Bioactive factor delivery strategies from engineered polymer hydrogels for therapeutic medicine.

Polymer hydrogels have been widely explored as therapeutic delivery matrices because of their ability to present sustained, localized and controlled release of bioactive factors. Bioactive factor delivery from injectable biopolymer hydrogels provides a versatile approach to treat a wide variety of diseases, to direct cell function and to enhance tissue regeneration. The innovative development and modification of both natural-(e.g., alginate (ALG), chitosan, hyaluronic acid (HA), gelatin, heparin (HEP), etc.) and synthetic-(e.g., polyesters, polyethyleneimine (PEI), etc.) based polymers has resulted in a variety of approaches to design drug delivery hydrogel systems from which loaded therapeutics are released. This review presents the state-of-the-art in a wide range of hydrogels that are formed though self-assembly of polymers and peptides, chemical crosslinking, ionic crosslinking and biomolecule recognition. Hydrogel design for bioactive factor delivery is the focus of the first section. The second section then thoroughly discusses release strategies of payloads from hydrogels for therapeutic medicine, such as physical incorporation, covalent tethering, affinity interactions, on demand release and/or use of hybrid polymer scaffolds, with an emphasis on the last 5 years.

Accidental section of the ulnar nerve in the wrist during arthroscopy.

Arthroscopy of the wrist is a frequently performed procedure. Its role in diagnosis and treatment is significant. The complications of arthroscopy are well known and are described in the literature. We describe a case of accidental section of the ulnar nerve during repair of the triangular fibrocartilage complex during arthroscopy. The nerve section was caused by the trocar used for drainage in the 6U portal. We propose to establish the injury mechanism and describe a safe procedure for this examination.

Hydrogel microspheres for spatiotemporally controlled delivery of RNA and silencing gene expression within scaffold-free tissue engineered constructs.

Delivery systems for controlled release of RNA interference (RNAi) molecules, including small interfering (siRNA) and microRNA (miRNA), have the potential to direct stem cell differentiation for regenerative musculoskeletal applications. To date, localized RNA delivery platforms in this area have focused predominantly on bulk scaffold-based approaches, which can interfere with cell-cell interactions important for recapitulating some native musculoskeletal developmental and healing processes in tissue regeneration strategies. In contrast, scaffold-free, high density human mesenchymal stem cell (hMSC) aggregates may provide an avenue for creating a more biomimetic microenvironment. Here, photocrosslinkable dextran microspheres (MS) encapsulating siRNA-micelles were prepared via an aqueous emulsion method and incorporated within hMSC aggregates for localized and sustained delivery of bioactive siRNA. siRNA-micelles released from MS in a sustained fashion over the course of 28 days, and the released siRNA retained its ability to transfect cells for gene silencing. Incorporation of fluorescently labeled siRNA (siGLO)-laden MS within hMSC aggregates exhibited tunable siGLO delivery and uptake by stem cells. Incorporation of MS loaded with siRNA targeting green fluorescent protein (siGFP) within GFP-hMSC aggregates provided sustained presentation of siGFP within the constructs and prolonged GFP silencing for up to 15 days. This platform system enables sustained gene silencing within stem cell aggregates and thus shows great potential in tissue regeneration applications. STATEMENT OF SIGNIFICANCE: This work presents a new strategy to deliver RNA-nanocomplexes from photocrosslinked dextran microspheres for tunable presentation of bioactive RNA. These microspheres were embedded within scaffold-free, human mesenchymal stem cell (hMSC) aggregates for sustained gene silencing within three-dimensional cell constructs while maintaining cell viability. Unlike exogenous delivery of RNA within culture medium that suffers from diffusion limitations and potential need for repeated transfections, this strategy provides local and sustained RNA presentation from the microspheres to cells in the constructs. This system has the potential to inhibit translation of hMSC differentiation antagonists and drive hMSC differentiation toward desired specific lineages, and is an important step in the engineering of high-density stem cell systems with incorporated instructive genetic cues for application in tissue regeneration.

Injectable poly(amidoamine)-poly(ethylene glycol)-poly(amidoamine) triblock copolymer hydrogel with dual sensitivities: pH and temperature.

A novel triblock copolymer for use in an injectable pH- and temperature-sensitive hydrogel is synthesized by conjugating poly(amidoamine) (PAA) to poly(ethylene glycol): poly(amidoamine)-poly(ethylene glycol)-poly(amidoamine) (PAA-PEG-PAA). The polymer was characterized with (1)H NMR and gel permeation chromatography in the diluents CDCl(3) and CHCl(3), respectively. The PAA block acts as a pH- and temperature-sensitive block. The PAA-PEG-PAA copolymer in aqueous solution (12.5 wt %) underwent a sol-gel transition as a function of pH and temperature. After injection into a rat, the copolymer solution (12.5 wt %) was immediately changed to a gel.

Covalently tethering siRNA to hydrogels for localized, controlled release and gene silencing.

Small interfering RNA (siRNA) has found many applications in tissue regeneration and disease therapeutics. Effective and localized siRNA delivery remains challenging, reducing its therapeutic potential. Here, we report a strategy to control and prolong siRNA release by directly tethering transfection-capable siRNA to photocrosslinked dextran hydrogels. siRNA release is governed via the hydrolytic degradation of ester and/or disulfide linkages between the siRNA and hydrogels, which is independent of hydrogel degradation rate. The released siRNA is shown to be bioactive by inhibiting protein expression in green fluorescent protein-expressing HeLa cells without the need of a transfection agent. This strategy provides an excellent platform for controlling nucleic acid delivery through covalent bonds with a biomaterial and regulating cellular gene expression, which has promising potential in many biomedical applications.

Dual non-viral gene delivery from microparticles within 3D high-density stem cell constructs for enhanced bone tissue engineering.

High-density mesenchymal stem cell (MSC) aggregates can be guided to form bone-like tissue via endochondral ossification in vitro when culture media is supplemented with proteins, such as growth factors (GFs), to first guide the formation of a cartilage template, followed by culture with hypertrophic factors. Recent reports have recapitulated these results through the controlled spatiotemporal delivery of chondrogenic transforming growth factor-ß1 (TGF-ß1) and chondrogenic and osteogenic bone morphogenetic protein-2 (BMP-2) from microparticles embedded within human MSC aggregates to avoid diffusion limitations and the lengthy, costly in vitro culture necessary with repeat exogenous supplementation. However, since GFs have limited stability, localized gene delivery is a promising alternative to the use of proteins. Here, mineral-coated hydroxyapatite microparticles (MCM) capable of localized delivery of Lipofectamine-plasmid DNA (pDNA) nanocomplexes encoding for TGF-ß1 (pTGF-ß1) and BMP-2 (pBMP-2) were incorporated, alone or in combination, within MSC aggregates from three healthy porcine donors to induce sustained production of these transgenes. Three donor populations were investigated in this work due to the noted MSC donor-to-donor variability in differentiation capacity documented in the literature. Delivery of pBMP-2 within Donor 1 aggregates promoted chondrogenesis at week 2, followed by an enhanced osteogenic phenotype at week 4. Donor 2 and 3 aggregates did not promote robust glycosaminoglycan (GAG) production at week 2, but by week 4, Donor 2 aggregates with pTGF-ß1/pBMP-2 and Donor 3 aggregates with both unloaded MCM and pBMP-2 enhanced osteogenesis compared to controls. These results demonstrate the ability to promote osteogenesis in stem cell aggregates through controlled, non-viral gene delivery within the cell masses. These findings also indicate the need to screen donor MSC regenerative potential in response to gene transfer prior to clinical application. Taken together, this work demonstrates a promising gene therapy approach to control stem cell fate in biomimetic 3D condensations for treatment of bone defects.

Cytocompatible Catalyst-Free Photodegradable Hydrogels for Light-Mediated RNA Release To Induce hMSC Osteogenesis.

Macroscopic hydrogels provide valuable platforms for controlling the release of genetic materials such as small interfering RNA (siRNA) and microRNA (miRNA) for biomedical applications. However, after these hydrogels are formed, it is challenging to alter the release rate of genetic materials. In this report, a Michael addition catalyst-free photodegradable poly(ethylene glycol) (PEG)-based hydrogel system has been developed that provides an active means of controlling the release of genetic materials postgelation using external UV light application. Photodegradation of photolabile linkages in the hydrogel network changes the hydrogel physiochemical properties such as swelling and degradation rate, augmenting the release rate of loaded genetic materials. In the absence of UV light, RNAs were released in a sustained fashion from both photodegradable and nonphotodegradable hydrogels. In contrast, RNA release rate from the photodegradable hydrogels was accelerated via UV light application, whereas it was not elevated with nonphotodegradable hydrogels. Regardless of the UV light exposure to the hydrogels, released siRNA against green fluorescent protein (siGFP) retained its bioactivity via effectively silencing GFP expression in destabilized GFP (deGFP)-expressing HeLa cells cultured in monolayer. Moreover, cells encapsulated in these hydrogels exhibited high cell viability, and loaded siGFP inhibited GFP expression of encapsulated deGFP-expressing HeLa cells with or without UV light application to the hydrogels. Importantly, released siRNA targeting noggin (siNoggin) and miRNA-20a from the hydrogels, with and without UV light application, induced osteogenic differentiation of human mesenchymal stem cells (hMSCs). This photodegradable hydrogel system may be a promising strategy for real-time, user-controlled release of genetic materials for tissue engineering and treatment of diseases such as cancer.

Photocrosslinkable, biodegradable hydrogels with controlled cell adhesivity for prolonged siRNA delivery to hMSCs to enhance their osteogenic differentiation.

Photocrosslinked, biodegradable hydrogels have been extensively investigated for biomedical applications, including drug delivery and tissue engineering. Here, dextran (DEX) was chemically modified with mono(2-acryloyloxyethyl) succinate (MAES) via an esterification reaction, resulting in macromers that could be photocrosslinked to form hydrolytically degradable hydrogels. Hydrogel swelling ratio and degradation rate were controlled by varying the degree of MAES modification. Thiolated cell adhesion peptides (GRGDSPC) were conjugated to acrylated dextran via thiol-acrylate reaction to regulate the interactions of human mesenchymal stem cells (hMSCs) with the photocrosslinkable hydrogels. The hydrogels permitted sustained release of short interfering RNA (siRNA) over 7 weeks and were cytocompatible with hMSCs. Sustained presentation of siRNA from these photocrosslinked DEX hydrogels enhanced the osteogenic differentiation of encapsulated hMSCs. These DEX hydrogels with tunable siRNA delivery and cell adhesive properties may provide an excellent platform for bioactive molecule delivery and tissue regeneration applications.

Photocleavable Hydrogels for Light-Triggered siRNA Release.

A photocleavable hydrogel system for on-demand delivery of genetic material is reported. The release of short interfering RNAs can be triggered by the application of UV light without any loss in bioactivity. This approach provides a promising external stimulus-based nucleic acid delivery platform for applications in disease therapeutics and tissue regeneration.

Light-triggered RNA release and induction of hMSC osteogenesis via photodegradable, dual-crosslinked hydrogels.

AIM: To engineer a photodegradable hydrogel system for actively controlled release of bioactive unmodified RNA at designated time points to induce hMSC osteogenesis. MATERIALS & METHODS: RNA/polyethylenimine complexes were loaded into dual-crosslinked photodegradable hydrogels to examine the capacity of UV light application to trigger their release. The ability of released RNA to drive hMSC osteogenic differentiation was also investigated. RESULTS & CONCLUSION: RNA release from photodegradable hydrogels was accelerated upon UV application, which was not observed in non-photodegradable hydrogels. Regardless of the presence of UV light, released siGFP exhibited high bioactivity by silencing GFP expression in HeLa cells. Importantly, siNoggin or miRNA-20a released from the hydrogels induced hMSC osteogenesis. This system provides a potentially valuable physician/patient-controlled 'on-demand' RNA delivery platform for biomedical applications.

Dually cationic and anionic pH/temperature-sensitive injectable hydrogels and potential application as a protein carrier.

Novel copolymers containing both anionic and cationic pH-sensitive moieties were reported. These amphoteric copolymers exhibited special closed-loop reversible sol-gel-sol phase transitions in response to both pH and temperature.

Synthesis, Characteristics and Potential Application of Poly(ß-Amino Ester Urethane)-Based Multiblock Co-Polymers as an Injectable, Biodegradable and pH/Temperature-Sensitive Hydrogel System.

Physical polymeric hydrogels have significant potential for use as injectable depot drug/protein-delivery systems. In this study, a series of novel injectable, biodegradable and pH/temperature-sensitive multiblock co-polymer physical hydrogels composed of poly(ethylene glycol) (PEG) and poly(ß-amino ester urethane) (PEU) was synthesized by the polyaddition between the isocyanate groups of 1,6-diisocyanato hexamethylene and the hydroxyl groups of PEG and a synthesized monomer BTB (or ETE) in chloroform in the presence of dibutyltin dilaurate as a catalyst. The synthesized co-polymers were characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy and gel-permeation chromatography. Aqueous solutions of the co-polymers showed a sol-to-gel phase transition with increasing pH and a gel-to-sol phase transition with increasing temperature. The gel regions covered the physiological conditions (37°C, pH 7.4) and could be controlled by changing the molecular weight of PEG, PEG/PEU ratio and co-polymer solution concentration. A gel formed rapidly in situ after injecting the co-polymer solution subcutaneously into SD rats and remained for more than 2 weeks in the body. The cytotoxicity tests confirmed the non-cytotoxicity of this co-polymer hydrogel. The controlled in vitro release of the model anticancer drug, doxorubicin, from this hydrogel occurred over a 7-day period. This hydrogel is a potential candidate for biomedical applications and drug/protein-delivery systems.

Biodegradable pH/temperature-sensitive oligo(ß-amino ester urethane) hydrogels for controlled release of doxorubicin.

An injectable biodegradable pH/temperature-sensitive oligo(ß-amino ester urethane) (OAEU) was synthesized. The OAEU was synthesized by addition polymerization between the isocyanate groups of 1,6-diisocyanato hexamethylene and the hydroxyl groups of a synthesized monomer piperazine dihydroxyl amino ester (monomer PDE) in chloroform in the presence of dibutyltin dilaurate as a catalyst. The synthesized OAEU was characterized by (1)H NMR spectroscopy, Fourier transform infrared spectroscopy and gel permeation chromatography. The aqueous solutions of OAEU showed a sol-to-gel-to-sol phase transition as a function of temperature and pH. The gel window covered the physiological conditions (37°C, pH 7.4) and could be controlled by changing the OAEU concentration. After a subcutaneous injection of the OAEU solution into Sprague-Dawley rats, a gel formed rapidly in situ and remained in the body for more than 2 weeks. The in vitro cytotoxicity test and in vitro degradation showed that the OAEU hydrogel was non-cytotoxic and biodegradable. The in vitro release of doxorubicin from this OAEU hydrogel was sustained for more than 10 days. This injectable biodegradable pH/temperature-sensitive OAEU hydrogel is a potential candidate as a drug/protein carrier and in biomedical applications.

pH-responsive polymeric micelle based on PEG-poly(ß-amino ester)/(amido amine) as intelligent vehicle for magnetic resonance imaging in detection of cerebral ischemic area.

A series of pH-responsive polymeric micelles is developed to act as intelligent carriers to deliver iron oxide (Fe(3)O(4)) nanoparticles and respond rapidly to an acidic stimuli environment for magnetic resonance imaging (MRI). The polymeric micelle can be self-assembled at physiological pH by a block copolymer, consisting of a hydrophilic methoxy poly(ethylene glycol) (PEG) and a pH-responsive poly(ß-amino ester)/(amido amine) block. Consequently, the Fe(3)O(4) nanoparticles can be well encapsulated into polymeric micelles due to the hydrophobic interaction, shielded by a PEG coronal shell. In an acidic environment, however, the pH-responsive component, which has ionizable tert-amino groups on its backbone, can become protonated to be soluble and release the hydrophobic Fe(3)O(4) nanoparticles. The Fe(3)O(4)-loaded polymeric micelle was measured by dynamic light scattering (DLS), superconducting quantum interference device (SQUID) and a 3.0T MRI scanner. To assess the ability of this MRI probe as a pH-triggered agent, we utilize a disease rat model of cerebral ischemia that produces acidic tissue due to its pathologic condition. We found gradual accumulation of Fe(3)O(4) nanoparticles in the brain ischemic area, indicating that the pH-triggered MRI probe may be effective for targeting the acidic environment and diagnostic imaging of pathologic tissue.

Oligo(amidoamine)s hydrogels with tunable gel properties.

A series of oligo(amidoamine)s (OAAs) that can be reversibly switched between sol and gel phases upon changes in pH and temperature have been synthesized and characterized. Their viscoelastic properties were significantly increased upon increasing the number of methylene groups, implying that viscoelasticity could clearly be tuned at the molecular level.

Injectable biodegradable hydrogels.

Injectable biodegradable copolymer hydrogels, which exhibit a sol-gel phase transition in response to external stimuli, such as temperature changes or both pH and temperature (pH/temperature) alterations, have found a number of uses in biomedical and pharmaceutical applications, such as drug delivery, cell growth, and tissue engineering. These hydrogels can be used in simple pharmaceutical formulations that can be prepared by mixing the hydrogel with drugs, proteins, or cells. Such formulations are administered in a straightforward manner, through site-specific control of release behavior, and the hydrogels are compatible with biological systems. This review will provide a summary of recent progress in biodegradable temperature-sensitive polymers including polyesters, polyphosphazenes, polypeptides, and chitosan, and pH/temperature-sensitive polymers such as sulfamethazine-, poly(beta-amino ester)-, poly(amino urethane)-, and poly(amidoamine)-based polymers. The advantages of pH/temperature-sensitive polymers over simple temperature-sensitive polymers are also discussed. A perspective on the future of injectable biodegradable hydrogels is offered.