Poly(ester-urethane) scaffolds: effect of structure on properties and osteogenic activity of stem cells

Versatile fiber-reinforced hydrogels to mimic the microstructure and mechanics of human vocal-fold upper layers

Human vocal folds are remarkable soft laryngeal structures that enable phonation due to their unique vibro-mechanical performances. These properties are tied to their specific fibrous architecture, especially in the upper layers, which comprise a gel-like composite called lamina propria. The lamina propria can withstand large and reversible deformations under various multiaxial loadings. Despite their importance, the relationships between the microstructure of vocal folds and their resulting macroscopic properties remain poorly understood. There is a need for versatile models that encompass their structural complexity while mimicking their mechanical features. In this study, we present a candidate model inspired by histological measurements of the upper layers of human vocal folds. Bi-photonic observations were used to quantify the distribution, orientation, width, and volume fraction of collagen and elastin fibers between histological layers. Using established biomaterials, polymer fiber-reinforced hydrogels were developed to replicate the fibrillar network and ground substance of native vocal fold tissue. To achieve this, jet-sprayed poly(ε-caprolactone) fibrillar mats were successfully impregnated with poly(L-lysine) dendrimers/polyethylene glycol hydrogels. The resulting composites exhibited versatile structural, physical and mechanical properties that could be customized through variations in the chemical formulation of their hydrogel matrix, the microstructural architecture of their fibrous networks (i.e., fiber diameter, orientation and volume fraction) and their assembly process. By mimicking the collagen network of the lamina propria with polymer fibers and the elastin/ground substance with the hydrogel composition, we successfully replicated the non-linear, anisotropic, and viscoelastic mechanical behavior of the vocal-fold upper layers, accounting for inter/intra-individual variations. The development of this mimetic model offers promising avenues for a better understanding of the complex mechanisms involved in voice production. STATEMENT OF SIGNIFICANCE: Human vocal folds are outstanding vibrating soft living tissues allowing phonation. Simple physical models that take into account the histological structure of the vocal fold and recapitulate its mechanical features are scarce. As a result, the relations between tissue components, organisation and vibro-mechanical performances still remain an open question. We describe here the development and the characterization of fiber-reinforced hydrogels inspired from the vocal-fold microstructure. These systems are able to reproduce the mechanics of vocal-fold tissues upon realistic cyclic and large strains under various multi-axial loadings, thus providing a mimetic model to further understand the impact of the fibrous network microstructure in phonation.

Use of Polyesters in Fused Deposition Modeling for Biomedical Applications

In recent years, 3D printing techniques experienced a growing interest in several sectors, including the biomedical one. Their main advantage resides in the possibility to obtain complex and personalized structures in a cost-effective way impossible to achieve with traditional production methods. This is especially true for Fused Deposition Modeling (FDM), one of the most diffused 3D printing methods. The easy customization of the final products' geometry, composition and physico-chemical properties is particularly interesting for the increasingly personalized approach adopted in modern medicine. Thermoplastic polymers are the preferred choice for FDM applications, and a wide selection of biocompatible and biodegradable materials is available to this aim. Moreover, these polymers can also be easily modified before and after printing to better suit the body environment and the mechanical properties of biological tissues. This review focuses on the use of thermoplastic aliphatic polyesters for FDM applications in the biomedical field. In detail, the use of poly(ε-caprolactone), poly(lactic acid), poly(lactic-co-glycolic acid), poly(hydroxyalkanoate)s, thermo-plastic poly(ester urethane)s and their blends has been thoroughly surveyed, with particular attention to their main features, applicability and workability. The state-of-the-art is presented and current challenges in integrating the additive manufacturing technology in the medical practice are discussed. This article is protected by copyright. All rights reserved.

Review of Low-Cost 3D Bioprinters: State of the Market and Observed Future Trends

Three-dimensional (3D) bioprinting has become mainstream for precise and repeatable high-throughput fabrication of complex cell cultures and tissue constructs in drug testing and regenerative medicine, food products, dental and medical implants, biosensors, and so forth. Due to this tremendous growth in demand, an overwhelming amount of hardware manufacturers have recently flooded the market with different types of low-cost bioprinter models-a price segment that is most affordable to typical-sized laboratories. These machines range in sophistication, type of the underlying printing technology, and possible add-ons/features, which makes the selection process rather daunting (especially for a nonexpert customer). Yet, the review articles available in the literature mostly focus on the technical aspects of the printer technologies under development, as opposed to explaining the differences in what is already on the market. In contrast, this paper provides a snapshot of the fast-evolving low-cost bioprinter niche, as well as reputation profiles (relevant to delivery time, part quality, adherence to specifications, warranty, maintenance, etc.) of the companies selling these machines. Specifically, models spanning three dominant technologies-microextrusion, droplet-based/inkjet, and light-based/crosslinking-are reviewed. Additionally, representative examples of high-end competitors (including up-and-coming microfluidics-based bioprinters) are discussed to highlight their major differences and advantages relative to the low-cost models. Finally, forecasts are made based on the trends observed during this survey, as to the anticipated trickling down of the high-end technologies to the low-cost printers. Overall, this paper provides insight for guiding buyers on a limited budget toward making informed purchasing decisions in this fast-paced market.

Bioinks-materials used in printing cells in designed 3D forms

Use of materials to activate non-functional or damaged organs and tissues goes back to early ages. The first materials used for this purpose were metals, and in time, novel materials such as ceramics, polymers and composites were introduced to the field to serve in medical applications. In the last decade, the advances in material sciences, cell biology, technology and engineering made 3D printing of living tissues or organ models in the designed structure and geometry possible by using cells alone or together with hydrogels through additive manufacturing. This review aims to give a brief information about the chemical structures and properties of bioink materials and their applications in the production of 3D tissue constructs.

Influence of hydroxyl-terminated polydimethylsiloxane on high-strength biocompatible polycarbonate urethane films

The present study describes a series of novel polycarbonate urethane films that were fabricated via the solution-casting method from 4,4'-methylenebis(cyclohexyl isocyanate) (H₁₂MDI) and 1,4-butanediol (BDO) chain extender as hard segments, poly(1,6-hexanediol)carbonate diols (PCDL) and hydroxyl-terminated polydimethylsiloxane (PDMS) as soft segments, with dibutyltin dilaurate as the catalyst. Varied molar ratios of PDMS (less than 30%) were utilized to enhance the mechanical properties and biocompatibilities. The microstructure and degrees of phase separation were characterized using atomic force microscopy. The chemical structure and surface morphology of the materials were further confirmed by attenuated total reflectance Fourier transform infrared spectroscopy, ¹H NMR and ¹³C NMR, water droplet contact angle and scanning electron microscopy. Thermal properties were measured by differential scanning calorimetry. MTT assay and hemolytic tests were studied for evaluating cellular viability and hemocompatibility of fabricated films using L929 fibroblast cells and adult rabbit blood. The results demonstrated polyurethane films with soft segments partially replaced by PDMS could remarkably improve the biocompatibility while maintaining relatively stable mechanical behavior, making them exciting potential candidates for artificial vessels or other tissue engineering applications.

Modified chitosan scaffolds: Proliferative, cytotoxic, apoptotic, and necrotic effects on Saos-2 cells and antimicrobial effect on Escherichia coli

Scaffolds used in tissue engineering applications should have high biocompatibility with minimum allergic, toxic, apoptotic, or necrotic effects on the growing cells and newly forming tissue and, if possible, have antimicrobial property to prevent infection at the host site. In this study, novel micro-fibrous chitosan scaffolds, having mineralized bioactive surface to enhance cell adhesion and a model antibiotic (gentamicin) to prevent bacterial attack, were prepared. The effects of the scaffolds on proliferation, viability, apoptosis, and necrosis of Saos-2 cells are reported for the first time. Wet spinning technique was used in the scaffold preparation and biomineralization was achieved by incubating them in five-time concentrated simulated body fluid for 2, 7, or 14 days (coded as CH-BM/2, CH-BM/7, and CH-BM/14, respectively). Gentamicin, an effectively used antibiotic in bone treatments, was loaded by vacuum-pressure cycle. Energy-dispersive X-ray results demonstrated that Ca/P ratio of the mineral phase varies depending on the incubation period. When the scaffolds were cultured with Saos-2 cells, cell adhesion and extracellular matrix formation occurred on all types of scaffolds. Alamar Blue cytotoxicity tests showed correlation among mineral concentration and cytotoxicity where CH-BM/2 had significantly more favorable properties. For all types of scaffolds, apoptosis and necrosis were less than 10%, meaning the samples are biocompatible. Gentamicin-loaded scaffolds showed high antimicrobial efficacy against Escherichia coli. The presence of mineral phase enhanced the adhesive capacity of cells and entrapment efficiency of antibiotic. These results suggest that the bioactive and antimicrobial scaffolds prepared in this study can act as promising matrices in bone tissue engineering applications.

Synthesis and surface modification of polyurethanes with chitosan for antibacterial properties

Surface modification and providing antibacterial properties to the materials or devices are getting great attention especially in the last decades. In this study, polyurethane (PU) films were prepared by synthesizing them in medical purity from toluene diisocyanate and polypropylene ethylene glycol without using any other ingredients and then the film surfaces were modified by covalent immobilization of chitosan (CH) which has antibacterial activity. CH immobilized PU films (PU-CH) were found to be more hydrophilic than control PU films. Electron Spectroscopy for Chemical Analysis (ESCA) and Atomic Force Microscopy (AFM) analyses showed higher nitrogen contents and rougher surface topography for PU-CH compared to PU films. Modification with CH significantly increased antibacterial activity against Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) bacteria. It was observed that the number of bacteria colonies were less about 10(2)-10(5) CFU/mL and number of attached viable bacteria decreased significantly after CH modification of PU films.