Microstereolithography and characterization of poly(propylene fumarate)-based drug-loaded microneedle arrays

Progress in Microneedle-Mediated Protein Delivery

The growing demand for patient-compliance therapies in recent years has led to the development of transdermal drug delivery, which possesses several advantages compared with conventional methods. Delivering protein through the skin by transdermal patches is extremely difficult due to the presence of the stratum corneum which restricts the application to lipophilic drugs with relatively low molecular weight. To overcome these limitations, microneedle (MN) patches, consisting of micro/miniature-sized needles, are a promising tool to perforate the stratum corneum and to release drugs and proteins into the dermis following a non-invasive route. This review investigates the fabrication methods, protein delivery, and translational considerations for the industrial scaling-up of polymeric MNs for dermal protein delivery.

Application of Micro-Scale 3D Printing in Pharmaceutics

3D printing, as one of the most rapidly-evolving fabrication technologies, has released a cascade of innovation in the last two decades. In the pharmaceutical field, the integration of 3D printing technology has offered unique advantages, especially at the micro-scale. When printed at a micro-scale, materials and devices can provide nuanced solutions to controlled release, minimally invasive delivery, high-precision targeting, biomimetic models for drug discovery and development, and future opportunities for personalized medicine. This review aims to cover the recent advances in this area. First, the 3D printing techniques are introduced with respect to the technical parameters and features that are uniquely related to each stage of pharmaceutical development. Then specific micro-sized pharmaceutical applications of 3D printing are summarized and grouped according to the provided benefits. Both advantages and challenges are discussed for each application. We believe that these technologies provide compelling future solutions for modern medicine, while challenges remain for scale-up and regulatory approval.

Three-dimensional printing for drug delivery devices: a state-of-the-art survey

Over the last several decades, 3D printing technology, which encompasses many different fabrication techniques, had emerged as a promising tool in many fields of production, including the pharmaceutical industry. Specifically, 3D printing may be advantageous for drug delivery systems, systems aiming to improve the pharmacokinetics of drugs. These advantages include the ease of designing complex shapes, printing of drugs on demand, tailoring dosage to the specific needs of the patient and enhancing the bioavailability of drugs. This paper reviews the most recent advancements in this field, presenting both the abilities and limitations of several promising 3D printing methods.

Poly(propylene fumarate)-based materials: Synthesis, functionalization, properties, device fabrication and biomedical applications

Poly(propylene fumarate) (PPF) is a biodegradable polymer that has been investigated extensively over the last three decades. It has led many scientists to synthesize and fabricate a variety of PPF-based materials for biomedical applications due to its controllable mechanical properties, tunable degradation and biocompatibility. This review provides a comprehensive overview of the progress made in improving PPF synthesis, resin formulation, crosslinking, device fabrication and post polymerization modification. Further, we highlight the influence of these parameters on biodegradation, biocompatibility, and their use in a number of regenerative medicine applications, especially bone tissue engineering. In particular, the use of 3D printing techniques for the fabrication of PPF-based scaffolds is extensively reviewed. The recent invention of a ring-opening polymerization method affords precise control of PPF molecular mass, molecular mass distribution (Ɖ_M) and viscosity. Low Ɖ_M facilitates time-certain resorption of 3D printed structures. Novel post-polymerization and post-printing functionalization methods have accelerated the expansion of biomedical applications that utilize PPF-based materials. Finally, we shed light on evolving uses of PPF-based materials for orthopedics/bone tissue engineering and other biomedical applications, including its use as a hydrogel for bioprinting.

Low cost additive manufacturing of microneedle masters

PURPOSE

Microneedle patches are arrays of tiny needles that painlessly pierce the skin to deliver medication into the body. Biocompatible microneedles are usually fabricated via molding of a master structure. Microfabrication techniques used for fabricating these master structures are costly, time intensive, and require extensive expertise to control the structure's geometry of the structure, despite evidence that microneedle geometry is a key design parameter. Here, a commercially available 3D printer is utilized, for the first time, to quickly and easily manufacture microneedle masters.

DESIGN/METHODOLOGY/APPROACH

Because commercially available 3D printers are not typically used for micron-scale fabrication, the influence of three different sources of error- stair-stepping, aliasing, and light abberations- on the resulting structure is investigated. A custom Matlab code is written to control the light intensity projected off of each individual micromirror (through grayscale) at a given time. The effect of the layer height, the number of layers, and grayscale on the sharpness, surface texture, and dimensional fidelity of the final structure is described.

FINDINGS

The Autodesk Ember is successfully utilized to fabricate sharp microneedles with a tip radius of approximately 15 μm in less than 30 min per patch (as compared to weeks to months for existing approaches). Utilization of grayscale improves surface texture and sharpness, and dimensional fidelity within ±5% of desired dimensions is achieved.

ORIGINALITY/VALUE

The described 3D printing technique enables investigators to accurately fabricate microneedles within minutes at low cost. Rapid, iterative optimization of microneedle geometry through 3D printing will accelerate microneedle research through improved understanding of the relationship between microneedle structure and function.

Addressing Unmet Clinical Needs with 3D Printing Technologies

Recent advances in 3D printing have enabled the creation of novel 3D constructs and devices with an unprecedented level of complexity, properties, and functionalities. In contrast to manufacturing techniques developed for mass production, 3D printing encompasses a broad class of fabrication technologies that can enable 1) the creation of highly customized and optimized 3D physical architectures from digital designs; 2) the synergistic integration of properties and functionalities of distinct classes of materials to create novel hybrid devices; and 3) a biocompatible fabrication approach that facilitates the creation and cointegration of biological constructs and systems. This progress report describes how these capabilities can potentially address a myriad of unmet clinical needs. First, the creation of 3D-printed prosthetics to regain lost functionalities by providing structural support for skeletal and tubular organs is highlighted. Second, novel drug delivery strategies aided by 3D-printed devices are described. Third, the advancement of medical research heralded by 3D-printed tissue/organ-on-chips systems is discussed. Fourth, the developments of 3D-printed tissue and organ regeneration are explored. Finally, the potential for seamless integration of engineered organs with active devices by leveraging the versatility of multimaterial 3D printing is envisioned.

Peptide-modified vemurafenib-loaded liposomes for targeted inhibition of melanoma via the skin

Vemurafenib is a chemotherapeutic drug recently approved by the FDA to treat melanoma. Because the drug is usually delivered orally, the route of administration readily causes damage to major organs with limited antitumor efficacy and bioavailability. In this study, we developed a peptide-modified vemurafenib-loaded liposome for the targeted inhibition of subcutaneous melanoma via the skin. First, the peptide-modified vemurafenib-loaded liposomes (Vem-TD-Lip) were prepared and characterized with respect to the size, shape and charge; the loading efficiency of vemurafenib; and the stability. Then, the intracellular uptake of these liposomes, their limited cytotoxicity, the selective inhibition of melanoma cells harboring BRAF mutations, and the liposome permeation ability were confirmed through in vitro experiments. Finally, the safety and antitumor activity of Vem-TD-Lip were evaluated in vivo. The results showed that transdermal delivery of Vem-TD-Lip effectively targeted and inhibited subcutaneous melanoma in male mice, the administration of Vem-TD-Lip through skin was better than that through oral administration and intravenous injection in terms of reducing damage to major organs and enhancing antitumor efficacy, and the peptide TD significantly enhanced the delivery of Vem-TD-Lip across the skin. This work provides a new strategy for delivering vemurafenib to target and inhibit subcutaneous melanoma.

Three-Dimensional (3D) Printed Microneedles for Microencapsulated Cell Extrusion

Cell-hydrogel based therapies offer great promise for wound healing. The specific aim of this study was to assess the viability of human hepatocellular carcinoma (HepG2) cells immobilized in atomized alginate capsules (3.5% (w/v) alginate, d = 225 µm ± 24.5 µm) post-extrusion through a three-dimensional (3D) printed methacrylate-based custom hollow microneedle assembly (circular array of 13 conical frusta) fabricated using stereolithography. With a jetting reliability of 80%, the solvent-sterilized device with a root mean square roughness of 158 nm at the extrusion nozzle tip (d = 325 μm) was operated at a flowrate of 12 mL/min. There was no significant difference between the viability of the sheared and control samples for extrusion times of 2 h (p = 0.14, α = 0.05) and 24 h (p = 0.5, α = 0.05) post-atomization. Factoring the increase in extrusion yield from 21.2% to 56.4% attributed to hydrogel bioerosion quantifiable by a loss in resilience from 5470 (J/m³) to 3250 (J/m³), there was no significant difference in percentage relative payload (p = 0.2628, α = 0.05) when extrusion occurred 24 h (12.2 ± 4.9%) when compared to 2 h (9.9 ± 2.8%) post-atomization. Results from this paper highlight the feasibility of encapsulated cell extrusion, specifically protection from shear, through a hollow microneedle assembly reported for the first time in literature.

3D printed microneedles for insulin skin delivery

In this study, polymeric microneedle patches were fabricated by stereolithography, a 3D printing technique, for the transdermal delivery of insulin. A biocompatible resin was photopolymerized to build pyramid and cone microneedle designs followed by inkjet print coating of insulin formulations. Trehalose, mannitol and xylitol were used as drug carriers with the aim to preserve insulin integrity and stability but also to facilitate rapid release rates. Circular dichroism and Raman analysis demonstrated that all carriers maintained the native form of insulin, with xylitol presenting the best performance. Franz cell release studies were used for in vitro determination of insulin release rates in porcine skin. Insulin was released rapidly within 30 min irrespectively of the microneedle design. 3D printing was proved an effective technology for the fabrication of biocompatible and scalable microneedle patches.

Recent advances of controlled drug delivery using microfluidic platforms

Conventional systematically-administered drugs distribute evenly throughout the body, get degraded and excreted rapidly while crossing many biological barriers, leaving minimum amounts of the drugs at pathological sites. Controlled drug delivery aims to deliver drugs to the target sites at desired rates and time, thus enhancing the drug efficacy, pharmacokinetics, and bioavailability while maintaining minimal side effects. Due to a number of unique advantages of the recent microfluidic lab-on-a-chip technology, microfluidic lab-on-a-chip has provided unprecedented opportunities for controlled drug delivery. Drugs can be efficiently delivered to the target sites at desired rates in a well-controlled manner by microfluidic platforms via integration, implantation, localization, automation, and precise control of various microdevice parameters. These features accordingly make reproducible, on-demand, and tunable drug delivery become feasible. On-demand self-tuning dynamic drug delivery systems have shown great potential for personalized drug delivery. This review presents an overview of recent advances in controlled drug delivery using microfluidic platforms. The review first briefly introduces microfabrication techniques of microfluidic platforms, followed by detailed descriptions of numerous microfluidic drug delivery systems that have significantly advanced the field of controlled drug delivery. Those microfluidic systems can be separated into four major categories, namely drug carrier-free micro-reservoir-based drug delivery systems, highly integrated carrier-free microfluidic lab-on-a-chip systems, drug carrier-integrated microfluidic systems, and microneedles. Microneedles can be further categorized into five different types, i.e. solid, porous, hollow, coated, and biodegradable microneedles, for controlled transdermal drug delivery. At the end, we discuss current limitations and future prospects of microfluidic platforms for controlled drug delivery.

3D Printing, Ink Casting and Micromachined Lamination (3D PICLμM): A Makerspace Approach to the Fabrication of Biological Microdevices

We present a novel benchtop-based microfabrication technology: 3D printing, ink casting, micromachined lamination (3D PICLμM) for rapid prototyping of lab-on-a-chip (LOC) and biological devices. The technology uses cost-effective, makerspace-type microfabrication processes, all of which are ideally suited for low resource settings, and utilizing a combination of these processes, we have demonstrated the following devices: (i) 2D microelectrode array (MEA) targeted at in vitro neural and cardiac electrophysiology, (ii) microneedle array targeted at drug delivery through a transdermal route and (iii) multi-layer microfluidic chip targeted at multiplexed assays for in vitro applications. The 3D printing process has been optimized for printing angle, temperature of the curing process and solvent polishing to address various biofunctional considerations of the three demonstrated devices. We have depicted that the 3D PICLμM process has the capability to fabricate 30 μm sized MEAs (average 1 kHz impedance of 140 kΩ with a double layer capacitance of 3 μF), robust and reliable microneedles having 30 μm radius of curvature and ~40 N mechanical fracture strength and microfluidic devices having 150 μm wide channels and 400 μm fluidic vias capable of fluid mixing and transmitted light microparticle visualization. We believe our 3D PICLμM is ideally suited for applications in areas such as electrophysiology, drug delivery, disease in a dish, organ on a chip, environmental monitoring, agricultural therapeutic delivery and genomic testing.

3D printing applications for transdermal drug delivery

The role of two and three-dimensional printing as a fabrication technology for sophisticated transdermal drug delivery systems is explored in literature. 3D printing encompasses a family of distinct technologies that employ a virtual model to produce a physical object through numerically controlled apparatuses. The applicability of several printing technologies has been researched for the direct or indirect printing of microneedle arrays or for the modification of their surface through drug-containing coatings. The findings of the respective studies are presented. The range of printable materials that are currently used or potentially can be employed for 3D printing of transdermal drug delivery (TDD) systems is also reviewed. Moreover, the expected impact and challenges of the adoption of 3D printing as a manufacturing technique for transdermal drug delivery systems, are assessed. Finally, this paper outlines the current regulatory framework associated with 3D printed transdermal drug delivery systems.

Zein Microneedles for Transcutaneous Vaccine Delivery: Fabrication, Characterization, and in Vivo Evaluation Using Ovalbumin as the Model Antigen

Transcutaneous antigen administration provides an alternative to invasive syringe injections. The objective of this study was to investigate the feasibility of fabrication and antigen delivery using microneedles made from corn protein, zein. Micromolding technique was used to cast cone-shaped zein microneedles (ZMNs). The insertion of ZMNs and the delivery of the model antigen, ovalbumin (OVA), into the skin was confirmed by histological examination and confocal microscopy. In addition, a significantly (p < 0.05) lower bacterial skin penetration was observed after ZMN application compared with hypodermic syringe application. OVA coated on ZMNs was stable after storage under ambient and refrigerator conditions. Transcutaneous immunization studies showed significantly (p < 0.001) greater antibody titers (total IgG, IgG1, and IgG2a) after the application of OVA-coated ZMNs and OVA intradermal injection compared with the control group. Taken together, antigen-coated ZMNs can be developed for transcutaneous vaccine delivery.