The role of porosity in polyester microparticles for drug delivery

Polymer microparticles are a cornerstone in the field of injectable sustained delivery systems: They allow the entrapment of various types of hydrophobic or hydrophilic drugs including biopharmaceuticals. Microparticles can be prepared from the material of choice and tailored to specific target sizes. Importantly, they can retain the drug at the local administration site to achieve a sustained drug release for long-term therapeutic effects. This review focuses on the role of porosity of microparticles as a tremendously important property. Principles to prepare porous carriers via different techniques and additives are discussed, emphasizing that porosity is not a static property but can be dynamic, e.g., for particles from polylactide or poly(lactide-co-glycolide). Considering the contribution of porosity in the overall assessment of drug carrier systems, as well as their manipulation/alteration post-production such as by pore closing, will enlarge the understanding of polymer microparticles as an important class of modern pharmaceutical dosage forms.

Polyurethane infused with heparin capped silver nanoparticles dressing for wound healing application: Synthesis, characterization and antimicrobial studies

Burn and diabetic wounds present significant challenges due to their complex nature, delayed healing, pain, and high susceptibility to bacterial infections. In this study, we developed and evaluated polyurethane (PU) nanofibers embedded with heparin-functionalized silver nanoparticles (hep-AgNPs) using an electrospinning technique. The choice to functionalize silver nanoparticles with heparin was based on heparin's established role in modulating inflammation and promoting angiogenesis. The electrospun nanofibers exhibited smooth, bead-free morphology with diameters ranging from 300 to 500 nm and demonstrated a sustained release of silver over seven days, offering continuous antimicrobial protection. Mechanical testing of the nanofibers revealed excellent strength and elasticity, making them well-suited for flexible wound dressings. The nanofibers also showed superior water absorption, fluid retention, and controlled water vapor transmission, essential for maintaining a moist wound environment conducive to healing. In vitro biocompatibility assays confirmed that the PU/hep-AgNPs bandages were non-toxic to keratinocytes and fibroblasts and significantly accelerated wound closure, as evidenced by scratch assays. The nanofibrous bandages also exhibited potent antibacterial activity against Staphylococcus aureus and Salmonella Typhimurium, two common wound pathogens. Overall, our findings demonstrate that PU/hep-AgNPs nanofibrous bandages are a promising candidate for chronic wound healing. They combine excellent biocompatibility, anti-inflammatory properties, and strong antimicrobial activity, which collectively contribute to faster wound healing and reduced risk of infection.

Synthesis, characterization, and surface modification of degradable polar hydrophobic ionic polyurethane nanoparticles for the delivery of therapeutics to vascular tissue

Degradable polar hydrophobic ionic polyurethanes (D-PHI) are an emerging class of biomaterials with particular significance for blood-contacting applications due to their immunomodulatory effects and highly customizable block chemistry. In this manuscript, D-PHI polymer was formulated as a nanoparticle excipient for the first time by inverse emulsion polymerization. The nanoparticles were optimized with consideration of diameter, surface charge, size variability, and yield as a delivery vehicle for a custom vascular therapeutic peptide. A layer-by-layer (LBL) surface modification technique using poly-L-lysine was integrated within the nanoparticle design to optimize therapeutic loading efficiency. Solvent pH played a pivotal role in emulsion micelle formation, LBL polymer secondary structure, and the polymer functional group interactions critical for high therapeutic loading. The resulting nanoparticle platform met target size (200 ± 20 nm), polydispersity (<0.07), and storage stability standards, was nontoxic, and did not affect therapeutic peptide bioactivity in vitro. Surface-modified D-PHI nanoparticles can be reproducibly manufactured at low cost, generating a highly customizable excipient platform suitable for delivery of biomolecular therapeutics. These nanoparticles have potential applications in vascular drug delivery via localized infusion, drug eluting stents, and drug-coated angioplasty balloons. STATEMENT OF SIGNIFICANCE: Nanoscale excipients have become critical in the delivery of many therapeutics to enhance drug stability and targeted biodistribution through careful design of nanoparticle composition, surface chemistry, and size. This manuscript describes the development of a nanoparticle excipient derived from an immunomodulatory degradable polar hydrophobic ionic polyurethane, in combination with a layer-by-layer surface modification approach utilizing poly-L-lysine, to transport a mimetic peptide targeting smooth muscle cell migration in vascular disease. The nanoparticle platform draws on the effect of pH to maximize drug loading and tailor particle properties. The low cost and easily reproducible system presents a highly customizable platform that can be adapted for therapeutic delivery across a wide range of clinical indications.

Microstructure, Physical and Biological Properties, and BSA Binding Investigation of Electrospun Nanofibers Made of Poly(AA-co-ACMO) Copolymer and Polyurethane

In this study, poly(AA-co-ACMO) and polyurethane-based nanofibers were prepared in a ratio of 1:1 (NF11) and 2:1 (NF21) as antimicrobial carriers for chronic wound management. Different techniques were used to characterize the nanofibers, and poly(AA-co-ACMO) was mostly found on the surface of PU. With an increase in poly(AA-co-ACMO) dose from 0 (PU) and 1:1 (NF11) to 2:1 (NF21) in the casting solution, the contact angle (CA) was reduced from 137 and 95 to 24, respectively, and hydrophilicity was significantly increased. As most medications inhibit biological processes by binding to a specific protein, in vitro protein binding was investigated mechanistically using a stopped-flow technique. Both NF11 and NF21 bind to BSA via two reversible steps: a fast second-order binding followed by a slow first-order one. The overall parameters for NF11 (K_a = 1.1 × 10⁴ M^-1, K_d = 89.0 × 10^-6, ΔG⁰ = -23.1 kJ mol^-1) and NF21 (K_a = 189.0 × 10⁴ M^-1, K_d = 5.3 × 10^-6 M, ΔG⁰ = -27.5 kJ mol^-1) were determined and showed that the affinity for BSA is approximately (NF11)/(NF21) = 1/180. This indicates that NF21 has much higher BSA affinity than NF11, although BSA interacts with NF11 much faster. NF21 with higher hydrophilicity showed effective antibacterial properties compared to NF11, in agreement with kinetic data. The study provided an approach to manage chronic wounds and treating protein-containing wastewater.

Surface Coating of Polyurethane Films with Gelatin, Aspirin and Heparin to Increase the Hemocompatibility of Artificial Vascular Grafts

Purpose: A hemocompatible substrate can offer a wonderful facility for nitric oxide (NO) production by vascular endothelial cells in reaction to the inflammation following injuries. NO inhibits platelet aggregation this is especially critical in small-diameter vessels. Methods: The substrate films were made of polyurethane (PU) in a casting process and after plasma treatments, their surface was chemically decorated with polyethylene glycol (PEG) 2000, gelatin, gelatin-aspirin, gelatin-heparin and gelatin-aspirin-heparin. The concentrations of these ingredients were optimized in order to achieve the biocompatible values and the resulting modifications were characterized by water contact angle and Fourier transform infra-red (FTIR) assays. The values of NO production and platelet adhesion were then examined. Results: The water contact angle of the modified surface was reduced to 26±4^∘ and the newly developed hydrophilic chemical groups were confirmed by FTIR. The respective concentrations of 0.05 mg/ml and 100 mg/mL were found to be the IC50 values for aspirin and heparin. However, after the surface modification with aspirin, the bioactivity of the substrate increased in compared to the other experimental groups. In addition, there was a synergistic effect between these reagents for NO synthesis. While, heparin inhibited platelet adhesion more than aspirin. Conclusion: Because of the highly hydrophilic nature of heparin, this reagent was hydrolyzed faster than aspirin and therefore its influence on platelet aggregation and cell growth was greater. Taken together, the results give the biocompatible concentrations of both biomolecules that are required for endothelial cell proliferation, NO synthesis and platelet adhesion.

Synthesis of Zwitterionic and Trehalose Polymers with Variable Degradation Rates and Stabilization of Insulin

Polymers that stabilize biomolecules are important as excipients in protein formulation. Herein, we describe a class of degradable polymers that have tunable degradation rates depending on the polymer backbone and can stabilize proteins to aggregation. Specifically, zwitterion- and trehalose-substituted polycaprolactone, polyvalerolactone, polycarbonate, and polylactide were prepared and characterized with regards to their hydrolytic degradation and ability to stabilize insulin to mechanical agitation during heat. Ring-opening polymerization (ROP) of allyl-substituted monomers was performed by using organocatalysis, resulting in well-defined alkene-substituted polymers with good control over molecular weight and dispersity. The polymers were then modified by using photocatalyzed thiol-ene reactions to install protein-stabilizing carboxybetaine and trehalose side chains. The resulting polymers were water-soluble and exhibited a wide range of half-lives, from 12 h to more than 3 months. The polymers maintained the ability to stabilize the therapeutic protein insulin from activity loss due to aggregation, demonstrating their potential as degradable excipients for protein formulation.

An overview of advanced biocompatible and biomimetic materials for creation of replacement structures in the musculoskeletal systems: focusing on cartilage tissue engineering

Tissue engineering, as an interdisciplinary approach, is seeking to create tissues with optimal performance for clinical applications. Various factors, including cells, biomaterials, cell or tissue culture conditions and signaling molecules such as growth factors, play a vital role in the engineering of tissues. In vivo microenvironment of cells imposes complex and specific stimuli on the cells, and has a direct effect on cellular behavior, including proliferation, differentiation and extracellular matrix (ECM) assembly. Therefore, to create appropriate tissues, the conditions of the natural environment around the cells should be well imitated. Therefore, researchers are trying to develop biomimetic scaffolds that can produce appropriate cellular responses. To achieve this, we need to know enough about biomimetic materials. Scaffolds made of biomaterials in musculoskeletal tissue engineering should also be multifunctional in order to be able to function better in mechanical properties, cell signaling and cell adhesion. Multiple combinations of different biomaterials are used to improve above-mentioned properties of various biomaterials and to better imitate the natural features of musculoskeletal tissue in the culture medium. These improvements ultimately lead to the creation of replacement structures in the musculoskeletal system, which are closer to natural tissues in terms of appearance and function. The present review article is focused on biocompatible and biomimetic materials, which are used in musculoskeletal tissue engineering, in particular, cartilage tissue engineering.

Vitamin C Loaded Poly(urethane-urea)/ZnAl-LDH Aligned Scaffolds Increase Proliferation of Corneal Keratocytes and Up-Regulate Vimentin Secretion

A novel poly(urethane-urea) (PUU) based on poly(glycolide-co-ε-caprolactone) macro-diol with tunable mechanical properties and biodegradation behavior is reported for corneal stromal tissue regeneration. Zn-Al layered double hydroxide (LDH) nanoparticles were synthesized and loaded with vitamin C (VC, VC-LDH) and dispersed in the PUU to control VC release in the cell culturing medium. To mimic the corneal stromal EC, scaffolds of the PUU and its nanocomposites with VC-LDH (PUU-LDH and PUU-VC-LDH) were fabricated via electrospinning. Average diameters of the aligned nanofibers were recorded as 325 ± 168, 343 ± 171, and 414 ± 275 nm for the PUU, PUU-LDH, and PUU-VC-LDH scaffolds, respectively. Results of hydrophilicity and mechanical properties measurements showed increased hydrophobicity and reduced tensile strength and elongation at break upon addition of nanoparticles to the PUU scaffold. VC release studies represented that intercalation of the drug in Zn-Al-LDH controlled the burst release and extended the release period from a few hours to 5 days. Viability and proliferation of stromal keratocyte cells on the scaffolds were investigated via AlamarBlue assay. After 24 h, the cells showed similar viability on the scaffolds and the control. After 1 week, the cells showed some degree of proliferation on the scaffolds, with the highest value recorded for PUU-VC-LDH. SEM images of the scaffolds after 24 h and 1 week confirmed good penetration and attachment of keratocytes on all the scaffolds and the cells oriented with the direction of nanofibers. After 1 week, the PUU-VC-LDH scaffold was fully covered by the cells. Immunocytochemistry assay (ICC) was performed to investigate secretion of vimentin protein, ALDH3A1, and α-SMA by the cells. After 24h and 1 week, remarkably higher levels of vimentin and ALDH3A1 and lower level of α-SMA were secreted by keratocytes on PUU-VC-LDH compared to those on the PUU and PUU-LDH scaffolds and the control. Our results suggest that the aligned PUU-VC-LDH is a promising candidate for corneal stromal tissue engineering due to the presence of zinc and vitamin C.

Synthesis and characterization of electrospun nanofibrous tissue engineering scaffolds generated from in situ polymerization of ionomeric polyurethane composites

Tissue scaffolds need to be engineered to be cell compatible, have timely biodegradable character, be functional with respect to providing niche cell support for tissue repair and regeneration, readily accommodate multiple cell types, and have mechanical properties that enable the simulation of the native tissue. In this study, electrospun degradable polar hydrophobic ionic polyurethane (D-PHI) scaffolds were generated in order to yield an extracellular matrix-like structure for tissue engineering applications. D-PHI oligomers were synthesized, blended with a degradable linear polycarbonate polyurethane (PCNU), and electrospun with simultaneous in situ UV cross-linking in order to generate aligned nanofibrous scaffolds in the form of elastomeric composite materials. The D-PHI/PCNU scaffold fibre morphology, cross-linking efficiency, surface nature, mechanical properties, in vivo degradation and integration, as well as in vitro cell compatibility were characterized. The results showed that D-PHI/PCNU scaffolds had a high cross-linking efficiency, stronger polar nature, and lower stiffness relative to PCNU scaffolds. In vivo, the D-PHI/PCNU scaffold degraded relatively slowly, thereby enabling new tissue time to form and yielding very good integration with the latter tissue. Based on a study with A10 vascular smooth muscle cells, the D-PHI/PCNU scaffold was able to support high cell viability, adhesion, and expression of typical smooth muscle cell markers after a 7-day culture period, which was comparable to PCNU scaffolds. These characterization results demonstrate that the unique properties of a D-PHI/PCNU scaffold, combined with the benefits of electrospinning, could allow for the generation of a tissue engineered scaffold that mimics important aspects of the native extracellular matrix and could be used for functional tissue regeneration. STATEMENT OF SIGNIFICANCE: Tissue engineered scaffolds should recapitulate native extracellular matrix features. This study investigates the processing of a classical polycarbonate polyurethane (PCNU) with a cross-linked and degradable ionomeric polyurethane (D-PHI), polymerized via in situ rapid light curing to yield a 3-dimensional co-electrospun nanofibre matrix with chemical diversity and low modulus character. This research advances the use of D-PHI for tissue engineering applications by providing a facile means of changing physical and chemical properties in classical PCNUs without the need to adjust spinning viscosities of the base polymer. Further, the in vivo and cell culture findings set the stage for introducing unique elastic materials which inherently support wound healing, repair, and regeneration in tissues, for applications that require the recapitulation of native extracellular matrix physical features.