Electroresponsive pulsatile depot delivery of insulin from poly(dimethylaminopropylacrylamide) gel in rats

A current era in pulsatile drug delivery system: Drug journey based on chronobiology

Almost all biological processes in the human body are regulated by circadian rhythm, which results in drastically different biochemical and physiological conditions throughout a 24 h period. Hence, suitable drug delivery systems should be efficiently monitored to attain the required therapeutic plasma concentration and therapeutic drug responses when needed as per chrono pharmacological concepts. "Chronotherapy" is the fast and transient release of a particular quantity of drug substance post a predetermined off-release period, termed as 'lag time'. Due to rhythmic variations, it is typically unnecessary to administer a medicine drug in an unhealthy condition constantly. Pulsatile drug delivery systems have received a lot of attention in pharmaceutical development because they give a quick or rate-controlled drug release after administration, followed by an anticipated lag period. Patients with various illnesses, such as asthma, hypertension, joint inflammation, and ulcers, can benefit from a pulsatile drug delivery system. Thus, a pulsatile drug delivery system may be a potential system for managing different diseases. This review mainly focuses on pulsatile drug delivery systems. It reviews and discusses the rationale, drug release mechanism, need, and system classification. In addition, it covers mainly externally regulated pulsatile drug delivery systems and recent advances in pulsatile systems like artificial intelligence and 3D printing. It also covers the ethical issues associated with pulsatile drug delivery systems.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as an insulin carrier in silk fibroin hydrogels for transdermal delivery via iontophoresis

In this study, silk fibroin (SF) was utilized as the starting material to fabricate physically crosslinked hydrogels. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was synthesized and characterized as a drug carrier, with insulin as the model drug. PEDOT:PSS, with a high electrical conductivity of 1666 ± 49 S cm-1, interacted with insulin molecules via electrostatic interaction by replacing the dopant PSS molecules. Insulin-loaded PEDOT:PSS embedded in the SF hydrogel resulted in an increase in the degree of swelling, pore size, and mesh size of the hydrogel. In the in vitro release and release-permeation experiments, the amounts of insulin release and release-permeation were investigated using a modified Franz diffusion cell, under the effects of SF concentrations, electric fields, and pH values. The amounts of insulin release and release-permeation from the pristine SF hydrogel and the PEDOT:PSS/SF hydrogel followed the power laws with the scaling exponents close to 0.5, indicating the Fickian diffusion or the concentration gradient. Under electric fields, with or without PEDOT:PSS used as the drug carrier, the insulin amount and diffusion coefficient were shown to increase with the increasing electric field due to the electro-repulsive forces between the cathode and insulin molecules and SF chains, electroosmosis, and SF matrix swelling. The SF hydrogel and PEDOT:PSS as the drug carrier are demonstrated herein as new components in the transdermal delivery system for the iontophoretically controlled insulin basal release applicable to diabetes patients.

Improved mechanical properties of antimicrobial poly(N-[3-(dimethylaminopropyl)] methacrylamide) hydrogels prepared by free radical polymerization in the presence of cetyltrimethylammonium bromide as a lyotropic liquid crystal template

The poor mechanical strength of the poly(N-[3-(dimethylamino)propyl] methacrylamide) (PDMAPMAAm) hydrogel limits its application as a drug delivery system and antimicrobial agent. In this study, both its morphology and antibacterial effectiveness were controlled through free radical solution polymerization in the presence of cetyltrimethylammonium bromide (CTAB; cationic nonreactive surfactant), forming lyotropic liquid crystal (LLC) mesophases. All the templated reactions proceeded in four different CTAB concentrations with three different concentrations of DMAPMAAm (2.0, 3.0 and 4.0 mol L^-1), which were carried out in distilled-deionized water (DDW) using potassium persulfate (KPS) and N,N'-methylenebisacrylamide (BIS) as the initiator and crosslinker, respectively. The pH-dependent phase transition temperature (34 °C at pH 14), compression moduli, antibacterial and diffusion properties, and the effect of the LLC mesophases of CTAB on the hydrogel properties were investigated by mechanical measurements, image analysis, inhibition zone tests, X-ray diffractograms and polarized optical microscopy (POM). It was found that the compression moduli of the templated (T)-PDMAPMAAm hydrogels increased by nearly ten times (from ∼3.0 to 30.0 kPa) compared to that of the isotropic (I) ones. The POM and XRD results before the removal of CTAB exhibited the formation of lamellar and hexagonal mesophases. Further, the inhibition zones showed the ability of the I-PDMAPMAAm hydrogels to reduce the activity of E. coli even in the absence of CTAB, gentamicin (GS) and ciprofloxacin (CF). This was because the quaternary ammonium (QA) groups on the DMAPMAAm units could interact with the bacterial membrane.

Polymer Nanocomposite Microactuators for On-Demand Chemical Release via High-Frequency Magnetic Field Excitation

On-demand delivery of substances has been demonstrated for various applications in the fields of chemistry and biomedical engineering. Single-pulse release profile has been shown previously for micro/nanoparticles in different form factors. However, to obtain a sustained release, a pulsatile release profile is needed. Here, we demonstrate such a release profile from polymer magnetic nanocomposite microspheres loaded with chemicals. By exciting the microactuators with AC magnetic fields, we could achieve up to 61% cumulative release over a five-day period. One of the main advantages of using a magnetic stimulus is that the properties of the environment (e.g., transparency, density, and depth) in which the particles are located do not affect the performance. The operating magnitude of the magnetic field used in this work is safe and does not interact with any nonmetallic materials. The proposed approach can potentially be used in microchemistry, drug delivery, lab-on-chip, and microrobots for drug delivery.

Physical triggering strategies for drug delivery

Physically triggered systems hold promise for improving drug delivery by enhancing the controllability of drug accumulation and release, lowering non-specific toxicity, and facilitating clinical translation. Several external physical stimuli including ultrasound, light, electric fields and magnetic fields have been used to control drug delivery and they share some common features such as spatial targeting, spatiotemporal control, and minimal invasiveness. At the same time, they possess several distinctive features in terms of interactions with biological entities and/or the extent of stimulus response. Here, we review the key advances of such systems with a focus on discussing their physical mechanisms, the design rationales, and translational challenges.

Advances in transdermal insulin delivery

Insulin therapy is necessary to regulate blood glucose levels for people with type 1 diabetes and commonly used in advanced type 2 diabetes. Although subcutaneous insulin administration via hypodermic injection or pump-mediated infusion is the standard route of insulin delivery, it may be associated with pain, needle phobia, and decreased adherence, as well as the risk of infection. Therefore, transdermal insulin delivery has been widely investigated as an attractive alternative to subcutaneous approaches for diabetes management in recent years. Transdermal systems designed to prevent insulin degradation and offer controlled, sustained release of insulin may be desirable for patients and lead to increased adherence and glycemic outcomes. A challenge for transdermal insulin delivery is the inefficient passive insulin absorption through the skin due to the large molecular weight of the protein drug. In this review, we focus on the different transdermal insulin delivery techniques and their respective advantages and limitations, including chemical enhancers-promoted, electrically enhanced, mechanical force-triggered, and microneedle-assisted methods.

Electric field-responsive nanoparticles and electric fields: physical, chemical, biological mechanisms and therapeutic prospects

Electric fields are among physical stimuli that have revolutionized therapy. Occurring endogenously or exogenously, the electric field can be used as a trigger for controlled drug release from electroresponsive drug delivery systems, can stimulate wound healing and cell proliferation, may enhance endocytosis or guide stem cell differentiation. Electric field pulses may be applied to induce cell fusion, can increase the penetration of therapeutic agents into cells, or can be applied as a standalone therapy to ablate tumors. This review describes the main therapeutic trends and overviews the main physical, chemical and biological mechanisms underlying the actions of electric fields. Overall, the electric field can be used in therapeutic approaches in several ways. The electric field can act on drug carriers, cells and tissues. Understanding the multiple effects of this powerful tool will help harnessing its full therapeutic potential in an efficient and safe way.

Manipulating nanoparticle transport within blood flow through external forces: an exemplar of mechanics in nanomedicine

A large number of nanoparticles (NPs) have been raised for diverse biomedical applications and some of them have shown great potential in treatment and imaging of diseases. Design of NPs is essential for delivery efficacy due to a number of biophysical barriers, which prevents the circulation of NPs in vascular flow and their accumulation at tumour sites. The physiochemical properties of NPs, so-called '4S' parameters, such as size, shape, stiffness and surface functionalization, play crucial roles in their life journey to be delivered to tumour sites. NPs can be modified in various ways to extend their blood circulation time and avoid their clearance by phagocytosis, and efficiently diffuse into tumour cells. However, it is difficult to overcome these barriers simultaneously by a simple combination of '4S' parameters for NPs. At this moment, external triggerings are necessary to guide the movement of NPs, which include light, ultrasound, magnetic field, electrical field and chemical interaction. The delivery system can be constructed to be sensitive to these external stimuli which can reduce the non-specific toxicity and improve the efficacy of the drug-delivery system. From a mechanics point of view, we discuss how different forces play their roles in the margination of NPs in blood flow and tumour microvasculature.

Smart Polymeric Hydrogels for Cartilage Tissue Engineering: A Review on the Chemistry and Biological Functions

Stimuli responsive hydrogels (SRHs) are attractive bioscaffolds for tissue engineering. The structural similarity of SRHs to the extracellular matrix (ECM) of many tissues offers great advantages for a minimally invasive tissue repair. Among various potential applications of SRHs, cartilage regeneration has attracted significant attention. The repair of cartilage damage is challenging in orthopedics owing to its low repair capacity. Recent advances include development of injectable hydrogels to minimize invasive surgery with nanostructured features and rapid stimuli-responsive characteristics. Nanostructured SRHs with more structural similarity to natural ECM up-regulate cell-material interactions for faster tissue repair and more controlled stimuli-response to environmental changes. This review highlights most recent advances in the development of nanostructured or smart hydrogels for cartilage tissue engineering. Different types of stimuli-responsive hydrogels are introduced and their fabrication processes through physicochemical procedures are reported. The applications and characteristics of natural and synthetic polymers used in SRHs are also reviewed with an outline on clinical considerations and challenges.

On-demand drug delivery from local depots

Stimuli-responsive polymeric depots capable of on-demand release of therapeutics promise a substantial improvement in the treatment of many local diseases. These systems have the advantage of controlling local dosing so that payload is released at a time and with a dose chosen by a physician or patient, and the dose can be varied as disease progresses or healing occurs. Macroscale drug depot can be induced to release therapeutics through the action of physical stimuli such as ultrasound, electric and magnetic fields and light as well as through the addition of pharmacological stimuli such as nucleic acids and small molecules. In this review, we highlight recent advances in the development of polymeric systems engineered for releasing therapeutic molecules through physical and pharmacological stimulation.

Stimulus-responsive hydrogels: Theory, modern advances, and applications

Over the past century, hydrogels have emerged as effective materials for an immense variety of applications. The unique network structure of hydrogels enables very high levels of hydrophilicity and biocompatibility, while at the same time exhibiting the soft physical properties associated with living tissue, making them ideal biomaterials. Stimulus-responsive hydrogels have been especially impactful, allowing for unprecedented levels of control over material properties in response to external cues. This enhanced control has enabled groundbreaking advances in healthcare, allowing for more effective treatment of a vast array of diseases and improved approaches for tissue engineering and wound healing. In this extensive review, we identify and discuss the multitude of response modalities that have been developed, including temperature, pH, chemical, light, electro, and shear-sensitive hydrogels. We discuss the theoretical analysis of hydrogel properties and the mechanisms used to create these responses, highlighting both the pioneering and most recent work in all of these fields. Finally, we review the many current and proposed applications of these hydrogels in medicine and industry.

From Drug Dosage Forms to Intelligent Drug-delivery Systems: a Change of Paradigm

The design of new drug-delivery systems (DDSs) able to regulate the moment and the rate at which the release should take place, and even to target the drug to specific tissues and cell compartments, has opened novel perspectives to improve the efficacy and safety of the therapeutic treatments. Ideally, the drug should only have access to its site of action and the release should follow the evolution of the disease or of certain biorhythms. The advances in the DDSs field are possible because of a better knowledge of the physiological functions and barriers to the drug access to the action site, but also due to the possibility of having “active” excipients that provide novel features. The joint work in a wide range of disciplines, comprising materials science, biomedical engineering and pharmaceutical technology, prompts the design and development of materials (lipids, polymers, hybrids) that can act as sensors of physiological parameters or external variables, and as actuators able to trigger or tune the release process. Such smart excipients lead to an advanced generation of DDSs designed as intelligent or stimuli-responsive. This chapter provides an overview of how the progress in DDSs is intimately linked to the evolution of the excipients, understood as a specific category of biomaterials. The phase transitions, the stimuli that can trigger them and the mechanisms behind the performance of the intelligent DDSs are analyzed as a whole, to serve as an introduction to the topics that are comprehensively discussed in the subsequent chapters of the book. A look to the future is also provided.

Electro-responsive drug delivery from hydrogels

Precise control over the release of drug from devices implanted in the body, such as quantity, timing, is highly desirable in order to optimise drug therapy. In this paper, the research on electrically-responsive drug delivery is reviewed. Electrically-controllable drug release from polyelectrolyte hydrogels has been demonstrated in vitro and in vivo (in rats). Pulsatile drug release profiles, in response to alternating application and removal of the electric field have been achieved. Responsive drug release from hydrogels results from the electro-induced changes in the gels, which may deswell, swell or erode in response to an electric field. The mechanisms of drug release include ejection of the drug from the gel as the fluid phase synereses out, drug diffusion along a concentration gradient, electrophoresis of charged drugs towards an oppositely charged electrode and liberation of the entrapped drug as the gel complex erodes. Electrically-responsive drug release is influenced by a number of factors such as the nature of the drug and of the gel, the experimental set-up, magnitude of the electric field etc. In this paper, electrically-responsive hydrogels, response of gels to an electric field and electrically-stimulated drug release are discussed.

Implantable, polymeric systems for modulated drug delivery

The ability to deliver therapeutic agents to a patient in a pulsatile or staggered release profile has been a major goal in drug delivery research over the last two decades. This review will cover methods that have been developed to control drug delivery profiles with implantable polymeric systems. Externally and internally controlled systems will be discussed, spanning a range of technologies that include pre-programmed systems, as well as systems that are sensitive to modulated enzymatic or hydrolytic degradation, pH, magnetic fields, ultrasound, electric fields, temperature, light and mechanical stimulation. Implantable systems have the potential to improve the quality of life for patients undergoing therapy with a variable dosing regime by eliminating the need for multiple intravenous injections. Ideally, these systems would also result in increased patient compliance with a given therapy due to the relative ease of self-dosing.