3D printed microneedle patches using stereolithography (SLA) for intradermal insulin delivery

An updated review on application of 3D printing in fabricating pharmaceutical dosage forms

The concept of "one size fits all" followed by the conventional healthcare system has drawbacks in providing precise pharmacotherapy due to variation in the pharmacokinetics of different patients leading to serious consequences such as side effects. In this regard, digital-based three-dimensional printing (3DP), which refers to fabricating 3D printed pharmaceutical dosage forms with variable geometry in a layer-by-layer fashion, has become one of the most powerful and innovative tools in fabricating "personalized medicine" to cater to the need of therapeutic benefits for patients to the maximum extent. This is achieved due to the tremendous potential of 3DP in tailoring various drug delivery systems (DDS) in terms of size, shape, drug loading, and drug release. In addition, 3DP has a huge impact on special populations including pediatrics, geriatrics, and pregnant women with unique or frequently changing medical needs. The areas covered in the present article are as follows: (i) the difference between traditional and 3DP manufacturing tool, (ii) the basic processing steps involved in 3DP, (iii) common 3DP methods with their pros and cons, (iv) various DDS fabricated by 3DP till date with discussing few research studies in each class of DDS, (v) the drug loading principles into 3D printed dosage forms, and (vi) regulatory compliance.

Progress of 3D Bioprinting in Organ Manufacturing

Three-dimensional (3D) bioprinting is a family of rapid prototyping technologies, which assemble biomaterials, including cells and bioactive agents, under the control of a computer-aided design model in a layer-by-layer fashion. It has great potential in organ manufacturing areas with the combination of biology, polymers, chemistry, engineering, medicine, and mechanics. At present, 3D bioprinting technologies can be used to successfully print living tissues and organs, including blood vessels, skin, bones, cartilage, kidney, heart, and liver. The unique advantages of 3D bioprinting technologies for organ manufacturing have improved the traditional medical level significantly. In this article, we summarize the latest research progress of polymers in bioartificial organ 3D printing areas. The important characteristics of the printable polymers and the typical 3D bioprinting technologies for several complex bioartificial organs, such as the heart, liver, nerve, and skin, are introduced.

An overview on the advantages and limitations of 3D printing of microneedles

The use of 3D printing (3DP) technology, which has been continuously evolving since the 1980s, has recently become common in healthcare services. The introduction of 3DP into the pharmaceutical industry particularly aims at the development of patient-centered dosage forms based on structure design. It is still a new research direction with potential to create the targeted release of drug delivery systems in freeform geometries. Although the use of 3DP technology for solid oral dosage forms is more preferable, studies on transdermal applications of the technology are also increasing. Microneedle sequences are one of the transdermal drug delivery (TDD) methods which are used to bypass the minimally invasive stratum corneum with novel delivery methods for small molecule drugs and vaccines. Microneedle arrays have advantages over many traditional methods. It is attractive with features such as ease of application, controlled release of active substances and patient compliance. Recently, 3D printers have been used for the production of microneedle patches. After giving a brief overview of 3DP technology, this article includes the materials necessary for the preparation of microneedles and microneedle patches specifically for penetration enhancement, preparation methods, quality parameters, and their application to TDD. In addition, the applicability of 3D microneedles in the pharmaceutical industry has been evaluated.

Opportunities and challenges of three-dimensional printing technology in pharmaceutical formulation development

Three-dimensional printing is a technology that prints the products layer-by-layer, in which materials are deposited according to the digital model designed by computer aided design (CAD) software. This technology has competitive advantages regarding product design complexity, product personalization, and on-demand manufacturing. The emergence of 3D technology provides innovative strategies and new ways to develop novel drug delivery systems. This review summarizes the application of 3D printing technologies in the pharmaceutical field, with an emphasis on the advantages of 3D printing technologies for achieving rapid drug delivery, personalized drug delivery, compound drug delivery and customized drug delivery. In addition, this article illustrates the limitations and challenges of 3D printing technologies in the field of pharmaceutical formulation development.

The role of microneedle arrays in drug delivery and patient monitoring to prevent diabetes induced fibrosis

Diabetes affects approximately 450 million adults globally. If not effectively managed, chronic hyperglycaemia causes tissue damage that can develop into fibrosis. Fibrosis leads to end-organ complications, failure of organ systems occurs, which can ultimately cause death. One strategy to tackle end-organ complications is to maintain normoglycaemia. Conventionally, insulin is administered subcutaneously. Whilst effective, this delivery route shows several limitations, including pain. The transdermal route is a favourable alternative. Microneedle (MN) arrays are minimally invasive and painless devices that can enhance transdermal drug delivery. Convincing evidence is provided on MN-mediated insulin delivery. MN arrays can also be used as a diagnostic tool and monitor glucose levels. Furthermore, sophisticated MN array-based systems that integrate glucose monitoring and drug delivery into a single device have been designed. Therefore, MN technology has potential to revolutionise diabetes management. This review describes the current applications of MN technology for diabetes management and how these could prevent diabetes induced fibrosis.

Machine learning predicts 3D printing performance of over 900 drug delivery systems

Three-dimensional printing (3DP) is a transformative technology that is advancing pharmaceutical research by producing personalized drug products. However, advances made via 3DP have been slow due to the lengthy trial-and-error approach in optimization. Artificial intelligence (AI) is a technology that could revolutionize pharmaceutical 3DP through analyzing large datasets. Herein, literature-mined data for developing AI machine learning (ML) models was used to predict key aspects of the 3DP formulation pipeline and in vitro dissolution properties. A total of 968 formulations were mined and assessed from 114 articles. The ML techniques explored were able to learn and provide accuracies as high as 93% for values in the filament hot melt extrusion process. In addition, ML algorithms were able to use data from the composition of the formulations with additional input features to predict the drug release of 3D printed medicines. The best prediction was obtained by an artificial neural network that was able to predict drug release times of a formulation with a mean error of ±24.29 min. In addition, the most important variables were revealed, which could be leveraged in formulation development. Thus, it was concluded that ML proved to be a suitable approach to modelling the 3D printing workflow.

Translation of Polymeric Microneedles for Treatment of Human Diseases: Recent Trends, Progress, and Challenges

The ongoing search for biodegradable and biocompatible microneedles (MNs) that are strong enough to penetrate skin barriers, easy to prepare, and can be translated for clinical use continues. As such, this review paper is focused upon discussing the key points (e.g., choice polymeric MNs) for the translation of MNs from laboratory to clinical practice. The review reveals that polymers are most appropriately used for dissolvable and swellable MNs due to their wide range of tunable properties and that natural polymers are an ideal material choice as they structurally mimic native cellular environments. It has also been concluded that natural and synthetic polymer combinations are useful as polymers usually lack mechanical strength, stability, or other desired properties for the fabrication and insertion of MNs. This review evaluates fabrication methods and materials choice, disease and health conditions, clinical challenges, and the future of MNs in public healthcare services, focusing on literature from the last decade.

3D Printing for Medical Applications: Current State of the Art and Perspectives during the COVID-19 Crisis

The coronavirus SARS-CoV-2 pandemic has affected over one hundred million people worldwide and has resulted in over two million deaths. In addition to the toll that coronavirus takes on the health of humans infected with the virus and the potential long term effects of infection, the repercussions of the pandemic on the economy as well as on the healthcare system have been enormous. The global supply of equipment necessary for dealing with the pandemic experienced extreme stress as healthcare systems around the world attempted to acquire personal protective equipment for their workers and medical devices for treating COVID-19. This review describes how 3D printing is currently being used in life saving surgeries such as heart and lung surgery and how 3D printing can address some of the worldwide shortage of personal protective equipment, by examining recent trends of the use of 3D printing and how these technologies can be applied during and after the pandemic. We review the use of 3D printed models for treating the long term effects of COVID-19. We then focus on methods for generating face shields and different types of respirators. We conclude with areas for future investigation and application of 3D printing technology.

Fabrication of novel-shaped microneedles to overcome the disadvantages of solid microneedles for the transdermal delivery of insulin

In this study, we fabricated two different microneedles (MNs) - semi-hollow and bird-bill - to overcome the limitations of solid and coated MNs, respectively. The two MN arrays were developed using a general injection molding process to obtain high-quality MNs with uniform shape. The semi-hollow and bird-bill MNs could penetrate the micropores of swine skin up to depths of 178.5 ± 27.6 µm and 232.1 ± 51.3 µm, respectively. When the semi-hollow MNs were used for the transdermal delivery of insulin in diabetic rats, it was observed that the blood glucose concentration (BGC) decreased remarkably within 30 min, and the desired effect of insulin was maintained for an additional 3 h after the removal of insulin from the skin surface. The bird-bill MN was able to load a coating gel at a maximum capacity of 3.20 ± 0.21 mg per MN array, and the BGC continued to decrease significantly after MN application for up to 2-6 h. In summary, we fabricated semi-hollow and bird-bill MN arrays using the injection molding method; these can be mass produced and are capable of effectively producing micro-holes in the stratum corneum. The two MN arrays could provide effective transdermal delivery of large-molecular-weight drugs such as insulin.

Three 'D's: Design approach, dimensional printing, and drug delivery systems as promising tools in healthcare applications

The development of pharmaceutical drug products is required for the treatment of disease, which has resulted in an increasing number of approvals by regulatory agencies across the globe. To establish a hassle-free manufacturing process, the systematic use of a quality-by-design (QbD) approach combined with process analytical technology (PAT) and printing techniques can revolutionize healthcare applications. Printing technology has been emerged in various dimensions, such as 3D, 4D, and 5D printing, with respect to their production capabilities, durability, and accuracy of pharmaceutical manufacturing, which can efficiently deliver novel patient-centric healthcare products with holistic characteristics. In this review, we provide current trends in pharmaceutical product development using a design approach and high-quality printing techniques.

Emerging 3D printing technologies for drug delivery devices: Current status and future perspective

The 'one-size-fits-all' approach followed by conventional drug delivery platforms often restricts its application in pharmaceutical industry, due to the incapability of adapting to individual pharmacokinetic traits. Driven by the development of additive manufacturing (AM) technology, three-dimensional (3D) printed drug delivery medical devices have gained increasing popularity, which offers key advantages over traditional drug delivery systems. The major benefits include the ability to fabricate 3D structures with customizable design and intricate architecture, and most importantly, ease of personalized medication. Furthermore, the emergence of multi-material printing and four-dimensional (4D) printing integrates the benefits of multiple functional materials, and thus provide widespread opportunities for the advancement of personalized drug delivery devices. Despite the remarkable progress made by AM techniques, concerns related to regulatory issues, scalability and cost-effectiveness remain major hurdles. Herein, we provide an overview on the latest accomplishments in 3D printed drug delivery devices as well as major challenges and future perspectives for AM enabled dosage forms and drug delivery systems.

Design and Optimization of 3D-Printed Gastroretentive Floating Devices by Central Composite Design

This study aimed to optimize the size of capsule-shaped 3D-printed devices (CPD) using an experimental design by the response surface methodology to provide a gastroretentive drug delivery system (GRDDS) with optimal floating time. The CPD was fabricated using a fused deposition modeling (FDM) 3D printer. The central composite design was employed for the optimization of the devices. The morphology of the CPD was observed using a digital microscope and scanning electron microscope (SEM). The in vitro floating time and drug release were evaluated using a USP dissolution apparatus II. Appropriate total floating time (TFT) of the devices (more than 3 h) was obtained with the device's body, cap, and bottom thickness of 1.2, 1.8, and 2.9 mm, respectively. The release kinetics of the drug from the devices fitted well with zero-order kinetics. In conclusion, the optimization of CPD for GRDDS using the experimental design provided the devices with desirable floating time and ideal drug release characteristics.

3D Printing-A "Touch-Button" Approach to Manufacture Microneedles for Transdermal Drug Delivery

Microneedles (MNs) represent the concept of attractive, minimally invasive puncture devices of micron-sized dimensions that penetrate the skin painlessly and thus facilitate the transdermal administration of a wide range of active substances. MNs have been manufactured by a variety of production technologies, from a range of materials, but most of these manufacturing methods are time-consuming and expensive for screening new designs and making any modifications. Additive manufacturing (AM) has become one of the most revolutionary tools in the pharmaceutical field, with its unique ability to manufacture personalized dosage forms and patient-specific medical devices such as MNs. This review aims to summarize various 3D printing technologies that can produce MNs from digital models in a single step, including a survey on their benefits and drawbacks. In addition, this paper highlights current research in the field of 3D printed MN-assisted transdermal drug delivery systems and analyzes parameters affecting the mechanical properties of 3D printed MNs. The current regulatory framework associated with 3D printed MNs as well as different methods for the analysis and evaluation of 3D printed MN properties are outlined.

3D printed hollow microneedles array using stereolithography for efficient transdermal delivery of rifampicin

A 3D printed assembly of hollow microneedles (HMNs) array, conjoined with a reservoir void, was designed and additively manufactured using stereolithography (SLA) technology utilizing a proprietary class-I resin. The HMNs array was utilized for transdermal delivery of high molecular weight antibiotics, i.e., rifampicin (M_w 822.94 g/mol), which suffers from gastric chemical instability, low bioavailability, and severe hepatotoxicity. HMNs morphology was designed with sub-apical holes present in a quarter of the needle tip to improve its mechanical strength and integrity of the HMNs array. The HMNs array was characterized by optical microscopy and electron microscopy to ascertain the print quality and uniformity across the array. The system was also subjected to mechanical characterization for failure and penetration analyses. The ex vivo permeation and consequent transport of rifampicin across porcine skin were systematically evaluated. Finally, in vivo examinations of rifampicin administration through the microneedle reservoir system in SD rats revealed efficient penetration and desired bioavailability.

Diving into 3D (bio)printing: A revolutionary tool to customize the production of drug and cell-based systems for skin delivery

The incorporation of 3D printing technologies in the pharmaceutical industry can revolutionize its R&D, by providing a simple and rapid method to produce tailored one-off batches, each with customized dosages, different compounds, shapes, sizes, and adjusted release rates. Particularly, this type of technology can be advantageous for the development of topical and transdermal drug delivery systems, including patches and microneedles. The use of both systems as drug carriers offers advantages over the oral administration, but the possibility of skin irritation and sensitization, and the high production costs, may hinder the expansion of this market. In this context, 3D printing, a high-resolution technique, allows the design of high quality, personalized, complex and sophisticated structures, thus reducing the production costs and improving the patient compliance. This review covers the 3D printing concept and discusses the relevance of this technology to the pharmaceutical industry, with a special focus on the development of topical and transdermal products - patches and microneedles. The potential of 3D bioprinting for skin applications is also presented, highlighting the development of patch-like skin constructs for wound and burn treatment, and skin equivalents for in vitro research and drug development. Several recent studies were selected to support the relevance of the subjects addressed herein. Additionally, the limitations of these printing technologies are discussed, including regulatory, quality and safety issues.

Multifaceted Design and Emerging Applications of Tissue Adhesives

Tissue adhesives can form appreciable adhesion with tissues and have found clinical use in a variety of medical settings such as wound closure, surgical sealants, regenerative medicine, and device attachment. The advantages of tissue adhesives include ease of implementation, rapid application, mitigation of tissue damage, and compatibility with minimally invasive procedures. The field of tissue adhesives is rapidly evolving, leading to tissue adhesives with superior mechanical properties and advanced functionality. Such adhesives enable new applications ranging from mobile health to cancer treatment. To provide guidelines for the rational design of tissue adhesives, here, existing strategies for tissue adhesives are synthesized into a multifaceted design, which comprises three design elements: the tissue, the adhesive surface, and the adhesive matrix. The mechanical, chemical, and biological considerations associated with each design element are reviewed. Throughout the report, the limitations of existing tissue adhesives and immediate opportunities for improvement are discussed. The recent progress of tissue adhesives in topical and implantable applications is highlighted, and then future directions toward next-generation tissue adhesives are outlined. The development of tissue adhesives will fuse disciplines and make broad impacts in engineering and medicine.

3D printing as a transformative tool for microneedle systems: Recent advances, manufacturing considerations and market potential

The present review aims at identifying the key progress points that have been made on the use of 3D printing to manufacture microneedles in the past 3 years. The advances in the field of photopolymerization and extrusion-based 3D printing are outlined. The study revealed that the printing resolution and the material properties are the two critical parameters that have the most influential effect on the outcome of every microneedle printing endeavour. Finally, the authors attempt to estimate the impact of 3D printing on the transdermal drug delivery market.

Polymeric drug delivery systems by additive manufacturing

Additive manufacturing (AM) is gaining interests in drug delivery applications, offering innovative opportunities for the design and development of systems with complex geometry and programmed controlled release profile. In addition, polymer-based drug delivery systems can improve drug safety, efficacy, patient compliance, and are the key materials in AM. Therefore, combining AM and polymers can be beneficial to overcome the existing limitations in the development of controlled release drug delivery systems. Considering these advantages, here we are focusing on the recent developments in the field of polymeric drug delivery systems prepared by AM. This review provides a comprehensive overview on a holistic polymer-AM perspective for drug delivery systems with discussion on the materials, properties, design and fabrication techniques and the mechanisms used to achieve a controlled release system. The current challenges and future perspectives for personalized medicine and clinical use of these systems are also briefly discussed.

Investigation on hot melt extrusion and prediction on 3D printability of pharmaceutical grade polymers

The development of printable filaments has been identified as a critical aspect for the processing of pharmaceutical grade polymers and the fabrication of oral solid dosage forms. In this study a range of plain and drug loaded polymers were investigated and assessed for their printability in comparison to commercial filaments. Physicochemical characterizations of the polymers included differential scanning calorimetry (DSC) thermogravimetric analysis (TGA) and rheology were studied prior to Hot Melt Extrusion processing for the filament fabrication. A texture analyser was used to study the filament mechanical properties in order to derive the maximum tensile strength, Young's Modulus and elongation at break. Principal component analysis was used to compare the printability of the polymer and to identify the contribution of each mechanical property. The analysis showed that maximum tensile strength with a threshold between 15 and 20 MPa is the most critical property for the prediction of the printability. Furthermore, printable filaments were processed using Fusion Deposition Modelling technology and optimal printing parameters were identified. The study demonstrated that the prediction of filament printability is feasible by evaluating the mechanical properties.

Emerging Functional Biomaterials as Medical Patches

Medical patches have been widely explored and applied in various medical fields, especially in wound healing, tissue engineering, and other biomedical areas. Benefiting from emerging biomaterials and advanced manufacturing technologies, great achievements have been made on medical patches to evolve them into a multifunctional medical device for diverse health-care purposes, thus attracting extensive attention and research interest. Here, we provide up-to-date research concerning emerging functional biomaterials as medical patches. An overview of the various approaches to construct patches with micro- and nanoarchitecture is presented and summarized. We then focus on the applications, especially the biomedical applications, of the medical patches, including wound healing, drug delivery, and real-time health monitoring. The challenges and prospects for the future development of the medical patches are also discussed.

A highly robust approach to fabricate the mass-customizable mold of sharp-tipped biodegradable polymer microneedles for drug delivery

A skin-perforable dissolving microneedle is a promising mediator for painlessly delivering active pharmaceutical compounds across the skin. All the microneedle manufacturing processes so far, however, are much sensitive to input variation and unfavorable for make-to-order approach. Here, a robust method for fabricating mass-customizable master molds is developed to prepare sharp-tipped biodegradable polymer microneedles. Our approach combines the predrying and chip casting (PCC) of an ultrathick photoresist layer with a substrateless, inclined, and rotational exposure (SIR exposure). The PCC achieves the uniform reduction of solvent across the photoresist thickness which is critically required for the formation of a sharp tip; the SIR exposure creates master molds whose geometry is easily customizable and virtually insensitive to a variation in ultraviolet (UV) exposure dose. A theoretical model for the spatiotemporal distribution of UV dose under SIR exposure is established to show the technological superiority of our method. Next, our method's applicability is proven by fabricating a set of poly(lactic-co-glycolic) acid (PLGA) microneedles and performing both porcine skin penetration test and their in vitro degradation test. Our approach is verified to be robust in manufacturing mass-customizable molds for skin-perforable dissolving microneedles and to have high compatibility with almost all existing biodegradable polymers. The findings of this study lead to both a significant growth of dissolving microneedle-mediated drug delivery and better understanding of drug release kinetics.

Hollow microneedles: A perspective in biomedical applications

Microneedles (MN) have the potential to become a highly progressive device for both drug delivery and monitoring purposes as they penetrate the skin and pierce the stratum corneum barrier, allowing the delivery of drugs in the viable skin layers and the extraction of body fluids. Despite the many years of research and the different types of MN developed, only hollow MN have reached the pharmaceutical market under the path of medical devices. Therefore, this review focuses on hollow MN, materials and methods for their fabrication as well as their application in drug delivery, vaccine delivery and monitoring purposes. Furthermore, novel approaches for the fabrication of hollow MN are included as well as prospects of microneedle-based products on the market.

2D and 3D inkjet printing of biopharmaceuticals - A review of trends and future perspectives in research and manufacturing

There is an ongoing global shift in pharmaceutical business models from small molecule drugs to biologics. This increase in complexity is in response to advancements in our diagnoses and understanding of diseases. With the more targeted approach coupled with its inherently more costly development and manufacturing, 2D and 3D printing are being explored as suitable techniques to deliver more personalised and affordable routes to drug discovery and manufacturing. In this review, we explore first the business context underlying this shift to biopharmaceuticals and provide an update on the latest work exploring discovery and pharmaceutics. We then draw on multiple disciplines to help reveal the shared challenges facing researchers and firms aiming to develop biopharmaceuticals, specifically when using the most commonly explored manufacturing routes of drop-on-demand inkjet printing and pneumatic extrusion. This includes separating out how to consider mechanical and chemical influences during manufacturing, the role of the chosen hardware and the challenges of aqueous formulation based on similar challenges being faced by the printing industry. Together, this provides a review of existing work and guidance for researchers and industry to help with the de-risking and rapid development of future biopharmaceutical products.

Microneedle-mediated transdermal drug delivery for treating diverse skin diseases

Transdermal drug delivery is an attractive route for dermatological disease therapy because it can directly target the lesion site on the skin, reduce adverse reactions associated with systemic administration, and improve patient compliance. However, the stratum corneum, as the main skin barrier, severely limits transdermal drug penetration, with compromised bioavailability. Microneedles (MNs), which are leveraged to markedly improve the penetration of therapeutic agents by piercing the stratum corneum and creating hundreds of reversible microchannels in a minimally invasive manner, have been envisioned as a milestone for effective transdermal drug delivery, especially for superficial disease therapy. Here, the emergence of versatile MNs for the transdermal delivery of various drugs is reviewed, particularly focusing on the application of MNs for the treatment of diverse skin diseases, including superficial tumors, scars, psoriasis, herpes, acne, and alopecia. Additionally, the promises and challenges of the widespread translation of MN-mediated transdermal drug delivery in the dermatology field are summarized.

Optimisation of Design and Manufacturing Parameters of 3D Printed Solid Microneedles for Improved Strength, Sharpness, and Drug Delivery

3D printing has emerged as a powerful manufacturing technology and has attracted significant attention for the fabrication of microneedle (MN)-mediated transdermal systems. In this work, we describe an optimisation strategy for 3D-printed MNs, ranging from the design to the drug delivery stage. The key relationships between design and manufacturing parameters and quality and performance are systematically explored. The printing and post-printing set parameters were found to influence quality and material mechanical properties, respectively. It was demonstrated that the MN geometry affected piercing behaviour, fracture, and coating morphology. The delivery of insulin in porcine skin by inkjet-coated MNs was shown to be influenced by MN design.

3D-printed microneedles in biomedical applications

Conventional needle technologies can be advanced with emerging nano- and micro-fabrication methods to fabricate microneedles. Nano-/micro-fabricated microneedles seek to mitigate penetration pain and tissue damage, as well as providing accurately controlled robust channels for administrating bioagents and collecting body fluids. Here, design and 3D printing strategies of microneedles are discussed with emerging applications in biomedical devices and healthcare technologies. 3D printing offers customization, cost-efficiency, a rapid turnaround time between design iterations, and enhanced accessibility. Increasing the printing resolution, the accuracy of the features, and the accessibility of low-cost raw printing materials have empowered 3D printing to be utilized for the fabrication of microneedle platforms. The development of 3D-printed microneedles has enabled the evolution of pain-free controlled release drug delivery systems, devices for extracting fluids from the cutaneous tissue, biosignal acquisition, and point-of-care diagnostic devices in personalized medicine.

Application of Spectroscopy in Additive Manufacturing

Additive manufacturing (AM) is a rapidly expanding material production technique that brings new opportunities in various fields as it enables fast and low-cost prototyping as well as easy customisation. However, it is still hindered by raw material selection, processing defects and final product assessment/adjustment in pre-, in- and post-processing stages. Spectroscopic techniques offer suitable inspection, diagnosis and product trouble-shooting at each stage of AM processing. This review outlines the limitations in AM processes and the prospective role of spectroscopy in addressing these challenges. An overview on the principles and applications of AM techniques is presented, followed by the principles of spectroscopic techniques involved in AM and their applications in assessing additively manufactured parts.

Design and applications of protein delivery systems in nanomedicine and tissue engineering

Proteins are biological macromolecules involved in a wide range of biological functions, which makes them very appealing as therapeutics agents. Indeed, compared to small molecule drugs, their endogenous nature ensures their biocompatibility and biodegradability, they can be used in a large range of applications and present a higher specificity and activity. However, they suffer from unfolding, enzymatic degradation, short half-life and poor membrane permeability. To overcome such drawbacks, the development of protein delivery systems to protect, carry and deliver them in a controlled way have emerged importantly these last years. In this review, the formulation of a wide panel of protein delivery systems either in the form of polymer or inorganic nanoengineered colloids and scaffolds are presented and the protein loading and release mechanisms are addressed. A section is also dedicated to the detection of proteins and the characterization methods of their release. Then, the main protein delivery systems developed these last three years for anticancer, tissue engineering or diabetes applications are presented, as well as the major in vivo models used to test them. The last part of this review aims at presenting the perspectives of the field such as the use of protein-rich material or the sequestration of proteins. This part will also deal with less common applications and gene therapy as an indirect method to deliver protein.

High-resolution two-photon polymerization: the most versatile technique for the fabrication of microneedle arrays

Microneedle patches have received much interest in the last two decades as drug/vaccine delivery or fluid sampling systems for diagnostic and monitoring purposes. Microneedles are manufactured using a variety of additive and subtractive micromanufacturing techniques. In the last decade, much attention has been paid to using additive manufacturing techniques in both research and industry, such as 3D printing, fused deposition modeling, inkjet printing, and two-photon polymerization (2PP), with 2PP being the most flexible method for the fabrication of microneedle arrays. 2PP is one of the most versatile and precise additive manufacturing processes, which enables the fabrication of arbitrary three-dimensional (3D) prototypes directly from computer-aided-design (CAD) models with a resolution down to 100 nm. Due to its unprecedented flexibility and high spatial resolution, the use of this technology has been widespread for the fabrication of bio-microdevices and bio-nanodevices such as microneedles and microfluidic devices. This is a pioneering transformative technology that facilitates the fabrication of complex miniaturized structures that cannot be fabricated with established multistep manufacturing methods such as injection molding, photolithography, and etching. Thus, microstructures are designed according to structural and fluid dynamics considerations rather than the manufacturing constraints imposed by methods such as machining or etching processes. This article presents the fundamentals of 2PP and the recent development of microneedle array fabrication through 2PP as a precise and unique method for the manufacture of microstructures, which may overcome the shortcomings of conventional manufacturing processes.

Biodegradable microneedles fabricated with carbohydrates and proteins: Revolutionary approach for transdermal drug delivery

There has been a surge in the use of transdermal drug delivery systems (TDDS) for the past few years. The market of TDDS is expected to reach USD 7.1 billion by 2023, from USD 5.7 billion in 2018, at a CAGR of 4.5%. Microneedles (MNs) are a novel class of TDDS with advantages of reduced pain, low infection risk, ease of application, controlled release of therapeutic agents, and enhanced bioavailability. Biodegradable MNs fabricated from natural polymers have become the center of attention among formulation scientists because of their recognized biodegradability, biocompatibility, ease of fabrication, and sustainable character. In this review, we summarize the various polysaccharides and polypeptide based biomaterials that are used to fabricate biodegradable MNs. Particular emphasis is given to cellulose and its derivatives, starch, and complex carbohydrate polymers such as alginates, chitosan, chondroitin sulfate, xanthan gum, pullulan, and hyaluronic acid. Additionally, novel protein-based polymers such as zein, collagen, gelatin, fish scale and silk fibroin (polyamino acid) biopolymers application in transdermal drug delivery have also been discussed. The current review will provide a unique perspective to the readers on the developments of biodegradable MNs composed of carbohydrates and protein polymers with their clinical applications and patent status.

Nanosuspensions and Microneedles Roller as a Combined Approach to Enhance Diclofenac Topical Bioavailability

Topical application of the anti-inflammatory drug diclofenac (DCF) reduces the severity of systemic unwanted effects compared to its oral administration. A number of transdermal formulations are available on the market and routinely used in clinical and home-care settings. However, the amount of DCF delivered across the skin remains limited and often insufficient, thus making the oral route still necessary for achieving sufficient drug concentration at the inflamed site. In attempting to improve the transdermal penetration, we explored the combined use of DCF nanosuspensions with a microneedle roller. Firstly, DCF nanosuspensions were prepared by a top-down media milling method and characterized by spectroscopic, thermal and electron microscopy analyses. Secondly, the pore-forming action of microneedle rollers on skin specimens (ex vivo) was described by imaging at different scales. Finally, DCF nanosuspensions were applied on newborn pig skin (in vitro) in combination with microneedles roller treatment, assessing the DCF penetration and distribution in the different skin layers. The relative contribution of microneedle length, nanosuspension stabilizer and application sequence could be identified by systemically varying these parameters.

Microneedles: Characteristics, Materials, Production Methods and Commercial Development

Although transdermal drug delivery systems (DDS) offer numerous benefits for patients, including the avoidance of both gastric irritation and first-pass metabolism effect, as well as improved patient compliance, only a limited number of active pharmaceutical ingredients (APIs) can be delivered accordingly. Microneedles (MNs) represent one of the most promising concepts for effective transdermal drug delivery that penetrate the protective skin barrier in a minimally invasive and painless manner. The first MNs were produced in the 90s, and since then, this field has been continually evolving. Therefore, different manufacturing methods, not only for MNs but also MN molds, are introduced, which allows for the cost-effective production of MNs for drug and vaccine delivery and even diagnostic/monitoring purposes. The focus of this review is to give a brief overview of MN characteristics, material composition, as well as the production and commercial development of MN-based systems.

Anti-biofilm multi drug-loaded 3D printed hearing aids

Over 5% of the world's population has disabling hearing loss, which affects approximately one third of individuals over 65 years. Hearing aids are commonly used in this population group, but prolonged use of these devices may cause ear infections. We describe for the first time, the use of 3D printing to fabricate hearing aids loaded with two antibiotics, ciprofloxacin and fluocinolone acetonide. Digital light processing 3D printing was employed to manufacture hearing aids from two polymer resins, ENG hard and Flexible. The inclusion of the antibiotics did not affect the mechanical properties of the hearing aids. All multi-drug-loaded devices exhibited a hydrophilic surface, excellent blood compatibility and anti-biofilm activity against P. aeruginosa and S. aureus. Hearing aids loaded with ciprofloxacin (6% w/w) and fluocinolone acetonide (0.5% w/w) sustained drug release for more than two weeks and inhibited biofilm formation on the surface of the devices and bacteria growth in the surrounding medium. In summary, this work highlights the potential of vat photopolymerization 3D printing as a versatile manufacturing approach to fabricate high-fidelity patient-specific medical devices with anti-bacterial properties.

Vat photopolymerization 3D printing for advanced drug delivery and medical device applications

Three-dimensional (3D) printing is transforming manufacturing paradigms within healthcare. Vat photopolymerization 3D printing technology combines the benefits of high resolution and favourable printing speed, offering a sophisticated approach to fabricate bespoke medical devices and drug delivery systems. Herein, an overview of the vat polymerization techniques, their unique applications in the fields of drug delivery and medical device fabrication, material examples and the advantages they provide within healthcare, is provided. The challenges and drawbacks presented by this technology are also discussed. It is forecast that the adoption of 3D printing could pave the way for a personalised health system, advancing from traditional treatments pathways towards digital healthcare.

Basit A. 3D Printing of Tunable Zero-Order Release Printlets

Zero-order release formulations are designed to release a drug at a constant rate over a prolonged time, thus reducing systemic side effects and improving patience adherence to the therapy. Such formulations are traditionally complex to manufacture, requiring multiple steps. In this work, fused deposition modeling (FDM) 3D printing was explored to prepare on-demand printlets (3D printed tablets). The design includes a prolonged release core surrounded by an insoluble shell able to provide zero-order release profiles. The effect of drug loading (10, 25, and 40% w/w paracetamol) on the mechanical and physical properties of the hot melt extruded filaments and 3D printed formulations was evaluated. Two different shell 3D designs (6 mm and 8 mm diameter apertures) together with three different core infills (100, 50, and 25%) were prepared. The formulations showed a range of zero-order release profiles spanning 16 to 48 h. The work has shown that with simple formulation design modifications, it is possible to print extended release formulations with tunable, zero-order release kinetics. Moreover, by using different infill percentages, the dose contained in the printlet can be infinitely adjusted, providing an additive manufacturing route for personalizing medicines to a patient.

Mathematical Modelling, Simulation and Optimisation of Microneedles for Transdermal Drug Delivery: Trends and Progress

In the last two decades, microneedles (MNs) have received significant interest due to their potential for painless transdermal drug delivery (TDD) and minimal skin damage. MNs have found applications in a range of research and development areas in drug delivery. They have been prepared using a variety of materials and fabrication techniques resulting in MN arrays with different dimensions, shapes, and geometries for delivery of a variety of drug molecules. These parameters play crucial roles in determining the drug release profiles from the MNs. Developing mathematical modelling, simulation, and optimisation techniques is vital to achieving the desired MN performances. These will then be helpful for pharmaceutical and biotechnological industries as well as professionals working in the field of regulatory affairs focusing on MN based TDD systems. This is because modelling has a great potential to reduce the financial and time cost of both the MNs' studies and manufacturing. For example, a number of robust mathematical models for predicting the performance of the MNs in vivo have emerged recently which incorporate the roles of the structural and mechanical properties of the skin. In addressing these points, this review paper aims to highlight the current status of the MN modelling research, in particular, the modelling, simulation and optimisation of the systems for drug delivery. The theoretical basis for the simulation of MN enhanced diffusion is discussed within this paper. Thus, this review paper provides a better understanding of the modelling of the MN mediated drug delivery process.

Emerging technologies for diagnostics and drug delivery in the fight against COVID-19 and other pandemics

INTRODUCTION

A pandemic is the worst-case scenario in the field of infectious diseases. Innovative technologies have the potential to address the challenges associated with the manufacture of personalized drug delivery systems, biosensors, and medical devices during a pandemic. 3D-Printing, microfluidics, and Microelectromechanical systems (MEMS) can provide an important part on this fight, as are cheap, easy to be operated, capable to provide rapid detection and monitoring of a disease, and deliver medicines.

AREAS COVERED

This manuscript answers the question of how these emerging technologies can save lives during a pandemic by avoiding supply chain delays and also by providing rapid diagnostics, disease monitoring, or by offering personalized treatments. The manuscript covers recent approaches in the topic with a focus in manuscripts published in the last year and by emphasising recent regulatory considerations by regulatory agencies in the manufacturing of 3DP systems or other medical devices during COVID.

EXPERT OPINION

New manufacturing techniques are emerging with the ability to address the challenges associated with the development of medical devices or diagnostics, during a pandemic. Are many challenges in order to achieve this and especially in short times that are required under a pandemic attack, which will also be covered in this manuscript.