Bioconjugate Materials Research Articles

Self-assembly of protein-polymer conjugates for drug delivery

Protein-polymer conjugates are a class of molecules that combine the stability of polymers with the diversity, specificity, and functionality of biomolecules. These bioconjugates can result in hybrid materials that display properties not found in their individual components and can be particularly relevant for drug delivery applications. Engineering amphiphilicity into these bioconjugate materials can lead to phase separation and the assembly of high-order structures. The assembly, termed self-assembly, of these hierarchical structures entails multiple levels of organization: at each level, new properties emerge, which are, in turn, influenced by lower levels. Here, we provide a critical review of protein-polymer conjugate self-assembly and how these materials can be used for therapeutic applications and drug delivery. In addition, we discuss central bioconjugate design questions and propose future perspectives for the field of protein-polymer conjugate self-assembly.

Polymer conjugation of proteins as a synthetic post-translational modification to impact their stability and activity.

For more than 40 years, protein-polymer conjugates have been widely used for many applications, industrially and biomedically. These bioconjugates have been shown to modulate the activity and stability of various proteins while introducing reusability and new activities that can be used for drug delivery, improve pharmacokinetic ability, and stimuli-responsiveness. Techniques such as RDRP, ROMP and "click" have routinely been utilized for development of well-defined bioconjugate and polymeric materials. Synthesis of bioconjugate materials often take advantage of natural amino acids present within protein and peptide structures for a host of coupling chemistries. Polymer modification may elicit increased or decreased activity, activity retention under harsh conditions, prolonged activity in vivo and in vitro, and introduce stimuli responsiveness. Bioconjugation has resulted to modulated thermal stability, chemical stability, storage stability, half-life and reusability. In this review we aim to provide a brief state of the field, highlight a wide range of behaviors caused by polymer conjugation, and provide areas of future work.

Branched porphyrins as functional scaffolds for multisite bioconjugation.

Bioconjugation is a rapidly expanding field because of the numerous potential applications of bioconjugate materials. We explored the usefulness of branched porphyrins as rigid scaffolds, bearing multiple sites for bioconjugation. To this end, we first selected the tetrakis(p-[aminomethyl] phenyl) porphyrin (TAMPP) macrocycle and developed a straightforward synthetic protocol, able to provide the desired tetraphenylporphyrin, carrying four functional amino groups. The partially protection of the amino groups by tert-butoxy-carbonyl allowed the selective and specific decoration of the porphyrin with different peptide sequences. To explore the utility of the macrocycle as molecular scaffold for bioconjugation, we selected peptide sequences able to function as thrombin inhibitors. In particular, two peptide sequences, named CS3 and ES7, able to interact, respectively, with the thrombin catalytic site and the fibrinogen recognition exosite, were joined onto the porphyrin macrocycle, providing the multisite-directed inhibitor CS3-TAMPP-ES7. This multisite inhibitor and its Mn(III) complex are able to inhibit α-thrombin-catalyzed hydrolysis of Tos-Gly-Pro-Arg-nitroanilide with inhibition constants in the micromolar range, as well as the hydrolysis of the natural substrate fibrinogen. The inhibitor is resistant against enzymatic degradation by thrombin and is highly selective. The Mn(III) complex is capable of interacting with clot-bound thrombin and partially inhibits clot growth in the presence of fibrinogen. The results herein reported are very promising, suggesting the potential of the newly developed conjugate as new imaging agents for clot detection.

Thiol coupling based synthesis of temperature-sensitive polymer–peptide conjugates with controlled architecture.

ABSTRACTA synthetic strategy to couple selectively an ionic complementary thiol modified octapeptide, that is able to gel at low temperature, to the thermoresponsive polymer poly(N-isopropylacrylamide) (pNIPAAm) with controlled molecular weight and narrow polydispersity is described. The polymer was synthesized by atom transfer radical polymerization (ATRP) affording halogen functionalized chain ends. This allowed subsequent coupling to a thiol terminated ionic complementary octapeptide via nucleophile substitution. Results indicated that the peptide was covalently attached to the polymer and that both the coil-globule phase transition of pNIPAAm and the gelation properties of the peptide were retained in the conjugated product. This method provides a versatile route for the synthesis of a range of bioconjugate materials with controlled architecture and dual self-assembling and thermoresponsive behavior.

Novel bio-conjugate materials: soybean peroxidase immobilized on bioactive glasses containing Au nanoparticles

In the field of implantation, the delivery and/or immobilization of biomolecules developing a specific action on bone mineralization has attracted great attention in the last few years. In fact, a wide spectrum of enzymes and proteins have been grafted with different methods onto/within implanted materials. Bioactive glasses and glass-ceramics, due to their tailorable properties in terms of chemical composition, reactivity, and easiness of manufacturing, represent good scaffolds for enzyme immobilization. These biomaterials are well known for their peculiar surface reactivity promoting, when contacted with real or simulated body fluids, the formation of an hydroxy-carbonate apatite layer. The aim of the present contribution has been to immobilize, via a covalent linkage, an enzyme on the glass surface through the formation of self-assembled monolayers (SAMs), in order to obtain a stable bio-conjugate useful as a material bio-implantable into the human body. The innovation of this study resides in the use of a new method of protein immobilization on the glass surface. Unlike other works, in which a preliminary silanization process has often been used, the introduction of gold nanoparticles (AuNPs) in the glass composition allowed us to exploit the easy SAMs formation process on the AuNPs dispersed in the bioactive glass matrix and, consequently, to immobilize an enzyme (soybean peroxidase, SBP, in the present case) on the SAMs. A thorough characterization of the materials, at different steps of the functionalization process, has been also reported, together with in vitro activity tests of immobilized SBP, compared with merely adsorbed SBP, and cytotoxicity tests using human osteoblast (MG-63) cells. Overall, a new bio-conjugate material, able to maintain its activity over time and to decrease the oxidative stress when in contact with MG-63 cells, has been obtained.

Baiting Proteins with C60

About 20 proteins are known to modify their activity upon interaction with C60. Their structures are present in a database that includes more than 1200 protein structures selected as possible targets for drugs and to represent the entire Protein Data Bank. The set was examined with an algorithm that appraises quantitatively the interaction of C60 and the surface of each protein. The redundancy of the set allows to establish the predictive power of the approach that finds explicitly the most probable site where C60 docks on each protein. About 80% of the known fullerene binding proteins fall in the top 10% of scorers. The close match between the model and experiments vouches for the accuracy of the model and validates its predictions. The sites of docking are shown and discussed in view of the existing experimental data available for protein-C60 interaction. A closer exam of the 10 top scorers is discussed in detail. New proteins that can interact with C60 are identified and discussed for possible future applications as drug targets and fullerene derivatives bioconjugate materials.

Role of Different Phospholipids in the Synthesis of Pearl-Necklace-Type Gold−Silver Bimetallic Nanoparticles as Bioconjugate Materials

A seed-growth (S-G) method has been used to synthesize gold (Au) and Au−silver (Ag) bimetallic pear-necklace-type nanoparticles (NP) as bioconjugate materials by using a series of phospho-glycerol (PG) and phospho-choline (PC) lipids as capping agents. All PG lipids produce a fine pear-necklace arrangement of Au NP with dimensions between 10 and 20 nm. Addition of Ag converts this arrangement into Au−Ag bimetallic NP with a diameter essentially close to that of Au NP. Use of PC lipids does not show this arrangement but promotes a significant anisotropic growth especially in the presence of Ag. This difference has been attributed to a difference in the capping ability of PG and PC lipids because of their anionic and zwitterionic nature, respectively. XPS results have demonstrated the presence of adsorbed PG and PC lipids on Au or Au−Ag bimetallic surfaces in their respective samples. The results also indicate a decrease in the capping amount of a lipid with an increase in the growth of Au−Ag bimetallic NP....

Encyclopedia of smart materials

Biomedical Sensing. Abstract. 1. Introduction. 2. Medical, Therapeutic, and Diagnostic Applications of Biosensors. 3. Polymers as Electrode Coatings and Biosensor Mediators. 4. Immobilization Techniques and Materials. 5. Smart Polymers for Immobilization and Bioconjugate Materials. 6. Biosensor Operation. 7. Glucose Sensors. 8. Other Analytes for Biological Sensing. 9. Modes of Response in Smart Polymers. 10. Molecular Imprinting. 11. Possibilities for Future Development. Bibliography. Figures. Tables.

Synthesis of a stable gold hydrosol by the reduction of chloroaurate ions by the amino acid, aspartic acid

Development of reliable protocols for the synthesis of nanoparticles of well-defined sizes and good monodispersity is an important aspect of nanotechnology. In this paper, we present details of the synthesis of gold nanoparticles of good monodispersity by the reduction of aqueous chloroaurate ions by the amino acid, aspartic acid. The colloidal gold solution thus formed is extremely stable in time, indicating electrostatic stabilization via nanoparticle surface-bound amino acid molecules. This observation has been used to modulate the size of the gold nanoparticles in solution by varying the molar ratio of chloroaurate ions to aspartic acid in the reaction medium. Characterization of the aspartic acid-reduced gold nanoparticles was carried out by UV-visible spectroscopy, thermogravimetric analysis and transmission electron microscopy. The use of amino acids in the synthesis and stabilization of gold nanoparticle in water has important implications in the development of new protocols for generation of bioconjugate materials.