Michael-type addition as a tool for surface functionalization

Disproof of the Structures and Biosynthesis of Ergoynes, Gs-Polyyne-l-Ergothioneine Cycloadducts from Gynuella sunshinyii YC6258

Some bacteria produce "bacterial polyynes" bearing a conjugated C≡C bond that starts with a terminal alkyne. Ergoynes A and B have been reported as sulfur-containing metabolites from Gynuella sunshinyii YC6258. These compounds were thought to be formed by cycloaddition between a bacterial polyyne (named Gs-polyyne) and l-ergothioneine. The biosynthetic gene clusters (BGCs), which may contribute to their synthesis, were present in the YC6258 genome. The biosynthetic origin of Gs-polyyne is interesting considering its rare 2-isopentyl fatty acyl skeleton. Here, the structures and biosynthesis of Gs-polyyne and ergoynes were verified by analytical, chemical, and genetic techniques. In the YC6258 extract, which was prepared considering their instability, Gs-polyyne was detected as a major LC peak, and ergoynes were not detected. The NMR data of the isolated Gs-polyyne contradicted the proposed structure and identified it as the previously reported protegenin A. The expression of Gs-polyyne BGC in Escherichia coli BL21(DE3) also yielded protegenin A. The cyclization between protegenin A and l-ergothioneine did not proceed during sample preparation; a base, such as potassium carbonate, was required. Overall, Gs-polyyne was identified as protegenin A, while ergoynes were determined to be artifacts. This cyclization may provide a derivatization to stabilize polyynes or create new chemical space.

Covalent drugs based on small molecules and peptides for disease theranostics

Biomacromolecules, such as proteins, nucleic acids and polysaccharides, are widely distributed in the human body, and some of them have been recognized as the targets of drugs for disease theranostics. Drugs typically act on targets in two ways: non-covalent bond and covalent bond. Non-covalent bond-based drugs have some disadvantages, such as structural instability and environmental sensitivity. Covalent interactions between drugs and targets have a longer action time, higher affinity and controllability than non-covalent interactions of conventional drugs. With the development of artificial intelligence, covalent drugs have received more attention and have been developed rapidly in pharmaceutical research in recent years. From the perspective of covalent drugs, this review summarizes the design methods and the effects of covalent drugs. Finally, we discuss the application of covalent peptide drugs and expect to provide a new reference for cancer treatment.

Semi-Synthetic Click-Gelatin Hydrogels as Tunable Platforms for 3D Cancer Cell Culture

Basement membrane extracts (BME) derived from Engelbreth-Holm-Swarm (EHS) mouse sarcomas such as Matrigel^® remain the gold standard extracellular matrix (ECM) for three-dimensional (3D) cell culture in cancer research. Yet, BMEs suffer from substantial batch-to-batch variation, ill-defined composition, and lack the ability for physichochemical manipulation. Here, we developed a novel 3D cell culture system based on thiolated gelatin (Gel-SH), an inexpensive and highly controlled raw material capable of forming hydrogels with a high level of biophysical control and cell-instructive bioactivity. We demonstrate the successful thiolation of gelatin raw materials to enable rapid covalent crosslinking upon mixing with a synthetic poly(ethylene glycol) (PEG)-based crosslinker. The mechanical properties of the resulting gelatin-based hydrogels were readily tuned by varying precursor material concentrations, with Young's moduli ranging from ~2.5 to 5.8 kPa. All hydrogels of varying stiffnesses supported the viability and proliferation of MDA-MB-231 and MCF-7 breast cancer cell lines for 14 and 21 days of cell culture, respectively. Additionally, the gelatin-based hydrogels supported the growth, viability, and osteogenic differentiation of patient-derived preosteoblasts over 28 days of culture. Collectively, our data demonstrate that gelatin-based biomaterials provide an inexpensive and tunable 3D cell culture platform that may overcome the limitations of traditional BMEs.

Immunomodulatory PEG-CRGD Hydrogels Promote Chondrogenic Differentiation of PBMSCs

Cartilage damage is a common injury. Currently, tissue engineering scaffolds with composite seed cells have emerged as a promising approach for cartilage repair. Polyethylene glycol (PEG) hydrogels are attractive tissue engineering scaffold materials as they have high water absorption capacity as well as nontoxic and nutrient transport properties. However, PEG is fundamentally bio-inert and lacks intrinsic cell adhesion capability, which is critical for the maintenance of cell function. Cell adhesion peptides are usually added to improve the cell adhesion capability of PEG-based hydrogels. The suitable cell adhesion peptide can not only improve cell adhesion capability, but also promote chondrogenesis and regulate the immune microenvironment. To improve the interactions between cells and PEG hydrogels, we designed cysteine-arginine-glycine-aspartic acid (CRGD), a cell adhesion peptide covalently cross-linked with PEG hydrogels by a Michael addition reaction, and explored the tissue-engineering hydrogels with immunomodulatory effects and promoted chondrogenic differentiation of mesenchymal stem cells (MSCs). The results indicated that CRGD improved the interaction between peripheral blood mesenchymal stem cells (PBMSCs) and PEG hydrogels. PEG hydrogels modified with 1 mM CRGD had the optimal capacity to promote chondrogenic differentiation, and CRGD could induce macrophage polarization towards the M2 phenotype to promote tissue regeneration and repair. PEG-CRGD hydrogels combined with PBMSCs have the potential to be suitable scaffolds for cartilage tissue engineering.

The Incorporation of Low-Molecular Weight Poly(Mannitol Sebacate)s on PLA Electrospun Fibers: Effects on the Mechanical Properties and Surface Chemistry

We offer a report on the synthesis of low-molecular weight biobased poly(mannitol sebacate) (PMS) and its functionalization with acrylate groups (PMSAc). These synthesized polyesters were blended at a low level (10 wt%) with poly (lactic acid) PLA to prepare aligned fibers by electrospinning, coupled with a rotatory collector. The obtained fibers were extensively studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXS), employing synchrotron radiation. The incorporation of the PMSs on the PLA fibers did not significantly affect the fiber diameters, whereas the alignment was almost maintained. The crystallinity and thermal properties were also slightly modified with the addition of PMSs, and an increase in the degree of crystallinity and in the glass transition temperature of the blend compared to PLA was observed. Remarkably, the PLA/PMSs fibers were more ductile due to the elastomeric character of PMS, with higher values of elongation at break and tensile strengths, and a smaller Young modulus in comparison with the PLA fibers. These modifications of the properties were more noticeable in the case of the acrylated PMS, which also provided readily available functional groups at the surface for further chemical reactions, such as the Michael addition or crosslinking processes.

Thiol–ene coupling reaction achievement and monitoring by “in situ” UV irradiation NMR spectroscopy

In this study, the possibilities of a new “in situ” LED UV illumination NMR spectroscopic technique for performing an initiator-free thiol–ene “click” coupling reaction of an allyl-functionalized poly(allyl glycidyl ether) (PAGE) prepolymer with a number of mono- and di-oligo polyethylene glycol (PEG) thiols is demonstrated. The state-of-the-art setup constructed with LEDs as UV light sources that illuminate through optical fibers directly into an NMR testing tube at a fixed wavelength of 365 nm is appropriate for various polymeric materials and biologically active substances. The selected experimental protocol uses a series of periods of irradiation and dark periods, thus providing opportunities to conduct an effective thiol–ene “click” reaction and simultaneously study the kinetics of the photochemical reaction with the exposure time, as well as macromolecular association directly in a solution applying the whole types of NMR methods: from conventional ¹H or ¹³C NMR to diffusion NMR spectroscopy (DOSY). In addition, the molecular mass characteristics of the prepared copolymers were studied by gel-permeation chromatography (GPC). The observed differences in the reaction rates as well as in the size of species formed (the corresponding hydrodynamic radiuses R_h of aggregates) as a result of the coupling process of parent PAGE prepolymers and model PEG thiols were thoroughly discussed and the reaction pathway proposed.

An “In situ” LED UV illumination NMR setup for achievement of initiator-free coupling reactions of allyl-functionalized poly(allyl glycidyl ether) with polyethylene glycols thiols.

Surface modification of model hydrogel contact lenses with hyaluronic acid via thiol-ene "click" chemistry for enhancing surface characteristics

Discontinuation of contact lens wear as a result of ocular dryness and discomfort is extremely common; as many as 26% of contact lens wearers discontinue use within the first year. While patients are generally satisfied with conventional hydrogel lenses, improving on-eye comfort continues to remain a goal. Surface modification with a biomimetic, ocular friendly hydrophilic layer of a wetting agent is hypothesized to improve the interfacial interactions of the contact lens with the ocular surface. In this work, the synthesis and characterization of poly(2-hydroxyethyl methacrylate) surfaces grafted with a hydrophilic layer of hyaluronic acid are described. The immobilization reaction involved the covalent attachment of thiolated hyaluronic acid (20 kDa) on acrylated poly(2-hydroxyethyl methacrylate) via nucleophile-initiated Michael addition thiol-ene "click" chemistry. The surface chemistry of the modified surfaces was analyzed by Fourier transform infrared spectroscopy-attenuated total reflectance and X-ray photoelectron spectroscopy. The appearance of N (1s) and S (2p) peaks on the low resolution X-ray photoelectron spectroscopy spectra confirmed successful immobilization of hyaluronic acid. Grafting hyaluronic acid to the poly(2-hydroxyethyl methacrylate) surfaces decreased the contact angle, the dehydration rate, and the amount of nonspecific sorption of lysozyme and albumin in comparison to pristine hydrogel materials, suggesting the development of more wettable surfaces with improved water-retentive and antifouling properties, while maintaining optical transparency (>92%). In vitro testing also showed excellent viability of human corneal epithelial cells with the hyaluronic acid-grafted poly(2-hydroxyethyl methacrylate) surfaces. Hence, surface modification with hyaluronic acid via thiol-ene "click" chemistry could be useful in improving contact lens surface properties, potentially alleviating symptoms of contact lens related dryness and discomfort during wear.

An antibody fragment functionalized dendritic PEGylated poly(2-(dimethylamino)ethyl diacrylate) as a vehicle of exogenous microRNA

The translation of interfering RNA to the clinic requires more effective delivery agents to enable safe and efficient delivery. The aim of this work was to create a multi-functional delivery agent using deactivation enhanced ATRP synthesis of poly(dimethylamino)ethyl methacrylate (pDMAEMA)-co-PEGMEA/PEGDA (pD-b-P/DA) with linear pDMAEMA as a macro-initiator. The pD-b-P/DA was characterized for its potential to bind synthetic microRNA mimics to form structures and reacted with antibody-derived fragments (Fabs) using Michael-type addition. Conjugation of antibody fragments was verified using SDS-PAGE. Functional delivery of these interfering RNA complexes was proven using a dual luciferase reporter assay. Functional silencing of a reporter gene was improved by complexation of microRNA mimics with pD-b-P/DA alone and with Fab-decorated pD-b-P/DA. The improved silencing with Fab-decorated pD-b-P/DA was evident at 48 h but disappeared at 96 h. The resultant agent enables complexation of nucleic acid (microRNA mimic) and facile conjugation of antibody fragments via a Michael-type addition. In conclusion, this platform is effective at silencing in this reporter system and has potential as an effective delivery system of interfering RNA.

Biomimetic materials for medical application through enzymatic modification

Living organisms synthesize functional materials, based on proteins and polysaccharides, using enzyme-catalyzed reactions. According to the biomimetic approach, biomaterial matrices for tissue engineering are designed to be able to mimic the properties and the functions of the extracellular matrix (ECM). In this chapter, the most significant research efforts dedicated to the study and the preparation of biomimetic materials through enzymatic modifications were reviewed. The functionalizations of different polymeric matrices obtained through the catalytic activity of two enzymes (Transglutaminase, TGase and Tyrosinase, TYRase) were discussed. Specifically, the biomimetic applications of TGase and TYRase to confer appropriate biomimetic properties to the biomaterials, such as the possibility to obtain in situ gelling hydrogels and the incorporation of bioactive molecules (growth factors) and cell-binding peptides into the scaffolds, were reviewed.

In vitro and in vivo demonstration of physically and chemically in situ gelling NIPAAm-based copolymer system

Poly(NIPAAm-co-hydroxyethylmethacarylate (HEMA)) acrylate and poly(NIPAAm-co-cysteine ethyl ester (CysOEt)) were synthesized and characterized by GPC(gel permeation chromatography), rheology, NMR (nuclear magnetic resonance), and Ellman's method. Upon mixing of these materials in aqueous solution, they formed gels immediately at body temperature owing to temperature-driven physical gelling, and gradually cured by chemical cross-linking through Michael-type addition reactions between thiols and acrylates. The rate of nucleophilic attack in the Michael-type addition reaction was shown to be highly dependent on the mole ratio of thiol to acrylate at neutral pH. Physical and chemical gelation improved the mechanical properties of the materials compared to purely physical gels. In vitro and in vivo results revealed that chemical and physical gels formed stiffer less viscoelastic materials compared to purely physical gels. Physical and chemical gel systems using thermosensitive polymer with acrylates and thermosensitive polymer with thiols showed minimum toxicity.

A fluorogenic monolayer to detect the co-immobilization of peptides that combine cartilage targeting and regeneration

Strategies to generate platforms combining tissue targeting and regeneration properties are in great demand in the regenerative medicine field. Here we employ an approach to directly visualize the immobilization of cysteine-terminated peptides on a novel fluorogenic surface. Peptides with relevant biological properties, CLPLGNSH and CLRGRYW, were synthesized to function as peptide binders to transforming growth factor (TGF)-β1 and collagen type II (CII). The selective immobilization of the peptides was directly detected using a fluorogenic surface. Adhered proteins were confined to patterns of these peptides matching with the fluorogenic areas. These results show that the fluorogenic signal can be used to detect the chemo-selective immobilization of non-fluorescent biomolecules and to correlate the cell response with the patterned peptides. After analyzing the sequence specificity and cross-reactivity of the binding of TGF-β1 and CII to the respective peptide regions employing immunofluorescence assays, both peptides were co-immobilized in a step-wise process as detected by the fluorogenic surface. TGF-β1 and CII could be self-sorted from a mixture in a regio-selective manner resulting in a bi-functional protein platform. Surfaces of CLPLGNSH pre-loaded with TGF-β1 showed excellent bioactivity in combination with human articular chondrocytes (HACs) and stimulated expression of chondrogenic markers.

Polymer-peptide block copolymers - an overview and assessment of synthesis methods

Incorporating peptide blocks into block copolymers opens up new realms of bioactive or smart materials. Because there are such a variety of peptides, polymers, and hybrid architectures that can be imagined, there are many different routes available for the synthesis of these chimera molecules. This review summarizes the contemporary strategies in combining synthesis techniques to create well-defined peptide-polymer hybrids that retain the vital aspects of each disparate block. Living polymerization can be united with the molecular-level control afforded by peptide blocks to yield block copolymers that not only have precisely defined primary structures, but that also interact with other (bio)molecules in a well defined manner.

Synthesis, Characterization and Cleavage of Linear Polymers Attached to Silica Nanoparticles Formed Using Thiol-acrylate Conjugate Addition Reactions

This study investigates the formation of linear polymer grafts using thiol-acrylate conjugate addition reactions on nanoparticle surfaces. Silica nanoparticles were first modified with an amine functionality, followed by the attachment of a photocleavable acrylate. Dithiol-diacrylate films were attached to the particles through the surface acrylate groups at various stoichiometric ratios of thiol to acrylate by conducting amine-catalyzed conjugate addition polymerizations. The particles were then exposed to UV light to release the grafted polymer by photocleavage. The cleaved, grafted polymers were analyzed using infrared spectroscopy (IR) and gel permeation chromatography (GPC) and compared to polymers formed in the bulk, which remained unattached to the particles. The measured number and weight average molecular weights were similar for both polymer types within experimental error and increased from 2000 to 5000 g/mol and 4000 to 10000 g/mol, respectively, as the ratio of limiting to excess functionality increased from 0.8 to 1. Both number and weight average molecular weights followed the trend of step growth polymers with the highest molecular weight achieved for stoichiometric monomeric mixtures. Surface coverage of the nanoparticles was estimated using the molecular weight and thermogravimetric data and was found to be uniform ( approximately 0.15chains/nm(2)) irrespective of the stoichiometry of the reacting monomers.

Peptide/protein-polymer conjugates: synthetic strategies and design concepts

This feature article provides a compilation of tools available for preparing well-defined peptide/protein-polymer conjugates, which are defined as hybrid constructs combining (i) a defined number of peptide/protein segments with uniform chain lengths and defined monomer sequences (primary structure) with (ii) a defined number of synthetic polymer chains. The first section describes methods for post-translational, or direct, introduction of chemoselective handles onto natural or synthetic peptides/proteins. Addressed topics include the residue- and/or site-specific modification of peptides/proteins at Arg, Asp, Cys, Gln, Glu, Gly, His, Lys, Met, Phe, Ser, Thr, Trp, Tyr and Val residues and methods for producing peptides/proteins containing non-canonical amino acids by peptide synthesis and protein engineering. In the second section, methods for introducing chemoselective groups onto the side-chain or chain-end of synthetic polymers produced by radical, anionic, cationic, metathesis and ring-opening polymerization are described. The final section discusses convergent and divergent strategies for covalently assembling polymers and peptides/proteins. An overview of the use of chemoselective reactions such as Heck, Sonogashira and Suzuki coupling, Diels-Alder cycloaddition, Click chemistry, Staudinger ligation, Michael's addition, reductive alkylation and oxime/hydrazone chemistry for the convergent synthesis of peptide/protein-polymer conjugates is given. Divergent approaches for preparing peptide/protein-polymer conjugates which are discussed include peptide synthesis from synthetic polymer supports, polymerization from peptide/protein macroinitiators or chain transfer agents and the polymerization of peptide side-chain monomers.

Improvement of dispersion stability and characterization of upconversion nanophosphors covalently modified with PEG as a fluorescence bioimaging probe

Upconverting (UC) phosphors (UCPs) are ceramic materials doped with rare earth ions. These materials can absorb and upconvert infrared (IR) radiation to emit visible light by the stepwise excitation among discrete energy levels of the rare earth ions. UCPs are potentially useful reagents for use in bioimaging since the use of low energy photons avoids photo-toxicity. The use of UCP nanoparticles as bioimaging probes requires surface modifications in an effort to improve dispersion stability in aqueous milieu. In this study, we covalently attached poly(ethylene glycol) (PEG) to the surface of Er-doped Y₂O₃ nanoparticles and firstly demonstrated that PEG covalently bound to the Y₂O₃ surface markedly improved dispersion stability in water. UC emission of PEG-modified Er-Y₂O₃ nanoparticles excited with IR light was successfully observed. We also showed that PEG-modified Er-Y₂O₃ nanoparticles exhibit no cell-toxicity. These observations lend strong support to the potential use of PEG-modified UCP nanoparticles as bioimaging tools.

Synthesis and characterization ofin situ chitosan-based hydrogel via grafting of carboxyethyl acrylate

We developed and characterized a novel in situ chitosan-poly(ethylene oxide) (PEO) hydrogel via two steps: 2-carboxyethyl acrylate molecules were grafted to the primary amine functional groups in chitosan in the first step and then Michael type addition reaction was processed between the grafted acrylate end groups and the thiol end groups in the PEO. Grafting of acrylate molecules to the amine groups in the deacetylated water soluble chitosan was confirmed by observing the new acrylate peaks by the FTIR and NMR spectra of the acrylated chitosan samples, as well as changes in relative viscosities of chitosan and acrylated chitosan. Formation of the chitosan-PEO hydrogel was visually observed with digital images after both gelation and hydration. Rheological analyses of the hydrogel formation were performed to detect its gelation time, phase angle changes, and visco-elastic properties over frequency and strain percentage. Their results indicated that the gelation process was completed within 10 min after mixing the precursor liquid solutions. An extent of water swelling, mechanical strength against compression and the morphologies of the hydrogel surface and cross sections after dehydration process were analyzed by microbalance measurement, texture analyzer, and scanning electron microscopy observation, respectively. Biological activities of the hydrogels were evaluated by observing smooth muscle cell behaviors such as cell adhesion and viability as well as by measuring the number of adhered cells on their surfaces.

Simultaneously physically and chemically gelling polymer system utilizing a poly(NIPAAm-co-cysteamine)-based copolymer

The objective of this work was to create an in situ physically and chemically cross-linking hydrogel for in vivo applications. N-Isopropylacrylamide (NIPAAm) was copolymerized with N-acryloxysuccinimide (NASI) via free radical polymerization. Poly(NIPAAm-co-NASI) was further modified to obtain poly(NIPAAm-co-cysteamine) through a nucleophilic attack on the carbonyl group of the NASI by the amine group of the cysteamine. Modification was verified by nuclear magnetic resonance. In addition to thermoresponsive physical gelling due to the presence of NIPAAm, this system also chemically gels via a Michael-type addition reaction when mixed with poly(ethylene glycol) diacrylate. The presence of both physical and chemical gelation resulted in material properties that are much improved compared to purely physical gels. The chemical gelation time of the copolymers was not significantly affected by the amount of thiol present due to the increased pKa of the copolymer containing more thiols. In addition, the swelling of the copolymers was highly dependent on the temperature and thiol content. Last, the rate of nucleophilic attack in the Michael-type addition reaction was shown to be highly dependent on pH and on the mole ratio of thiol to acrylate. Due to the improved mechanical properties, this material may be better suited for long-term functional replacement applications than other thermosensitive physical gels. With further development and biocompatibility testing, this material could potentially be applied as a temperature-responsive injectable biomaterial for functional embolization.

Enhanced osteoblast‐like cell adhesion and proliferation using sulfonate‐bearing polymeric scaffolds

Orthopedic malfunction, degeneration, or damage remains a serious healthcare issue despite advances in medical technology. Proactive extracellular matrix (ECM)-mimetic scaffolds are being researched to orchestrate the activation of diverse osteogenic signaling cascades, facilitating osteointegration. We hypothesized that sulfonated functionalities incorporated into synthetic hydrogels would simulate anionic, sulfate-bearing proteoglycans, abundant in the ECM. Using this rationale, we successfully developed differentially sulfonated hydrogels, polymerizing a range of sulfopropyl acrylate potassium-acrylamide (SPAK-AM) mole ratios as monomer feeds under room temperature conditions. For anchorage-dependent cells, such as osteoblasts, adhesion is a critical prerequisite for subsequent osteointegration and cell specialization. The introduction of the sulfonated monomer, SPAK, resulted in favorable uptake of serum proteins with proportional increase in adhesion and proliferation rates of model cell lines, which included NIH/3T3 fibroblasts, MG-63 osteoblasts, and MC3T3-E1 subclone 4 preosteoblasts. In fact, higher proportions of sulfonate content (pSPAK75, pSPAK100) exhibited comparable or even higher degrees of adhesion and proliferation, relative to commercial grade tissue culture polystyrene in vitro. These results indicate promising potentials of sulfonated ECM-mimetic hydrogels as potential osteogenic tissue engineering scaffolds.

A Reactive Poly(ethylene glycol) Layer To Achieve Specific Surface Plasmon Resonance Sensing with a High S/N Ratio: The Substantial Role of a Short Underbrushed PEG Layer in Minimizing Nonspecific Adsorption

A reactive poly(ethylene glycol) (PEG)-brushed layer was constructed on a surface plasmon resonance (SPR) sensor chip using a heterobifunctional PEG possessing an acetal group at one end and a mercapto group at the other end (alpha-acetal-omega-mercapto-PEG). The density of the PEG brushed layer substantially increased with repetitive adsorption/rinse cycles of the PEG on the sensor chip, allowing dramatic reduction of nonspecific protein adsorption. Notably, formation of a short, filler layer of PEG (2 kDa) in the preconstructed longer PEG brushed layer (5 kDa) achieved almost complete prevention of nonspecific protein adsorption. The acetal group located at the distal end of the tethered PEG was converted to an aldehyde group by the acid treatment, followed by the installation of biocytin hydrazide through Schiff base formation. SPR sensing of streptavidin was done with a very high S/N ratio even in a proteinous medium using the biotinylated PEG (5 kDa) tethered chip with an inert filler layer of short PEG (2 kDa). Furthermore, the specific affinity of streptavidin for the biotinylated PEG was highly influenced by the length of the filler PEG and was significantly reduced when the length of the filler PEG was longer than that of the biotinylated PEG. This result clearly revealed the substantial importance of the steric factor on biospecific interaction at the distal end of tethered PEG on the sensor surface.

Network Formation and Degradation Behavior of Hydrogels Formed by Michael-Type Addition Reactions

Hydrolytically labile poly(ethylene glycol)-based hydrogels are fabricated via a Michael-type addition reaction between unsaturated acrylate moieties and nucleophilic thiols. Although these gels offer the advantage of selective, in situ polymerization and potential as biocompatible matrixes for cell and protein encapsulation, a thorough understanding of the complex structure-property relationships that control the macroscopic behaviors of these cross-linked networks before and during hydrolytic degradation does not exist. Therefore, in this work, a novel theoretical model is presented to describe the formation and hydrolytic degradation of the step-polymerized gels. The model accounts for variations in hydrolysis kinetics as well as structural effects such as precursor functionality and the presence of primary cycles or other structural nonidealities that lower the cross-linking efficiency of the networks. Comparison of model predictions and experimental data validate this methodology for optimizing biomaterial design and reveal that structural nonidealities play a key role in determining the degradation behavior of real cross-linked systems. Decreasing precursor concentration and functionality during network formation generate high concentrations of network nonidealities that ultimately lead to higher initial swelling ratios and faster apparent rates of degradation.

Versatile functionalization and grafting of poly(ε-caprolactone) by Michael-type addition

The Michael-type addition of aliphatic (co)polyesters onto gamma-acryloyloxy epsilon-caprolactone units is a very straightforward technique of functionalization and grafting, which is tolerant to a variety of functional groups and does not require intermediate protection/deprotection steps.