Biodegradable Injectable In Situ Depot-Forming Drug Delivery Systems

Exploring the Frontier of Biopolymer-Assisted Drug Delivery: Advancements, Clinical Applications, and Future Perspectives in Cancer Nanomedicine

The burgeoning global mortality rates attributed to cancer have precipitated a critical reassessment of conventional therapeutic modalities, most notably chemotherapy, due to their pronounced adverse effects. This reassessment has instigated a paradigmatic shift towards nanomedicine, with a particular emphasis on the potentialities of biopolymer-assisted drug delivery systems. Biopolymers, distinguished by their impeccable biocompatibility, versatility, and intrinsic biomimetic properties, are rapidly ascending as formidable vectors within the cancer theragnostic arena. This review endeavors to meticulously dissect the avant-garde methodologies central to biopolymer-based nanomedicine, exploring their synthesis, functional mechanisms, and subsequent clinical ramifications. A key focus of this analysis is the pioneering roles and efficacies of lipid-based, polysaccharide, and composite nano-carriers in enhancing drug delivery, notably amplifying the enhanced permeation and retention effect. This examination is further enriched by referencing flagship nano formulations that have received FDA endorsement, thereby underscoring the transformative potential and clinical viability of biopolymer-based nanomedicines. Furthermore, this discourse illuminates groundbreaking advancements in the realm of photodynamic therapy and elucidates the implications of advanced imaging techniques in live models. Conclusively, this review not only synthesizes current research trajectories but also delineates visionary pathways for the integration of cutting-edge biomaterials in cancer treatment. It charts a course for future explorations within the dynamic domain of biopolymer-nanomedicine, thereby contributing to a deeper understanding and enhanced application of these novel therapeutic strategies.

Construction and evaluation of a phospholipid-based phase transition in situ gel system for brexpiprazole

The objective of this study was to develop phospholipid-based injectable phase transition in situ gels (PTIGs) for the sustained release of Brexpiprazole (Brex). Phospholipid (Lipoid S100, S100) and stearic acid (SA) were used as the gel matrix which was dissolved in biocompatible solvent medium-chain triglyceride (MCT), N-methyl pyrrolidone (NMP), and ethanol to obtain PTIGs solution. The Brex PTIG showed a solution condition of low viscosity in vitro and was gelatinized in situ in vivo after subcutaneous injection. Both in vitro release assay and in vivo pharmacokinetics study in SD rats displayed that Brex in PTIGs could achieve a sustained release, compared with brexpiprazole solution (Brex-Sol) or brexpiprazole suspension (Brex-Sus). The Brex-PTIGs had good degradability and biocompatibility in vivo with rare inflammation at the injection site. Among the three Brex-PTIG formulations, Brex-PTIG-3 with the SA in the formulation had the greatest gelation viscosity, the lowest initial release rate, and the most stable release profile with sustained release of up to 60 days. The above results indicated that, as a novel drug delivery system, the Brex-PTIGs offered a new option for the clinical treatment of patients with schizophrenia.

Effects of extended-release 7-nitroindazole gel formulation treatment on the behavior of Shank3 mouse model of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by behavioral deficits such as abnormalities in communication, social interaction, anxiety, and repetitive behavior. We have recently shown that the Shank3 mutation in mice representing a model of ASD causes excessive nitric oxide (NO) levels and aberrant protein S-nitrosylation. Further, 10-day daily injections of 7-NI, a neuronal nitric oxide synthase inhibitor, into Shank3Δ4-22 and Cntnap2(-/-) mutant mice (models of ASD) at a dose of 80 mg/kg reversed the manifestations of ASD phenotype. In this study, we proposed an extended release of 7-NI using a novel drug system. Importantly, unlike the intraperitoneal injections, our new preparation of poly (sebacic acid-co-ricinoleic acid) (PSARA) gel containing 7-NI was injected subcutaneously into the mutant mice only once. The animals underwent behavioral testing starting from day 3 post-injection. It should be noted that the developed PSARA gel formulation allowed a slow release of 7-NI maintaining the plasma level of the drug at ∼45 μg/ml/day. Further, we observed improved memory and social interaction and reduced anxiety-like behavior in Shank3 mutant mice. This was accompanied by a reduction in 3-nitrotyrosine levels (an indicator of nitrative/nitrosative stress) in plasma. Overall, we suggest that our single-dose formulation of PSARA gel is very efficient in rendering a therapeutic effect of 7-NI for at least 10 days. This approach may provide in the future a rational design of an effective ASD treatment using 7-NI and its clinical translation.

Advancement in Biopolymer Assisted Cancer Theranostics

Applications of nanotechnology have increased the importance of research and nanocarriers, which have revolutionized the method of drug delivery to treat several diseases, including cancer, in the past few years. Cancer, one of the world's fatal diseases, has drawn scientists' attention for its multidrug resistance to various chemotherapeutic drugs. To minimize the side effects of chemotherapeutic agents on healthy cells and to develop technological advancement in drug delivery systems, scientists have developed an alternative approach to delivering chemotherapeutic drugs at the targeted site by integrating it inside the nanocarriers like synthetic polymers, nanotubes, micelles, dendrimers, magnetic nanoparticles, quantum dots (QDs), lipid nanoparticles, nano-biopolymeric substances, etc., which has shown promising results in both preclinical and clinical trials of cancer management. Besides that, nanocarriers, especially biopolymeric nanoparticles, have received much attention from researchers due to their cost-effectiveness, biodegradability, treatment efficacy, and ability to target drug delivery by crossing the blood-brain barrier. This review emphasizes the fabrication processes, the therapeutic and theragnostic applications, and the importance of different biopolymeric nanocarriers in targeting cancer both in vitro and in vivo, which conclude with the challenges and opportunities of future exploration using biopolymeric nanocarriers in onco-therapy with improved availability and reduced toxicity.

Polymeric in situ forming depots for long-acting drug delivery systems

Polymeric in situ forming depots have emerged as highly promising drug delivery systems for long-acting applications. Their effectiveness is attributed to essential characteristics such as biocompatibility, biodegradability, and the ability to form a stable gel or solid upon injection. Moreover, they provide added versatility by complementing existing polymeric drug delivery systems like micro- and nanoparticles. The formulation's low viscosity facilitates manufacturing unit operations and enhances delivery efficiency, as it can be easily administered via hypodermic needles. The release mechanism of drugs from these systems can be predetermined using various functional polymers. To enable unique depot design, numerous strategies involving physiological and chemical stimuli have been explored. Important assessment criteria for in situ forming depots include biocompatibility, gel strength and syringeability, texture, biodegradation, release profile, and sterility. This review focuses on the fabrication approaches, key evaluation parameters, and pharmaceutical applications of in situ forming depots, considering perspectives from academia and industry. Additionally, insights about the future prospects of this technology are discussed.

Smart stimuli-responsive hydrogels for drug delivery in periodontitis treatment

Periodontitis is a chronic inflammatory disease initiated by pathogenic biofilms and host immunity that damages tooth-supporting tissues, including the gingiva, periodontal ligament and alveolar bone. The physiological functions of the oral cavity, such as saliva secretion and chewing, greatly reduce the residence of therapeutic drugs in the area of a periodontal lesion. In addition, complex and diverse pathogenic mechanisms make effectively treating periodontitis difficult. Therefore, designing advanced local drug delivery systems and rational therapeutic strategies are the basis for successful periodontitis treatment. Hydrogels have attracted considerable interest in the field of periodontitis treatment due to their biocompatibility, biodegradability and convenient administration to the periodontal pocket. In recent years, the focus of hydrogel research has shifted to smart stimuli-responsive hydrogels, which can undergo flexible sol-gel transitions in situ and control drug release in response to stimulation by temperature, light, pH, ROS, glucose, or enzymes. In this review, we systematically introduce the development and rational design of emerging smart stimuli-responsive hydrogels for periodontitis treatment. We also discuss the state-of-the-art therapeutic strategies of smart hydrogels based on the pathogenesis of periodontitis. Additionally, the challenges and future research directions of smart hydrogels for periodontitis treatment are discussed from the perspective of developing efficient hydrogel delivery systems and potential clinical applications.

Silk fibroin based interpenetrating network hydrogel for corneal stromal regeneration

There is a need to develop tissue engineering based approaches to address the shortage of donor corneas worldwide for transplantation. To do this a novel approach to fabricate three-dimensional hydrogels using free-radical polymerization was investigated to generate constructs for corneal stromal tissue regeneration. Different ratios of silk fibroin (SF) to polyacrylamide (PA) were used to fabricate semi-interpenetrating hydrogels. Scanning electron micrograph displayed the interconnectivity of pores within the fabricated hydrogels. Pore sizes ranged from 25 to 66 μm. Scaffolds with increasing concentration of SF had enhanced β-sheet structure (verified by Fourier transform infrared spectroscopy). The biological response of human corneal stromal cells to these hydrogels was examined using cellular adhesion, proliferation, cytoskeleton organization, gene expression and immunocytochemical analysis. The fabricated hydrogels possess rapid gelation (∼3 min) at 37 °C, 84 % porosity facilitating keratocyte migration during healing, improved cellular adhesion and no cytotoxicity, indicating their efficiency for in-situ corneal tissue regeneration. Presence of SF in semi-interpenetrating network hydrogel enhanced cellular proliferation, elevated GAG deposition, and increased expression of keratocyte genes, normally associated with healthy corneal stromal tissue. This study acts as an initial step towards fabricating SF based semi-interpenetrating network hydrogels for developing clinically applicable ocular implants.

Sustained drug delivery strategies for treatment of common substance use disorders: Promises and challenges

Substance use disorders (SUDs) are a leading cause of death and other ill health effects in the United States and other countries in the world. Several approaches ranging from detoxification, behavioral therapy, and the use of antagonists or drugs with counter effects are currently being applied for its management. Amongst these, drug therapy is the mainstay for some drug abuse incidences, as is in place specifically for opioid abuse or alcohol dependence. The severity of the havocs observed with the SUDs has triggered constant interest in the discovery and development of novel medications as well as suitable or most appropriate methods for the delivery of these agents. The chronic need of such drugs in users warrants the need for their prolonged or sustained systemic availability. Further, the need to improve patient tolerance to medication, limit invasive drug use and overall treatment outcome are pertinent considerations for embracing sustained release designs for medications used in managing SUDs. This review aims to provide an overview on up-to-date advances made with regards to sustained delivery systems for the drugs for treatment of different types of SUDs such as opioid, alcohol, tobacco, cocaine, and cannabis use disorders. The clinical relevance, promises and the limitations of deployed sustained release approaches along with future opportunities are discussed.

In-situforming drug-delivery systems for periodontal treatment: current knowledge and perspectives

Several chemical compounds are considered to be promising as adjuvants in the treatment of periodontitis. Antimicrobials, anti-inflammatory drugs or, more recently, pro-regenerative or antioxidant molecules have shown a very interesting potential to improve the outcomes of mechanical biofilm removal and promote the healing of the damaged tissues. However, their clinical effect is often limited by the challenge of achieving effective and prolonged drug delivery within the periodontal lesion, while limiting the risk of toxicity.In-situforming implants (ISFI) are 'implantable' drug-delivery systems that have gained considerable attention over the last few decades due to their multiple biomedical applications. They are liquids that, when injected at the site to be treated, form a semi-solid or solid dosage form that provides safe and locally controlled drug release. This review discusses current data and future prospects for the use of ISFI in periodontal treatment.

What do we know about the mechanisms of action of probiotics on factors involved in the pathogenesis of periodontitis? A scoping review of in vitro studies

OBJECTIVE

Probiotics are increasingly used in oral prevention and treatment conditions, but little is known about their abilities. The aim of this review is to clarify, summarize and disseminate current knowledge about the mode of action of in vitro probiotics on factors involved in the pathogenesis of periodontitis.

METHOD

2495 articles were identified in three databases (Medline, Web of Science, SpringerLink) and 26 studies included in this scoping review.

RESULTS

Twenty-three probiotic species were identified, the majority of which were Lactobacilli or Bifidobacteria. Lactobacillus rhamnosus (30.8 %) and Lactobacillus reuteri (42.3 %) were found to be the two predominantly studied probiotic species and three main mechanisms of action of probiotics could be classified as: (i) modulation of the immuno-inflammatory response, (ii) direct actions of probiotics on periodontopathogens by adhesion or nutritive competitions and/or the secretion of antimicrobial molecules and (iii) indirect actions through environmental modifications. A combination of several probiotic strains seems to be beneficial via synergistic action amplifying the functions of each strain used. However, heterogeneity of the methodologies and probiotic species included in studies leads us to consider the following avenues for future research: (i) implementation of standardized periodontal models as close as possible to in vivo periodontal conditions to identify the functions of each strain for appropriate medication, (ii) updating data about interactions within oral biofilms to identify new candidates and to predict then analyze their behavior within these biofilms.

CONCLUSION

Probiotics may have their place in the response to inter-individual variability in periodontitis, provided that the choice of the probiotic strain or combination of them will be personalized and optimal for each patient.

In Situ-Forming Microparticles for Controlled Release of Rivastigmine: In Vitro Optimization and In Vivo Evaluation

In this work, sucrose acetate isobutyrate (SAIB) and polylactic co-glycolic acid (PLGA) were used alone or in combination as a matrix-former (MF) to prepare long-acting injectable rivastigmine (RV) in situ-forming microparticles (ISM). RV-ISM were prepared by the emulsification of an internal phase, containing the drug and the matrix former(s), into an external oily phase containing a stabilizer. The statistical design, Central Composite Design (CCD), was adopted as a quality by design (QbD) approach to optimize the formulation of RV-ISM systems. The fabricated RV-ISM systems was designed to minimize the initial burst drug release and maximize the sustainment of RV release from the ISM and ease of injection. The influence of critical formulation variables such as the matrix-former to drug (MF/D) ratio and SAIB to PLGA (S/P) ratio in the internal phase with respect to critical quality attributes (CQAs), such as the percentage drug release within the first day (Q₁), the time required for 50% drug release (T_50%) and the rate of injection, were studied using the CCD. The optimal RV-ISM system with the highest desirability value (0.74) was predicted to have an MF/D ratio of 11.7:1 (w/w) and an S/P ratio of 1.64:1 (w/w). The optimal RV-ISM system was assessed for its release profile, injectability, rheological properties, morphology, effect on cell viability, tolerance to γ-sterilization and in vivo performance in male albino rabbits. In vitro release studies revealed that the optimal RV-ISM system released 100% of its drug content throughout a release period of 30 days with only 15.5% drug release within the first day (Q₁) and T_50% of 13.09 days. Moreover, the optimal system showed a high injection rate of 1.012 mL/min, pseudoplastic flow, uniform spherical globules with homogenous particle size, minimal cytotoxicity and high tolerability to γ-sterilization. In vivo pharmacokinetic (PK) studies revealed that the rate of absorption of RV from the optimal RV-ISM system was controlled compared to a drug solution following either intramuscular (IM) or subcutaneous (SC) injection. Furthermore, the optimal RV-ISM was found to follow flip-flop PK with poor correlation between in vitro release and in vivo findings. These findings suggest that the optimal RV-ISM is a promising tool to achieve a sustained release therapy for RV; however, further investigation is still required to optimize the in vivo performance of RV-ISM.

Chitosan hydrogels for sustained drug delivery

Sustainable and controlled delivery of drugs is at the centre of a huge amount of undertaken researches. The ability of hydrogels, high water content materials, to achieve a local and delayed-delivery has already been demonstrated for a wide variety of therapeutic agents and various polymer natures. In particular, chitosan, a natural polymer, stands out as a first choice material for hydrogels elaboration in biomedical, cosmetic, and health related applications, owing to its interesting properties (as biocompatibility, biodegradability, antimicrobial capacity, and mucoadhesivity). Moreover, chitosan also allows drugs to go easier through biological barriers. The main objective of this review is to report the various uses of chitosan hydrogels as drug delivery devices to control and/or delay the release of drugs loaded into their three dimensional matrix. A wide spectrum of corresponding biomedical applications of these systems can be encountered in the literature, whatever the physicochemical nature of drugs (hydrophilic, hydrophobic, macromolecular), as detailed in this review.

Design and Characterization of Injectable Poly(Lactic-Co-Glycolic Acid) Pastes for Sustained and Local Drug Release

PURPOSE

We describe the preparation of injectable polymeric paste (IPP) formulations for local and sustained release of drugs. Furthermore, we include the characterization and possible applications of such pastes. Particular attention is paid to characteristics relevant to the successful clinical formulation development, such as viscosity, injectability, degradation, drug release, sterilization, stability performance and pharmacokinetics.

METHODS

Paste injectability was characterized using measured viscosity and the Hagen-Poiseuille equation to determine injection forces. Drug degradation, release and formulation stability experiments were performed in vitro and drug levels were quantified using HPLC-UV methods. Pharmacokinetic evaluation of sustained-release lidocaine IPPs used five groups of six rats receiving increasing doses subcutaneously. An anti-cancer formulation was evaluated in a subcutaneous tumor xenograft mouse model.

RESULTS

The viscosity and injectability of IPPs could be controlled by changing the polymeric composition. IPPs demonstrated good long-term stability and tunable drug-release with low systemic exposure in vivo in rats. Preliminary data in a subcutaneous tumor model points to a sustained anticancer effect.

CONCLUSIONS

These IPPs are tunable platforms for local and sustained delivery of drugs and have potential for further clinical development to treat a number of diseases.

Optimized Synthesis of Poly(deoxyribose) Isobutyrate, a Viscous Biomaterial for Bone Morphogenetic Protein-2 Delivery

Injectable and phase-transitioning carriers from natural polysaccharides have great potential for the minimally invasive delivery of therapeutic proteins in the field of bone tissue engineering. In this study, a novel and highly viscous drug carrier was synthesized by a sequential process of deoxyribose polycondensation and esterification. The effect of synthesis parameters on the molecular weight, viscosity, and adhesion of the material was studied and correlated to temperature and time of polycondensation ( T_p and t_p), time and temperature of esterification ( T_e and t_e), and the molar ratio of the monomer ( R). The formulations were evaluated for molecular weight and distribution properties using GPC, chemical structures by FTIR and NMR spectra, and rheological properties using a rheometer. Formulations illustrated a wide range of viscosities (0.736 to 2225 Pa s), adhesion (0.896 to 58.45 N), and molecular weights (637 to 4216 Da), where viscosity was significantly reduced in the presence of low amounts of solvents (10-20%). The sustained release of BSA was observed over 42 days in vitro. The biocompatibility of poly(deoxyribose) isobutyrate (PDIB) as well as its potential as a bone morphogenetic protein delivery system was assessed in vivo using a rat ectopic bone model, where bone nodules were observed at 2 weeks. In summary, PDIB is a promising molecule with multiple applications for protein delivery, including for bone tissue engineering.

Synthesis, Characterization and Biocompatibility of N-palmitoyl L-alanine-based Organogels as Sustained Implants of Granisetron and Evaluation of thier Antiemetic Effect

PURPOSE

To assess the gelation power of N-palmitoyl L-alanine derivatives in injectable oils and to use the best chosen organogel as parenteral implant of granisetron for the treatment of emesis.

METHODS

Twelve N-palmitoyl L-alanine derived organogels were developed and evaluated in terms of morphology, thermal properties and in vivo performance. The ability of the selected formula to form in situ gel upon subcutaneous injection in rats and its biocompatibility were monitored over 2 weeks by histopathological examination of the injection site.

RESULTS

The acid derivative (N-palmitoyl L-alanine; PA) was superior to ester derivatives. The chosen formula (PA/safflower oil 10% w/v) was successful in forming an in situ gel of granisetron when subcutaneously injected in rats, lasting for 2 weeks and proved to be biocompatible by histopathological examination. Moreover, it exerted an extended antiemetic activity by decreasing the cisplatin-induced pica for a duration of 96 h and reduced preprotachykinin A mRNA expression and Substance P level for up to 4 days (gastric tissue) or 5 days (medulla oblongata) in rats.

CONCLUSION

Granisetron organogel could be considered as a safe, sustained-release and supportive anticancer treatment in both acute and chronic emesis as well as an accompanying treatment with chemotherapeutics in cancer cases.

Injectable In Situ Forming Depot Systems for Long-Acting Contraception

Up to date, no long-acting reversible contraceptive (LARC) is developed to be injectable through needles smaller than 18 G and can also provide contraception for more than 3 months after single injection. In this study, injectable polymeric in situ forming depot (ISD) systems are developed to have injectability through 21-23 G needles, and capability of sustained release of levonorgestrel (LNG) for at least 7 months in vitro and in vivo after single subcutaneous injection in rats. The systems are polymeric solutions composed of biodegradable poly(lactide-co-glycolide) and poly(lactic acid) polymers dissolved in a mixture of solvents like N-methyl-2-pyrrolidone and benzyl benzoate or triethyl citrate. LNG released from ISD systems successfully suppressed the estrous cycle of rats at plasma concentration above 0.35 ng mL^-1 . At the end of the treatment, when LNG plasma concentration drops down to be nondetectable, predictable return of fertility is observed in rats. The designed ISD systems have great potential to be further developed into robust injectable LARCs that can be injected through a 21 G or smaller needle and achieve a variety of contraception durations with high patient compliance and low cost.

Synthesis, characterisation and phase transition behaviour of temperature-responsive physically crosslinked poly (N-vinylcaprolactam) based polymers for biomedical applications

Poly (N-vinylcaprolactam) (PNVCL) is a polymer which offers superior characteristics for various potential medical device applications. In particular it offers unique thermoresponsive capabilities, which fulfils the material technology constraints required in targeted drug delivery applications. PNVCL phase transitions can be tailored in order to suit the requirements of current and next generation devices, by modifying the contents with regard to the material composition and aqueous polymer concentration. In this study, physically crosslinked Poly (N-vinylcaprolactam)-Vinyl acetate (PNVCL-VAc) copolymers were prepared by photopolymerisation. The structure of the polymers was established by Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. The polymers were further characterised using differential scanning calorimetry and swelling studies. Determination of the LCST of the polymers in aqueous solution was achieved by employing four techniques; cloud point, UV-spectrometry, differential scanning calorimetry and rheometry. Sol-gel transition was established using tube inversion method and rheological analysis. This study was conducted to determine the characteristics of PNVCL with the addition of VAc, and to establish the effects on the phase transition. The PNVCL based polymers exhibited a decrease in the LCST as the composition of VAc increased. Sol-gel transition could be controlled by altering the monomeric feed ratio and polymer concentration in aqueous milieu. Importantly all copolymers (10wt% in solution) underwent gelation between 33.6 and 35.9°C, and based on this and the other materials properties recorded in this study, these novel copolymers have potential for use as injectable in situ forming drug delivery systems for targeted drug delivery.

Branched polyesters: Preparative strategies and applications

In the last 20years, the availability of precision chemical tools (e.g. controlled/living polymerizations, 'click' reactions) has determined a step change in the complexity of both the macromolecular architecture and the chemical functionality of biodegradable polyesters. A major part in this evolution has been played by the possibilities that controlled macromolecular branching offers in terms of tailored physical/biological performance. This review paper aims to provide an updated overview of preparative techniques that derive hyperbranched, dendritic, comb, grafted polyesters through polycondensation or ring-opening polymerization mechanisms.

Poly(lactic acid) for delivery of bioactive macromolecules

Therapeutic biomolecules often require frequent administration and supramolecular dosing to achieve therapeutic efficiencies and direct infusion into treatment or defect sites results in inadequate physiological response and at times severe side effects or mis-targeting. Delivery systems serve several purposes such as increased circulatory time, increased biomolecule half-life, and incorporation of new innovations can enable highly specific cell targeting and improved cell and nucleus permeability. Poly(lactic acid) (PLA) has become a "material of choice" due to wide availability, reproducible synthetic route, customization, versatility, biodegradability and biocompatibility. Furthermore, PLA is amenable to a variety of fabrication methodologies and chemistries allowing an expansive library correlating physio-chemical properties, characteristics, and applications. This article discusses challenges to biomolecule delivery, and classical approaches of PLA based biomolecule delivery and targeting strategies under development and in trials.

Poly(lactic acid) based hydrogels

Polylactide (PLA) and its copolymers are hydrophobic polyesters used for biomedical applications. Hydrogel medicinal implants have been used as drug delivery vehicles and scaffolds for tissue engineering, tissue augmentation and more. Since lactides are non-functional, they are copolymerized with hydrophilic monomers or conjugated to a hydrophilic moiety to form hydrogels. Copolymers of lactic and glycolic acids with poly(ethylene glycol) (PEG) provide thermo-responsive hydrogels. Physical crosslinking mechanisms of PEG-PLA or PLA-polysaccharides include: lactic acid segment hydrophobic interactions, stereocomplexation of D and L-lactic acid segments, ionic interactions, and chemical bond formation by radical or photo crosslinking. These hydrogels may also be tailored as stimulus responsive (pH, photo, or redox). PLA and its copolymers have also been polymerized to include urethane bonds to fabricate shape memory hydrogels. This review focuses on the synthesis, characterization, and applications of PLA containing hydrogels.

Peripheral Administration of a Long-Acting Peptide Oxytocin Receptor Agonist Inhibits Fear-Induced Freezing

Oxytocin (OT) modulates the expression of social and emotional behaviors and consequently has been proposed as a pharmacologic treatment of psychiatric diseases, including autism spectrum disorders and schizophrenia; however, endogenous OT has a short half-life in plasma and poor permeability across the blood-brain barrier. Recent efforts have focused on the development of novel drug delivery methods to enhance brain penetration, but few efforts have aimed at improving its half-life. To explore the behavioral efficacy of an OT analog with enhanced plasma stability, we developed PF-06655075 (PF1), a novel non–brain-penetrant OT receptor agonist with increased selectivity for the OT receptor and significantly increased pharmacokinetic stability. PF-06478939 was generated with only increased stability to disambiguate changes to selectivity versus stability. The efficacy of these compounds in evoking behavioral effects was tested in a conditioned fear paradigm. Both central and peripheral administration of PF1 inhibited freezing in response to a conditioned fear stimulus. Peripheral administration of PF1 resulted in a sustained level of plasma concentrations for greater than 20 hours but no detectable accumulation in brain tissue, suggesting that plasma or cerebrospinal fluid exposure was sufficient to evoke behavioral effects. Behavioral efficacy of peripherally administered OT receptor agonists on conditioned fear response opens the door to potential peripheral mechanisms in other behavioral paradigms, whether they are mediated by direct peripheral activation or feed-forward responses. Compound PF1 is freely available as a tool compound to further explore the role of peripheral OT in behavioral response.

Engineered in-situ depot-forming hydrogels for intratumoral drug delivery

Chemotherapy is the traditional treatment for intermediate and late stage cancers. The search for treatment options with minimal side effects has been ongoing for several years. Drug delivery technologies that result in minimal or no side effects with improved ease of use for the patients are receiving increased attention. Polymer drug conjugates and nanoparticles can potentially offset the volume of drug distribution while enhancing the accumulation of the active drug in tumors thereby reducing side effects. Additionally, development of localized drug delivery platforms is being investigated as another key approach to target tumors with minimal or no toxicity. Development of in-situ depot-forming gel systems for intratumoral delivery of immuno-oncology actives can enhance drug bioavailability to the tumor site and reduce systemic toxicity. This field of drug delivery is critical to develop given the advent of immunotherapy and the availability of novel biological molecules for treating solid tumors. This article reviews the advances in the field of engineered in-situ gelling platforms as a practical tool for local delivery of active oncolytic agents to tumor sites.

Pharmacokinetics studies of enrofloxacin injectable in situ forming gel in dogs

The objective of this study was to evaluate the pharmacokinetic characteristics of enrofloxacin (ENR) injectable in situ gel we developed in dogs following a single intramuscular (i.m.) administration. Twelve healthy dogs were randomly divided into two groups (six dogs per group), then administrated a single 20 mg/kg body weight (b.w.) ENR injectable in situ gel and a single 5 mg/kg b.w. ENR conventional injection, respectively. High-performance liquid chromatography (HPLC) was used to determine ENR plasma concentrations. The pharmacokinetic parameters of ENR injectable in situ gel and conventional injection in dogs are as follows: MRT (mean residence time) (45.59 ± 14.05) h verse (11.40 ± 1.64) h, AUC (area under the blood concentration vs. time curve) (28.66 ± 15.41) μg·h/mL verse (11.06 ± 3.90) μg·h/mL, cmax (maximal concentration) (1.59 ± 0.35) μg/mL verse (1.46 ± 0.07) μg/mL, tmax (time needed to reach cmax ) (1.25 ± 1.37) h verse (1.40 ± 0.55) h, t1/2λz (terminal elimination half-life) (40.27 ± 17.79) h verse (10.32 ± 0.97) h. The results demonstrated that the in situ forming gel system could increase dosing interval of ENR and thus reduced dosing frequency during long-term treatment. Therefore, the ENR injectable in situ gel seems to be worth popularizing in veterinary clinical application.

In vitro-controlled release delivery system for hydrogen sulfide donor

Hydrogen sulfide (H2S) is having many potential pharmacological and physiological actions which reported that therapeutically useful concentration is low (100-160 μM) and a higher concentration could be toxic. Most of its donors produce it on coming into contact with water. All of these problems could be solved by a controlled-release delivery system which does not utilize water in any of its development steps. Therefore, 12 sustained release formulations were prepared by dissolving sodium hydrogen sulfide (NaHS)-a model H2S donor-in polymer solutions, prepared by dissolving polymers (consisted of either polylactide (PLA) or polylactide co-glycolide (PLGA), containing free carboxylic acid or capped allyl ester end group) in a mixture of benzyl benzoate (BB) and benzyl alcohol (BA). The formulation was injected in simulated tear fluid (STF) from which samples were withdrawn at specified times and assayed for NaHS content. We found decrease in burst and overall release with increase in polymer concentration from 10 to 20% w/v. The formulations containing free end group showed significant (p < 0.05) reduction of burst release (11% vs 21%). However, the overall release or the average amount released per hour was found to be significantly (p < 0.05) increased for formulations containing polymers with free end group than those with capped end group. A sustained level of H2S was found to be maintained for 72 h which should be further increased to a month to make it a viable H2S donor delivery system in addition to investigating toxicity profile specifically for the purpose of subconjunctival ocular delivery.

Highly porous drug-eluting structures: from wound dressings to stents and scaffolds for tissue regeneration

For many biomedical applications, there is need for porous implant materials. The current article focuses on a method for preparation of drug-eluting porous structures for various biomedical applications, based on freeze drying of inverted emulsions. This fabrication process enables the incorporation of any drug, to obtain an "active implant" that releases drugs to the surrounding tissue in a controlled desired manner. Examples for porous implants based on this technique are antibiotic-eluting mesh/matrix structures used for wound healing applications, antiproliferative drug-eluting composite fibers for stent applications and local cancer treatment, and protein-eluting films for tissue regeneration applications. In the current review we focus on these systems. We show that the release profiles of both types of drugs, water-soluble and water-insoluble, are affected by the emulsion's formulation parameters. The former's release profile is affected mainly through the emulsion stability and the resulting porous microstructure, whereas the latter's release mechanism occurs via water uptake and degradation of the host polymer. Hence, appropriate selection of the formulation parameters enables to obtain desired controllable release profile of any bioactive agent, water-soluble or water-insoluble, and also fit its physical properties to the application.

Drug-releasing implants: current progress, challenges and perspectives

This review presents the different types and concepts of drug-releasing implants using new nanomaterials and nanotechnology-based devices.

Rheological study of chitosan/polyol-phosphate systems: influence of the polyol part on the thermo-induced gelation mechanism

Thermo-sensitive gelling systems, like chitosan/polyol-phosphate, are candidates with a high potential for the design of biodegradable drug delivery systems, notably for in situ forming depots. They consist of stable and low viscosity aqueous solutions, liquid at room temperature, which turn into a gel state upon an increase of temperature (e.g., after subcutaneous administration). This technology enables a sustained release of potentially encapsulated active substances. Despite these thermo-gelling solutions being widely studied for the development of parenteral drug delivery systems, most commonly using β-glycerophosphate (β-GP) as gelling agent, the mechanism inducing the gelation and the role of the polyol part in this mechanism has not been clearly elucidated. To investigate the mechanism of the gelation process, comprehensive rheological studies were performed, comparing different chitosan/polyol-phosphate systems varying in the chemical structure of the polyol parts of the gelling agents. As reference, β-GP was compared to glucose-1-phosphate (G1-P) and glucose-6-phosphate (G6-P) and to a polyol-free phosphate salt, Na2HPO4, as well. Frequency sweep experiments at different temperatures or different gelling agent concentrations, temperature, and time sweep tests were performed as complementary experimental approaches. The results disclosed significant trends with widespread implications, establishing a relationship between the chemical structure of the polyol part and the macroscopic gelling behavior of the solutions, that is, transition temperature, gelation time, and gel strength. The new results presented in this study show that increasing the size of the polyol part prevents the interactions between the chitosan chains, strongly influencing the gelling process.

Low-molecular-weight gelators consisting of hybrid cyclobutane-based peptides

Some hybrid tetrapeptides consisting of (1R,2S)-2-aminocyclobutane-1-carboxylic acid and glycine, β-alanine, or γ-aminobutyric acid (GABA) joined in alternation, compounds 1-3, respectively, have been investigated to gain information on the non-covalent interactions responsible for their self-assembly to form ordered aggregates, as well as on parameters such as their morphology and size. All three peptides formed nice gels in many organic solvents and significant difference in their behaviour was not observed. Scanning electron microscopy (SEM) and circular dichroism (CD) pointed out that peptide 1, which contains the shortest C2 linear residue, presented the most defined fibril network and afforded nanoscale helical aggregates. Tetrapeptide 3, with C4 linear residues in its structure, also showed bundles of fibres whereas a homogeneous spherulitic network was observed for tetrapeptide 2, with a C3 spacer between cyclobutane residues. Computational calculations for 1 allowed us to model the self-assembly of the molecules and suggested a head-to-head arrangement to give helical structures corresponding to hydrogen-bonded single chains. These features were corroborated by a high-resolution NMR spectroscopy study of the dynamics of the gelation process in toluene-d8 which evidenced that molecules self-assemble to afford ordered aggregates with a supramolecular chirality.

L-cysteine-derived ambidextrous gelators of aromatic solvents and ethanol/water mixtures

A series of L-cysteine-derived double hydrocarbon chain amphiphilic gelators L-(3-alkyl-carbamoylsulfanyl)-2-(3-alkylurido)propionic acid with different hydrocarbon chain lengths (C6-C16) was designed and synthesized. These gelators efficiently gelate only aromatic solvents. The gelation ability increased with the increase of chain length up to C14, but then it dropped with further increase of chain length. The C12 and C14 derivatives also gelled ethanol/water mixtures. The gels were characterized by a number of methods, including FT-IR, NMR, and XRD spectroscopy, electron microscopy, and rheology. The amphiphiles were observed to form either flat lamellar or ribbonlike aggregates in aromatic solvents as well as in ethanol/water mixtures. The gelation in all the solvents employed was observed to be thermoreversible. The gel-to-sol transition temperature as well as mechanical strength of the organogels were observed to increase with the hydrocarbon chain length. Both types of gels of C8-C16 amphiphiles have gel-to-sol transition temperatures above the physiological temperature (310 K). FT-IR and variable temperature (1)H NMR measurements suggested that van der Waals interactions have major contribution in the gelation process. The gel-to-sol transition temperature and mechanical strength of the organogels in ethanol/water mixtures was observed to be higher than those of benzene organogel.

Injectable implants for the sustained release of protein and peptide drugs

Protein and peptide macromolecules have emerged as promising therapeutic agents in recent years. However, their delivery to the target site can be challenging owing to their susceptibility to denaturation and degradation, short half-life and, therefore, poor bioavailability. In situ-forming implants present an attractive parenteral delivery platform for proteins and peptides because of their ease of application, sustained-release properties, tissue biocompatibility and simple manufacture. In this review, we discuss the various mechanisms by which polymer systems assemble in situ to form implant devices for sustained release of therapeutic macromolecules, and highlight recent advances in polymer systems that gel in response to a combination of these mechanisms. Finally, we examine release mechanisms, marketed products and limitations of injectable implants.

Silk sericin/polyacrylamide in situ forming hydrogels for dermal reconstruction

In situ forming tissue sealants are advantageous due to ease in application, complete coverage of defect site and assured comfort levels to patients. The interconnected three-dimensional hydrophilic networks perfectly manage typical dermal wounds by suitably scaffolding skin fibroblast, diffusing the nutrients, therapeutics and exudates while still maintaining an adequately moist environment. We evaluate the cell homing ability of semi-interpenetrating non-mulberry tropical tasar silk sericin/polyacrylamide hydrophilic network with a keen understanding of its network characteristics and correlation of protein concentration with the performance as cell scaffold. Interconnectivity of porous networks observed through scanning electron micrograph revealed pore sizes ranging from 23 to 52 μm. The enhanced β-sheet content with the increasing sericin concentration in far red spectroscopy study supported their corresponding improved compressive strength. These semi-interpenetrating networks were found to possess a maximum fluid uptake of 112% of its weight, hence preventing the accumulation of exudates at the wound area. The present systems appear to possess characteristics like rapid gelation (~5min) at 37 °C, 98% porosity enabling the migration of fibroblasts during healing (observed through confocal and scanning electron micrographs), cell adhesion together with the absence of any cyto-toxic effect suggesting its potential as in situ tissue sealants. The compressive strength up to 61 kPa ensured ease in handling even when wet. The results prove the suitability to use non-mulberry tasar cocoon silk sericin/polyacrylamide semi-interpenetrating network as a reconstructive dermal sealant.

Accelerated in-vitro release testing methods for extended-release parenteral dosage forms

OBJECTIVES

This review highlights current methods and strategies for accelerated in-vitro drug release testing of extended-release parenteral dosage forms such as polymeric microparticulate systems, lipid microparticulate systems, in-situ depot-forming systems and implants.

KEY FINDINGS

Extended-release parenteral dosage forms are typically designed to maintain the effective drug concentration over periods of weeks, months or even years. Consequently, 'real-time' in-vitro release tests for these dosage forms are often run over a long time period. Accelerated in-vitro release methods can provide rapid evaluation and therefore are desirable for quality control purposes. To this end, different accelerated in-vitro release methods using United States Pharmacopeia (USP) apparatus have been developed. Different mechanisms of accelerating drug release from extended-release parenteral dosage forms, along with the accelerated in-vitro release testing methods currently employed are discussed.

SUMMARY

Accelerated in-vitro release testing methods with good discriminatory ability are critical for quality control of extended-release parenteral products. Methods that can be used in the development of in-vitro-in-vivo correlation (IVIVC) are desirable; however, for complex parenteral products this may not always be achievable.

Encapsulation of curcumin in self-assembling peptide hydrogels as injectable drug delivery vehicles

Curcumin, a hydrophobic polyphenol, is an extract of turmeric root with antioxidant, anti-inflammatory and anti-tumorigenic properties. Its lack of water solubility and relatively low bioavailability set major limitations for its therapeutic use. In this study, a self-assembling peptide hydrogel is demonstrated to be an effective vehicle for the localized delivery of curcumin over sustained periods of time. The curcumin-hydrogel is prepared in-situ where curcumin encapsulation within the hydrogel network is accomplished concurrently with peptide self-assembly. Physical and in vitro biological studies were used to demonstrate the effectiveness of curcumin-loaded β-hairpin hydrogels as injectable agents for localized curcumin delivery. Notably, rheological characterization of the curcumin-loaded hydrogel before and after shear flow have indicated solid-like properties even at high curcumin payloads. In vitro experiments with a medulloblastoma cell line confirm that the encapsulation of the curcumin within the hydrogel does not have an adverse effect on its bioactivity. Most importantly, the rate of curcumin release and its consequent therapeutic efficacy can be conveniently modulated as a function of the concentration of the MAX8 peptide.

A semi-degradable composite scaffold for articular cartilage defects

Few options exist to replace or repair damaged articular cartilage. The optimal solution that has been suggested is a scaffold that can carry load and integrate with surrounding tissues; but such a construct has thus far been elusive. The objectives of this study were to manufacture and characterize a nondegradable hydrated scaffold. Our hypothesis was that the polymer content of the scaffold can be used to control its mechanical properties, while an internal porous network augmented with biological agents can facilitate integration with the host tissue. Using a two-step water-in-oil emulsion process a porous polyvinyl alcohol (PVA) hydrogel scaffold combined with alginate microspheres was manufactured. The scaffold had a porosity of 11-30% with pore diameters of 107-187 μm, which readily allowed for movement of cells through the scaffold. Alginate microparticles were evenly distributed through the scaffold and allowed for the slow release of biological factors. The elastic modulus (Es ) and Poisson's ratio (υ), Aggregate modulus (Ha ) and dynamic modulus (ED ) of the scaffold were significantly affected by % PVA, as it varied from 10 to 20% wt/vol. Es and υ were similar to that of articular cartilage for both polymer concentrations, while Ha and ED were similar to that of cartilage only at 20% PVA. The ability to control scaffold mechanical properties, while facilitating cellular migration suggest that this scaffold is a potentially viable candidate for the functional replacement of cartilage defects.

Polymeric Microspheres for Medical Applications

Synthetic polymeric microspheres find application in a wide range of medical applications. Among other applications, microspheres are being used as bulking agents, embolic- or drug-delivery particles. The exact composition of the spheres varies with the application and therefore a large array of materials has been used to produce microspheres. In this review, the relation between microsphere synthesis and application is discussed for a number of microspheres that are used for different treatment strategies.