Poly(glutamic acid) poly(ethylene glycol) hydrogels prepared by photoinduced polymerization: Synthesis,characterization, and preliminary release studies of protein drugs

A class of new biodegradable hydrogels based on poly(ethylene glycol) methacrylate-graft-poly(glutamic acid) and poly(ethylene glycol) dimethacrylate was synthesized by photoinduced polymerization. Because all the polymeric constituents were highly hydrophilic, crosslinking could be performed in aqueous solutions. This type of crosslinked hydrogel was prepared by modifying a select number of acidic side-groups on poly(glutamic acid) with poly(ethylene glycol) methacrylate. These modified chains were then crosslinked in the presence of poly(ethylene glycol) dimethacrylate under a photoinduced polymerization at a wavelength of 365 nm. Swelling experiments were conducted to study the crosslinking density, pH-responsive behavior, and degradation of the hydrogel. Results showed that the degree of swelling of this type of hydrogels increased as the crosslinker concentration (or density) was reduced. Because of the presence of acidic side chains on poly(glutamic acid), swelling behavior was found to be pH-responsive, increasing at high pH in response to the increase in the amount of ionized acidic side chains. The degradation rate of these hydrogels also varied with pH. More rapid degradation was observed under stronger alkaline conditions because of the hydrolysis of the ester bonds between the crosslinker and the polymer backbone. Practically useful degradation rates could be achieved for such hydrogels under physiological conditions. Drug release rates from these hydrogels were found to be proportional to the protein molecular weight and the crosslinker density; increasing at lower protein molecular weight or crosslinker density. The preliminary findings presented in this article suggest that this class of biodegradable hydrogels could be an attractive avenue for drug delivery applications. The specific photoinduced crosslinking chemistry used would permit hydrogels to be synthesized in existence of the entrapped macromolecular drugs including peptides, proteins, and cells. In addition, the rapid feature of this polymerization procedure along with the ability to perform hydrogel synthesis and drug loading in an aqueous environment would offer great advantages in retaining drug activity during hydrogel synthesis.     

Oligo(trimethylene carbonate)-poly(ethylene glycol)-oligo(trimethylene carbonate) triblock-based hydrogels for cartilage tissue engineering

A triblock co-polymer of oligo(trimethylene carbonate)-block-poly(ethylene glycol) 20000-block-oligo(trimethylene carbonate) diacrylate (TMC20) was used as a photo-polymerizable precursor for the encapsulation of primary articular chondrocytes. The efficacy of TMC20 as a biodegradable scaffold for cartilage tissue engineering was compared with non-degradable poly(ethylene glycol) 20000 diacrylate (PEG20) hydrogel. Chondrocytes encapsulated in PEG hydrogels containing oligo(trimethylene carbonate) (OTMC) moieties underwent spontaneous aggregation during in vitro culture, which was not observed in the PEG hydrogel counterparts. The aggregation of cells was found to be dependent on the initial cell density, as well as the mesh size of the hydrogels. Similarly, cell aggregation was also found in biodegradable PEG hydrogels containing caprolactone moieties. The aggregation of cells in TMC20 hydrogels resulted in enhanced cartilage matrix production compared with their PEG20 counterparts over 3 weeks of culture. Taken together, these results indicate that PEG hydrogels containing degradable OTMC moieties promote the aggregation and biosynthetic activity of encapsulated chondrocytes, indicating their potential as scaffolds for the repair of cartilage tissue.     

Photo-cross-linkable and thermo-responsive hydrogels containing chitosan and Pluronic for sustained release of human growth hormone (hGH)

A Pluronic/chitosan hydrogel was prepared by employing di-acrylated Pluronic and acrylated chitosan for thermo-responsive and photo-cross-linkable in situ gelation. Mixtures of diacrylated Pluronic and acrylated chitosan were transformed to physical gels at elevated temperatures and the gelation temperature of the hydrogels gradually increased by increasing chitosan content in the hydrogels from 0% to 15%. Photo-cross-linked Pluronic/chitosan hydrogels were prepared by UV irradiation of the physical gels above their gelation temperatures. Hydrogels with a long photo-cross-linking time showed low degradation rates and chitosan contents in the hydrogels also impeded the degradation rates of the hydrogels, which was caused by a high degree of inter-connected polymer networks between acrylated Pluronic and acrylated chitosan. Human growth hormone (hGH), mixed with the mixture of Pluronic and chitosan, was photo-cross-linked to prepare biodegradable hGH hydrogels. The hydrogels containing hGH showed sustained release profiles for those with long photo-cross-linking times and high chitosan contents in the hydrogel. The hydrogels with a long cross-linking time showed impeded release of the protein and high content of chitosan in the hydrogels also decreased burst release of hGH from the hydrogels while hGH was rapidly released out for the hydrogels with low content of chitosan.     

Photo-cross-linkable and thermo-responsive hydrogels containing chitosan and Pluronic for sustained release of human growth hormone (hGH)

A Pluronic/chitosan hydrogel was prepared by employing di-acrylated Pluronic and acrylated chitosan for thermo-responsive and photo-cross-linkable in situ gelation. Mixtures of diacrylated Pluronic and acrylated chitosan were transformed to physical gels at elevated temperatures and the gelation temperature of the hydrogels gradually increased by increasing chitosan content in the hydrogels from 0% to 15%. Photo-cross-linked Pluronic/chitosan hydrogels were prepared by UV irradiation of the physical gels above their gelation temperatures. Hydrogels with a long photo-cross-linking time showed low degradation rates and chitosan contents in the hydrogels also impeded the degradation rates of the hydrogels, which was caused by a high degree of inter-connected polymer networks between acrylated Pluronic and acrylated chitosan. Human growth hormone (hGH), mixed with the mixture of Pluronic and chitosan, was photo-cross-linked to prepare biodegradable hGH hydrogels. The hydrogels containing hGH showed sustained release profiles for those with long photo-cross-linking times and high chitosan contents in the hydrogel. The hydrogels with a long cross-linking time showed impeded release of the protein and high content of chitosan in the hydrogels also decreased burst release of hGH from the hydrogels while hGH was rapidly released out for the hydrogels with low content of chitosan.     

Biodegradable DNA-enabled poly(ethylene glycol) hydrogels prepared by copper-free click chemistry

Significant research has focused on investigating the potential of hydrogels in various applications and, in particular, in medicine. Specifically, hydrogels that are biodegradable lend promise to many therapeutic and biosensing applications. Endonucleases are critical for mechanisms of DNA repair. However, they are also known to be overexpressed in cancer and to be present in wounds with bacterial contamination. In this work, we set out to demonstrate the preparation of DNA-enabled hydrogels that could be degraded by nucleases. Specifically, hydrogels were prepared through the reaction of dibenzocyclooctyne-functionalized multi-arm poly(ethylene glycol) with azide-functionalized single-stranded DNA in aqueous solutions via copper-free click chemistry. Through the use of this method, biodegradable hydrogels were formed at room temperature in buffered saline solutions that mimic physiological conditions, avoiding possible harmful effects associated with other polymerization techniques that can be detrimental to cells or other bioactive molecules. The degradation of these DNA-cross-linked hydrogels upon exposure to the model endonucleases Benzonase^® and DNase I was studied. In addition, the ability of the hydrogels to act as depots for encapsulation and nuclease-controlled release of a model protein was demonstrated. This model has the potential to be tailored and expanded upon for use in a variety of applications where mild hydrogel preparation techniques and controlled material degradation are necessary including in drug delivery and wound healing systems.     

An injectable and self-healing hydrogel for spatiotemporal protein release via fragmentation after passing through needles

A dynamic hydrogel formulated by mixing a glycol chitosan (GC) and an oxidized dextran (Odex) were studied for protein-controlled release in conjunction with the hydrogel fragmentation. A series of injectable dynamic hydrogels were derived from GC and Odex upon simple mixing without the addition of chemical crosslinking agents. The gelation readily took place at physiological pH and temperature. The influence of the concentration of GC and Odex on the gelation time, mechanical properties, water content, in vitro degradation were investigated. The Odex/GC hydrogels showed good self-healing ability under physiological conditions and kept the dynamic Schiff-base linkage at over 2 wt %. The release kinetics of a model protein (bovine serum albumin) was found to be controlled by changing the needle size upon injection, attributed to modulation of apparent size and shape of the fragmented hydrogels even in the self-healed state. Therefore, the GC-based injectable and dynamic hydrogels are expected to be a promising platform for protein delivery system and various biomedical applications.     

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.     

Cathepsin K-sensitive poly(ethylene glycol) hydrogels for degradation in response to bone resorption

We propose a new strategy of biomaterial design to achieve selective cellular degradation by the incorporation of cathepsin K-degradable peptide sequences into a scaffold structure so that scaffold biodegradation can be induced at the end of the bone formation process. Poly(ethylene glycol) diacrylate (PEGDA) hydrogels were used as a model biomaterial system in this study. A cathepsin K-sensitive peptide, GGGMGPSGPWGGK (GPSG), was synthesized and modified with acryloyl-PEG-succinimidyl carbonate to produce a cross-linkable cathepsin K-sensitive polymer that can be used to form a hydrogel. Specificity of degradation of the GPSG hydrogels was tested with cathepsin K and proteinase K as a positive control, with both resulting in significant degradation compared to incubation with nonspecific collagenases over a 24-h time period. No degradation was observed when the hydrogels were incubated with plasmin or control buffers. Cell-induced degradation was evaluated by seeding differentiated MC3T3-E1 osteoblasts and RAW264.7 osteoclasts on GPSG hydrogels that were also modified with the cell adhesion peptide RGDS. Resulting surface features and resorption pits were analyzed by differential interference contrast (DIC) and fluorescent images obtained with confocal microscopy. Results from both analyses demonstrated that GPSG hydrogels can be degraded specifically in response to osteoclast attachment but not in response to osteoblasts. In summary, we have demonstrated that by incorporating a cathepsin K-sensitive peptide into a synthetic polymer structure, we can generate biomaterials that specifically respond to cues from the natural process of bone remodeling.     

Synthesis and characterization of hyaluronic acid–poly(ethylene glycol) hydrogels via Michael addition: An injectable biomaterial for cartilage repair

Injectable hydrogels based on hyaluronic acid (HA) and poly(ethylene glycol) (PEG) were designed as biodegradable matrices for cartilage tissue engineering. Solutions of HA conjugates containing thiol functional groups (HA-SH) and PEG vinylsulfone (PEG-VS) macromers were cross-linked via Michael addition to form a three-dimensional network under physiological conditions. Gelation times varied from 14 min to less than 1 min, depending on the molecular weights of HA-SH and PEG-VS, degree of substitution (DS) of HA-SH and total polymer concentration. When the polymer concentration was increased from 2% to 6% (w/v) in the presence of 100 U ml^?1 hyaluronidase the degradation time increased from 3 to 15 days. Hydrogels with a homogeneous distribution of cells were obtained when chondrocytes were mixed with the precursor solutions. Culturing cell–hydrogel constructs prepared from HA185k-SH with a DS of 28 and cross-linked with PEG5k-4VS for 3 weeks in vitro revealed that the cells were viable and that cell division took place. Gel–cell matrices degraded in approximately 3 weeks, as shown by a significant decrease in dry gel mass. At day 21 glycosaminoglycans and collagen type II were found to have accumulated in hydrogels. These results indicate that these injectable hydrogels have a high potential for cartilage tissue engineering.     

Biodegradable hydrogels composed of oxime crosslinked poly(ethylene glycol), hyaluronic acid and collagen: a tunable platform for soft tissue engineering

In situ crosslinking hydrogels are attractive for application as injectable hydrogel-based tissue scaffolds that adapt to fill patient-specific cavities. Oxime click chemistry was used to crosslink hydrogels that were biodegradable, soft and supportive of cell adhesion. Linear poly(ethylene glycol)s (PEGs, Mn 2 or 4 kDa) terminated at both ends with aminooxy moieties and hyaluronic acid (HA, Mn 2 MDa) derivatives displaying aldehydes were non-toxic towards primary Schwann cells. The PEG and HA derivatives form oxime crosslinked hydrogels with mechanical and swelling properties that were tunable based on the composition of the hydrogels to values analogous to soft tissues such as those found in the central or peripheral nervous system. Gels incorporating collagen-1 supported the adhesion of human mesenchymal stem cells. Such chemistry has the potential to generate clinically relevant injectable hydrogels for minimally invasive personalized medical procedures in the central or peripheral nervous systems.     

Enzyme-mediated fast in situ formation of hydrogels from dextran-tyramine conjugates

Dextran hydrogels were formed in situ by enzymatic crosslinking of dextran-tyramine conjugates and their mechanical, swelling and degradation properties were evaluated. Two types of dextran-tyramine conjugates (M(n,dextran)=14k, M(w)/M(n)=1.45), i.e. dextran-tyramine linked by a urethane bond (denoted as Dex-TA) or by an ester-containing diglycolic group (denoted as Dex-DG-TA), with different degrees of substitution (DS) were prepared. Hydrogels were rapidly formed under physiological conditions from Dex-TA DS 10 or 15 and Dex-DG-TA DS 10 at or above a concentration of 2.5 wt% in the presence of H(2)O(2) and horseradish peroxidase (HRP). The gelation time ranged from 5s to 9 min depending on the polymer concentration and HRP/TA and H(2)O(2)/TA ratios. Rheological analysis showed that these hydrogels are highly elastic. The storage modulus (G'), which varied from 3 to 41 kPa, increased with increasing polymer concentration, increasing HRP/TA ratio and decreasing H(2)O(2)/TA ratio. The swelling/degradation studies showed that under physiological conditions, Dex-TA hydrogels are rather stable with less than 25% loss of gel weight in 5 months, whereas Dex-DG-TA hydrogels are completely degraded within 4-10d. These results demonstrate that enzymatic crosslinking is an efficient way to obtain fast in situ formation of hydrogels. These dextran-based hydrogels are promising for use as injectable systems for biomedical applications including tissue engineering and protein delivery.     

Liquid acrylate-endcapped biodegradable poly(epsilon-caprolactone-co-trimethylene carbonate). I. Preparation and visible light-induced photocuring characteristics

Photocurable liquid biodegradable copolymers were prepared by ring-opening copolymerization of epsilon-caprolactone (CL) and trimethylene carbonate (TMC) in the presence of a multifunctional hydroxyl group-bearing substance (di-, tri-, and tetra-functional alcohol and poly(ethylene glycol) (PEG) and its four-branched derivative) as an initiator and subsequent endcapping with acryloyl chloride at their hydroxyl terminals. These multifunctional, viscous liquid copolymers (molecular weights; approximately 2 x 10(3) to 7 x 10(3) g/mol) were converted to crosslinked solids by visible-light irradiation in the presence of camphorquinone as an initiator. The photocuring rate of these copolymers was enhanced by both higher functionality and lower molecule weight of the copolymers used. The photocuring rate depended on the amount of reducing agent (methacrylic acid 2-dimethylaminoethyl ester). Upon immersion in a phosphate buffer solution (pH 7.4), hydrolysis occurred preferentially on the surface except for photocured PEG-based copolymers that were degraded faster via both surface erosion and bulk degradation than low molecular weight alcohols-based copolymers. Cylindrical photocured constructs prepared by photoirradiation to the whole body in a mold filled with the liquid copolymer was demonstrated as an example of shape fabrication of biodegradable biomedical devices.     

Novel biodegradable cholesterol-modified polyrotaxane hydrogels for cartilage regeneration

Cholesterol was introduced to a hydrolyzable polyrotaxane (PRx), not only to improve cell proliferation and glycosaminoglycan (GAG) production, but also to control the degradation rate of the hydrogels. The cholesterol was introduced to hydrolyzable PRx species by threading many alpha-cyclodextrins (alpha-CDs) on a poly(ethylene glycol) (PEG) chain having hydrolyzable ester linkages at the terminals; the PRx species were then cross-linked with other PEGs to prepare cholesterol-modified PRx hydrogels. The degree of cholesterol substitution was varied in the range of 1-25%. These hydrogels were examined to clarify the effect of cholesterol groups on mechanical properties, erosion time and chondrocyte proliferation. Highly porous biodegradable cholesterol-modified PRx hydrogels were fabricated using a combination of potassium hydrogen carbonate (as an effervescent salt) and citric acid. This fabrication process enabled the homogeneous expansion of pores within the polymer matrices, leading to well-interconnected macroporous hydrogels with a mean pore size of around 200-400 microm, ideal for high-density chondrocyte seeding. Time to complete degradation of the hydrogels was shortened by increasing the degree of substitution due to the aggregation of alpha-CDs through hydrophobic interaction of cholesterol groups. The presence of approx. 10% cholesterol improved the chondrocyte proliferation and GAG production. The modification of cholesterols to PRx is a good approach for creating new biodegradable hydrogels in terms of chondrocyte culture and controlling degradation time of the hydrogels.     

Effect of drying history on swelling properties and cell attachment to oligo(poly(ethylene glycol) fumarate) hydrogels for guided tissue regeneration applications

In these experiments, the effects of the drying history of hydrogels made from a novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF) with two different poly(ethylene glycol) (PEG) molecular weights (approximately 920 (1K) and 9110 (10K) g/mol), were investigated. The hydrogels were either formed, dried and then swelled, representing what may occur in the case of a pre-formed membrane for guided tissue regeneration, or were formed and swelled immediately, as may occur with an injectable material for such applications. Subsequently, swelling properties, sol fraction and polymer network structure (as indicated by differential scanning calorimetry), as well as attachment of human dermal fibroblasts to these hydrogels at 4 and 24 h was examined. It was found that drying before swelling caused a significant reduction in final fold swelling of OPF hydrogels, regardless of OPF formulation or method of drying (air-dried or vacuum-dried) (e.g. PEG 10K swollen first: 13.94 +/- 0.35 vs. vacuum first: 6.53 +/- 0.12; PEG 1K swollen first: 8.99 +/- 0.47 vs. vacuum first: 2.26 +/- 0.08). This decreased swelling correlated to significantly higher cell attachment (% seeded) to these hydrogels at 24 h (PEG 10K vacuum first: 21.1 +/- 4.7% vs. swollen first: 7.1 +/- 5.5%; PEG 1K vacuum first: 58.2 +/- 2% vs. swollen first: 7.4 +/- 2.2%). LIVE/DEAD staining followed by microscopic analysis revealed attached cells were viable, yet rounded, and that, in the case of the PEG 1K dried-first samples, undulations in the surface visible in the hydrated state may have affected cell adhesion. Regardless of treatment, all hydrogels showed significantly less cell attachment than the tissue culture polystyrene control after 24 h (104.9 +/- 4.4%). These results suggest that, by altering the PEG molecular weight used in synthesis, OPF hydrogels may be tailored to produce desired swelling properties and reduce non-specific cell adhesion for either injectable or pre-formed applications, thus providing a potential alternative material for use in guided tissue regeneration procedures.     

Double-stimuli-responsive degradation of hydrogels consisting of oligopeptide-terminated poly(ethylene glycol) and dextran with an interpenetrating polymer network

Biodegradable hydrogels consisting of oligopeptide-terminated poly(ethylene glycol) (PEG) and dextran (Dex) with an interpenetrating polymer network (IPN) structure were prepared as models of novel biomaterials exhibiting a double-stimuli-response function. The IPN-structured hydrogels were synthesized by sequential cross-linking reaction of N-methacryloyl-glycylglycylglycyl-terminated PEG and Dex. In vitro degradation of the IPN-structured hydrogels was examined using papain and dextranase as model enzymes of hydrolyzing oligopeptide and Dex, respectively. Specific degradation in the presence of papain and dextranase was observed in the IPN-structured hydrogel with a particular composition of oligopeptide-PEG and Dex. This same hydrogel was not degraded by one of the two enzymes. The IPN-structured hydrogels were characterized by water content, thermal mechanical analysis, and wide-angle X-ray diffraction, and the results were compared with those of co-cross-linked hydrogels consisting of N-methacryloyl-glycylglycylglycyl-terminated PEG and methacryloyl Dex. The results suggest that the IPN-structured hydrogels contain physical chain entanglements between networks as well as chemical cross-linked networks. It is concluded that the double-stimuli-responsive degradation observed in the IPN-structured hydrogel is achieved by controlling the chain entanglements between the two biodegradable polymers. Such degradation property of the IPN-structured hydrogel can be useful as a fail-safe system for guaranteed drug delivery and/or medical micromachines.     

Cell viability of chitosan-containing semi-interpenetrated hydrogels based on PCL-PEG-PCL diacrylate macromer

Chitosan-modified biodegradable hydrogels were prepared by UV irradiation of solutions in mild aqueous acidic media of poly(caprolactone)-co-poly(ethylene glycol)-co-poly(caprolactone) diacrylate (PCL-PEG-PCL-DA) and chitosan. Hydrogels obtained were characterized using FT-IR, DSC, TGA and XPS. FT-IR, TGA and DSC revealed the semi-interpenetrating polymer network structure formed in the hydrogel. Though the water swelling degree of these chitosan-modified hydrogels was substantial in the range of 322-539%, it was found that fibroblasts could still attach, spread and grow on them; this is in contrast to the commonly investigated PEG-diacrylate hydrogel. The MTT assay demonstrated that cells could grow better on 3 or 6% chitosan-modified hydrogel than unmodified PCL-PEG-PCL-DA hydrogels or low-content (1%) chitosan-modified PCL-PEG-PCL-DA hydrogel. Increased chitosan content resulted in increased cell interaction and also decreased water swelling, both of which results in increased cell attachment and spread.     

Biodegradable and thermoreversible PCLA-PEG-PCLA hydrogel as a barrier for prevention of post-operative adhesion

Biodegradable polymers can serve as barriers to prevent the post-operative intestinal adhesion. Herein, we synthesized a biodegradable triblock copolymer poly(?-caprolactone-co-lactide)-b-poly(ethylene glycol)-b-poly(?-caprolactone-co-lactide) (PCLA-PEG-PCLA). The concentrated polymeric aqueous solution was injectable, and a hydrogel could be rapidly formed due to percolation of a self-assembled micelle network at the body temperature without requirement of any chemical reactions. This physical hydrogel retained its integrity in vivo for a bit more than 6 weeks and was eventually degraded due to hydrolysis. The synthesized polymer exhibited little cytotoxicity and hemolysis; the acute inflammatory response after implanting the hydrogel was acceptable, and the degradation products were less acidic than those of other polyester-containing materials. A rabbit model of sidewall defect-bowel abrasion was employed, and a significant reduction of post-operative peritoneal adhesion has been found in the group of in situ formed PCLA-PEG-PCLA hydrogels.     

Effect of drying history on swelling properties and cell attachment to oligo(poly(ethylene glycol) fumarate) hydrogels for guided tissue regeneration applications

In these experiments, the effects of the drying history of hydrogels made from a novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF) with two different poly(ethylene glycol) (PEG) molecular weights (approximately 920 (1K) and 9110 (10K) g/mol), were investigated. The hydrogels were either formed, dried and then swelled, representing what may occur in the case of a pre-formed membrane for guided tissue regeneration, or were formed and swelled immediately, as may occur with an injectable material for such applications. Subsequently, swelling properties, sol fraction and polymer network structure (as indicated by differential scanning calorimetry), as well as attachment of human dermal fibroblasts to these hydrogels at 4 and 24 h was examined. It was found that drying before swelling caused a significant reduction in final fold swelling of OPF hydrogels, regardless of OPF formulation or method of drying (air-dried or vacuum-dried) (e.g. PEG 10K swollen first: 13.94 ± 0.35 vs. vacuum first: 6.53 ± 0.12; PEG 1K swollen first: 8.99 ± 0.47 vs. vacuum first: 2.26 ± 0.08). This decreased swelling correlated to significantly higher cell attachment (% seeded) to these hydrogels at 24 h (PEG 10K vacuum first: 21.1 ± 4.7% vs. swollen first: 7.1 ± 5.5%; PEG 1K vacuum first: 58.2 ± 2% vs. swollen first: 7.4 ± 2.2%). LIVE/DEAD staining followed by microscopic analysis revealed attached cells were viable, yet rounded, and that, in the case of the PEG 1K dried-first samples, undulations in the surface visible in the hydrated state may have affected cell adhesion. Regardless of treatment, all hydrogels showed significantly less cell attachment than the tissue culture polystyrene control after 24 h (104.9 ± 4.4%). These results suggest that, by altering the PEG molecular weight used in synthesis, OPF hydrogels may be tailored to produce desired swelling properties and reduce non-specific cell adhesion for either injectable or pre-formed applications, thus providing a potential alternative material for use in guided tissue regeneration procedures.     

Effect of hydrophilicity and agmatine modification on degradation of poly(propylene fumarate-co-ethylene glycol) hydrogels

We synthesized positively charged biodegradable hydrogels with different poly(propylene fumarate-co-ethylene glycol) [P(PF-co-EG)] block copolymers and agmatine-modified poly(ethylene glycol)-tethered fumarate [Agm-PEGF] by radical crosslinking and investigated the effect of copolymer composition and agmatine modification on their degradation. Hydrogels were incubated in phosphate-buffered saline (PBS) at 37 degrees C with periodic PBS changes. All hydrogels experienced a slight mass loss over 4 weeks, ranging from 10-20%. Hydrogels with a molar ratio of ethylene glycol repeating units to propylene fumarate repeating units (EG/PF) of 9.3 degraded faster than hydrogels with an EG/PF ratio of 0.6. Agmatine-modified hydrogels degraded faster than unmodified hydrogels. The weight swelling ratio of the hydrogels at pH 7 increased over 4 weeks while increases in the EG/PF ratio and agmatine modification showed greater swelling. After 2 weeks, degraded hydrogels swollen at pH 3 demonstrated significantly lower weight swelling ratios than at pH 5, 7, and 9. Our results suggest that the hydrophilicity of the P(PF-co-EG) copolymer and agmatine modification have a small effect on the degradation of P(PF-co-EG) hydrogels.     

In vivo bone and soft tissue response to injectable,biodegradable oligo(poly(ethylene glycol) fumarate) hydrogels

This study was designed to assess in vivo bone and soft tissue behavior of novel oligo(poly(ethylene glycol) fumarate) (OPF) hydrogels using a rabbit model. In vitro degradation of the OPF hydrogels was also investigated in order to compare with in vivo characteristics. Four groups of OPF hydrogel implants were synthesized by alternation of crosslinking density, poly(ethylene glycol) (PEG) block length of OPF, and cell-binding peptide content. The in vitro degradation rate of OPF hydrogels increased with decreasing crosslinking density of hydrogels, which was characterized by measuring weight loss and swelling ratio of hydrogels and medium pH change. Examination of histological sections of the subcutaneous and cranial implants showed that an uniform thin circumferential fibrous capsule was formed around the OPF hydrogel implants. Quantitative evaluation of the tissue response revealed that no statistical difference existed in capsule quality or thickness between implant groups, implantation sites or implantation times. At 4 weeks, there was a very limited number of inflammatory and multinuclear cells at the implant-fibrous capsule interface for all implants. However, at 12 weeks, OPF hydrogels with PEG block length of number average molecular weight 6090+/-90 showed extensive surface erosion and superficial fragmentation that was surrounded by a number of inflammatory cells, while OPF hydrogels with PEG block length of number average molecular weight 930+/-10 elicited minimal degradation. Constant fibrous capsule layers and number of inflammatory cells were observed regardless of the incorporation of cell-binding peptide and crosslinking density of OPF hydrogels with PEG block length of number average molecular weight 930+/-90. These results confirm that the degradation of implants can be controlled by tailoring the macromolecular structure of OPF hydrogels. Additionally, histological evaluation of implants proved that the OPF hydrogel is a promising material for biodegradable scaffolds in tissue engineering.