Biofunctional polymer nanoparticles for intra-articular targeting and retention in cartilage

Nanoparticles for improved local retention after intra-articular injection into the knee joint

Purpose

To evaluate using cationic polymeric nanoparticles that interact with hyaluronate to form ionically cross-linked hydrogels to increase the intra-articular retention time of osteoarthritis drugs in the synovial cavity.

Methods

In vitro tests included nanoparticle release from cross-linked hydrogels using syringe and membrane dissolution tests, viscosity measurement of synovial fluid containing hydrogels, and release-rate measurement for a model active conjugated to a cationically substituted dextran using a hydrolyzable ester linkage in a sink dissolution test. Nanoparticle retention after intra-articular injection into rat knees was measured in vivo using fluorescence molecular tomography.

Results

Diffusional and convective transport of cationic nanoparticles from ionically cross-linked hydrogels formed in synovial fluid was slower in vitro than for uncharged nanoparticles. Hydrogels formed after the nanoparticles were mixed with synovial fluid did not appreciably alter the viscosity of the synovial fluid in vitro. In vitro release of a conjugated peptide from the cationic nanoparticles was approximately 20% per week. After intra-articular injection in rat knees, 70% of the nanoparticles were retained in the joint for 1 week.

Conclusions

This study demonstrates the feasibility of using cationic polymeric nanoparticles to increase the retention of therapeutic agents in articular joints for indications such as osteoarthritis.

Targeting collagen strands by photo-triggered triple-helix hybridization

Collagen remodeling is an integral part of tissue development, maintenance, and regeneration, but excessive remodeling is associated with various pathologic conditions. The ability to target collagens undergoing remodeling could lead to new diagnostics and therapeutics as well as applications in regenerative medicine; however, such collagens are often degraded and denatured, making them difficult to target with conventional approaches. Here, we present caged collagen mimetic peptides (CMPs) that can be photo-triggered to fold into triple helix and bind to collagens denatured by heat or by matrix metalloproteinase (MMP) digestion. Peptide-binding assays indicate that the binding is primarily driven by stereo-selective triple-helical hybridization between monomeric CMPs of high triple-helical propensity and denatured collagen strands. Photo-triggered hybridization allows specific staining of collagen chains in protein gels as well as photo-patterning of collagen and gelatin substrates. In vivo experiments demonstrate that systemically delivered CMPs can bind to collagens in bones, as well as prominently in articular cartilages and tumors characterized by high MMP activity. We further show that CMP-based probes can detect abnormal bone growth activity in a mouse model of Marfan syndrome. This is an entirely new way to target the microenvironment of abnormal tissues and could lead to new opportunities for management of numerous pathologic conditions associated with collagen remodeling and high MMP activity.

Virtual interactomics of proteins from biochemical standpoint

Virtual interactomics represents a rapidly developing scientific area on the boundary line of bioinformatics and interactomics. Protein-related virtual interactomics then comprises instrumental tools for prediction, simulation, and networking of the majority of interactions important for structural and individual reproduction, differentiation, recognition, signaling, regulation, and metabolic pathways of cells and organisms. Here, we describe the main areas of virtual protein interactomics, that is, structurally based comparative analysis and prediction of functionally important interacting sites, mimotope-assisted and combined epitope prediction, molecular (protein) docking studies, and investigation of protein interaction networks. Detailed information about some interesting methodological approaches and online accessible programs or databases is displayed in our tables. Considerable part of the text deals with the searches for common conserved or functionally convergent protein regions and subgraphs of conserved interaction networks, new outstanding trends and clinically interesting results. In agreement with the presented data and relationships, virtual interactomic tools improve our scientific knowledge, help us to formulate working hypotheses, and they frequently also mediate variously important in silico simulations.

Hydrolase stabilization via entanglement in poly(propylene sulfide) nanoparticles: stability towards reactive oxygen species

In the advancement of green syntheses and sustainable reactions, enzymatic biocatalysis offers extremely high reaction rates and selectivity that goes far beyond the reach of chemical catalysts; however, these enzymes suffer from typical environmental constraints, e.g. operational temperature, pH and tolerance to oxidative environments. A common hydrolase enzyme, diisopropylfluorophosphatase (DFPase, EC 3.1.8.2), has demonstrated a pronounced efficacy for the hydrolysis of a variety of substrates for potential toxin remediation, but suffers from the aforementioned limitations. As a means to enhance DFPase's stability in oxidative environments, enzymatic covalent immobilization within the polymeric matrix of poly(propylene sulfide) (PPS) nanoparticles was performed. By modifying the enzyme's exposed lysine residues via thiolation, DFPase is utilized as a comonomer/crosslinker in a mild emulsion polymerization. The resultant polymeric polysulfide shell acts as a 'sacrificial barrier' by first oxidizing to polysulfoxides and polysulfones, rendering DFPase in an active state. DFPase-PPS nanoparticles thus retain activity upon exposure to as high as 50 parts per million (ppm) of hypochlorous acid (HOCl), while native DFPase is observed as inactive at 500 parts per billion (ppb). This trend is also confirmed by enzyme-generated (chloroperoxidase (CPO), EC 1.11.1.10) reactive oxygen species (ROS) including both HOCl (3 ppm) and ClO(2) (100 ppm).

X-ray microscopy and tomography detect the accumulation of bare and PEG-coated gold nanoparticles in normal and tumor mouse tissues

We demonstrate that, with appropriate staining, high-resolution X-ray microscopy can image complicated tissue structures--cerebellum and liver--and resolve large or small amounts of Au nanoparticles in these tissues. Specifically, images of tumor tissue reveal high concentrations of accumulated Au nanoparticles. PEG (poly(ethylene glycol)) coating is quite effective in enhancing this accumulation and significantly modifies the mechanism of uptake by reticuloendothelial system (RES) organs.

Self-assembling nanoparticles for intra-articular delivery of anti-inflammatory proteins

Intra-articular delivery of therapeutics to modulate osteoarthritis (OA) is challenging. Delivery of interleukin-1 receptor antagonist (IL-1Ra), the natural protein inhibitor of IL-1, to modulate IL-1-based inflammation through gene therapy or bolus protein injections has emerged as a promising therapy for OA. However, these approaches suffer from rapid clearance and reduced potency over time. Nano/microparticles represent a promising strategy for overcoming the shortcomings of intra-articular drug delivery. However, these delivery vehicles are limited for delivery of protein therapeutics due to their hydrophobic character, low drug loading efficiency, and harsh chemical conditions during particle processing. We designed a new block copolymer that assembles into submicron-scale particles and provides for covalently tethering proteins to the particle surface for controlled intra-articular protein delivery. This block copolymer self-assembles into 300 nm-diameter particles with a protein tethering moiety for surface covalent conjugation of IL-1Ra protein. This copolymer particle system efficiently bound IL-1Ra and maintained protein bioactivity in vitro. Furthermore, particle-tethered IL-1Ra bound specifically to target synoviocyte cells via surface IL-1 receptors. Importantly, IL-1Ra nanoparticles inhibited IL-1-mediated signaling to equivalent levels as soluble IL-1Ra. Finally, the ability of nanoparticles to retain IL-1Ra in the rat stifle joint was evaluated by in vivo imaging over 14 days. IL-1Ra-tethered nanoparticles significantly increased the retention time of IL-1Ra in the rat stifle joint over 14 days with enhanced IL-1Ra half-life (3.01 days) compared to that of soluble IL-1Ra (0.96 days) and without inducing degenerative changes in cartilage structure or composition.

From nano- to macro-scale: nanotechnology approaches for spatially controlled delivery of bioactive factors for bone and cartilage engineering

The field of biomaterials has advanced towards the molecular and nanoscale design of bioactive systems for tissue engineering, regenerative medicine and drug delivery. Spatial cues are displayed in the 3D extracellular matrix and can include signaling gradients, such as those observed during chemotaxis. Architectures range from the nanometer to the centimeter length scales as exemplified by extracellular matrix fibers, cells and macroscopic shapes. The main focus of this review is the application of a biomimetic approach by the combination of architectural cues, obtained through the application of micro- and nanofabrication techniques, with the ability to sequester and release growth factors and other bioactive agents in a spatiotemporal controlled manner for bone and cartilage engineering.

FGFR3 targeting strategies for achondroplasia

Mutations that exaggerate signalling of the receptor tyrosine kinase fibroblast growth factor receptor 3 (FGFR3) give rise to achondroplasia, the most common form of dwarfism in humans. Here we review the clinical features, genetic aspects and molecular pathogenesis of achondroplasia and examine several therapeutic strategies designed to target the mutant receptor or its signalling pathways, including the use of kinase inhibitors, blocking antibodies, physiologic antagonists, RNAi and chaperone inhibitors. We conclude by discussing the challenges of treating growth plate disorders in children.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

Blood clearance and biodistribution of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization

The physiological properties of polymer brush-afforded silica particles prepared by surface-initiated living radical polymerization were investigated in terms of the circulation lifetime in the blood and distribution in tissues. Hydrophilic polymers consisting mainly of poly(poly(ethylene glycol) methyl ether methacrylate) were grafted onto silica particles by surface-initiated atom transfer radical polymerization that was mediated by a copper complex to produce hairy hybrid particles. A series of hybrid particles was synthesized by varying the diameter of the silica core and the chain length of the polymer brush to examine the relationship between their physicochemical and physiological properties. The hybrid particles were injected intravenously into mice to investigate systematically their blood clearance and body distribution. It was revealed that the structural features of the hybrid particles significantly affected their in vivo pharmacokinetics. Some hybrid particles exhibited an excellently prolonged circulation lifetime in the blood with a half life of ∼20 h. When such hybrid particles were injected intravenously into a tumor-bearing mouse, they preferentially accumulated in tumor tissue. The tumor-targeted delivery was optically visualized using hybrid particles grafted with fluorescence-labeled polymer brushes.

Engineering approaches toward deconstructing and controlling the stem cell environment

Stem cell-based therapeutics have become a vital component in tissue engineering and regenerative medicine. The microenvironment within which stem cells reside, i.e., the niche, plays a crucial role in regulating stem cell self-renewal and differentiation. However, current biological techniques lack the means to recapitulate the complexity of this microenvironment. Nano- and microengineered materials offer innovative methods to (1) deconstruct the stem cell niche to understand the effects of individual elements; (2) construct complex tissue-like structures resembling the niche to better predict and control cellular processes; and (3) transplant stem cells or activate endogenous stem cell populations for regeneration of aged or diseased tissues. In this article, we highlight some of the latest advances in this field and discuss future applications and directions of the use of nano- and microtechnologies for stem cell engineering.

Encapsulation and enzyme-mediated release of molecular cargo in polysulfide nanoparticles

Poly(propylene sulfide) nanoparticles (<150 nm) have been synthesized by an anionic, ring-opening emulsion polymerization. Upon exposure to parts per million (ppm) levels of oxidizing agent (NaOCl), hydrophobic polysulfide particles are oxidized to hydrophilic polysulfoxides and polysulfones. Utilizing this mechanism, the encapsulation of hydrophobic molecular cargo, including Nile red and Reichardt's dye, within polysulfide nanoparticles has been characterized by a variety of microscopic and spectroscopic methods and its release demonstrated via chemical oxidation. Moreover, release of cargo has been enzymatically driven by oxidoreductase enzymes such as chloroperoxidase and myeloperoxidase in the presence of low concentrations of sodium chloride (200 mM) and hydrogen peroxide (500 μM). This oxidation-driven mechanism holds promise for controlled encapsulation and release of a variety of hydrophobic cargos.

Evolving the use of peptides as components of biomaterials

This manuscript is part of a debate on the statement that "the use of short synthetic adhesion peptides, like RGD, is the best approach in the design of biomaterials that guide cell behavior for regenerative medicine and tissue engineering". We take the position that although there are some acknowledged disadvantages of using short peptide ligands within biomaterials, it is not necessary to discard the notion of using peptides within biomaterials entirely, but rather to reinvent and evolve their use. Peptides possess advantageous chemical definition, access to non-native chemistries, amenability to de novo design, and applicability within parallel approaches. Biomaterials development programs that require such aspects may benefit from a peptide-based strategy.

Targeted delivery of non-viral vectors to cartilage in vivo using a chondrocyte-homing peptide identified by phage display

Gene therapy is a promising method for osteoarthritis and cartilage injury. However, specifically delivering target genes into chondrocytes is a great challenge because of their non-vascularity and the dense extracellular matrix of cartilage. In our study, we identified a chondrocyte-affinity peptide (CAP, DWRVIIPPRPSA) by phage display technology. Subsequent analysis suggests that the peptide can efficiently interact specifically with chondrocytes without any species specificity. Polyethylenimine (PEI) was covalently modified with CAP to construct a non-viral vector for cartilage-targeted therapy. To investigate the cartilage-targeting property of the CAP-modified vector, FITC-labeled CAP conjugated PEI/DNA particles were injected into rabbit knee joints, and visualized under confocal microscope. Higher concentrations of CAP-modified vector were detected in the cartilage and specifically taken up by chondrocytes compared with a randomly scrambled peptide (SP)-modified vector. To evaluate cartilage-targeting transfection efficiency, the GFP and luciferase genes were delivered into knee joints using CAP- and SP-modified PEI. Cartilage transfections mediated by CAP-modified PEI were much more efficient and specific than those by SP-modified PEI. This result suggests that CAP-modified PEI could be used as a specific cartilage-targeting vector for cartilage disorders.

On-demand drug delivery from self-assembled nanofibrous gels: a new approach for treatment of proteolytic disease

Local delivery of drugs offers the potential for high local drug concentration while minimizing systemic toxicity, which is often observed with oral dosing. However, local depots are typically administered less frequently and include an initial burst followed by a continuous release. To maximize efficiency of therapy, it is critical to ensure that drug is only released when needed. One of the hallmarks of rheumatoid arthritis, for example, is its variable disease activity consisting of exacerbations of inflammation punctuated by periods of remission. This presents significant challenges for matching localized drug delivery with disease activity. An optimal system would be nontoxic and only release drugs during the period of exacerbation, self-titrating in response to the level of inflammation. We report the development of an injectable self-assembled nanofibrous hydrogel, from a generally recognized as safe material, which is capable of encapsulation and release of agents in response to specific enzymes that are significantly upregulated in a diseased state including matrix metalloproteinases (MMP-2 and MMP-9) and esterases. We show that these self-assembled nanofibrous gels can withstand shear forces that may be experienced in dynamic environments such as joints, can remain stable following injection into healthy joints of mice, and can disassemble in vitro to release encapsulated agents in response to synovial fluid from arthritic patients. This novel approach represents a next-generation therapeutic strategy for localized treatment of proteolytic diseases.

Controlling forces and pathways in self-assembly using viruses and DNA

The ability of both viruses and DNA to self-assemble in solution has continues to enable numerous applications at the nanoscale. Here we review the relevant interactions dictating the assembly of these structures, as well as discussing how they can be exploited experimentally. Because self-assembly is a process, we discuss various strategies for achieving spatial and temporal control. Finally, we highlight a few examples of recent advances that exploit the features of these nanostructures.

Biotinylated thermoresponsive core cross-linked nanoparticles via RAFT polymerization and "click" chemistry

A straightforward approach to the synthesis of "clickable" thermoresponsive core cross-linked (CCL) nanoparticles was developed. This approach was based on reversible addition-fragmentation chain transfer (RAFT) radical cross-linking polymerization of styrene and divinylbenzene with azide-functionalized poly(N-isopropylacrylamide) (PNIPAM-N(3)) as macro chain transfer agent in a selective solvent. Spherical nanoparticles with a diameter of 12nm were obtained after 24h polymerization. When the lyophilized CCL nanoparticles were dispersed in THF, spherical nanoparticles were observed, confirming the stability of CCL nanoparticles. The transmission electron microscopy (TEM) studies demonstrated that spherical nanoparticles and wormlike structure coexisted in the aqueous solution. The CCL nanoparticles have a lower critical solution temperature (LCST) at about 29.6°C, a little lower than that of PNIPAM homopolymer. Biotin molecules were conjugated to the surface of CCL nanoparticles via "click" chemistry in aqueous media. After bioconjugation, the LCST shifted to 28.3°C. The bioavailability of biotin to protein avidin was evaluated by a 4'-hydroxyazobenzene-2-carboxylic acid/avidin (HABA/avidin) binding assay and TEM.

Impact of biological agents and tissue engineering approaches on the treatment of rheumatic diseases

The treatment of rheumatic diseases has been the focus of many clinical studies aiming to achieve the best combination of drugs for symptom reduction. Although improved understanding of the pathophysiology of rheumatic diseases has led to the identification of effective therapeutic strategies, its cure remains unknown. Biological agents are a breakthrough in the treatment of these diseases. They proved to be more effective than the other conventional therapies in refractory inflammatory rheumatic diseases. Among them, tumor necrosis factor inhibitors are widely used, namely Etanercept, Infliximab, or Adalimumab, alone or in combination with disease-modifying antirheumatic drugs. Nevertheless, severe adverse effects have been detected in patients with history of recurrent infections, including cardiac failure or malignancy. Currently, most of the available therapies for rheumatic diseases do not have sufficient tissue specificity. Consequently, high drug doses must be administrated systemically, leading to adverse side effects associated with its possible toxicity. Drug delivery systems, by its targeted nature, are excellent solutions to overcome this problem. In this review, we will describe the state-of-the-art in clinical studies on the treatment of rheumatic diseases, emphasizing the use of biological agents and target drug delivery systems. Some alternative novel strategies of regenerative medicine and its implications for rheumatic diseases will also be discussed.

Achondroplasia: pathogenesis and implications for future treatment

PURPOSE OF REVIEW

Although the genetic defect underlying achondroplasia has been known for over a decade, no effective therapies to stimulate bone growth have emerged. Here we review the recent literature and summarize the molecular mechanisms underlying disease pathology and examine their potential as therapeutic targets. Currently used preclinical models are discussed in the context of recent advances with a special focus on C-type natriuretic peptide.

RECENT FINDINGS

Research on the mutation in Fibroblast Growth Factor Receptor 3 (FGFR3) that causes achondroplasia suggests that disease results from increased signal transduction from the mutant receptor. Thus, current therapeutic strategies have focused on reducing signals emanating from FGFR3. First-generation therapies directly targeting FGFR3, such as kinase inhibitors and neutralizing antibodies, designed for targeting FGFR3 in cancer, are still in the preclinical phase and have yet to translate into the management of achondroplasia. Counteracting signal transduction pathways downstream of FGFR3 holds promise with the discovery that administration of C-type natriuretic peptide to achondroplastic mice ameliorates their clinical phenotype. However, more research into long-term effectiveness and safety of this strategy is needed. Direct targeting of therapeutic agents to growth plate cartilage may enhance efficacy and minimize side effects of these and future therapies.

SUMMARY

Current research into the pathogenesis of achondroplasia has expanded our understanding of the mechanisms of FGFR3-induced disease and has increased the number of approaches that we may use to potentially correct it. Further research is needed to validate these approaches in preclinical models of achondroplasia.

Wound Healing Versus Regeneration: Role of the Tissue Environment in Regenerative Medicine

One of the major challenges in the field of regenerative medicine is how to optimize tissue regeneration in the body by therapeutically manipulating its natural ability to form scar at the time of injury or disease. It is often the balance between tissue regeneration, a process that is activated at the onset of disease, and scar formation, which develops as a result of the disease process that determines the ability of the tissue or organ to be functional. Using biomaterials as scaffolds often can provide a "bridge" for normal tissue edges to regenerate over small distances, usually up to 1 cm. Larger tissue defect gaps typically require both scaffolds and cells for normal tissue regeneration to occur without scar formation. Various strategies can help to modulate the scar response and can potentially enhance tissue regeneration. Understanding the mechanistic basis of such multivariate interactions as the scar microenvironment, the immune system, extracellular matrix, and inflammatory cytokines may enable the design of tissue engineering and wound healing strategies that directly modulate the healing response in a manner favorable to regeneration.

Synthesis of pyridyl disulfide-functionalized nanoparticles for conjugating thiol-containing small molecules, peptides, and proteins

Previously we reported emulsion polymerization of propylene sulfide with Pluronic F127 as an emulsifier, yielding nanoparticles (NPs) in the 25 nm size range. Immunologically functional NPs were prepared by adding an antigen-Pluronic conjugate to the polymerization mixture ( Reddy , S. T. , et al. ( 2007 ) Nat. Biotechnol. 25, 1159 ). We sought a more flexible scheme for conjugation of antigens and other biomolecules to the NP surfaces that would allow for milder reaction conditions than achievable during the polymerization step. Here, we present the synthesis of such functionalizable NPs in the form of NPs that carry thiol-reactive groups, to which thiol-containing antigens (peptide or protein) or other biomolecules can be conjugated under mild conditions to yield immunofunctional NPs. The Pluronic-stabilized poly(propylene sulfide) (PPS) NPs with thiol-reactive pyridyl disulfide groups are prepared in two steps by (1) emulsion polymerization of propylene sulfide in the presence of a carboxylate-Pluronic and (2) reaction of the carboxylic acid groups on the NP surface with cysteamine pyridyl disulfide and a water-soluble carbodiimide reagent. We choose pyridyl disulfide groups to have a reduction-sensitive disulfide bond linking the antigen to the NP surface, allowing efficient release of antigen inside the cell in response to the reductive conditions within the endosome. The functionalizable NPs are characterized by proton NMR, dynamic light scattering (DLS), UV/vis spectroscopy, and transmission electron microscopy (TEM). Conjugation of small molecules and protein to the NP surface is presented.

Kinetic study of the formation of polypyrrole nanoparticles in water-soluble polymer/metal cation systems: a light-scattering analysis

A facile way to synthesize nanometer-sized polymer (polypyrrole, PPy) particles is explored on the basis of the formation of complexes between water-soluble polymers and metal cations in aqueous solution. The metal cation is used as an oxidizing agent to initiate the chemical oxidation polymerization of the corresponding monomer, and the water-soluble polymer effectively provides a steric stability for the growth of polymer nanoparticles during the polymerization process. Light-scattering analyses are performed to give insight into the behavior of the complexes in aqueous solution. In addition, major physical parameters affecting the formation of polymer nanoparticles are investigated, including hydrodynamic radius, radius of gyration, shape factor, and viscosity. By judicious control of these parameters, PPy nanoparticles with narrow size distribution can be readily fabricated in large quantities. It is also possible to control the diameter of the nanoparticles by changing critical synthetic variables. Importantly, PPy nanoparticles of approximately 20-60 nm in diameter can be prepared without using any surfactants or specific templates; this novel strategy offers great possibility for mass production of polymer nanoparticles.

Spatiotemporal controlled delivery of nanoparticles to injured vasculature

There are a number of challenges associated with designing nanoparticles for medical applications. We define two challenges here: (i) conventional targeting against up-regulated cell surface antigens is limited by heterogeneity in expression, and (ii) previous studies suggest that the optimal size of nanoparticles designed for systemic delivery is approximately 50-150 nm, yet this size range confers a high surface area-to-volume ratio, which results in fast diffusive drug release. Here, we achieve spatial control by biopanning a phage library to discover materials that target abundant vascular antigens exposed in disease. Next, we achieve temporal control by designing 60-nm hybrid nanoparticles with a lipid shell interface surrounding a polymer core, which is loaded with slow-eluting conjugates of paclitaxel for controlled ester hydrolysis and drug release over approximately 12 days. The nanoparticles inhibited human aortic smooth muscle cell proliferation in vitro and showed greater in vivo vascular retention during percutaneous angioplasty over nontargeted controls. This nanoparticle technology may potentially be used toward the treatment of injured vasculature, a clinical problem of primary importance.

Designing materials to direct stem-cell fate

Proper tissue function and regeneration rely on robust spatial and temporal control of biophysical and biochemical microenvironmental cues through mechanisms that remain poorly understood. Biomaterials are rapidly being developed to display and deliver stem-cell-regulatory signals in a precise and near-physiological fashion, and serve as powerful artificial microenvironments in which to study and instruct stem-cell fate both in culture and in vivo. Further synergism of cell biological and biomaterials technologies promises to have a profound impact on stem-cell biology and provide insights that will advance stem-cell-based clinical approaches to tissue regeneration.

Peptide- and aptamer-functionalized nanovectors for targeted delivery of therapeutics

Targeted delivery of therapeutics is an area of vigorous research, and peptide- and aptamer-functionalized nanovectors are a promising class of targeted delivery vehicles. Both peptide- and aptamer-targeting ligands can be readily designed to bind a target selectively with high affinity, and more importantly are molecules accessible by chemical synthesis and relatively compact compared with antibodies and full proteins. The multitude of peptide ligands that have been used for targeted delivery are covered in this review, with discussion of binding selectivity and targeting performance for these peptide sequences where possible. Aptamers are RNA or DNA strands evolutionarily engineered to specifically bind a chosen target. Although use of aptamers in targeted delivery is a relatively new avenue of research, the current state of the field is covered and promises of future advances in this area are highlighted. Liposomes, the classic drug delivery vector, and polymeric nanovectors functionalized with peptide or aptamer binding ligands will be discussed in this review, with the exclusion of other drug delivery vehicles. Targeted delivery of therapeutics, from DNA to classic small molecule drugs to protein therapeutics, by these targeted nanovectors is reviewed with coverage of both in vitro and in vivo deliveries. This is an exciting and dynamic area of research and this review seeks to discuss its broad scope.

Artificial stem cell niches

Stem cells are characterized by their dual ability to reproduce themselves (self-renew) and specialize (differentiate), yielding a plethora of daughter cells that maintain and regenerate tissues. In contrast to their embryonic counterparts, adult stem cells retain their unique functions only if they are in intimate contact with an instructive microenvironment, termed stem cell niche. In these niches, stem cells integrate a complex array of molecular signals that, in concert with induced cell-intrinsic regulatory networks, control their function and balance their numbers in response to physiologic demands. This progress report provides a perspective on how advanced materials technologies could be used (i) to engineer and systematically analyze specific aspects of functional stem cells niches in a controlled fashion in vitro and (ii) to target stem cell niches in vivo. Such "artificial niches" constitute potent tools for elucidating stem cell regulatory mechanisms with the capacity to directly impact the development of novel therapeutic strategies for tissue regeneration.

Injectable biomaterials for regenerating complex craniofacial tissues

Engineering complex tissues requires a precisely formulated combination of cells, spatiotemporally released bioactive factors, and a specialized scaffold support system. Injectable materials, particularly those delivered in aqueous solution, are considered ideal delivery vehicles for cells and bioactive factors and can also be delivered through minimally invasive methods and fill complex 3D shapes. In this review, we examine injectable materials that form scaffolds or networks capable of both replacing tissue function early after delivery and supporting tissue regeneration over a time period of weeks to months. The use of these materials for tissue engineering within the craniofacial complex is challenging but ideal as many highly specialized and functional tissues reside within a small volume in the craniofacial structures and the need for minimally invasive interventions is desirable due to aesthetic considerations. Current biomaterials and strategies used to treat craniofacial defects are examined, followed by a review of craniofacial tissue engineering, and finally an examination of current technologies used for injectable scaffold development and drug and cell delivery using these materials.

Intra-articular drug delivery systems: Overcoming the shortcomings of joint disease therapy

BACKGROUND

Intra-articular drug delivery is very useful for treating local disease flare-ups, synovitis and pain in joints. However, the effectiveness of drugs following intra-articular administration is limited by drug delivery issues.

AIM

This review addresses critical drug delivery parameters that influence the biocompatibility, tolerability and efficacy of intra-articular administrations and offers an opinion on aspects of formulation design.

METHODS

The relevant literature was reviewed, focusing on factors influencing tissue targeting, safety and effectiveness of particulate formulations.

RESULTS/CONCLUSION

Therapeutic applications of novel drug delivery systems for the localized treatment of joints have lagged significantly. Future innovations in the field will require the discovery of new therapeutic agents for regional delivery, combination regimens, novel biomaterials as drug carriers and targeting carriers to specific molecules.

Phototocatalytic lithography of poly(propylene sulfide) block copolymers: toward high-throughput nanolithography for biomolecular arraying applications

Photocatalytic lithography (PCL) is an inexpensive, fast, and robust method of oxidizing surface chemical moieties to produce patterned substrates. This technique has utility in basic biological research as well as various biochip applications. We report on porphyrin-based PCL for patterning poly(propylene sulfide) block copolymer films on gold substrates on the micrometer and submicrometer scales. We confirm chemical patterning with imaging ToF-SIMS and low-voltage SEM. Biomolecular patterning on micrometer and submicrometer scales is demonstrated with proteins, protein-linked beads. and fluorescently labeled proteins.

Probing fibronectin-surface interactions: a multitechnique approach

The development of adhesive as well as antiadhesive surfaces is essential in various biomaterial applications. In this study, we have used a multidisciplinary approach that combines biological and physicochemical methods to progress in our understanding of cell-surface interactions. Four model surfaces have been used to investigate fibronectin (Fn) adsorption and the subsequent morphology and adhesion of preosteoblasts. Such experimental conditions lead us to distinguish between anti- and proadhesive substrata. Our results indicate that Fn is not able to induce cell adhesion on antiadhesive materials. On adhesive substrata, Fn did not increase the number of adherent cells but favored their spreading. This work also examined Fn-surface interactions using ELISA immunoassays, fluorescent labeling of Fn, and force spectroscopy with Fn-modified tips. The results provided clear evidence of the advantages and limitations of each technique. All of the techniques confirmed the important adsorption of Fn on proadhesive surfaces for cells. By contrast, antiadhesive substrata for cells avoided Fn adsorption. Furthermore, ELISA experiments enabled us to verify the accessibility of cell binding sites to adsorbed Fn molecules.

Emerging intra-articular drug delivery systems for the temporomandibular joint

Temporomandibular joint (TMJ) disorders are a heterogeneous group of diseases that cause progressive joint degeneration leading to chronic pain and reduced quality of life. Both effective pain reduction and restoration of TMJ function remain unmet challenges. Intra-articular injections of corticosteroids and hyaluronic acid are currently used to treat chronic pain, but these methods require multiple injections that increase the risk of iatrogenic joint damage and other complications. The small and emerging field of TMJ tissue engineering aims to reduce pain and disability through novel strategies that induce joint tissue regeneration. Development of methods for sustained, intra-articular release of growth factors and other pro-regenerative signals will be critical for the success of TMJ tissue engineering strategies. This review discusses methods of intra-articular drug delivery to the TMJ, as well as emerging injectable controlled release systems with potential to improve TMJ drug delivery, to encourage further research in the development of sustained release systems for both long-term pain management and to enhance tissue engineering strategies for TMJ regeneration.

Folate-mediated Cell Uptake of Shell-crosslinked Spheres and Cylinders

This paper reports the synthesis of shell crosslinked nanoparticles (SCKs) of spherical and cylindrical shapes, and their functionalization with folate using a poly(ethylene glycol) (PEG) construct that has folate and an amine group as the opposing chain termini. By use of confocal microscopy, we demonstrate the selective delivery of folate conjugated SCKs to human KB cells, a cell line that overexpresses the folate receptor (FR). A higher extent of polymer uptake by the cells occurred with the cylindrical SCK morphology, relative to the spherical SCKs, when both samples had the same fluorescein-5-thiosemicarbazide and polymer concentrations. In both cases, by using excess free folic acid as a block or SCKs lacking the folate-PEG conjugate, cell uptake was significantly reduced. These results suggest that particle shape may play an important role in receptor-mediated cell uptake, and may be exploited in the targeted delivery of nanoscopic drugs.