Microspheres for Drug Delivery

Advanced 3D Printing Strategies for the Controlled Delivery of Growth Factors

The controlled delivery of growth factors (GFs) from tissue engineered constructs represents a promising strategy to improve tissue repair and regeneration. However, despite their established key role in tissue regeneration, the use of GFs is limited by their short half-life in the in vivo environment, their dose-dependent effectiveness, and their space- and time-dependent activity. Promising results have been obtained both in vitro and in vivo in animal models. Nevertheless, the clinical application of tissue engineered constructs releasing GFs is still challenging due to the several limitations and risks associated with their use. 3D printing and bioprinting, by allowing the microprecise spatial deposition of multiple materials and the fabrication of complex geometries with high resolution, offer advanced strategies for an optimal release of GFs from tissue engineered constructs. This review summarizes the strategies that have been employed to include GFs and their delivery system into biomaterials used for 3D printing applications to optimize their controlled release and to improve both the in vitro and in vivo regeneration processes. The approaches adopted to overcome the above-mentioned limitations are presented, showing the potential of the technology of 3D printing to get one step closer to clinical applications.

Single Infrared Spectrum Enables Simultaneous Identification of (Bio)Chemical Nature and Particle Size of Microorganisms and Synthetic Microplastic Beads

Populations of nearly identical chemical and biological microparticles include the synthetic microbeads used in cosmetic, biomedical, agri-food, and pharmaceutical industries as well as the class of living microorganisms such as yeast, pollen, and biological cells. Herein, we identify simultaneously the size and chemical nature of spherical microparticle populations with diameters larger than 1 μm. Our analysis relies on the extraction of both physical and chemical signatures from the same optical spectrum recorded using attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectroscopy. These signatures are the spectral resonances caused by the microparticles, which depend on their size and the absorption peaks revealing their chemical nature. We validate the method first on separated and mixed groups of spherical microplastic particles of two different diameters, where the method is used to calculate the diameter of the microspherical particles. Then, we apply the method to correctly identify and measure the diameter of Saccharomyces cerevisiae yeast cells. Theoretical simulations to help in understanding the effect of size distribution and dispersion support our results.

Gellan Gum/Alginate Microparticles as Drug Delivery Vehicles: DOE Production Optimization and Drug Delivery

Gellan gum is a biocompatible and easily accessible polysaccharide with excellent properties to produce microparticles as drug delivery systems. However, the production methods often fail in reproducibility, compromising the translational potential of such systems. In this work, the production of gellan gum-based microparticles was optimized using the coaxial air flow method, and an inexpensive and reproducible production method. A design of experiments was used to identify the main parameters that affect microparticle production and optimization, focusing on diameter and dispersibility. Airflow was the most significant factor for both parameters. Pump flow affected the diameter, while the gellan gum/alginate ratio affected dispersibility. Microparticles were revealed to be sensitive to pH with swelling, degradation, and encapsulation efficiency affected by pH. Using methylene blue as a model drug, higher encapsulation, and swelling indexes were obtained at pH 7.4, while a more pronounced release occurred at pH 6.5. Within PBs solutions, the microparticles endured up to two months. The microparticle release profiles were studied using well-known models, showing a Fickian-type release, but with no alteration by pH. The developed microparticles showed promising results as drug-delivery vehicles sensitive to pH.

Continuous Processing of Micropellets via Hot-Melt Extrusion

Microparticulate drug delivery systems, e.g., micropellets (MPs), are used in a variety of pharmaceutical formulations such as suspensions, injectable systems, and capsules. MPs are currently manufactured mainly via batch, solvent-based processes, e.g., spray-drying and solvent evaporation-extraction. In this paper, we present a novel, solvent-free, continuous hot-melt extrusion-based approach with an inline cold pelletization step and the potential of unprecedented on-the-fly formulation changes, aiming at producing the smallest particles usable for injectable applications. A biodegradable, crystalline dispersion consisting of poly(DL-lactic acid) (PLA) filled with metformin as the model drug was chosen on purpose to elucidate the broad applicability of the process also to formulations with limited stretchability and complex pelletizability. Next to optical/statistical particle analyses and in-line high-speed camera investigations providing insights into the pelletization process, the injectability of the most promising micropellets was compared to that of one marketed formulation. Fast extrudate haul-off speeds and high numbers of pelletizer knives resulted in particles with a narrow and small particle size distribution with a d₅₀ below 270 µm and aspect ratios close to 1. To omit protruding drug particles to ensure sufficient extrudate stretchability and allow for the smallest MPs, it was found that the d₉₀ of the embedded drug must be significantly below the extrudate diameter. Upon adapting the syringe diameter, the produced micropellets revealed similar injectability parameters to the marketed formulation, showcasing the potential that the proposed setup has for the manufacturing of novel microparticulate formulations.

Advances in biomaterials for the treatment of retinoblastoma

Retinoblastoma is the most common primary intraocular malignancy in children. Although traditional chemotherapy has shown some success in retinoblastoma management, there are several shortcomings to this approach, including inadequate pharmacokinetic parameters, multidrug resistance, low therapeutic efficiency, nonspecific targeting, and the need for adjuvant therapy, among others. The revolutionary developments in biomaterials for drug delivery have enabled breakthroughs in cancer management. Today, biomaterials are playing a crucial role in developing more efficacious retinoblastoma treatments. The key goal in the evolution of drug delivery biomaterials for retinoblastoma therapy is to resolve delivery-associated obstacles and lower nonlocal exposure while ameliorating certain adverse effects. In this review, we will first delve into the historical perspective of retinoblastoma with a focus on the classical treatments currently used in clinics to enhance patients' quality of life and survival rate. As we move along, we will discuss biomaterials for drug delivery applications. Various aspects of biomaterials for drug delivery will be dissected, including their features and recent advances. In accordance with the current advances in biomaterials, we will deliver a synopsis on the novel chemotherapeutic drug delivery strategies and evaluate these approaches to gain new insights into retinoblastoma treatment.

Efficient aqueous remote loading of peptides in poly(lactic-co-glycolic acid)

Poly(lactic-co-glycolic acid) (PLGA) long-acting release depots are effective for extending the duration of action of peptide drugs. We describe efficient organic-solvent-free remote encapsulation based on the capacity of common uncapped PLGA to bind and absorb into the polymer phase net positively charged peptides from aqueous solution after short exposure at modest temperature. Leuprolide encapsulated by this approach in low-molecular-weight PLGA 75/25 microspheres slowly and continuously released peptide for over 56 days in vitro and suppressed testosterone production in rats in an equivalent manner as the 1-month Lupron Depot®. The technique is generalizable to encapsulate a number of net cationic peptides of various size, including octreotide, with competitive loading and encapsulation efficiencies to traditional methods. In certain cases, in vitro and in vivo performance of remote-loaded PLGA microspheres exceeded that relative to marketed products. Remote absorption encapsulation further removes the need for a critical organic solvent removal step after encapsulation, allowing for simple and cost-effective sterilization of the drug-free microspheres before encapsulation of the peptide.

Systematic Review and Pharmacokinetic Meta-analysis of Doxorubicin Exposure in Transcatheter Arterial Chemoembolization and Doxorubicin-Eluted Beads Chemoembolization for Treatment of Unresectable Hepatocellular Carcinoma

BACKGROUND

Almost 15 years after the introduction of transarterial chemoembolization (TACE) with drug-eluting beads (DEB-TACE) for hepatocellular carcinoma (HCC) therapy, the mean peak plasma concentration (C_max) and area under the concentration-time curve (AUC) for doxorubicin have still not been systematically reviewed or meta-analyzed.

OBJECTIVE

To conduct a systematic review and meta-analysis of available data and establish a reference range for C_max and AUC of doxorubicin DEB-TACE and TACE, as well as explore the potential influence of microspheres' size and type on these parameters.

METHODS

PubMed, EMBASE, and Web of Science were searched from August 1992 through December 2021. Studies measuring exposure parameters among HCC patients treated with doxorubicin DEB-TACE without restriction on language were included. Two independent reviewers extracted and unified data sets for pooled estimate analysis. The quality of the evidence was assessed via the Grading of Recommendations Assessment, Development and Evaluation framework. The ClinPK Statement checklist and Newcastle-Ottawa Scale (NOS) were used to determine the quality of studies.

RESULTS

Out of 666 studies, 246 full-text were reviewed, and 8 studies entered the meta-analysis (120 patients). C_max and AUC of doxorubicin were 7.52-fold (95% CI 7.65 to 7.42-fold; P < 0.0001) and 1.91-fold (95% CI 1.95 to 1.88-fold; P = 0.0001) lower with DEB-TACE compared to TACE. Significant reduction in pooled standardized mean difference (SMD) of C_max and AUC was observed with DEB-TACE versus TACE in direct comparison analysis (- 2.93; 95% CI - 3.60 to - 2.26, P < 0.00001, and - 1.73 95% CI - 2.55 to - 0.91, P < 0.0001, respectively). Moreover, in DEB-TACE stratification analysis, small microspheres revealed higher C_max, AUC and tumor response rate as well as lower complication rate.

LIMITATION

The heterogeneity could not be completely addressed through sensitivity and stratification analysis.

CONCLUSION

This meta-analysis provides exposure parameters of doxorubicin and justifies the advantage of DEB-TACE over TACE in terms of safety for patients with unresectable HCC. This study showed a marked association between the size of microsphere and exposure parameters of doxorubicin supporting the preference for small microspheres in DEB-TACE. The moderate and low quality of evidence is assigned to the C_max and AUC, respectively.

An overview of the production methods for core-shell microspheres for parenteral controlled drug delivery

Core-shell microspheres hold great promise as a drug delivery system because they offer several benefits over monolithic microspheres in terms of release kinetics, for instance a reduced initial burst release, the possibility of delayed (pulsatile) release, and the possibility of dual-drug release. Also, the encapsulation efficiency can significantly be improved. Various methods have proven to be successful in producing these core-shell microspheres, both the conventional bulk emulsion solvent evaporation method and methods in which the microspheres are produced drop by drop. The latter have become increasingly popular because they provide improved control over the particle characteristics. This review assesses various production methods for core-shell microspheres and summarizes the characteristics of formulations prepared by the different methods, with a focus on their release kinetics.

Microfluidic Chip Device for In Situ Mixing and Fabrication of Hydrogel Microspheres via Michael-Type Addition

Hydrogel microspheres are sought for a variety of biomedical applications, including therapeutic and cellular delivery, sensors, and lubricants. Robust fabrication of hydrogel microspheres with uniform sizes and properties can be achieved using microfluidic systems that rely on droplet formation and subsequent gelation to form microspheres. Such systems work well when gelation is initiated after droplet formation but are not practical for timed gelation systems where gelation is initiated prior to droplet formation; premature gelation can lead to device blockage, variable microsphere diameter due to viscosity changes in the precursor solution, and limited numbers of microspheres produced in a single run. To enable microfluidic fabrication of microspheres from timed gelation hydrogel systems, an in situ mixing region is needed so that various hydrogel precursor components can be added separately. Here, we designed and evaluated three mixing devices for their effectiveness at mixing hydrogel precursor solutions prior to droplet formation and subsequent gelation. The serpentine geometry was found to be the most effective and was further improved with the inclusion of a pillar array to increase agitation. The optimized device was shown to fully mix precursor solutions and enable the fabrication of monodisperse polyethylene glycol microspheres, offering great potential for use with timed gelation hydrogel systems.

Micronutrients encapsulation by starch as an enhanced efficiency fertilizer

Developing different paths to achieve sustainable agriculture is no longer an option; it is a necessity. EEF materials are alternatives to improve the efficacy of the agrochemicals in the soil and plant, reducing wasting and environmental contamination. The present work aims to develop EEF materials based on starch and micronutrients, considering few works address EEFs materials with micronutrients. Monoelementary dispersions of gelatinized starch with micronutrients (Fe, Cu, Mn) were spray-dried and thermally, structurally, and morphologically characterized. We evaluated water-medium nutrient release, release kinetics, and the swelling degree. Different micronutrients affect morphology, size distribution, swelling degree, release, kinetics, and interaction between polymer-nutrient. Bigger particle sizes achieved a higher swelling degree, which led to decreased micronutrient release in the water. The Peppas-Sahlin model mainly ruled the release kinetics (fitted to all the materials). This result confirmed our hypothesis that a swelling starch delays the release.

A Recent Update on Drug Delivery Systems for Pain Management

Pain remains a global health challenge affecting approximately 1.5 billion people worldwide. Pain has been an implicit variable in the equation of human life for many centuries considering different types and the magnitude of pain. Therefore, developing an efficacious drug delivery system for pain management remains an open challenge for researchers in the field of medicine. Lack of therapeutic efficacy still persists, despite high throughput studies in the field of pain management. Research scientists have been exploiting different alternatives to curb the adverse side effects of pain medications or attempting a more substantial approach to minimize the prevalence of pain. Various drug delivery systems have been developed such as nanoparticles, microparticles to curb adverse side effects of pain medications or minimize the prevalence of pain. This literature review firstly provides a brief introduction of pain as a sensation and its pharmacological interventions. Second, it highlights the most recent studies in the pharmaceutical field for pain management and serves as a strong base for future developments. Herein, we have classified drug delivery systems based on their sizes such as nano, micro, and macro systems, and for each of the reviewed systems, design, formulation strategies, and drug release performance has been discussed.

Mechanical properties of cell- and microgel bead-laden oxidized alginate-gelatin hydrogels

3D-printing technologies, such as biofabrication, capitalize on the homogeneous distribution and growth of cells inside biomaterial hydrogels, ultimately aiming to allow for cell differentiation, matrix remodeling, and functional tissue analogues. However, commonly, only the mechanical properties of the bioinks or matrix materials are assessed, while the detailed influence of cells on the resulting mechanical properties of hydrogels remains insufficiently understood. Here, we investigate the properties of hydrogels containing cells and spherical PAAm microgel beads through multi-modal complex mechanical analyses in the small- and large-strain regimes. We evaluate the individual contributions of different filler concentrations and a non-fibrous oxidized alginate-gelatin hydrogel matrix on the overall mechanical behavior in compression, tension, and shear. Through material modeling, we quantify parameters that describe the highly nonlinear mechanical response of soft composite materials. Our results show that the stiffness significantly drops for cell- and bead concentrations exceeding four million per milliliter hydrogel. In addition, hydrogels with high cell concentrations (≥6 mio ml^-1) show more pronounced material nonlinearity for larger strains and faster stress relaxation. Our findings highlight cell concentration as a crucial parameter influencing the final hydrogel mechanics, with implications for microgel bead drug carrier-laden hydrogels, biofabrication, and tissue engineering.

Scar free healing of full thickness diabetic wounds: A unique combination of silver nanoparticles as antimicrobial agent, calcium alginate nanoparticles as hemostatic agent, fresh blood as nutrient/growth factor supplier and chitosan as base matrix

Healing of diabetic wounds present a big challenge due to insufficient vascular supply and bacterial infection. We developed chitosan based biodegradable polymeric hydrogel containing silver nanoparticles (AgNPs) as antimicrobial agent and calcium alginate nanoparticles (Ca-AlgNps) as hemostatic agent to address this problem. The prepared Chitosan/Ca-AlgNps/AgNPs hydrogel showed broad spectrum antimicrobial properties against both Gram negative (E. coli, P. aeruginosa) and Gram positive (B. subtilis, S. aureus) bacteria. Taken into account the blood as a vital material containing various circulatory fibrocytes, growth factors, cytokines, platelets and macrophages etc., we incorporated the fresh blood of the same animal to the prepared Chitosan/Ca-Alg Nps/AgNPs hydrogel. In-vivo animal studies of Chitosan/Ca-AlgNps/AgNPs hydrogel and blood mixed Chitosan/Ca-AlgNps/AgNPs hydrogel exhibit 83.5 ± 4.4% and 99.8 ± 2.0% closure of wound respectively, on day 15 as compared to 41.5 ± 3.2% in diabetic control and 60.3 ± 2.2% in commercially available wound healing cream, Silverex Heal. The incorporation of fresh blood to the prepared hydrogel has advantage in terms of supplying growth factors, platelets, circulatory fibrocytes and cytokines which further enhanced the wound healing mechanism in diabetic rats. This work opens a novel idea to formulate hydrogels based dressings for diabetic wound healing.

Flow rate effect on partially modified potato starch microspheres formation process

Natural biopolymers are the most likely choice for biomedical applications, and starches can be considered the best materials for such applications. This comes from the fact of their natural origin and their high biodegradable behavior. Native starches have weak hydrogen bonding and a leaching behavior – making it a candidate for drug delivery application. Still, to make starch useful as a drug delivery carrier, this hydrogen bonding must be strengthened. In this work, native sweet potato starch was used, and the hydrogen bonding between starch molecules was enhanced by introducing glycerol as a hydrogen bonding source and sodium alginate (SA) as a thickener. This blend was tested by means of FTIR and DSC, and based on the test results, improved hydrogen bonding had taken place. Furthermore, potato starch microspheres were successfully produced at different flow rates. In the work, a microfluidic capillary device was harnessed to form microsphere generating total flow rates ranging between (0.00031 and 0.00054) cm3/sec. Herein, a starch/sodium alginate/glycerol mixture was used as a dispersed phase and PVA+tween 80 was used as continuous phase. At high flow rates (0.00062-0.00054) cm3/sec, the microspheres took an oval shape. At flow rates (0.00034-0.00048) cm3/sec, the microspheres took a spherical shape. At very low flow rate (0.00031) cm3/sec, the microspheres shell was weak and caused core oozing. In this work, starch microspheres were successfully formed with diameter ranging from (151-263) µm.

A Novel Prototype Device for Microencapsulation of Benznidazole: In Vitro/In Vivo Studies

This study was aimed to design a simple and novel prototype device for the production of polymeric microparticles. To prove the effectiveness of this device, benznidazole microparticles using chitosan as carrier and NaOH, KOH, or SLS as counter ions were used. For comparison, benznidazole microparticles were prepared by the conventional dripping technique (syringe and gauge) using the same excipients. Microparticles were characterized in terms of encapsulation efficiency, particle shape, size and surface topography, crystallinity characteristics, thermal behavior, and dissolution rate. Then, the pharmacokinetic parameters were evaluated after the oral administration of the microparticles to healthy Wistar rats. The prepared formulations, by means of this device, showed good drug encapsulation efficiency (> 70%). Release studies revealed an increased dissolution of benznidazole from chitosan microparticles prepared using the novel device. It achieved more than 90% in 60 min, while those of the conventional microparticles and raw drug achieved 65% and 68%, respectively, during the same period. Almost spherical benznidazole microparticles with a smooth surface and size around 10-30 μm were observed using scanning electron microscopy. Thermal analysis and X-ray diffraction studies suggested a partial reduction of drug crystallinity. Moreover, the relative oral bioavailability of the novel benznidazole microparticles showed that the area under the curve for the microencapsulated drug was 10.3 times higher than the raw drug. Thus, these findings indicate that the designed glass prototype device is a useful alternative to formulate benznidazole polymeric microparticles with improved biopharmaceutical properties and could be useful for other therapeutic microparticulate systems.

Flow-through cell-based in vitro release method for triamcinolone acetonide poly (lactic-co-glycolic) acid microspheres

The main objective of the current research was to develop a compendial flow-through cell apparatus based in vitro release testing method for sustained-release triamcinolone acetonide-loaded poly (lactic-co-glycolic) acid (PLGA) microspheres. Media-based and instrument-based parameters, such as surfactant type, concentration, media volume, flow rate, and testing temperature, were investigated. In addition, a detailed exploration was performed to reveal polymer degradation encompassing pore formation, channeling, and triamcinolone acetonide release from microspheres using freeze-fracture scanning electron microscopy. The developed USP apparatus 4 method demonstrated more than 85% drug release from the microspheres in 12 days and showcased reproducibility between different microsphere batches. Large medium volume (15 times saturation solubility) at low surfactant concentration was identified as a critical media-based parameter, with potential application in testing of other sensitive poorly soluble drugs. At 35 °C, drug release via pore channeling to the surface was evident, whereas at 39 °C, drug release slowed due to polymer plasticization. It was demonstrated here for the first time that elevated temperature-accelerated testing does not work for all PLGA-based microsphere products.

Entrapment and release kinetics study of dyes from BSA microspheres forming a matrix and a reservoir system

Two kinds of Bovine Serum Albumin (BSA)-loaded microspheres were prepared in water-organic bilayer systems using ultrasonic irradiation.

The Extracellular Matrix and Biocompatible Materials in Glioblastoma Treatment

During cancer genesis, the extracellular matrix (ECM) in the human brain undergoes important transformations, starting to resemble embryonic brain cell milieu with a much denser structure. However, the stiffness of the tumor ECM does not preclude cancer cells from migration. The importance of the ECM role in normal brain tissue as well as in tumor homeostasis has engaged much effort in trials to implement ECM as a target and an instrument in the treatment of brain cancers. This review provides a detailed analysis of both experimental and applied approaches in combined therapy for gliomas in adults. In general, matrix materials for glioma treatment should have properties facilitating the simplest delivery into the body. Hence, to deliver an artificial implant directly into the operation cavity it should be packed into a gel form, while for bloodstream injections matrix needs to be in the form of polymer micelles, nanoparticles, etc. Furthermore, the delivered material should mimic biomechanical properties of the native tissue, support vital functions, and slow down or stop the proliferation of surrounding cells for a prolonged period. The authors propose a two-step approach aimed, on the one hand, at elimination of remaining cancer cells and on the other hand, at restoring normal brain tissue. Thereby, the first bioartificial matrix to be applied should have relatively low elastic modulus should be loaded with anticancer drugs, while the second material with a higher elastic modulus for neurite outgrowth support should contain specific factors stimulating neuroregeneration.

In vitro cellular testing of strontium/calcium substituted phosphate glass discs and microspheres shows potential for bone regeneration

Phosphate-based glasses (PBGs) are ideal materials for regenerative medicine strategies because their composition, degradation rates, and ion release profiles can easily be controlled. Strontium has previously been found to simultaneously affect bone resorption and deposition. Therefore, by combining the inherent properties of resorbable PBG and therapeutic activity of strontium, these glasses could be used as a delivery device of therapeutic factors for the treatment of orthopaedic diseases such as osteoporosis. This study shows the cytocompatibility and osteogenic potential of PBGs where CaO is gradually replaced by SrO in the near invert glass system 40P2 O5 ·(16-x)CaO·20Na2 O·24MgO·xSrO (x = 0, 4, 8, 12, and 16 mol%). Direct seeding of MG63 cells onto glass discs showed no significant difference in cell metabolic activity and DNA amount measurement across the different formulations studied. Cell attachment and spreading was confirmed via scanning electron microscopy (SEM) imaging at Days 3 and 14. Alkaline phosphatase (ALP) activity was similarly maintained across the glass compositions. Follow-on studies explored the effect of each glass composition in microsphere conformation (size: 63-125 μm) on human mesenchymal stem cells (hMSCs) in 3D cultures, and analysis of cell metabolic activity and ALP activity showed no significant differences at Day 14 over the compositional range investigated, in line with the observations from MG63 cell culture studies. Environmental SEM and live cell imaging at Day 14 of hMSCs seeded on the microspheres showed cell attachment and colonisation of the microsphere surfaces, confirming these formulations as promising candidates for regenerative medicine strategies addressing compromised musculoskeletal/orthopaedic diseases.

Materials Science and Design Principles of Growth Factor Delivery Systems in Tissue Engineering and Regenerative Medicine

Growth factors (GFs) are signaling molecules that direct cell development by providing biochemical cues for stem cell proliferation, migration, and differentiation. GFs play a key role in tissue regeneration, but one major limitation of GF-based therapies is dosage-related adverse effects. Additionally, the clinical applications and efficacy of GFs are significantly affected by the efficiency of delivery systems and other pharmacokinetic factors. Hence, it is crucial to design delivery systems that provide optimal activity, stability, and tunable delivery for GFs. Understanding the physicochemical properties of the GFs and the biomaterials utilized for the development of biomimetic GF delivery systems is critical for GF-based regeneration. Many different delivery systems have been developed to achieve tunable delivery kinetics for single or multiple GFs. The identification of ideal biomaterials with tunable properties for spatiotemporal delivery of GFs is still challenging. This review characterizes the types, properties, and functions of GFs, the materials science of widely used biomaterials, and various GF loading strategies to comprehensively summarize the current delivery systems for tunable spatiotemporal delivery of GFs aimed for tissue regeneration applications. This review concludes by discussing fundamental design principles for GF delivery vehicles based on the interactive physicochemical properties of the proteins and biomaterials.

Novel Pathway for Efficient Covalent Modification of Polyester Materials of Different Design to Prepare Biomimetic Surfaces

To form modern materials with biomimic surfaces, the novel pathway for surface functionalization with specific ligands of well-known and widely used polyester-based rigid media was developed and optimized. Two types of material bases, namely, poly(lactic acid) and poly(ε-caprolactone), as well as two types of material design, e.g., supermacroporous matrices and nanoparticles (NPs), were modified via covalent attachment of preliminary oxidized polyvinylsaccharide poly(2-deoxy-N-methacryloylamido-d-glucose) (PMAG). This polymer, being highly biocompatible and bioinspired, was used to enhance hydrophilicity of the polymer surface and to provide the elevated concentration of reactive groups required for covalent binding of bioligands of choice. The specialties of the interaction of PMAG and its preliminary formed bioconjugates with a chemically activated polyester surface were studied and thoroughly discussed. The supermacroporous materials modified with cell adhesion motifs and Arg-Gly-Asp-containing peptide (RGD-peptide) were tested in the experiments on bone tissue engineering. In turn, the NPs were modified with bioligands ("self-peptide" or camel antibodies) to control their phagocytosis that can be important, for example, for the preparation of drug delivery systems.

Innovations in gene and growth factor delivery systems for diabetic wound healing

The rise in lower extremity amputations due to nonhealing of foot ulcers in diabetic patients calls for rapid improvement in effective treatment regimens. Administration of growth factors (GFs) are thought to offer an off-the-shelf treatment; however, the dose- and time-dependent efficacy of the GFs together with the hostile environment of diabetic wound beds impose a major hindrance in the selection of an ideal route for GF delivery. As an alternative, the delivery of therapeutic genes using viral and nonviral vectors, capable of transiently expressing the genes until the recovery of the wounded tissue offers promise. The development of implantable biomaterial dressings capable of modulating the release of either single or combinatorial GFs/genes may offer solutions to this overgrowing problem. This article reviews the state of the art on gene and protein delivery and the strategic optimization of clinically adopted delivery strategies for the healing of diabetic wounds.

Preparation, structural characterisation and release study of novel hybrid microspheres entrapping nanoselenium, produced by green synthesis

The main goal of this study was to synthesise and characterise different formulations based on alginate and alginate/chitosan microspheres containing nanoselenium (nano-Se) for controlled delivery applications. Nanosize elemental selenium was produced by using probiotic yogurt bacteria (Lactobacillus casei) in a fermentation procedure. The structural and morphological characterisation of the microspheres was performed by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. FTIR and XRD pattern indicated that was an effective cross-linking of selenium nanoparticles within the polymeric matrix in both cases. The SEM images reveal that selenium nanoparticles are mainly exposed on the surface of alginate, in contrast to porous structure of alginate/chitosan/nano-Se, interconnected in a regular network. This architecture type has a considerable importance in the delivery process, as demonstrated by differential pulse voltammetry. Selenium release from both matrices is pH sensitive. Moreover, chitosan blended with alginate minimise the release of encapsulated selenium, in simulated gastric fluid, and prolong the duration of release in intestinal fluid. The overall effect is the enhancement of total percentage release concomitant with the longer duration of action. The authors' formulation based on alginate/chitosan is a convenient matrix to be used for selenium delivery in duodenum, caecum and colon.

3D printing integrated with controlled delivery for musculoskeletal tissue engineering

3D printing is an emerging tool to fabricate scaffolds for tissue engineering and regenerative medicine, benefited by customized design, tunable internal microstructure and a wide range of applicable materials. As a recent technical advancement, 3D-printed scaffolds have been incorporated with a controlled delivery of growth factors and/or other bioactive cues to facilitate tissue regeneration, in addition to providing a temporal structural substrate for cell and tissue ingrowth. This review covers a number of the existing approaches to incorporate a controlled delivery system in 3D-printed scaffolds from hydrogel adsorption and surface coating to chemical integration and embedding microspheres. In addition, we discuss the advantages and disadvantages of each delivery method integrated in 3D-printed scaffolds, outstanding challenges and future directions.

Preparation of a reproducible long-acting formulation of risperidone-loaded PLGA microspheres using microfluidic method

The aim of the present study is to prepare risperidone-loaded poly lactic-co-glycolic acid (PLGA) microspheres within microfluidic system and to achieve a formulation with uniform size and monotonic and reproducible release profile. In comparison to batch method, T-junction and serpentine chips were utilized and optimizing study was carried out at different processing parameters (e.g. PLGA and surfactant concentration and flow rates ratio of outer to inner phase). The computational fluid dynamic (CFD) modeling was performed, and loading and release study were carried out. CFD simulation indicates that increasing the flow rate of aqueous phase cause to decrease the droplet size, while the change in size of microspheres did not follow a specific pattern in the experimental results. The most uniform microspheres and narrowest standard deviation (66.79 μm ± 3.32) were achieved using T-junction chip, 1% polyvinylalcohol, 1% PLGA and flow rates ratio of 20. The microfluidic-assisted microspheres were more uniform with narrower size distribution. The release of risperidone from microspheres produced by the microfluidic method was more reproducible and closer to zero-order kinetic model. The release profile of formulation with 2:1 drug-to-polymer ratio was the most favorable release, in which 41.85% release could be achieved during 24 days.

Extended release, 6-month formulations of leuprolide acetate for the treatment of advanced prostate cancer: achieving testosterone levels below 20 ng/dl

INTRODUCTION

Luteinizing hormone-releasing hormone agonists such as leuprolide acetate (LA) are the most frequently utilized treatment of advanced prostate cancer as the regimen for achieving androgen deprivation therapy (ADT). The efficacy of LA is determined by extent of testosterone (T) suppression in prostate cancer patients. Although, the historical castrate T suppression target has been defined as < 50 ng/dl, this level may not be as low as required to deliver equivalent suppression as achieved by surgical castration. Recent studies have demonstrated that a T level as low as 20 ng/dl may produce improved clinical outcomes.

AREAS COVERED

LA is available in long-acting formulations that deliver active drug over the course of 1-6 months from a single-dose administration. The technologies utilized to provide sustained drug delivery differ: one mode of administration uses microspheres, which encapsulate the drug and are injected as a suspension intramuscularly; another mode of administration uses a liquid polymer that creates a single, solid depot after injection subcutaneously. This article will review the safety and efficacy of both 6-month LA formulations, as well as their impact in prostate cancer treatment.

EXPERT OPINION

As the understanding of optimal T castrate level evolves and may be refined pending new data from contemporaneous trials, achievement and maintenance of T levels well below 50 ng/dl may be important in evaluating potential differences in ADT regimens.

Development of microspheres for biomedical applications: a review

An overview of microspheres manufactured for use in biomedical applications based on recent literature is presented in this review. Different types of glasses (i.e. silicate, borate, and phosphates), ceramics and polymer-based microspheres (both natural and synthetic) in the form of porous , non-porous and hollow structures that are either already in use or are currently being investigated within the biomedical area are discussed. The advantages of using microspheres in applications such as drug delivery, bone tissue engineering and regeneration, absorption and desorption of substances, kinetic release of the loaded drug components are also presented. This review also reports on the preparation and characterisation methodologies used for the manufacture of these microspheres. Finally, a brief summary of the existing challenges associated with processing these microspheres which requires further research and development are presented.

In vitro evaluation of effects of sustained anti-TNF release from MPEG-PCL-MPEG and PCL microspheres on human rheumatoid arthritis synoviocytes

Anti-tumor necrosis factor α (TNFα) drugs such as etanercept (ETN) have been mostly used in systemic treatment of rheumatoid arthritis. To eliminate the side effects in long-term treatments and to achieve a local sustained anti-inflammatory effect, a controlled drug delivery system is needed for anti-TNFα drugs. This study aims to develop novel injectable microcarriers of ETN that can provide long-term controlled release of this protein drug upon intra-articular application. In this study, poly(ε-caprolactone) (PCL) and its copolymer with poly(ethylene glycol), methoxypoly(ethylene glycol)-poly(ε-caprolactone)-methoxypoly(ethylene glycol) microspheres (MPEG-PCL-MPEG) were compared for their prospective success in rheumatoid arthritis treatment. Microspheres with smooth surface of a mean particle diameter of approximately 5 μm were prepared with both polymers. MPEG-PCL-MPEG microspheres had higher encapsulation efficiency than PCL microspheres. The activity of encapsulated ETN within MPEG-PCL-MPEG microspheres also retained while 90% of the activity of ETN within PCL microspheres could retain during 90-day release. MPEG-PCL-MPEG microspheres showed faster ETN release compared to PCL microspheres in various release media. Cumulative amounts of ETN released from both types of microspheres were significantly lower in cell culture medium and in synovial fluids than in phosphate buffered saline. This was mainly due to protein adsorption onto microspheres. Hydrophilic MPEG segment enhanced ETN release while preventing protein adsorption on microspheres compared to PCL. Sustained ETN release from microspheres resulted with a significant decrease in pro-inflammatory cytokines (TNFα, IFNγ, IL-6, IL-17) and MMP levels (MMP-3, MMP-13), while conserving viability of fibroblast-like synoviocytes compared to the free drug. Results suggest that MPEG-PCL-MPEG is a potential copolymer of PCL that can be used in development of biomedical materials for effective local treatment purposes in chronic inflammatory arthritis owing to enhanced hydrophilicity. Yet, PCL microspheres are also promising systems having good compatibility to synoviocytes and would be especially the choice for treatment approach requiring longer term and slower release.

Solvent-free fabrication of polyHIPE microspheres for controlled release of growth factors

The growth factor bone morphogenetic protein 2 (BMP-2) is utilized in surgical procedures to improve bone regeneration; however, current treatments deliver BMP-2 at amounts greater than 100,000 fold of physiological levels, which increases treatment costs and risk of side effects. Drug-eluting microcarriers developed to improve these therapies have faced significant commercialization challenges including particle size distributions, solvent removal, low encapsulation efficiency, and bioactivity loss. In this study, a solvent-free method is presented for fabrication of uniform polyHIPE microspheres for controlled growth factor release. Emulsion templating principles and fluid dynamics were used to fabricate uniform particles with tunable particle size (200-800 μm) and pore size (10-30 μm). The ability to independently tune particle and pore size is expected to provide excellent control of release kinetics. Overall, this solvent-free method for making porous microspheres displays strong promise for the controlled release of BMP-2 and other growth factors.

Making the leap from daily oral dosing to long-acting injectables: lessons from the antipsychotics

There are now long-acting versions of six antipsychotic drugs on the U.S. market, and with them, five unique combinations of molecular form and delivery strategy long-acting-injectable-antipsychotics (LAIAs) show evidence of reduced relapses of schizophrenia, but their introduction has been slow, taking at least nine years after the approval of each oral drug. Oily solutions of lipophilic prodrugs were the first to enter the LAIA market, but they relied on esterification of a hydroxyl handle that was lost with the emergence of the atypical antipsychotics. A review of the literature and patents shows that companies tested many different approaches before reaching the currently marketed versions, including aqueous suspensions of poorly soluble salts, polymeric microspheres, and new approaches to making prodrugs. Yet, very little has been published to support faster development of safe long-acting injectables (LAIs). This review introduces some of the critical considerations in creating an LAI; then it analyzes the existing products and discusses areas where further research is needed. The available literature suggests that lipophilic prodrugs may be inherently safer than poorly soluble salts as LAIs. Other areas needing additional study include (1) the range of physical properties acceptable for LAIs and the effect of prodrug tail length in achieving them, and (2) the role of physiological responses at the injection site in the release of drug from a depot.

General synthesis of discrete mesoporous carbon microspheres through a confined self-assembly process in inverse opals

A general confined coassembly process has been demonstrated to produce discrete uniform mesoporous carbon microspheres with 0.8-1 μm particle size using 3-D-ordered macroporous silica as the template. The obtained mesoporous carbon microspheres (MC-MSs) have uniform and discrete spherical morphology, variable symmetry (hexagonal p6mm or cubic Im3m) of mesostructures, high specific surface areas (500-1100 m(2)/g), large pore volumes (0.6-2.0 cm(3)/g), and highly accessible large mesopores (7-10.3 nm). The particle size of the carbon microspheres can be easily tuned by simply using templates with different macropore sizes. It was found that the smaller MC-MSs (330 nm) with higher surface-to-volume ratio tend to shape into an integral monolithic MC-MS matrix and larger MC-MSs (>800 nm) with lower surface-to-volume ratio to discrete spherical morphology. This feature is attributed to the difference in shrinkage behavior of mesoporous carbon spheres confined in the macropores caused by the interaction between the silica wall and carbon microspheres. Adsorption experiments indicate that the cobalt-based nanoparticle-incorporated mesoporous carbon microspheres exhibit excellent size selectivity for protein adsorption in a complex solution and good magnetic separability for easy recycling.