An in situ forming biodegradable hydrogel-based embolic agent for interventional therapies

We present here the characteristics of an in situ forming hydrogel prepared from carboxymethyl chitosan and oxidized carboxymethyl cellulose for interventional therapies. Gelation, owing to the formation of Schiff bases, occurred both with and without the presence of a radiographic contrast agent. The hydrogel exhibited a highly porous internal structure (pore diameter 17 ± 4 μm), no cytotoxicity to human umbilical vein endothelial cells, hemocompatibility with human blood, and degradability in lysozyme solutions. Drug release from hydrogels loaded with a sclerosant, tetracycline, was measured at pH 7.4, 6 and 2 at 37 °C. The results showed that tetracycline was more stable under acidic conditions, with a lower release rate observed at pH 6. An anticancer drug, doxorubicin, was loaded into the hydrogel and a cumulative release of 30% was observed over 78 h in phosphate-buffered saline at 37 °C. Injection of the hydrogel precursor through a 5-F catheter into a fusiform aneurysm model was feasible, leading to complete filling of the aneurysmal sac, which was visualized by fluoroscopy. The levels of occlusion by hydrogel precursors (1.8% and 2.1%) and calibrated microspheres (100–300 μm) in a rabbit renal model were compared. Embolization with hydrogel precursors was performed without clogging and the hydrogel achieved effective occlusion in more distal arteries than calibrated microspheres. In conclusion, this hydrogel possesses promising characteristics potentially beneficial for a wide range of vascular intervention procedures that involve embolization and drug delivery.     

Poly(l-glutamic acid)/chitosan polyelectrolyte complex porous microspheres as cell microcarriers for cartilage regeneration

In this study a novel kind of porous poly(l-glutamic acid) (PLGA)/chitosan polyelectrolyte complex (PEC) microsphere was developed through electrostatic interaction between PLGA and chitosan. By adjusting the formula parameters chitosan microspheres with an average pore size of 47.5 ± 5.4 μm were first developed at a concentration of 2 wt.% and freeze temperature of −20 °C. For self-assembly of the PEC microspheres porous chitosan microspheres were then incubated in PLGA solution at 37 °C. Due to electrostatic interaction a large amount of PLGA (110.3 μg mg⁻¹) was homogeneously absorbed within the chitosan microspheres. The developed PEC microspheres retained their original size, pore diameters and interconnected porous structure. Fourier transform infrared spectroscopy, thermal gravimetric analysis and zeta potential analysis revealed that the PEC microspheres were successfully prepared through electrostatic interaction. Compared with microspheres fabricated from chitosan, the porous PEC microspheres were shown to efficiently promote chondrocyte attachment and proliferation. After injection subcutaneously for 8 weeks PEC microspheres loaded with chondrocytes were found to produce significant more cartilaginous matrix than chitosan microspheres. These results indicate that these novel fabricated porous PLGA/chitosan PEC microspheres could be used as injectable cell carriers for cartilage tissue engineering.     

Low density biodegradable shape memory polyurethane foams for embolic biomedical applications

Low density shape memory polymer foams hold significant interest in the biomaterials community for their potential use in minimally invasive embolic biomedical applications. The unique shape memory behavior of these foams allows them to be compressed to a miniaturized form, which can be delivered to an anatomical site via a transcatheter process and thereafter actuated to embolize the desired area. Previous work in this field has described the use of a highly covalently crosslinked polymer structure for maintaining excellent mechanical and shape memory properties at the application-specific ultralow densities. This work is aimed at further expanding the utility of these biomaterials, as implantable low density shape memory polymer foams, by introducing controlled biodegradability. A highly covalently crosslinked network structure was maintained by use of low molecular weight, symmetrical and polyfunctional hydroxyl monomers such as polycaprolactone triol (PCL-t, Mn = 900 g), N,N,N0,N0-tetrakis(hydroxypropyl)ethylenediamine and tris(2-hydroxyethyl)amine. Control over the degradation rate of the materials was achieved by changing the concentration of the degradable PCL-t monomer and by varying the material hydrophobicity. These porous SMP materials exhibit a uniform cell morphology and excellent shape recovery, along with controllable actuation temperature and degradation rate. We believe that they form a new class of low density biodegradable SMP scaffolds that can potentially be used as “smart” non-permanent implants in multiple minimally invasive biomedical applications.     

Poly(ethylene glycol) methacrylate hydrolyzable microspheres for transient vascular embolization

Poly(ethylene glycol) methacrylate (PEGMA) hydrolyzable microspheres intended for biomedical applications were readily prepared from poly(lactide-co-glycolide) (PLGA)–poly(ethylene glycol) (PEG)–PLGA crosslinker and PEGMA as a monomer using a suspension polymerization process. Additional co-monomers, methacrylic acid and 2-methylene-1,3-dioxepane (MDO), were incorporated into the initial formulation to improve the properties of the microspheres. All synthesized microspheres were spherical in shape, calibrated in the 300–500 μm range, swelled in phosphate-buffered saline (PBS) and easily injectable through a microcatheter. Hydrolytic degradation experiments performed in PBS at 37 °C showed that all of the formulations tested were totally degraded in less than 2 days. The resulting degradation products were a mixture of low-molecular-weight compounds (PEG, lactic and glycolic acids) and water-soluble polymethacrylate chains having molecular weights below the threshold for renal filtration of 50 kg mol⁻¹ for the microspheres containing MDO. Both the microspheres and the degradation products were determined to exhibit minimal cytotoxicity against L929 fibroblasts. Additionally, in vivo implantation in a subcutaneous rabbit model supported the in vitro results of a rapid degradation rate of microspheres and provided only a mild and transient inflammatory reaction comparable to that of the control group.     

Mechanical properties and dual drug delivery application of poly(lactic-co-glycolic acid) scaffolds fabricated with a poly(β-amino ester) porogen

Polymeric scaffolds that are biocompatible and biodegradable are widely used for tissue engineering applications. Scaffolds can be further enhanced by enabling the release of one or more drugs to stimulate regeneration or for the treatment of a specific disease or condition. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres were mixed with poly(β-amino ester) (PBAE) particles to create novel hybrid scaffolds capable of dual release of drug and growth factor. Fast-degrading PBAE particles loaded with the drug ketoprofen acted as porogens that provided a rapid 12 h release. The PLGA microspheres were loaded with a growth factor, bone morphogenetic protein 2, and fused together around the porogens to create a slow-degrading matrix that provided sustained release lasting 70 days. Drug release was further tailored by varying the amount of porogen added to the scaffold. Bioactivity measurements demonstrated that the scaffold fabrication technique did not damage the drug or protein. The compressive modulus was affected by the amount of porogen added, extending from 50 to 111 MPa for loadings from 60 to 40% PBAE, and after 5 days of degradation, it decreased to 0.6 to 1.1 kPa when the porogen was gone. PLGA containing a quick-degrading porogen can be used to release two drugs while developing a porous microarchitecture for cell ingrowth with in a matrix capable of maintaining a compressive modulus applicable for soft tissue implants.     

A novel carboxymethyl chitosan–quantum dot-based intracellular probe for Zn2+ ion sensing in prostate cancer cells

In this paper, we fabricated novel carboxymethyl chitosan-coated CdTe quantum dots (CMC–CdTe QDs) via the electrostatic interaction between amino groups in the carboxymethyl chitosan polymeric chains and carboxyl groups of the CdTe QDs. Carboxymethyl chitosan on the surface of CdTe QDs had strong binding ability with Zn²⁺, resulting in the obvious enhancement of the photoluminescence of CdTe QDs. The photoluminescence intensity of CMC–CdTe QDs probe was proportional to the concentration of Zn²⁺ in the range of 5.0 × 10⁻⁶ to 5.0 × 10⁻³ mol l⁻¹. The detection limit for Zn²⁺ was 4.5 × 10⁻⁶ mol l⁻¹. The experimental results indicate that the CMC–CdTe QDs possess favorable cell compatibility, good sensitivity and selectivity for intracellular Zn²⁺ sensing, and are promising candidates for cellular imaging and sensing in prostate cancer cells. The present study also provides an approach for the further development of nanoprobes dedicated to intracellular sensing.     

The in vivo performance of CaP/PLGA composites with varied PLGA microsphere sizes and inorganic compositions

Enrichment of calcium phosphate (CaP) bone substitutes with poly(lactic-co-glycolic acid) (PLGA) microspheres to create porosity overcomes the problem of poor CaP degradation. The degradation of CaP–PLGA composites can be customized by changing the physical and chemical properties of PLGA and/or CaP. However, the effect of the size of dense (solid rather than hollow) PLGA microspheres in CaP has not previously been described. The present study aimed at determining the effect of different dense (i.e. solid) PLGA microsphere sizes (small (S) ～20 μm vs. large (L) ～130 μm) and of CaP composition (CaP with either anhydrous dicalcium phosphate (DCP) or calcium sulphate dihydrate (CSD)) on CaP scaffold biodegradability and subsequent bone in-growth. To this end mandibular defects in minipigs were filled with pre-set CaP–PLGA implants, with autologous bone being used as a control. After 4 weeks the autologous bone group outperformed all CaP–PLGA groups in terms of the amount of bone present at the defect site. On the other hand, at 12 weeks substantial bone formation was observed for all CaP–PLGA groups (ranging from 47 ± 25% to 62 ± 15%), showing equal amounts of bone compared with the autologous bone group (82 ± 9%), except for CaP with DCP and large PLGA microspheres (47 ± 25%). It was concluded that in the current study design the difference in PLGA microsphere size and CaP composition led to similar results with respect to scaffold degradation and subsequent bone in-growth. Further, after 12 weeks all CaP–PLGA composites proved to be effective for bone substitution.     

A multilayered scaffold of a chitosan and gelatin hydrogel supported by a PCL core for cardiac tissue engineering

A three-dimensional scaffold composed of self-assembled polycaprolactone (PCL) sandwiched in a gelatin–chitosan hydrogel was developed for use as a biodegradable patch with a potential for surgical reconstruction of congenital heart defects. The PCL core provides surgical handling, suturability and high initial tensile strength, while the gelatin–chitosan scaffold allows for cell attachment, with pore size and mechanical properties conducive to cardiomyocyte migration and function. The ultimate tensile stress of the PCL core, made from blends of 10, 46 and 80 kDa (Mn) PCL, was controllable in the range of 2–4 MPa, with lower average molecular weight PCL blends correlating with lower tensile stress. Blends with lower molecular weight PCL also had faster degradation (controllable from 0% to 7% weight loss in saline over 30 days) and larger pores. PCL scaffolds supporting a gelatin–chitosan emulsion gel showed no significant alteration in tensile stress, strain or tensile modulus. However, the compressive modulus of the composite tissue was similar to that of native tissue (～15 kPa for 50% gelatin and 50% chitosan). Electron microscopy revealed that the gelatin–chitosan gel had a three-dimensional porous structure, with a mean pore diameter of ～80 μm, showed migration of neonatal rat ventricular myocytes (NRVM), maintained NRVM viability for over 7 days, and resulted in spontaneously beating scaffolds. This multi-layered scaffold has sufficient tensile strength and surgical handling for use as a cardiac patch, while allowing migration or pre-loading of cardiac cells in a biomimetic environment to allow for eventual degradation of the patch and incorporation into native tissue.     

Heparin crosslinked chitosan microspheres for the delivery of neural stem cells and growth factors for central nervous system repair

An effective paradigm for transplanting large numbers of neural stem cells after central nervous system (CNS) injury has yet to be established. Biomaterial scaffolds have shown promise in cell transplantation and in regenerative medicine, but improved scaffolds are needed. In this study we designed and optimized multifunctional and biocompatible chitosan-based films and microspheres for the delivery of neural stem cells and growth factors for CNS injuries. The chitosan microspheres were fabricated by coaxial airflow techniques, with the sphere size controlled by varying the syringe needle gauge and the airflow rate. When applying a coaxial airflow at 30 standard cubic feet per hour, ～300 μm diameter spheres were reproducibly generated that were physically stable yet susceptible to enzymatic degradation. Heparin was covalently crosslinked to the chitosan scaffolds using genipin, which bound fibroblast growth factor-2 (FGF-2) with high affinity while retaining its biological activity. At 1 μg ml^?1 approximately 80% of the FGF-2 bound to the scaffold. A neural stem cell line, GFP + RG3.6 derived from embryonic rat cortex, was used to evaluate cytocompatibility, attachment and survival on the crosslinked chitosan–heparin complex surfaces. The MTT assay and microscopic analysis revealed that the scaffold containing tethered FGF-2 was superior in sustaining survival and growth of neural stem cells compared to standard culture conditions. Altogether, our results demonstrate that this multifunctional scaffold possesses good cytocompatibility and can be used as a growth factor delivery vehicle while supporting neural stem cell attachment and survival.     

Bacterial-binding chitosan microspheres for gastric infection treatment and prevention

Helicobacter pylori (H. pylori) colonizes the gastric mucosa of over 50% of the world population, causing several pathologies, such as gastric ulcers and gastric cancer. Since current antibiotic treatments are inefficient in 20% of cases alternative therapies are needed. This work reports the ability of chitosan microspheres to adhere to H. pylori and prevent/remove H. pylori colonization. Adhesion of H. pylori strains with different functional adhesins (BabA and/or SabA) to chitosan microspheres (diameter 167 ± 27 μm) occurs at both pH 2.6 and 6.0, but is higher at pH 6.0. Bacterial adhesion to a gastric cell line expressing sialylated carbohydrates (SabA receptors) was performed at the same pH values using H. pylori strains with and without SabA. At both pH values addition of microspheres to gastric cells before and after pre-incubation with H. pylori decreased bacterial adhesion to cells. Furthermore, the chitosan microspheres were non-cytotoxic. These findings reveal the potential of chitosan microspheres as an alternative or complementary treatment for H. pylori gastric eradication or prevention of H. pylori colonization.     

Hollow hydroxyapatite microspheres: A novel bioactive and osteoconductive carrier for controlled release of bone morphogenetic protein-2 in bone regeneration

The regeneration of large bone defects is a common and significant clinical problem. Limitations associated with existing treatments such as autologous bone grafts and allografts have increased the need for synthetic bone graft substitutes. The objective of this study was to evaluate the capacity of novel hollow hydroxyapatite (HA) microspheres to serve as a carrier for controlled release of bone morphogenetic-2 (BMP2) in bone regeneration. Hollow HA microspheres (106–150 μm) with a high surface area (>100 m² g^?1) and a mesoporous shell wall (pore size 10–20 nm) were created using a glass conversion technique. The release of BMP2 from the microspheres into a medium composed of diluted fetal bovine serum in vitro was slow, but it occurred continuously for over 2 weeks. When implanted in rat calvarial defects for 3 or 6 weeks, the microspheres loaded with BMP2 (1 μg per defect) showed a significantly better capacity to regenerate bone than those without BMP2. The amount of new bone in the defects implanted with the BMP2-loaded microspheres was 40% and 43%, respectively, at 3 and 6 weeks, compared to 13% and 17%, respectively, for the microspheres without BMP2. Coating the BMP2-loaded microspheres with a biodegradable polymer, poly(lactic-co-glycolic acid), reduced the amount of BMP2 released in vitro and, above a certain coating thickness, significantly reduced bone regeneration in vivo. The results indicate that these hollow HA microspheres could provide a bioactive and osteoconductive carrier for growth factors in bone regeneration.     

Photocrosslinkable biodegradable elastomers based on cinnamate-functionalized polyesters

Synthetic biodegradable elastomers are an emerging class of materials that play a critical role in supporting innovations in bioabsorbable medical implants. This paper describes the synthesis and characterization of poly(glycerol-co-sebacate)-cinnamate (PGS-CinA), a biodegradable elastomer based on hyperbranched polyesters derivatized with pendant cinnamate groups. PGS-CinA can be prepared via photodimerization in the absence of photoinitiators using monomers that are found in common foods. The resulting network exhibits a Young’s modulus of 50.5–152.1 kPa and a projected in vitro degradation half-life time between 90 and 140 days. PGS-CinA elastomers are intrinsically cell-adherent and support rapid proliferation of fibroblasts. Spreading and proliferation of fibroblasts are loosely governed by the substrate stiffness within the range of Young’s moduli in PGS-CinA networks that were prepared. The thermo-mechanical properties, biodegradability and intrinsic support of cell attachment and proliferation suggest that PGS-CinA networks are broadly applicable for use in next generation bioabsorable materials including temporary medical devices and scaffolds for soft tissue engineering.     

Synthesis,characterization and cytotoxicity of photo-crosslinked maleic chitosan–polyethylene glycol diacrylate hybrid hydrogels

Synthetic hydrogels are important biomaterials for many biomedical applications and hydrogels produced via photo-gelation have shown particular promise. In this paper, we describe a new family of biodegradable hybrid hydrogels fabricated in aqueous solution via long wavelength UV photo-crosslinking using maleic chitosan and polyethylene glycol diacrylate (PEGDA) as precursors. The maleic chitosan precursor was prepared by a simple one-step chemical modification of chitosan, with high yields, and characterized by Fourier transform infrared spectroscopy, ¹H NMR and ¹³C NMR. Maleic chitosan and PEGDA precursors at a wide range of weight feed ratios were mixed in aqueous solution and directly photo-crosslinked for 10 min under a long wavelength UV light (365 nm) using 4-(2-hydroxyethoxy) phenyl-(2-hydroxy-2-propyl) ketone (Irgacure 2959) as photoinitiator. It was observed that as the weight feed ratio of maleic chitosan to PEGDA decreased the pore sizes of the hydrogel samples decreased, thereby increasing the densities of the hydrogel networks and producing a lower swelling ratio and a higher compressive modulus. The molecular weight of PEGDA had a similar effect. Preliminary cell cytotoxicity tests of both the maleic chitosan precursor and maleic chitosan/PEGDA hydrogels, based on the MTT assay and live–dead assay, respectively, showed that these new chitosan-based biodegradable biomaterials were relatively non-toxic to bovine aortic endothelial cells at low dosages.     

Branched chitosans II: Effects of branching on degradation,protein adsorption and cell growth properties

The demand for biodegradable implant materials has fueled interest in chitosan as a biomaterial. In previous work, branched chitosans were synthesized and structurally characterized. In this study the biological properties of branched chitosans were explored. Branched chitosans were synthesized by grafting low molecular weight chitosan chains (1.6, 16 and 80 kDa) to high molecular weight (600 kDa) linear chitosans via reductive amination. Films of the branched materials were evaluated with regard to: lysozyme-mediated degradation; protein adsorption; cell adhesion and proliferation. Branched chitosan with a 1.6 kDa branch length exhibited higher degradation rates than either linear or higher branch length materials. Branched chitosans also exhibited reduced adsorption of bovine serum albumin that was more pronounced with thicker films. Branched chitosans supported proliferation of rat endothelial cells, but growth rates were significantly lower than on linear chitosan. The results of this study demonstrate that control of many aspects of chitosan’s physical and biological properties can be achieved by changes in molecular architecture.     

A study of a biodegradable Mg–3Sc–3Y alloy and the effect of self-passivation on the in vitro degradation

Magnesium and its alloys have been investigated for their potential application as biodegradable implant materials. Although properties of magnesium such as biocompatibility and susceptibility to dissolution are desirable for biodegradable implant applications, its high degradation rate and low strength pose a significant challenge. A potential way to reduce the initial degradation rate is to form a self-passivating protective layer on the surface of the alloy. Oxides with a low enthalpy of formation result in a strong thermodynamic driving force to produce oxide surfaces that are more stable than the native oxide (MgO), and possibly reduce the initial degradation rate in these alloys. In the present study a ternary Mg–3 wt.% Sc–3 wt.% Y alloy was investigated and its oxidation behavior studied. The effect of surface passivation on the in vitro degradation rate was studied and the degradation products identified. The results show that the oxide provided an initial degradation barrier and 24 h oxidation resulted in a negligible degradation rate for up to 23 days. Furthermore, the degradation products of the alloy showed no significant toxicity to osteoblastic cells, and cell proliferation studies confirmed cell attachment and proliferation on the surface of the oxidized alloy.     

Dual pH- and temperature-responsive microparticles for protein delivery to ischemic tissues

Injectable “smart” microspheres that are sensitive to both temperature and pH have been fabricated and tested for controlled delivery of therapeutic proteins to ischemic skeletal muscle. A library of copolymers composed of N-isopropyl acrylamide (NIPAAm), propyl acrylic acid (PAA), and butyl acrylate (BA) was used to fabricate microspheres using a double emulsion method, and an optimal formulation made from copolymers composed of 57 mol.% NIPAAm, 18 mol.% PAA and 25 mol.% BA copolymers was identified. At 37 °C and pH representative of ischemic muscle (i.e. pH 5.2–7.2), these microspheres produced sustained, diffusion-controlled release, and at normal, physiological pH (i.e. pH 7.4), they underwent dissolution and rapid clearance. Delivery of fibroblast growth factor 2 was used to confirm that protein bioactivity was retained following microsphere encapsulation/release based on a dose-dependent increase in NIH3T3 fibroblast proliferation in vitro. Microsphere-loaded or free Cy5.5-labeled albumin was injected into ischemic and control gastrocnemii of mice following unilateral induction of hind limb ischemia to model peripheral arterial disease. In the ischemic limb at days 3.5 and 7, there was higher local retention of the protein delivered via microspheres relative to injected free protein (p < 0.05). However, clearance of protein delivered via microspheres was equivalent to free protein at later time points that correspond to ischemic recovery in this model. Finally, histological analysis of the gastrocnemius revealed that the polymeric microspheres did not produce any microscopic signs of toxicity near the injection site. These combined results suggest that the pH- and temperature-responsive microspheres presented herein are a promising technological platform for controlled protein delivery to ischemic tissue.     

Single-step electrochemical deposition of antimicrobial orthopaedic coatings based on a bioactive glass/chitosan/nano-silver composite system

Composite orthopaedic coatings with antibacterial capability containing chitosan, Bioglass® particles (9.8 μm) and silver nanoparticles (Ag-np) were fabricated using a single-step electrophoretic deposition (EPD) technique, and their structural and preliminary in vitro bactericidal and cellular properties were investigated. Stainless steel 316 was used as a standard metallic orthopaedic substrate. The coatings were compared with EPD coatings of chitosan and chitosan/Bioglass®. The ability of chitosan as both a complexing and stabilizing agent was utilized to form uniformly deposited Ag-np. Due to the presence of Bioglass® particles, the coatings were bioactive in terms of forming carbonated hydroxyapatite in simulated body fluid (SBF). Less than 7 wt.% of the incorporated silver was released over the course of 28 days in SBF and the possibility of manipulating the release rate by varying the deposition order of coating layers was shown. The low released concentration of Ag ions (<2.5 ppm) was efficiently antibacterial against Staphyloccocus aureus up to 10 days. Although chitosan and chitosan/Bioglass® coating supported proliferation of MG-63 osteoblast-like cells up to 7 days of culture, chitosan/Bioglass®/Ag-np coatings containing 342 μg of Ag-np showed cytotoxic effects. This was attributed to the relatively high concentration of Ag-np incorporated in the coatings.     

A temperature-cured dissolvable gelatin microsphere-based cell carrier for chondrocyte delivery in a hydrogel scaffolding system

In this study, a novel therapeutic cell delivery methodology in the form of hydrogel encapsulating cell-laden microspheres was developed and investigated. As a model cell for cartilage tissue engineering, chondrocytes were successfully encapsulated in gelatin-based microspheres (mostly of diameter 50–100 μm, centred at 75–100 μm) with high cell viability during the formation of microspheres via a water-in-oil single emulsion process under a low temperature without any chemical treatment. These cell-laden microspheres were then encapsulated in alginate-based hydrogel constructs. By elevating the temperature to 37 °C, the cell-laden microspheres were completely dissolved within 2 days, resulting in the same number of same-sized spherical cavities in hydrogel bulk, along with which the encapsulated cells were released from the microspheres and suspended inside the cavities to be cultivated for further development. In this cell delivery system, the microspheres played a dual role as both removable cell vehicles and porogens for creation of the intra-hydrogel cavities, in which the delivered cells were provided with both free living spaces and a better permeable environment. This temperature-cured dissolvable gelatin microsphere-based cell carrier (tDGMC) associating with cell-laden hydrogel scaffold was attempted and evaluated through WST-1, quantitative polymerase chain reaction, biochemical assays and various immunohistochemistry and histology stains. The results indicate that tDGMC technology can facilitate the delivery of chondrocytes, as a non-anchorage-dependent therapeutic cell, with significantly greater efficiency.     

Characterization of novel photocrosslinked carboxymethylcellulose hydrogels for encapsulation of nucleus pulposus cells

Back pain is a significant clinical concern often associated with degeneration of the intervertebral disc (IVD). Tissue engineering strategies may provide a viable IVD replacement therapy; however, an ideal biomaterial scaffold has yet to be identified. One candidate material is carboxymethylcellulose (CMC), a water-soluble derivative of cellulose. In this study, 90 and 250 kDa CMC polymers were modified with functional methacrylate groups and photocrosslinked to produce hydrogels at different macromer concentrations. At 7 days, bovine nucleus pulposus (NP) cells encapsulated in these hydrogels were viable, with values for the elastic modulus ranging from 1.07 ± 0.06 to 4.29 ± 1.25 kPa. Three specific formulations were chosen for further study based on cell viability and mechanical integrity assessments: 4% 90 kDa, 2% 250 kDa and 3% 250 kDa CMC. The equilibrium weight swelling ratio of these formulations remained steady throughout the 2 week study (46.45 ± 3.14, 48.55 ± 2.91 and 42.41 ± 3.06, respectively). The equilibrium Young’s modulus of all cell-laden and cell-free control samples decreased over time, with the exception of cell-laden 3% 250 kDa CMC constructs, indicating an interplay between limited hydrolysis of interchain crosslinks and the elaboration of a functional matrix. Histological analyses of 3% 250 kDa CMC hydrogels confirmed the presence of rounded cells in lacunae and the pericellular deposition of chondroitin sulfate proteoglycan, a phenotypic NP marker. Taken together, these studies support the use of photocrosslinked CMC hydrogels as tunable biomaterials for NP cell encapsulation.     

Ultrathin chitosan–poly(ethylene glycol) hydrogel films for corneal tissue engineering

Due to the high demand for donor corneas and their low supply, autologous corneal endothelial cell (CEC) culture and transplantation for treatment of corneal endothelial dysfunction would be highly desirable. Many studies have shown the possibility of culturing CECs in vitro, but lack potential robust substrates for transplantation into the cornea. In this study, we investigate the properties of novel ultrathin chitosan–poly(ethylene glycol) (PEG) hydrogel films (CPHFs) for corneal tissue engineering applications. Cross-linking of chitosan films with diepoxy-PEG and cystamine was employed to prepare ～50 μm (hydrated) hydrogel films. Through variation of the PEG content (1.5–5.9 wt.%) it was possible to tailor the CPHFs to have tensile strains and ultimate stresses identical to or greater than those of human corneal tissue while retaining similar tensile moduli. Light transmission measurements in the visible spectrum (400–700 nm) revealed that the films were >95% optically transparent, above that of the human cornea (maximum ～90%), whilst in vitro degradation studies with lysozyme revealed that the CPHFs maintained the biodegradable characteristics of chitosan. Cell culture studies demonstrated the ability of the CPHFs to support the attachment and proliferation of sheep CECs. Ex vivo surgical trials on ovine eyes demonstrated that the CPHFs displayed excellent characteristics for physical manipulation and implantation purposes. The ultrathin CPHFs display desirable mechanical, optical and degradation properties whilst allowing attachment and proliferation of ovine CECs, and as such are attractive candidates for the regeneration and transplantation of CECs, as well as other corneal tissue engineering applications.