A new era for sterilization based on supercritical CO2 technology

Additive Manufacturing of Nanocellulose Aerogels with Structure-Oriented Thermal, Mechanical, and Biological Properties

Additive manufacturing (AM) is widely recognized as a versatile tool for achieving complex geometries and customized functionalities in designed materials. However, the challenge lies in selecting an appropriate AM method that simultaneously realizes desired microstructures and macroscopic geometrical designs in a single sample. This study presents a direct ink writing method for 3D printing intricate, high-fidelity macroscopic cellulose aerogel forms. The resulting aerogels exhibit tunable anisotropic mechanical and thermal characteristics by incorporating fibers of different length scales into the hydrogel inks. The alignment of nanofibers significantly enhances mechanical strength and thermal resistance, leading to higher thermal conductivities in the longitudinal direction (65 mW m-1 K-1) compared to the transverse direction (24 mW m-1 K-1). Moreover, the rehydration of printed cellulose aerogels for biomedical applications preserves their high surface area (≈300 m2 g-1) while significantly improving mechanical properties in the transverse direction. These printed cellulose aerogels demonstrate excellent cellular viability (>90% for NIH/3T3 fibroblasts) and exhibit robust antibacterial activity through in situ-grown silver nanoparticles.

Optical fiber biosensors toward in vivo detection

This review takes stock of the various optical fiber-based biosensors that could be used for in vivo applications. We discuss the characteristics that biosensors must have to be suitable for such applications and the corresponding transduction modes. In particular, we focus on optical fiber biosensors based on fluorescence, evanescent wave, plasmonics, interferometry, and Raman phenomenon. The operational principles, implemented solutions, and performances are described and debated. The different sensing configurations, such as the side- and tip-based fiber biosensors, are illustrated, and their adaptation for in vivo measurements is discussed. The required implementation of multiplexed biosensing on optical fibers is shown. In particular, the use of multi-fiber assemblies, one of the most optimal configurations for multiplexed detection, is discussed. Different possibilities for multiple localized functionalizations on optical fibers are presented. A final section is devoted to the practical in vivo use of fiber-based biosensors, covering regulatory, sterilization, and packaging aspects. Finally, the trends and required improvements in this promising and emerging field are analyzed and discussed.

Development and optimization of a one step process for the production and sterilization of liposomes using supercritical CO2

Liposomes are very interesting drug delivery systems for pharmaceutical and therapeutic purposes. However, liposome sterilization as well as their industrial manufacturing remain challenging. Supercritical carbon dioxide is an innovative technology that can potentially overcome these limitations. The aim of this study was to optimize a one-step process for producing and sterilizing liposomes using supercritical CO2. For this purpose, a design of experiment was conducted. The analysis of the experimental design showed that the temperature is the most influential parameter to achieve the sterility assurance level (SAL) required for liposomes (≤10-6). Optimal conditions (80 °C, 240 bar, 30 min) were identified to obtain the fixed critical quality attributes of liposomes. The conditions for preparing and sterilizing empty liposomes of various compositions, as well as liposomes containing the poorly water-soluble drug budesonide, were validated. The results indicate that the liposomes have appropriate physicochemical characteristics for drug delivery, with a size of 200 nm or less and a PdI of 0.35 or less. Additionally, all liposome formulations demonstrated the required SAL and sterility at concentrations of 5 and 45 mM, with high encapsulation efficiency.

Vancomycin-loaded methylcellulose aerogel scaffolds for advanced bone tissue engineering

Scaffolds grafting combined with local delivery of antibiotics at the injury site may promote bone regeneration along with prevention of infections. In this work, a processing strategy combining the 3D-printing of polysaccharide-based inks with supercritical (sc)CO2 technology was employed to manufacture drug-loaded, nanostructured, and personalized-to-patient aerogels for the first time. Methylcellulose (MC) was employed as graft matrix endowed with nanohydroxyapatite (nHA) to confer bioactivity as required in bone tissue engineering (BTE). MC-nHA aerogels were obtained through the 3D-printing of hydrogel-based scaffolds followed by scCO2 drying. Aerogels were loaded with vancomycin (VAN), an antibiotic employed in the management of bone infections. Textural properties and printing fidelity of scaffolds were studied as well as VAN release, long-term bioactivity, and pre-osteoblasts mineralization. In vitro cell studies and in vivo Artemia salina tests were carried out to evaluate the potential toxicity of the antibiotic-loaded aerogels. Aerogels efficacy in inhibiting bacterial growth was assessed by antimicrobial tests with Staphylococcus aureus. Textural stability of the aerogels after 7 months of storage was also evaluated. Obtained results showed that the scaffolds promoted the intended two-in-one effect (bone repair and infection management simultaneously) in a personalized way, regulating formulation design, drug dose, and porosity.

Rise of tissue- and species-specific 3D bioprinting based on decellularized extracellular matrix-derived bioinks and bioresins

Thanks to its natural complexity and functionality, decellularized extracellular matrix (dECM) serves as an excellent foundation for creating highly cell-compatible bioinks and bioresins. This enables the bioprinted cells to thrive in an environment that closely mimics their native ECM composition and offers customizable biomechanical properties. To formulate dECM bioinks and bioresins, one must first pulverize and/or solubilize the dECM into non-crosslinked fragments, which can then be chemically modified as needed. In bioprinting, the solubilized dECM-derived material is typically deposited and/or crosslinked in a layer-by-layer fashion to build 3D hydrogel structures. Since the introduction of the first liver-derived dECM-based bioinks, a wide variety of decellularized tissue have been employed in bioprinting, including kidney, heart, cartilage, and adipose tissue among others. This review aims to summarize the critical steps involved in tissue-derived dECM bioprinting, starting from the decellularization of the ECM to the standardized formulation of bioinks and bioresins, ultimately leading to the reproducible bioprinting of tissue constructs. Notably, this discussion also covers photocrosslinkable dECM bioresins, which are particularly attractive due to their ability to provide precise spatiotemporal control over the gelation in bioprinting. Both in extrusion printing and vat photopolymerization, there is a need for more standardized protocols to fully harness the unique properties of dECM-derived materials. In addition to mammalian tissues, the most recent bioprinting approaches involve the use of microbial extracellular polymeric substances in bioprinting of bacteria. This presents similar challenges as those encountered in mammalian cell printing and represents a fascinating frontier in bioprinting technology.

Photodegradation of polylactic acid: Characterisation of glassy and melt behaviour as a function of molecular weight

During the COVID-19 pandemic, UV-C germicidal lamps became widely available, even for household applications. However, their long-term degradation effects on the mechanical and rheological properties of polylactic acid (PLA) are still not well established. The relationship between degradation and its effects on the molecular structure and macroscale properties are hardly known. In this study, we investigated the effects of long-term exposure to UV-C irradiation on the properties of PLA and interpreted the results at the molecular scale. We performed gel permeation chromatography, Fourier-transform infrared spectroscopy and UV-Vis spectroscopy to analyse changes in chemical structure induced by the UV-irradiation. Then, we carried out thermal, rheological and tensile tests to investigate mechanical and melting properties, and we investigated the applicability of these test results to estimate molecular weight loss. We have created a 3D irradiation map that can facilitate the design of disinfection devices. Based on our results, we propose a maximum number of sterilisation cycles (13 cycles) for the tested PLA films that do not result in significant changes in tensile strength and modulus.

Effect of ScCO2 on the decontamination of PECs-based cryogels: A comparison with H2O steam and H2O2 nebulization methods

Biopolymers present ideal properties to be used in wound dressing solutions. By mixing two oppositely charged macromolecules it is possible to form polyelectrolyte complex (PEC) based cryogels using lyophilization. Their application in the biomedical field is limited due to their sterilization requirements, as conventional methods compromise their physicochemical properties. ScCO2 appears as an alternative method for decontamination. This work assessed several cryogel PEC formulations, chitosan-pectin, gelatine-xanthan gum and alginate-gelatine. PEC formation was confirmed by FTIR and rheological analysis. While steam sterilization compromised cryogels' chemical and morphological properties, decontamination with scCO2 proved to be a promising method for decontamination of PEC-cryogels, because, similarly to what is observed with hydrogen peroxide, it does not compromise their physicochemical properties.

Sterilization of 20 billion medical devices by ethylene oxide (ETO): Consequences of ETO closures and alternative sterilization technologies/solutions

BACKGROUND

To prevent healthcare-associated infections, it is essential that critical medical devices be sterilized before use. Although there are several sterilization technologies for medical devices, only ethylene oxide (ETO) sterilization has virtually universal material compatibility.

METHODS

We searched the published English literature (Google, Google scholar and PubMed) for articles on the sterilization of medical devices by ethylene oxide, the consequences of ETO closures, and alternative sterilization technologies/solutions.

RESULTS

ETO's compatibility and effectiveness with medical products allows for sterilization of many medical devices that would otherwise be rendered ineffective or unsafe if sterilized with an alternative method.

CONCLUSIONS

At present, there are no alternatives to ETO that provide the same sterility assurance and result in the same device performance as ETO; therefore, it is likely irreplaceable for years.

Supercritical CO2 Processing of White Grape Must as a Strategy to Reduce the Addition of SO2

In winemaking, sulfur dioxide addition is the most common procedure to prevent enzymatic and microbial alterations. However, the enological industry looks for safer alternatives to preserve enological products, and high-pressure treatments with supercritical CO2 are a suitable alternative. This study evaluates the effectiveness of this process in the stabilization and preservation of white grape must, studying the influence of time, pressure, and CO2 percentage on must characteristics. In spite of the percentage of CO2 turned out to be the variable that affects the most the process, no remarkable differences were observed in pH, acidity, and color intensity between untreated and treated musts. Moreover, this technique has proven to be very efficient in the reduction of aerobic mesophilic microorganisms as well as in the reduction of residual polyphenol oxidase activities, being lower than those obtained with SO2 addition (60 and 160 mg/L). Based on the results, the most convenient conditions were 100 bar and 10% CO2, for 10 min treatment.

The cell-assembled extracellular matrix: A focus on the storage stability and terminal sterilization of this human "bio" material

The Cell-Assembled extracellular Matrix (CAM) is an attractive biomaterial because it provided the backbone of vascular grafts that were successfully implanted in patients, and because it can now be assembled in "human textiles". For future clinical development, it is important to consider key manufacturing questions. In this study, the impact of various storage conditions and sterilization methods were evaluated. After 1 year of dry frozen storage, no change in mechanical nor physicochemical properties were detected. However, storage at 4 °C and room temperature resulted in some mechanical changes, especially for dry CAM, but physicochemical changes were minor. Sterilization modified CAM mechanical and physicochemical properties marginally except for hydrated gamma treatment. All sterilized CAM supported cell proliferation. CAM ribbons were implanted subcutaneously in immunodeficient rats to assess the impact of sterilization on the innate immune response. Sterilization accelerated strength loss but no significant difference could be shown at 10 months. Very mild and transient inflammatory responses were observed. Supercritical CO2 sterilization had the least effect. In conclusion, the CAM is a promising biomaterial since it is unaffected by long-term storage in conditions available in hospitals (hydrated at 4 °C), and can be sterilized terminally (scCO2) without compromising in vitro nor in vivo performance. STATEMENT OF SIGNIFICANCE: In the field of tissue engineering, the use of extracellular matrix (ECM) proteins as a scaffolding biomaterial has become very popular. Recently, many investigators have focused on ECM produced by cells in vitro to produce unprocessed biological scaffolds. As this new kind of "biomaterial" becomes more and more relevant, it is critical to consider key manufacturing questions to facilitate future transition to the clinic. This article presents an extensive evaluation of long-term storage stability and terminal sterilization effects on an extracellular matrix assembled by cells in vitro. We believe that this article will be of great interest to help tissue engineers involved in so-called scaffold-free approaches to better prepare the translation from benchtop to bedside.

Effects of Gamma Irradiation and Supercritical Carbon Dioxide Sterilization on Methacrylated Gelatin/Hyaluronan Hydrogels

Biopolymer hydrogels have become an important group of biomaterials in experimental and clinical use. However, unlike metallic or mineral materials, they are quite sensitive to sterilization. The aim of this study was to compare the effects of gamma irradiation and supercritical carbon dioxide (scCO₂) treatment on the physicochemical properties of different hyaluronan (HA)- and/or gelatin (GEL)-based hydrogels and the cellular response of human bone marrow-derived mesenchymal stem cells (hBMSC). Hydrogels were photo-polymerized from methacrylated HA, methacrylated GEL, or a mixture of GEL/HA. The composition and sterilization methods altered the dissolution behavior of the biopolymeric hydrogels. There were no significant differences in methacrylated GEL release but increased methacrylated HA degradation of gamma-irradiated samples. Pore size/form remained unchanged, while gamma irradiation decreased the elastic modulus from about 29 kPa to 19 kPa compared to aseptic samples. HBMSC proliferated and increased alkaline phosphatase activity (ALP) particularly in aseptic and gamma-irradiated methacrylated GEL/HA hydrogels alike, while scCO₂ treatment had a negative effect on both proliferation and osteogenic differentiation. Thus, gamma-irradiated methacrylated GEL/HA hydrogels are a promising base for multi-component bone substitute materials.

Comparative Verification of the Accuracy of Implant Models Made of PLA, Resin, and Silicone

Polylactic acid (PLA) has gained considerable attention as an alternative to petroleum-based materials due to environmental concerns. We fabricated implant models with fused filament fabrication (FFF) 3D printers using PLA, and the accuracies of these PLA models were compared with those of plaster models made from silicone impressions and resin models made with digital light processing (DLP). A base model was obtained from an impact-training model. The scan body was mounted on the plaster, resin, and PLA models obtained from the base model, and the obtained information was converted to stereolithography (STL) data by the 3D scanner. The base model was then used as a reference, and its data were superimposed onto the STL data of each model using Geomagic control. The horizontal and vertical accuracies of PLA models, as calculated using the Tukey-Kramer method, were 97.2 ± 48.4 and 115.5 ± 15.1 μm, respectively, which suggests that the PLA model is the least accurate among the three models. In both cases, significant differences were found between PLA and gypsum and between the PLA and resin models. However, considering that the misfit of screw-retained implant frames should be ≤150 µm, PLA can be effectively used for fabricating implant models.

Full physicochemical and biocompatibility characterization of a supercritical CO2 sterilized nano-hydroxyapatite/chitosan biodegradable scaffold for periodontal bone regeneration

Despite bone's innate self-renewal capability, some periodontal pathologic and traumatic defects' size inhibits full spontaneous regeneration. This current research characterized a 3D porous biodegradable nano-hydroxyapatite/chitosan (nHAp/CS, 70/30) scaffold for periodontal bone regeneration, which preparation method includes the final solvent extraction and sterilization through supercritical CO₂ (scCO₂). Micro-CT analysis revealed the fully interconnected porous microstructure of the nHAp/CS scaffold (total porosity 78 %, medium pore size 200 μm) which is critical for bone regeneration. Scanning electron microscopy (SEM) showed HAp crystals forming on the surface of the nHAp/CS scaffold after 21 days in simulated body fluid, demonstrating its bioactivity in vitro. The presence of nHAp in the scaffolds promoted a significantly lower biodegradation rate compared to a plain CS scaffold in PBS. Dynamic mechanical analysis confirmed their viscoelasticity, but the presence of nHAp significantly enhanced the storage modulus (42.34 ± 6.09 kPa at 10 Hz after 28 days in PBS), showing that it may support bone ingrowth at low-load bearing bone defects. Both scaffold types significantly inhibited the growth, attachment and colony formation abilities of S. aureus and E. coli, enhancing the relevance of chitosan in the grafts' composition for the naturally contaminated oral environment. At SEM and laser scanning confocal microscopy, MG63 cells showed normal morphology and could adhere and proliferate inside the biomaterials' porous structure, especially for the nHAp/CS scaffold, reaching higher proliferative rate at day 14. MG63 cells seeded within nHAp/CS scaffolds presented a higher expression of RUNX2, collagen A1 and Sp7 osteogenic genes compared to the CS samples. The in vivo subcutaneous implantation in mice of both scaffold types showed lower biodegradability with the preservation of the scaffolds porous structure that allowed the ingrowth of connective tissue until 5 weeks. Histology shows an intensive and progressive ingrowth of new vessels and collagen between the 3^rd and the 5^th week, especially for the nHAp/CS scaffold. So far, the scCO₂ method enabled the production of a cost-effective and environment-friendly ready-to-use nHAp/CS scaffold with microstructural, chemical, mechanical and biocompatibility features that make it a suitable bone graft alternative for defect sites in an adverse environment as in periodontitis and peri-implantitis.

Scaffold-based tissue engineering: Supercritical carbon dioxide as an alternative method for decellularization and sterilization of dense materials

Development of ready-to-use biomaterials and scaffolds is vital for further advancement of scaffold-based tissue engineering in clinical practice. Scaffolds need to mimic 3D ultrastructure, have adequate mechanical strength, are biocompatible, non-immunogenic and need to promote tissue regeneration in vivo. Although decellularization of native tissues seems promising to deliver scaffolds that meet these criteria, adequate decellularization of hard, poorly penetrable and poorly diffusible tissues remains challenging whilst being a very time-consuming process. In this study, a method to decellularize hard, dense tissues using supercritical carbon-dioxide preceded by a freeze/thaw cycle and followed by several washing steps is presented, demonstrating decellularisation efficiency and substantially reduced production/handling time. Additionally, supercritical carbon-dioxide treatment was used as sterilization method, further reducing the time required to produce the final scaffold. Histological evaluation showed that, after fine-tuning of the process, a partially acellular scaffold was obtained, with preservation of glycosaminoglycans and collagen fibers, albeit that the amount of residual dsDNA was still higher then chemically decellularized tissue. Biomechanical properties of the scaffold were similar to the native, non-decellularized tissue. After sterilization with supercritical carbon-dioxide the simulated functional outcome was more similar to native trachea, when compared to sterilization using gamma irradiation. Thus, decellularization and sterilization using supercritical carbon-dioxide with washing steps is an effective method for dense cartilaginous materials, and tuneable to meet different demands in other applications, but further optimization may be required. STATEMENT OF SIGNIFICANCE: Further advancement of the use of tissue engineered tracheal constructs is restricted by the lack of the ideal scaffold. Decellularized trachea is considered a promising scaffold, but the hard, poorly diffusible tissue remains challenging while forming a very time consumable process. Decellularization using supercritical carbon dioxide (scCO₂) seems promising, resulting in efficient removal of cellular material while reducing production and handling time. Addition of scCO₂ as a sterilization method resulted in further time reduction while improving functional outcome in comparison with traditional sterilization methods. This study presents an promising alternative method for decellularization and sterilization of dense materials, which can be tuned to meet different demands in other applications.

The effect of supercritical carbon dioxide on the physiochemistry, endogenous enzymes, and nutritional composition of fruit and vegetables and its prospects for industrial application: a overview

Consumers have an increasing demand for fruit and vegetables with high nutritional value worldwide. However, most fruit and vegetables are vulnerable to quality loss and spoilage during processing, transportation, and storage. Among the recently introduced emerging technologies, supercritical carbon dioxide (SCCO2) has been extensively utilized to treat and maintain fruit and vegetables mainly due to its nontoxicity, safety, and environmentally friendly. SCCO2 technology generates low processing costs and mild processing conditions (temperature and pressure) that allow for the application of CO2 at a supercritical state. This review aimed to summarize the current knowledge on the influence of SCCO2 technology on the quality attributes of fruit and vegetable products, such as physicochemical properties (pH, color, cloud, particle size distribution, texture), sensory quality, and nutritional composition (ascorbic acid, phenolic compounds, anthocyanins, carotenoids, and betalains). In addition, the effects and mechanisms of the SCCO2 technique on endogenous enzyme inactivation (polyphenol oxidase, peroxidase, and pectin methylesterase) were also elucidated. Finally, the prospects of the SCCO2 technique for industrial application was discussed from the economic and regulatory aspect.

Acellular nerve xenografts based on supercritical extraction technology for repairing long-distance sciatic nerve defects in rats

Compared to conventional artificial nerve guide conduits (NGCs) prepared using natural polymers or synthetic polymers, acellular nerve grafts (ACNGs) derived from natural nerves with eliminated immune components have natural bionic advantages in composition and structure that polymer materials do not have. To further optimize the repair effect of ACNGs, in this study, we used a composite technology based on supercritical carbon dioxide (scCO₂) extraction to process the peripheral nerve of a large mammal, the Yorkshire pig, and obtained an innovative Acellular nerve xenografts (ANXs, namely, CD + scCO₂ NG). After scCO₂ extraction, the fat and DNA content in CD + scCO₂ NG has been removed to the greatest extent, which can better supported cell adhesion and proliferation, inducing an extremely weak inflammatory response. Interestingly, the protein in the CD + scCO₂ NG was primarily involved in signaling pathways related to axon guidance. Moreover, compared with the pure chemical decellularized nerve graft (CD NG), the DRG axons grew naturally on the CD + scCO₂ NG membrane and extended long distances. In vivo studies further revealed that the regenerated nerve axons had basically crossed the CD + scCO₂ NG 3 weeks after surgery. 12 weeks after surgery, CD + scCO2 NG was similar to autologous nerves in improving the quality of nerve regeneration, target muscle morphology and motor function recovery and was significantly better than hollow NGCs and CD NG. Therefore, we believe that the fully decellularized and fat-free porcine ACNGs may be the most promising “bridge” for repairing human nerve defects at this stage and for some time to come.

•

The native adipose tissue inside acellular nerve xenografts hinders regenerated nerve fibers.

•

Environmentally friendly scCO2 extraction has natural advantages in reducing fat content.

•

Natural three-dimensional nerve basement membrane tube structure guides regenerating axons.

Inactivation of Clostridium Spores in Honey with Supercritical CO2 and in Combination with Essential Oils

The presence of tens of Clostridium botulinum spores per gram of honey can cause infantile botulism. Thermal treatment is insufficient to inactivate these resistant forms. This study explored the effectiveness of supercritical CO2 (scCO2) on its own and combined with lemon (LEO), clove (CLEO), and cinnamon (CEO) essential oils on the inactivation of Clostridium sporogenes (CECT 553) as a surrogate of Clostridium botulinum. In water, the degree of inactivation at 10 MPa after 60 min increased with the increasing temperature, reducing the population by 90% at 40 °C and by 99.7% at 80 °C. In contrast, when applied to honey, scCO2 did not inactivate Clostridium spores satisfactorily at temperatures below 70 °C, which was related to the protective effect of honey. Meanwhile, scCO2 modified with CEO (<0.4% mass) improved the inactivation degree, with a 1.3-log reduction achieved at 60 °C. With this same mixture, a reduction of 3.7 logs was accomplished in a derivative with 70% moisture. Honey was very sensitive to the temperature of the applied CO2. The obtained product could be used as a novel food, food ingredient, cosmetic, or medicine.

3D-Printed PLA Medical Devices: Physicochemical Changes and Biological Response after Sterilisation Treatments

Polylactic acid (PLA) has become one of the most commonly used polymers in medical devices given its biocompatible, biodegradable and bioabsorbable properties. In addition, due to PLA’s thermoplastic behaviour, these medical devices are now obtained using 3D printing technologies. Once obtained, the 3D-printed PLA devices undergo different sterilisation procedures, which are essential to prevent infections. This work was an in-depth study of the physicochemical changes caused by novel and conventional sterilisation techniques on 3D-printed PLA and their impact on the biological response in terms of toxicity. The 3D-printed PLA physicochemical (XPS, FTIR, DSC, XRD) and mechanical properties as well as the hydrophilic degree were evaluated after sterilisation using saturated steam (SS), low temperature steam with formaldehyde (LTSF), gamma irradiation (GR), hydrogen peroxide gas plasma (HPGP) and CO₂ under critical conditions (SCCO). The biological response was tested in vitro (fibroblasts NCTC-929) and in vivo (embryos and larvae wild-type zebrafish Danio rerio). The results indicated that after GR sterilisation, PLA preserved the O:C ratio and the semi-crystalline structure. Significant changes in the polymer surface were found after HPGP, LTSF and SS sterilisations, with a decrease in the O:C ratio. Moreover, the FTIR, DSC and XRD analysis revealed PLA crystallisation after SS sterilisation, with a 52.9% increase in the crystallinity index. This structural change was also reflected in the mechanical properties and wettability. An increase in crystallinity was also observed after SCCO and LTSF sterilisations, although to a lesser extent. Despite these changes, the biological evaluation revealed that none of the techniques were shown to promote the release of toxic compounds or PLA modifications with toxicity effects. GR sterilisation was concluded as the least reactive technique with good perspectives in the biological response, not only at the level of toxicity but at all levels, since the 3D-printed PLA remained almost unaltered.

Electrospun Polylactic Acid-Based Fibers Loaded with Multifunctional Antibacterial Biobased Polymers

Here, we report the development of antibacterial and compostable electrospun polylactic acid (PLA) fibers by incorporation of a multifunctional biobased polymer in the process. The multifunctional polymer was synthesized from the bio-sourced itaconic acid building block by radical polymerization followed by click chemistry reaction with hydantoin groups. The resulting polymer possesses triazole and hydantoin groups available for further N-alkylation and chlorination reaction, which provide antibacterial activity. This polymer was added to the electrospinning PLA solution at 10 wt %, and fiber mats were successfully prepared. The obtained fibers were surface-modified through the accessible functional groups, leading to the corresponding cationic triazolium and N-halamine groups. The fibers with both antibacterial functionalities demonstrated high antibacterial activity against Gram-positive and Gram-negative bacteria. While the fibers with cationic surface groups are only effective against Gram-positive bacteria (Staphylococcus epidermidis and Staphylococcus aureus), upon chlorination, the activity against Gram-negative Escherichia coli and Pseudomonas aeruginosa is significantly improved. In addition, the compostability of the electrospun fibers was tested under industrial composting conditions, showing that the incorporation of the antibacterial polymer does not impede the disintegrability of the material. Overall, this study demonstrates the feasibility of this biobased multifunctional polymer as an antibacterial agent for biodegradable polymeric materials with potential application in medical uses.

3D-Printed, Dual Crosslinked and Sterile Aerogel Scaffolds for Bone Tissue Engineering

The fabrication of bioactive three-dimensional (3D) hydrogel scaffolds from biocompatible materials with a complex inner structure (mesoporous and macroporous) and highly interconnected porosity is crucial for bone tissue engineering (BTE). 3D-printing technology combined with aerogel processing allows the fabrication of functional nanostructured scaffolds from polysaccharides for BTE with personalized geometry, porosity and composition. However, these aerogels are usually fragile, with fast biodegradation rates in biological aqueous fluids, and they lack the sterility required for clinical practice. In this work, reinforced alginate-hydroxyapatite (HA) aerogel scaffolds for BTE applications were obtained by a dual strategy that combines extrusion-based 3D-printing and supercritical CO₂ gel drying with an extra crosslinking step. Gel ageing in CaCl₂ solutions and glutaraldehyde (GA) chemical crosslinking of aerogels were performed as intermediate and post-processing reinforcement strategies to achieve highly crosslinked aerogel scaffolds. Nitrogen adsorption–desorption (BET) and SEM analyses were performed to assess the textural parameters of the resulting alginate-HA aerogel scaffolds. The biological evaluation of the aerogel scaffolds was performed regarding cell viability, hemolytic activity and bioactivity for BTE. The impact of scCO₂-based post-sterilization treatment on scaffold properties was also assessed. The obtained aerogels were dual porous, bio- and hemocompatible, as well as endowed with high bioactivity that is dependent on the HA content. This work is a step forward towards the optimization of the physicochemical performance of advanced biomaterials and their sterilization.

Contributions of supercritical fluid technology for advancing decellularization and postprocessing of viable biological materials

The demand for tissue and organ transplantation worldwide has led to an increased interest in the development of new therapies to restore normal tissue function through transplantation of injured tissue with biomedically engineered matrices. Among these developments is decellularization, a process that focuses on the removal of immunogenic cellular material from a tissue or organ. However, decellularization is a complex and often harsh process that frequently employs techniques that can negatively impact the properties of the materials subjected to it. The need for a more benign alternative has driven research on supercritical carbon dioxide (scCO₂) assisted decellularization. scCO₂ can achieve its critical point at relatively low temperature and pressure conditions, and for its high transfer rate and permeability. These properties make scCO₂ an appealing methodology that can replace or diminish the exposure of harsh chemicals to sensitive materials, which in turn could lead to better preservation of their biochemical and mechanical properties. The presented review covers relevant literature over the last years where scCO₂-assisted decellularization is employed, as well as discussing major topics such as the mechanism of action behind scCO₂-assisted decellularization, CO₂ and cosolvents' solvent properties, effect of the operational parameters on decellularization efficacy and on the material's properties.

Combined sterilization and fabrication of drug-loaded scaffolds using supercritical CO2 technology

The access of biodegradable scaffolds to the clinical arena is constrained by the absence of a suitable sterilization technique for the processing of advanced polymeric materials. Sterilization with supercritical CO₂ (scCO₂) may circumvent some technological limitations (e.g., low temperature, no chemical residues on the material), although scCO₂ can plasticize the polymer depending on the processing conditions used. In this latter case, the integration of the manufacturing and sterilization processes is of particular interest to obtain sterile and customized scaffolds in a single step. In this work, scCO₂ was exploited as a concomitantly foaming and sterilizing agent for the first time, developing a one-step process for the production of vancomycin-loaded poly(ε-caprolactone) (PCL) bone scaffolds. The effect of the CO₂ contact time on the sterility levels of the procedure was investigated, and the sterilization efficiency was evaluated against dry spores (Bacillus stearothermophilus, Bacillus pumilus and Bacillus atrophaeus). Vancomycin-loaded PCL scaffolds had relevant sustained release profiles for the prophylaxis of infections at the grafted area, even those caused by methicillin-resistant Staphylococcus aureus (MRSA). The biological performance of the scaffolds was evaluated in vitro regarding human mesenchymal stem cells (hMSCs) attachment and growth. Finally, the biocompatibility and angiogenic response of the manufactured sterile scaffolds was assessed in ovo through chick chorioallantoic membrane (CAM) assays.

Transcriptome analysis reveals the molecular mechanisms of the novel Lactobacillus pentosus pentocin against Bacillus cereus

The objective of this study was to investigate the antibacterial effect and mechanism of Lactobacillus pentosus pentocin against Bacillus cereus. The dynamic growth of B. cereus showed that the pentocin had strong antibacterial activity against the strain. The antibacterial mechanism focused on cytomembrane destruction, biofilms formation, DNA replication and protein synthesis of B. cereus. The scanning electron microscopy, transmission electron microscopy and flow cytometry analysis illustrated that the cytomembranes were destroyed, causing the leakage of internal cellular components. Transcriptome sequencing indicated that the genes (KinB, KinC and Spo0B) in two component systems signal pathway were down-regulated, which resulted in the inhibition of the spores and biofilms formation of B. cereus. The phosphorylation and autoinducer-2 import were inhibited by down-regulating the expression levels of LuxS and LsrB genes in quorum sensing signal pathway, which also suppressed biofilms formation of B. cereus. The K⁺ leakage activated the K⁺ transport channels by up-relating the genes (KdpA, KdpB and KdpC), promoting the entry of K⁺ from the extracellular. In addition, the pentocin interfered DNA replication and protein synthesis by regulating the genes associated with DNA replication (dnaX and holB), RNA degradation (cshA, rho, rnj, deaD, rny, dnaK, groEL and hfq) and ribosome function (rpsA, rpsO and rplS). In this article, we provide some novel insights into the molecular mechanism responsible for high antibacterial activity of the L. pentosus pentocin against B. cereus. And the pentocin might be a very promising natural preservative for controlling the B. cereus contaminations in foods.

Marine origin materials on biomaterials and advanced therapies to cartilage tissue engineering and regenerative medicine

The body's self-repair capacity is limited, including injuries on articular cartilage zones. Over the past few decades, tissue engineering and regenerative medicine (TERM) has focused its studies on the development of natural biomaterials for clinical applications aiming to overcome this self-therapeutic bottleneck. This review focuses on the development of these biomaterials using compounds and materials from marine sources that are able to be produced in a sustainable way, as an alternative to mammal sources (e.g., collagens) and benefiting from their biological properties, such as biocompatibility, low antigenicity, biodegradability, among others. The structure and composition of the new biomaterials require mimicking the native extracellular matrix (ECM) of articular cartilage tissue. To design an ideal temporary tissue-scaffold, it needs to provide a suitable environment for cell growth (cell attachment, proliferation, and differentiation), towards the regeneration of the damaged tissues. Overall, the purpose of this review is to summarize various marine sources to be used in the development of different tissue-scaffolds with the capability to sustain cells envisaging cartilage tissue engineering, analysing the systems displaying more promising performance, while pointing out current limitations and steps to be given in the near future.

Current Trends on Protein Driven Bioinks for 3D Printing

In the last decade, three-dimensional (3D) extrusion bioprinting has been on the top trend for innovative technologies in the field of biomedical engineering. In particular, protein-based bioinks such as collagen, gelatin, silk fibroin, elastic, fibrin and protein complexes based on decellularized extracellular matrix (dECM) are receiving increasing attention. This current interest is the result of protein's tunable properties, biocompatibility, environmentally friendly nature and possibility to provide cells with the adequate cues, mimicking the extracellular matrix's function. In this review we describe the most relevant stages of the development of a protein-driven bioink. The most popular formulations, molecular weights and extraction methods are covered. The different crosslinking methods used in protein bioinks, the formulation with other polymeric systems or molecules of interest as well as the bioprinting settings are herein highlighted. The cell embedding procedures, the in vitro, in vivo, in situ studies and final applications are also discussed. Finally, we approach the development and optimization of bioinks from a sequential perspective, discussing the relevance of each parameter during the pre-processing, processing, and post-processing stages of technological development. Through this approach the present review expects to provide, in a sequential manner, helpful methodological guidelines for the development of novel bioinks.

Supercritical Fluid Extraction Kinetics of Cherry Seed Oil: Kinetics Modeling and ANN Optimization

This study was primarily focused on the supercritical fluid extraction (SFE) of cherry seed oil and the optimization of the process using sequential extraction kinetics modeling and artificial neural networks (ANN). The SFE study was organized according to Box-Behnken design of experiment, with additional runs. Pressure, temperature and flow rate were chosen as independent variables. Five well known empirical kinetic models and three mass-transfer kinetics models based on the Sovová’s solution of SFE equations were successfully applied for kinetics modeling. The developed mass-transfer models exhibited better fit of experimental data, according to the calculated statistical tests (R², SSE and AARD). The initial slope of the SFE curve was evaluated as an output variable in the ANN optimization. The obtained results suggested that it is advisable to lead SFE process at an increased pressure and CO₂ flow rate with lower temperature and particle size values to reach a maximal initial slope.

How to Sterilize Polylactic Acid Based Medical Devices?

How sterilization techniques accurately affect the properties of biopolymers continues to be an issue of discussion in the field of biomedical engineering, particularly now with the development of 3D-printed devices. One of the most widely used biopolymers in the manufacture of biomedical devices is the polylactic acid (PLA). Despite the large number of studies found in the literature on PLA devices, relatively few papers focus on the effects of sterilization treatments on its properties. It is well documented in the literature that conventional sterilization techniques, such as heat, gamma irradiation and ethylene oxide, can induced damages, alterations or toxic products release, due to the thermal and hydrolytical sensitivity of PLA. The purposes of this paper are, therefore, to review the published data on the most common techniques used to sterilize PLA medical devices and to analyse how they are affecting their physicochemical and biocompatible properties. Emerging and alternative sterilization methods for sensitive biomaterials are also presented.

Bioaerogels: Promising Nanostructured Materials in Fluid Management, Healing and Regeneration of Wounds

Wounds affect one's quality of life and should be managed on a patient-specific approach, based on the particular healing phase and wound condition. During wound healing, exudate is produced as a natural response towards healing. However, excessive production can be detrimental, representing a challenge for wound management. The design and development of new healing devices and therapeutics with improved performance is a constant demand from the healthcare services. Aerogels can combine high porosity and low density with the adequate fluid interaction and drug loading capacity, to establish hemostasis and promote the healing and regeneration of exudative and chronic wounds. Bio-based aerogels, i.e., those produced from natural polymers, are particularly attractive since they encompass their intrinsic chemical properties and the physical features of their nanostructure. In this work, the emerging research on aerogels for wound treatment is reviewed for the first time. The current scenario and the opportunities provided by aerogels in the form of films, membranes and particles are identified to face current unmet demands in fluid managing and wound healing and regeneration.

The potential application of supercritical CO2 in microbial inactivation of food raw materials and products

The purpose of this study was to review the possibility of using supercritical CO₂ as a green and sustainable technology for microbial inactivation of raw material for further application in the food industry. The history of the development of supercritical CO₂ microbial inactivation has been widely described in this article. The fundamental scientific part of the process like mechanism of bactericidal action of CO₂ or inactivation of key enzymes were characterized in detail. In summary, this study provides an overview of the latest literature on the use of supercritical carbon dioxide in microbial inactivation of food raw materials and products.

Aerogels in drug delivery: From design to application

Aerogels are the lightest processed solid materials on Earth and with the largest empty volume fraction in their structure. Composition versatility, modularity, and feasibility of industrial scale manufacturing are behind the fast emergence of aerogels in the drug delivery field. Compared to other 3D materials, the high porosity (interconnected mesopores) and high specific surface area of aerogels may allow faster loading of small-molecule drugs, less constrained access to inner regions of the matrix, and more efficient interactions of the biological milieu with the polymer matrix. Processing in supercritical CO₂ medium for both aerogel production (drying) and drug loading (impregnation) has remarkable advantages such as absence of an oxidizing environment, clean manufacture, and easiness for the scale-up under good manufacturing practices. The aerogel solid skeleton dictates the chemical affinity to the different drugs, which in turn determines the loading efficiency and the release pattern. Aerogels can be used to increase the solubility of BCS Class II and IV drugs because the drug can be deposited in amorphous state onto the large surface area of the skeleton, which facilitates a rapid contact with the body fluids, dissolution, and release. Conversely, tuning the aerogel structure by functionalization with drug-binding moieties or stimuli-responsive components, application of coatings and incorporation of drug-loaded aerogels into other matrices may enable site-specific, stimuli-responsive, or prolonged drug release. The present review deals with last decade advances in aerogels for drug delivery. An special focus is paid first on the loading efficiency of active ingredients and release kinetics under biorelevant conditions. Subsequent sections deal with aerogels intended to address specific therapeutic demands. In addition to oral delivery, the physical properties of the aerogels appear to be very advantageous for mucosal administration routes, such as pulmonary, nasal, or transdermal. A specific section devoted to recent achievements in gene therapy and theranostics is also included. In the last section, scale up strategies and life cycle assessment are comprehensively addressed.

Effect of Cellulose Characteristics on the Properties of the Wet-Spun Aerogel Fibers

Cellulose aerogels (CAs) from plant or bacterial-derived cellulose have advantages such as low density, high porosity, and high specific surface area and have been used in various applications including biomedical fields. One limiting factor in developing CAs is their demanding shaping process since it involves several steps of dissolution/dispersion of cellulose, geometry configurations using molds or nozzles, coagulation and washing of the gel body, and drying techniques. CA fibers can be converted into textiles and enhance the design ability, stiffness, and flexibility of the CAs. This study aims to understand the correlations between the initial cellulose characteristics, aerogel’s internal structure, and its prospective biomedical application. Wet-spun CA fibers were obtained by supercritical CO2 drying from low and high molecular weight microcrystalline cellulose in calcium thiocyanate tetrahydrate solution. Fiber spinning, thermal behavior, textural properties, and biological assessments of the CA fibers were inspected. The CA microfibers from high molecular weight cellulose proved to have a higher surface area (~197 m2/g), denser structure, and finer nanofibrils (~2 nm) with better thermal stability in comparison with the fibers produced from low molecular weight cellulose. The fibers were nontoxic, and cell proliferation was observed over time. CA fibers showed promising results to be used for biomedical applications such as tissue engineering and wound care.

Sterilization methods of liposomes: Drawbacks of conventional methods and perspectives

Liposomes are targeted drug delivery systems that are of great pharmaceutical and therapeutic interest. Parenteral route is the main way used for liposome administration. In this case, their sterility is a requirement. However, due to the particular sensitivity of liposomes and their tendency to physicochemical alterations, their sterilization remains a real challenge. Conventional sterilization methods such as heat, ethylene oxide, ultraviolet and gamma irradiations are considered as unsuitable for liposome sterilization and the recommended methods for obtaining sterility of liposomes are filtration and aseptic manufacturing. Unfortunately, these recommended methods are not without limitations. This review outlines the difficulties associated with the use of these different classical methods for obtaining liposome sterility. The effects on liposome physicochemical and biopharmaceutical characteristics as well as efficacy, toxicity and practical problems of these sterilization techniques have been discussed. The search for an alternative method being therefore necessary, the applicability of supercritical carbon dioxide (ScCO₂) technology, which is nowadays a promising strategy for the sterilization of sensitive products such as liposomes, is also examined. It appears from this analysis that ScCO₂ could effectively be an interesting alternative to achieve sterility of liposomes, but for this, sterilization assays including challenge tests and optimization studies are needed.

Management of environmental health to prevent an outbreak of COVID-19

The World Health Organization (WHO) has recently pronounced severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as a serious pandemic. It is, therefore, mandatory for public health authorities to have an environmental health management plan against COVID-19. This chapter summarizes articles and official reports related to environmental health management and prevention policies against COVID-19. Because medical sectors require comprehensive guidelines to follow in such pandemic situations, this chapter highlights the significant factors of COVID-19 transmission in our environment (e.g., air), waste management for COVID-19, and protection and disinfection policies against COVID-19. At present, scientists are still discovering more about COVID-19 and its effect on the environment and the health sector. As such, further research is required to increase knowledge about the structural and pathogenic features of COVID-19 and to find effective treatments to dominate this epidemic.

Use of supercritical carbon dioxide technology for fabricating a tissue engineering scaffold for anterior cruciate ligament repair

Tissue-engineered grafts may be useful in Anterior Cruciate Ligament (ACL) repair and provide a novel, alternative treatment to clinical complications of rupture, harvest site morbidity and biocompatibility associated with autografts, allografts and synthetic grafts. We successfully used supercritical carbon dioxide (Sc-CO₂) technology for manufacturing a “smart” biomaterial scaffold, which retains the native protein conformation and tensile strength of the natural ACL but is decellularized for a decreased immunogenic response. We designed and fabricated a new scaffold exhibiting (1) high tensile strength and biomechanical properties comparable to those of the native tissue, (2) thermodynamically-stable extra-cellular matrix (ECM), (3) preserved collagen composition and crosslinking, (4) a decellularized material milieu with potential for future engineering applications and (5) proven feasibility and biocompatibility in an animal model of ligament reconstruction. Because of the “smart” material ECM, this scaffold may have the potential for providing a niche and for directing stem cell growth, differentiations and function pertinent to new tissue formation. Sc-CO₂-related technology is advanced and has the capability to provide scaffolds of high strength and durability, which sustain a lifetime of wear and tear under mechanical loading in vivo.

Solvent-Free Approaches for the Processing of Scaffolds in Regenerative Medicine

The regenerative medicine field is seeking novel strategies for the production of synthetic scaffolds that are able to promote the in vivo regeneration of a fully functional tissue. The choices of the scaffold formulation and the manufacturing method are crucial to determine the rate of success of the graft for the intended tissue regeneration process. On one hand, the incorporation of bioactive compounds such as growth factors and drugs in the scaffolds can efficiently guide and promote the spreading, differentiation, growth, and proliferation of cells as well as alleviate post-surgical complications such as foreign body responses and infections. On the other hand, the manufacturing method will determine the feasible morphological properties of the scaffolds and, in certain cases, it can compromise their biocompatibility. In the case of medicated scaffolds, the manufacturing method has also a key effect in the incorporation yield and retained activity of the loaded bioactive agents. In this work, solvent-free methods for scaffolds production, i.e., technological approaches leading to the processing of the porous material with no use of solvents, are presented as advantageous solutions for the processing of medicated scaffolds in terms of efficiency and versatility. The principles of these solvent-free technologies (melt molding, 3D printing by fused deposition modeling, sintering of solid microspheres, gas foaming, and compressed CO2 and supercritical CO2-assisted foaming), a critical discussion of advantages and limitations, as well as selected examples for regenerative medicine purposes are herein presented.