Biological responses to cationically charged phosphorylcholine-based materials in vitro

Therapeutic contact lenses for the treatment of corneal and ocular surface diseases: advances in extended and targeted drug delivery

The eye is one of the most important organs in the human body providing critical information on the environment. Many corneal diseases can lead to vision loss affecting the lives of people around the world. Ophthalmic drug delivery has always been a major challenge in the medical sciences. Since traditional methods are less efficient (∼ 5%) at delivering drugs to ocular tissues, contact lenses have generated growing interest in ocular drug delivery due to their potential to enhance drug bioavailability in ocular tissues. The main techniques used to achieve sustained release are discussed in this review, including soaking in drug solutions, incorporating drug into multilayered contact lenses, use of vitamin E barriers, molecular imprinting, nanoparticles, micelles and liposomes. The most clinically relevant results on different eye pathologies are presented. In addition, this review summarizes the benefits of contact lenses over eye drops, strategies for incorporating drugs into lenses to achieve sustained release, results of in vitro and in vivo studies, and the recent advances in the commercialization of therapeutic contact lenses for allergic conjunctivitis.

Biomimetic immunomodulation strategies for effective tissue repair and restoration

Inflammation plays a central role in wound healing following injury or disease and is mediated by a precise cascade of cellular and molecular events. Unresolved inflammatory processes lead to chronic inflammation and fibrosis, which can result in prolonged wound healing lasting months or years that hampers tissue function. Therapeutic interventions mediated by immunomodulatory drugs, cells, or biomaterials, are therefore most effective during the inflammatory phase of wound healing when a pro-regenerative environment is essential. In this review, we discuss the advantages of exploiting knowledge of the native tissue microenvironment to develop therapeutics capable of modulating the immune response and promoting functional tissue repair. In particular, we provide examples of the most recent biomimetic platforms proposed to accomplish this goal, with an emphasis on those able to induce macrophage polarization towards a pro-regenerative phenotype.

Injectable Hyaluronic Acid/Poly(γ-glutamic acid) Hydrogel with Step-by-step Tunable Properties for Soft Tissue Engineering

Injectable hydrogels as an important class of biomaterials have gained much attention in tissue engineering. However, their crosslinking degree is difficult to be controlled after being injected into body. As we all know, the crosslinking degree strongly influences the physicochemical properties of hydrogels. Therefore, developing an injectable hydrogel with tunable crosslinking degree in vivo is important for tissue engineering. Herein, we present a dual crosslinking strategy to prepare injectable hydrogels with step-by-step tunable crosslinking degree using Schiff base reaction and photopolymerization. The developed hyaluronic acid/poly(γ-glutamic acid) (HA/γ-PGA) hydrogels exhibit step-by-step tunable swelling behavior, enzymatic degradation behavior and mechanical properties. Mechanical performance tests show that the storage moduli of HA/γ-PGA hydrogels are all less than 2000 Pa and the compressive moduli are in kilopascal, which have a good match with soft tissue. In addition, NIH 3T3 cells encapsulated in HA/γ-PGA hydrogel exhibit a high cell viability, indicating a good cytocompatibility of HA/γ-PGA hydrogel. Therefore, the developed HA/γ-PGA hydrogel as an injectable biomaterial has a good potential in soft tissue engineering.

Hydrogel hybrid porcine pericardium for the fabrication of a pre-mounted TAVI valve with improved biocompatibility

Transcatheter aortic valve implantation (TAVI) has been developed years ago for patients who cannot undergo a surgical aortic valve replacement (SAVR). Although TAVI possesses the advantages of lower trauma and simpler manipulation compared to SAVR, the need for storage in glutaraldehyde (GLU) and a tedious intraoperative assembly process have caused great inconvenience for its further application. A pre-mounted TAVI valve assembled by mounting a dry valve frame to a delivery system is expected to address these problems. However, the currently used GLU treated leaflet cannot unfold normally after being crimped for a long-term and loses its function when the BHV is assembled to the catheter. Besides, its cytotoxicity and immune response after implantation are still problems to be solved. In the present study, a hydrogel hybrid porcine pericardium (HHPP) approach was developed to endow the BHVs with a favorable unfolding property and good biocompatibility. Three monomers with different charge characteristics (sodium acrylate, 2-methacryloyloxyethyl phosphorylcholine, and acryloyloxyethyltrimethyl ammonium chloride) were complexed with GLU treated PP (GLU-PP) to form three kinds of HHPPs (SAAH-PP, MPCH-PP, and DACH-PP). The results of the crimping simulation experiment showed that all HHPPs could quickly recover in PBS after being folded for 10 days, while the traditional BHVs (GLU-PP) could not recover under the same conditions. Bovine serum albumin adsorption and platelet adhesion test showed that SAAH-PP and MPCH-PP had good anti-adhesion abilities. A cell culture study indicated that all the three HHPPs promoted HUVEC growth and proliferation. In vivo biocompatibility studies showed that the immune response induced by MPCH-PP was reduced compared to that by GLU-PP. These studies demonstrated that the strategy of MPC hydrogel hybridization may be an effective approach to prepare a pre-mounted TAVI valve with improved biocompatibility.

The effect of cationically-modified phosphorylcholine polymers on human osteoblasts in vitro and their effect on bone formation in vivo

The effect of introducing cationic charge into phosphorylcholine (PC)-based polymers has been investigated in this study with a view to using these materials as coatings to improve bone formation and osseointegration at the bone-implant interface. PC-based polymers, which have been used in a variety of medical devices to improve biocompatibility, are associated with low protein adsorption resulting in reduced complement activation, inflammatory response and cell adhesion. However, in some applications, such as orthopaedics, good integration between the implant and bone is needed to allow the distribution of loading stresses and a bioactive response is required. It has previously been shown that the incorporation of cationic charge into PC-based polymers may increase protein adsorption that stimulates subsequent cell adhesion. In this paper, the effect of cationic charge in PC-based polymers on human osteoblasts (HObs) in vitro and the effect of these polymers on bone formation in the rat tibia was assessed. Increasing PC positive surface charge increased HOb cell adhesion and stimulated increased cell differentiation and the production of calcium phosphate deposits. However, when implanted in bone these materials were at best biotolerant, stimulating the production of fibrous tissue and areas of loosely associated matrix (LAM) around the implant. Their development, as formulated in this study, as bone interfacing implant coatings is therefore not warranted.

Recommendations of the Oligonucleotide Safety Working Group's Formulated Oligonucleotide Subcommittee for the Safety Assessment of Formulated Oligonucleotide-Based Therapeutics

The use of lipid formulations has greatly improved the ability to effectively deliver oligonucleotides and has been instrumental in the rapid expansion of therapeutic development programs using oligonucleotide drugs. However, the development of such complex multicomponent therapeutics requires the implementation of unique, scientifically sound approaches to the nonclinical development of these drugs, based upon a hybrid of knowledge and experiences drawn from small molecule, protein, and oligonucleotide therapeutic drug development. The relative paucity of directly applicable regulatory guidance documents for oligonucleotide therapeutics in general has resulted in the generation of multiple white papers from oligonucleotide drug development experts and members of the Oligonucleotide Safety Working Group (OSWG). The members of the Formulated Oligonucleotide Subcommittee of the OSWG have utilized their collective experience working with a variety of formulations and their associated oligonucleotide payloads, as well as their insights into regulatory considerations and expectations, to generate a series of consensus recommendations for the pharmacokinetic characterization and nonclinical safety assessment of this unique class of therapeutics. It should be noted that the focus of Subcommittee discussions was on lipid nanoparticle and other types of particulate formulations of therapeutic oligonucleotides and not on conjugates or other types of modifications of oligonucleotide structure intended to facilitate delivery.

Discovery and Characterization of a Potent and Specific Peptide Ligand Targeting Endothelial Progenitor Cells and Endothelial Cells for Tissue Regeneration

Endothelial progenitor cells (EPCs) and endothelial cells (ECs) play a vital role in endothelialization and vascularization for tissue regeneration. Various EPC/EC targeting biomolecules have been investigated to improve tissue regeneration with limited success often due to their limited functional specificity and structural stability. One-bead one-compound (OBOC) combinatorial technology is an ultrahigh throughput chemical library synthesis and screening method suitable for ligand discovery against a wide range of biological targets, such as integrins. In this study, using primary human EPCs/ECs as living probes, we identified an αvβ3 integrin ligand LXW7 discovered by OBOC combinatorial technology as a potent and specific EPC/EC targeting ligand. LXW7 overcomes the major barriers of other functional biomolecules that have previously been used to improve vascularization for tissue regeneration and possesses optimal stability, EPC/EC specificity, and functionality. LXW7 is a disulfide cyclic octa-peptide (cGRGDdvc) containing unnatural amino acids flanking both sides of the main functional motif; therefore it will be more resistant to proteolysis and more stable in vivo compared to linear peptides and peptides consisting of only natural amino acids. Compared with the conventional αvβ3 integrin ligand GRGD peptide, LXW7 showed stronger binding affinity to primary EPCs/ECs but weaker binding to platelets and no binding to THP-1 monocytes. In addition, ECs bound to the LXW7 treated culture surface exhibited enhanced biological functions such as proliferation, likely due to increased phosphorylation of VEGF receptor 2 (VEGF-R2) and activation of mitogen-activated protein kinase (MAPK) ERK1/2. Surface modification of electrospun microfibrous PLLA/PCL biomaterial scaffolds with LXW7 via Click chemistry resulted in significantly improved endothelial coverage. LXW7 and its derivatives hold great promise for EPC/EC recruitment and delivery and can be widely applied to functionalize various biological and medical materials to improve endothelialization and vascularization for tissue regeneration applications.

Synthesis and characterization of bifunctional dendrimers: preliminary use for the coating of gold surfaces and the proliferation of human osteoblasts (HOB)

Dendrimers having one dithiolane and ammonium or carboxylate functions have been synthesized for coating gold surfaces interacting with human osteoblasts.

Self-assembly of novel lipid-mimicking brush polymers in nanoscale thin films

A series of well-defined poly(oxy(11-phosphorylcholineundecylthiomethyl)ethylene-ran-oxy(n-dodecylthiomethyl)ethylene) (PECH-PCm: m = 0-100 mol% phosphorylcholine (PC)) polymers were used to prepare nanoscale thin films that were characterized by synchrotron X-ray reflectivity (XR) analysis. The quantitative XR analysis provided structural insights into the PECH-PCm thin films. The PECH-PC0 polymer film formed a well-ordered in-plane oriented molecular multibilayer structure, whose individual layers consisted of two sublayers. One sublayer was composed of the fully extended backbones and inner part of the bristles, exhibiting a relatively low electron density, whereas the other sublayer was composed of a bilayer of the outer parts of the bristles without interdigitation. The PECH-PC100 polymer film also formed a well-ordered in-plane oriented molecular multibilayer structure, the individual layers of which were composed of four sublayers rather than two. The bristles in the layer were interdigitated in part via the zwitterionic interactions of the PC end groups. Surprisingly, regardless of the copolymer composition, the PECH-PCm random copolymer molecules in the thin films self-assembled to form a multilayered structure that resembled the structure formed by the PECH-PC100 polymer. These properties have not been observed in other conventional random brush copolymer films. The remarkable multibilayer structures originated from the zwitterionic PC end groups and their favorable interactions and interdigitated structures, which overcame any negative contributions caused by the heterogeneity of the bristles. The unique self-assembly properties of the PECH-PCm polymers always provide a PC-rich surface. The PECH-PCm random copolymers successfully mimicked the molecular bilayer structures formed by natural lipids.

Electric-field-enhanced nutrient consumption in dielectric biomaterials that contain anchorage-dependent cells

This research contribution addresses electric-field stimulation of intra-tissue mass transfer and cell proliferation in viscoelastic biomaterials. The unsteady state reaction-diffusion equation is solved according to the von Kármán-Pohlhausen integral method of boundary layer analysis when nutrient consumption and tissue regeneration occur in response to harmonic electric potential differences across a parallel-plate capacitor in a dielectric-sandwich configuration. The partial differential mass balance with diffusion and electro-kinetic consumption contains the Damköhler (Λ(2)) and Deborah (De) numbers. Zero-field and electric-field-sensitive Damköhler numbers affect nutrient boundary layer growth. Diagonal elements of the 2nd-rank diffusion tensor are enhanced in the presence of weak electric fields, in agreement with the formalism of equilibrium and nonequilibrium thermodynamics. Induced dipole polarization density within viscoelastic biomaterials is calculated via the real and imaginary components of the complex dielectric constant, according to the Debye equation, to quantify electro-kinetic stimulation. Rates of nutrient consumption under zero-field conditions are described by third-order kinetics that include local mass densities of nutrients, oxygen, and attached cells. Thinner nutrient boundary layers are stabilized at shorter dimensionless diffusion times when the zero-field intra-tissue Damköhler number increases above its initial-condition-sensitive critical value [i.e., {Λ(2)(zero-field)}(critical)≥53, see Eq. (23)], such that the biomaterial core is starved of essential ingredients required for successful proliferation. When tissue regeneration occurs above the critical electric-field-sensitive intra-tissue Damköhler number, the electro-kinetic contribution to nutrient consumption cannot be neglected. The critical electric-field-sensitive intra-tissue Damköhler number is proportional to the Deborah number.

Well-defined DNA-mimic brush polymers bearing adenine moieties: synthesis, layer-by-layer self-assembly, and biocompatibility

Two new DNA-mimicking brush polymers were synthesized: poly[oxy(11-(3-(9-adeninyl)propionato)-undecanyl-1-thiomethyl)ethylene] (PECH-AP) and poly[oxy(11-(5-(9-adenylethyloxy)-4-oxopentanoato)undecanyl-1-thiomethyl)ethylene] (PECH-AS). These polymers were found to be thermally stable up to 220 °C and could be applied easily by conventional coating processes to produce good quality films. Interestingly, both brush polymers formed molecular multibilayer structures to provide an adenine-rich surface. Despite the structural similarities, PECH-AS surprisingly exhibited higher hydrophilicity and better water sorption properties than PECH-AP. These differences were attributed to the chemical structures in the bristles of the polymers. The adenine-rich surfaces of the polymer films demonstrated selective protein adsorption, suppressed bacterial adherence, facilitated HEp-2 cell adhesion, and exhibited good biocompatibility in mice. However, the high hydrophilicity and good water sorption characteristics of the PECH-AS film suggest that this brush polymer is better suited to applications requiring good biocompatibility and reduced chance of bacterial infection compared with the PECH-AP film.

Controlled delivery of antisense oligonucleotides: a brief review of current strategies

Antisense therapy has been investigated extensively over the past two decades, either experimentally for gene functional research or clinically as therapeutic agents owing to the conceptual simplicity, ease of design and low cost. The concept of this therapeutic approach is promising because short antisense oligonucleotides (ASOs) can be delivered into target cells for specific hybridisation with target mRNA, resulting in the inhibition of the expression of pathogenic genes. However, the efficient delivery of the ASO molecules into target cells remains challenging; this bottleneck together with several other technical hurdles need to be overcome before this approach becomes effective and widely adopted. A variety of vectors such as lipids, polymers, peptides and nanoparticles have been explored. This review outlines the recent advances of the non-viral ASO delivery strategies. Several recent scientific studies, including authors' contributions, have been selected to highlight the technical aspects of ASO delivery.

Controlled delivery of anti-sense oligodeoxynucleotide from multilayered biocompatible phosphorylcholine polymer films

Fabrication of polymeric multilayered films based on the electrostatic self-assembly of polycations and polyanions is a promising approach for controlled loading and release in gene delivery. In this study, we have fabricated a series of multilayered films based on alternate deposition between positively-charged cationic phosphorylcholine copolymer (PC copolymer) and negatively-charged c-myc anti-sense oligodeoxynucleotide (AS-ODN). The growth of film thickness and increase of ODN loading capacity were monitored by spectroscopic ellipsometry (SE) and confocal laser scanning microscopy (CLSM). After elution into PBS buffer under physiological conditions, the elution profile was monitored by UV spectrometry and gel electrophoresis. Employing a secondary transgenic vector, the cellular uptake of the eluted AS-ODN into HeLa cells was evaluated by fluorescent microscopy and FACS analysis. The biological effect of eluted AS-ODN was evaluated by cell growth inhibition. The results showed that AS-ODN loading capacity increased almost linearly with the number of PC polymer/ODN bilayers and was also strongly dependent upon the cationic charge density. Through swelling, a non-degradable release mechanism, the AS-ODN release was characterized by two distinguishable release regimes: a fast release regime during the first 6 hour period and a slow release regime from 6 hour to the 8th day, both of which were characterized by zero-order kinetics. Gel electrophoresis showed excellent DNA integrity and strong transfection was observed when the eluted ODN was transfected into HeLa cells. Cell growth was significantly inhibited by eluted AS-ODN, indicating its full bioactivity. These results demonstrate that PC multilayered polymer films are capable of delivering a prescribed amount of anti-sense ODN with a controllable kinetic profile and that the multilayer process is more efficient and reliable than most other existing coating approaches largely based on single-layer fabrication.

Zwitterionic phosphorylcholine as a better ligand for stabilizing large biocompatible gold nanoparticles

Zwitterionic phosphorylcholine showed better stabilization than oligo(ethylene glycol) in protecting big gold nanoparticles.

Biocompatibility: meeting a key functional requirement of next-generation medical devices

The array of polymeric, biologic, metallic, and ceramic biomaterials will be reviewed with respect to their biocompatibility, which has traditionally been viewed as a requirement to develop a safe medical device. With the emergence of combination products, a paradigm shift is occurring that now requires biocompatibility to be designed into the device. In fact, next-generation medical devices will require enhanced biocompatibility by using, for example, pharmacological agents, bioactive coatings, nano-textures, or hybrid systems containing cells that control biologic interactions to have desirable biologic outcomes. The concept of biocompatibility is moving from a "do no harm" mission (i.e., nontoxic, nonantigenic, nonmutagenic, etc.) to one of doing "good," that is, encouraging positive healing responses. These new devices will promote the formation of normal healthy tissue as well as the integration of the device into adjacent tissue. In some contexts, biocompatibility can become a disruptive technology that can change therapeutic paradigms (e.g., drug-coated stents). New database tools to access biocompatibility data of the materials of construction in existing medical devices will facilitate the use of existing and new biomaterials for new medical device designs.

Fibroblast interaction with carboxymethylchitosan-based hydrogels

The interaction between L929 cells and carboxymethylchitosan (CM-chitosan)-based hydrogels, hydrogels from pure CM-chitosan and its blends, was examined in this study. Cytotoxicity of all materials was also assessed. The cellular morphology and behavior on the surfaces of the hydrogels were observed by scanning electron microscopy (SEM). The effects of various parameters, e.g., type and content of blended polymers, surface structure of hydrogels, and steaming condition used for the preparation of the hydrogels, on the cell-material response were investigated. The results of the cytotoxicity test revealed that all hydrogels were non-cytotoxic. The SEM micrographs demonstrated that the cells proliferated and spread onto a porous CM-chitosan sample. Better cell spreading was found on a flat surface of a CM-chitosan film. Rounded cells were observed when poly(vinyl alcohol) (PVA) was incorporated into CM-chitosan. Fewer cells were found when the content of PVA increased. Spherical clusters of the aggregated cells existed in the blends with ultra high viscosity carboxymethylcellulose (CM-cellulose). In contrast, with the use of low viscosity CM-cellulose, the cells appeared more spreading. The attached cells on the CM-chitosan film steamed at the highest temperature and longest period appeared to spread the most among all tested steaming conditions.

Molecularly engineered hydrogels for implant biocompatibility

The biocompatibility of biosmart polymer membranes synthesized from cross-linkable (2-hydroxyethyl methacrylate) (HEMA) and tetraethylene glycol diacrylate and containing different mole-percent polyethylene glycol methacrylate (PEGMA) and methacryloyloxyethyl phosphorylcholine (MPC), a phosphorylcholine-containing co-monomer, was investigated. The cytotoxicity (cell viability and proliferation) and the adhesion of extra cellular matrix proteins to these hydrogel surfaces were separately tested. Cell proliferation assays were conducted by cultivating human skeletal muscle fibroblasts onto the surfaces of these polymeric membranes prepared by in-situ polymerization in chemically derivatized 8-well cell-culture plates. The compositions containing MPC and PEGMA concentrations greater than 1.0 and 0.05 mole% respectively demonstrated good protein adhesion and cell viability (>90%) of human muscle fibroblast cells. Morphological deviances and partial colonization of the hydrogel surface has been noticed and suggests good compatibility of hydrogels for cellular viability but restricted proliferation. It is well known that the adsorption of proteins onto biomaterial surfaces modulates the cellular interaction with these surfaces. The extent of adsorption of fluorescein labeled proteins (laminin, collagen, and fibronectin) onto these polymer membrane surfaces was evaluated by measuring the resultant fluorescence intensity using a confocal fluorescence scanner.

Effects of biomaterial surface chemistry on the adhesion and biofilm formation of Staphylococcus epidermidis in vitro

The formation of biofilm, a structured community of bacteria enclosed in slime, is a significant virulence factor in medical-device-centered infection. The development of cardiovascular device infection can be separated into two phases: initial bacterial adhesion and aggregation, followed by proliferation and production of slime. It is possible to modulate the adhesion and biofilm formation of Staphylococcus epidermidis, a commensal skin bacterium commonly found on infected medical devices, through biomaterial surface chemistry. This study examines bacterial adhesion and biofilm formation on surface-modified polyethylene terephthalate (PET), including surfaces with varying hydrophilic, hydrophobic, and ionic character. Bacterial adhesion and biofilm formation were observed over 48 hours in phosphate-buffered saline (PBS) and 20% pooled human serum. The hydrophilic surface (PAAm) had significantly less nonspecific adhesion of bacteria than that in the control (PET) and other surfaces, when cultured in PBS (P < 0.0001). Charged surfaces, both anionic and cationic, had increased adhesion and aggregation of bacteria in comparison with the control (PET) in the presence of serum proteins over 24 hours (P < 0.0001). Bacteria cultured in serum on the charged surfaces did not have significantly different amounts of biofilm formation compared with that of the control (PET) surface after 48 hours. This study showed that biomaterial surface chemistry characteristics impact initial adhesion and aggregation of S. epidermidis on biomaterials.

Investigation into potential mechanisms promoting biocompatibility of polymeric biomaterials containing the phosphorylcholine moiety

Phosphorylcholine (PC) moieties were chemically attached to surfaces of polymer microparticles by addition of 2-methylacryloyloxyethyl phosphorylcholine monomer to the seeded, semi-continuous polymerisations of methyl methacrylate (MMA) and butyl acrylate (BA). The surface of the bio-functionalised polymer microparticles was principally characterised using X-ray photoelectron spectroscopy (XPS), dynamic nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), acoustophoresis and enzyme-linked immunosorbent assays (ELISA). It was found that the persulphate initiating species are concealed behind the phosphorylcholine containing monomer sequence located on the surface of the microparticles. The combination of analytical techniques showed that the surfaces of the polymer microparticles are extremely mobile above the glass transition temperature of the co-polymer and able to rearrange depending on the environment in which they are placed. This allows the phosphorylcholine moiety to be preferentially expressed at the surface in aqueous media, but not so in the dry state or conditions of ultra-high vacuum. In terms of the nature of the biocompatibility of phosphorylcholine containing polymers, no evidence was found for the irreversible structuring of water molecules around the phosphorylcholine moiety in the wet state. The results of this work suggest that a more likely contributory reason for the protein-resistant nature of phosphorylcholine containing polymers is the mobility of the phosphorylcholine moiety. Increases in biocompatibility correspond with increases in the hydrophilicity of a polymer surface when phosphorylcholine is preferentially expressed. A large free water fraction may be present in the phosphorylcholine containing monomer sequence, as part of a hydrogel structure located at the surface of the polymer microparticles. This, coupled with concomitant modification of the local electrical double-layer very close to the surface may also play a critical role in reducing protein-surface interactions.

Bacterial adhesion to phosphorylcholine-based polymers with varying cationic charge and the effect of heparin pre-adsorption

The steady increase in the use of medical implants and the associated rise of medical device infections has fuelled the need for the production of biomaterials with improved biocompatibility. 2-(methacryloyloxyethyl phosphorylcholine) (MPC) based coatings have been used to improve the biocompatibility of a number of different medical devices. Recent studies have investigated the use of a phosphorylcholine modified with cationic charge to encourage specific bio-interaction. Until now the affect of cationic charge incorporation in MPC copolymers on bacterial adhesion has not been investigated. This study attempts to address this by investigating the affect of charge on four different strains of bacteria commonly associated with medical device infections. In addition, the affect of pre-incubating these MPC-copolymers in heparin is also evaluated as this has previously been shown to improve biocompatibility and reduce bacterial adhesion. Bacterial adhesion was assessed by ATP bioluminescence and Scanning Electron Microscopy (SEM). Results suggest that bacterial adhesion generally increased with increasing cationic charge. When samples were however, pre-incubated with heparin a significant reduction in bacterial adhesion to the MPC-based samples was observed. The heparin remained bound and effective at reducing bacterial adhesion to the cationic MPC-based samples even after three weeks incubation in PBS. To conclude, the MPC-based cationic polymer coatings complexed with heparin may provide a promising solution to reduce medical device related infections.

Solution pH-regulated interfacial adsorption of diblock phosphorylcholine copolymers

Spectroscopic ellipsometry has been used to examine the pH-responsive interfacial adsorption of a series of biocompatible diblock copolymers incorporating 2-methacryloyloxyethyl phosphorylcholine-based (MPC) residues and 2-(dialkylamino)ethyl methacrylate residues, with a specific focus on 2-(diethylamino)ethyl groups (referred to as MPCm-DEAn, where m and n refer to the mean degrees of polymerization of each block) at the hydrophilic silicon oxide/water interface. For all the copolymers studied the surface excess shows only weak concentration dependence. Increasing the length of the DEA block has little effect on the dynamic or equilibrated adsorption at pH 7, indicating that the DEA block adopts a flat conformation on the silicon oxide surface at this pH. With increasing pH, however, the surface excess shows a dramatic increase, followed by a subsequent decline. The observed maximum in surface excess represents a balance between charge over-compensation of the copolymer with the oppositely charged surface and the subsequently reduced charge density of the copolymer. Variations in the observed maxima for various MPCm-DEAn diblock copolymers indicate different surface conformations at high pH. Salt addition does not affect copolymer adsorption. This behavior is attractive for biomedical applications in which the ionic strength is variable. It was also found that the preadsorbed diblock copolymers immobilized DNA from solution to an extent that is proportional to the relative charge ratio between the anionic DNA and the cationic DEA block of the copolymer.

Hybrid films from blends of chitosan and egg phosphatidylcholine for localized delivery of paclitaxel

Chitosan and egg phosphatidylcholine (ePC) were used as a unique combination to prepare composite films for localized drug delivery. In comparison to other phospholipids analyzed, ePC was found to produce chitosan-based films with minimal swelling and a high degree of stability. The properties of the chitosan-ePC films were characterized and found to be dependent on the ratio of chitosan:ePC present. FTIR analysis of chitosan-ePC films revealed that their high stability may be attributed to interactions present between these two biomaterials. In vitro evaluation of the cytotoxicity and protein adsorption properties of the films were used to provide a preliminary indication of their biocompatibility. The chitosan-ePC film was also evaluated as a matrix for the localized delivery of the anti-cancer agent, paclitaxel. Nanoparticles containing paclitaxel were dispersed throughout the chitosan-ePC film to result in a drug:material ratio of 1:8 (wt/wt). The film was found to provide a sustained release of paclitaxel over a 4-month period in biologically relevant media. The biological activity of paclitaxel loaded in the chitosan-ePC film was confirmed in SKOV-3 human ovarian cancer cells.

Biological evaluation and drug delivery application of cationically modified phospholipid polymers

Phospholipid-like polymers based on 2-methacryloyloxyethyl phosphorylcholine containing varying amounts of the cationically charged monomer choline methacrylate (CMA) from 0 to 30 wt% have been prepared. Substrates coated with these materials were shown to bind significantly lower amounts of specific proteins compared to the uncoated control. ELISA assays demonstrated that fibrinogen did not bind appreciably to coatings containing 0-30% CMA, whereas albumin binding was seen to increase significantly as the CMA content of the coating increased. Platelet activation assays, measurement of plasma coagulation time and whole blood contact scanning electron micrography demonstrated that the haemocompatibility of the coatings was shown to be unaffected by the CMA component. The CMA polymer coatings have been shown to absorb/adsorb many different drug compounds covering a wide range of molecular weights and release these in a controlled fashion. The range of cationic polymers assessed can interact with the net negative charge found in many large therapeutic biomolecules, such as DNA fragments used in gene therapy, that may be of interest in the preventative treatment of conditions such as restenosis. Coronary stents coated with 6% or 20% CMA-containing polymers have been shown to load and release this type of genetic material irrespective of molecular weight of the biomolecule. Ex vivo and in vivo studies have shown that these compounds can be delivered to the stented section of the vessel with very low quantities delivered outside the vessel target area.