Delivering DNA from photocrosslinked, surface eroding polyanhydrides

Photo-cross-linked Hydrogels for Cartilage and Osteochondral Repair

Photo-cross-linked hydrogels, which respond to light and induce structural or morphological transitions, form a microenvironment that mimics the extracellular matrix of native tissue. In the last decades, photo-cross-linked hydrogels have been widely used in cartilage and osteochondral tissue engineering due to their good biocompatibility, ease of fabrication, rapid in situ gel-forming ability, and tunable mechanical and degradable properties. In this review, we systemically summarize the different types and physicochemical properties of photo-cross-linked hydrogels (including the materials and photoinitiators) and explore the biological properties modulated through the incorporation of additives, including cells, biomolecules, genes, and nanomaterials, into photo-cross-linked hydrogels. Subsequently, we compile the applications of photo-cross-linked hydrogels with a specific focus on cartilage and osteochondral repair. Finally, current limitations and future perspectives of photo-cross-linked hydrogels are also discussed.

Polyanhydride Chemistry

Polyanhydrides (PAs) are a class of synthetic biodegradable polymers employed as controlled drug delivery vehicles. They can be synthesized and scaled up from low-cost starting materials. The structure of PAs can be manipulated synthetically to meet desirable characteristics. PAs are biocompatible, biodegradable, and generate nontoxic metabolites upon degradation, which are easily eliminated from the body. The rate of water penetrating into the polyanhydride (PA) matrix is slower than the anhydride bond cleavage. This phenomenon sets PAs as "surface-eroding drug delivery carriers." Consequently, a variety of PA-based drug delivery carriers in the form of solid implants, pasty injectable formulations, microspheres, nanoparticles, etc. have been developed for the sustained release of small molecule drugs, and vaccines, peptide drugs, and nucleic acid-based active agents. The rate of drug delivery is often controlled by the polymer erosion rate, which is influenced by the polymer structure and composition, crystallinity, hydrophobicity, pH of the release medium, device size, configuration, etc. Owing to the above-mentioned interesting physicochemical and mechanical properties of PAs, the present review focuses on the advancements made in the domain of synthetic biodegradable biomedical PAs for therapeutic delivery applications. Various classes of PAs, their structures, their unique characteristics, their physicochemical and mechanical properties, and factors influencing surface erosion are discussed in detail. The review also summarizes various methods involved in the synthesis of PAs and their utility in the biomedical domain as drug, vaccine, and peptide delivery carriers in different formulations are reviewed.

Colonic Delivery of Nutrients for Sustained and Prolonged Release of Gut Peptides: A Novel Strategy for Appetite Management

Obesity is one of the major global threats to human health and risk factors for cardiometabolic diseases and certain cancers. Glucagon-like peptide-1 (GLP-1) plays a major role in appetite and glucose homeostasis and recently the USFDA approved GLP-1 agonists for the treatment of obesity and type 2 diabetes. GLP-1 is secreted from enteroendocrine L-cells in the distal part of the gastrointestinal (GI) tract in response to nutrient ingestion. Endogenously released GLP-1 has a very short half-life of <2 min and most of the nutrients are absorbed before reaching the distal GI tract and colon, which hinders the use of nutritional compounds for appetite regulation. The review article focuses on nutrients that endogenously stimulate GLP-1 and peptide YY (PYY) secretion via their receptors in order to decrease appetite as preventive action. In addition, various delivery technologies such as pH-sensitive, mucoadhesive, time-dependent, and enzyme-sensitive systems for colonic targeting of nutrients delivery are described. Sustained colonic delivery of nutritional compounds could be one of the most promising approaches to prevent obesity and associated metabolic diseases by, e.g., sustained GLP-1 release.

Systematic Investigation of Biocompatible Cationic Polymeric Nucleic Acid Carriers for Immunotherapy of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the third-largest cause of cancer death worldwide, while immunotherapy is rapidly being developed to fight HCC with great potential. Nucleic acid drugs are the most important modulators in HCC immunotherapy. To boost the efficacy of therapeutics and amplify the efficiency of genetic materials, biocompatible polymers are commonly used. However, under the strong need of a summary for current developments of biocompatible polymeric nucleic acid carriers for immunotherapy of HCC, there is rare review article specific to this topic to our best knowledge. In this article, we will discuss the current progress of immunotherapy for HCC, biocompatible cationic polymers (BCPs) as nucleic acid carriers used (or potential) to fight HCC, the roles of biocompatible polymeric carriers for nucleic acid delivery, and nucleic acid delivery by biocompatible polymers for immunotherapy. At the end, we will conclude the review and discuss future perspectives. This article discusses biocompatible polymeric nucleic acid carriers for immunotherapy of HCC from multidiscipline perspectives and provides a new insight in this domain. We believe this review will be interesting to polymer chemists, pharmacists, clinic doctors, and PhD students in related disciplines.

Stem cell therapy in the heart: Biomaterials as a key route

Cardiovascular diseases are one of the main concerns, nowadays causing a high rate of mortality in the world. The majority of conventional treatment protects the heart from failure progression. As a novel therapeutic way, Regenerative medicine in the heart includes cellular and noncellular approaches. Despite the irrefutable privileges of noncellular aspects such as administration of exosomes, utilizing of miRNAs, and growth factors, they cannot reverse necrotic or ischemic myocardium, hence recruiting of stem cells to help regenerative therapy in the heart seems indispensable. Stem cell lineages are varied and divided into two main groups namely pluripotent and adult stem cells. Not only has each of which own regenerative capacity, benefits, and drawbacks, but their turnover also close correlates with the target organ and/or tissue as well as the stage and level of failure. In addition to inefficient tissue integration due to the defects in delivering methods and poor retention of transplanted cells, the complexity of the heart and its movement also make more rigorous the repair process. Hence, utilizing biomaterials can make a key route to tackle such obstacles. In this review, we evaluate some natural products which can help stem cells in regenerative medicine of the cardiovascular system.

Drug Delivery and Drug Efficacy from Amorphous Poly(thioether anhydrides)

The correlation between erosion and drug (lidocaine and 6-mercaptopurine, 6-MP) release from amorphous poly(thioether anhydrides), which are synthesized using radical-mediated thiol-ene polymerization, is reported. Cytotoxicity studies of the polymer toward human fibroblast human dermal fibroblasts adult, melanoma A-375, and breast cancer MCF-7 cells are conducted, and drug efficacy of a cancer and autoimmune disease drug (6-MP) when released from the poly(thioether anhydrides) is examined against two cancerous cell types (A-375 and MCF-7). Erosion and drug release studies reveal that lidocaine release is governed by network erosion whereas 6-MP is released by a combination of erosion and diffusion. The cytotoxicity studies show that all three cell types demonstrate high viability, thus cytocompatibility, to poly(thioether anhydrides). Toxicity to the material is dose dependent and comparable to other polyanhydride systems. The 6-MP cancer drug is shown to remain bioactive after encapsulation in the poly(thioether anhydride) matrix and the polymer does not appear to modify the efficacy of the drug.

Photo-crosslinked anhydride-modified polyester and -ethers for pH-sensitive drug release

Photo-crosslinkable polymers have a great potential for the delivery of sensitive drugs. They allow preparation of drug releasing devices by photo-crosslinking, thus avoiding high processing temperatures. In this study, the hydrolysis behavior and drug release of three different photo-crosslinkable poly(ether anhydride)s and one poly(ester anhydride) were investigated. Three-arm poly(ethylene glycol) or polycaprolactone was reacted with succinic anhydride to obtain carboxylated macromers, and further functionalized with methacrylic anhydride to form methacrylated marcromers with anhydride linkages. The synthetized macromers were used to prepare photo-crosslinked matrices with different hydrolytic degradation times for active agent release purposes. The hydrolysis was clearly pH-sensitive: polymer networks degraded slowly in acidic conditions, and degradation rate increased as the pH shifted towards basic conditions. Drug release was studied with two water-soluble model drugs lidocaine (234 mol/g) and vitamin B₁₂ (1355 g/mol). Vitamin B₁₂ was released mainly due to polymer network degradation, whereas smaller molecule lidocaine was released also through diffusion and swelling of polymer network. Only a small amount of vitamin B₁₂ was released in acidic conditions (pH 1.3 and pH 2.1). These polymers have potential in colon targeted drug delivery as the polymer could protect sensitive drugs from acidic conditions in the stomach, and the drug would be released as the conditions change closer to neutral pH in the intestine.

Recent Advances in Polyanhydride Based Biomaterials

This review focusses on recent developments of polyanhydrides, a class of degradable synthetic biopolymers. Polyanhydrides have been used as carriers for controlled delivery of drugs. A polyanhydride copolymer of carboxyphenoxy propane and sebacic acid has been used in Gliadel brain tumor implants for the controlled delivery of carmustine or bis-chloroethylnitrosourea. They are easy and inexpensive to synthesize (especially scale up). However, polyanhydrides possess a short shelf-life. Hydrolytic cleavage and anhydride interchanges lower their molecular weights during storage. One of the highlights in recent developments of polyanhydride chemistry is the discovery of alternating copolymers having extended shelf-life. Other highlights include their applications in biomedical electronics, vaccine delivery, and nano/micro particulate delivery systems. This review examines approaches for polyanhydride synthesis followed by their recent developments in biomedical applications.

Topologically frustrated dynamics of crowded charged macromolecules in charged hydrogels

Movement of charged macromolecules in crowded aqueous environments is a ubiquitous phenomenon vital to the various living processes and formulations of materials for health care. While study of diffusion of tracer amounts of probe macromolecules trapped inside concentrated solutions, gels, or random media has led to an enhanced understanding of this complex process, the collective dynamics of charged macromolecules embedded inside congested charge-bearing matrices still remains to be fully explored. Here we report a frustrated dynamics of DNA and synthetic polyelectrolytes inside a charged host hydrogel where the guest molecules do not diffuse. Instead, they exhibit a family of relaxation processes arising from a combination of conformational entropy and local chain dynamics, which are frustrated by the confinement from the gel. We also have developed a model explaining this new universality class of non-diffusive topologically frustrated dynamics of charged macromolecules.

Diffusion of molecules in crowded environment is important for various living systems, but the dynamics of charged molecules in charged matrices remains still unexplored. Here the authors report a dynamics of DNA and polyelectrolytes in a charged hydrogel where the guest molecules do not diffuse but experience topologically frustrated dynamics.

Synthesis and Characterization of Salicylic Acid-Based Poly(Anhydride-Ester) Copolymers

A series of poly(anhydride-esters) based on poly(1,10-bis(o-car-boxyphenoxy)decanoate) (CPD) and poly(1,6-bis(p-carboxyphenoxy)hexane) (p-CPH) were synthesized by melt-condensation polymerization. Poly-(anhydride-esters) that contain CPD hydrolytically degraded into salicylic acid, however, these homopolymers have mechanical and thermal characteristics that limit their use in clinical applications. The synthesis and characterization of copolymers of CPD with p-CPH, a monomer known to generate mechanically stable homopolymers, was investigated. By changing the CPD to p-CPH monomer ratios, the salicylic acid loading and thermal/mechanical properties of the copolymers was a controlling factor; increasing the CPD concentration increased the salicylate loading but decreased the polymer stability; whereas increasing the p-CPH concentration increased the thermal and mechanical stability of the copolymers. Specifically, decreasing the CPD:p-CPH ratio resulted in lower salicylate loading and increased thermal decomposition temperatures. The glass transition temperatures (°C) varied from 27 to 38°C, a desirable range for elastomeric biomedical implants.

Marine Origin Polysaccharides in Drug Delivery Systems

Oceans are a vast source of natural substances. In them, we find various compounds with wide biotechnological and biomedical applicabilities. The exploitation of the sea as a renewable source of biocompounds can have a positive impact on the development of new systems and devices for biomedical applications. Marine polysaccharides are among the most abundant materials in the seas, which contributes to a decrease of the extraction costs, besides their solubility behavior in aqueous solvents and extraction media, and their interaction with other biocompounds. Polysaccharides such as alginate, carrageenan and fucoidan can be extracted from algae, whereas chitosan and hyaluronan can be obtained from animal sources. Most marine polysaccharides have important biological properties such as biocompatibility, biodegradability, and anti-inflammatory activity, as well as adhesive and antimicrobial actions. Moreover, they can be modified in order to allow processing them into various shapes and sizes and may exhibit response dependence to external stimuli, such as pH and temperature. Due to these properties, these biomaterials have been studied as raw material for the construction of carrier devices for drugs, including particles, capsules and hydrogels. The devices are designed to achieve a controlled release of therapeutic agents in an attempt to fight against serious diseases, and to be used in advanced therapies, such as gene delivery or regenerative medicine.

A UV-sensitive hydrogel based combinatory drug delivery chip (UV gel-Drug Chip) for cancer cocktail drug screening

Photosensitive PEGDA hydrogel based platform for high dynamic range testing of combinatorial cocktail drug screening by using FSC method for colon cancer.

Polyanhydrides: Synthesis, Properties, and Applications

This review focusses on polyanhydrides, a fascinating class of degradable polymers that have been used in and investigated for many bio-related applications because of their degradability and capacity to undergo surface erosion. This latter phenomenon is driven by hydrolysis of the anhydride moieties at the surface and high hydrophobicity of the polymer such that degradation and mass loss (erosion) occur before water can penetrate deep within the bulk of the polymer. As such, when surface-eroding polymers are used as therapeutic delivery vehicles, the rate of delivery is often controlled by the rate of polymer erosion, providing predictable and controlled release rates that are often zero-order. These desirable attributes are heavily influenced by polymer composition and morphology, and therefore also monomer structure and polymerization method. This review examines approaches for polyanhydride synthesis, discusses their general thermomechanical properties, surveys their hydrolysis and degradation processes along with their biocompatibility, and looks at recent developments and uses of polyanhydrides in drug delivery, stimuli-responsive materials, and novel nanotechnologies.

Paclitaxel Release from Polyether-Anhydrides Prepared with UV-Curing Process

Polyanhydrides have been used as drug delivery systems to achieve a long-term delivery due to its hydrophobicity and surface erosion degradation behavior. In order to develop a simple, economical, and rapid approach to synthesize polyanhydrides, we prepared a series of polyether-anhydride membranes composed of different mass fractions of sebacic acid, polyethylene glycol dimethacrylate, and poly(tetramethylene oxide) dimethacrylate by ultraviolet curing process. The chemical structure and thermal properties of target polyanhydrides were characterized, while the paclitaxel releases from the polymer matrix were evaluated by HPLC. The results demonstrated that the UV-curing process is a good method to synthesize the target polymers in a short time, and the paclitaxel release procedure can be controlled by changing the component in the copolymers.

Photocrosslinkable polyesters and poly(ester anhydride)s for biomedical applications

Crosslinking is a feasible way to prepare biodegradable polymers with potential in biomedical applications such as controlled release of active agents and tissue engineering. A synthesis route in which functional telechelic aliphatic polyester oligomers are used as precursors for the preparation of crosslinked polyesters and poly(ester anhydride)s is described. Mechanical properties, degradation characteristics and rate, and bioactivity can be modified widely by controlling the chemical composition and architecture of the crosslinkable oligomers. In tissue engineering, photocrosslinking allows to use crosslinkable oligomers in advanced manufacturing techniques like micromolding in capillaries, stereolithography and two-photon polymerization.

Both the transplantation of somatic cell nuclear transfer- and fertilization-derived mouse embryonic stem cells with temperature-responsive chitosan hydrogel improve myocardial performance in infarcted rat hearts

The transplantation of embryonic stem cells could improve cardiac function but was limited by immune rejection as well as low cell retention and survival within the ischemic tissues. The somatic cell nuclear transfer (SCNT) is practical to generate autologous histocompatible stem (nuclear-transferred embryonic stem [NTES]) cells for diseases, but NTES may be arguably unsafe for therapeutic application. The temperature-responsive chitosan hydrogel is a suitable matrix in cell transplantation. As the scaffold, chitosan hydrogel was coinjected with NTES cells into the left ventricular wall of rat infarction models. Detailed histological analysis and echocardiography were performed to determine the structure and functional consequences of transplantation. The myocardial performance in SCNT- and fertilization-derived mouse ES cell transplantation with chitosan hydrogel was also compared. The results showed that both the 24-h cell retention and 4-week graft size were significantly greater in the NTES + chitosan group than that of NTES + phosphate-buffered saline (PBS) group (p < 0.01). The NTES cells might differentiate into cardiomyocytes in vivo. The heart function improved significantly in the chitosan + NTES group (fractional shortening: 28.7% +/- 2.8%) compared with that of PBS + NTES group (fractional shortening: 25.2% +/- 2.9%) at 4 weeks after transplantation (p < 0.01). In addition, the arteriole/venule densities within the infarcted area improved significantly in the chitosan + NTES group (280 +/- 17/mm(2)) compared with that of PBS + NTES group (234 +/- 16/mm(2)) at 4 weeks after transplantation (p < 0.01). There was no difference in the myocardial performance in SCNT- and fertilization-derived mouse ES cell transplantation with chitosan hydrogel. The NTES cells with chitosan hydrogel have been proved to possess therapeutic potential to improve the function of infarcted heart. Thus the method of in situ injectable tissue engineering is promising clinically.

Improved myocardial performance in infarcted rat heart by co-injection of basic fibroblast growth factor with temperature-responsive chitosan hydrogel

BACKGROUND

Basic fibroblast growth factor (bFGF) stimulates neoangiogenesis. The sustained release of bFGF by using biomaterials helped to enhance its angiogenic activity in vivo. In this study we investigated the effects of co-injection of bFGF with temperature-responsive chitosan hydrogel on myocardial performance in a rat model of infarction.

METHODS

Myocardial infarction was induced in rats using coronary artery ligation. Temperature-responsive chitosan hydrogel was prepared and injected intramyocardially into the left ventricular wall of rat infarction models alone or together with bFGF. Detailed histologic analysis and echocardiography were used to determine the structural and functional consequences 4 weeks after injection.

RESULTS

Heart function improved significantly in the chitosan+bFGF group compared with the phosphate-buffered saline (PBS)+bFGF group with regard to left ventricular ejection fraction (LVEF) and LV fractional shortening (LVFS) 4 weeks after transplantation (p < 0.05, n = 8 per group). In addition, arteriole densities within the infarcted area improved significantly (p < 0.01) in the chitosan+bFGF group (259 +/- 22/mm(2)) compared with the PBS+bFGF group (95 +/- 18/mm(2); n = 8 per group) at 4 weeks after transplantation. Infarct size and fibrotic area decreased significantly (p < 0.05) in the chitosan+bFGF group (39.64 +/- 1.75% and 25.09 +/- 3.31%, respectively) compared with the PBS+bFGF group (48.91 +/- 1.39% and 48.0 +/- 3.83%, respectively; n = 8 per group). No significant difference (p > 0.05) was noted between the PBS and PBS+bFGF groups.

CONCLUSIONS

Co-injection of bFGF with temperature-responsive chitosan hydrogels enhanced the effects of bFGF on arteriogenesis, ventricular remodeling and cardiac function. Our findings suggest a new approach to improve infarcted repairs in the prevention of adverse remodeling after myocardial infarction.

Development of delivery methods for carbohydrate-based drugs: controlled release of biologically-active short chain fatty acid-hexosamine analogs

Carbohydrates are attractive candidates for drug development because sugars are involved in many, if not most, complex human diseases including cancer, immune dysfunction, congenital disorders, and infectious diseases. Unfortunately, potential therapeutic benefits of sugar-based drugs are offset by poor pharmacologic properties that include rapid serum clearance, poor cellular uptake, and relatively high concentrations required for efficacy. To address these issues, pilot studies are reported here where 'Bu(4)ManNAc', a short chain fatty acid-monosaccharide hybrid molecule with anti-cancer activities, was encapsulated in polyethylene glycol-sebacic acid (PEG-SA) polymers. Sustained release of biologically active compound was achieved for over a week from drug-laden polymer formulated into microparticles thus offering a dramatic improvement over the twice daily administration currently used for in vivo studies. In a second strategy, a tributanoylated ManNAc analog (3,4,6-O-Bu(3)ManNAc) with anti-cancer activities was covalently linked to PEG-SA and formulated into nanoparticles suitable for drug delivery; once again release of biologically active compound was demonstrated.

Concurrent release of admixed antimicrobials and salicylic acid from salicylate-based poly(anhydride-esters)

A polymer blend consisting of antimicrobials (chlorhexidine, clindamycin, and minocycline) physically admixed at 10% by weight into a salicylic acid-based poly (anhydride-ester) (SA-based PAE) was developed as an adjunct treatment for periodontal disease. The SA-based PAE/antimicrobial blends were characterized by multiple methods, including contact angle measurements and differential scanning calorimetry. Static contact angle measurements showed no significant differences in hydrophobicity between the polymer and antimicrobial matrix surfaces. Notable decreases in the polymer glass transition temperature (T(g)) and the antimicrobials' melting points (T(m)) were observed indicating that the antimicrobials act as plasticizers within the polymer matrix. In vitro drug release of salicylic acid from the polymer matrix and for each physically admixed antimicrobial was concurrently monitored by high pressure liquid chromatography during the course of polymer degradation and erosion. Although the polymer/antimicrobial blends were immiscible, the initial 24 h of drug release correlated to the erosion profiles. The SA-based PAE/antimicrobial blends are being investigated as an improvement on current localized drug therapies used to treat periodontal disease.

Cytocompatibility studies of an in situ photopolymerized thermoresponsive hydrogel nanoparticle system using human aortic smooth muscle cells

We have been investigating thermoresponsive hydrogel nanoparticle composite networks to develop photopolymerized hydrogels to deliver drugs for prevention of restenosis after angioplasty. These composite systems can form a gel under physiological conditions and release drugs in response to temperature changes. Our novel system, consisting of poly(N-isopropylacrylamide) thermoresponsive nanoparticles, photo cross-linker poly(ethylene glycol) diacrylate, and UV photoinitiator, 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone-1-one (Irgacure 2959), would be photopolymerized in situ in the presence of UV light. The focus of this study was to evaluate the effects of photoinitiator and UV exposure on human aortic smooth muscle cells (HASMCs). We found that the exposure to UV light did not significantly affect the cellular survival within doses required for photopolymerization. The photoinitiator was cytocompatible at low concentrations (< or = 0.015% w/v); however, cytotoxicity increased with increasing photoinitiator concentrations. In addition, free radicals formed in the presence of a photoinitiator and UV light caused significant levels of cell death. An antioxidant (free radical scavenger), ascorbic acid, added to the cell media, significantly improved relative cell survival but increased the hydrogel gelation time. Finally, HASMC survival when exposed to all potential cytotoxic components was also evaluated by exposing HASMCs to media incubated with our composite hydrogels. In summary, our studies show that the photoinitiator and free radicals are responsible for the cytotoxicity on HASMCs, and the addition of antioxidants can significantly reduce these harmful effects.

Photoinitiated polymerization of PEG-diacrylate with lithium phenyl-2,4,6-trimethylbenzoylphosphinate: polymerization rate and cytocompatibility

Due to mild reaction conditions and temporal and spatial control over material formation, photopolymerization has become a valuable technique for the encapsulation of living cells in three dimensional, hydrated, biomimetic materials. For such applications, 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (I2959) is the most commonly used photoinitiator (by virtue of its moderate water solubility), yet this initiator has an absorption spectrum that is poorly matched with wavelengths of light generally regarded as benign to living cells, limiting the rate at which it may initiate polymerization in their presence. In contrast, acylphosphine oxide photoinitiators, generally exhibit absorption spectra at wavelengths suitable for cell encapsulation, yet commercially available initiators of this class have low water solubility. Here, a water soluble lithium acylphosphinate salt is evaluated for its ability to polymerize diacrylated poly(ethylene glycol) (PEGDA) monomers rapidly into hydrogels, while maintaining high viability during direct encapsulation of cells. Through rheometric measurements, the time to reach gelation of a PEGDA solution with the phosphinate initiator is one tenth the time for that using I2959 at similar concentrations, when exposed to 365 nm light. Further, polymerization with the phosphinate initiator at 405 nm visible light exposure is achieved with low initiator concentrations and light intensities, precluded in polymerizations initiated with I2959 by its absorbance profile. When examined 24h after encapsulation, survival rates of human neonatal fibroblasts encapsulated in hydrogels polymerized with the phosphinate initiator exceed 95%, demonstrating the cytocompatibility of this initiating system.

Functional improvement of infarcted heart by co-injection of embryonic stem cells with temperature-responsive chitosan hydrogel

Transplantation of embryonic stem cells (ESCs) can improve cardiac function in treatment of myocardial infarction. The low rate of cell retention and survival within the ischemic tissues makes the application of cell transplantation techniques difficult. In this study, we used a temperature-responsive chitosan hydrogel (as scaffold) combined with ESCs to maintain viable cells in the infarcted tissue. Temperature-responsive chitosan hydrogel was prepared and injected into the infarcted heart wall of rat infarction models alone or together with mouse ESCs. The result showed that the 24-h cell retention and 4 week graft size of both groups was significantly greater than with a phosphate buffered saline control. After 4 weeks of implantation, heart function, wall thickness, and microvessel densities within the infarct area improved in the chitosan + ESC, chitosan, and ESC group more than the PBS control. Of the three groups, the chitosan + ESC performed best. Results of this study indicate that temperature-responsive chitosan hydrogel is an injectable scaffold that can be used to deliver stem cells to infarcted myocardium. It can also increase cell retention and graft size. Cardiac function is well preserved, too.

Poly(ethylene glycol) hydrogels formed by thiol-ene photopolymerization for enzyme-responsive protein delivery

Degradable hydrogels have been extensively used in biomedical applications such as drug delivery, and recent interest has grown in hydrogels that degrade in recognition of a cellular response. This contribution describes a poly(ethylene glycol) (PEG) hydrogel platform with human neutrophil elastase (HNE) sensitive peptide cross-links formed using thiol-ene photopolymerization rendering the gel degradable at sites of inflammation. Further, protein therapeutics can be physically entrapped within the network and selectively released upon exposure to HNE. HNE-responsive hydrogels exhibited surface erosion where the degradation kinetics was influenced by changes in peptide k(cat), concentration of HNE, and concentration of peptide within the gel. Using this platform, we were able to achieve controlled, zero-order release of bovine serum albumin (BSA) in the presence of HNE, and release was arrested in the absence of HNE. To further exploit the advantages of surface eroding delivery systems, a smaller protein (carbonic anhydrase) was delivered at the same rate as BSA and only dependent on gel formulation and environmental conditions. Also, protein release was predicted from a 3-layered hydrogel device using mass loss data. Lastly, the bioactivity of lysozyme was maintained above 90% following the exposure to thiol-ene photopolymerization conditions.

Comparison of salicylate-based poly(anhydride-esters) formed via melt-condensation versus solution polymerization

Salicylate-based poly(anhydride-esters) were synthesized via two different methods, melt-condensation and solution polymerization, and the resulting polymers were compared. Acetylsalicylic acid was used as a model compound to mimic the active polymer chain-ends during melt-condensation, and formed a low-molecular-weight (<1500) polymer when subjected to melt-condensation polymerization conditions. The polymers and model compounds were analyzed by NMR ((1)H and (13)C) and IR spectroscopies to elucidate the structures. Spectroscopic analysis revealed the formation of a thermodynamically stable salicylate ester via salicylate-anhydride rearrangement during melt-condensation polymerization, which did not occur during solution polymerization. The salicylate-based poly(anhydride-esters) undergo a thermodynamic rearrangement during melt-condensation polymerization that is not observed for solution polymerization.

Tuning stability of mesoporous silica films under biologically relevant conditions through processing with supercritical CO2

Mesoporous materials have been proposed for use in numerous biological environments such as substrates for cell culture and controlled release for drug delivery. Although mesoporous silica synthesis is facile, recent reports (Dunphy et al. Langmuir 2003, 19, 10403; Bass et al. Chem. Mater. 2007, 19, 4349) have demonstrated instability (dissolution) of pure mesoporous silica films under biologically relevant conditions. In this work, we demonstrate a simple processing handle (pressure) to control the dissolution of mesoporous silica films that are synthesized using preformed template films and supercritical CO 2. Spectroscopic ellipsometry is utilized to quantify changes in both the film thickness and porosity; these properties provide insight into the dissolution mechanism. The pore size increases as the films are exposed to phosphate-buffered saline (PBS) through preferential dissolution at the pore wall in comparison to the film surface; a mechanism reminiscent of bulk erosion of scaffolds for drug delivery. Thin mesoporous silica film lifetimes can be extended from several hours using traditional sol-gel approaches to days by using CO 2 processing for identical film thickness. Osteoblast attachment and viability on these films was found to correlate with their increased stability. This enhanced stability opens new possibilities for the utilization of mesoporous silica for biological applications, including drug delivery and tissue engineering.

Modifying network chemistry in thiol-acrylate photopolymers through postpolymerization functionalization to control cell-material interactions

Thiol-acrylate photopolymers often contain pendant, unreacted thiol groups even following complete reaction of the acrylate functional groups. The results presented herein demonstrate a high throughput method for quantifying pendant thiol group concentrations using FTIR spectra of thiol-acrylate microspot arrays. Using this technique, more than 25% of the original thiol groups were detected as pendant groups in microspots made from monomer solutions containing at least 40 mol % thiol functional groups. Subsequent modification reactions allowed postpolymerization tailoring of the network chemistry. The extent of modification was controlled by the concentration of the pendant thiols (ranging from 0.01 to 0.4M) and the duration of the modification reaction (0-10 min for photocoupling reactions, 0-24 h for Michael-type addition reactions). Further, when photocoupling was used to modify the networks, spatial and temporal control of the light exposure facilitated the formation of chemical patterns on the surface and throughout the material.

Treatment of osteomyelitis in rats by injection of degradable polymer releasing gentamicin

We evaluated the potential of an injectable degradable polymer-poly(sebacic-co-ricinoleic-ester-anhydride) containing gentamicin for the treatment of osteomyelitis. Osteomyelitis of both tibiae was induced in 13 female Fischer rats by injecting a suspension containing approximately 105 (CFU)/ml of S. aureus into the tibial medullar canal. Three weeks later both tibiae were X-rayed, drilled down the medullar canal, washed with 50 microl gentamicin solution (80 mg/2 ml) and then injected with 50 microl P(SA-RA)+gentamycin 20% w/v to the right tibia and 50 microl P(SA-RA) without gentamicin to the left tibia. After an additional 3 weeks, the rats were sacrificed, and radiographs of the tibiae were taken. Histopathological evaluation of the tibiae was done in a blinded manner. X-ray radiographs showed that all tibiae developed changes compatible with osteomyelitis in 3 weeks. Histological evaluation revealed significant differences between right and left tibiae in 10 rats. In the left tibia moderate intramedullary abscess formation occurred. In most treated tibiae typical changes included the absence (or minimal grade only) of abscesses. The treated group developed significantly less intramedullary abscesses; the p value was 0.028. Locally injected degradable polymer releasing gentamicin proved to be efficient histologically in the treatment of osteomyelitis.

Characterization and in vitro degradation of poly(octadecanoic anhydride)

Poly(octadecanoic anhydride) (POA) has been prepared by melt polycondensation of octadecanoic diacid. POA was characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The results of in vitro degradation and SEM micrographs show that the erosion process of POA is neither bulk nor perfect surface erosion but rather has elements of both in phosphate buffer at 37 degrees C. The moving erosion front is characteristic of surface erosion whereas the remaining porous shell stems from bulk erosion. While a significant special degradation property of POA is that POA presents a very slow degradation rate in acidic condition (pH 5.98), only 1.64% weight loss for 20 days, and it completely degrades after 18 days in basic buffer (pH 7.4). Comparing with poly(sebacic anhydride) (PSA), POA has the higher crystallization degree, and the slower hydrolytic rate.

In Vitro Hydrolytic Degradation of Hydroxyl-Functionalized Poly(α-hydroxy acid)s

The in vitro hydrolytic degradation of hydroxyl-functionalized poly(alpha-hydroxy acid)s was investigated. Benzyl-ether-protected hydroxyl-functionalized dilactones (S)-3-benzyloxymethyl-(S)-6-methyl-1,4-dioxane-2,5-dione (1a) and (S)-3-benzyloxymethyl-1,4-dioxane-2,5-dione (1b) were copolymerized in a melt with various amounts of L-lactide using benzyl alcohol and SnOct2 as the initiator and catalyst, respectively. The benzyl groups were removed by hydrogenation to yield polyesters with hydroxyl functional groups, poly(lactic acid-co-hydroxymethyl glycolic acid) and poly(lactic acid-co-glycolic acid-co-hydroxymethyl glycolic acid) (2a and 2b). Degradation of the hydroxyl-functionalized polyesters and poly(lactic-co-glycolic acid) (50/50) was studied by incubation of pellets of these polymers in phosphate buffer (174 mM, pH 7.4) at 37 degrees C. Polymer degradation was monitored by mass-loss measurements and by gel permeation chromatography, differential scanning calorimetry, and 1H NMR analysis. The degradation times ranging from less than 1 day (for the homopolymer of 2a) to 2 months (copolymer of 25% 2a and 75% lactide) were found. The degradation rates increased with increasing hydroxyl density of the polymers, which was associated with a switch from bulk to surface erosion. NMR and thermal analysis showed that the moieties with the hydroxyl groups were preferentially removed from the degrading polymer. In conclusion, this study shows that the degradation rate of polyesters containing 2a and 2b can be tailored from a few days to 2 months, making them very suitable for biomedical and pharmaceutical applications.

Effects of neighboring sulfides and pH on ester hydrolysis in thiol-acrylate photopolymers

Networks synthesized through thiol-acrylate photopolymerization or Michael-type addition step growth reactions contain esters with neighboring sulfide groups. Previous work has demonstrated that these esters are readily hydrolyzable at physiological pH. Here, the influence of the distance between the sulfide and ester, as well as the water concentration, on ester hydrolysis was characterized. These preliminary results indicate that reducing the number of carbons between the sulfide and the ester from 2 to 1 increased the rate of ester hydrolysis from 0.022+/-0.001 to 0.08+/-0.015days(-1). Increases in ester hydrolysis rates were also observed as hydrophilicity increased for oligomers prepared from a trithiol, tetrathiol and dithiol monomer (0.012+/-0.003, 0.032+/-0.004, and 0.091+/-0.003days(-1), respectively). Additionally, in bulk-eroding polymeric biomaterials, variations in pH impacted the ester hydrolysis rate. This work confirms that small variations in buffer pH predictably alter the mass loss profile of a thiol-acrylate photopolymer. More specifically, as buffer pH was changed from 7.4 to 8.0, the rate of ester hydrolysis increased from 0.074+/-0.003 to 0.28+/-0.005days(-1). The magnitude of this observed change in ester hydrolysis rate was correlated to the increase in hydroxide ion concentration that accompanied this pH change.

Characterizing multilaminated hydrogels with spatially varying network structure and solute loading using confocal laser scanning microscopy

Multilaminated controlled release devices were formed through photopolymerization techniques to produce hydrogels with spatially varying solute loadings and network structures composed of poly(hydroxyl ethyl methacrylate) (PHEMA) and poly(ethylene glycol) (PEG). Using low molecular weight fluorescent dyes as model drugs, the distribution profiles were characterized non-invasively in pseudo-real-time with confocal laser scanning microscopy (CLSM) during release studies. For comparison, theoretical modeling based on Fickian diffusion theory was performed in conjunction with experimental work to identify any deviations from expected behavior and to guide in the development of future devices. In multilaminates composed of only PHEMA, the evolution of dye distribution during release and cumulative release profiles agreed well with theoretically predicted data, indicating continuity of diffusion and insignificant interfacial hindrance between layers. However, in devices composed of alternating layers of PHEMA and PEG, differences from predicted behavior were experimentally observed in both concentration profiles and release rates, suggesting interfacial obstruction of diffusion, possibly due to the formation of interpenetrating networks. Finally, the simultaneous release of two dyes at different rates from a PEG/PHEMA multilaminate was monitored to demonstrate the usefulness of CLSM in understanding the complex temporal changes in solute distributions in gel devices.

Development and Characterization of Degradable Thiol-Allyl Ether Photopolymers

Degradable thiol-ene photopolymer networks were formed through radically mediated step growth reactions. Variations in the network structure were used to alter the initial and temporal moduli, mass loss profiles, and equilibrium swelling ratios. Mass loss rates varied with changes in the solvent concentration, monomer molecular weight, average monomer functionality, and concentration of degradable linkages. The time required for the networks to degrade completely ranged from 1.20 ± 0.01 to 24.5 ± 0.1 days, which corresponded to hydrolysis rates of 0.18 ± 0.01 and 0.021 ± 0.0003 days(-1). Initial moduli also varied considerably as a function of network structure, ranging from 150 ± 35 to nearly 5000 ± 100 kPa, and initial equilibrium swelling ratios ranged from 2.5 ± 0.01 to 18.7 ± 2. Collectively, these results demonstrate how the material properties and the mass loss behavior of thiol-ene networks can be independently tuned for specific applications.

Synthesis and Erosion Properties of PEG-Containing Polyanhydrides

To tailor the erosion rate of polyanhydrides while retaining their surface erosion characteristics, new three-component polyanhydrides of sebacic acid, 1,3-bis(p-carboxyphenoxy)propane and poly(ethylene glycol) were synthesized. The hydrophilicity of the polymer increased and its mechanical strength decreased with increasing PEG content. Correspondingly, the erosion rate increases with increasing PEG content, whereas it decreases with increasing specimen thickness. This indicates that the incorporation of poly(ethylene glycol) into traditional two-component polyanhydrides retains their surface erosion properties while making the erosion rate tunable. The new polyanhydrides hold potential for drug delivery applications.