Current challenges in non-invasive insulin delivery systems: a comparative review

Microemulsion-based approach for oral delivery of insulin: formulation design and characterization

Oral delivery of insulin provides a good alternative because it is non-invasive and patient-friendly. However, multiple challenges affected this route. To overcome barriers for oral delivery of insulin, we aimed to develop a novel insulin-loaded microemulsion system based on snail mucin for oral administration. The strategy in the novel system of using mucin loading insulin into the inner core of prepared water in oil microemulsion to provide sustained released, increased in vivo stability and enhanced drug absorption in the gastrointestinal tract. We report how microemulsion composed of varying ratios of snail mucin and Tween® 80 (1:9–9:1) using oil/water emulsion preparation method influenced insulin performance after oral administration. The results obtained include an encapsulation efficiency of above 70 %; in vitro release was sustained over 10 h and in vivo evaluations in diabetic rat model shows that insulin-loaded microencapsulation effectively reduced blood glucose levels over a period >8 h after oral administration. Therefore, we suggest that the developed formulation for oral insulin can be a promising alternative dosage form for oral protein delivery.

Polymeric nano-vesicles via intermolecular action to load and orally deliver insulin with enhanced hypoglycemic effect

Insulin (INS) was loaded into PEOP nano-vesicles via intermolecular actions and delivered orally through lymphatic transport with promising hypoglycemic effect.

Cholesterol moieties as building blocks for assembling nanoparticles to achieve effective oral delivery of insulin

The amphiphilic cholesterol-phosphate conjugate can fabricate into cholesterol-coated nanoparticles by reverse emulsion method. The nanoparticles generated a rapid-onset and long-lasting hypoglycemic effect following gavage in T1DM rats.

Exploring the mucoadhesive behavior of sucrose acetate isobutyrate: a novel excipient for oral delivery of biopharmaceuticals

Oral drug delivery is an attractive noninvasive alternative to injectables. However, oral delivery of biopharmaceuticals is highly challenging due to low stability during transit in the gastrointestinal tract (GIT), resulting in low systemic bioavailability. Thus, novel formulation strategies are essential to overcome this challenge. An interesting approach is increasing retention in the GIT by utilizing mucoadhesive biomaterials as excipients. Here, we explored the potential of the GRAS excipient sucrose acetate isobutyrate (SAIB) to obtain mucoadhesion in vivo. Mucoadhesive properties of a 90% SAIB/10% EtOH (w/w) drug delivery system (DDS) were assessed using a biosimilar mucus model and evaluation of rheological behavior after immersion in biosimilar intestinal fluid. To ease readability of this manuscript, we will refer to this as SAIB DDS. The effect of SAIB DDS on cell viability and epithelial membrane integrity was tested in vitro prior to in vivo studies that were conducted using SPECT/CT imaging in rats. When combining SAIB DDS with biosimilar mucus, increased viscosity was observed due to secondary interactions between biosimilar mucus and sucrose ester predicting considerable mucoadhesion. Mucoadhesion was confirmed in vivo, as radiolabeled insulin entrapped in SAIB DDS, remained in the small intestine for up to 22 h after administration. Moreover, the integrity of the system was investigated using the dynamic gastric model under conditions simulating the chemical composition of stomach fluid and physical shear stress in the antrum under fasted conditions. In conclusion, SAIB is an interesting and safe biomaterial to promote high mucoadhesion in the GIT after oral administration.

Nanoparticle Delivery Systems in the Treatment of Diabetes Complications

Diabetes mellitus, an incurable metabolic disease, is characterized by changes in the homeostasis of blood sugar levels, being the subcutaneous injection of insulin the first line treatment. This administration route is however associated with limited patient's compliance, due to the risk of pain, discomfort and local infection. Nanoparticles have been proposed as insulin carriers to make possible the administration of the peptide via friendlier pathways without the need of injection, i.e., via oral or nasal routes. Nanoparticles stand for particles in the nanometer range that can be obtained from different materials (e.g., polysaccharides, synthetic polymers, lipid) and are commonly used with the aim to improve the physicochemical stability of the loaded drug and thereby its bioavailability. This review discusses the use of different types of nanoparticles (e.g., polymeric and lipid nanoparticles, liposomes, dendrimers, niosomes, micelles, nanoemulsions and also drug nanosuspensions) for improved delivery of different oral hypoglycemic agents in comparison to conventional therapies.

Hydrogels For Peptide Hormones Delivery: Therapeutic And Tissue Engineering Applications

Peptides are the most abundant biological compounds in the cells that act as enzymes, hormones, structural element, and antibodies. Mostly, peptides have problems to move across the cells because of their size and poor cellular penetration. Therefore, a carrier that could transfer peptides into cells is ideal and would be effective for disease treatment. Until now, plenty of polymers, e.g., polysaccharides, polypeptides, and lipids were used in drug delivery. Hydrogels made from polysaccharides showed significant development in targeted delivery of peptide hormones because of their natural characteristics such as networks, pore sizes, sustainability, and response to external stimuli. The main aim of the present review was therefore, to gather the important usages of the hydrogels as a carrier in peptide hormone delivery and their application in tissue engineering and regenerative medicine.

The Why, Where, Who, How, and What of the vesicular delivery systems

Though vesicular delivery systems have been widely explored and reviewed, no comprehensive review exists that covers their development from the inception of the concept to its culmination in the form of regulated marketed formulations. With the advancement of scientific research in the field of nanomedicine, certain category of vesicular delivery systems have successfully reached the global market. Despite extensive research and highly encouraging results in a plethora of pathological conditions in the preclinical studies, translation of these nanomedicines from laboratory to market has been very limited. Aim of this review is to describe comprehensively the various colloidal delivery systems, focusing mainly on their conventional and advanced methods of preparation, different characterization techniques and main success stories of their journey from bench to bedside of the patient. The review also touches the finer nuances of the use of modern formulation approach of DoE (Design of Experiments) in their formulation and the status of regulatory guidelines for the approval of these nanomedicines.

Hydrogels Based Drug Delivery Synthesis, Characterization and Administration

Hydrogels represent 3D polymeric networks specially designed for various medical applications. Due to their porous structure, they are able to swollen and to entrap large amounts of therapeutic agents and other molecules. In addition, their biocompatibility and biodegradability properties, together with a controlled release profile, make hydrogels a potential drug delivery system. In vivo studies have demonstrated their effectiveness as curing platforms for various diseases and affections. In addition, the results of the clinical trials are very encouraging and promising for the use of hydrogels as future target therapy strategies.

Improving the hypoglycemic effect of insulin via the nasal administration of deep eutectic solvents

This study aimed to develop biocompatible deep eutectic solvents (DESs) as carriers for improving the nasal delivery of insulin. The DES was prepared from malic acid and choline chloride broadly used in foods, drugs, or cosmetics as biocompatible additives. The DES of choline chloride and malic acid (CM-DES) demonstrated lower melting point (-59.1 °C) and higher viscosity (120,000 cP) compared with hydrogels based on sodium carboxyl methyl cellulose (CMC-Na). The conformational structure of insulin does not change in CM-DES as characterized by circular dichroism. The in vitro results showed that CM-DES dissociated gradually but did not disintegrate immediately upon contact with water. CM-DES was able to improve the hypoglycemic effect of insulin significantly at different doses compared with hydrogels or solutions of insulin, which could be ascribed to facilitated penetration of insulin across the nasal epithelia by CM-DES. The hypoglycemic effect of CM-DES loading insulin at a dose of 25 IU/kg was similar to that of subcutaneous insulin at 1 IU/kg. In addition, no evident toxicity to nasal epithelia was observed after nasal administration to rats for seven consecutive days. In conclusion, CM-DES showed promising potential in enhancing the hypoglycemic effect of insulin via the nasal route.

Enhanced oral absorption of insulin using colon-specific nanoparticles co-modified with amphiphilic chitosan derivatives and cell-penetrating peptides

In this study, amphipathic chitosan derivative (ACS) and cell-penetrating peptide (CPP) co-modified colon-specific nanoparticles (CS-CPP NPs) were prepared and evaluated to improve the oral bioavailability of protein and peptide drugs. ACS modification was harnessed to protect CPPs from degradation in the stomach and small intestine after oral administration and achieve colon-specific drug delivery. After CS-CPP NPs reached the colon, ACSs on the surface of the NPs were gradually degraded and CPPs were exposed to bring into play the penetration efficacy in the colon epithelium. Herein, we synthesized four types of ACSs (TOCS, TDCS, TPCS and TSCS) and adopted three types of CPPs (Tat, Penetratin and R8) to prepare NPs (TOCS-Tat NPs, TDCS-Tat NPs, TPCS-Tat NPs, TSCS-Tat NPs, TDCS-Pen NPs and TDCS-R8 NPs). The study of the protective effects of ACS upon Tat showed that the modification of ACS exerted favourable protection upon Tat in the stomach and small intestine. ACS degradation in the colon was indirectly determined in the viscosity method, which indicated that ACS could be gradually degraded in the colon. Using Caco-2 cell monolayers as cell models, it was found that the cellular uptake amount and transcellular transportation performance of CS-CPP NPs were much enhanced compared with those of TDCS NPs and PVA NPs. With Bama mini-pigs as animal models, the pharmacodynamic study demonstrated that the hypoglycemic effect for insulin-loaded TDCS-Tat NPs was more significant than that for TDCS NPs, lowering the blood glucose by 40%. The pharmacokinetic study indicated that the AUC and Cmax for TDCS-Tat NPs were respectively increased by 1.45 times and 1.82 times compared with those of TDCS NPs. In conclusion, CS-CPP NPs as vehicles for colon-specific drug delivery systems may be an efficient approach to improve the oral absorption of protein and peptide drugs.

Magnetic nanocarriers: Evolution of spinel ferrites for medical applications

A valuable site-directed application in the field of nanomedicine is targeted drug delivery using magnetic metal oxide nanoparticles by applying an external magnetic field at the target tissue. The magnetic property of these structures allows controlling the orientation and location of particles by changing the direction of the applied external magnetic field. Pharmaceutical design and research in the field of nanotechnology offer novel solutions for diagnosis and therapies. This review summarizes magnetic nanoparticles and magnetic spinel ferrit's properties, remarkable approaches in magnetic liposomes, magnetic polymeric nanoparticles, MRI, hyperthermia and especially magnetic drug delivery systems, which have recently developed in the field of magnetic nanoparticles and their medicinal applications. Here, we discuss spinel ferrite (SF) as magnetic materials that are a significant class of composite metal oxides. They contain ferric ions and have the general structural formula M²⁺Fe₂³⁺O₄ (where M = Co,Ni,Zn,etc.). This structure indicates unique multifunctional properties, such as excellent magnetic characteristics, high specific surface area, surface active sites, high chemical stability, tuneable shape and size, and options for functionalization. The review assesses the current efforts on synthesis, properties and medical application of magnetic spinel ferrites nanoparticles based on cobalt, nickel and zinc. Based on this review, it can be concluded that MNPs and SFNPs have unlimited ability in biomedical applications. However, the practical application of SFNPs on a huge scale still needs to be considered and evaluated.

Polyglutamic Acid Functionalization of Chitosan Nanoparticles Enhances the Therapeutic Efficacy of Insulin Following Oral Administration

In the present study, stable chitosan nanoparticles (Ch-NPs) were developed using the ionotropic gelation method, where poly(sodium 4-styrenesulfonate) (PSS) was used as a cross-linking agent while polyglutamic acid (PGA) for functionalization to improve the oral uptake through calcium-sensing receptors and amino acid transporters present in intestinal epithelium. Formulation was optimized by the design of experiments (DoE) approach using a three-level central composite design and characterized for in vitro parameters such as morphology, particle size, polydispersity index (PDI), entrapment efficiency and zeta potential. Morphological analysis demonstrated the formation of spherical NPs with particle size, zeta potential, and entrapment efficiency in the range of 210 nm ± 2.8 nm, 18.1 mV ± 0.14 mV, and 85.9% ± 0.28%, respectively. The developed NPs exhibited sustained release at different pH conditions and almost threefold higher uptake in comparison with non-functionalized NPs in Caco-2 cell uptake studies. In vivo studies in diabetic animals demonstrated low levels of plasma glucose for almost 24 h. Pharmacological availability (PA) of insulin administered through Ch-PSS-PGA NPs (17.28 ± 0.9) was significantly higher as compared to that of insulin administered through control NPs, i.e., Ch-PGA NPs (10.9 ± 1.5) and Ch-PSS NPs (12.9 ± 1.8). Data on hand suggest the ability of the developed NPs in overcoming the poor stability and, thus, poor therapeutic efficacy following oral administration.

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.

Strategies for improving diabetic therapy via alternative administration routes that involve stimuli-responsive insulin-delivering systems

The encapsulation of insulin in micro- or nanodelivery systems may eliminate the need for frequent subcutaneous injections, improving the quality of life of diabetic patients. Formulations for oral, intranasal, pulmonary, subcutaneous, and transdermal administration have been developed. The use of stimuli-responsive polymeric carriers that can release the encapsulated drug in response to changes of the environmental stimuli or external activation enables the design of less invasive or non-invasive systems for smart insulin delivery from depots in the body. This article will look at strategies for the development of responsive delivery systems and the future meeting of the demands of new modes of insulin delivery.

Preparation, Optimization and In vitro Evaluation of Glipizide Nanoparticles Integrated with Eudragit RS-100

BACKGROUND

Solubility is an important criterion for drug efficacy, independent of the route of administration. It also poses a major challenge for pharmaceutical industries, which are developing new pharmaceutical products, since 40% of the active substances being identified are either insoluble or poorly soluble in aqueous media.

OBJECTIVE

The objective of this study was to develop nanoformulation of glipizide drugloaded nanoparticles providing controlled release formulation.

METHOD

Nanoparticles were prepared by the solvent evaporation method. Eudragit RS100, a nonbiodegradable polymer with varying ratios was used for making the formulation. The effect of key formulation variables on the particle size and entrapment efficiency and drug loading of nanoparticles were studied by using factorial design.

RESULTS

DSC thermograms indicate that glipizide was dispersed in an amorphous state in the polymer. TEM study indicates that the nanoparticles were in spherical shape. The mean diameter was dependent on the presence of the amount of Eudragit RS100 and viscosity of the organic phase. The in vitro study showed that the cumulative drug release was from 69.52-81.44 % in 10 hrs at pH 6.8 in phosphate buffer respectively.

CONCLUSION

The developed NPs could reduce dose frequency, decrease side effects, and improve patient compliance. Using factorial design, maximum entrapment efficiency with minimum particle size could be achieved with a few experiments.

Transdermal Evaporation Drug Delivery System: Concept to Commercial Products

Since two decades or so transdermal route established itself as better alternative to traditional oral route. This is possible due to continuous innovations in transdermal drug delivery (TDD), which not only enables researchers from academia and industry to successfully develop and launch many new pharmaceuticals but also allow to include new classes of drugs that can be developed into transdermal formulations. These successes are achieved due to the use of novel techniques based on either physical or chemical approaches. However, both of these techniques suffer due to their own disadvantages. Comparatively, a simple method of supersaturation to enhance drug permeation across skin has created a new wave of interest. Even though the application supersaturated principle in topical and TDD has been used from 1960s, but proper control of drug release and formation of stable supersaturated states has been the core of intense research in the last decade. Out of various methods used to get supersaturated system, evaporation method is considered as most efficient and practically feasible for TDD. Therefore, in this review concept of supersaturation, selection of solvent system and the mechanism of inhibition of crystallization are discussed. Application of evaporation systems in the development of transdermal formulations such as solutions, semisolids and metered dose therapeutic systems (MDTS) and the commercial evaporative systems are also discussed in this review.

Nitrilotriacetic Acid-Functionalized Glucose-Responsive Complex Micelles for the Efficient Encapsulation and Self-Regulated Release of Insulin

Insulin plays a significant role in diabetes treatment. Although a huge number of insulin-loaded, glucose-responsive nanocarriers have been developed in past decades, most of them showed a lower loading capacity and efficiency due to the weak interaction between insulin and nanocarriers. In this work, a novel insulin-encapsulated glucose-responsive polymeric complex micelle (CM) is devised, showing (i) enhanced insulin-loading efficiency owing to the zinc ions' chelation by nitrilotriacetic acid (NTA) groups of NTA-functioned glycopolymer and the histidine imidazole of insulin, (ii) the glucose-triggered pulse release of insulin, and (iii) long stability under physiological conditions. This CM was fabricated by the self-assembly of block copolymer PEG- b-P(Asp- co-AspPBA) and glycopolymer P(Asp- co-AspGA- co-AspNTA), resulting in complex micelles with a PEG shell and a cross-linked core composed of phenylboronic acid (PBA)/glucose complexations. Notably, the modified nitrilotriacetic acid (NTA) groups of CM could specifically bind insulin via chelated zinc ions, thus enhancing the loading efficacy of insulin compared to that of nonmodified CM. The dynamic PBA/glucose complexation core of CM dissociates under the trigger of high glucose concentration (>2 g/L) while being quite stable in low glucose concentrations (<2 g/L), as demonstrated by the pulse release of insulin in vitro. Finally, in a murine model of type 1 diabetes, NTA-modified complex micelles loading an insulin (NTA-CM-INS) group exhibited a long hypoglycemic effect which is superior to that of free insulin in the PBS (PBS-INS) group and insulin-loaded complex micelles without an NTA modification (CM-INS) group. This long-term effect benefited from Zn(II) chelation by NTA-modified complex micelles and could avoid hypoglycemia caused by the burst release of insulin. Taken together, this constitutes a highly effective way to encapsulate insulin and release insulin via an on-demand manner for blood glucose control in diabetes.

Combination Strategy with Complexation Hydrogels and Cell-Penetrating Peptides for Oral Delivery of Insulin

In previous studies we showed that the complexation hydrogels based in poly(methacrylic acid-g-ethylene glycol) [P(MAA-g-EG)] rapidly release insulin in the intestine owing to their pH-dependent complexation properties; they also exhibit a high insulin-loading efficiency, enzyme-inhibiting properties, and mucoadhesive characteristics. Cell-penetrating peptides (CPPs), such as oligoarginines [hexa-arginine (R6), comprising six arginine residues], have been employed as useful tools for the oral delivery of therapeutic macromolecules. The aim of our study was to investigate the combination strategy of using P(MAA-g-EG) hydrogels with R6-based CPPs to improve the intestinal absorption of insulin. A high efficiency of loading into crosslinked P(MAA-g-EG) hydrogels was observed for insulin (96.1±1.4%) and R6 (46.6±3.8%). In addition, immediate release of the loaded insulin and R6 from these hydrogels was observed at pH 7.4 (80% was released in approximately 30 min). Consequently, a strong hypoglycemic response was observed (approximately 18% reduction in blood glucose levels) accompanied by an improvement in insulin absorption after the co-administration of insulin-loaded particles (ILP) and R6-loaded particles (ALP) into closed rat ileal segments compared with that after ILP administration alone. These results indicate that the combination of P(MAA-g-EG) hydrogels with CPPs may be a promising strategy for the oral delivery of various insulin preparations as an alternative to conventional parenteral routes.

Synthesis and characterization of a novel peptide-grafted Cs and evaluation of its nanoparticles for the oral delivery of insulin, in vitro, and in vivo study

Background

Despite years of experience and rigorous research, injectable insulin is the sole trusted treatment method to control the blood glucose level in diabetes type 1 patients, but injection of insulin is painful and poses a lot of stress to the patients, especially children, therefore, development of a non-injectable formulation of insulin is a major breakthrough in the history of medicine and pharmaceutical sciences.

Methods

In this study, a novel peptide grafted derivative of chitosan (CPP-g- chitosan) is synthesized and its potential for oral delivery of proteins and peptides is evaluated. Drug-loaded nanoparticles were developed from this derivative using ionic gelation method with application of sodium tripolyphosphate (TPP) as a cross-linking agent. Human insulin was used as the model protein drug and release kinetic was studied at gastrointestinal pH. Finally the developed nanoparticles were filled into very tiny enteric protective capsules and its effects on blood glucose level are evaluated in laboratory animals.

Results

Presence of the positively charged cell-penetrating peptide moiety in the structure of chitosan polymer had slight inhibitory effects on the release of insulin from the nanoparticles in simulated gastric fluid (pH 1.2) comparing to native chitosan. The nanoparticles were positively charged in gastrointestinal pH with size ranging from 180 nm to 326 nm. The polypeptide grafted to chitosan is a novel analog of Penetratin, presenting both the hydrophilic and hydrophobic characteristics altering the release behavior of the nanoparticles and significantly increase the absorption of insulin into the rat epithelium comparing to nanoparticles from simple chitosan. In-vivo results in diabetic rat proved that this nanoparticulate system can significantly lower the blood glucose levels in diabetic rats and remain effective for a duration of 9–11 hours.

Conclusion

The results indicate that nanoparticles developed from this new peptide conjugated derivative of chitosan are very promising for oral delivery of proteins and peptides.

Safety of intranasal human insulin: A review

AIMS

To conduct a review in order to assess the safety of intranasal human insulin in clinical studies as well as the temporal stability of nasal insulin sprays.

MATERIAL AND METHODS

An electronic search was performed using MEDLINE. We selected original research on intranasal human insulin without further additives in humans. The studies included could be of any design as long as they used human intranasal insulin as their study product. All outcomes and adverse side effects were extracted.

RESULTS

A total of 38 studies in 1092 individuals receiving acute human intranasal insulin treatment and 18 studies in 832 individuals receiving human intranasal insulin treatment lasting between 21 days and 9.7 years were identified. No cases of symptomatic hypoglycaemia or severe adverse events (AEs) were reported. Transient local side effects in the nasal area were frequently experienced after intranasal insulin and placebo spray, while other AEs were less commonly reported. There were no reports of participants being excluded as a result of AEs. No instances of temporal stability of nasal insulin were reported in the literature. Tests on insulin that had been repacked into spray flasks showed that it had a chemical stability of up to 57 days.

CONCLUSIONS

Our retrospective review of published studies on intranasal insulin did not reveal any safety concerns; however, there were insufficient data to ensure the long-term safety of this method of chronic insulin administration. Improved insulin preparations that cause less nasal irritation would be desirable for future treatment.

Glucose- and H2O2-Responsive Polymeric Vesicles Integrated with Microneedle Patches for Glucose-Sensitive Transcutaneous Delivery of Insulin in Diabetic Rats

Herein, a dual-responsive insulin delivery device by integrating glucose- and H₂O₂-responsive polymeric vesicles (PVs) with transcutaneous microneedles (MNs) has been designed. This novel microneedle delivery device achieves a goal of fast response, excellent biocompatibility, and painless administration. The PVs are self-assembled from a triblock copolymer including poly(ethylene glycol), poly(phenylboronic acid) (glucose-sensitive block), and poly(phenylboronic acid pinacol ester) (H₂O₂-sensitive block). After loading with insulin and glucose oxidase (GO _x), the drug-loaded PVs display a basal insulin release as well as a promoted insulin release in response to hyperglycemic states. The insulin release rate responds quickly to elevated glucose and can be further promoted by the incorporated GO _x, which will generate the H₂O₂ at high glucose levels and further break the chemical links of phenylboronic acid pinacol ester group. Finally, the transdermal delivery of insulin to the diabetic rats ((insulin + GO _x)-loaded MNs) presents an effective hypoglycemic effect compared to that of subcutaneous injection or only insulin-loaded MNs, which indicates the as-prepared MNs insulin delivery system could be of great importance for the applications in the therapy of diabetes.

Delivering natural products and biotherapeutics to improve drug efficacy

Due to the increasing problem of drug resistance, new and improved medicines are required. Natural products and biotherapeutics offer a vast resource for new drugs; however, challenges, including the cost and time taken for traditional drug discovery processes and the subsequent lack of investment from the pharmaceutical industry, are associated with these areas. New techniques are producing compounds with appropriate activity at a faster rate. While the formulation of these combined with drug-delivery systems offers a promising approach for expanding the drug developments available to modern medicine. Here, various classes of drug-delivery systems are described and the advantages they bring to small molecule and biotherapeutic targeting are highlighted. This is an attractive approach to the pharmaceutical industry and the rising trend in research in this area is examined in brief. [Formula: see text].

Biomimetic Viruslike and Charge Reversible Nanoparticles to Sequentially Overcome Mucus and Epithelial Barriers for Oral Insulin Delivery

Nanoparticles (NPs) for oral delivery of peptide/protein drugs are largely limited due to the coexistence of intestinal mucus and epithelial barriers. Sequentially overcoming these two barriers is intractable for a single nanovehicle due to the requirements of different or even contradictory surface properties of NPs. To solve this dilemma, a mucus-penetrating virus-inspired biomimetic NP with charge reversal ability (P-R8-Pho NPs) was developed by densely coating poly(lactic- co-glycolic acid) NPs with cationic octa-arginine (R8) peptide and specific anionic phosphoserine (Pho). The small size (81.81 nm) and viruslike neutral charged surface (-2.39 mV) of the biomimetic NPs achieved rapid mucus penetration, which was almost equal to that of the conventional PEGylated mucus-penetrating nanoparticles. The hydrolysis of surface-anchored anionic Pho was achieved by intestinal alkaline phosphatase, which led to the turnover of ζ potential to positive (+7.37 mV). This timely charge reversal behavior also exposed cationic R8 peptide and induced efficient cell-penetrating peptide (CPP)-mediated cellular uptake and transepithelial transport on Caco-2/E12 cocultured cell model. What's more, P-R8-Pho NPs showed excellent stability in simulated gastrointestinal conditions and enhanced absorption in intestine in vivo. Finally, oral administration of insulin-loaded P-R8-Pho NPs enabled to induce a preferable hypoglycemic effect and a 1.9-fold higher oral bioavailability was achieved compared with single CPP-modified P-R8 NPs on diabetic rats. The combinative application of biomimetic mucus-penetrating strategy and enzyme-responsive charge reversal strategy in a single nanovehicle could sequentially overcome mucus and epithelial barriers, thus showing great potential for the oral peptide/protein delivery.

Insulin delivery systems combined with microneedle technology

Diabetes, a metabolic disorder of glucose, is a serious chronic disease and an important public health problem. Insulin is one of the hormones for modulating blood glucose level and the products of which is indispensable for most diabetes patients. Introducing microneedles (MNs) to insulin delivery is promising to pave the way for modulating glucose level noninvasively of diabetes patients, as which born to be painless, easy to handle and no need of any power supply. In this work, we review the process of insulin delivery systems (IDSs) based on MN technology in terms of two categories: drug free MNs and drug loaded MNs. Drug free MNs include solid MNs ("poke and patch"), hollow MNs ("poke and flow") and reservoir-based swelling MNs ("poke and swell R-type"), and drug loaded MNs include coated MNs ("coat and poke"), dissolving MNs ("poke and release") and insulin incorporated swelling MNs ("poke and swell I-type"). Majority researches of MN-based IDSs have been conducted by using hollow MNs or dissolving MNs, and almost all clinical trials for MN-based IDSs have employed hollow MNs. "Poke and patch" approach dramatically increase skin permeability compared to traditional transdermal patch, but MNs fabricated from silicon or metal may leave sharp waste in the skin and cause a safety issue. "Poke and flow" approach, similar to transitional subcutaneous (SC) injection, is capable of producing faster insulin absorption and action than SC injection but may associate with blockage, leakage and low flow rate. Coated MNs are able of retaining the activity of drug, which loaded in a solid phase, for a long time, however have been relatively less studied for insulin application as the low drug dosing. "Poke and release" approach leaves no biohazardous sharp medical waste and is capable of rapid drug release. "Poke and swell R-type" can be seen as a combination of "poke and flow" and "poke and patch" approach, while "poke and swell I-type" is an approach between "coat and poke" and "poke and release" approach. Insulin MNs are promising for painless diabetes therapeutics, and additional efforts for addressing fundamental issues including the drug loading, the PK/PD profile, the storage and the safety of insulin MNs will accelerate the clinical transformation.

Hydrogels for Hydrophobic Drug Delivery. Classification, Synthesis and Applications

Hydrogels have been shown to be very useful in the field of drug delivery due to their high biocompatibility and ability to sustain delivery. Therefore, the tuning of their properties should be the focus of study to optimise their potential. Hydrogels have been generally limited to the delivery of hydrophilic drugs. However, as many of the new drugs coming to market are hydrophobic in nature, new approaches for integrating hydrophobic drugs into hydrogels should be developed. This article discusses the possible new ways to incorporate hydrophobic drugs within hydrogel structures that have been developed through research. This review describes hydrogel-based systems for hydrophobic compound delivery included in the literature. The section covers all the main types of hydrogels, including physical hydrogels and chemical hydrogels. Additionally, reported applications of these hydrogels are described in the subsequent sections.

Microparticles, microcapsules and microspheres: A review of recent developments and prospects for oral delivery of insulin

Diabetes mellitus is a chronic metabolic health disease affecting the homeostasis of blood sugar levels. However, subcutaneous injection of insulin can lead to patient non-compliance, discomfort, pain and local infection. Sub-micron sized drug delivery systems have gained attention in oral delivery of insulin for diabetes treatment. In most of the recent literature, the terms "microparticles" and "nanoparticle" refer to particles where the dimensions of the particle are measured in micrometers and nanometers respectively. For instance, insulin-loaded particles are defined as microparticles with size larger than 1 μm by most of the research groups. The size difference between nanoparticles and microparticles proffers numerous effects on the drug loading efficiency, aggregation, permeability across the biological membranes, cell entry and tissue retention. For instance, microparticulate drug delivery systems have demonstrated a number of advantages including protective effect against enzymatic degradation, enhancement of peptide stability, site-specific and controlled drug release. Compared to nanoparticulate drug delivery systems, microparticulate formulations can facilitate oral absorption of insulin by paracellular, transcellular and lymphatic routes. In this article, we review the current status of microparticles, microcapsules and microspheres for oral administration of insulin. A number of novel techniques including layer-by-layer coating, self-polymerisation of shell, nanocomposite microparticulate drug delivery system seem to be promising for enhancing the oral bioavailability of insulin. This review draws several conclusions for future directions and challenges to be addressed for optimising the properties of microparticulate drug formulations and enhancing their hypoglycaemic effects.

Functional nanocarrier for drug and gene delivery via local administration in mucosal tissues

Local administration has many advantages for treating diseases. However, the surface mucus layer becomes a major obstacle that easily traps and fast removes local administrated drugs and genes in mucosal tissues. Fortunately, the rapidly developing nanocarriers with special physical and chemical properties may help to refine the treatment of mucosal tissues via delivering drugs and genes to the target tissue, and prolong the drug action time. Therefore, this review focuses on the strategies to apply different nanocarriers for drug-delivery in mucosal tissues, including mucoadhesive and mucus-penetrating types. Delivering drugs and genes to anatomical sites with high mucus turnover becomes more feasible and effective, and maintains sufficient local drug concentration to improve treatment efficacy.

Novel bilayer dissolving microneedle arrays with concentrated PLGA nano-microparticles for targeted intradermal delivery: Proof of concept

Polymeric microneedle (MN) arrays continue to receive growing attention due to their ability to bypass the skin's stratum corneum barrier in a minimally-invasive fashion and achieve enhanced transdermal drug delivery and "targeted" intradermal vaccine administration. In this research work, we fabricated biodegradable bilayer MN arrays containing nano - microparticles for targeted and sustained intradermal drug delivery. For this study, model drug (vitamin D₃, VD₃)-loaded PLGA nano- and microparticles (NMP) were prepared by a single emulsion solvent evaporation method with 72.8% encapsulation of VD₃. The prepared NMP were directly mixed 20% w/v poly(vinyl pyrrolidone) (PVP) gel, with the mixture filled into laser engineered micromoulds by high-speed centrifugation (30min) to concentrate NMP into MN shafts. The particle size of PLGA NMP ranged from 300nm to 3.5μm and they retained their particle size after moulding of bilayer MN arrays. The relatively wide particle size distribution of PLGA NMP was shown to be important in producing a compact structure in bilayer conical, as well as pyramidal, MN, as confirmed by scanning electron microscopy. The drug release profile from PLGA NMP was tri-phasic, being sustained over 5days. The height of bilayer MN arrays was influenced by the weight ratio of NMP and 20% w/v PVP. Good mechanical and insertion profiles (into a skin simulant and excised neonatal porcine skin) were confirmed by texture analysis and optical coherence tomography, respectively. Ex vivo intradermal neonatal porcine skin penetration of VD₃ NMP from bilayer MN was quantitatively analysed after cryostatic skin sectioning, with 74.2±9.18% of VD₃ loading delivered intradermally. The two-stage novel processing strategy developed here provides a simple and easy method for localising particulate delivery systems into dissolving MN. Such systems may serve as promising means for controlled transdermal delivery and targeted intradermal administration.

Electrostatic Self-Assembled Chitosan-Pectin Nano- and Microparticles for Insulin Delivery

A polyelectrolyte complex system of chitosan-pectin nano- and microparticles was developed to encapsulate the hormone insulin. The aim of this work was to obtain small particles for oral insulin delivery without chemical crosslinkers based on natural and biodegradable polysaccharides. The nano- and microparticles were developed using chitosans (with different degrees of acetylation: 15.0% and 28.8%) and pectin solutions at various charge ratios (n⁺/n^- given by the chitosan/pectin mass ratio) and total charge. Nano- and microparticles were characterized regarding particle size, zeta potential, production yield, encapsulation efficiency, stability in different media, transmission electron microscopy and cytotoxicity assays using Caco-2 cells. The insulin release was evaluated in vitro in simulated gastric and intestinal media. Small-sized particles (~240-~1900 nm) with a maximum production yield of ~34.0% were obtained. The highest encapsulation efficiency (~62.0%) of the system was observed at a charge ratio (n⁺/n^-) 5.00. The system was stable in various media, particularly in simulated gastric fluid (pH 1.2). Transmission electron microscopy (TEM) analysis showed spherical shape particles when insulin was added to the system. In simulated intestinal fluid (pH 6.8), controlled insulin release occurred over 2 h. In vitro tests indicated that the proposed system presents potential as a drug delivery for oral administration of bioactive peptides.

Binary and Tertiary Complex Based on Short-Chain Glucan and Proanthocyanidins for Oral Insulin Delivery

The present study was performed to investigate binary and tertiary nanocomposites between short-chain glucan (SCG) and proanthocyanidins (PAC) for the oral delivery of insulin. There was a large decrease in fluorescence intensity of insulin in the presence of SCG or the combination of SCG with PAC. Fourier transform infrared spectroscopy revealed that the binary and tertiary nanocomposites were synthesized due to the hydrogen bonding and hydrophobic interactions. The insulin entrapped in the nanocomposites was in an amorphous state confirmed by X-ray diffraction. The cell culture demonstrated that both the nanocomposites showed no detectable cytotoxicity with relative cell viability all above 85%. The pharmacological bioavailability after oral administration of insulin-SCG-PAC at a dose of 100 IU/kg was found to be 6.98 ± 1.20% in diabetic rats without any sharp fluctuations in 8 h.

Squid suckerin microneedle arrays for tunable drug release

Microneedles are increasingly used in transdermal delivery of therapeutic agents due to the elimination of first-pass metabolism, simplicity of operation, and lack of pain, which collectively lead to improved patient compliance. However, microneedles are still met by challenges with regard to the choice of biocompatible materials and the control of drug release profiles. Herein, we tackle these limitations by producing microneedles from a biocompatible robust biopolymer, namely squid sucker ring teeth (SRT) proteins (suckerins), using a soft lithography method. Taking advantage of the modular sequence design of suckerins leading to their self-assembly into β-sheet enriched structures, suckerin microneedles display an accurate replication of their templates with robust mechanical properties, endowing them with a high skin penetration capability. Critically, the β-sheet content in the microneedles can be modulated by varying the solvent conditions, which allows tuning of the mechanical response, and in turn the drug release rates by more than one order of magnitude. In vitro skin permeation studies of suckerin microneedles using human cadaver skin samples suggest a fast onset and enhanced skin permeation of drugs compared to flat patches. The skin permeation can also be tailored 10-fold by applying hydrogen bond disruptor solutions. As a proof-of-concept, the anti-bacterial drug kanamycin is encapsulated within the microneedles, leading to efficient anti-bacterial activity and offering an additional benefit to further minimize the risk of infections caused by microneedle-based drug delivery systems. Lastly, suckerin microneedles are found to be biocompatible in cell culture studies, opening the door to further clinical applications.