Synthesis and characterization of injectable poly(N-isopropylacrylamide-co-acrylic acid) hydrogels with proteolytically degradable cross-links

Hydrogels composed of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) were prepared by redox polymerization with peptide cross-linkers to create an artificial extracellular matrix (ECM) amenable for testing hypotheses regarding cell proliferation and migration in three dimensions. Peptide degradable cross-linkers were synthesized by the acrylation of the amine groups of glutamine and lysine residues within peptide sequences potentially cleavable by matrix metalloproteinases synthesized by mammalian cells (e.g., osteoblasts). With the peptide cross-linker, loosely cross-linked poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAAm-co-AAc)] hydrogels were prepared, and their phase transition behavior, lower critical solution temperature (LCST), water content, and enzymatic degradation properties were investigated. The peptide-cross-linked P(NIPAAm-co-AAc) hydrogels were pliable and fluidlike at room temperature and could be injected through a small-diameter aperture. The LCST of peptide-cross-linked hydrogel was influenced by the monomer ratio of NIPAAm/AAc but not by cross-linking density within the polymer network. A peptide-cross-linked hydrogel with a 97/3 molar ratio of NIPAAm/AAc exhibited a LCST of approximately 34.5 degrees C. Swelling was influenced by NIPAAm/AAc monomer ratio, cross-linking density, and swelling media; however, all hydrogels maintained more than 90% water even at 37 degrees C. In enzymatic degradation studies, breakdown of the peptide-cross-linked P(NIPAAm-co-AAc) hydrogels was dependent on both the concentration of collagenase and the cross-linking density. These results suggest that peptide-cross-linked P(NIPAAm-co-AAc) hydrogels can be tailored to create environmentally-responsive artificial extracellular matrixes that are degraded by proteases.     

Copolymerization of 2-carboxyisopropylacrylamide with N-isopropylacrylamide accelerates cell detachment from grafted surfaces by reducing temperature

Acrylic acid (AAc) has been utilized to introduce reactive carboxyl groups to a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm). However, AAc introduction shifts the copolymer phase transition temperatures higher and dampens the steep homopolymer phase transition with increasing AAc content. We previously synthesized 2-carboxyisopropylacrylamide (CIPAAm) having both a similar side chain structure to IPAAm and a functional carboxylate group in order to overcome these shortcomings. In the present study, these copolymers, grafted onto cell culture plastic, were assessed for cell adhesion control using their phase transition. AAc introduction to PIPAAm-grafted surfaces resulted in excessive surface hydration and hindered cell spreading in culture at 37 degrees C. In contrast, CIPAAm-containing copolymer-grafted surfaces exhibited relatively weak hydrophobicity similar to both homopolymer PIPAAm-grafted surfaces as well as commercial ungrafted tissue culture polystyrene dish surfaces. Cells adhered and spread well on these surfaces at 37 degrees C in culture. As observed previously on PIPAAm-grafted surfaces, cells were spontaneously detached from the copolymer-grafted surfaces by reducing culture temperature. Cell detachment was accelerated on the CIPAAm copolymer-grafted surfaces compared to pure IPAAm surfaces, suggesting that hydrophilic carboxyl group microenvironment in the monomer and polymer is important to accelerate grafted surface hydration below the lower critical solution temperature, detaching cells.     

Preparation and properties of a pH/temperature-responsive carboxymethyl chitosan/poly(N-isopropylacrylamide)semi-IPN hydrogel for oral delivery of drugs

Thermo- and pH-responsive semi-IPN polyampholyte hydrogels were prepared by using carboxymethylchitosan and poly(N-isopropylacrylamide) with N,N'-methylenebisacrylamide (BIS) as the crosslinking agent. The swelling characteristics of these hydrogels at distinct compositions as a function of pH and temperature were investigated. It was found that the semi-IPN hydrogels demonstrated the pH- and temperature-responsive nature of the materials, and it also showed good reversibility. The study on the release of coenzyme A (CoA) showed that within 24h the cumulative release ratio of CoA was 22.6% in pH 2.1 solution and 89.1% in pH 7.4 solution at 37 degrees C, respectively. The release rate of CoA was higher at 37 degrees C than 25 degrees C in a pH 7.4 buffer solution. An increased release rate of CoA was observed with the content of carboxymethylchitosan increasing in the hydrogel at 25 degrees C in pH 7.4 solution. These results show that semi-IPN hydrogel seems to be of great promise in pH-temperature oral drug delivery systems.     

Resorbable and highly elastic block copolymers from 1,5-dioxepan-2-one and L-lactide with controlled tensile properties and hydrophilicity

New resorbable and elastomeric ABA tri- and multiblock copolymers have been successfully synthesized by combining ring-opening polymerization with ring-opening polycondensation. Five different poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) triblock copolymers and one new poly(L-lactide-b-1,5-dioxepan-2-one) multiblock copolymer have been synthesized. The triblock copolymers were obtained by ring-opening polymerization of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with a cyclic tin initiator. The new multiblock copolymer was prepared by ring-opening polycondensation of a low molecular weight triblock copolymer with succinyl chloride. The molecular weight and the composition of the final copolymers were easily controlled by adjusting the monomer feed ratio, and all of the polymers obtained had a narrow molecular weight distribution. It was possible to tailor the hydrophilicity of the materials by changing the DXO content. Copolymers with a high DXO content had a more hydrophilic surface than those with a low DXO content. The receding contact angle varied from 27 to 44 degrees. The tensile properties of the copolymers were controlled by altering the PDXO block length. The tensile testing showed that all the polymers were very elastic and had very high elongations-at-break (epsilon(b)). The copolymers retained very good mechanical properties (epsilon(b) approximately 600-800% and sigma(b) approximately 8-20 MPa) throughout the in vitro degradation study (59 days).     

Acid catalyzed transesterification as a route to poly(3-hydroxybutyrate-co-epsilon-caprolactone) copolymers from their homopolymers

Copolymers of (R)-3-hydroxybutyric acid (HB) and epsilon-caprolactone (CL) with a composition ranging from 28 to 81 mol % of HB were synthesized by transesterification of the corresponding homopolymers in solution in the presence of 4-toluenesulfonic acid. The copolyesters were characterized with regard to their molecular weights, thermal properties, molar compositions, and average block length of repeating units by gel permeation chromatography (GPC), differential scanning calorimetry, (1)H NMR, and (13)C NMR, respectively. Random and microblock copolymers could be obtained depending on experimental conditions, with weight-average molecular weights of up to 20,000. The glass transition temperature decreased from 2 to -42 degrees C as the CL content was increased from 0 to 72 mol %. The melting temperature (T(m)) of the PCL phase decreased from 70 to 46 degrees C as the HB content changed from 0 to 47 mol %, while the T(m) of the PHB phase decreased from 177 degrees C to 163 degrees C as the CL content changed from 0 to 72 mol %. Matrix-assisted laser desorption ionization time-of-flight mass spectra of GPC fractionated samples allowed us to ascertain that copolymers rich in HB units have mostly hydroxyl and carboxyl end groups, while copolymers rich in CL units have mostly tosyl and carboxyl end groups.     

In-situ formation of biodegradable hydrogels by stereocomplexation of PEG-(PLLA)8 and PEG-(PDLA)8 star block copolymers

Eight-arm poly(ethylene glycol)-poly(L-lactide), PEG-(PLLA)(8), and poly(ethylene glycol)-poly(D-lactide), PEG-(PDLA)(8), star block copolymers were synthesized by ring-opening polymerization of either L-lactide or D-lactide at room temperature in the presence of a single-site ethylzinc complex and 8-arm PEG (M(n) = 21.8 x 10(3) or 43.5 x 10(3)) as a catalyst and initiator, respectively. High lactide conversions (>95%) and well-defined copolymers with PLLA or PDLA blocks of the desired molecular weights were obtained. Star block copolymers were water-soluble when the number of lactyl units per poly(lactide) (PLA) block did not exceed 14 and 17 for PEG21800-(PLA)(8) and PEG43500-(PLA)(8), respectively. PEG-(PLA)(8) stereocomplexed hydrogels were prepared by mixing aqueous solutions with equimolar amounts of PEG-(PLLA)(8) and PEG-(PDLA)(8) in a polymer concentration range of 5-25 w/v % for PEG21800-(PLA)(8) star block copolymers and of 6-8 w/v % for PEG43500-(PLA)(8) star block copolymers. The gelation is driven by stereocomplexation of the PLLA and PDLA blocks, as confirmed by wide-angle X-ray scattering experiments. The stereocomplexed hydrogels were stable in a range from 10 to 70 degrees C, depending on their aqueous concentration and the PLA block length. Stereocomplexed hydrogels at 10 w/v % polymer concentration showed larger hydrophilic and hydrophobic domains as compared to 10 w/v % single enantiomer solutions, as determined by cryo-TEM. Correspondingly, dynamic light scattering showed that 1 w/v % solutions containing both PEG-(PLLA)(8) and PEG-(PDLA)(8) have larger "micelles" as compared to 1 w/v % single enantiomer solutions. With increasing polymer concentration and PLLA and PDLA block length, the storage modulus of the stereocomplexed hydrogels increases and the gelation time decreases. Stereocomplexed hydrogels with high storage moduli (up to 14 kPa) could be obtained at 37 degrees C in PBS. These stereocomplexed hydrogels are promising for use in biomedical applications, including drug delivery and tissue engineering, because they are biodegradable and the in-situ formation allows for easy immobilization of drugs and cells.     

Novel lipase-catalyzed ring-opening copolymerization of lactide and trimethylene carbonate forming poly(ester carbonate)s.

Poly(lactide-co-trimethylene carbonate)s were prepared by the lipase-catalyzed ring-opening copolymerization of lactide and trimethylene carbonate having carbonate content from 0 to 100%. Their thermal properties and enzymatic degradability were measured. The L,L-, D,D- and D,L-lactides were copolymerized with trimethylene carbonate by porcine pancreatic lipase to produce random copolymers having molecular weights of up to 21000. The glass transition temperature (Tg of the copolymer was dependent on the carbonate content and the Tg values linearly decreased from 35 degrees C (polylactide) to -8 degrees C [poly(trimethylene carbonate)]. Among the lipases tested, the porcine pancreatic lipase and proteinase K showed biodegradability towards poly(ester-carbonate)s.     

High-efficient and synergetic antibacterial nanocomposite hydrogel with quaternized chitosan/Ag nanoparticles prepared by one-pot UV photochemical synthesis

Hydrogel dressings have significant advantages such as absorption of tissue exudate, maintenance of proper moist environment, and promotion of cell proliferation. However, facile preparation method and high-efficient antibacterial hydrogel dressings are still a great challenge. In this study, a facile approach to prepare antibacterial nanocomposite hydrogel dressing to accelerate healing was explored. The hydrogels consisted of quaternized chitosan and chemically cross-linked polyacrylamide, as well as silver nanoparticles (AgNPs) stabilized by chitosan. The synthesis of the hydrogels including the formation of AgNPs and polymerization of acrylamide was accomplished simultaneously under UV irradiation in 1 hour without adding initiator. The hydrogels showed favorable tensile strength of ∼100 kPa with elongation at break over 1000% and shear modulus of ∼10⁴ Pa as well as suitable swelling ratio, which were appropriate for wound dressing. The combination of quaternized chitosan and AgNPs exhibited high-efficient and synergetic antibacterial performance with low cytotoxicity. In vivo animal experiments showed that the hydrogel can effectively prevent wound infection and promote wound healing. This study provides a facile method to produce antibacterial hydrogel wound dressing materials.     

Controlled thermoresponsive hydrogels by stereocomplexed PLA-PEG-PLA prepared via hybrid micelles of pre-mixed copolymers with different PEG lengths

The stereocomplexed hydrogels derived from the micelle mixture of two enantiomeric triblock copolymers, PLLA-PEG-PLLA and PDLA-PEG-PDLA, reported in 2001 exhibited sol-to-gel transition at approximately body temperature upon heating. However, the showed poor storage modulus (ca. 1000 Pa) determined their insufficiency as injectable implant biomaterials for many applications. In this study, the mechanical property of these hydrogels was significantly improved by the modifications of molecular weights and micelle structure. Co-micelles composed of block copolymers with two sizes of PEG block length were shown to possess unique and dissimilar properties from the micelles composed of single-sized block copolymers. The stereomixture of PLA-PEG-PLA comicelles showed a controllable sol-to-gel transition at a wide temperature range of 4 and 80 °C. The sol-gel phase diagram displays a linear relationship of temperature versus copolymer composition; hence, a transition at body temperature can be readily achieved by adjusting the mixed copolymer ratio. The resulting thermoresponsive hydrogels exhibit a storage modulus notably higher (ca. 6000 Pa) than that of previously reported hydrogels. As a physical network solely governed by self-reorganization of micelles, followed by stereocomplexation, this unique system offers practical, safe, and simple implantable biomaterials.     

Reversible hydrogels from self-assembling genetically engineered protein block copolymers

A series of triblock protein copolymers composed of a central water-soluble polyelectrolyte segment flanked by two coiled-coil domains was synthesized by genetic engineering methods. The copolymers self-assembled into reversible hydrogels in response to changes in temperature, pH, and the presence or absence of denaturating agent (guanidine hydrochloride, GdnHCl). Hydrogel formation was concentration-dependent, and the concentration needed for hydrogel formation correlated with the oligomerization state of the coiled-coil domains in the protein copolymers. The morphology of the hydrogels, as determined by scanning electron microscopy (SEM), indicated the presence of porous interconnected networks. The thermal stabilities and self-assembling properties of the protein copolymers were successfully controlled by manipulating the amino acid sequences of the coiled-coil domains. The stimuli responsiveness and reversibility of the hydrogel self-assembly suggest that these protein copolymers may have potential in biomedical applications.     

Thermogelling aqueous solutions of alternating multiblock copolymers of poly(L-lactic acid) and poly(ethylene glycol)

We are reporting alternating multiblock copolymers of poly(L-lactic acid)/poly(ethylene glycol) aqueous solution (> 15 wt %) undergoing sol-gel-sol transition as the temperature increases from 20 to 60 degrees C. Micelles of the multiblock copolymers (in water) are about 20 nm in radius at low temperature. They are aggregated to a larger size as the temperature increases, which should play a critical role in the sol-to-gel transition. The transition temperature and gel window were affected by the molecular weight and composition of the multiblock copolymer. In particular, the aqueous solution of an alternating multiblock copolymer (Mn approximately 6700 daltons) prepared from poly(ethylene glycol) (Mn approximately 600 daltons) and poly(L-lactic acid) (Mn approximately 1300 daltons) showed a maximum modulus at body temperature (37 degrees C). The in situ gel forming ability of the polymer aqueous solution in vivo as well as in vitro indicates that it can be a promising injectable biomaterial.     

Biosynthesis and properties of medium-chain-length polyhydroxyalkanoates with enriched content of the dominant monomer

When grown in a nonanoic acid-limited chemostat at a dilution rate of 0.25 h(-1), Pseudomonas putida KT2440 produced poly(3-hydroxynonanoate-co-3-hydroxyheptanoate) containing 68 mol % 3-hydroxynonanoate (C9) and 32 mol % 3-hydroxyheptanoate (C7). Under the same conditions, but in the presence of acrylic acid, a fatty acid β-oxidation inhibitor, the C9 monomer content increased to 88 mol %. Cofeeding glucose (3.9 g L(-1)) and nonanoic acid (2.9 ± 0.1 g L(-1)) in continuous culture with 0.2 g L(-1) of acrylic acid in the feed, further increased the C9 content to 95 mol %. A yield of PHA from nonanoic acid of 0.93 mol mol(-1) was attained. PHA with a 3-hydroxyoctanoate (C8) content of 98 mol % was produced with the same cofeeding methodology from octanoic acid. As the dominant monomer content increased, the melting point of the poly(3-hydroxynonanoate) copolymers increased from 46 to 63 °C and that of the poly(3-hydroxyoctanoate) copolymers from 54 to 62 °C. All copolymer compositions resulted in elongation to break values of about 1300%, but tensile strength at break and Young's modulus both increased with increasing amounts of the dominant monomer.     

聚乳酸基热固性聚氨酯及其形状记忆性能

通过聚乳酸二元醇和聚乳酸-聚己内酯共聚物二元醇与六亚甲基二异氰酸酯(HDI)三聚体交联反应合成了一系列生物基热固性聚氨酯(Bio-PUs)。利用傅里叶红外(FTIR)、差示扫描量热分析(DSC)、热失重分析(TGA)、万能拉伸机和细胞毒性等测试方法对获得的聚乳酸基聚氨酯进行了表征。结果表明,与聚乳酸二元醇相比,聚乳酸-聚己内酯共聚物二元醇降低了生物基热固性聚氨酯的玻璃化温度(Tg),提高了热固性聚氨酯的热稳定性;且聚乳酸-聚己内酯型聚氨酯的力学性能和形状记忆性能更为优异。其中,聚乳酸-聚己内酯共聚物二元醇分子量为3 000时得到的热固性聚氨酯(Bio-PU2-3000)的杨氏模量为277.7 MPa,伸长率为230%;聚乳酸-聚己内酯共聚物二元醇分子量为1 000得到的热固性聚氨酯(Bio-PU2-1000)在人体体温下的形变回复时间仅为93 s。另外,通过显微镜观察到细胞在含聚乳酸基热固性聚氨酯的培养液中生长状态良好,表明制备得到的生物基聚氨酯无细胞毒性。     

Thermo-responsive PNiPAAm-g-PEG films for controlled cell detachment

A series of graft copolymers consisting of either poly(N-isopropylacrylamide) (PNiPAAm) or poly(N,N-diethylacrylamide) (PDEAAm) as a thermo-responsive component in the polymer backbone and poly(ethyleneglycol) (PEG) were immobilized as thin films and cross-linked on a fluoropolymer substrate using low-pressure argon plasma treatment. The surface-immobilized hydrogels exhibit a transition from partially collapsed to completely swollen, which is in the range of 32-35 degrees C and corresponds to the lower critical solution temperature of the soluble polymers. The hydrogels were used as cell carriers in culture experiments with L929 mouse fibroblast cells to probe for cell adhesion, proliferation, and temperature-dependent detachment of cell layers. The fibroblast cells adhere, spread, and proliferate on the hydrogel layers at 37 degrees C and become completely detached after reducing the temperature by 3 K. The cell release characteristics were further correlated to the swelling and collapsing behavior of the hydrogel films and the polymer solutions as measured in PBS solution and RPMI cell cultivation medium. It could be shown that, long before the swelling has completed upon temperature reduction, the cells detach. This can be attributed to the large content of PEG present in the hydrogel, which weaken the cell adhesion strength to the hydrogel layers.     

Collagen, collagenase and collagenolytic activity in rat Graafian follicles during follicular growth and ovulation

Follicles were dissected from the ovaries of immature rats at intervals after subcutaneous injection of 20 IU of pregnant mare's serum gonadotropin. A surge of luteinizing hormone was observed at 54 h and ovulation occurred at 64-66 h. The follicular volume between 36 and 48 h, then doubled again shortly before ovulation. The collagen content of the follicles increased 3-fold from 35 to 56 h, but decreased significantly (25%) from 61 to 66 h. Follicle homogenates, activated with trypsin or aminophenylmercuric acetate, digested Type I collagen at 28 degrees C to produce typical of a true collagenase. Collagenolytic activity assayed against endogenous collagen at 37 degrees C did not change significantly between 38 and 66 h.     

Thermally cross-linked oligo(poly(ethylene glycol) fumarate) hydrogels support osteogenic differentiation of encapsulated marrow stromal cells in vitro

A novel polymer, oligo(poly(ethylene glycol) fumarate) (OPF), cross-linked with a thermal radical initiation system has recently been developed in our laboratory as an injectable, biodegradable cell carrier for regeneration of orthopaedic tissues. The cross-linking, swelling, and degradative properties of hydrogels prepared from OPF with poly(ethylene glycol) of two different chain lengths were assessed. The two OPF types had similar gelation onset times ( approximately 3.6 min) but, when cross-linked for 8 min at 37 degrees C, exhibited significantly different swelling characteristics (fold swelling: 17.5 +/- 0.2 vs 13.4 +/- 0.4). Rat marrow stromal cells (MSCs) were then directly combined with the hydrogel precursors and encapsulated in a model OPF formulation at approximately 14 million cells/mL, cultured in vitro in the presence of osteogenic supplements (dexamethasone), and monitored over 28 days via histology. MSC differentiation in these samples (6 mm diameter x 0.5 mm thick before swelling), as determined by Von Kossa staining for calcified matrix, was apparent by day 21. At day 28, mineralized matrix could be seen throughout the samples, many microns away from the cells. These experiments strongly support the usefulness of thermally cross-linked OPF hydrogels as injectable cell carriers for bone regeneration.     

Functional characteristics of shrimp chitosan and its membranes as affected by the degree of deacetylation

The functional properties of three shrimp chitosan preparations with different degrees of deacetylation (75%, 87% and 96% DD) but with a constant molecular weight (about 810 kDa) were investigated. Chitosan with 75% DD had a 1.5 times higher water absorption, probably due to its 20% lower level of crystallinity. Membranes cast from this chitosan also exhibited 1.5 times more water absorption and 2 times higher permeability. However, chitosan with 87% and 96% DD had 1.5-2 times higher absorption of fat and the orange II dye. This is attributed to the higher content of positively charged amine groups in the polymer. Cast into membrane, chitosan of higher degree of deacetylation showed a higher tensile strength and a higher elongation at break, probably due to the higher level of crystallinity.     

Decellularization of porcine skeletal muscle extracellular matrix for the formulation of a matrix hydrogel: a preliminary study

Extracellular matrix (ECM) hydrogels are used as scaffolds to facilitate the repair and reconstruction of tissues. This study aimed to optimize the decellularization process of porcine skeletal muscle ECM and to formulate a matrix hydrogel scaffold. Five multi‐step methods (methods A–E) were used to generate acellular ECM from porcine skeletal muscle [rinsing in SDS, trypsin, ethylenediaminetetraacetic acid (EDTA), Triton X‐100 and/or sodium deoxycholate at 4–37°C]. The resulting ECM was evaluated using haematoxylin and eosin, 4‐6‐diamidino‐2‐phenylindole (DAPI) staining, and DNA quantification. Acellular matrix was dissolved in pepsin and gelled at 37°C. Hydrogel response to temperature was observed in vivo and in vitro. ECM components were assessed by Masson, Sirius red, and alcian blue staining, and total protein content. Acellular porcine skeletal muscle exhibited a uniform translucent white appearance. No intact nuclear residue was detected by haematoxylin and eosin staining, while DAPI staining showed a few nuclei in the matrixes produced by methods B, C, and D. Method A generated a gel that was too thin for gelation. However, the matrix obtained by rinsing in 0.2% trypsin/0.1% EDTA, 0.5% Triton X‐100, and 1% Triton X‐100/0.2% sodium deoxycholate was nuclei‐free and produced a viscous solution that formed a structurally stable white jelly‐like hydrogel. The residual DNA content of this solution was 49.37 ± 0.72 ng/mg, significantly less than in fresh skeletal muscle, and decreased to 19.22 ± 0.85 ng/mg after gelation (P < 0.05). The acellular matrix was rich in collagen and glycosaminoglycan, with a total protein concentration of 64.8 ± 6.9%. An acellular ECM hydrogel from porcine skeletal muscle was efficiently produced.     

Morphology and gelation of thermosensitive xyloglucan hydrogels

Galactose modified xyloglucan is a thermally reversible hydrogel that is increasingly used in the biomedical field due to the ease of altering the gelation time and temperature by modifying the galactose removal ratio. However there is little information concerning the morphology and rheological properties of the hydrogel under physiological conditions. Differential scanning microcalorimetry (DSmicroC) showed the thermal gelation process to occur over a broad temperature range (5-50 degrees C). The rheological properties of the hydrogels were investigated as a function of concentration, temperature and ionic strength. The final elastic moduli of the hydrogels increased with increases in concentration. Isothermal rheology suggests that the gelation occurred in two distinct stages, which was influenced by the solution media. Scanning electron microscopy (SEM) was used to characterize the morphology of the xyloglucan which were thermally gelled at 37 degrees C. The resultant morphology was strongly dependent on the concentration of the hydrogel. Strong hydrogels were only obtained at 3 wt.% at 37 degrees C, and the morphology characterized by an open 3-dimensional network, comprised of thin membranes. It is proposed that the first stage of the isothermal gelation is the formation and growth of the thin membranes, followed by the formation of a three dimensional network.     

Synthesis and characterization of thermally and chemically gelling injectable hydrogels for tissue engineering

Novel, injectable hydrogels were developed that solidify through a physical and chemical dual-gelation mechanism upon preparation and elevation of temperature to 37 °C. A thermogelling, poly(N-isopropylacrylamide)-based macromer with pendant epoxy rings and a hydrolytically degradable polyamidoamine-based diamine cross-linker were synthesized, characterized, and combined to produce in situ forming hydrogel constructs. Network formation through the epoxy-amine reaction was shown to be rapid and facile, and the progressive incorporation of the hydrophilic polyamidoamine cross-linker into the hydrogel was shown to mitigate the often problematic tendency of thermogelling materials to undergo significant postformation gel syneresis. The results suggest that this novel class of injectable hydrogels may be attractive substrates for tissue engineering applications due to the synthetic versatility of the component materials and beneficial hydrogel gelation kinetics and stability.