In vitro and in vivo biological characterization of poly(lactic acid) fiber scaffolds synthesized by air jet spinning

Biomaterials / bioinks and extrusion bioprinting

Bioinks are formulations of biomaterials and living cells, sometimes with growth factors or other biomolecules, while extrusion bioprinting is an emerging technique to apply or deposit these bioinks or biomaterial solutions to create three-dimensional (3D) constructs with architectures and mechanical/biological properties that mimic those of native human tissue or organs. Printed constructs have found wide applications in tissue engineering for repairing or treating tissue/organ injuries, as well as in vitro tissue modelling for testing or validating newly developed therapeutics and vaccines prior to their use in humans. Successful printing of constructs and their subsequent applications rely on the properties of the formulated bioinks, including the rheological, mechanical, and biological properties, as well as the printing process. This article critically reviews the latest developments in bioinks and biomaterial solutions for extrusion bioprinting, focusing on bioink synthesis and characterization, as well as the influence of bioink properties on the printing process. Key issues and challenges are also discussed along with recommendations for future research.

3D-bioimplants mimicking the structure and function of spine units for the treatment of spinal tuberculosis

Approximately 1-2% of the reported tuberculosis (TB) cases have skeletal system problems, particularly spinal TB. The complications of spinal TB involve the destruction of vertebral body (VB) and intervertebral disc (IVD) which consequently leads to kyphosis. This work aimed at utilizing different technologies to develop, for the first time, a functional spine unit (FSU) replacement to mimic the structure and function of the VB and IVD along with a good ability to treat spinal TB. 3D-printed scaffolds with different porous patterns (hexagonal or grid) were fabricated from biocompatible acrylonitrile butadiene styrene, and polylactic acid to replace damaged VB and IVD, respectively. The VB scaffold is filled with gelatine-based semi-IPN hydrogel containing mesoporous silica nanoparticles loaded with two antibiotics, rifampicin and levofloxacin, to act against TB. The IVD scaffold incorporates a gelatin hydrogel loaded with regenerative platelet-rich plasma and anti-inflammatory simvastatin-loaded mixed nanomicelles. The obtained results confirmed the superior mechanical strength of both 3D-printed scaffolds and loaded hydrogels as compared to normal bone and IVD with high in vitro (cell proliferation, anti-inflammation and anti-TB), and in vivo biocompatibility profiles. Moreover, the custom-designed replacements have achieved the expected prolonged release of antibiotics up to 60 days. Given the promising study findings, the utilization of the developed drug-eluting scaffold system can be extrapolated to treat not only spinal TB but also to resolve diverse backbone/spine problems that need a critical surgical process including degenerative IVD and its consequences like atherosclerosis, sliding or spondylolisthesis and severe traumatic bone fracture.

Stereochemistry Determines Immune Cellular Responses to Polylactide Implants

Repeating l- and d-chiral configurations determine polylactide (PLA) stereochemistry, which affects its thermal and physicochemical properties, including degradation profiles. Clinically, degradation of implanted PLA biomaterials promotes prolonged inflammation and excessive fibrosis, but the role of PLA stereochemistry is unclear. Additionally, although PLA of varied stereochemistries causes differential immune responses in vivo, this observation has yet to be effectively modeled in vitro. A bioenergetic model was applied to study immune cellular responses to PLA containing >99% l-lactide (PLLA), >99% d-lactide (PDLA), and a 50/50 melt-blend of PLLA and PDLA (stereocomplex PLA). Stereocomplex PLA breakdown products increased IL-1β, TNF-α, and IL-6 protein levels but not MCP-1. Expression of these proinflammatory cytokines is mechanistically driven by increases in glycolysis in primary macrophages. In contrast, PLLA and PDLA degradation products selectively increase MCP-1 protein expression. Although both oxidative phosphorylation and glycolysis are increased with PDLA, only oxidative phosphorylation is increased with PLLA. For each biomaterial, glycolytic inhibition reduces proinflammatory cytokines and markedly increases anti-inflammatory (IL-10) protein levels; differential metabolic changes in fibroblasts were observed. These findings provide mechanistic explanations for the diverse immune responses to PLA of different stereochemistries and underscore the pivotal role of immunometabolism in the biocompatibility of biomaterials applied in medicine.

Recent progress in fiber-based soft electronics enabled by liquid metal

Soft electronics can seamlessly integrate with the human skin which will greatly improve the quality of life in the fields of healthcare monitoring, disease treatment, virtual reality, and human-machine interfaces. Currently, the stretchability of most soft electronics is achieved by incorporating stretchable conductors with elastic substrates. Among stretchable conductors, liquid metals stand out for their metal-grade conductivity, liquid-grade deformability, and relatively low cost. However, the elastic substrates usually composed of silicone rubber, polyurethane, and hydrogels have poor air permeability, and long-term exposure can cause skin redness and irritation. The substrates composed of fibers usually have excellent air permeability due to their high porosity, making them ideal substrates for soft electronics in long-term applications. Fibers can be woven directly into various shapes, or formed into various shapes on the mold by spinning techniques such as electrospinning. Here, we provide an overview of fiber-based soft electronics enabled by liquid metals. An introduction to the spinning technology is provided. Typical applications and patterning strategies of liquid metal are presented. We review the latest progress in the design and fabrication of representative liquid metal fibers and their application in soft electronics such as conductors, sensors, and energy harvesting. Finally, we discuss the challenges of fiber-based soft electronics and provide an outlook on future prospects.

Polypropylene mesh combined with electrospun poly (L-lactic acid) membrane in situ releasing sirolimus and its anti-adhesion efficiency in rat hernia repair

This study developed, a novel polypropylene (PP) mesh combined with poly (L-lactic acid) (PLA) electrospun nanofibers loaded sirolimus (SRL). The PP mesh was combined with PLA/SRL (1/0, 1/0.01, 1/0.02; mass ratios) composed electrospun membrane characterized by FTIR spectroscopy, XPS and SEM, and evaluated for cytocompatibility in vitro. In an in vivo study, a total of 84 Sprague-Dawley rats were employed to evaluate the efficacy of the novel composite PP mesh anti-adhesion, mechanical properties and inflammation. As a results, the PLA/SRL membrane could compound with PP mesh stably and load SRL. Although tensile testing showed that the mechanical properties of composite mesh decreased in vivo, the integration strength between the tissue and mesh was still able to counteract intra-abdominal pressure. Compared with the native PP mesh group, the novel PP mesh group showed a lower score for abdominal adhesion and inflammation. More importantly, the novel PP mesh completely integrated with the abdominal wall and had sufficient mechanical strength to repair abdominal wall defects.

3D-Printed Tubular Scaffolds Decorated with Air-Jet-Spun Fibers for Bone Tissue Applications

The fabrication of instructive materials to engineer bone substitute scaffolds is still a relevant challenge. Current advances in additive manufacturing techniques make possible the fabrication of 3D scaffolds with even more controlled architecture at micro- and submicrometric levels, satisfying the relevant biological and mechanical requirements for tissue engineering. In this view, integrated use of additive manufacturing techniques is proposed, by combining 3D printing and air-jet spinning techniques, to optimize the fabrication of PLA tubes with nanostructured fibrous coatings for long bone defects. The physicochemical characterization of the 3D tubular scaffolds was performed by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, profilometry, and mechanical properties. In vitro biocompatibility was evaluated in terms of cell adhesion, proliferation, and cell–material interactions, by using human fetal osteoblasts to validate their use as a bone growth guide. The results showed that 3D-printed scaffolds provide a 3D architecture with highly reproducible properties in terms of mechanical and thermal properties. Moreover, nanofibers are collected onto the surface, which allows forming an intricate and interconnected network that provides microretentive cues able to improve adhesion and cell growth response. Therefore, the proposed approach could be suggested to design innovative scaffolds with improved interface properties to support regeneration mechanisms in long bone treatment.

Composite Fiber Spun Mat Synthesis and In Vitro Biocompatibility for Guide Tissue Engineering

Composite scaffolds are commonly used strategies and materials employed to achieve similar analogs of bone tissue. This study aims to fabricate 10% wt polylactic acid (PLA) composite fiber scaffolds by the air-jet spinning technique (AJS) doped with 0.5 or 0.1 g of zirconium oxide nanoparticles (ZrO₂) for guide bone tissue engineering. ZrO₂ nanoparticles were obtained by the hydrothermal method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). SEM and fourier-transform infrared spectroscopy (FTIR) analyzed the synthesized PLA/ZrO₂ fiber scaffolds. The in vitro biocompatibility and bioactivity of the PLA/ZrO₂ were studied using human fetal osteoblast cells. Our results showed that the hydrothermal technique allowed ZrO₂ nanoparticles to be obtained. SEM analysis showed that PLA/ZrO₂ composite has a fiber diameter of 395 nm, and the FITR spectra confirmed that the scaffolds’ chemical characteristics are not affected by the synthesized technique. In vitro studies demonstrated that PLA/ZrO₂ scaffolds increased cell adhesion, cellular proliferation, and biomineralization of osteoblasts. In conclusion, the PLA/ZrO₂ scaffolds are bioactive, improve osteoblasts behavior, and can be used in tissue bone engineering applications.

Physical Properties, Chemical Analysis, and Evaluation of Antimicrobial Response of New Polylactide/Alginate/Copper Composite Materials

In recent years, due to an expansion of antibiotic-resistant microorganisms, there has been growing interest in biodegradable and antibacterial polymers that can be used in selected biomedical applications. The present work describes the synthesis of antimicrobial polylactide-copper alginate (PLA-ALG-Cu2+) composite fibers and their characterization. The composites were prepared by immersing PLA fibers in aqueous solution of sodium alginate, followed by ionic cross-linking of alginate chains within the polylactide fibers with Cu(II) ions to yield PLA-ALG-Cu2+ composite fibers. The composites, so prepared, were characterized by scanning electron microscopy (SEM), UV/VIS transmittance and attenuated total reflection Fourier-transform infrared spectroscopy ATR-FTIR, and by determination of their specific surface area (SSA), total/average pore volumes (through application of the 5-point Brunauer-Emmett-Teller method (BET)), and ability to block UV radiation (determination of the ultraviolet protection factor (UPF) of samples). The composites were also subjected to in vitro antimicrobial activity evaluation tests against colonies of Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria and antifungal susceptibility tests against Aspergillus niger and Chaetomium globosum fungal mold species. All the results obtained in this work showed that the obtained composites were promising materials to be used as an antimicrobial wound dressing.

The effects of alignment and diameter of electrospun fibers on the cellular behaviors and osteogenesis of BMSCs

Electrospun fiber scaffolds, due to their mimicry of bone extracellular matrix (ECM), have become an important biomaterial widely applied in bone tissue engineering in recent years. While topographic cues of electrospun membranes such as alignment and diameter played vital roles in determining cellular behaviors. Yet few researches about the effects of these two significant parameters on osteogenesis have been reported. Thus, the present work explored the influence of aligned and random poly (L-lactic acid) (PLLA) fiber matrices with diameters of nanoscale (0.6 μm) and microscale (1.2 μm), respectively, on cellular responses of bone marrow mesenchymal stem cells (BMSCs), such as cell adhesion, migration, proliferation and osteogenesis. Our results revealed that aligned nanofibers (AN) could affect cell morphology and promote the migration of BMSCs after 24 h of cell culturing. Besides, AN group was observed to possess excellent biocompatibility and have significantly improved cell growth comparing with random nanofibers. More importantly, in vitro osteogenesis researches including ALP and Alizarin Red S staining, qRT-PCR and immunofluorescence staining demonstrated that BMSCs culturing on AN group exhibited higher osteogenic induction proficiency than that on aligned microfibers (AM) and random fiber substrates (RN and RM). Accordingly, aligned nanofiber scaffolds have greater application potential in bone tissue engineering.

Influence of ZnO, SiO2 and TiO2 on the aging process of PLA fibers produced by electrospinning method

The aim of this work was to study the effect of ceramics particles addition (SiO₂, ZnO, TiO₂) on the ultraviolet (UV) aging of poly(lactic acid) nonwovens fabricated using electrospinning method. The resistance to aging is a key factor for outdoor and medical applications (UV light sterilization). Nonwovens were placed in special chamber with UV light. Changes of physicochemical properties were recorded using differential scanning calorimetry and attenuated total reflection Fourier-transform infrared spectroscopy. The fibers' morphology was studied by using scanning electron microscopy. Obtained results clearly showed that only PLA fibers with ZnO particles gained an increase in UV resistance. The paper presents a description of structural changes taking place under the influence of UV aging processes and describes the mechanisms of this process and the effect of ceramic addition on the lifetime of such materials.