A general route for the synthesis of functional, protein-based hydrogel microspheres using tailored protein charge

Dynamic, Bioresponsive Hydrogels via Changes in DNA Aptamer Conformation

DNA aptamers are integrated into synthetic hydrogel networks with the aim of creating hydrogels that undergo volume changes when exposed to target molecules. Specifically, single-stranded DNA aptamers in cDNA-bound, extended state are incorporated into hydrogel networks as cross-links, so that the nanoscale conformational change of DNA aptamers upon binding to target molecules will induce macroscopic volume decreases of hydrogels. Hydrogels incorporating adenosine triphosphate (ATP)-binding aptamers undergo controllable volume decreases of up to 40.3 ± 4.6% when exposed to ATP, depending on the concentration of DNA aptamers incorporated in the hydrogel network, temperature, and target molecule concentration. Importantly, this approach can be generalized to aptamer sequences with distinct binding targets, as demonstrated here that hydrogels incorporating an insulin-binding aptamer undergo volume changes in response to soluble insulin. This work provides an example of bioinspired hydrogels that undergo macroscopic volume changes that stem from conformational shifts in resident DNA-based cross-links.

Dynamic protein hydrogels with reversibly tunable stiffness regulate human lung fibroblast spreading reversibly

Fibroblast cells change their morphology reversibly in response to changes in protein hydrogel stiffness.

Bioinspired dynamic microcapsules

There is an increasing interest in bioinspired dynamic materials. Abundant illustrations of protein domains exist in nature, with remarkable ligand binding characteristics and structures that undergo conformational changes. For example, calmodulin (CaM) can have three conformational states, which are the unstructured Apo-state, Ca²⁺-bound ligand-exposed binding state, and compact ligand-bound state. CaM's mechanical response to biological cues is highly suitable for engineering dynamic materials. The distance between CaM globular terminals in the Ca²⁺-bound state is 5 nm and in the ligand-bound state is 1.5 nm. CaM's nanoscale conformational changes have been used to develop dynamic hydrogel microspheres that undergo reversible volume changes. The current work presents the fabrication and preliminary results of layer-by-layer (LbL) self-assembled Dynamic MicroCapsules (DynaMicCaps) whose multilayered shell walls are composed of polyelectrolytes and CaM. Quasi-dynamic perfusion results show that the DynaMicCaps undergo drastic volume changes, with up to ∼1500% increase, when exposed to a biochemical ligand trifluoperazine (TFP) at pH 6.3. Under similar test conditions, microcapsules without CaM also underwent volume changes, with only up to ∼290% increase, indicating that CaM's bio-responsiveness was retained within the shell walls of the DynaMicCaps. Furthermore, DynaMicCaps exposed to 0.1 M NaOH underwent volume changes, with only up to ∼580% volume increase. Therefore, DynaMicCaps represent a new class of polyelectrolyte multilayer (PEM) capsules that can potentially be used to release their payload at near physiological pH. With over 200 proteins that undergo marked, well-characterized conformational changes in response to specific biochemical triggers, several other versions of DynaMicCaps can potentially be developed.

Dynamic Behavior in Enzyme-Polymer Surfactant Hydrogel Films

Dynamic protein-polymer surfactant films are highly hydrophilic and show a soft solid to hydrogel transition upon hydration to produce a swollen hydrogel. An unusual reversible autospreading/self-folding response is observed when the water-saturated films are transferred from water into air.

Multi-responsive polyethylene-polyamine/gelatin hydrogel induced by non-covalent interactions

By simply introducing a gelatin aqueous solution, the polyethylene-polyamine (PPA)/gelatin hydrogel with multi-stimuli-responsive properties was obtained.

Growth factor delivery: how surface interactions modulate release in vitro and in vivo

Biomaterial scaffolds have been extensively used to deliver growth factors to induce new bone formation. The pharmacokinetics of growth factor delivery has been a critical regulator of their clinical success. This review will focus on the surface interactions that control the non-covalent incorporation of growth factors into scaffolds and the mechanisms that control growth factor release from clinically relevant biomaterials. We will focus on the delivery of recombinant human bone morphogenetic protein-2 from materials currently used in the clinical practice, but also suggest how general mechanisms that control growth factor incorporation and release delineated with this growth factor could extend to other systems. A better understanding of the changing mechanisms that control growth factor release during the different stages of preclinical development could instruct the development of future scaffolds for currently untreatable injuries and diseases.

Recent advances in polymeric microspheres for parenteral drug delivery--part 2

INTRODUCTION

Currently marketed microsphere products are manufactured with the use of organic solvents which have a negative impact on the environment and stability of biological molecules. With recent advances in fabrication technologies, solvent free methods have demonstrated potential for the preparation of microspheres.

AREAS COVERED

New technical advances recently achieved in solvent based microsphere manufacturing processes have allowed for major improvement in product quality and properties. Novel solvent free fabrication methods combined with newly functionalized biodegradable polymers have been explored for their application in the preparation of microspheres containing biological molecules.

EXPERT OPINION

Novel fabrication methods for microspheres have been recently reported but technical challenges and development risks remain high for scale up from bench to industrial commercialization. While the applications of microspheres for delivery of proteins, genes and vaccines have shown promise for clinical use, the approval of newly functionalized polymers as carriers may still face scrutiny on safety and biocompatibility, which can be key factors in securing the regulatory approval of the product.

Hydrogel biopolymer created from the self-assembly of a designed protein containing a four-helix bundle forming motif

A protein hydrogel system based on the assembly of a four-helix bundle motif was proposed and synthesized by genetic engineering methods. This new polypeptide, named GBH1, consists of identical amphipathic helices of 22 residues in length oriented in opposite fashion to one another at each end of a polypeptide with a total length of 227 amino acids. The middle portion of the polypeptide (residues 79-147) is an unstructured random coil. The region between the amphipathic and unstructured segment is an α-helical stretch (23-78 and 148-204) not possessing a sequence compatible with a coiled-coil conformation, but rather possesses regions that have overwinding of the helix. The thermal unfolding of GBH1 shows more than one inflection point (T(m1) = 30.5 °C, T(m2) = 64.6 °C), indicative of a partially unfolded intermediate and, thus, multiple interactions in the folded state. A qualitative assessment of hydrogel formation with varying pH showed that acidic conditions did not support the gel state, indirectly indicating that the proposed four-helix bundle is the major cross-linking structure and not a leucine zipper motif. Scanning electron microscopy reveals a network of interacting protein molecules forming a spongelike matrix with numerous pores that would be occupied with water molecules.

Emerging area: biomaterials that mimic and exploit protein motion

Traditional dynamic hydrogels have been designed to respond to changes in physicochemical inputs, such as pH and temperature, for a wide range of biomedical applications. An emerging strategy that may allow for more specific "bio-responsiveness" in synthetic hydrogels involves mimicking or exploiting nature's dynamic proteins. Hundreds of proteins are known to undergo pronounced conformational changes in response to specific biochemical triggers, and these responses represent a potentially attractive toolkit for design of dynamic materials. This "emerging area" review focuses on the use of protein motions as a new paradigm for design of dynamic hydrogels. In particular, the review emphasizes early examples of dynamic hydrogels that harness well-known protein motions. These examples then serve as templates to discuss challenges and suggest emerging directions in the field. Successful early examples of this approach, coupled with the fundamental properties of nature's protein motions, suggest that protein-based materials may ultimately achieve specific, multiplexed responses to a range of biochemical triggers. Applications of this new class of materials include drug delivery, biosensing, bioactuation, and tissue engineering.