Additive manufacturing of sustainable biomaterials for biomedical applications

Recent developments in 3D printing pharmaceutical, bioprinting and implant for tissue engineering formulations

This review article explores how 3D printing has the diversity in the drug development and the delivery of personalized medicine. The paradigm shift is from conventional methods to tailormade dosages and exploring the intricate interplay of drug selection, polymer compatibility alongwith technological advancements within the pharmaceutical arena. 3D printing is positioned as a crucial tool for catering to the specific requirements of patient-focused fields like pediatrics and geriatrics, ranging from addressing individual needs to improving dosage precision. By harnessing genetic profiles, physiological nuances, and disease conditions, this technology enables the creation of bespoke medications with unique drug loading and release profiles. In developing the newer implants the 3D printing has to be developed alongwith consideration of biological aspects as well as technical aspects. It has to be aligned with multifunctional aspects to cater one optimized product. Furthermore, this paper elucidates the regulatory considerations and industrial implications surrounding 3D printing in pharmaceuticals. Emphasizing compliance with current Good Manufacturing Practices (CGMP) and its potential for streamlined production in regulated markets, the paper underscores the transformative power of 3D printing in reshaping clinical practice and optimizing patient outcomes.

A review of the advances in implant technology: accomplishments and challenges for the design of functionalized surface structures

Biomedical implants are extensively utilized to replace hard-tissue defects owing to their biocompatibility and remarkable tissue-affinity. The materials and functional design are selected based on the resultant osseointegration level and resistance to infection, and these considerations constitute the dominant research topic in this field. However, high rates of implantation failure and peri-implantitis have been reported. Current research on biomedical-implant design encompasses enhancement of the implant surface properties, such as the roughness, nano/micro topography, and hydrophilicity, along with the realization of advanced features including antibacterial properties and cell and immunomodulation regulation. This review considers the two achievements of contemporary implant manufacturing; namely, osseointegration and the realization of antibacterial properties. Present mainstream surface modifications and coatings are discussed, along with functional design technologies and achievements. The impacts of direct surface-treatment techniques and osteogenic functional coatings on osseointegration performance and antibacterial surface structures are elucidated, considering inorganic and organic coatings with antibacterial properties as well as antibiotic-releasing coatings. Furthermore, this review highlights recent advancements in physically driven antimicrobial strategies. Expanding upon existing research, future directions for implant studies are proposed, including the realization of comprehensive functionality that integrates osseointegration and antibacterial properties, as well as patient-specific design. Our study presents a comprehensive review and offers a novel perspective on the design of biomedical implants for enhanced versatility. An in-depth exploration of future research directions will also stimulate subsequent investigations.

Strategic Implementation of Multimaterial Additive Manufacturing: Bridging Research and Real-World Applications

The single-material additive manufacturing revolution has accelerated innovation in the manufacturing field, enabling the combination of multiple materials in one operation using additives of metals, ceramics, and polymers. Although still in its infancy, researchers are adopting this strategy, indicating a shift from research and development to practical applications. By aggregating numerous materials with different properties concurrently, the multimaterial additive manufacturing approach entitles the simplest fabrication of multifunctional systems and devices. A review focuses on the opportunities and challenges presented by the trend toward recent advancements in the multinozzle system. Multinozzle 3D printing has great applications in bioprinting and tissue engineering, electronics integration, and civil/structural engineering. This review highlights the exciting opportunities and challenges that come with it. Additionally, this review showcases the recent advancements in the multinozzle system that have made it a promising solution in this field.

An injectable multifunctional nanocomposite hydrogel promotes vascularized bone regeneration by regulating macrophages

The local inflammatory microenvironment, insufficient vascularization, and inadequate bone repair materials are the three key factors that constrain the repair of bone defects. Here, we synthesized a composite nanoparticle, TPQ (TCP-PDA-QK), with a core‒shell structure. The core consists of nanotricalcium phosphate (TCP), and the shell is derived from polydopamine (PDA). The surface of the shell is modified with a vascular endothelial growth factor (VEGF) mimic peptide (QK peptide). TPQ was then embedded in porous methacrylate gelatin (GelMA) to form a TPQGel hydrogel. In the inflammatory environment, the TPQGel hydrogel can gradually release drugs through pH responsiveness, promoting M2 macrophage polarization, vascularization and bone regeneration in turn. In addition, reprogrammed M2 macrophages stimulate the generation of anti-inflammatory and pro-healing growth factors, which provide additional support for angiogenesis and bone regeneration. The TPQGel hydrogel can not only accurately fill irregular bone defects but also has excellent biocompatibility, making it highly suitable for the minimally invasive treatment of bone defects. Transcriptomic tests revealed that the TPQGel hydrogel achieved macrophage reprogramming by regulating the PI3K-AKT signalling pathway. Overall, the TPQGel hydrogel can be harnessed for safe and efficient therapeutics that accelerate the repair of bone defects.

Using Three-Dimensional Bioprinting to Generate Realistic Models of Wound Healing

Significance: The skin serves as the primary defense against external stimuli, making it vulnerable to damage. Injuries can cause a dysregulated environment, resulting in chronic inflammation and inhibition of cell proliferation and migration, which delays recovery. Innovative approaches, such as three-dimensional (3D) bioprinting, can foster a controlled healing environment by promoting synergy between the skin microbiome and cells. Recent Advances: Traditional approaches to wound healing have focused on fostering an environment conducive to the interplay between cells, extracellular proteins, and growth factors. 3D bioprinting, a manufacturing technology with applications in tissue engineering, deposits biomaterial-based bioink containing living cells to fabricate custom-designed tissue scaffolds in a layer-by-layer fashion. This process controls the architecture and composition of a construct, producing multilayered and complex structures such as skin. Critical Issues: The selection of biomaterials for scaffolds has been a challenge when 3D skin tissue engineering. While prioritizing mechanical properties, current biomaterials often lack the ability to interact with environmental stimuli such as pH, temperature, or oxygen levels. Employing smart biomaterials that integrate bioactive molecules and adapt to external conditions could overcome these limitations. This innovation would enable scaffolds to create a sustainable wound-healing environment, fostering microbiome balance, reducing inflammation, and facilitating cellular recovery and tissue restoration, addressing critical gaps in existing wound care solutions. Future Directions: Novel bioink formulations for skin injury recovery are focused on improving long-term cell viability, proliferation, vascularization, and immune integration. Efficient recovery of the skin microbiome using bioactive molecules has the potential to create microenriched environments that support the recovery of the skin microbiome and restore immune regulation. This promising direction for future research aims to improve patient outcomes in wound care.

The Printed Path to Healing: Advancing Wound Dressings through Additive Manufacturing

Wound care challenges healthcare systems worldwide as traditional dressings often fall short in addressing the diverse and complex nature of wound healing. Given conventional treatments limitations, innovative alternatives are urgent. Additive manufacturing (AM) has emerged as a distinct and transformative approach for developing advanced wound dressings, offering unprecedented functionality and customization. Besides exploring the AM processes state-of-the-art, this review comprehensively examines the application of AM to produce cellular-compatible and bioactive, therapeutic agent delivery, patient-centric, and responsive dressings. This review distinguishes itself from the published literature by covering a variety of wound types and by summarizing important data, including used materials, process/technology, printing parameters, and findings from in vitro, ex vivo, and in vivo studies. The prospects of AM in enhancing wound healing outcomes are also analyzed in a translational and cost-effective manner.

Chitosan fabricated silver nitroprusside nanocomposites prepared for enhanced antibacterial and cytocompatibility applications through controlled release of metal ions and nitric oxide

Silver nitroprusside complex nanoparticles (AgN NPs) have garnered significant attention for their antimicrobial properties. However, challenges such as toxicity and limited biocompatibility often hinder their practical applications. Therefore, this study introduces a combined approach to fabricating AgN NPs with chitosan (CS), resulting in CS-AgN nanocomposites (CS-AgN NCs) with cytocompatibility. AgN NPs exhibited a distinct cubic morphology with a mean size of 52.88 ± 15.45 nm, while CS-AgN NCs showed a smaller, spherical, and elongated structure. The incorporation of CS led to significant changes in AgN NPs, including a reduction in the zeta potential from -46.63 ± 1.25 mV to -13.0 ± 2.12 mV and alterations in crystallinity. A key finding was that nitric oxide (NO) release was highly pH-dependent, which could offer targeted therapeutic potential. Both nano systems demonstrated potent antibacterial effects, with minimum inhibitory concentrations (MICs) as low as 6.25 μg/mL against E. coli, alongside strong biofilm inhibition (≥80 % at 12.5-25 μg/mL). The CS-AgN NCs also exhibited superior antioxidant activity compared to AgN NPs without compromising cell viability or causing hemolysis, and low toxicity to Artemia salina, making them promising candidates for biomedical applications. This work highlights the unique interplay between AgN NPs and CS, offering insights into their potential for next-generation antimicrobial therapies.

Materials designed to degrade: structure, properties, processing, and performance relationships in polyhydroxyalkanoate biopolymers

Conventional plastics pose significant environmental and health risks across their life cycle, driving intense interest in sustainable alternatives. Among these, polyhydroxyalkanoates (PHAs) stand out for their biocompatibility, degradation characteristics, and diverse applications. Yet, challenges like production cost, scalability, and limited chemical variety hinder their widespread adoption, impacting material selection and design. This review examines PHA research through the lens of the classical materials tetrahedron, exploring property-structure-processing-performance (PSPP) relationships. By analyzing recent literature and addressing current limitations, we gain valuable insights into PHA development. Despite challenges, we remain optimistic about the role of PHAs in transitioning towards a circular plastic economy, emphasizing the need for further research to unlock their full potential.

Dynamic Double-Networked Hydrogels by Hybridizing PVA and Herbal Polysaccharides: Improved Mechanical Properties and Selective Antibacterial Activity

Chinese herbal medicine has offered an enormous source for developing novel bio-soft materials. In this research, the natural polysaccharide isolated from the Chinese herbal medicine Dendrobium was employed as the secondary building block to fabricate a "hybrid" hydrogel with synthetic poly (vinyl alcohol) (PVA) polymers. Thanks to the presence of mannose units that contain cis-diol motifs on the chain of the Dendrobium polysaccharides, efficient crosslinking with the borax is allowed and reversible covalent borate ester bonds are formed. Eventually, highly dynamic and double-networked hydrogels were successfully prepared by the integration of Dendrobium polysaccharides and PVA. Interestingly, the introduction of polysaccharides has given rise to more robust and dynamic hydrogel networks, leading to enhanced thermal stability, mechanical strength, and tensile capacity (>1000%) as well as the rapid self-healing ability (<5 s) of the "hybrid" hydrogels compared with the PVA/borax single networked hydrogel. Moreover, the polysaccharides/PVA double network hydrogel showed selective antibacterial activity towards S. aureus. The reported polysaccharides/PVA double networked hydrogel would provide a scaffold to hybridize bioactive natural polysaccharides and synthetic polymers for developing robust but dynamic multiple networked hydrogels that are tailorable for biomedical applications.

Advanced Hybrid Strategies of GelMA Composite Hydrogels in Bone Defect Repair

To date, severe bone defects remain a significant challenge to the quality of life. All clinically used bone grafts have their limitations. Bone tissue engineering offers the promise of novel bone graft substitutes. Various biomaterial scaffolds are fabricated by mimicking the natural bone structure, mechanical properties, and biological properties. Among them, gelatin methacryloyl (GelMA), as a modified natural biomaterial, possesses a controllable chemical network, high cellular stability and viability, good biocompatibility and degradability, and holds the prospect of a wide range of applications. However, because they are hindered by their mechanical properties, degradation rate, and lack of osteogenic activity, GelMA hydrogels need to be combined with other materials to improve the properties of the composites and endow them with the ability for osteogenesis, vascularization, and neurogenesis. In this paper, we systematically review and summarize the research progress of GelMA composite hydrogel scaffolds in the field of bone defect repair, and discuss ways to improve the properties, which will provide ideas for the design and application of bionic bone substitutes.

Materials for 3D printing in healthcare sector: A review

Additive Manufacturing (AM) encompasses various techniques creating intricate components from digital models. The aim of incorporating 3D printing (3DP) in the healthcare sector is to transform patient care by providing personalized solutions, improving medical procedures, fostering research and development, and ultimately optimizing the efficiency and effectiveness of healthcare delivery. This review delves into the historical beginnings of AM's 9 integration into medical contexts exploring various categories of AM methodologies and their roles within the medical sector. This survey also dives into the issue of material requirements and challenges specific to AM's medical applications. Emphasis is placed on how AM processes directly enhance human well-being. The primary focus of this paper is to highlight the evolution and incentives for cross-disciplinary AM applications, particularly in the realm of healthcare by considering their principle, materials and applications. It is designed for a diverse audience, including manufacturing professionals and researchers, seeking insights into this transformative technology's medical dimensions.

Development of bio-based polymeric blends - a comprehensive review

The current impetus to develop bio-based polymers for greater sustainability and lower carbon footprint is necessitated due to the alarming depletion of fossil resources, concurrent global warming, and related environmental issues. This article reviews the development of polymeric blends based on bio-based polymers. The focus on bio-based polymers is due to their greater 'Sustainability factor' as they are derived from renewable resources. The article delves into the synthesis of both conventional and highly biodegradable bio-based polymers, each crafted from feedstocks derived from nature's bounty. What sets this work apart is the exploration of blending existing bio-based polymers, culminating in the birth of entirely new materials. This review provides a comprehensive overview of the recent advancements in the development of bio-based polymeric blends, covering their synthesis, properties, applications, and potential contributions to a more sustainable future. Despite their potential benefits, bio-based materials face obstacles such as miscibility, processability issues and disparities in physical properties compared to conventional counterparts. The paper also discusses significance of compatibilizers, additives and future directions for the further advancement of these bio-based blends. While bio-based polymer blends hold promise for environmentally benign applications, many are still in the research phase. Ongoing research and technological innovations are driving the evolution of these blends as viable alternatives, but continued efforts are needed to ensure their successful integration into mainstream industrial practices. Concerted efforts from both researchers and industry stakeholders are essential to realize the full potential of bio-based polymers and accelerate their adoption on a global scale.

Comparative Analysis of Impact Strength among Various Polymeric Materials for Orthotic Production

Orthotic devices play an important role in medical treatment, addressing various pathologies and promoting patient recovery. Customization of orthoses to fit individual patient morphologies and needs is essential for optimal functionality and patient comfort. The advent of additive manufacturing has revolutionized the biomedical field, offering advantages such as cost reduction, increased personalization, and enhanced dimensional adaptability for orthotics manufacturing. This research focuses on the impact strength of nine polymeric materials printed by additive manufacturing, including an evaluation of the materials' performance under varying conditions comprising different printing directions (vertical and horizontal) and exposure to artificial sweat for different durations (0 days, 24 days, and 189 days). The results showed that Nylon 12 is good for short-term (24 days) immersion, with absorbed energies of 78 J and 64 J for the vertical and horizontal directions, whereas Polycarbonate (PC) is good for long-term immersion (189 days), with absorbed energies of 66 J and 78 J for the vertical and horizontal directions. Overall, the findings contribute to a better understanding of the suitability of these materials for biomedical applications, considering both short-term and long-term exposure to physiological and environmental conditions.

Magnetic Stimulation for Programmed Shape Morphing: Review of Four-Dimensional Printing, Challenges and Opportunities

In the field of Additive Manufacturing, four-dimensional (4D) printing has emerged as a promising technique to fabricate smart structures capable of undergoing shape morphing in response to specific stimuli. Magnetic stimulation offers a safe, remote, and rapid actuation mechanism for magnetically responsive structures. This review provides a comprehensive overview of the various strategies and manufacturing approaches employed in the development of magnetically stimulated shape morphing 4D-printed structures, based on an extensive literature search. The review explores the use of magnetic stimulation either individually or in combination with other stimuli. While most of the literature focuses on single-stimulus responsive structures, a few examples of multi-stimuli responsive structures are also presented. We investigate the influence of the orientation of magnetic particles in smart material composites, which can be either random or programmed during or after printing. Finally, the similarities and differences among the different strategies and their impact on the resulting shape-morphing behavior are analyzed. This systematic overview functions as a guide for readers in selecting a manufacturing approach to achieve a specific magnetically actuated shape-morphing effect.

Three-Dimensional Bioprinting in Vascular Tissue Engineering and Tissue Vascularization of Cardiovascular Diseases

In the 21st century, significant progress has been made in repairing damaged materials through material engineering. However, the creation of large-scale artificial materials still faces a major challenge in achieving proper vascularization. To address this issue, researchers have turned to biomaterials and three-dimensional (3D) bioprinting techniques, which allow for the combination of multiple biomaterials with improved mechanical and biological properties that mimic natural materials. Hydrogels, known for their ability to support living cells and biological components, have played a crucial role in this research. Among the recent developments, 3D bioprinting has emerged as a promising tool for constructing hybrid scaffolds. However, there are several challenges in the field of bioprinting, including the need for nanoscale biomimicry, the formulation of hydrogel blends, and the ongoing complexity of vascularizing biomaterials, which requires further research. On a positive note, 3D bioprinting offers a solution to the vascularization problem due to its precise spatial control, scalability, and reproducibility compared with traditional fabrication methods. This paper aims at examining the recent advancements in 3D bioprinting technology for creating blood vessels, vasculature, and vascularized materials. It provides a comprehensive overview of the progress made and discusses the limitations and challenges faced in current 3D bioprinting of vascularized tissues. In addition, the paper highlights the future research directions focusing on the development of 3D bioprinting techniques and bioinks for creating functional materials.

Application of 3D, 4D, 5D, and 6D bioprinting in cancer research: what does the future look like?

The application of three- and four-dimensional (3D/4D) printing in cancer research represents a significant advancement in understanding and addressing the complexities of cancer biology. 3D/4D materials provide more physiologically relevant environments compared to traditional two-dimensional models, allowing for a more accurate representation of the tumor microenvironment that enables researchers to study tumor progression, drug responses, and interactions with surrounding tissues under conditions similar to in vivo conditions. The dynamic nature of 4D materials introduces the element of time, allowing for the observation of temporal changes in cancer behavior and response to therapeutic interventions. The use of 3D/4D printing in cancer research holds great promise for advancing our understanding of the disease and improving the translation of preclinical findings to clinical applications. Accordingly, this review aims to briefly discuss 3D and 4D printing and their advantages and limitations in the field of cancer. Moreover, new techniques such as 5D/6D printing and artificial intelligence (AI) are also introduced as methods that could be used to overcome the limitations of 3D/4D printing and opened promising ways for the fast and precise diagnosis and treatment of cancer.

Sustainable Composite Materials Based on Carnauba Wax and Montmorillonite Nanoclay for Energy Storage

Sustainable composite materials, including carnauba wax, can store energy in the form of latent heat, and containing the wax may allow form-stable melting and crystallization cycles to be performed. Here, it is shown that carnauba wax in the molten state and the abundant nanoclay montmorillonite form stable composites with mass ratios of 50-70% (w/w). Transmission electron microscopy analysis reveals the inhomogeneous distribution of the nanoclay in the wax matrix. Analyses with infrared and multinuclear solid-state nuclear magnetic resonance (NMR) spectroscopy prove the chemical inertness of the composite materials during preparation. No new phases are formed according to studies with powder X-ray diffraction. The addition of the nanoclay increases the thermal conductivity and prevents the leakage of the phase change material, as well as reducing the time intervals of the cycle of accumulation and the return of heat. The latent heat increases in the row 69.5 ± 3.7 J/g, 95.0 ± 2.5 J/g, and 107.9 ± 1.7 J/g for the composite materials containing resp. 50%, 60% and 70% carnauba wax. Analysis of temperature-dependent 13C cross-polarization solid-state NMR spectra reveal the enhanced amorphization and altered molecular dynamics of the carnauba wax constituents in the composite materials. The amorphization also defines changes in the thermal transport mechanism in the composites compared to pure wax at elevated temperatures.

The contemporary nexus of medicines security and bioprospecting: a future perspective for prioritizing the patient

Reacting to the challenges presented by the evolving nexus of environmental change, defossilization, and diversified natural product bioprospecting is vitally important for advancing global healthcare and placing patient benefit as the most important consideration. This overview emphasizes the importance of natural and synthetic medicines security and proposes areas for global research action to enhance the quality, safety, and effectiveness of sustainable natural medicines. Following a discussion of some contemporary factors influencing natural products, a rethinking of the paradigms in natural products research is presented in the interwoven contexts of the Fourth and Fifth Industrial Revolutions and based on the optimization of the valuable assets of Earth. Following COP28, bioprospecting is necessary to seek new classes of bioactive metabolites and enzymes for chemoenzymatic synthesis. Focus is placed on those performance and practice modifications which, in a sustainable manner, establish the patient, and the maintenance of their prophylactic and treatment needs, as the priority. Forty initiatives for natural products in healthcare are offered for the patient and the practitioner promoting global action to address issues of sustainability, environmental change, defossilization, quality control, product consistency, and neglected diseases to assure that quality natural medicinal agents will be accessible for future generations.

Biomaterials for Drug Delivery and Human Applications

Biomaterials embody a groundbreaking paradigm shift in the field of drug delivery and human applications. Their versatility and adaptability have not only enriched therapeutic outcomes but also significantly reduced the burden of adverse effects. This work serves as a comprehensive overview of biomaterials, with a particular emphasis on their pivotal role in drug delivery, classifying them in terms of their biobased, biodegradable, and biocompatible nature, and highlighting their characteristics and advantages. The examination also delves into the extensive array of applications for biomaterials in drug delivery, encompassing diverse medical fields such as cancer therapy, cardiovascular diseases, neurological disorders, and vaccination. This work also explores the actual challenges within this domain, including potential toxicity and the complexity of manufacturing processes. These challenges emphasize the necessity for thorough research and the continuous development of regulatory frameworks. The second aim of this review is to navigate through the compelling terrain of recent advances and prospects in biomaterials, envisioning a healthcare landscape where they empower precise, targeted, and personalized drug delivery. The potential for biomaterials to transform healthcare is staggering, as they promise treatments tailored to individual patient needs, offering hope for improved therapeutic efficacy, fewer side effects, and a brighter future for medical practice.

Investigation of the in vitro biological activities of polyethylene glycol-based thermally stable polyurethane elastomers

The intense urge to replace conventional polymers with ecofriendly monomers is a step towards green products. The novelty of this study is the extraction of starch from the biowaste of wheat bran (WB) and banana peel (BP) for use as a monomer in the form of chain extenders. For the synthesis of polyurethane (PU) elastomers, polyethylene glycol (PEG) bearing an average molecular weight Mn = 1000 g mol-1 was used as a macrodiol, which was reacted with isophorone diisocyanate (IPDI) to develop NCO-terminated prepolymer chains. These prepolymer chains were terminated with chain extenders. Two series of linear PU elastomers were prepared by varying the concentration of chain extenders (0.5-2.5 mol%), inducing a variation of 40 to 70 wt% in the hard segment (HS). Fourier-transform infrared (FTIR) spectroscopy confirmed the formation of urethane linkages. Thermal gravimetric analysis (TGA) showed a thermal stability of up to 250 °C. Dynamic mechanical analysis (DMA) revealed a storage modulus (E') of up to 140 MPa. Furthermore, the hemolytic activities of up to 8.97 ± 0.1% were recorded. The inhibition of biofilm formation was investigated against E. coli and S. aureus (%), which was supported by phase contrast microscopy.

Nanomechanical Mapping of Three Dimensionally Printed Poly-ε-Caprolactone Single Microfibers at the Cell Scale for Bone Tissue Engineering Applications

Poly-ε-caprolactone (PCL) has been widely used in additive manufacturing for the construction of scaffolds for bone tissue engineering. However, its use is limited by its lack of bioactivity and inability to induce cell adhesion, hence limiting bone tissue regeneration. Biomimicry is strongly influenced by the dynamics of cell-substrate interaction. Thus, characterizing scaffolds at the cell scale could help to better understand the relationship between surface mechanics and biological response. We conducted atomic force microscopy-based nanoindentation on 3D-printed PCL fibers of ~300 µm thickness and mapped the near-surface Young's modulus at loading forces below 50 nN. In this non-disruptive regime, force mapping did not show clear patterns in the spatial distribution of moduli or a relationship with the topographic asperities within a given region. Remarkably, we found that the average modulus increased linearly with the logarithm of the strain rate. Finally, a dependence of the moduli on the history of nanoindentation was demonstrated on locations of repeated nanoindentations, likely due to creep phenomena capable of hindering viscoelasticity. Our findings can contribute to the rational design of scaffolds for bone regeneration that are capable of inducing cell adhesion and proliferation. The methodologies described are potentially applicable to various tissue-engineered biopolymers.

Progress in methods for evaluating Schwann cell myelination and axonal growth in peripheral nerve regeneration via scaffolds

Peripheral nerve injury (PNI) is a neurological disorder caused by trauma that is frequently induced by accidents, war, and surgical complications, which is of global significance. The severity of the injury determines the potential for lifelong disability in patients. Artificial nerve scaffolds have been investigated as a powerful tool for promoting optimal regeneration of nerve defects. Over the past few decades, bionic scaffolds have been successfully developed to provide guidance and biological cues to facilitate Schwann cell myelination and orientated axonal growth. Numerous assessment techniques have been employed to investigate the therapeutic efficacy of nerve scaffolds in promoting the growth of Schwann cells and axons upon the bioactivities of distinct scaffolds, which have encouraged a greater understanding of the biological mechanisms involved in peripheral nerve development and regeneration. However, it is still difficult to compare the results from different labs due to the diversity of protocols and the availability of innovative technologies when evaluating the effectiveness of novel artificial scaffolds. Meanwhile, due to the complicated process of peripheral nerve regeneration, several evaluation methods are usually combined in studies on peripheral nerve repair. Herein, we have provided an overview of the evaluation methods used to study the outcomes of scaffold-based therapies for PNI in experimental animal models and especially focus on Schwann cell functions and axonal growth within the regenerated nerve.

Sustained Release of Voriconazole Using 3D-Crosslinked Hydrogel Rings and Rods for Use in Corneal Drug Delivery

Corneal disorders and diseases are prevalent in the field of clinical ophthalmology. Fungal keratitis, one of the major factors leading to visual impairment and blindness worldwide, presents significant challenges for traditional topical eye drop treatments. The objective of this study was to create biocompatible 3D-crosslinked hydrogels for drug delivery to the cornea, intending to enhance the bioavailability of ophthalmic drugs. Firstly, a series of flexible and porous hydrogels were synthesized (free-radical polymerization), characterized, and evaluated. The materials were prepared by the free-radical polymerization reaction of 1-vinyl-2-pyrrolidinone (also known as N-vinylpyrrolidone or NVP) and 1,6-hexanediol dimethacrylate (crosslinker) in the presence of polyethylene glycol 1000 (PEG-1000) as the porogen. After the physicochemical characterization of these materials, the chosen hydrogel demonstrated outstanding cytocompatibility in vitro. Subsequently, the selected porous hydrogels could be loaded with voriconazole, an antifungal medication. The procedure was adapted to realize a loading of 175 mg voriconazole per ring, which slightly exceeds the amount of voriconazole that is instilled into the eye via drop therapy (a single eye drop corresponds with approximately 100 mg voriconazole). The voriconazole-loaded rings exhibited a stable zero-order release pattern over the first two hours, which points to a significantly improved bioavailability of the drug. Ex vivo experiments using the established porcine eye model provided confirmation of a 10-fold increase in drug penetration into the cornea (after 2 h of application of the hydrogel ring, 35.8 ± 3.2% of the original dose is retrieved from the cornea, which compares with 3.9 ± 1% of the original dose in the case of eye drop therapy). These innovative hydrogel rods and rings show great potential for improving the bioavailability of ophthalmic drugs, which could potentially lead to reduced hospitalization durations and treatment expenses.

3D/4D printing of cellulose nanocrystals-based biomaterials: Additives for sustainable applications

Cellulose nanocrystals (CNCs) have gained significant attraction from both industrial and academic sectors, thanks to their biodegradability, non-toxicity, and renewability with remarkable mechanical characteristics. Desirable mechanical characteristics of CNCs include high stiffness, high strength, excellent flexibility, and large surface-to-volume ratio. Additionally, the mechanical properties of CNCs can be tailored through chemical modifications for high-end applications including tissue engineering, actuating, and biomedical. Modern manufacturing methods including 3D/4D printing are highly advantageous for developing sophisticated and intricate geometries. This review highlights the major developments of additive manufactured CNCs, which promote sustainable solutions across a wide range of applications. Additionally, this contribution also presents current challenges and future research directions of CNC-based composites developed through 3D/4D printing techniques for myriad engineering sectors including tissue engineering, wound healing, wearable electronics, robotics, and anti-counterfeiting applications. Overall, this review will greatly help research scientists from chemistry, materials, biomedicine, and other disciplines to comprehend the underlying principles, mechanical properties, and applications of additively manufactured CNC-based structures.

Three-Dimensional Printing of Polycaprolactone/Nano-Hydroxyapatite Composite Scaffolds with a Pore Size of 300/500 µm is Histocompatible and Promotes Osteogenesis Using Rabbit Cortical Bone Marrow Stem Cells

BACKGROUND Many patients have bone defects that exceed the healing size. This study aimed to construct polycaprolactone/nano-hydroxyapatite (PCL/nHA) composite scaffolds with different pore sizes and investigate the osteogenesis and histocompatibility of cortical bone mesenchymal stem cells (BMSCs-C) seeded on it after inoculation. MATERIAL AND METHODS After mixing PCL and nHA proportionally, three-dimensional (3D) printing was used to print scaffolds. Porosity, compressive strength, and elastic modulus of PCL/nHA scaffolds were tested. The proliferation of BMSCs-C cells was examined and osteogenesis, chondrogenesis, and adipogenesis were evaluated. BMSCs-C cells were inoculated into 3D printing scaffolds, and histocompatibility between BMSCs-C cells and scaffolds was observed by the cell count kit (CCK-8) assay and LIVE/DEAD staining. After inoculating BMSCs-C cells into scaffolds, alkaline phosphatase (ALP) activity and calcium content were measured. RESULTS There was no obvious difference in characteristics between the 3 PCL/nHA composite scaffolds. The porosity, compressive strength, and elastic modulus of the 300/500-μm scaffold were between those of the 300-μm and 500-μm scaffolds. With increasing pore size, the mechanical properties of the scaffold decrease. BMSCs-C cells demonstrated faster growth and better osteogenic, adipogenic, and chondrogenic differentiation; therefore, BMSCs-C cells were selected as seed cells. PCL/nHA composite scaffolds with different pore sizes had no obvious toxicity and demonstrated good biocompatibility. All scaffolds showed higher ALP activity and calcium content. CONCLUSIONS The 300/500 μm mixed pore size scaffold took into account the mechanical properties of the 300 μm scaffold and the cell culture area of the 500 μm scaffold, therefore, 300/500 μm scaffold is a better model for the construction of tissue engineering scaffolds.

Fabrication and In Vitro Biological Assay of Thermo-Mechanically Tuned Chitosan Reinforced Polyurethane Composites

The progressive trend of utilizing bioactive materials constitutes diverse materials exhibiting biocompatibility. The innovative aspect of this research is the tuning of the thermo-mechanical behavior of polyurethane (PU) composites with improved biocompatibility for vibrant applications. Polycaprolactone (CAPA) Mn = 2000 g-mol-1 was used as a macrodiol, along with toluene diisocyanate (TDI) and hexamethylene diisocyanate (HMDI), to develop prepolymer chains, which were terminated with 1,4 butane diol (BD). The matrix was reinforced with various concentrations of chitosan (1-5 wt %). Two series of PU composites (PUT/PUH) based on aromatic and aliphatic diisocyanate were prepared by varying the hard segment (HS) ratio from 5 to 30 (wt %). The Fourier-transformed infrared (FTIR) spectroscopy showed the absence of an NCO peak at 1730 cm-1 in order to confirm polymer chain termination. Thermal gravimetric analysis (TGA) showed optimum weight loss up to 500 °C. Dynamic mechanical analysis (DMA) showed the complex modulus (E*) ≥ 200 MPa. The scanning electron microscope (SEM) proved the ordered structure and uniform distribution of chain extender in PU. The hemolytic activities were recorded up to 15.8 ± 1.5% for the PUH series. The optimum values for the inhibition of biofilm formation were recorded as 46.3 ± 1.8% against E. coli and S. aureus (%), which was supported by phase contrast microscopy.

Degradable Plasma-Polymerized Poly(Ethylene Glycol)-Like Coating as a Matrix for Food-Packaging Applications

Currently, there is considerable interest in seeking an environmentally friendly technique that is neither thermally nor organic solvent-dependent for producing advanced polymer films for food-packaging applications. Among different approaches, plasma polymerization is a promising method that can deposit biodegradable coatings on top of polymer films. In this study, an atmospheric-pressure aerosol-assisted plasma deposition method was employed to develop a poly(ethylene glycol) (PEG)-like coating, which can act as a potential matrix for antimicrobial agents, by envisioning controlled-release food-packaging applications. Different plasma operating parameters, including the input power, monomer flow rate, and gap between the edge of the plasma head and substrate, were optimized to produce a PEG-like coating with a desirable water stability level and that can be biodegradable. The findings revealed that increased distance between the plasma head and substrate intensified gas-phase nucleation and diluted the active plasma species, which in turn led to the formation of a non-conformal rough coating. Conversely, at short plasma-substrate distances, smooth conformal coatings were obtained. Furthermore, at low input powers (<250 W), the chemical structure of the precursor was mostly preserved with a high retention of C-O functional groups due to limited monomer fragmentation. At the same time, these coatings exhibit low stability in water, which could be attributed to their low cross-linking degree. Increasing the power to 350 W resulted in the loss of the PEG-like chemical structure, which is due to the enhanced monomer fragmentation at high power. Nevertheless, owing to the enhanced cross-linking degree, these coatings were more stable in water. Finally, it could be concluded that a moderate input power (250-300 W) should be applied to obtain an acceptable tradeoff between the coating stability and PEG resemblance.

Sustainable Bioplastics for Food Packaging Produced from Renewable Natural Sources

It is crucial to find an effective, environmentally acceptable solution, such as bioplastics or biodegradable plastics, to the world's rising plastics demand and the resulting ecological destruction. This study has focused on the environmentally friendly production of bioplastic samples derived from corn starch, rice starch, and tapioca starch, with various calcium carbonate filler concentrations as binders. Two different plasticizers, glycerol and sorbitol, were employed singly and in a rich blend. To test the differences in the physical and chemical properties (water content, absorption of moisture, water solubility, dissolution rate in alcohol, biodegradation in soil, tensile strength, elastic modulus, and FT-IR) of the produced samples, nine samples from each of the three types of bioplastics were produced using various ratios and blends of the fillers and plasticizers. The produced bioplastic samples have a multitude of features that make them appropriate for a variety of applications. The test results show that the starch-based bioplastics that have been suggested would be a better alternative material to be used in the packaging sectors.

Synthesis, Characterization and Application of Biobased Unsaturated Polyester Resin Reinforced with Unmodified/Modified Biosilica Nanoparticles

This paper presents sustainable technology for environmentally friendly composite production. Biobased unsaturated polyester resin (b-UPR), synthesized from waste polyethylene terephthalate (PET) glycosylate and renewable origin maleic anhydride (MAnh) and propylene glycol (PG), was reinforced with unmodified and vinyl-modified biosilica nanoparticles obtained from rice husk. The structural and morphological properties of the obtained particles, b-UPR, as well as composites, were characterized by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The study of the influence of biosilica modification on the mechanical properties of composites was supported by hardness modeling. Improvement of the tensile strength of the b-UPR-based composite at 2.5 wt.% addition of biosilica modified with vinyl silane, named "b-UPR/SiO2-V" composite, has been achieved with 88% increase. The thermal aging process applied to the b-UPR/SiO2-V composite, which simulates use over the product's lifetime, leads to the deterioration of composites that were used as fillers in commercial unsaturated polyester resin (c-UPR). The grinded artificially aged b-UPR composites were used as filler in c-UPR for the production of a table top layer with outstanding mechanical properties, i.e., impact resistance and microhardness, as well as fire resistance rated in the V-0 category according to the UL-94 test. Developing sustainable composites that are chemically synthesized from renewable sources is important from the aspect of preserving the environment and existing resources as well as the extending their life cycle.

Effects of Slit Edge Notches on Mechanical Properties of 3D-Printed PA12 Nylon Kirigami Specimens

Kirigami structures, a Japanese paper-cutting art form, has been widely adopted in engineering design, including robotics, biomedicine, energy harvesting, and sensing. This study investigated the effects of slit edge notches on the mechanical properties, particularly the tensile stiffness, of 3D-printed PA12 nylon kirigami specimens. Thirty-five samples were designed with various notch sizes and shapes and printed using a commercial 3D printer with multi-jet fusion (MJF) technique. Finite element analysis (FEA) was employed to determine the mechanical properties of the samples computationally. The results showed that the stiffness of the kirigami samples is positively correlated with the number of edges in the notch shape and quadratically negatively correlated with the notch area of the samples. The mathematical relationship between the stretching tensile stiffness of the samples and their notch area was established and explained from an energy perspective. The relationship established in this study can help fine-tune the stiffness of kirigami-inspired structures without altering the primary parameters of kirigami samples. With the rapid fabrication method (e.g., 3D printing technique), the kirigami samples with suitable mechanical properties can be potentially applied to planar springs for hinge structures or energy-absorbing/harvesting structures. These findings will provide valuable insights into the development and optimization of kirigami-inspired structures for various applications in the future.

Overview and Comparison of PLA Filaments Commercially Available in Europe for FFF Technology

This study presents a comprehensive techno-economic analysis of PLA materials for fused filament fabrication (FFF) from eight European manufacturers. The comparison involved rigorous experimental assessments of the mechanical properties, dimensional accuracy, and print quality using standardized methods and equipment such as tensile and CT testing. What makes this study unique is the consistent methodology applied, considering factors such as material color, printing temperature, printing orientation, filament diameter, and printer selection, to ensure meaningful and reliable results. Contrary to the common belief that a higher price implies better quality, the study revealed that the second cheapest PLA material achieved the best overall performance within the methodology employed. The study also confirmed certain observations, such as the influence of printing orientation and geometry on dimensional accuracy and mechanical properties, as well as the significant disparities between manufacturer-provided values and actual measured mechanical properties, highlighting the importance of experimental verification. Hence, the findings of this study hold value not only for the scientific community but also for hobbyist printers and beginners in the 3D printing realm seeking guidance in material selection for their projects. Furthermore, the methodology employed in this research can be adapted for evaluating a broad range of other 3D printing materials.

Straightforward Enzymatic Methacrylation of Poly(Glycerol Adipate) for Potential Applications as UV Curing Systems

Enzymatic one-pot synthesis procedures in a one-step and two-step monomers addition were developed to obtain poly(glycerol adipate) macromers with methacrylate end-functional groups under the presence of 1 and 3 wt% of Candida antarctica lipase B (CALB). Glycerol, divinyl adipate, and vinyl methacrylate were enzymatically reacted (vinyl methacrylate was either present from the beginning in the monomers solution or slowly dropped after 6 h of reaction) in tetrahydrofuran (THF) at 40 °C over 48 h. Macromers with a methacrylate end groups fraction of ≈52% in a simple one-pot one-step procedure were obtained with molecular weights (M_n) of ≈7500-7900 g/mol. The obtained products under the one-pot one-step and two steps synthesis procedures carried out using 1 and 3 wt% of a CALB enzymatic catalyst were profusely characterized by NMR (¹H and ¹³C), MALDI-TOF MS, and SEC. The methacrylate functional macromers obtained with the different procedures and 1 wt% of CALB were combined with an Irgacure^® 369 initiator to undergo homopolymerization under UV irradiation for 10 and 30 min, in order to test their potential to obtain amorphous networks within minutes with similar properties to those typically obtained by complex acrylation/methacrylation procedures, which need multiple purification steps and harsh reagents such as acyl chlorides. To the best of our knowledge, this is the first time that it has been demonstrated that the obtention of methacrylate-functional predominantly linear macromers based on poly(glycerol adipate) is able to be UV crosslinked in a simple one-step procedure.

3D and 4D Bioprinting Technologies: A Game Changer for the Biomedical Sector?

Bioprinting is an innovative and emerging technology of additive manufacturing (AM) and has revolutionized the biomedical sector by printing three-dimensional (3D) cell-laden constructs in a precise and controlled manner for numerous clinical applications. This approach uses biomaterials and varying types of cells to print constructs for tissue regeneration, e.g., cardiac, bone, corneal, cartilage, neural, and skin. Furthermore, bioprinting technology helps to develop drug delivery and wound healing systems, bio-actuators, bio-robotics, and bio-sensors. More recently, the development of four-dimensional (4D) bioprinting technology and stimuli-responsive materials has transformed the biomedical sector with numerous innovations and revolutions. This issue also leads to the exponential growth of the bioprinting market, with a value over billions of dollars. The present study reviews the concepts and developments of 3D and 4D bioprinting technologies, surveys the applications of these technologies in the biomedical sector, and discusses their potential research topics for future works. It is also urged that collaborative and valiant efforts from clinicians, engineers, scientists, and regulatory bodies are needed for translating this technology into the biomedical, pharmaceutical, and healthcare systems.

Synthesis, Characterization, Properties, and Biomedical Application of Chitosan-Based Hydrogels

The prospective applications of chitosan-based hydrogels (CBHs), a category of biocompatible and biodegradable materials, in biomedical disciplines such as tissue engineering, wound healing, drug delivery, and biosensing have garnered great interest. The synthesis and characterization processes used to create CBHs play a significant role in determining their characteristics and effectiveness. The qualities of CBHs might be greatly influenced by tailoring the manufacturing method to get certain traits, including porosity, swelling, mechanical strength, and bioactivity. Additionally, characterization methods aid in gaining access to the microstructures and properties of CBHs. Herein, this review provides a comprehensive assessment of the state-of-the-art with a focus on the affiliation between particular properties and domains in biomedicine. Moreover, this review highlights the beneficial properties and wide application of stimuli-responsive CBHs. The main obstacles and prospects for the future of CBH development for biomedical applications are also covered in this review.

Dental Materials Applied to 3D and 4D Printing Technologies: A Review

As computer-aided design and computer-aided manufacturing (CAD/CAM) technologies have matured, three-dimensional (3D) printing materials suitable for dentistry have attracted considerable research interest, owing to their high efficiency and low cost for clinical treatment. Three-dimensional printing technology, also known as additive manufacturing, has developed rapidly over the last forty years, with gradual application in various fields from industry to dental sciences. Four-dimensional (4D) printing, defined as the fabrication of complex spontaneous structures that change over time in response to external stimuli in expected ways, includes the increasingly popular bioprinting. Existing 3D printing materials have varied characteristics and scopes of application; therefore, categorization is required. This review aims to classify, summarize, and discuss dental materials for 3D printing and 4D printing from a clinical perspective. Based on these, this review describes four major materials, i.e., polymers, metals, ceramics, and biomaterials. The manufacturing process of 3D printing and 4D printing materials, their characteristics, applicable printing technologies, and clinical application scope are described in detail. Furthermore, the development of composite materials for 3D printing is the main focus of future research, as combining multiple materials can improve the materials' properties. Updates in material sciences play important roles in dentistry; hence, the emergence of newer materials are expected to promote further innovations in dentistry.