3D printing of polylactic acid: recent advances and opportunities

3D printed microneedles: revamping transdermal drug delivery systems

One of the advancements of the transdermal drug delivery system (TDDS) is the development of microneedles (MNs). These micron-sized needles are used for delivering various types of drugs to address the disadvantage of other transdermal techniques as well as oral drug delivery systems. MNs have high patient acceptance due to self-administration with minimally invasive and pain compared to the parenteral drug delivery. Over the years, various methods have been adopted to evolve the MNs and make them more cost-effective, accurate, and suitable for multiple applications. One such method is the 3D printing of MNs. The development of MN platforms using 3D printing has been made possible by improved features like precision, printing resolution, and the feasibility of using low-cost raw materials. In this review, we have tried to explain various types of MNs, fabrication methods, materials used in the formulation of MNs, and the recent applications that utilize 3D-printed MNs.

Biocomposites and Poly(lactic acid) in Active Packaging: A Review of Current Research and Future Directions

The alarming rise in environmental pollution, depletion of global resources, and increasing health consciousness have placed significant pressure on the development of eco-friendly, sustainable materials. Consequently, green, environmentally friendly materials made from biobased and/or biodegradable sources are gaining recognition and political support as sustainable alternatives to petroleum-based, non-biodegradable materials. Bio-based packaging materials, in particular, are widely used across all industrial sectors, with a growing demand for solutions that preserve food quality and extend shelf life. Within this context, the concept of "active packaging" (AP) is attracting considerable interest. While the traditional view of packaging materials is that they should be basically inert, active packaging involves intentional interactions with the packaged product or surrounding atmosphere, providing enhanced protection against degradation caused by human actions and environmental factors. This work aims to highlight the significant impact of biocomposites in the active packaging sector, driven by the synergistic integration of nanofillers and active agents, while providing an in-depth analysis of the key mechanisms and strategies underlying their functionality. Particular emphasis is placed on poly(lactic acid)(PLA), presenting a comprehensive review of innovative approaches to enhance the performance of PLA-based packaging, with a focus on improving antioxidant and antimicrobial properties to meet the demands of sustainable and efficient packaging solutions.

Influence of Structural Optimization on the Physical Properties of an Innovative FDM 3D Printed Thermal Barrier

This article describes an innovative thermal insulation barrier in the form of a sandwich panel manufactured using 3D FDM printing technology. The internal structure (core structure) of the barrier is based on the Kelvin foam model. This paper presents the influence of the parameters (the height h and the porosity P of a single core cell) of the barrier on its properties (thermal conductivity, thermal resistance, compressive strength, and quasi-static indentation strength). The dominant influence of the porosity of the structure on the determined physical properties of the fabricated samples was demonstrated. The best insulation results were obtained for single-layer composites with a cell height of 4 mm and a porosity of 90%, where the thermal conductivity coefficient was 0.038 W/(m·K) and the thermal resistance 0.537 (m2·K)/W. In contrast, the best compressive strength properties were obtained for the 50% porosity samples and amounted to about 350 MPa, while the moduli for the 90% porosity samples were 14 times lower and amounted to about 26 MPa. The porosity (P) of the composite structure also had a significant effect on the punch shear strength of the samples produced, and the values obtained for the 90% porosity samples did not exceed 1 MPa. In conclusion, the test showed that the resulting 3D cellular composites offer an innovative and environmentally friendly approach to thermal insulation.

Tailoring the Mechanical Properties of Fungal Mycelium Mats with Material Extrusion Additive Manufacturing of PHBH and PLA Biopolymers

To advance the concept of a circular economy, fungal mycelium-based materials are drawing increased attention as substitutes for nonsustainable materials, such as petroleum-based and animal-derived products, due to their biodegradability, low carbon footprint, and cruelty-free nature. Addressing the challenge of mechanical properties in fungal mycelium products, this study presents a straightforward approach for reinforcing fungal mycelium mats. This is achieved by using two bio-based and biodegradable polymers, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) and polylactic acid (PLA), via material extrusion additive manufacturing (MEX AM), commonly known as 3D printing, to produce fungal mycelium-biopolymer composites. By analyzing the mechanical properties, roughness, and morphology, this study demonstrates significant improvements in ultimate tensile strength with the application of PHBH and even more with PLA, while elasticity is reduced. The study also discusses potential improvements to enhance the quality of the fungal mycelium-biopolymer composites without trading off bio-based and biodegradable features, offering a promising pathway for the development of more durable and sustainable fungal mycelium products.

Influence of Recycling and UV Exposure on the Properties of 3D Printing Polymer Materials

The use of polymer materials in various fields has increased significantly due to their ease of thermoforming and relatively low production costs. The production volume of these materials is extremely high, and according to forecasts from global statistical centers, it is expected to continue rising in the future. However, the extensive use and easy availability of polymeric materials have caused significant ecological problems. The world faces large amounts of polymer waste and environmental pollution. Plastic recycling remains challenging due to issues related to sorting polymer waste and separating it according to polymer types. Recycling certain plastics requires only a quarter of the energy needed to produce new plastic. To address this, circular economy principles should be applied to 3D printing products made from polymeric materials. A particularly wide application of these technologies is found when polymeric materials are used due to their low cost, low melting temperatures, and other advantageous properties. This paper investigates the impact of plastic recycling on the quality of 3D-printed products. During the research, samples were 3D printed and tested using both virgin and recycled PLA, ABS, and PET-G materials. The samples underwent static and dynamic tests to determine their mechanical properties, such as tensile strength, elongation, and impact resistance. The research results showed that the properties of recycled polymer materials deteriorate, with relative elongation of recycled and 3D-printed materials decreased by 16-45%. Despite this, recycled polymer materials can still be used, but it is necessary to account for the reduction in plasticity when creating products that will be exposed to dynamic loads. The impact strength is reduced by 6% for PLA, 54% for ABS, and 58% for PET-G. Additionally, the research included tests on samples printed with 3D printing technology that were exposed to UV irradiation. The results indicated similar dependences, as UV exposure also affects the reduction of material plasticity. After 66 Wh/m2 of UV radiation, the tensile strength of PET-G and PLA decreased by 17%, while ABS showed a reduction of about 5%.

Bio-based polylactic acid labware as a sustainable alternative for microbial cultivation in life science laboratories

Single-use plastics (SUPs) in life science laboratories account for approximately 5.5 million tonnes of waste per year globally. Of SUPs used in life science laboratories, Petri dishes, centrifuge tubes, and inoculation loops are some of the most common. In order to reduce the reliance on petrochemical-based SUPs in the life science research laboratory and minimize the negative environmental impacts associated with SUPs, this research investigates the applicability of polylactic acid (PLA) in single-use labware as a replacement for petrochemical-based plastics. PLA is one of the most well-studied biodegradable plastics that can be produced from sustainable resources. Commercially available PLA was used to 3D print a select range of labware to test the suitability of PLA-based material for routine microbiology work. An injection moulded PLA-based Petri dish was also designed and produced, for increased optical clarity. The biocompatibility was tested against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus epidermidis) strains of bacteria. The PLA-based labware did not negatively impact the cell growth, viability, and metabolic activity of the bacterial cultures. The injection moulded PLA Petri dish showed a reduced colony forming unit count for the Gram-negative E. coli strain compared to the polystyrene Petri dish, ∼1.5 × 109 CFU/mL and ∼3.0 × 109 CFU/mL respectively, during late-exponential growth. The colony counts were, however, in the same order of magnitude. This observed difference may be due to the internal environment inside the Petri dish, hence the internal O2 concentration, humidity, and temperature during bacterial growth were investigated. This work demonstrates, for the first time, a full successful workflow of bacterial growth using a sustainable bioplastic, providing a pathway to reducing the environmental impacts of SUPs in life science laboratories.

Learning program enhances rehabilitation professionals' perceived ease of using 3d printing: a pilot randomized controlled trial

The pilot study evaluated whether a learning program enhances a positive perception of 3D printing technology in rehabilitation professionals. Physical therapists, occupational therapists and speech-language-hearing therapists were recruited from a rehabilitation department in a middle-sized hospital. Participants were randomized to the control group (n = 13) or the intervention group (n = 14). An eight-week learning program consisted of a lecture on using a 3D printer and related software, a group discussion to integrate 3D printing into their clinical practices, and the implementation in their workplace. Outcome measures included the perception of 3D printing technology assessed by the Japanese version of the modified Technology Acceptance Model questionnaire for 3D printing technology (TAM-J). Assessment time points were pre-and post-intervention. As a result, all participants in the intervention group became capable of producing 3D-printed customized assistive devices. In the within-group analyses, the intervention group showed significant improvements in the TAM-J perception ease of use score (p = 0.012) with a large effect size (r = 0.75). Between-group analyses showed that the intervention group gained an additional improvement in the TAM-J perception ease of use score (p = 0.027) with a moderate effect size (r = 0. 43), indicating a significant improvement in the perceived ease of use of 3D printing technology in the intervention group. These observations suggest the 3D printing learning program could provide rehabilitation professionals with a positive perception of the technical aspect of 3D printing in their workplace.

3D-printed microfluidic-microwave device for droplet network formation and characterisation

Microfluidic-microwave devices (MMDs) have emerged as precision tools for the rapid, accurate, sensitive, and non-invasive characterisation of liquids in low-volumes. However, the fabrication of MMDs remains a significant challenge. This is due to the complexities associated with integrating fluidic ducts and electronic components. Herein, we present a versatile and economical 3D-printing approach using ducts filled with liquid metal as an electrical conductor. Cyclic olefin copolymer, polylactic acid, and polypropylene were identified as printable dielectric materials for MMD fabrication. Substrates of 3D-printed cyclic olefin copolymer exhibited the lowest loss tangent (0.002 at 2.7 GHz), making them suitable materials for high-frequency microwave devices. Liquid metal, specifically gallium-indium eutectic, was injected into the printed ducts to form electrically conductive microwave structures. Exemplary MMDs operating at 2 GHz integrated split-ring microwave resonators that serve as sensitive detection geometries able to measure changes in dielectric properties, with droplet-forming fluidic junctions and flow channels. The performance of 3D-printed MMDs for microwave droplet sensing was comprehensively evaluated. These devices were used in the formation and characterisation of water-in-oil emulsions, constructing definable lipid-segregated droplet interface bilayer (DIB) networks. This work indicates the feasibility of using 3D-printed manifolds for the rapid prototyping of customised MMDs, and also demonstrates the potential of MMDs as new analytical research tools in droplet-based materials and biochemistry studies.

Osteogenic citric acid linked chitosan coating of 3D-printed PLA scaffolds for preventing implant-associated infections

>25 % of the patients who receive orthopedic implants have been reported with implant-associated osteomyelitis, which can result in inflammation, osteolysis, and aseptic loosening of implants. Current treatment methods doesn't ensure defect healing and prevention from reinfection. Thermoplastic-based 3D-printed scaffolds offer a bioresorbable, biocompatible, and mechanical strong implant system. However, the hydrophobicity and bio-inertness of these polymers prevent their use in clinics. In this study, we developed dual functionalized scaffolds with osteogenic and antibacterial properties by immobilizing citric acid-linked chitosan on oxygen plasma etched 3D-printed PLA scaffolds through an EDC-NHS coupling reaction. Acellular mineralization of these scaffolds in DMEM demonstrated the deposition of crystalline hydroxyapatite. In addition, the antibacterial properties of these surface-modified scaffolds have been determined against E. coli and S. aureus, where the citric-linked chitosan biofunctionalized 3D-printed PLA scaffolds showed significantly higher antibacterial activity in comparison to oxygen-etched PLA and PLA scaffolds due to the synergistic effect of citric acid and chitosan functionalities. MG-63 cells exhibited increased proliferation and osteogenic activity on the modified scaffolds compared to the PLA and OP-PLA. These 3D-printed scaffolds, coated with citric-linked chitosan, can be a potential solution to orthopedic complications such as critical-sized bone defects and implant-associated osteomyelitis.

A starfish-inspired 4D self-healing morphing structure

Inspired by the starfish's unique ability to achieve flexibility and posture-holding with minimal energy expenditure, we present a novel bioinspired morphing structure. Our two-component design, consisting of a thermoplastic mesh and elastomeric jacket, effectively mimics the functions of the starfish's ossicles, mutable collagenous tissues, and derma. This structure exhibits a remarkable combination of self-healing, time-dependent shape memory, and self-posture-holding properties. Systematic variations in mesh geometry demonstrate precise control over structural stiffness and thermal response, enabling customization for specific applications. The structure's scalability and ease of fabrication further enhance its adaptability. We experimentally demonstrate the potential of our biomimetic morphing structure using several prototypes. This work lays the foundation for developing a new type of versatile morphing structures with applications in diverse fields, including robotics, biomedical devices, and adaptive structures.

The Development of Poly(lactic acid) (PLA)-Based Blends and Modification Strategies: Methods of Improving Key Properties towards Technical Applications-Review

The widespread use of poly(lactic acid) (PLA) from packaging to engineering applications seems to follow the current global trend. The development of high-performance PLA-based blends has led to the commercial introduction of various PLA-based resins with excellent thermomechanical properties. The reason for this is the progress in the field of major PLA limitations such as low thermal resistance and poor impact strength. The main purpose of using biobased polymers in polymer blends is to increase the share of renewable raw materials in the final product rather than its possible biodegradation. However, in the case of engineering applications, the focus is on achieving the required properties rather than maximizing the percentage of biopolymer. The presented review article discusses the current strategies to optimize the balance of the key features such as stiffness, toughness, and heat resistance of PLA-based blends. Improving of these properties requires molecular structural changes, which together with morphology, crystallinity, and the influence of the processing conditions are the main subjects of this article. The latest research in this field clearly indicates the high potential of using PLA-based materials in highly demanding applications. In the case of impact strength modification, it is possible to obtain values close to 800 J/m, which is a value comparable to polycarbonate. Significant improvement can also be confirmed for thermal resistance results, where heat deflection temperatures for selected types of PLA blends can reach even 130 °C after modification. The modification strategies discussed in this article confirm that a properly conducted process of selecting the blend components and the conditions of the processing technique allows for revealing the potential of PLA as an engineering plastic.

Copper nanoparticles loaded gelatin/ polyvinyl alcohol/ guar gum-based 3D printable multimaterial hydrogel for tissue engineering applications

Hydrogels are becoming increasingly significant in tissue engineering because of their numerous benefits, including biocompatibility, biodegradability, and their ability to provide a supportive structure for cell proliferation. This study presents the synthesis and characterization of a new multimaterial hydrogel with 3D-printing capabilities composed of copper nanoparticle-reinforced gelatin, polyvinyl alcohol (PVA), and guar gum-based biomaterials intended for tissue engineering applications. Combining CuNPs aims to enhance the hydrogel's antibacterial properties, mechanical strength, and bioactivity, which are essential for successful tissue regeneration. Hydrogels are chemically cross-linked with glyoxal and analyzed through different assessments to examine the compressive behavior, surface morphology, sorbing capacity, biocompatibility, thermal stability, and degradation properties. The results demonstrated that including CuNPs significantly improved the hydrogel's compressive modulus (4.18 MPa) for the hydrogel with the CuNPs and provided better antibacterial activity against common pathogens with controlled degradation. All the hydrogels exhibited a lower coefficient of friction, which was below 0.1. In vitro cell culture studies using chondrocytes indicated that the CuNPs-loaded hydrogel supported cell proliferation and growth of chondrogenic genes such as collagen type II (COL2) and aggrecan (ACAN). The biocompatibility and enhanced mechanical properties of the multimaterial hydrogel make it a promising candidate for developing customized, patient-specific tissue engineering scaffolds.

Effect of Degradation of Polylactic Acid (PLA) on Dynamic Mechanical Response of 3D Printed Lattice Structures

Material-extrusion-based 3D printing with polylactic acid (PLA) has transformed the production of lightweight lattice structures with a high strength-to-weight ratio for various industries. While PLA offers advantages such as eco-friendliness, affordability, and printability, its mechanical properties degrade due to environmental factors. This study investigated the impact resistance of PLA lattice structures subjected to material degradation under room temperature, humidity, and natural light exposure. Four lattice core types (auxetic, negative-to-positive (NTP) gradient in terms of Poisson's ratio, positive-to-negative (PTN) gradient in terms of Poisson's ratio, and honeycomb) were analyzed for variations in mechanical properties due to declines in yield stress and failure strain. Mechanical testing and numerical simulations at various yield stress and failure strain levels evaluated the degradation effect, using undegraded material as a reference. The results showed that structures with a negative Poisson's ratio exhibited superior resistance to local crushing despite material weakening. Reducing the material's brittleness (failure strain) had a greater impact on impact response compared to reducing its yield stress. This study also revealed the potential of gradient cores, which exhibited a balance between strength (maintaining similar peak force to auxetic cores around 800 N) and energy absorption (up to 40% higher than auxetic cores) under moderate degradation (yield strength and failure strain at 60% and 80% of reference values). These findings suggest that gradient structures with varying Poisson's ratios employing auxetic designs are valuable choices for AM parts requiring both strength and resilience in variable environmental conditions.

Reinforcing Efficiency of Recycled Carbon Fiber PLA Filament Suitable for Additive Manufacturing

The use of 3D printing technology for manufacturing new products based on sustainable materials enables one to take advantage of secondary raw materials derived from recycling. This work investigates the structural performances of 3D printing composite filaments based on polylactic acid (PLA), as a matrix, reinforced by recycled carbon fiber (rCF). Carbon fibers were recovered from industrial scraps by a patented thermal process and used to produce thermoplastic composite filaments for additive manufacturing without any additional treatment and additives. The influence of the recovered carbon fiber (rCF) content on the thermal properties, mechanical properties and microstructure of the composites was studied in the range of 3-20 wt%. The recorded TGA curves exhibited a one-stage weight loss within the temperature range 290-380 °C for all samples and the residual rCF content was in good agreement with the theoretical fiber loading. The Young modulus of the extruded filaments strongly increased below a critical content (5 wt%), while at higher content the improvement was reduced. An increase in the storage modulus of 54% compared to neat PLA 3D printed sample resulted in a printed specimen with a higher rCF content. SEM images highlighted a strong rCF prevailing alignment in the direction of the extrusion flow, creating almost unidirectional reinforcement inside the filament. These findings suggest that homogeneous composite filaments reinforced with well-dispersed recycled CF without additional chemical modification and additives are suitable materials for additive manufacturing. The effect of rCF topological distribution within the material on the mechanical performances has been discussed, highlighting that the isolated fibers could efficiently transfer loads with respect to the percolated 3D network and have been correlated with the microstructure.

Emerging Biomedical and Clinical Applications of 3D-Printed Poly(Lactic Acid)-Based Devices and Delivery Systems

Poly(lactic acid) (PLA) is widely used in the field of medicine due to its biocompatibility, versatility, and cost-effectiveness. Three-dimensional (3D) printing or the systematic deposition of PLA in layers has enabled the fabrication of customized scaffolds for various biomedical and clinical applications. In tissue engineering and regenerative medicine, 3D-printed PLA has been mostly used to generate bone tissue scaffolds, typically in combination with different polymers and ceramics. PLA's versatility has also allowed the development of drug-eluting constructs for the controlled release of various agents, such as antibiotics, antivirals, anti-hypertensives, chemotherapeutics, hormones, and vitamins. Additionally, 3D-printed PLA has recently been used to develop diagnostic electrodes, prostheses, orthoses, surgical instruments, and radiotherapy devices. PLA has provided a cost-effective, accessible, and safer means of improving patient care through surgical and dosimetry guides, as well as enhancing medical education through training models and simulators. Overall, the widespread use of 3D-printed PLA in biomedical and clinical settings is expected to persistently stimulate biomedical innovation and revolutionize patient care and healthcare delivery.

Enzymatic degradation of polylactic acid (PLA)

Environmental concerns arising from the increasing use of polluting plastics highlight polylactic acid (PLA) as a promising eco-friendly alternative. PLA is a biodegradable polyester that can be produced through the fermentation of renewable resources. Together with its excellent properties, suitable for a wide range of applications, the use of PLA has increased significantly over the years and is expected to further grow. However, insufficient degradability under natural conditions emphasizes the need for the exploration of biodegradation mechanisms, intending to develop more efficient techniques for waste disposal and recycling or upcycling. Biodegradation occurs through the secretion of depolymerizing enzymes, mainly proteases, lipases, cutinases, and esterases, by various microorganisms. This review focuses on the enzymatic degradation of PLA and presents different enzymes that were isolated and purified from natural PLA-degrading microorganisms, or recombinantly expressed. The review depicts the main characteristics of the enzymes, including recent advances and analytical methods used to evaluate enantiopurity and depolymerizing activity. While complete degradation of solid PLA particles is still difficult to achieve, future research and improvement of enzyme properties may provide an avenue for the development of advanced procedures for PLA degradation and upcycling, utilizing its building blocks for further applications as envisaged by circular economy principles. KEY POINTS: • Enzymes can be promisingly utilized for PLA upcycling. • Natural and recombinant PLA depolymerases and methods for activity evaluation are summarized. • Approaches to improve enzymatic degradation of PLA are discussed.

Computational Analysis of Polymeric Biodegradable and Customizable Airway Stent Designs

The placement of endotracheal prostheses is a procedure used to treat tracheal lesions when no other surgical options are available. Unfortunately, this technique remains controversial. Both silicon and metallic stents are used with unpredictable success rates, as they have advantages but also disadvantages. Typical side effects include restenosis due to epithelial hyperplasia, obstruction and granuloma formation. Repeat interventions are often required. Biodegradable stents are promising in the field of cardiovascular biomechanics but are not yet approved for use in the respiratory system. The aim of the present study is to summarize important information and to evaluate the role of different geometrical features for the fabrication of a new tracheo-bronchial prosthesis prototype, which should be biodegradable, adaptable to the patient's lesion and producible by 3D printing. A parametric design and subsequent computational analysis using the finite element method is carried out. Two different stent designs are parameterized and analyzed. The biodegradable material chosen for simulations is polylactic acid. Experimental tests are conducted for assessing its mechanical properties. The role of the key design parameters on the radial force of the biodegradable prosthesis is investigated. The computational results allow us to elucidate the role of the pitch angle, the wire thickness and the number of cells or units, among other parameters, on the radial force. This work may be useful for the design of ad hoc airway stents according to the patient and type of lesion.

Selection and Optimization of Carbon-Reinforced Polyether Ether Ketone Process Parameters in 3D Printing-A Rotating Component Application

The selection of process parameters is crucial in 3D printing for product manufacturing. These parameters govern the operation of production machinery and influence the mechanical properties, production time, and other aspects of the final product. The optimal process parameter settings vary depending on the product and printing application. This study identifies the most suitable cluster of process parameters for producing rotating components, specifically impellers, using carbon-reinforced Polyether Ether Ketone (CF-PEEK) thermoplastic filament. A mathematical programming technique using a rating method was employed to select the appropriate process parameters. The research concludes that an infill density of 70%, a layer height of 0.15 mm, a printing speed of 60 mm/s, a platform temperature of 195 °C, an extruder temperature of 445 °C, and an extruder travel speed of 95 mm/s are optimal process parameters for manufacturing rotating components using carbon-reinforced PEEK material.

FDM 3D Printing and Properties of PBAT/PLA Blends

Biodegradable polylactic acid (PLA) has been widely used in fused deposition modeling (FDM) 3D printing. In order to improve its comprehensive properties in 3D printing, in this study, 0-40% content of polybutylene adipate terephthalate(PBAT) was selected to be blended with PLA in a twin-screw extruder; the resulting pellets were drawn into a homogeneous filament; then, PBAT/PLA samples were prepared by FDM 3D printing, and the effects of the dosage of PBAT on the mechanical properties, thermal behavior, surface wettability and melt flowability of the samples were investigated. The results showed that all the samples could be printed smoothly, and the ductility was slightly improved by the increase in the PBAT dosage; the thermal stability of PLA was enhanced by blending with PBAT, and the crystallinity increased monotonically with the increase in PBAT. After blending with PBAT, the surfaces of the samples were more hydrophilic and flowable. The important conclusion achieved in this work was that the PBAT/PLA blends, especially those containing 30%PBAT, showed great potential to replace petroleum-based plastics and are suitable for use in FDM 3D printing technologies for different applications.

Effect of Aging on Tensile and Chemical Properties of Polylactic Acid and Polylactic Acid-Like Polymer Materials for Additive Manufacturing

Additive manufacturing, with its fast development and application of polymeric materials, led to the wide utilization of polylactic acid (PLA) materials. As a biodegradable and biocompatible aliphatic polyester, produced from renewable sources, PLA is widely used in different sectors, from industry to medicine and science. The aim of this research is to determine the differences between two forms of the PLA material, i.e., fused deposition modeling (FDM) printed filament and digital light processing (DLP) printed resin, followed by aging due to environmental and hygiene maintenance conditions for a period of two months. Specimens underwent 3D scanning, tensile testing, and Fourier transform infrared (FTIR) spectrometry to obtain insights into the material changes that occurred. Two-way Analysis of Variance (ANOVA) statistical analysis was subsequently carried out to determine the statistical significance of the determined changes. Significant impairment can be observed in the dimensional accuracies between both materials, whether they are non-aged or aged. The mechanical properties fluctuated for aged FDM specimens: 15% for ultimate tensile stress, 15% for elongation at yield, and 12% for elastic modulus. Regarding the DLP aged specimens, the UTS decreased by 61%, elongation at yield by around 61%, and elastic modulus by 62%. According to the FTIR spectral analysis, the PLA materials degraded, especially in the case of resin specimens. Aging also showed a significant influence on the elastic modulus, ultimate tensile stress, elongation at yield, elongation at break, and toughness of both materials, which was statistically shown by means of a two-way ANOVA test. The data collected in this research give a better understanding of the underlying aging mechanism of PLA materials.

Advancements in wound healing: integrating biomolecules, drug delivery carriers, and targeted therapeutics for enhanced tissue repair

Wound healing, a critical biological process vital for tissue restoration, has spurred a global market exceeding $15 billion for wound care products and $12 billion for scar treatment. Chronic wounds lead to delayed or impaired wound healing. Natural bioactive compounds, prized for minimal side effects, stand out as promising candidates for effective wound healing. In response, researchers are turning to nanotechnology, employing the encapsulation of these agents into drug delivery carriers. Drug delivery system will play a crucial role in enabling targeted delivery of therapeutic agents to promote tissue regeneration and address underlying issues such as inflammation, infection, and impaired angiogenesis in chronic wound healing. Drug delivery carriers offer distinct advantages, exhibiting a substantial ratio of surface area to volume and altered physical and chemical properties. These carriers facilitate sustained and controlled release, proving particularly advantageous for the extended process of wound healing, that typically comprise a diverse range of components, integrating both natural and synthetic polymers. Additionally, they often incorporate bioactive molecules. Despite their properties, including poor solubility, rapid degradation, and limited bioavailability, various natural bioactive agents face challenges in clinical applications. With a global research, emphasis on harnessing nanomaterial for wound healing application, this research overview engages advancing drug delivery technologies to augment the effectiveness of tissue regeneration using bioactive molecules. Recent progress in drug delivery has poised to enhance the therapeutic efficacy of natural compounds in wound healing applications.

A critical review on plastic waste life cycle assessment and management: Challenges, research gaps, and future perspectives

The global production and consumption of plastics, as well as their deposition in the environment, are experiencing exponential growth. In addition, mismanaged plastic waste (PW) losses into drainage channels are a growing source of microplastic (MP) pollution concern. However, the complete understanding of their environmental implications throughout their life cycle is yet to be fully understood. Determining the potential extent to which MPs contribute to overall ecotoxicity is possible through the monitoring of PW release and MP removal during remediation. Life cycle assessments (LCAs) have been extensively utilized in many comparative analyses, such as comparing petroleum-based plastics with biomass and single-use plastics with multi-use alternatives. These assessments typically yield unexpected or paradoxical results. Nevertheless, there is still a paucity of reliable data and tools for conducting LCAs on plastics. On the other hand, the release and impact of MP have so far not been considered in LCA studies. This is due to the absence of inventory-related data regarding MP releases and the characterization factors necessary to quantify the effects of MP. Therefore, this review paper conducts a comprehensive literature review in order to assess the current state of knowledge and data regarding the environmental impacts that occur throughout the life cycle of plastics, along with strategies for plastic management through LCA.

Investigation into the Acoustic Properties of Polylactic Acid Sound-Absorbing Panels Manufactured by 3D Printing Technology: The Influence of Nozzle Diameters and Internal Configurations

Sound-absorbing panels are widely used in the acoustic design of aircraft parts, buildings and vehicles as well as in sound insulation and absorption in areas with heavy traffic. This paper studied the acoustic properties of sound-absorbing panels manufactured with three nozzle diameters (0.4 mm, 0.6 mm and 0.8 mm) by 3D printing from three types of polylactic acid filaments (Grey Tough PLA; Black PLA Pro; Natural PLA) and with six internal configurations with labyrinthine zigzag channels (Z1 and Z2). The absorption coefficient of the sample with the Z2 pattern, a 5.33 mm height, a 0.6 mm nozzle diameter and with Black PLA Pro showed the maximum value (α = 0.93) for the nozzle diameter of 0.6 mm. Next in position were the three samples with the Z1 pattern (4 mm height) made from all three materials used and printed with a nozzle diameter of 0.4 mm with a sound absorption coefficient value (α = 0.91) at 500 Hz. The highest value of the sound transmission loss (56 dB) was found for the sample printed with a nozzle size of 0.8 mm with the Z2 pattern (8 mm height) and with Black PLA Pro. The extruded material, the nozzle diameter and the internal configuration had a significant impact on the acoustic performance of the 3D-printed samples.

Reconstruction of tracheal window-shape defect by 3D printed polycaprolatone scaffold coated with Silk Fibroin Methacryloyl

In this study, we aimed to utilize autologous tracheal epithelia and BMSCs as the seeding cells, utilize PCL coated with SilMA as the hybrid scaffold to carry the cells and KGN, which can selectively stimulate chondrogenic differentiation of BMSCs. This hybrid tracheal substitution was carried out to repair the tracheal partial window-shape defect. Firstly, SilMA with the concentration of 10%, 15% and 20% was prepared, and the experiment of swelling and degradation was performed. With the increase of the concentration, the swelling ratio of SilMA decreased, and the degradation progress slowed down. Upon the result of CCK-8 test and HE staining of 3D co-culture, the SilMA with concentration of 20% was selected. Next, SilMA and the cells attached to SilMA were characterized by SEM. Furthermore, in vitro cytotoxicity test shows that 20% SilMA has good cytocompatibility. The hybrid scaffold was then made by PCL coated with 20% SilMA. The mechanical test shows this hybrid scaffold has better biomechanical properties than native trachea. In vivo tracheal defect repair assays were conducted to evaluate the effect of the hybrid substitution. H&E staining, IHC staining and IF staining showed that this hybrid substitution ensured the viability, proliferation and migration of epithelium. However, it is sad that the results of chondrogenesis were not obvious. This study is expected to provide new strategies for the fields of tracheal replacement therapy needing mechanical properties and epithelization.

3D Printing for Cardiovascular Surgery and Intervention: A Review Article

3D printing technology can be applied to practically every aspect of modern life, fulfilling the needs of people from various backgrounds. The utilization of 3D printing in the context of adult heart disease can be succinctly categorized into 3 primary domains: preoperative strategizing or simulation, medical instruction, and clinical consultations. 3D-printed model utilization improves surgical planning and intraoperative decision-making and minimizes surgical risks, and it has demonstrated its efficacy as an innovative educational tool for aspiring surgeons with limited practical exposure. Despite all the applications of 3D printing, it has not yet been shown to improve long-term outcomes, including safety. There are no data on the outcomes of controlled trials available. To appropriately diagnose heart disease, 3D-printed models of the heart can provide a better understanding of the intracardiac anatomy and provide all the information needed for operative planning. Experientially, 3D printing provides a wide range of perceptions for understanding lower extremity arteries' spatial geometry and anatomical features of pathology. Practicing cardiac surgery processes using objects printed using 3D imaging data can become the norm rather than the exception, leading to improved accuracy and quality of treatment. This study aimed to review the various applications of 3D printing technology in cardiac surgery and intervention.

Biocompatibility of ABS and PLA Polymers with Dental Pulp Stem Cells Enhance Their Potential Biomedical Applications

Polylactic Acid (PLA) and Acrylonitrile-Butadiene-Styrene (ABS) are commonly used polymers in 3D printing for biomedical applications. Dental Pulp Stem Cells (DPSCs) are an accessible and proliferative source of stem cells with significant differentiation potential. Limited knowledge exists regarding the biocompatibility and genetic safety of ABS and PLA when in contact with DPSCs. This study aimed to investigate the impact of PLA and ABS on the adhesion, proliferation, osteogenic differentiation, genetic stability, proteomics, and immunophenotypic profile of DPSCs. A total of three groups, 1- DPSC-control, 2- DPSC+ABS, and 3- DPSC+PLA, were used in in vitro experiments to evaluate cell morphology, proliferation, differentiation capabilities, genetic stability, proteomics (secretome), and immunophenotypic profiles regarding the interaction between DPSCs and polymers. Both ABS and PLA supported the adhesion and proliferation of DPSCs without exhibiting significant cytotoxic effects and maintaining the capacity for osteogenic differentiation. Genetic stability, proteomics, and immunophenotypic profiles were unaltered in DPSCs post-contact with these polymers, highlighting their biosafety. Our findings suggest that ABS and PLA are biocompatible with DPSCs and demonstrate potential in dental or orthopedic applications; the choice of the polymer will depend on the properties required in treatment. These promising results stimulate further studies to explore the potential therapeutic applications in vivo using prototyped polymers in personalized medicine.

Empowering Precision Medicine: The Impact of 3D Printing on Personalized Therapeutic

This review explores recent advancements and applications of 3D printing in healthcare, with a focus on personalized medicine, tissue engineering, and medical device production. It also assesses economic, environmental, and ethical considerations. In our review of the literature, we employed a comprehensive search strategy, utilizing well-known databases like PubMed and Google Scholar. Our chosen keywords encompassed essential topics, including 3D printing, personalized medicine, nanotechnology, and related areas. We first screened article titles and abstracts and then conducted a detailed examination of selected articles without imposing any date limitations. The articles selected for inclusion, comprising research studies, clinical investigations, and expert opinions, underwent a meticulous quality assessment. This methodology ensured the incorporation of high-quality sources, contributing to a robust exploration of the role of 3D printing in the realm of healthcare. The review highlights 3D printing's potential in healthcare, including customized drug delivery systems, patient-specific implants, prosthetics, and biofabrication of organs. These innovations have significantly improved patient outcomes. Integration of nanotechnology has enhanced drug delivery precision and biocompatibility. 3D printing also demonstrates cost-effectiveness and sustainability through optimized material usage and recycling. The healthcare sector has witnessed remarkable progress through 3D printing, promoting a patient-centric approach. From personalized implants to radiation shielding and drug delivery systems, 3D printing offers tailored solutions. Its transformative applications, coupled with economic viability and sustainability, have the potential to revolutionize healthcare. Addressing material biocompatibility, standardization, and ethical concerns is essential for responsible adoption.

FDM 3D Printing and Properties of PBS/PLA Blends

Poly(lactic acid) (PLA) and Poly(butylene succinate) (PBS) were chosen as raw materials and melt blended by a twin screw extruder and pelletized; then, the pellets were extruded into filaments; after that, various PBS/PLA blending samples were prepared by Fused Deposition Molding (FDM) 3D printing technology using the filaments obtained and the effect of the dosage of PBS on technological properties of 3D-printed specimens was investigated. For comparison, the PLA specimen was also prepared by FDM printing. The tensile strength, tensile modulus, thermal stability, and hydrophilicity became poorer with increasing the dosage of PBS, while the flexural strength, flexural modulus, impact strength, and crystallinity increased first and then decreased. The blend containing 10% PBS (10% PBS/PLA) had the greatest flexural strength of 60.12 MPa, tensile modulus of 2360.04 MPa, impact strength of 89.39 kJ/m2, and crystallinity of 7.4%, which were increased by 54.65%, 61.04%, 14.78%, and 51.02% compared to those of printed PLA, respectively; this blend also absorbed the least water than any other specimen when immersed in water. Different from the transparent PLA filament, 10% PBS/PLA filament presented a milky white appearance. The printed 10% PBS/PLA specimen had a smooth surface, while the surface of the printed PLA was rough. All the results indicated that the printed 10% PBS/PLA specimen had good comprehensive properties, including improved mechanical properties, crystallization performance, and surface quality than PLA, as well as proper wettability and water absorption. The prominent conclusion achieved in this work was that 10% PBS/PLA should be an ideal candidate for biodegradable feedstock among all the PBS/PLA blends for FDM 3D printing.

Innovations in Food Packaging for a Sustainable and Circular Economy

Packaging is fundamental to maintaining the quality of food, but its contribution with a negative footprint to the environment must be completely changed worldwide to reduce pollution and climate change. Innovative and sustainable packaging and new strategies of reutilization are necessary to reduce plastic waste accumulation, maintain food quality and safety, and reduce food losses and waste. The purpose of this chapter is to present innovations in food packaging for a sustainable and circular economy. First, to present the eco-design packaging approach as well as new strategies for recycled or recyclable materials in food packaging. Second, to show current trends in new packaging materials developed from the use of agro-industrial wastes as well as new methods of production, including 3D/4D printing, electrostatic spinning, and the use of nanomaterials.

Recycled PLA for 3D Printing: A Comparison of Recycled PLA Filaments from Waste of Different Origins after Repeated Cycles of Extrusion

The objective of this work is to evaluate the reprocessing of PLA 3D printing waste from different origins, into filaments and films, and without the addition of any additive. Two types of waste were considered: a blend of different printing wastes (masks, visors, other components) of personal protective equipment coming from an association of Spanish coronamakers, and PLA waste from a single known commercial source. Both types of materials were subjected to repeated extrusion cycles and processed into films by compression molding. Samples were characterized after each cycle and their mechanical and viscosity properties evaluated. Diffusion-ordered NMR spectroscopy (DOSY) experiments were also carried out to estimate molecular weights. The results show a better performance for the PLA waste from the known origin, capable of withstanding up to three re-extrusion cycles per two for the waste blending, without significant degradation. Additionally, a model to address collection and mechanical recycling cycles under two different scenarios (full traceability and not full traceability) was proposed.

Interpretable Machine Learning Methods for Monitoring Polymer Degradation in Extrusion of Polylactic Acid

This work investigates real-time monitoring of extrusion-induced degradation in different grades of PLA across a range of process conditions and machine set-ups. Data on machine settings together with in-process sensor data, including temperature, pressure, and near-infrared (NIR) spectra, are used as inputs to predict the molecular weight and mechanical properties of the product. Many soft sensor approaches based on complex spectral data are essentially 'black-box' in nature, which can limit industrial acceptability. Hence, the focus here is on identifying an optimal approach to developing interpretable models while achieving high predictive accuracy and robustness across different process settings. The performance of a Recursive Feature Elimination (RFE) approach was compared to more common dimension reduction and regression approaches including Partial Least Squares (PLS), iterative PLS (i-PLS), Principal Component Regression (PCR), ridge regression, Least Absolute Shrinkage and Selection Operator (LASSO), and Random Forest (RF). It is shown that for medical-grade PLA processed under moisture-controlled conditions, accurate prediction of molecular weight is possible over a wide range of process conditions and different machine settings (different nozzle types for downstream fibre spinning) with an RFE-RF algorithm. Similarly, for the prediction of yield stress, RFE-RF achieved excellent predictive performance, outperforming the other approaches in terms of simplicity, interpretability, and accuracy. The features selected by the RFE model provide important insights to the process. It was found that change in molecular weight was not an important factor affecting the mechanical properties of the PLA, which is primarily related to the pressure and temperature at the latter stages of the extrusion process. The temperature at the extruder exit was also the most important predictor of degradation of the polymer molecular weight, highlighting the importance of accurate melt temperature control in the process. RFE not only outperforms more established methods as a soft sensor method, but also has significant advantages in terms of computational efficiency, simplicity, and interpretability. RFE-based soft sensors are promising for better quality control in processing thermally sensitive polymers such as PLA, in particular demonstrating for the first time the ability to monitor molecular weight degradation during processing across various machine settings.

Recent advances in modified poly (lactic acid) as tissue engineering materials

As an emerging science, tissue engineering and regenerative medicine focus on developing materials to replace, restore or improve organs or tissues and enhancing the cellular capacity to proliferate, migrate and differentiate into different cell types and specific tissues. Renewable resources have been used to develop new materials, resulting in attempts to produce various environmentally friendly biomaterials. Poly (lactic acid) (PLA) is a biopolymer known to be biodegradable and it is produced from the fermentation of carbohydrates. PLA can be combined with other polymers to produce new biomaterials with suitable physicochemical properties for tissue engineering applications. Here, the advances in modified PLA as tissue engineering materials are discussed in light of its drawbacks, such as biological inertness, low cell adhesion, and low degradation rate, and the efforts conducted to address these challenges toward the design of new enhanced alternative biomaterials.