Polycaprolactone thin-film drug delivery systems: Empirical and predictive models for device design

Engineered Geobacillus lipolytic enzymes - Attractive polyesterases that degrade polycaprolactones and simultaneously produce esters

Plastic pollution is one of the biggest environmental problems plaguing the modern world. Polyester-based plastics contribute significantly to this ecological safety concern. In this study, lipolytic biocatalysts GD-95RM and GDEst-lip developed based on lipase/esterase produced by Geobacillus sp. 95 strain were applied for the degradation of polycaprolactone films (Mn 45.000 (PCL45000) and Mn 80.000 (PCL80000)). The degradation efficiency was significantly enhanced by the addition of short chain alcohols. Lipase GD-95RM (1 mg) can depolymerize 264.0 mg and 280.7 mg of PCL45000 and PCL80000, films respectively, in a 24 h period at 30 °C, while the fused enzyme GDEst-lip (1 mg) is capable of degrading 145.5 mg PCL45000 and 134.0 mg of PCL80000 films in 24 h. The addition of ethanol (25 %) improves the degradation efficiency ~2.5 fold in the case of GD-95RM. In the case of GDEst-lip, 50 % methanol was found to be the optimal alcohol solution and the degradation efficiency was increased by ~3.25 times. The addition of alcohols not only increased degradation speeds but also allowed for simultaneous synthesis of industrially valuable 6-hydroxyhexonic acid esters. The suggested system is an attractive approach for removing of plastic waste and supports the principles of bioeconomics.

Encapsulation of Carbon Dots in a Core-Shell Mesh through Coaxial Direct Ink Writing for Improved Crop Growth

Through coaxial direct ink writing, we fabricated a core-shell mesh system for the controlled release of carbon dots (C-dots). In the core ink, we developed an ink formulation with tuned viscosity using hydroxypropyl cellulose and polyethylene glycol to host C-dots. Polycaprolactone was employed as the main shell material, in combination with sodium alginate, to control the degradation rate of the shell. We investigated the degradation profile of the 3D-printed meshes and tracked the weekly release of C-dots in an aqueous medium by spectrofluorometry. We tested the efficacy of the C-dot release on plants by placing the meshes in transparent soil with Triticum aestivum L. seeds. We observed the in vivo translocation of the C-dots in the plant using confocal microscopy. We measured the root elongation and shoot length to assess the effect of C-dots on plant growth. Our study revealed that the plants exposed to C-dots grew 2.5-fold faster than the control group, indicating that C-dots are promising nanofertilizers for aggrotech and non-toxic fluorescent biolabels for in vivo applications.

Polymer-Based Nanostructures for Pancreatic Beta-Cell Imaging and Non-Invasive Treatment of Diabetes

Diabetes poses major economic, social, and public health challenges in all countries worldwide. Besides cardiovascular disease and microangiopathy, diabetes is a leading cause of foot ulcers and lower limb amputations. With the continued rise of diabetes prevalence, it is expected that the future burden of diabetes complications, early mortality, and disabilities will increase. The diabetes epidemic is partly caused by the current lack of clinical imaging diagnostic tools, the timely monitoring of insulin secretion and insulin-expressing cell mass (beta (β)-cells), and the lack of patients' adherence to treatment, because some drugs are not tolerated or invasively administrated. In addition to this, there is a lack of efficient topical treatment capable of stopping the progression of disabilities, in particular for treating foot ulcers. In this context, polymer-based nanostructures garnered significant interest due to their tunable physicochemical characteristics, rich diversity, and biocompatibility. This review article emphasizes the last advances and discusses the prospects in the use of polymeric materials as nanocarriers for β-cell imaging and non-invasive drug delivery of insulin and antidiabetic drugs in the management of blood glucose and foot ulcers.

Reservoir-Style Polymeric Drug Delivery Systems: Empirical and Predictive Models for Implant Design

Controlled drug delivery systems can provide sustained release profiles, favorable pharmacokinetics, and improved patient adherence. Here, a reservoir-style implant comprising a biodegradable polymer, poly(ε-caprolactone) (PCL), was developed to deliver drugs subcutaneously. This work addresses a key challenge when designing these implantable drug delivery systems, namely the accurate prediction of drug release profiles when using different formulations or form factors of the implant. The ability to model and predict the release behavior of drugs from an implant based on their physicochemical properties enables rational design and optimization without extensive and laborious in vitro testing. By leveraging experimental observations, we propose a mathematical model that predicts the empirical parameters describing the drug diffusion and partitioning processes based on the physicochemical properties of the drug. We demonstrate that the model enables an adequate fit predicting empirical parameters close to experimental values for various drugs. The model was further used to predict the release performance of new drug formulations from the implant, which aligned with experimental results for implants exhibiting zero-order release kinetics. Thus, the proposed empirical models provide useful tools to inform the implant design to achieve a target release profile.

Drug release kinetics and biological properties of a novel local drug carrier system

Background:

The purpose of this in vitro study was to investigate drug release kinetics and cytotoxicity of a novel drug delivery system for treatment of periodontitis.

Materials and Methods:

This in vitro study addresses the fabrication of a polycaprolactone/alginic acid-based polymeric film loaded with metronidazole, as a basic drug in the treatment of periodontal diseases. Films were prepared by solvent casting technique. Four formulations with different percentages of drug by weight (3%, 5%, 9%, and 13%) were prepared. Drug release kinetics were investigated using ultraviolet–visible spectroscopy during (one week). Data were analyzed using repeated measures ANOVA. Cytotoxicity of drug-loaded system extracts was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using L929 cells after 24-h incubation. The results were evaluated according to ISO standard 10993-5 and assessed using ANOVA and Tukey's tests at a significance level of P < 0.05.

Results:

All polymeric films showed a burst drug release followed by a gradual release. Drug release data were fitted well with the first-order kinetic model in all drug-containing formulations indicating that drug release is a fraction of remaining drug in the matrix. Drug release is mainly driven by diffusion of medium into the composite matrix. 3%wt metronidazole-containing formulation exhibited the best MTT result.

Conclusion:

The findings of this study supported the synthesis of drug-loaded periodontal films with 3% metronidazole due to better biological properties along with the ability of acceptable drug release to eradicate anaerobic periodontal bacteria.

Precipitation dominated thin films of acetaminophen fabricated by meniscus guided coating

Crystallization above the solvent boiling point facilitates the identification of a new precipitation dominant morphology during meniscus guided coating.

Development of Novel Thin Polycaprolactone (PCL)/Clay Nanocomposite Films with Antimicrobial Activity Promoted by the Study of Mechanical, Thermal, and Surface Properties

Infection with pathogenic microorganisms is of great concern in many areas, especially in healthcare, but also in food packaging and storage, or in water purification systems. Antimicrobial polymer nanocomposites have gained great popularity in these areas. Therefore, this study focused on new approaches to develop thin antimicrobial films based on biodegradable polycaprolactone (PCL) with clay mineral natural vermiculite as a carrier for antimicrobial compounds, where the active organic antimicrobial component is antifungal ciclopirox olamine (CPX). For possible synergistic effects, a sample in combination with the inorganic antimicrobial active ingredient zinc oxide was also prepared. The structures of all the prepared samples were studied by X-ray diffraction, FTIR analysis and, predominantly, by SEM. The very different structure properties of the prepared nanofillers had a fundamental influence on the final structural arrangement of thin PCL nanocomposite films as well as on their mechanical, thermal, and surface properties. As sample PCL/ZnOVER_CPX possessed the best results for antimicrobial activity against examined microbial strains, the synergic effect of CPX and ZnO combination on antimicrobial activity was proved, but on the other hand, its mechanical resistance was the lowest.

All-polymeric transient neural probe for prolonged in-vivo electrophysiological recordings

Transient bioelectronics has grown fast, opening possibilities never thought before. In medicine, transient implantable devices are interesting because they could eliminate the risks related to surgical retrieval and reduce the chronic foreign body reaction. Despite recent progress in this area, the potential of transient bioelectronics is still limited by their short functional lifetime owed to the fast dissolution rate of degradable metals, which is typically a few days or weeks. Here we report that a switch from degradable metals to an entirely polymer-based approach allows for a slower degradation process and a longer lifetime of the transient probe, thus opening new possibilities for transient medical devices. As a proof-of-concept, we fabricated all-polymeric transient neural probes that can monitor brain activity in mice for a few months, rather than a few days or weeks. Also, we extensively evaluated the foreign body reaction around the implant during the probe degradation. This kind of devices might pave the way for several applications in neuroprosthetics.

Biotechnology and Biomaterial-Based Therapeutic Strategies for Age-Related Macular Degeneration. Part I: Biomaterials-Based Drug Delivery Devices

Age-related Macular Degeneration (AMD) is an up-to-date untreatable chronic neurodegenerative eye disease of multifactorial origin, and the main causes of blindness in over 65 years old people. It is characterized by a slow progression and the presence of a multitude of factors, highlighting those related to diet, genetic heritage and environmental conditions, present throughout each of the stages of the illness. Current therapeutic approaches, mainly consisting of intraocular drug delivery, are only used for symptoms relief and/or to decelerate the progression of the disease. Furthermore, they are overly simplistic and ignore the complexity of the disease and the enormous differences in the symptomatology between patients. Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, the development of biomaterials-based approaches for a personalized and controlled delivery of therapeutic drugs and biomolecules represents the main challenge for the defeat of this neurodegenerative disease. Here we present a critical review of the available and under development AMD therapeutic approaches, from a biomaterials and biotechnological point of view. We highlight benefits and limitations and we forecast forthcoming alternatives based on novel biomaterials and biotechnology methods. In the first part we expose the physiological and clinical aspects of the disease, focusing on the multiple factors that give origin to the disorder and highlighting the contribution of these factors to the triggering of each step of the disease. Then we analyze available and under development biomaterials-based drug-delivery devices (DDD), taking into account the anatomical and functional characteristics of the healthy and ill retinal tissue.

Performance and Stability of Tenofovir Alafenamide Formulations within Subcutaneous Biodegradable Implants for HIV Pre-Exposure Prophylaxis (PrEP)

A critical need exists to develop diverse biomedical strategies for the widespread use of HIV Pre-Exposure Prophylaxis (HIV PrEP). This manuscript describes a subcutaneous reservoir-style implant for long-acting delivery of tenofovir alafenamide (TAF) for HIV PrEP. We detail key parameters of the TAF formulation that affect implant performance, including TAF ionization form, the selection of excipient and the exposure to aqueous conditions. Both in-vitro studies and shelf stability tests demonstrate enhanced performance for TAF freebase (TAFFB) in this long-acting implant platform, as TAFFB maintains higher chemical stability than the TAF hemifumarate salt (TAFHF). We also examined the hydrolytic degradation profiles of various formulations of TAF and identified inflection points for the onset of the accelerated drug hydrolysis within the implant using a two-line model. The compositions of unstable formulations are characterized by liquid chromatography-mass spectrometry (LC-MS) and are correlated to predominant products of the TAF hydrolytic pathways. The hydrolysis rate of TAF is affected by pH and water content in the implant microenvironment. We further demonstrate the ability to substantially delay the degradation of TAF by reducing the rates of drug release and thus lowering the water ingress rate. Using this approach, we achieved sustained release of TAFFB formulations over 240 days and maintained > 93% TAF purity under simulated physiological conditions. The opportunities for optimization of TAF formulations in this biodegradable implant supports further advancement of strategies to address long-acting HIV PrEP.

Controlled Drug Release from Biodegradable Polymer Matrix Loaded in Microcontainers Using Hot Punching

Microcontainers are reservoir-based advanced drug delivery systems (DDS) that have proven to increase the bioavailibity of the small-molecule drugs, targeting of biomolecules, protection of vaccines and improved treatment of Pseudomonas aeruginosa. However, high-throughput loading of these micron-sized devices with drug has been challenging. Hot punching is a new technique that is a fast, simple and single-step process where the microdevices are themselves used as mold to punch biocompatible and biodegradable drug-polymer films, thereby loading the containers. Here, we investigate the effect of hot punching on the drug distribution as well as drug release from the loaded drug-polymer matrices. Zero-order sustained drug release is observed for the model drug Furosemide embedded in biodegradable polymer, Poly-ε-caprolactone, which is attributed to the unique spatial distribution of Furosemide during the loading process.

Characterization of a Reservoir-Style Implant for Sustained Release of Tenofovir Alafenamide (TAF) for HIV Pre-Exposure Prophylaxis (PrEP)

Long-acting (LA) HIV pre-exposure prophylaxis (PrEP) offers the potential to improve adherence by lowering the burden of daily or on-demand regimens of antiretroviral (ARV) drugs. This paper details the fabrication and in vitro performance of a subcutaneous and trocar-compatible implant for the LA delivery of tenofovir alafenamide (TAF). The reservoir-style implant comprises an extruded tube of a biodegradable polymer, poly(ε-caprolactone) (PCL), filled with a formulation of TAF and castor oil excipient. Parameters that affect the daily release rates of TAF are described, including the surface area of the implant, the thickness of the PCL tube walls (between 45 and 200 µm), and the properties of the PCL (e.g., crystallinity). In vitro studies show a linear relationship between daily release rates and surface area, demonstrating a membrane-controlled release mechanism from extruded PCL tubes. Release rates of TAF from the implant are inversely proportional to the wall thickness, with release rates between approximately 0.91 and 0.15 mg/day for 45 and 200 µm, respectively. The sustained release of TAF at 0.28 ± 0.06 mg/day over the course of 180 days in vitro was achieved. Progress in the development of this implant platform addresses the need for new biomedical approaches to the LA delivery of ARV drugs.

Recent advances in intraocular sustained-release drug delivery devices

Topical eye-drop administration and intravitreal injections are the current standard for ocular drug delivery. However, patient adherence to the drug regimen and insufficient administration frequency are well-documented challenges to this field. In this review, we describe recent advances in intraocular implants designed to deliver therapeutics for months to years, to obviate the issues of patient adherence. We highlight recent advances in monolithic ocular implants in the literature, the commercialization pipeline, and approved for the market. We also describe design considerations based on material selection, active pharmaceutical ingredient, and implantation site.

Development of a dual extrusion printing technique for an acid- and thermo-labile drug

Over the last years fused deposition modeling has been increasingly considered as a game-changing technique for the preparation of individualized pharmaceutical products. Until now investigations have mainly focused on dosage forms loaded with very stable drugs or model substances. Going beyond this early stage of research, developers will also have to deal with more challenging active substances. In this work different printing designs for tablets containing the acid- and thermo-labile drug pantoprazole sodium were tested. Initial dual extrusion printing of a cellulose acetate phthalate coat and a tablet core of polyethylene glycol 6000 with 10% (m/m) pantoprazole sodium resulted in thermal degradation of pantoprazole at cellulose acetate phthalate printing temperatures of 141 °C. Therefore, different tablet designs were developed. The sectioning of the design of the tablet coat in a gastro-resistant cellulose acetate phthalate bottom part and an upper nearly insoluble polycaprolactone part printed at only 58 °C was suitable to prevent visible signs of thermal degradation. Dissolution testing indicated also no drug loss during dual extrusion printing. However, printed enteric tablets with shell thicknesses of 0.4 to 0.5 mm were not completely gastro-resistant. Drug release at intestinal pH values was delayed compared to uncoated cores. In conclusion, 3D-printing of gastro-resistant tablets containing thermo- and acid-labile drugs seems in principle possible. However, it remains an unsolved challenge to meet United States Pharmacopeia requirements.

Investigation of in vitro hydrophilic and hydrophobic dual drug release from polymeric films produced by sodium alginate-MaterBi® drying emulsions

Emulsions are known to be effective carriers of hydrophobic drugs, and particularly injectable emulsions have been successfully implemented for in vivo controlled drug release. Recently, high internal phase emulsions have also been used to produce porous polymeric templates for pharmaceutical applications. However, emulsions containing dissolved biopolymers both in the oil and water phases are very scarce. In this study, we demonstrate such an emulsion, in which the oil phase contains a hydrophobic biodegradable polymer, MaterBi®, and the water phase is aqueous sodium alginate dispersion. The two phases were emulsified simply by ultrasonic processing without any surfactants. The emulsions were stable for several days and were dried into composite solid films with varying MaterBi®/alginate fractions. The films were loaded with two model drugs, a hydrophilic eosin-based cutaneous antiseptic and the hydrophobic curcumin. Drug release capacity of the films was investigated in detail, and controlled release of each model drug was achieved either by tuning the polymer fraction in the films during emulsification or by crosslinking sodium alginate fraction of the films by calcium salt solution immersion. The emulsions can be formulated to carry either a single model drug or both drugs depending on the desired application. Films demonstrate excellent cell biocompatibility against human dermal fibroblast, adult cells.

Long acting systemic HIV pre-exposure prophylaxis: an examination of the field

Oral pre-exposure prophylaxis for the prevention of HIV-1 transmission (HIV PrEP) has been widely successful as demonstrated by a number of clinical trials. However, studies have also demonstrated the need for patients to tightly adhere to oral dosing regimens in order to maintain protective plasma and tissue concentrations. This is especially true for women, who experience less forgiveness from dose skipping than men in clinical trials of HIV PrEP. There is increasing interest in long-acting (LA), user-independent forms of HIV PrEP that could overcome this adherence challenge. These technologies have taken multiple forms including LA injectables and implantables. Phase III efficacy trials are ongoing for a LA injectable candidate for HIV PrEP. This review will focus on the design considerations for both LA injectable and implantable platforms for HIV PrEP. Additionally, we have summarized the existing LA technologies currently in clinical and pre-clinical studies for HIV PrEP as well as other technologies that have been applied to HIV PrEP and contraceptives. Our discussion will focus on the potential application of these technologies in low resource areas, and their use in global women's health.

Biocatalytic Route for the Synthesis of Oligoesters of Hydroxy-Fatty acids and ϵ-Caprolactone

Developments of past years placed the bio-based polyesters as competitive substitutes for fossil-based polymers. Moreover, enzymatic polymerization using lipase catalysts has become an important green alternative to chemical polymerization for the synthesis of polyesters with biomedical applications, as several drawbacks related to the presence of traces of metal catalysts, toxicity and higher temperatures could be avoided. Copolymerization of ϵ-caprolactone (CL) with four hydroxy-fatty acids (HFA) from renewable sources, 10-hydroxystearic acid, 12-hydroxystearic acid, ricinoleic acid, and 16-hydroxyhexadecanoic acid, was carried out using commercially available immobilized lipases from Candida antarctica B, Thermomyces lanuginosus, and Pseudomonas stutzeri, as well as a native lipase. MALDI-TOF-MS and 2D-NMR analysis confirmed the formation of linear/branched and cyclic oligomers with average molecular weight around 1200 and polymerization degree up to 15. The appropriate selection of the biocatalyst and reaction temperature allowed the tailoring of the non-cyclic/cyclic copolymer ratio and increase of the total copolymer content in the reaction product above 80%. The catalytic efficiency of the best performing biocatalyst (Lipozyme TL) is evaluated during four reaction cycles, showing excellent operational stability. The thermal stability of the reaction products is assessed based on TG and DSC analysis. This new synthetic route for biobased oligomers with novel functionalities and properties could have promising biomedical applications.

Enzymatic Synthesis of Amino Acids Endcapped Polycaprolactone: A Green Route Towards Functional Polyesters

ε-caprolactone (CL) has been enzymatically polymerized using α-amino acids based on sulfur (methionine and cysteine) as (co-)initiators and immobilized lipase B of Candida antarctica (CALB) as biocatalyst. In-depth characterizations allowed determining the corresponding involved mechanisms and the polymers thermal properties. Two synthetic strategies were tested, a first one with direct polymerization of CL with the native amino acids and a second one involving the use of an amino acid with protected functional groups. The first route showed that mainly polycaprolactone (PCL) homopolymer could be obtained and highlighted the lack of reactivity of the unmodified amino acids due to poor solubility and affinity with the lipase active site. The second strategy based on protected cysteine showed higher monomer conversion, with the amino acids acting as (co-)initiators, but their insertion along the PCL chains remained limited to chain endcapping. These results thus showed the possibility to synthesize enzymatically polycaprolactone-based chains bearing amino acids units. Such cysteine endcapped PCL materials could then find application in the biomedical field. Indeed, subsequent functionalization of these polyesters with drugs or bioactive molecules can be obtained, by derivatization of the amino acids, after removal of the protecting group.

Biocompatibility and Pharmacokinetic Analysis of an Intracameral Polycaprolactone Drug Delivery Implant for Glaucoma

Purpose

We developed polycaprolactone (PCL) implants that achieve zero-order release of a proprietary ocular hypotensive agent (DE-117) over 6 months.

Methods

The release rates of DE-117–loaded PCL devices were tuned based on an established predictive model and confirmed by in vitro release studies. Devices containing DE-117 and empty devices were implanted intracamerally in normotensive rabbits for up to 8 weeks' duration. Devices were retrieved after rabbits were euthanized and evaluated for tissue adherence. The drug remaining in each device was analyzed by high performance liquid chromatography. Drug distribution in ocular tissues was measured by liquid chromatography coupled with a tandem mass spectrometry (LC/MS/MS).

Results

In vitro release of DE-117 showed zero-order release with a release rate of 0.5 μg/day over 6 months. Implantation in rabbit eyes demonstrated that the devices were well tolerated in the intracameral space. Quantification of DE-117 and hDE-117 (the hydrolyzed active form of DE-117) in ocular tissues (cornea, iris-ciliary body, aqueous humor, and vitreous humor) indicated sustained release of DE-117 and its conversion to hDE-117 when released from the device. Analysis of drug remaining in the device found that concentration of hDE-117 was below the limit of detection, indicating the encapsulated drug was protected from hydrolysis in the device.

Conclusions

Proof-of-concept PCL drug delivery devices containing DE-117 show promise as a long-term glaucoma treatment based on their zero-order drug release profile in vitro, biocompatibility in vivo, and effective distribution of released drug in relevant ocular tissues.

A Tunable, Biodegradable, Thin-Film Polymer Device as a Long-Acting Implant Delivering Tenofovir Alafenamide Fumarate for HIV Pre-exposure Prophylaxis

PURPOSE

The effectiveness of Tenofovir based HIV pre-exposure prophylaxis (PrEP) is proven, but hinges on correct and consistent use. User compliance and therapeutic effectiveness can be improved by long acting drug delivery systems. Here we describe a thin-film polymer device (TFPD) as a biodegradable subcutaneous implant for PrEP.

METHODS

A thin-film polycaprolactone (PCL) membrane controls drug release from a reservoir. To achieve membrane controlled release, TAF requires a formulation excipient such as PEG300 to increase the dissolution rate and reservoir solubility. Short-term In vitro release studies are used to develop an empirical design model, which is applied to the production of in vitro prototype devices demonstrating up to 90-days of linear release and TAF chemical stability.

RESULTS

The size and shape of the TFPD are tunable, achieving release rates ranging from 0.5 to 4.4 mg/day in devices no larger than a contraceptive implant. Based on published data for oral TAF, subcutaneous constant-rate release for HIV PrEP is estimated at <2.8 mg/day. Prototype devices demonstrated linear release at 1.2 mg/day for up to 90 days and at 2.2 mg/day for up to 60 days.

CONCLUSIONS

We present a biodegradable TFPD for subcutaneous delivery of TAF for HIV PrEP. The size, shape and release rate of the device are tunable over a >8-fold range.