Controlled release of low-molecular weight, polymer-free corticosteroid coatings suppresses fibrotic encapsulation of implanted medical devices.

Inflammation-driven foreign body reactions, and the frequently associated encapsulation by fibrogenic fibroblasts, reduce the functionality and longevity of implanted medical devices and materials. Anti-inflammatory drugs, such as dexamethasone, can suppress the foreign body reaction for a few days post-surgery, but lasting drug delivery strategies for long-term implanted materials remain an unmet need. We here establish a thin-coating strategy with novel low molecular weight corticosteroid dimers to suppress foreign body reactions and fibrotic encapsulation of subcutaneous silicone implants. The dimer coatings are >75% dexamethasone by mass and directly processable into conformal coatings using conventional solvent-based techniques, such as casting or spray coating without added polymers or binding agents. In vitro, surface erosion of the coating, and subsequent hydrolysis, provide controlled release of free dexamethasone. In a rat subcutaneous implantation model, the resulting slow and sustained release profile of dexamethasone is effective at reducing the number and activation of pro-fibrotic macrophages both acutely and at chronic time points. Consequently, fibroblast activation, collagen deposition and fibrotic encapsulation are suppressed at least 45 days post-implantation. Thus, our approach to protect implants from host rejection is advantageous over polymeric drug delivery systems, which typically have low drug loading capacity (<30%), initial burst release profiles, and unpredictable release kinetics.

Polymer-free corticosteroid dimer implants for controlled and sustained drug delivery.

Polymeric drug carriers are widely used for providing temporal and/or spatial control of drug delivery, with corticosteroids being one class of drugs that have benefitted from their use for the treatment of inflammatory-mediated conditions. However, these polymer-based systems often have limited drug-loading capacity, suboptimal release kinetics, and/or promote adverse inflammatory responses. This manuscript investigates and describes a strategy for achieving controlled delivery of corticosteroids, based on a discovery that low molecular weight corticosteroid dimers can be processed into drug delivery implant materials using a broad range of established fabrication methods, without the use of polymers or excipients. These implants undergo surface erosion, achieving tightly controlled and reproducible drug release kinetics in vitro. As an example, when used as ocular implants in rats, a dexamethasone dimer implant is shown to effectively inhibit inflammation induced by lipopolysaccharide. In a rabbit model, dexamethasone dimer intravitreal implants demonstrate predictable pharmacokinetics and significantly extend drug release duration and efficacy (>6 months) compared to a leading commercial polymeric dexamethasone-releasing implant.

Influence of ciprofloxacin-based additives on the hydrolysis of nanofiber polyurethane membranes.

A degradable polycarbonate urethane (PCNU) and an antimicrobial oligomer (AO) were used to generate anti-infective nanofiber scaffolds through blend electrospinning. The AO consists of two molecules of ciprofloxacin (CF) bound through hydrolysable linkages to triethylene glycol. The membranes were conceived for use as tissue engineering scaffolds for the regeneration of soft tissues for the periodontium, where there would be a need for a local dose of antibiotic to the periodontal space as the scaffold degrades in order to prevent biomaterial-associated infection. Scaffolds were made using AO at 7 and 15% w/w equivalent CF, and compared to scaffolds with 15% w/w CF (with HCl counterion). AO was hydrolyzed and released CF continuously over 28 days, while the 15% w/w CF HCl scaffolds showed a burst release within hours, with no subsequent release in the subsequent 28 day period. Released CF from both the AO and CF HCl scaffolds had a similar minimum inhibitory concentration to that of off-the-shelf CF. Interestingly, the introduction of drug in either form (AO or CF HCl) was found to increase the hydrolytic stability of the electrospun degradable PCNU scaffold matrix itself. The alteration of hydrolysis kinetics was attributed to changes in the hydrogen bonding character and microstructure within the scaffolds, introduced by the presence of CF. This study has revealed that in generating in situ drug release systems, the secondary effects of the added drug on the degradation properties of the polymeric carriers must be considered, particularly for systems that act dually as tissue engineering scaffolds. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1211-1222, 2018.

Electrospun polyurethane nanofiber scaffolds with ciprofloxacin oligomer versus free ciprofloxacin: Effect on drug release and cell attachment.

An electrospun degradable polycarbonate urethane (PCNU) nanofiber scaffold loaded with antibiotic was investigated in terms of antibacterial efficacy and cell compatibility for potential use in gingival tissue engineering. Antimicrobial oligomer (AO), a compound which consists of two molecules of ciprofloxacin (CF) covalently bound via hydrolysable linkages to triethylene glycol (TEG), was incorporated via a one-step blend electrospinning process using a single solvent system at 7 and 15% w/w equivalent CF with respect to the PCNU. The oligomeric form of the drug was used to overcome the challenge of drug aggregation and burst release when antibiotics are incorporated as free drug. Electrospinning parameters were optimized to obtain scaffolds with similar alignment and fiber diameter to non-drug loaded fibers. AO that diffused from the fibers was hydrolysed to release CF slowly and in a linear manner over the duration of the study, whereas scaffolds with CF at the same concentration but in free form showed a burst release within 1h with no further release throughout the study duration. Human gingival fibroblast (HGF) adhesion and spreading was dependent on the concentration and form the CF was loaded (AO vs. free CF), which was attributed in part to differences in scaffold surface chemistry. Surface segregation of AO was quantified using surface-resolved X-ray photoelectron spectroscopy (XPS). These findings are encouraging and support further investigation for the use of AO as a means of attenuating the rapid release of drug loaded into nanofibers. The study also demonstrates through quantitative measures that drug additives have the potential to surface-locate without phase separating from the fibers, leading to fast dissolution and differential fibroblast cell attachment.

Fiber alignment and coculture with fibroblasts improves the differentiated phenotype of murine embryonic stem cell-derived cardiomyocytes for cardiac tissue engineering.

Embryonic stem cells (ESCs) are an important source of cardiomyocytes for regenerating injured myocardium. The successful use of ESC-derived cardiomyocytes in cardiac tissue engineering requires an understanding of the important scaffold properties and culture conditions to promote cell attachment, differentiation, organization, and contractile function. The goal of this work was to investigate how scaffold architecture and coculture with fibroblasts influences the differentiated phenotype of murine ESC-derived cardiomyocytes (mESCDCs). Electrospinning was used to process an elastomeric biodegradable polyurethane (PU) into aligned or unaligned fibrous scaffolds. Bioreactor produced mESCDCs were seeded onto the PU scaffolds either on their own or after pre-seeding the scaffolds with mouse embryonic fibroblasts (MEFs). Viable mESCDCs attached to the PU scaffolds and were functionally contractile in all conditions tested. Importantly, the aligned scaffolds led to the anisotropic organization of rod-shaped cells, improved sarcomere organization, and increased mESCDC aspect ratio (length-to-diameter ratio) when compared to cells on the unaligned scaffolds. In addition, pre-seeding the scaffolds with MEFs improved mESCDC sarcomere formation compared to mESCDCs cultured alone. These results suggest that both fiber alignment and pre-treatment of scaffolds with fibroblasts improve the differentiation of mESCDCs and are important parameters for developing engineered myocardial tissue constructs using ESC-derived cardiac cells.

Development of biodegradable polyurethane scaffolds using amino acid and dipeptide-based chain extenders for soft tissue engineering.

The inherent flexibility of polyurethane (PU) chemistry allows the incorporation of specific chemical moieties into the backbone structure conferring a unique biological function to these synthetic polymers. We describe here the synthesis and characterization of a PU containing a Gly-Leu linkage, the cleavage site of several matrix metalloproteinases. A Gly-Leu dipeptide was introduced into the chain extender of the polyurethane through the reaction with 1,4-cyclohexane dimethanol. PUs synthesized with the Gly-Leu-based chain extender had a high weight-average molecular weight (M(w) > 125 x 10(3)) and were phase segregated, semi-crystalline polymers with a low soft-segment glass-transition temperature (T(g) < -50 degrees C). Uniaxial tensile testing of PU films indicated that the polymer could withstand high ultimate tensile strengths (approx. 13 MPa) and were flexible with breaking strains of approx. 900%. The Gly-Leu PU had a significantly higher initial modulus, yield stress and ultimate stress compared to a PU previously developed in our laboratory containing a phenylalanine-based chain extender (Phe PU). The Gly-Leu-based chain extender allowed for better hard segment packing and hydrogen bonding leading to enhanced mechanical properties. Electrospinning was used to form scaffolds with randomly organized fibers and an average fiber diameter of approx. 3.6 mum for both the Gly-Leu and Phe PUs. Mouse embryonic fibroblasts were successfully cultured on the PU scaffolds out to 28 days. Further investigations into cell-mediated polymer degradation will help to identify the suitability of this new biomaterial as scaffolds for soft tissue applications.

Culture on electrospun polyurethane scaffolds decreases atrial natriuretic peptide expression by cardiomyocytes in vitro.

The function of the mammalian heart depends on the functional alignment of cardiomyocytes, and controlling cell alignment is an important consideration in biomaterial design for cardiac tissue engineering and research. The physical cues that guide functional cell alignment in vitro and the impact of substrate-imposed alignment on cell phenotype, however, are only partially understood. In this report, primary cardiac ventricular cells were grown on electrospun, biodegradable polyurethane (ES-PU) with either aligned or unaligned microfibers. ES-PU scaffolds supported high-density cultures and cell subpopulations remained intact over two weeks in culture. ES-PU cultures contained electrically-coupled cardiomyocytes with connexin-43 localized to points of cell:cell contact. Multi-cellular organization correlated with microfiber orientation and aligned materials yielded highly oriented cardiomyocyte groupings. Atrial natriuretic peptide, a molecular marker that shows decreasing expression during ventricular cell maturation, was significantly lower in cultures grown on ES-PU scaffolds than in those grown on tissue culture polystyrene. Cells grown on aligned ES-PU had significantly lower steady state levels of ANP and constitutively released less ANP over time indicating that scaffold-imposed cell organization resulted in a shift in cell phenotype to a more mature state. We conclude that the physical organization of microfibers in ES-PU scaffolds impacts both multi-cellular architecture and cardiac cell phenotype in vitro.