Controlling Burst and Final Drug Release Times from Porous Polylactide Devices Derived from Co-continuous Polymer Blends

Liposome-Hydrogel Composites for Controlled Drug Delivery Applications

Various controlled delivery systems (CDSs) have been developed to overcome the shortcomings of traditional drug formulations (tablets, capsules, syrups, ointments, etc.). Among innovative CDSs, hydrogels and liposomes have shown great promise for clinical applications thanks to their cost-effectiveness, well-known chemistry and synthetic feasibility, biodegradability, biocompatibility and responsiveness to external stimuli. To date, several liposomal- and hydrogel-based products have been approved to treat cancer, as well as fungal and viral infections, hence the integration of liposomes into hydrogels has attracted increasing attention because of the benefit from both of them into a single platform, resulting in a multifunctional drug formulation, which is essential to develop efficient CDSs. This short review aims to present an updated report on the advancements of liposome-hydrogel systems for drug delivery purposes.

Modulating Drug Release from Short Poly(ethylene glycol) Block Initiated Poly(L-lactide) Di-block Copolymers

This paper investigates drug release from a novel series of mPEG-functionalised PLLA polymers whose individual components (PEG and PLLA) have regulatory FDA approval. Two processing methods were explored to understand their effect on the morphology and drug release profiles of the polymers, with and without mPEG functionalisation. In the first method the polymer and Propranolol.HCl drug powders were mixed together before injection moulding. In the second method, supercritical CO2 was used to mix the polymer and drug before injection moulding. When non-functionalised PLLA was processed through injection moulding alone, there were no signs of polymer-drug interaction, and the drug was confined to crystals on the surface. This resulted in up to 85 wt% burst release of propranolol.HCl after one day of incubation. By contrast, injection moulding of mPEG-functionalised polymers resulted in the partial dissolution of drug in the polymer matrix and a smaller burst (50 wt% drug) followed by sustained release. This initial burst release was completely eliminated from the profile of mPEG-functionalised polymers processed via supercritical CO2. The addition of mPEG facilitated the distribution of the drug into the bulk matrix of the polymer. Paired with supercritical CO2 processing, the drug release profile showed a slow, sustained release throughout the 4 months of the study.

Zero-order drug delivery: State of the art and future prospects

Pharmaceutical drugs are an important part of the global healthcare system, with some estimates suggesting over 50% of the world's population takes at least one medication per day. Most drugs are delivered as immediate-release formulations that lead to a rapid increase in systemic drug concentration. Although these formulations have historically played an important role, they can be limited by poor patient compliance, adverse side effects, low bioavailability, or undesirable pharmacokinetics. Drug delivery systems featuring first-order release kinetics have been able to improve pharmacokinetics but are not ideal for drugs with short biological half-lives or small therapeutic windows. Zero-order drug delivery systems have the potential to overcome the issues facing immediate-release and first-order systems by releasing drug at a constant rate, thereby maintaining drug concentrations within the therapeutic window for an extended period of time. This release profile can be used to limit adverse side effects, reduce dosing frequency, and potentially improve patient compliance. This review covers strategies being employed to attain zero-order release or alter traditionally first-order release kinetics to achieve more consistent release before discussing opportunities for improving device performance based on emerging materials and fabrication methods.

Cationic osteogenic peptide P15-CSP coatings promote 3-D osteogenesis in poly(epsilon-caprolactone) scaffolds of distinct pore size

P15-CSP is a biomimetic cationic fusion peptide that stimulates osteogenesis and inhibits bacterial biofilm formation when coated on 2-D surfaces. This study tested the hypothesis that P15-CSP coatings enhance 3-D osteogenesis in a porous but otherwise hydrophobic poly-(ɛ-caprolactone) (PCL) scaffold. Scaffolds of 84 µm and 141 µm average pore size were coated or not with Layer-by-Layer polyelectrolytes followed by P15-CSP, seeded with adult primary human mesenchymal stem cells (MSCs), and cultured 10 days in proliferation medium, then 21 days in osteogenic medium. Atomic analyses showed that P15-CSP was successfully captured by LbL. After 2 days of culture, MSCs adhered and spread more on P15-CSP coated pores than PCL-only. At day 10, all constructs contained nonmineralized tissue. At day 31, all constructs became enveloped in a "skin" of tissue that, like 2-D cultures, underwent sporadic mineralization in areas of high cell density that extended into some 141 µm edge pores. By quantitative histomorphometry, 2.5-fold more tissue and biomineral accumulated in edge pores versus inner pores. P15-CSP specifically promoted tissue-scaffold integration, fourfold higher overall biomineralization, and more mineral deposits in the outer 84 µm and inner 141 µm pores than PCL-only (p < 0.05). 3-D Micro-CT revealed asymmetric mineral deposition consistent with histological calcium staining. This study provides proof-of-concept that P15-CSP coatings are osteoconductive in PCL pore surfaces with 3-D topography. Biomineralization deeper than 150 µm from the scaffold edge was optimally attained with the larger 141 µm peptide-coated pores. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2171-2181, 2017.

Poly(lactic acid) blends in biomedical applications

Poly(lactic acid) (PLA) has become a "material of choice" in biomedical applications for its ability to fulfill complex needs that typically include properties such as biocompatibility, biodegradability, mechanical strength, and processability. Despite the advantages of pure PLA in a wider spectrum of applications, it is limited by its hydrophobicity, low impact toughness, and slow degradation rate. Blending PLA with other polymers offers a convenient option to enhance its properties or generate novel properties for target applications without the need to develop new materials. PLA blends with different natural and synthetic polymers have been developed by solvent and melt blending techniques and further processed based on end-use applications. A variety of PLA blends has been explored for biomedical applications such as drug delivery, implants, sutures, and tissue engineering. This review discusses the opportunities for PLA blends in the biomedical arena, including the overview of blending and postblend processing techniques and the applications of PLA blends currently in use and under development.

Powering tyrosol antioxidant capacity and osteogenic activity by biocatalytic polymerization

Oxidative polymerization of tyrosol afforded a mixture of oligomers (OligoTyr) which proved to be more active than tyrosol as antioxidant and as stimulator of alkaline phosphatase (ALP) activity when loaded into polylactic acid (PLA) scaffolds.

Biodegradable liposome-encapsulated hydrogels for biomedical applications: a marriage of convenience

Liposome-encapsulated hydrogels have emerged as an attractive strategy for medical and pharmaceutical applications.

Crystallization-modulated nanoporous polymeric materials with hierarchical patterned surfaces and 3D interpenetrated internal channels

Poly(oxymethylene)/poly(L-lactic acid) (POM/PLLA) blends are typical melt-miscible binary systems. During isothermal crystallization at various temperatures, in the presence of amorphous PLLA chains, POM crystallizes into banded spherulites with different band spaces, which forms a continuous crystalline phase and serves as a sturdy frame in the final porous materials. On the other hand, the amorphous PLLA chains are simultaneously expelled out from POM crystal lamellae to generate the other continuous phase during the crystallization of POM. Consequently, the interpenetration of the POM lamellae and the amorphous PLLA phase construct a cocontinuous phase structure. All the PLLA constituents are fully included in the interlamellar or interfibrillar of POM crystals. Thus, nanoporous POM materials with hierarchical patterned surface and 3D interpenetrated internal channels have been successfully obtained by extracting the amorphous PLLA phase. It is further found that the POM crystal morphologies in the blends are much dependent on the crystallization conditions. Therefore, the hierarchical patterned structure and the size of internal channels (pore size) can be modulated by adjusting the crystallization conditions.

Electrospun Fibers of Enteric Polymer for Controlled Drug Delivery

The production of electrospun fibers of enteric polymer for controlled delivery of drugs represents a simple and low cost procedure with promising advantages relative to the longer therapeutic window provided by cylindrical geometry in association with intrinsic properties of pH-dependent drug carriers. In this work, we have explored the incorporation of additives (block copolymers of poly(ethylene)-b-poly(ethylene oxide)) into matrix of Eudragit L-100 and the effective action of hybrid composites on delivery of nifedipine, providing improvement in the overall process of controlled release of loaded drug.

Banded spherulite templated three-dimensional interpenetrated nanoporous materials

Unique 3-D interconnected nanoporous polymer materials were fabricated by using the banded spherulites as the templates.

Triple shape memory effects of cross-linked polyethylene/polypropylene blends with cocontinuous architecture

In this paper, the triple shape memory effects (SMEs) observed in chemically cross-linked polyethylene (PE)/polypropylene (PP) blends with cocontinuous architecture are systematically investigated. The cocontinuous window of typical immiscible PE/PP blends is the volume fraction of PE (v(PE)) of ca. 30-70 vol %. This architecture can be stabilized by chemical cross-linking. Different initiators, 2,5-dimethyl-2,5-di(tert-butylperoxy)-hexane (DHBP), dicumylperoxide (DCP) coupled with divinylbenzene (DVB) (DCP-DVB), and their mixture (DHBP/DCP-DVB), are used for the cross-linking. According to the differential scanning calorimetry (DSC) measurements and gel fraction calculations, DHBP produces the best cross-linking and DCP-DVB the worst, and the mixture, DHBP/DCP-DVB, is in between. The chemical cross-linking causes lower melting temperature (Tm) and smaller melting enthalpy (ΔHm). The prepared triple shape memory polymers (SMPs) by cocontinuous immiscible PE/PP blends with v(PE) of 50 vol % show pronounced triple SMEs in the dynamic mechanical thermal analysis (DMTA) and visual observation. This new strategy of chemically cross-linked immiscible blends with cocontinuous architecture can be used to design and prepare new SMPs with triple SMEs.

Electric field induced morphological transitions in polyelectrolyte multilayers

In this work, the morphological transitions in weak polyelectrolyte (PE) multilayers (PEMs) assembled from linear poly(ethylene imine) (LPEI) and poly(acrylic acid) (PAA) upon application of an electric field were studied. Exposure to an electric field results in the creation of a porous structure, which can be ascribed to local changes in pH from the hydrolysis of water and subsequent structural rearrangements of the weak PE constituents. Depending on the duration of application of the field, the porous transition gradually develops into a range of structures and pore sizes. It was discovered that the morphological transition of the LbL films starts at the multilayer-electrode interface and propagates through the film. First an asymmetrical structure forms, consisting of microscaled pores near the electrode and nanoscaled pores near the surface in contact with the electrolyte solution. At longer application of the field the porous structures become microscaled throughout. The results revealed in this study not only demonstrate experimental feasibility for controlling variation in pore size and porosity of multilayer films but also deepens the understanding of the mechanism of the porous transition. In addition, electrical potential is used to release small molecules from the PEMs.

Modification of the release characteristics of estradiol encapsulated in PLGA particles via surface coating

Background: Drug-loaded poly(lactide-co-glycolide) particles (100–4500 nm in diameter) were prepared via the electrospraying method. An extensive study was then carried out to determine the parameters affecting the release profile of estradiol (the drug or active pharmaceutical ingredient) in order to facilitate minimum initial burst release of estradiol. Results and discussion: The three most important factors affecting estradiol release were identified as: particle size, coating of the particles with chitosan/gelatin and the concentration of the coating agent. It was shown that coating the particles with chitosan significantly reduced the burst and initial release without affecting the subsequent release profile. Conclusions: This work demonstrates a powerful method of generating drug-loaded polymeric particles with modified release behavior and control over the initial release phase. The surface-modified particles may be useful in controlled therapeutic delivery systems to minimize undesirable side effects.