Supercritical CO2 technology: The next standard sterilization technique?

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.

Effect of gamma irradiation and supercritical carbon dioxide sterilization with Novakill™ or ethanol on the fracture toughness of cortical bone

Sterilization of structural bone allografts is a critical process prior to their clinical use in large cortical bone defects. Gamma irradiation protocols are known to affect tissue integrity in a dose dependent manner. Alternative sterilization treatments, such as supercritical carbon dioxide (SCCO2 ), are gaining popularity due to advantages such as minimal exposure to denaturants, the lack of toxic residues, superior tissue penetration, and minor impacts on mechanical properties including strength and stiffness. The impact of SCCO2 on the fracture toughness of bone tissue, however, remains unknown. Here, we evaluate crack initiation and growth toughness after 2, 6, and 24 h SCCO2 -treatment using Novakill™ and ethanol as additives on ~11 samples per group obtained from a pair of femur diaphyses of a canine. All mechanical testing was performed at ambient air after 24 h soaking in Hanks' balanced salt solution (HBSS). Results show no statistically significant difference in the failure characteristics of the Novakill™-treated groups whereas crack growth toughness after 6 and 24 h of treatment with ethanol significantly increases by 37% (p = .010) and 34% (p = .038), respectively, compared to an untreated control group. In contrast, standard 25 kGy gamma irradiation causes significantly reduced crack growth resistance by 40% (p = .007) compared to untreated bone. FTIR vibrational spectroscopy, conducted after testing, reveals a consistent trend of statistically significant differences (p < .001) with fracture toughness. These trends align with variations in the ratios of enzymatic mature to immature crosslinks in the collagen structure, suggesting a potential association with fracture toughness. Additional Raman spectroscopy after testing shows a similar trend with statistically significant differences (p < .005), which further supports that collagen structural changes occur in the SCF-treated groups with ethanol after 6 and 24 h. Our work reveals the benefits of SCCO2 sterilization compared to gamma irradiation.

Combining High-Pressure Processing and Supercritical Carbon Dioxide for Inactivation of Listeria innocua

The effect of high-pressure treatment with supercritical CO2 on the inactivation of Listeria innocua in a fish soup was investigated. The soup was inoculated with L. innocua, packaged in modified atmosphere with 50:50 or 95:5 CO2:N2, high-pressure processed (300, 350, 400 and 600 MPa, 2 min) under subcritical (T < 304 K) or supercritical conditions (T > 304 K) and stored at 4 °C for up to 53 days. Treatment at 400 and 600 MPa had a significant (p < 0.05) effect on L. innocua under both supercritical and subcritical conditions. In contrast, pressurization at 350 MPa and supercritical conditions were needed to significantly (p < 0.05) inactive L. innocua. Increased levels of CO2 in the headspace significantly (p < 0.05) reduced the bacterial load during processing, and supercritical conditions had a significant (p < 0.01) interaction with both CO2 levels and pressure. Increased storage time gave significantly increased levels of L. innocua at 400 and 600 MPa. In addition, high levels of CO2 significantly decreased (p < 0.001) growth. However, 350 MPa under supercritical conditions seemed to set the L. innocua in a permanent lag phase, with slow and steadily decreasing numbers of bacteria during storage. All the design variables resulted in significant inactivation of L. innocua, and supercritical conditions combined with high levels of CO2 inhibited the recovery of L. innocua to a large degree.

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.

Ozone Decontamination of Medical and Nonmedical Devices: An Assessment of Design and Implementation Considerations

The control of infectious diseases can be improved via carefully designed decontamination equipment and systems. Research interest in ozone (a powerful antimicrobial agent) has significantly increased over the past decade. The COVID-19 pandemic has also instigated the development of new ozone-based technologies for the decontamination of personal protective equipment, surfaces, materials, and indoor environments. As this interest continues to grow, it is necessary to consider key factors affecting the applicability of lab-based findings to large-scale systems utilizing ozone. In this review, we present recent developments on the critical factors affecting the successful deployments of industrial ozone technologies. Some of these include the medium of application (air or water), material compatibility, efficient circulation and extraction, measurement and control, automation, scalability, and process economics. We also provide a comparative assessment of ozone relative to other decontamination methods/sterilization technologies and further substantiate the necessity for increased developments in gaseous and aqueous ozonation. Modeling methodologies, which can be applied for the design and implementation of ozone contacting systems, are also presented in this review. Key knowledge gaps and open research problems/opportunities are extensively covered including our recommendations for the development of novel solutions with industrial importance.

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.

Use of supercritical CO2 for the sterilization of liposomes: Study of the influence of sterilization conditions on the chemical and physical stability of phospholipids and liposomes

The effects of four potential supercritical carbon dioxide (ScCO₂) sterilization conditions on the chemical stability of 9 phospholipids and on the physicochemical characteristics of liposomes consisting of stable phospholipids, as well as their sterilization efficiency were evaluated. These conditions were : C1 (ScCO₂/70 °C/150 bar/240 min), C2 (ScCO₂/0.25 % water/ 0.15% H₂O₂/ 0.5% acetic anhydride/38° C/85 bar/45 min), C3 (ScCO₂/0.08 % peracetic acid/35° C/104 bar/180 min) and C4 (ScCO₂/200 ppm H₂O₂/40 °C/270 bar/90 min). The results showed for phospholipids, a significant increase in hydrolysis products of 3.77 to 14.50 % and an increase in oxidation index of 6.10 to 430.50 % with unsaturated phospholipids for all tested conditions while with saturated phospholipids, no significant degradation was observed. Concerning the liposome formulation, no change in dispersion color and no phospholipid degradation were observed. However, a decrease in liposome size from 126.90 nm to 111.80 nm, 96.27 nm, 99.60 nm and 109.13 nm and an increase in the PdI from 0.208 to 0.271, 0.233, 0.285, and 0.298 were found with conditions C1, C2, C3 and C4 respectively. For the sterilization efficiency, conditions C1, C2 and C3 achieved the required sterility assurance level (SAL) of 10^-6 for liposomes.

Hemocompatibility of cellulose phosphate aerogel membranes with potential use in bone tissue engineering

Cellulose is an appealing material for tissue engineering. In an attempt to overcome some obstacles with cellulose II cell scaffolding materials related to insufficient biomineralization, lack of micron-size porosity, and deficiency in surface charge, respective solutions have been proposed. These included covalent phosphorylation of different cellulose materials targeting relatively low degrees of substitution (DS 0.18-0.23) and processing these cellulose derivatives into scaffolding materials by a dissolution/coagulation approach employing the hitherto rarely used TBAF/DMSO/H₂O system for cellulose dissolution. Here, we report bioactivity and preliminary hemocompatibility testing of dual-porous cellulose phosphate aerogels (contrasted with the phosphate-free reference) obtained via coagulation (water/ethanol), solvent exchange and scCO₂ drying. Deposition of hydroxyapatite from simulated body fluid (7 days of immersion) revealed good bioactivity (1.5-2.2 mg Ca²⁺ per mg scaffold). Incubation of the scCO₂-dried and rehydrated scaffolding materials in heparin anticoagulated human whole blood was conducted to study selected parameters of hemostasis (prothrombin F1+2 fragment, PF4, count of thrombocyte-leukocyte conjugates) and inflammatory response (C5a fragment, leukocyte activation marker CD11b). Adhesion of leukocytes on the surface of the incubated substrates was assessed by scanning electron and fluorescence microscopy (DAPI staining). The results suggest that phosphorylation at low DS does not increase platelet activation. However, a significant increase in platelet activation and thrombin formation was observed after a certain fraction of the negative surface charges had been compensated by Ca²⁺ ions. The combination of both phosphorylation and calcification turned out to be a potent means for controlling the inflammatory response, which was close to baseline level for some of the studied samples.

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.

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.

Application of sonodynamic technology and sonosensitizers in food sterilization: a review of developments, trends and challenges

Food safety and food waste have always been hot topics of discussion in recent years. However, the infection of human pathogenic bacteria and the waste of food resources caused by microbial-contaminated food remains common. Although traditional sterilization technology has been very mature, it causes changes in food flavor and excessive energy consumption to a certain extent. Moreover, the widespread bacterial resistance has also sounded a warning for researchers and finding a new alternative to antibiotics is urgently needed. The application of sonodynamic sterilization technology in medical treatment has aroused the interest of researchers. It provides ideas for new food sterilization technology. As a new non-thermal sterilization technology, sonodynamic sterilization technology has strong penetration, safety, less residue and by-products, and will less change the quality of the food itself. Therefore, sonodynamic sterilization technology has great potential applied in food sterilization technology. This review describes the concept of sonodynamic sterilization technology, the sterilization mechanism of sonodynamic sterilization and the inactivation mechanism of various pathogens, the classification and application of sonosensitizers, and the ultrasonic technology in sonodynamic sterilization in the application over the recent years. It provides a scientific reference for the application of sonodynamic sterilization technology in the field of food sterilization.

Supercritical CO2 Extract from Microalga Tetradesmus obliquus: The Effect of High-Pressure Pre-Treatment

High-pressure pre-treatment followed by supercritical carbon dioxide (ScCO₂) extraction (300 bar, 40 °C) was applied for the attainment of the lipophilic fraction of microalga Tetradesmus obliquus. The chemical profile of supercritical extracts of T. obliquus was analyzed by ultra-high-performance liquid chromatography-high-resolution mass spectrometry with electrospray ionization (UHPLC-ESI-HRMS). Moreover, the impact of ScCO₂ on the microbiological and metal profile of the biomass was monitored. The application of the pre-treatment increased the extraction yield approximately three-fold compared to the control. In the obtained extracts (control and pre-treated extracts), the identified components belonged to triacylglyceroles, fatty acid derivatives, diacylglycerophosphocholines and diacylglycerophosphoserines, pigments, terpenes, and steroids. Triacylglycerols (65%) were the most dominant group of compounds in the control extract. The pre-treatment decreased the percentage of triacylglycerols to 2%, while the abundance of fatty acid derivatives was significantly increased (82%). In addition, the pre-treatment led to an increase in the percentages of carotenoids, terpenoids, and steroids. Furthermore, it was determined that ScCO₂ extraction reduced the number of microorganisms in the biomass. Considering its microbiological and metal profiles, the biomass after ScCO₂ can potentially be used as a safe and important source of organic compounds.

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.

Methods of Liposomes Preparation: Formation and Control Factors of Versatile Nanocarriers for Biomedical and Nanomedicine Application

Liposomes are nano-sized spherical vesicles composed of an aqueous core surrounded by one (or more) phospholipid bilayer shells. Owing to their high biocompatibility, chemical composition variability, and ease of preparation, as well as their large variety of structural properties, liposomes have been employed in a large variety of nanomedicine and biomedical applications, including nanocarriers for drug delivery, in nutraceutical fields, for immunoassays, clinical diagnostics, tissue engineering, and theranostics formulations. Particularly important is the role of liposomes in drug-delivery applications, as they improve the performance of the encapsulated drugs, reducing side effects and toxicity by enhancing its in vitro- and in vivo-controlled delivery and activity. These applications stimulated a great effort for the scale-up of the formation processes in view of suitable industrial development. Despite the improvements of conventional approaches and the development of novel routes of liposome preparation, their intrinsic sensitivity to mechanical and chemical actions is responsible for some critical issues connected with a limited colloidal stability and reduced entrapment efficiency of cargo molecules. This article analyzes the main features of the formation and fabrication techniques of liposome nanocarriers, with a special focus on the structure, parameters, and the critical factors that influence the development of a suitable and stable formulation. Recent developments and new methods for liposome preparation are also discussed, with the objective of updating the reader and providing future directions for research and development.

Application of supercritical fluid carbon dioxide in improving food shelf-life and safety by inactivating spores: a review

Extending shelf-life of food, ensuring it is safe for consumers and meeting regulatory standards is the food industry's governing principle. Food safety is an essential aspect of food processing. Spores-forming microbes such as Bacillus spp. and Clostridium spp. are problematic in the food industry because of their ability to form endospores and survive processing conditions. Hence, their germination in food poses a threat to both shelf-life and safety of food. This paper reports on the current state of supercritical fluid carbon dioxide (SF-CO₂) application in the inactivation of spores-forming microbes in food. Unlike high hydrostatic pressure and thermal processes which struggle to deactivate and destroy spores, and if they do, it impacts adversely on the food nutritional and quality attributes. This technique is viable to inactivate spores and maintain the foods structural and nutritional characteristics. The mechanisms of inactivation can be grouped into: (1) release of cellular content due to rupture of the cell wall, coat and cortex, and disruption of membranes, (2) degradation of proteins as a result of interaction with permeated and penetrated SF-CO₂ and (3) deactivation of enzymatic activities. It was discovered that the synergistic effect of ultrasound another non-thermal technique or addition of co-solvent such as water, hydrogen peroxide and ethanol or antimicrobial peptide greatly enhanced inactivation of spores. This work harmonizes published perspectives on spores' inactivation mechanisms, and will help inform further research into the application of SF-CO₂ in the sterilization of food products.

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.

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.

Combination of supercritical CO2 and high-power ultrasound for the inactivation of fungal and bacterial spores in lipid emulsions

For the first time, this study addresses the intensification of supercritical carbon dioxide (SC-CO2) treatments using high-power ultrasound (HPU) for the inactivation of fungal (Aspergillus niger) and bacterial (Clostridium butyricum) spores in oil-in-water emulsions. The inactivation kinetics were analyzed at different pressures (100, 350 and 550 bar) and temperatures (50, 60, 70, 80, 85 °C), depending on the microorganism, and compared to the conventional thermal treatment. The inactivation kinetics were satisfactorily described using the Weibull model. Experimental results showed that SC-CO2 enhanced the inactivation level of both spores when compared to thermal treatments. Bacterial spores (C.butyricum) were found to be more resistant to SC-CO2 + HPU, than fungal (A.niger) ones, as also observed in the thermal and SC-CO2 treatments. The application of HPU intensified the SC-CO2 inactivation of C.butyricum spores, e.g. shortening the total inactivation time from 10 to 3 min at 85 °C. However, HPU did not affect the SC-CO2 inactivation of A.niger spores. The study into the effect of a combined SC-CO2 + HPU treatment has to be necessarily extended to other fungal and bacterial spores, and future studies should elucidate the impact of HPU application on the emulsion's stability.

Evaluation of supercritical CO2 sterilization efficacy for sanitizing personal protective equipment from the coronavirus SARS-CoV-2

The purpose of this research is to evaluate the supercritical carbon dioxide (scCO₂) sterilization-based NovaClean process for decontamination and reprocessing of personal protective equipment (PPE) such as surgical masks, cloth masks, and N95 respirators. Preliminarily, Bacillus atrophaeus were inoculated into different environments (dry, hydrated, and saliva) to imitate coughing and sneezing and serve as a "worst-case" regarding challenged PPE. The inactivation of the microbes by scCO₂ sterilization with NovaKill or H₂O₂ sterilant was investigated as a function of exposure times ranging from 5 to 90 min with a goal of elucidating possible mechanisms. Also, human coronavirus SARS-CoV-2 and HCoV-NL63 were inoculated on the respirator material, and viral activity was determined post-treatment. Moreover, we investigated the reprocessing ability of scCO₂-based decontamination using wettability testing and surface mapping. Different inactivation mechanisms have been identified in scCO₂ sanitization, such as membrane damage, germination defect, and dipicolinic acid leaks. Moreover, the viral sanitization results showed a complete inactivation of both coronavirus HCoV-NL63 and SARS-CoV-2. We did not observe changes in PPE morphology, topographical structure, or material integrity, and in accordance with the WHO recommendation, maintained wettability post-processing. These experiments establish a foundational understanding of critical elements for the decontamination and reuse of PPE in any setting and provide a direction for future research in the field.

Cellulose-Based Hydrogels and Aerogels Embedded with Silver Nanoparticles: Preparation and Characterization

The paper presents the preparation and characterization of novel composite materials based on microcrystalline cellulose (MCC) with silver nanoparticles (Ag NPs) in powder and gel forms. We use a promising synthetic conception to form the novel composite biomaterials. At first MCC was modified with colloidal solution of Ag NPs in isopropyl alcohol prepared via metal vapor synthesis. Then Ag-containing MCC powder was used as precursor for further preparation of the gels. The hydrogels were prepared by dissolving pristine MCC and MCC-based composite at low temperatures in aqueous alkali solution and gelation at elevated temperature. To prepare aerogels the drying in supercritical carbon dioxide was implemented. The as-prepared cellulose composites were characterized in terms of morphology, structure, and phase composition. Since many functional properties, including biological activity, in metal-composites are determined by the nature of the metal-to-polymer matrix interaction, the electronic state of the metal was carefully studied. The studied cellulose-based materials containing biologically active Ag NPs may be of interest for use as wound healing or water-purification materials.

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.

Stereocomplex Polylactide for Drug Delivery and Biomedical Applications: A Review

Polylactide (PLA) is among the most common biodegradable polymers, with applications in various fields, such as renewable and biomedical industries. PLA features poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) enantiomers, which form stereocomplex crystals through racemic blending. PLA emerged as a promising material owing to its sustainable, eco-friendly, and fully biodegradable properties. Nevertheless, PLA still has a low applicability for drug delivery as a carrier and scaffold. Stereocomplex PLA (sc-PLA) exhibits substantially improved mechanical and physical strength compared to the homopolymer, overcoming these limitations. Recently, numerous studies have reported the use of sc-PLA as a drug carrier through encapsulation of various drugs, proteins, and secondary molecules by various processes including micelle formation, self-assembly, emulsion, and inkjet printing. However, concerns such as low loading capacity, weak stability of hydrophilic contents, and non-sustainable release behavior remain. This review focuses on various strategies to overcome the current challenges of sc-PLA in drug delivery systems and biomedical applications in three critical fields, namely anti-cancer therapy, tissue engineering, and anti-microbial activity. Furthermore, the excellent potential of sc-PLA as a next-generation polymeric material is discussed.

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.

Supercritical carbon dioxide decellularization of plant material to generate 3D biocompatible scaffolds

The use of plant-based biomaterials for tissue engineering has recently generated interest as plant decellularization produces biocompatible scaffolds which can be repopulated with human cells. The predominant approach for vegetal decellularization remains serial chemical processing. However, this technique is time-consuming and requires harsh compounds which damage the resulting scaffolds. The current study presents an alternative solution using supercritical carbon dioxide (scCO2). Protocols testing various solvents were assessed and results found that scCO2 in combination with 2% peracetic acid decellularized plant material in less than 4 h, while preserving plant microarchitecture and branching vascular network. The biophysical and biochemical cues of the scCO2 decellularized spinach leaf scaffolds were then compared to chemically generated scaffolds. Data showed that the scaffolds had a similar Young's modulus, suggesting identical stiffness, and revealed that they contained the same elements, yet displayed disparate biochemical signatures as assessed by Fourier-transform infrared spectroscopy (FTIR). Finally, human fibroblast cells seeded on the spinach leaf surface were attached and alive after 14 days, demonstrating the biocompatibility of the scCO2 decellularized scaffolds. Thus, scCO2 was found to be an efficient method for plant material decellularization, scaffold structure preservation and recellularization with human cells, while performed in less time (36 h) than the standard chemical approach (170 h).

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.

Injectable Hydrogels for Improving Cardiac Cell Therapy-In Vivo Evidence and Translational Challenges

Cell therapy has the potential to regenerate cardiac tissue and treat a variety of cardiac diseases which are currently without effective treatment. This novel approach to treatment has demonstrated clinical efficiency, despite low retention of the cell products in the heart. It has been shown that improving retention often leads to improved functional outcome. A feasible method of improving cell graft retention is administration of injectable hydrogels. Over the last decade, a variety of injectable hydrogels have been investigated preclinically for their potential to improve the effects of cardiac cell therapy. These hydrogels are created with different polymers, properties, and additional functional motifs and differ in their approaches for encapsulating different cell types. Only one combinational therapy has been tested in a clinical randomized controlled trial. In this review, the latest research on the potential of injectable hydrogels for delivery of cell therapy is discussed, together with potential roadblocks for clinical translation and recommendations for future explorations to facilitate future translation.

Non-thermal pasteurization of lipid emulsions by combined supercritical carbon dioxide and high-power ultrasound treatment

Supercritical carbon dioxide (SC-CO₂) is a novel method for food pasteurization, but there is still room for improvement in terms of the process shortening and its use in products with high oil content. This study addressed the effect of high power ultrasound (HPU) on the intensification of the SC-CO₂ inactivation of E. coli and B. diminuta in soybean oil-in-water emulsions. Inactivation kinetics were obtained at different pressures (100 and 350 bar), temperatures (35 and 50 °C) and oil contents (0, 10, 20 and 30%) and were satisfactorily described using the Weibull model. The experimental results showed that for SC-CO₂ treatments, the higher the pressure or the temperature, the higher the level of inactivation. Ultrasound greatly intensified the inactivation capacity of SC-CO₂, shortening the process time by approximately 1 order of magnitude (from 50 to 90 min to 5-10 min depending on the microorganism and process conditions). Pressure and temperature also had a significant (p < 0.05) effect on SC-CO₂ + HPU inactivation for both bacteria, although the effect was less intense than in the SC-CO₂ treatments. E. coli was found to be more resistant than B. diminuta in SC-CO₂ treatments, while no differences were found when HPU was applied. HPU decreased the protective effect of oil in the inactivation and similar microbial reductions were obtained regardless of the oil content in the emulsion. Therefore, HPU intensification of SC-CO₂ treatments is a promising alternative to the thermal pasteurization of lipid emulsions with heat sensitive compounds.

Supercritical carbon dioxide techniques for processing microbial exopolysaccharides used in biomedical applications

Microbial exopolysaccharides are polymers that show a great potential for biomedical applications, such as tissue engineering applications and drug delivery, due to their biocompatibility, biodegradability and their gelling properties. These polysaccharides are obtained from a microorganism culture with a relatively straightforward downstream process thanks to their extracellular character, and can be processed to obtain aerogels, fibers and micro- or nano-particles with conventional techniques. However, these techniques present several disadvantages in that they involve time-consuming processes and the use of toxic solvents. Supercritical carbon dioxide techniques can overcome these drawbacks, but their use for processing microbial exopolysaccharides is not extended in the scientific community. This review describes the most frequently used exopolysaccharides in biomedical applications and how they can be obtained, as well as the different supercritical carbon dioxide techniques that can be used for processing them and their challenges. Specifically, high pressure shows a great potential to process and sterilize exopolysaccharide biomaterials for biomedical applications (e.g. tissue engineering or drug delivery systems) in spite of the disadvantage concerning the hydrophilicity of this type of polymers.

Polyisocyanopeptide Hydrogels Are Effectively Sterilized Using Supercritical Carbon Dioxide

Adequate sterilization procedures for soft biomaterials such as hydrogels are known to be challenging. These materials are delicate in structure, making them sensitive to harsh conditions and prone to damage. In this study, a suitable sterilization method for hydrogels composed of tri(ethylene glycol)-functionalized polyisocyanopeptides (PIC) was explored. These high biomimetic hydrogels are temperature and strain sensitive and have been presented as novel cell culturing matrices, wound dressings, and drug carriers. The methods that were investigated include autoclaving, γ-irradiation, ultraviolet (UV) light irradiation, and supercritical CO₂ (scCO₂) treatment. The results show that autoclaving and γ-irradiation have deleterious effects on the gelation behavior and mechanical characteristics of PIC. For γ-irradiation, cooling the gels on dry ice alleviated this negative impact, but not sufficiently enough to make the method viable. In contrast, UV light and scCO₂ treatment do not affect the mechanical properties of the PIC gels. Studies with gels inoculated with 10⁷ CFU/mL Gram-positive bacteria Staphylococcus aureus show that only scCO₂ is capable of successfully sterilizing PIC hydrogels by achieving a 6-log reduction in bacterial load. It was concluded that, within the range of tested techniques, the sterilization of PIC is limited to scCO₂.

Sterilization of epidermal growth factor with supercritical carbon dioxide and peracetic acid; analysis of changes at the amino acid and protein level

Aseptic processing and terminal sterilization become increasingly challenging as medical devices become more complex and include active biologics. Terminal sterilization is preferred for patient safety and production costs. We aimed to determine how sterilization using supercritical CO₂ (scCO₂) with low levels of peracetic acid (PAA) affects amino acids and human epidermal growth factor (EGF) as a model protein. In a benchtop reactivity test, the amino acids methionine, tryptophan, arginine and lysine reacted with low levels of PAA in solution. At PAA levels used for scCO₂ sterilization, however, mass spectrometry only identified oxidative adducts on methionine and tryptophan. Mass spectrometry analysis of EGF exposed to scCO₂/PAA identified oxidative adducts on residues Met₂₁, Trp₄₉ and Trp₅₀, as well as a low level of truncations after residues Trp₄₉ and Trp₅₀. Importantly, processing of EGF in solution with scCO₂ did not affect its native conformation, and sterilized EGF maintained its activity in cell proliferation assays. When processing samples in lyophilized form with scCO₂/PAA, amino acids did not react with PAA and the presence of adducts was strongly reduced on methionine and tryptophan, both as single amino acids and in EGF. Truncation after tryptophan residues did not occur. EGF sterilized in the lyophilized form retained its activity when processing occurred with added moisture. These results have significant implications for the maintenance of biological function in sterilized decellularized scaffolds and the ability to manufacture terminally sterilized combination devices containing therapeutic peptides or proteins.

Effect of different sterilization methods on the properties of commercial biodegradable polyesters for single-use, disposable medical devices

The increasing employment of non-degradable polymers based single-use, disposable medical devices have led to huge environmental pressure. Replacement of non-degradable polymers with biodegradable alternatives could be one solution. Since terminal sterilization is a necessary procedure for medical devices to eliminate infections, in this paper, the modifications of sterilization on the transparency, yellow index, dimensional stability and mechanical properties of commercial biodegradable poly(lactic acid) (PLA), poly(butylenes adipate-co-terephthalate) (PBAT) and their blends were investigated. The samples were prepared by compression molding and exposed to four sterilization treatments including ethylene oxide gas (EtO), saturated steam (SS), electron beam (EB), and hydrogen peroxide gas plasma (HPGP). It is concluded that EB can be applied for the sterilization of all the materials investigated, while SS and EtO are not recommended for PLA, and HPGP is not for PBAT and PLA/PBAT blends. This study demonstrates that, when a suitable sterilization process is chosen, PLA has potential to be used for transparent medical devices such as the barrel of syringes or microfluidic chips, while PBAT and PLA/PBAT blends for other non-transparent medical packaging applications.