesis to obtain polymers with high molar masses up to 126.5 kg mol-1 is optimized and a thorough chemical and thermal analysis is performed. The polymers are 3D-printed into personalized cardiovascular stents using the state-of-the-art solvent-cast direct-writing technique, the potential of these stents to expand using their shape memory behavior is established, and it is shown that the stents are more resistant to compression than the poly(l-lactide) benchmark. Furthermore, the polymer's hydrolytic stability is demonstrated in an accelerated degradation study of 6 months. Finally, the stents are subjected to an in vitro biological evaluation, revealing that the polymer is non-hemolytic and supports significant endothelialization after only 7 days, demonstrating the enormous potential of these polymers to serve cardiovascular applications. Solvent-cast direct-writing enables the additive manufacturing of personalized cardiovascular stents based on poly(hexamethylene terephthalate) with a high molar mass. These stents are hydrolytically stable, not hemolytic, and enable self-expansion due to their shape memory behavior. Significant and rapid endothelialization is achieved after 7 days of incubation with endothelial cells, demonstrating the enormous potential of these polymers to serve cardiovascular applications. imag