Investigation of 3D-Printed Polycaprolactone-/Polyvinylpyrrolidone-Based Constructs

Bioinks for engineering gradient-based osteochondral and meniscal tissue substitutes: a review

Gradient tissues are anisotropic structure with gradual transition in structural and biological properties. The gradient in structural, mechanical and biochemical properties of osteochondral and meniscal tissues play a major role in defining tissue functions. Designing tissue substitutes that replicate these gradient properties is crucial to facilitate regeneration of tissue functions following injuries. Advanced manufacturing technologies such as 3D bioprinting hold great potentials for recreating gradient nature of tissues through using zone-specific bioinks and layer-by-layer deposition of spatially defined biomaterials, cell types and bioactive cues. This review highlighted the gradients in osteochondral and meniscal tissues in detail, elaborated on individual components of the bioink, and reviewed recent advancements in 3D gradient-based osteochondral and meniscal tissue substitutes. Finally, key challenges of the field and future perspectives for developing gradient-based tissue substitutes were discussed. The insights from these advances can broaden the possibilities for engineering gradient tissues.

Three-Dimensional Printing/Bioprinting and Cellular Therapies for Regenerative Medicine: Current Advances

The application of three-dimensional (3D) printing/bioprinting technologies and cell therapies has garnered significant attention due to their potential in the field of regenerative medicine. This paper aims to provide a comprehensive overview of 3D printing/bioprinting technology and cell therapies, highlighting their results in diverse medical applications, while also discussing the capabilities and limitations of their combined use. The synergistic combination of 3D printing and cellular therapies has been recognised as a promising and innovative approach, and it is expected that these technologies will progressively assume a crucial role in the treatment of various diseases and conditions in the foreseeable future. This review concludes with a forward-looking perspective on the future impact of these technologies, highlighting their potential to revolutionize regenerative medicine through enhanced tissue repair and organ replacement strategies.

3D-Printed Gelatin-Based Scaffold Crosslinked by Genipin: Evaluation of Mechanical Properties and Biological Effect

In this study, scaffolds based on natural polymer gelatin A, blended with polyvinylpyrrolidone were crosslinked by genipin (0.5 and 1 wt%), in order to investigate their mechanical performance and potential for biomedical application. Semi-solid extrusion (SSE) 3D printing technique was used, enabling in situ crosslinking of the blend during processing. Swelling test showed that the swelling ratio reduces with higher concentration of genipin due to an increased crosslinking. The FTIR analysis confirmed the crosslinking of scaffolds by genipin. DSC analysis and mechanical testing have shown improved thermal and mechanical properties. Morphological analysis of scaffolds by FESEM showed increased toughening of the material with the crosslinking. Tensile strength and microhardness showed a significant rise in scaffolds with the increase in genipin content, which was up to 93.8% and 125.3%, respectively. These findings were in accordance with morphological features present in samples. The biological effect of the scaffold matrix system was evaluated by qualitative and quantitative cytotoxicity assessment in vitro, demonstrating the absence of cytotoxicity in tested preparations in a direct test. The cytotoxicity index based on the metabolic activity of cells in an indirect test showed up to 20% reduction of viability compared with the control, confirming the absence of cytotoxicity, which was additionally verified by propidium iodine staining of the cells exposed to scaffolds. The presented gelatin-based crosslinked scaffolds obtained by 3D printing represent good candidates for biomedical application and future research that includes further in vitro and in vivo analysis.

Newly Designed PCL-Wrapped Cryogel-Based Conduit Activated with IKVAV Peptide Derivative for Peripheral Nerve Repair

Background: The combination of macroporous cryogels with synthetic peptide factors represents a promising but poorly explored strategy for the development of extracellular matrix (ECM)-mimicking scaffolds for peripheral nerve (PN) repair. Methods: In this study, IKVAV peptide was functionalized with terminal lysine residues to allow its in situ cross-linking with gelatin macromer, resulting in the formation of IKVAV-containing proteinaceous cryogels. The controllable inclusion and distribution of the peptide molecules within the scaffold was verified using a fluorescently labelled peptide counterpart. The optimized cryogel scaffold was combined with polycaprolactone (PCL)-based shell tube to form a suturable nerve conduit (NC) to be implanted into sciatic nerve diastasis in rats. Results: The NC constituents did not impair the viability of primary skin fibroblasts. Concentration-dependent effects of the peptide component on interrelated viscoelastic and swelling properties of the cryogels as well as on proliferation and morphological differentiation of neurogenic PC-12 cells were established, also indicating the existence of an optimal-density range of the introduced peptide. The in vivo implanted NC sustained the connection of the nerve stumps with partial degradation of the PCL tube over eight weeks, whereas the core-filling cryogel profoundly improved local electromyographic recovery and morphological repair of the nerve tissues, confirming the regenerative activity of the developed scaffold. Conclusions: These results provide proof-of-concept for the development of a newly designed PN conduit prototype based on IKVAV-activated cryogel, and they can be exploited to create other ECM-mimicking scaffolds.

Poly (lactic acid) electrospun nanofiber membranes: Advanced characterization for biomedical applications with drug loading performance studies

Traditional dressings have shortcomings such as poor moisture absorption and easy to adhere, making the development of new dressings crucial. In this work, a PLA/PVP crosslinked drug-loaded nanofiber membrane was prepared through electrospinning and ultraviolet crosslinking, with poly (lactic acid) (PLA), polyvinylpyrrolidone (PVP), and salicylic acid (SA) as starting materials. The results demonstrated that the inclusion of PVP notably boosted the viscosity and conductivity of the blend spinning solution. The roughness of the fabricated fiber was elevated, and the diameter of the fibers was more uniform. Additionally, the incorporation of PVP not only enhanced the porosity of the fiber membrane but also effectively decreased its contact angle. Notably, when the PVP content reached 40 %, the contact angle underwent a substantial reduction, decreasing significantly from 125.4° to 82.2°. The SA drug-loaded fiber membrane exhibited a notable bacteriostatic effect against Escherichia coli and Staphylococcus aureus, with its release behavior adhering to Fick's diffusion law. In the cell viability experiment, the cell proliferation rate increased from 94 % to 129 % after 3 days. This shows that the prepared membrane has good antibacterial effect and cell compatibility, which provides a theoretical basis for the construction of a new medical dressing.

Evaluation of MDR-specific phage Pɸ-Mi-Pa loaded mucoadhesive electrospun nanofibrous scaffolds against drug-resistant Pseudomonas aeruginosa- induced wound infections in an animal model

Given the escalating prevalence of drug-resistant wounds, there is a justified imperative to explore innovative and more efficacious therapies that diverge from conventional, ineffective wound healing approaches. This research has introduced a strategy to address multi-drug resistant (MDR) Pseudomonas aeruginosa infections in a chronic wound model, employing MDR-specific phage Pɸ-Mi-Pa loaded onto mucoadhesive electrospun scaffolds. A cocktail of three isolates of P. aeruginosa-specific lytic phages, Pɸ-Mi-Pa 51, Pɸ-Mi-Pa 120, and Pɸ-Mi-Pa 133 were incorporated into varying ratios of fabricated PCL-PVP polymer. These formulations were assessed for their therapeutic efficacy in achieving bacterial clearance in P. aeruginosa-induced wound infections. The study encompassed biological characterization through in vivo wound healing assessments, histology, and histomorphometry. Additionally, morphological, mechanical, and chemical analyses were conducted on the fabricated PCL-PVP electrospun nanofibrous scaffolds. Three clonal differences of the MDR P. aeruginosa-specific phages (Pɸ-Mi-Pa 51, Pɸ-Mi-Pa 120, and Pɸ-Mi-Pa 133) produced lytic activity and were seen to produce distinct and clear zones of inhibition against MDR P. aeruginosa strains Pa 051, Pa 120 and Pa 133 respectively. The average porosity of the nanofibrous scaffolds PB 1, PB 2, PB 3, and PB 4 were 12.2 ± 0.3 %, 22.1 ± 0.7 %, 31.1 ± 2.4 %, 28.0 ± 0.8 % respectively. In vitro cumulative release of MDR-specific phage Pɸ-Mi-Pa from the mucoadhesive electrospun nanofibrous scaffolds was found to be 70.91 % ± 1.02 % after 12 h of incubation after an initial release of 42.8 % ± 3.01 % after 1 h. Results from the in vivo wound healing study revealed a substantial reduction in wound size, with formulations PB 2 and PB 3 exhibiting the most significant reduction in wound size, demonstrating statistically significant results on day 5 (100 % ± 31.4 %). These findings underscore the potential of bacteriophage-loaded electrospun PCL-PVP nanofibrous scaffolds for treating drug-resistant wounds, generating tissue substitutes, and overcoming certain limitations associated with conventional wound care matrices.

Bioprinting: Mechanical Stabilization and Reinforcement Strategies in Regenerative Medicine

Bioprinting describes the printing of biomaterials and cell-laden or cell-free hydrogels with various combinations of embedded bioactive molecules. It encompasses the precise patterning of biomaterials and cells to create scaffolds for different biomedical needs. There are many requirements that bioprinting scaffolds face, and it is ultimately the interplay between the scaffold's structure, properties, processing, and performance that will lead to its successful translation. Among the essential properties that the scaffolds must possess-adequate and appropriate application-specific chemical, mechanical, and biological performance-the mechanical behavior of hydrogel-based bioprinted scaffolds is the key to their stable performance in vivo at the site of implantation. Hydrogels that typically constitute the main scaffold material and the medium for the cells and biomolecules are very soft, and often lack sufficient mechanical stability, which reduces their printability and, therefore, the bioprinting potential. The aim of this review article is to highlight the reinforcement strategies that are used in different bioprinting approaches to achieve enhanced mechanical stability of the bioinks and the printed scaffolds. Enabling stable and robust materials for the bioprinting processes will lead to the creation of truly complex and remarkable printed structures that could accelerate the application of smart, functional scaffolds in biomedical settings. Impact statement Bioprinting is a powerful tool for the fabrication of 3D structures and scaffolds for biomedical applications. It has gained tremendous attention in recent years, and the bioink library is expanding to include more and more material combinations. From the practical application perspective, different properties need to be considered, such as the printed structure's chemical, mechanical, and biological performances. Among these, the mechanical behavior of the printed constructs is critical for their successful translation into the clinic. The aim of this review article is to explore the different reinforcement strategies used for the mechanical stabilization of bioinks and bioprinted structures.

Biofabrication methods for reconstructing extracellular matrix mimetics

In the human body, almost all cells interact with extracellular matrices (ECMs), which have tissue and organ-specific compositions and architectures. These ECMs not only function as cellular scaffolds, providing structural support, but also play a crucial role in dynamically regulating various cellular functions. This comprehensive review delves into the examination of biofabrication strategies used to develop bioactive materials that accurately mimic one or more biophysical and biochemical properties of ECMs. We discuss the potential integration of these ECM-mimics into a range of physiological and pathological in vitro models, enhancing our understanding of cellular behavior and tissue organization. Lastly, we propose future research directions for ECM-mimics in the context of tissue engineering and organ-on-a-chip applications, offering potential advancements in therapeutic approaches and improved patient outcomes.

Cell Encapsulation and 3D Bioprinting for Therapeutic Cell Transplantation

The promise of cell therapy has been augmented by introducing biomaterials, where intricate scaffold shapes are fabricated to accommodate the cells within. In this review, we first discuss cell encapsulation and the promising potential of biomaterials to overcome challenges associated with cell therapy, particularly cellular function and longevity. More specifically, cell therapies in the context of autoimmune disorders, neurodegenerative diseases, and cancer are reviewed from the perspectives of preclinical findings as well as available clinical data. Next, techniques to fabricate cell-biomaterials constructs, focusing on emerging 3D bioprinting technologies, will be reviewed. 3D bioprinting is an advancing field that enables fabricating complex, interconnected, and consistent cell-based constructs capable of scaling up highly reproducible cell-biomaterials platforms with high precision. It is expected that 3D bioprinting devices will expand and become more precise, scalable, and appropriate for clinical manufacturing. Rather than one printer fits all, seeing more application-specific printer types, such as a bioprinter for bone tissue fabrication, which would be different from a bioprinter for skin tissue fabrication, is anticipated in the future.

Ex Vivo Maturation of 3D-Printed, Chondrocyte-Laden, Polycaprolactone-Based Scaffolds Prior to Transplantation Improves Engineered Cartilage Substitute Properties and Integration

OBJECTIVE

The surgical management of nasal septal defects due to perforations, malformations, congenital cartilage absence, traumatic defects, or tumors would benefit from availability of optimally matured septal cartilage substitutes. Here, we aimed to improve in vitro maturation of 3-dimensional (3D)-printed, cell-laden polycaprolactone (PCL)-based scaffolds and test their in vivo performance in a rabbit auricular cartilage model.

DESIGN

Rabbit auricular chondrocytes were isolated, cultured, and seeded on 3D-printed PCL scaffolds. The scaffolds were cultured for 21 days in vitro under standard culture media and normoxia or in prochondrogenic and hypoxia conditions, respectively. Cell-laden scaffolds (as well as acellular controls) were implanted into perichondrium pockets of New Zealand white rabbit ears (N = 5 per group) and followed up for 12 weeks. At study end point, the tissue-engineered scaffolds were extracted and tested by histological, immunohistochemical, mechanical, and biochemical assays.

RESULTS

Scaffolds previously matured in vitro under prochondrogenic hypoxic conditions showed superior mechanical properties as well as improved patterns of cartilage matrix deposition, chondrogenic gene expression (COL1A1, COL2A1, ACAN, SOX9, COL10A1), and proteoglycan production in vivo, compared with scaffolds cultured in standard conditions.

CONCLUSIONS

In vitro maturation of engineered cartilage scaffolds under prochondrogenic conditions that better mimic the in vivo environment may be beneficial to improve functional properties of the engineered grafts. The proposed maturation strategy may also be of use for other tissue-engineered constructs and may ultimately impact survival and integration of the grafts in the damaged tissue microenvironment.

Remote Eradication of Bacteria on Orthopedic Implants via Delayed Delivery of Polycaprolactone Stabilized Polyvinylpyrrolidone Iodine

Bacteria-associated late infection of the orthopedic devices would further lead to the failure of the implantation. However, present ordinary antimicrobial strategies usually deal with early infection but fail to combat the late infection of the implants due to the burst release of the antibiotics. Thus, to fabricate long-term antimicrobial (early antibacterial, late antibacterial) orthopedic implants is essential to address this issue. Herein, we developed a sophisticated MAO-I₂-PCLx coating system incorporating an underlying iodine layer and an upper layer of polycaprolactone (PCL)-controlled coating, which could effectively eradicate the late bacterial infection throughout the implantation. Firstly, micro-arc oxidation was used to form a microarray tubular structure on the surface of the implants, laying the foundation for iodine loading and PCL bonding. Secondly, electrophoresis was applied to load iodine in the tubular structure as an efficient bactericidal agent. Finally, the surface-bonded PCL coating acts as a controller to regulate the release of iodine. The hybrid coatings displayed great stability and control release capacity. Excellent antibacterial ability was validated at 30 days post-implantation via in vitro experiments and in vivo rat osteomyelitis model. Expectedly, it can become a promising bench-to-bedside strategy for current infection challenges in the orthopedic field.

Lyophilized Polyvinylpyrrolidone Hydrogel for Culture of Human Oral Mucosa Stem Cells

This work shows the synthesis of a polyvinylpyrrolidone (PVP) hydrogel by heat-activated polymerization and explores the production of hydrogels with an open porous network by lyophilisation to allow the three-dimensional culture of human oral mucosa stem cells (hOMSCs). The swollen hydrogel showed a storage modulus similar to oral mucosa and elastic solid rheological behaviour without sol transition. A comprehensive characterization of porosity by scanning electron microscopy, mercury intrusion porosimetry and nano-computed tomography (with spatial resolution below 1 μm) showed that lyophilisation resulted in the heterogeneous incorporation of closed oval-like pores in the hydrogel with broad size distribution (5 to 180 μm, d₅₀ = 65 μm). Human oral mucosa biopsies were used to isolate hOMSCs, expressing typical markers of mesenchymal stem cells in more than 95% of the cell population. Direct contact cytotoxicity assay demonstrated that PVP hydrogel have no negative effect on cell metabolic activity, allowing the culture of hOMSCs with normal fusiform morphology. Pore connectivity should be improved in future to allow cell growth in the bulk of the PVP hydrogel.