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Islet transplantation is a promising curative treatment option for type 1 diabetes (T1D) as it can provide physiological blood glucose control. The widespread utilization of islet transplantation is limited due to systemic immunosuppression requirements, persisting graft immunodestruction, and poor islet engraftment. Traditional macro- and micropolymeric encapsulation strategies can alleviate the need for antirejection immunosuppression, yet the increased graft volume and diffusional distances imparted by these coatings can be detrimental to graft viability and glucose control. Additionally, systemic administration of pro-engraftment and antirejection therapeutics leaves patients vulnerable to adverse off-target side effects. Nanoscale engineering techniques can be used to immunocamouflage islets, modulate the transplant microenvironment, and provide localized pro-engraftment cues. In this review, we discuss the applications of nanotechnology to advance the clinical potential of islet transplantation, with a focus on cell surface engineering, bioactive functionalization, and use of nanoparticles in T1D cell-based treatments.

Solubilization of membrane proteins by poly(styrene-co-maleic acid) salts (pSMA-S) has significant potential for membrane protein studies. This approach provides an opportunity to overcome many disadvantages associated with a traditional detergent-based technique including protein denaturation and displacement of boundary lipids which may offer both structural and functional stability to membrane proteins. Thylakoid membranes (TMs) from photosynthetic organisms are well studied protein-rich membranes that host several multi-subunit protein complexes associated with oxygenic photosynthesis. These protein complexes are important for applied photosynthesis and by being extracted and purified they can be used in the near future for direct energy conversion. In this study, we used spinach TMs isolated from purified intact chloroplasts to systematically test the solubilization efficacy of 12 commercially available styrene-maleic acid (SMA) copolymers that vary in size, styrene-to-maleic acid molar ratio, and type of ester group. The efficacy of these pSMA-S to solubilize protein-containing biomembranes was evaluated via quantification of protein and chlorophyll content in the resulting SMA Lipid Particles (SMALPs). In addition, the extracted polymer-lipid-protein complexes were studied by low temperature fluorescence, sodium dodecyl sulfate and clear native polyacrylamide gel electrophoresis (SDS- and CN-PAGE), and immunoblot analysis. Our results indicate considerable variability in the solubilization efficacy of commercially available pSMA-S with at least 5 polymer formulations being able to efficiently extract membrane proteins from TMs. These 5 SMA copolymers may also be effective in extraction of membrane proteins from other biomembranes.

Imbalance of oxidants is a universal contributor to the failure of implanted devices and tissues. A sustained oxidative environment leads to cytotoxicity, prolonged inflammation, and ultimately host rejection of implanted devices/grafts. The incorporation of antioxidant materials can inhibit this redox/inflammatory cycle and enhance implant efficacy. Cerium oxide nanoparticles (CONP) is a highly promising agent that exhibits potent, ubiquitous, and self-renewable antioxidant properties. Integrating CONP as surface coatings provides ease in translating antioxidant properties to various implants/grafts. Herein, we describe the formation of CONP coatings, generated via the sequential deposition of CONP and alginate, and the impact of coating properties, pH, and polymer molecular weight, on their resulting redox profile. Investigation of CONP deposition, layer formation, and coating uniformity/thickness on their resulting oxidant scavenging activity identified key parameters for customizing global antioxidant properties. Results found lower molecular weight alginates and physiological pH shift CONP activity to a higher H(2)O(2) to O(2)(−)-scavenging capability. The antioxidant properties measured for these various coatings translated to distinct antioxidant protection to the underlying encapsulated cells. Information gained from this work can be leveraged to tailor coatings towards specific oxidant-scavenging applications and prolong the function of medical devices and cellular implants.

Islet cell transplantation can lead to insulin independence, reduced hypoglycemia, and amelioration of diabetes complications in patients with type 1 diabetes. The systemic delivery of anti-inflammatory agents, while considered crucial to limit the early loss of islets associated with intrahepatic infusion, increases the burden of immunosuppression. In an effort to decrease the pharmaceutical load to the patient, we modified the pancreatic islet surface with long-chain poly(ethylene glycol) (PEG) to mitigate detrimental host-implant interactions. The effect of PEGylation on islet engraftment and long-term survival was examined in a robust nonhuman primate model via three paired transplants of dosages 4300, 8300, and 10 000 islet equivalents per kg body weight. A reduced immunosuppressive regimen of anti-thymocyte globulin induction plus tacrolimus in the first posttransplant month followed by maintenance with sirolimus monotherapy was employed. To limit transplant variability, two of the three pairs were closely MHC-matched recipients and received MHC-disparate PEGylated or untreated islets isolated from the same donors. Recipients of PEGylated islets exhibited significantly improved early c-peptide levels, reduced exogenous insulin requirements, and superior glycemic control, as compared to recipients of untreated islets. These results indicate that this simple islet modification procedure may improve islet engraftment and survival in the setting of reduced immunosuppression.

For type 1 diabetics, islet transplantation can induce beneficial outcomes, including insulin independence and improved glycemic control. The long-term function of the grafted tissue, however, is challenged by host inflammatory and immune responses. Cell encapsulation can decrease detrimental host responses to the foreign implant, but standard microencapsulation imparts large transplant volumes and impaired metabolite and nutrient diffusion. To mitigate these effects, we developed an efficient covalent Layer-by-Layer (cLbL) approach for live-cell nanoencapsulation, based on oppositely charged hyperbranched polymers functionalized with complementary Staudinger ligation groups. Reliance on cationic polymers for cLbL, however, is problematic due to their poor biocompatibility. Herein, we incorporated the additional feature of supramolecular self-assembly of the dendritic polymers to enhance layer uniformity and decrease net polymer charge. Functionalization of poly (amino amide) (PAMAM) with triethoxysilane decreased polymer charge without compromising the uniformity and stability of resulting nanoscale islet coatings. Encapsulated pancreatic rat islets were viable and functional. The implantation of cLbL islets into diabetic mice resulted in stable normoglycemia, at equivalent dosage and efficiency as uncoated islets, with no observable alterations in cellular engraftment or foreign body responses. By balancing multi-functionality and self-assembly, nano-scale and stable covalent layer-by-layer polymeric coatings could be efficiently generated onto cellular organoids, presenting a highly adaptable platform for broad use in cellular transplantation.

The microencapsulation of cells has shown promise as a therapeutic vehicle for the treatment of a wide variety of diseases. While alginate microcapsules provide an ideal cell encapsulation material, polycations coatings are commonly employed to enhance stability and impart permselectivity. In this study, functionalized hyperbranched alginate and dendrimer polymers were used to generate discreet nanoscale coatings onto alginate microbeads via covalent layer-by-layer assembly. The bioorthogonal Staudinger ligation scheme was used to chemoselectively crosslink azide functionalized hyperbranched alginate (alginate-hN3) to methyl-2-diphenylphosphino-terephthalate (MDT) linked PAMAM dendrimer (PAMAM-MDT). Covalent layer-by-layer deposition of PAMAM-MDT/alginate-hN3 coatings onto alginate microbeads resulted in highly stable coatings, even after the inner alginate gel was liquefied to form microcapsules. The permselectivity of the coated microcapsules could be manipulated via the charge density of the PAMAM, the number of layers deposited, and the length of the functional arms. The cytocompatibility of the resulting PAMAM-MDT/alginate-hN3 coating was evaluated using a beta cell line, with no significant detrimental response observed. The biocompatibility of the coatings in vivo was also found comparable to uncoated alginate beads. The remarkable stability and versatile nature of these coatings provides an appealing option for bioencapsulation and the release of therapeutic agents.

In type 1 diabetes, the replacement of the destroyed beta cells could restore physiological glucose regulation and eliminate the need for exogenous insulin. Immunoisolation of these foreign cellular transplants via biomaterial encapsulation is widely used to prevent graft rejection. While highly effective in blocking direct cell-to-cell contact, non-specific inflammatory reactions to the implant lead to the overproduction of reactive oxygen species (ROS), which contribute to foreign body reaction and encapsulated cell loss. For antioxidant protection, cerium oxide nanoparticles (CONP) are a self-renewable, ubiquitous, free radical scavenger currently explored in several biomedical applications. Herein, 2 to 12 alternating layers of CONP/alginate were assembled onto alginate microbeads containing beta cells using a layer-by-layer (LbL) technique. The resulting nano-composite coatings demonstrated robust antioxidant activity. The degree of cytoprotection correlated with layer number, indicating tunable antioxidant protection. Coating of alginate beads with 12-layers of CONP/alginate provided complete protection to the entrapped beta cells from exposure to 100 μM H(2)O(2), with no significant changes in metabolic activity, oxidant capacity, or insulin secretion dynamics, when compared to untreated controls. The flexibility of this LbL method, as well as its nano-scale profile, provides a versatile approach for imparting antioxidant protection to numerous biomedical implants, including beta cell transplantation.

The encapsulation of viable tissues via layer-by-layer polymer assembly provides a versatile platform for cell surface engineering, with nanoscale control over capsule properties. Herein, we report the development of a hyperbranched polymer-based, ultrathin capsule architecture expressing bioorthogonal functionality and tailored physiochemical properties. Random carbodiimide-based condensation of 3,5-dicarboxyphenyl glycineamide on alginate yielded a highly branched polysaccharide with multiple, spatially restricted, and readily functionalizable terminal carboxylate moieties. Poly(ethylene glycol) (PEG) was utilized to link azido end groups to the structured alginate. Together with phosphine functionalized poly(amido amine) (PAMAM) dendrimer, nanoscale layer-by-layer coatings, covalently stabilized via Staudinger ligation, were assembled onto solid surfaces and pancreatic islets. The effects of electrostatic and/or bioorthogonal covalent interlayer interactions on the resulting coating efficiency and stability, as well as pancreatic islet viability and function, were studied. These hyperbranched polymers provide a flexible platform for the formation of covalently stabilized ultrathin coatings on viable cells and tissues. In addition, the hyperbranched nature of the polymers presents a highly functionalized surface capable of bioorthogonal conjugation of additional bioactive or labeling motifs.

Islet transplantation is a promising therapy for Type 1 diabetes mellitus; however, host inflammatory and immune responses lead to islet dysfunction and destruction, despite potent systemic immunosuppression. Grafting of poly(ethylene glycol) (PEG) to the periphery of cells or tissues can mitigate inflammation and immune recognition via generation of a steric barrier. Herein, we sought to evaluate the complementary impact of islet PEGylation with a short-course immunotherapy on the survival of fully-MHC mismatched islet allografts (DBA/2 islets into diabetic C57BL/6J recipients). Anti-Lymphocyte Function-associated Antigen 1 (LFA-1) antibody was selected as a complementary, transient, systemic immune monotherapy. Islets were PEGylated via an optimized protocol, with resulting islets exhibiting robust cell viability and function. Following transplantation, a significant subset of diabetic animals receiving PEGylated islets (60%) or anti-LFA-1 antibody (50%) exhibited long-term (>100 d) normoglycemia. The combinatorial approach proved synergistic, with 78% of the grafts exhibiting euglycemia long-term. Additional studies examining graft cellular infiltrates at early time points characterized the local impact of the transplant protocol on graft survival. Results illustrate the capacity of a simple polymer grafting approach to impart significant immunoprotective effects via modulation of the local transplant environment, while short-term immunotherapy serves to complement this effect. Statement of Significance We believe this study is important and of interest to the biomaterials and transplant community for several reasons: 1) it provides an optimized protocol for the PEGylation of islets, with minimal impact on the coated islets, which can be easily translated for clinical applications; 2) this optimized protocol demonstrates the benefits of islet PEGylation in providing modest immunosuppression in a murine model; 3) this work demonstrates the combinatory impact of PEGylation with short-course immunotherapy (via LFA-1 blockage), illustrating the capacity of PEGylation to complement existing immunotherapy; and 4) it suggests macrophage phenotype shifting as the potential mechanism for this observed benefit.

Functionalized alginate and poly(ethylene glycol) (PEG) polymers were used to generate covalently linked alginate–PEG (XAlgPEG) microbeads of high stability. The cell-compatible Staudinger ligation scheme was used to cross-link phosphine-terminated PEG chemoselectively to azide-functionalized alginate, resulting in XAlgPEG hydrogels. XAlgPEG microbeads were formed by co-incubation of the two polymers, followed by ionic cross-linking of the alginate using barium ions. The enhanced stability and gel properties of the resulting XAlgPEG microbeads, as well as the compatibility of these polymers for the encapsulation of islets and beta cells lines, were investigated. The data show that XAlgPEG microbeads exhibit superior resistance to osmotic swelling compared with traditional barium cross-linked alginate (Ba–Alg) beads, with a five-fold reduction in observed swelling, as well as resistance to dissolution via chelation solution. Diffusion and porosity studies found XAlgPEG beads to exhibit properties comparable with standard Ba–Alg. XAlgPEG microbeads were found to be highly cell compatible with insulinoma cell lines, as well as rat and human pancreatic islets, where the viability and functional assessment of cells within XAlgPEG are comparable with Ba–Alg controls. The remarkable improved stability, as well as demonstrated cellular compatibility, of XAlgPEG hydrogels makes them an appealing option for a wide variety of tissue engineering applications.

Microgels were prepared within reverse micelles via photocrosslinking. Gelation resulted from the [2 + 2] photodimerization reaction of nitrocinnamoyl (NC) groups on multi-arm polyethylene glycol (PEG) or gelatin. Because of the potential for biomedical and chemical applications, immobilization capacity within the microgels was investigated. Quantum dots (QDs), for example, share a similar size scale with proteins and can be physically trapped within the microgels. In addition, the optoelectronic properties of QDs could be utilized for analytical, imaging, and therapeutic purposes. Small molecules and recognition sequences (e.g. biotin) can also be covalently immobilized within the microgel networks through the photodimerization reaction. In the presence of biotin-PEG-NC, the resulting microgels added to streptavidin-coated plates. The microgel properties such as biodegradability and degree of swelling may be engineered for particular applications including targeted monitoring and controlled drug delivery systems.

Trioctylphosphine oxide (TOPO) capped CdSe and (CdSe)ZnS quantum dots (QDs) were prepared. The surface chemistry behavior of both QDs at the air–water interface was carefully examined by various physical measurements. Stable Langmuir films were formed for both QDs. The average limiting nanoparticle area derived from the π – A isotherms of the QDs could be used to estimate the average size of the QDs if the thickness of TOPO shell was counted. The epifluorescence image of the QDs Langmuir films revealed an aggregation in 2D during the early stage of the compression process. On the other hand, a diacetylene-peptide (PDA-Cys-Cys-Gly-OH) derivative, namely PDA-CCG, was used to modify the surface of QDs. This modification resulted in a robust and homogeneous Langmuir film, which is photopolymerizable and contains active binding sites for the binding of biomolecules.

The surface of 4.1 nm CdSe/ZnS, core/shell, quantum dots was stabilized with cysteine (Cys) or thioglycolic acid (TGA) ligands. Electrostatic interactions between the polyanionic quantum dots (QDs) and positively charged toluidine blue were studied by UV–vis absorption spectroscopy and Forster resonance energy transfer. The surface net charge on the QDs highly correlated with the dye's degree of metachromasia, which served as a direct and convenient surface electrostatic probe for negatively-charged nanoparticles.

Langmuir film properties, UV-vis spectroscopy, epifluorescence microscopy, and transmission electron microscopy were used to study CdSe quantum dots (QDs) in 2D. By combining these results, it was possible to determine the molar absorptivity, limiting nanoparticle area, luminescence property, and arrangement of the QDs in the monolayer films at the air-water interface. Either trioctylphosphine oxide (TOPO) or 1-octadecanethiol (ODT) stabilized the QDs. The data collected reveal that TOPO forms close-packed monolayers on the surface of the QDs and that ODT-stabilized QDs undergo alkyl chains interdigitation. It was also found that varying the nanoparticle size, nature of surfactant, surface pressure, and mixed monolayers could help engineer the 2D self-assembly of the QDs at the air-water interface. Of practical importance is the transfer of these monolayer films onto hydrophilic or hydrophobic solid substrates, which could be successfully accomplished via the Langmuir-Blodgett film deposition technique.

Thioglycolic acid-capped CdSe quantum dots (QDs) were assembled on glass substrates with two distinct polyelectrolytes, viz poly(allylamine hydrochloride) (PAH) and poly(amidoamine) (PAMAM), generation 4 dendrimer, via the layer-by-layer (LbL) technique. Films containing up to 30 polyelectrolyte/QD bilayers were prepared. The growth of the multilayers was monitored with UV–vis spectroscopy, which showed an almost linear increase in the absorbance of the 2.8 nm QDs at 535 nm with the number of deposited bilayers. AFM measurements estimated a film thickness of 3 nm per bilayer for the PAH/CdSe films. The adsorption process and the optical properties of the PAMAM/CdSe LbL films were further analyzed layer-by-layer using surface plasmon resonance (SPR), from which a thickness of 3.2 nm was found for a PAMAM/CdSe bilayer. Photoluminescence measurements revealed higher photooxidation of the quantum dots in PAH/CdSe than in PAMAM/CdSe films.

Trioctylphosphine oxide- (TOPO-) capped (CdSe)ZnS quantum dots (QDs) were prepared through a stepwise synthesis. The surface chemistry behavior of the QDs at the air-water interface was carefully examined by various physical measurements. The surface pressure-area isotherm of the Langmuir film of the QDs gave an average diameter of 4.4 nm, which matched very well with the value determined by transmission electron microscopy (TEM) measurements if the thickness of the TOPO cap was counted. The stability of the Langmuir film of the QDs was tested by two different methods, compression/decompression cycling and kinetic measurements, both of which indicated that TOPO-capped (CdSe)ZnS QDs can form stable Langmuir films at the air-water interface. Epifluorescence microscopy revealed the two-dimensional aggregation of the QDs in Langmuir films during the early stage of the compression process. However, at high surface pressures, the Langmuir film of QDs was more homogeneous and was capable of being deposited on a hydrophobic quartz slide by the Langmuir-Blodgett (LB) film technique. Photoluminescence (PL) spectroscopy was utilized to characterize the LB films. The PL intensity of the LB film of QDs at the first emission maximum was found to increase linearly with increasing number of layers deposited onto the hydrophobic quartz slide, which implied a homogeneous deposition of the Langmuir film of QDs at surface pressures greater than 20 mN.m(-1).

Gelatin having p-nitrocinnamate pendant groups (Gel-NC) was prepared via an efficient one-pot synthesis, yield87%. (1)H NMR data indicated that 1 mol of gelatin was modified with 18 +/- 6 mol of the photosensitive group. Upon exposure to low-intensity 365 nm UV light and in the absence of photoinitiators or catalysts, Gel-NC cross-linked within minutes into a gelatin-based hydrogel as monitored by UV-vis spectroscopy. The degree of swelling of this biodegradable hydrogel in aqueous solutions responded to changes in Gel-NC concentration levels, the ionic strength of the aqueous solutions, and photo-cross-linking time. Topography changes associated with phase transition resulting from "photocleavage" of the hydrogel network with 254 nm UV light were studied with AFM. Both Gel-NC and its hydrogel expressed low toxicity to human neonatal fibroblast cells. In addition, gelatin-based microgels were prepared via the photo-cross-linking of Gel-NC within inverse micelles.

Layer-by-layer (LbL) assembly has been utilized to fabricate an ultrathin film of polyelectrolytes. The architecture was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. The topography of the films was studied using epifluorescence microscopy imaging. The photoluminescence property of the functionalized QDs improved when sandwiched between the polycation layers. The enhanced optical property of QDs allowed easy monitoring of LbL growth and detection of paraoxon with high sensitivity. The presence of organophosphorus compounds was confirmed through UV−vis and emission spectroscopies.

An inorganic/organic composite hybrid nano-system has been successfully synthesized in which nanocrystalline quantum dots (QDs) were effectively immobilized within a photo-cross-linked poly(ethylene glycol) (PEG) hydrogel. The immobilization of 3.5−6.0 nm CdTe and 2.0−3.5 nm CdSe QDs within the PEG hydrogel network has been shown to be effective through utilization of physical trapping. These QD-immobilized gel systems demonstrated luminescence characteristics unique to semiconductor QD nanocrystals. Controlled particle extraction from the PEG hydrogel matrix may be possible via a photocleavage process. The solubility property of QDs was controlled through surface functionalization. It is envisioned that the unique photophysical properties of this new material can be utilized as a convenient signal transducer for chemo-/bio-sensing. A promising application of the described QD/PEG-NC hybrid system may be in the fields of fluoroimmunoassay and as a monitoring system for drug delivery and wound healing.

Since luminescent CdSe quantum dots (QDs) have shown great potential in biological labeling, the surface chemistry behavior of QDs at interfaces is of great research interest. In the present study, CdSe QDs with green luminescence were modified with hydrophobic chains of varying lengths [from C6 to C18]. These modified QDs can be utilized to form stable monolayers at the air/water interface. Surface pressure-area isotherms of modified QDs have been measured and limiting molecular areas have also been extrapolated in order to analyze the size of the QDs. UV absorption spectra of modified QDs at various surface pressures were also determined. Surface chemistry, as well as the topographic properties, of modified QDs in Langmuir and L-B films was discussed.

A polymeric hydrogel film was made photochemically for the fluorescent detection of copper ions. An eight-branched PEG macromer having a nitrocinnamate (NC) moiety as the pendant group was synthesized and found to form a gel upon exposure to 365-nm irradiation in the absence of any photoinitiators or catalysts. Peptide 1 (Dns-Gly-His-Lys(NC)) was synthesized with Fmoc solid-phase method and contained three essential parts: a dansyl fluorophore for fluorescent signal transduction, a metal binding site for selective recognition of copper ions from aqueous solution, and a NC group for interaction with PEG-NC macromer. The peptide was found to be efficiently immobilized within the hydrogel network during the photo-cross-linking process. The prepared PEG-NC/1 gel film is strongly fluorescent and can be quenched by the presence of copper ions. The quenching process was reversed by acid treatment and an excellent reversibility was obtained. The designed membrane sensor showed a superior selectivity toward coppe...

A polyelectrolyte architecture was fabricated that was composed of chitosan and organophosphorus hydrolase polycations along with thioglycolic acid-capped CdSe quantum dots (QDs) as the polyanion. This film was imaged by epifluorescence microscopy. UV−vis and emission spectroscopies were used to monitor the growth of the bilayer film due to the enhanced optical property of QDs. Photoluminescence of the functionalized QDs improved when sandwiched between the polycations layers. The presence of organophosphorus compounds was confirmed through photoluminescence spectroscopy.

Molecules of pentadecafluorooctanoyl chloride (PFC) were grafted onto alginate (Alg) using a linear poly(ethylene glycol) linker and amide bonds. The resulting Alg-PFC material was characterized by proton nuclear magnetic resonance and infrared spectroscopies. The degree of PFC functionalization significantly influenced the physical and chemical properties of Alg-PFC, particularly when the resulting polymer was ionically crosslinked into hydrogels. Alg-PFC hydrogel beads fabricated via Ba(2+) crosslinking were found to match the permeability properties of control alginate beads, except upon swelling over time in culture media. When used to encapsulate MIN6 cells, a beta cell line, Alg-PFC beads demonstrated enhanced cell proliferation over alginate control beads. These results indicate that Alg-PFC hydrogels retain some of the PFC's biological-relevant benefits, such as enhancement of mass transport and bioinertness, to enhance cellular viability within alginate three-dimensional hydrogel environments. We envision these functionalized hydrogels to be particularly useful in the encapsulation of cells with a high metabolic demand, such as pancreatic islets.

Cellular encapsulation within alginate hydrogel capsules has broad applications in tissue engineering. In seeking to improve the inherent instability of ionically cross-linked alginate hydrogels, we previously demonstrated the covalent stabilization of Ba2+ cross-linked alginate-azide beads via chemoselective Staudinger ligation using a 1-methyl-2-diphenylphosphino-terephthalate (MDT) terminated poly(ethylene glycol) (PEG) linker. In this study, we functionalized variant PEG, linear and branched, and alginate polymers with MDT groups to evaluate the effect of size, structural design, number of functional groups, and charge on the resulting hydrogel bead. All cross-linkers resulted in enhanced covalent stabilization of alginate beads, with significant decreases in swelling and resistance to dissolution via Ba2+ chelation. The MDT-functionalized alginate resulted in the most stable and homogeneous bead, with the most restrictive permeability even after EDTA exposure. Co-encapsulation of MIN6 cells within the cross-linked alginate hydrogel beads resulted in minimal effects on viability, whereas the degree of proliferation following culture varied with cross-linker type. Altogether, the results illustrate that manipulating the cross-linker structural design permits flexibility in resulting alginate beads characteristics. Covalent stabilization of alginate hydrogel beads with these chemoselective alginate and PEG-based cross-linkers provides a unique platform for cellular encapsulation. © 2011 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 99A: 47–57, 2011.

In this study, we demonstrate the applicability of functionalized alginate to serve as a platform for the covalent cross-linking or immobilization of complementary phosphine functionalized groups via the chemoselective Staudinger ligation scheme. Azide groups were covalently linked to alginate through a heterobifunctional polyethylene glycol (PEG) linker and carbodiimide. Degree of azide functionalization was varied as a function of carbodiimide concentration and determined by proton nuclear magnetic resonance ((1)H NMR) and infrared spectroscopy. Spontaneous and covalently cross-linked alginate-PEG gels were generated via the Staudinger ligation scheme upon incubation of the azide functionalized alginate with PEG chains having 1-methyl-2-diphenylphosphino-terephthalate (MDT) as end groups. Modulation of the MDT to N(3) ratio resulted in variability of gel characteristics. In addition, azide functionalized alginate retained its capacity to instantaneously form hydrogels via electrostatic interaction with multivalent cations such as Ca(2+) and Ba(2+). Subsequently, covalent linkage of phosphine functionalized agents postgelation of the alginate was feasible, as illustrated via linkage of MDT-PEG-carboxyfluorescein. Capitalization of the chemoselective and cell compatible Staudinger ligation scheme for covalent cross-linking of alginate hydrogels may enhance the utility of this polymer for the stable encapsulation of various cell types, in addition to their use in the immobilization of labeling agents, proteins, and other bioactive molecules.

Photostable, highest emission QD fluorochromes are introduced for enzyme-organelle studies in nanocompartments of living cells. Progress towards intracellular localizations is foreseeable using high-resolution digital photography applied to genomics, proteomics, diagnostics-prognostics, and drug trials.

A new peptidyl fluorescent chemosensor for the selective detection of copper ions was studied.

Gly-His-Leu-Leu-Cys coated CdS quantum dots detected Cu2+ and Ag+ selectively with high sensitivity, below 0.5 microM.

A direct conjugation of organophosphorus acid anhydrolase (OPAA) with CdS quantum dots was prepared via arrested precipitation within the enzyme matrix. The bio-conjugate was found not only to retain enzyme conformational structure but also to retain enzyme activity and be effective at detecting diisopropyl fluorophosphate (DFP) at the micro molar level.

Bioactive scaffolds impregnated with multiple growth factors that are released at controlled rates, offer the possibility of enhancing the healing process by mimicking the work of the natural tissue. We have developed photoresponsive and biodegradable hydrogel matrices based on natural and synthetic polymers that can undergo phase transformations upon exposure to alternating wavelengths of irradiation. Photo-polymerization provides an effective and benign method for in situ hydrogelation with spatial and temporal control of the polymerization reaction. Polyethylene glycol, heparin and gelatin molecules have been modified at high yields with photosensitive groups that can be rapidly and reversibly photocrosslinked to hydrogel scaffolds in the absence of initiators. We are currently exploring the efficacy of these scaffolds as depots for the controlled delivery of basic fibroblast growth factor in cutaneous regeneration. We have demonstrated that the stability of b-FGF is enhanced by its incorporation within the gel matrix and its complexation with components of the scaffold (i.e. heparin) while the releasing peptide maintains its activity. Cell proliferation and partial thickness wound studies demonstrated that b-FGF could be affectively released from the scaffolds at controlled rates and its wound healing properties were a function of the mode of delivery. Rate changes up to 60% on the kinetics of peptide release could be easily achieved by altering the exposure times (seconds to minutes range). Similarly, we were able to alter the release profile of b-FGF by adjusting the ratio of the photosensitive polymeric macromers prior to crosslinking. These results suggest that the proposed photoresponsive gels scaffolds could serve as bioactive peptide delivery vehicles in a number of tissue engineering applications.