Hydrophobic Modification of Polymer Surfaces via “Grafting to” Approach

Recent advances in photo-crosslinkable methacrylated silk (Sil-MA)-based scaffolds for regenerative medicine: A review

Silks fibroin can be chemically modified through amino acid side chains to obtain methacrylated silk (Sil-MA). Sil-MA could be processed into a variety of scaffold forms and combine synergistically with other biomaterials to form composites vehicle. The advent of Sil-MA material has enabled impressive progress in the development of various scaffolds based on Sil-MA type to imitate the structural and functional characteristics of natural tissues. This review highlights the reasonable design and bio-fabrication strategies of diverse Sil-MA-based tissue constructs for regenerative medicine. First, we elucidate modification methodology and characteristics of Sil-MA. Next, we describe characteristics of Sil-MA hydrogels, and focus on the design approaches and formation of different types of Sil-MA-based hydrogels. Thereafter, we present an overview of the recent advances in the application of Sil-MA based scaffolds for regenerative medicine, including detailed strategies for the engineering methods and materials used. Finally, we summarize the current research progress and future directions of Sil-MA in regenerative medicine. This review not only delineates the representative design strategies and their application in regenerative medicine, but also provides new direction in the fabrication of biomaterial constructs for the clinical translation in order to stimulate the future development of implants.

Development of thermo-responsive polycaprolactone macrocarriers conjugated with Poly(N-isopropyl acrylamide) for cell culture

Poly(N-isopropyl acrylamide) (PNIPAAm) is a well-known 'smart' material responding to external stimuli such as temperature. PNIPAAm was successfully conjugated to polycaprolactone (PCL) bead surfaces through amidation reaction. Functionalization steps were characterized and confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and Energy Dispersion Spectroscopy. PNIPAAm-conjugated PCL allowed human dermal fibroblast cells (HDF) and mesenchymal stem cells (MSC) to adhere, spread, and grow successfully. By reducing the temperature to 30 °C, more than 70% of HDF were detached from PNIPAAm-conjugated PCL macrocarriers with 85% viability. The cell detachment ratio by trypsin treatment was slightly higher than that induced by reduced temperature, however, cell detachment from PNIPAAm-conjugated macrocarriers by lowering the temperature significantly reduced cell death and increased both cell viability and the recovery potential of the detached cells. HDF attachment and detachment were also observed by Live-Dead staining and phase contrast imaging. The expression of extracellular matrix proteins such as Laminin and Fibronectin was also affected by the trypsinization process but not by the reduced temperature process. Taken together, our results showed that thermo-responsive macrocarriers could be a promising alternative method for the non-invasive detachment of cells, in particular for tissue engineering, clinical applications and the use of bioreactors.

Surface modification of polypropylene surgical meshes for improving adhesion with poloxamine hydrogel adhesive

Tissue adhesive has notable clinical benefits in hernia repair fixation. A novel poloxamine tissue adhesive was previously shown to successfully bond collagen tissue with adequate adhesive strength. In application related to attachment of polypropylene (PP) mesh, the adhesive strength between the mesh and poloxamine hydrogel adhesive is limited by the hydrophobicity of PP monofilaments and lack of covalent bond formation. The purpose of this study was to compare two different surface modifications [bovine serum albumin (BSA) adsorption and poly-glycidyl methacrylate/human serum albumin (PGMA/HSA) grafting] of PP mesh for improving the adhesive strength between poloxamine hydrogel adhesive and PP mesh. The PGMA/HSA surface modification significantly improved the adhesive strength for meshes attached with poloxamine hydrogel tissue adhesive compared with unmodified meshes and meshes modified by BSA adsorption. An area of 1 cm² adhesive provided for a maximum adhesive strength of 65-70 kPa for meshes modified by PGMA/HSA, 4-13 kPa for meshes modified by BSA, and 22-45 kPa for unmodified meshes. Optical microscopy and infrared spectroscopy (FTIR) confirmed the improved adhesive strength was achieved through mechanical interlock of the hydrogel tissue adhesive into the PP mesh pores and chemical bonding of the albumin after successful PGMA/HSA grafting onto the PP monofilaments. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1047-1055, 2019.

En Route to Practicality of the Polymer Grafting Technology: One-Step Interfacial Modification with Amphiphilic Molecular Brushes

Surface modification with polymer grafting is a versatile tool for tuning the surface properties of a wide variety of materials. From a practical point of view, such a process should be readily scalable and transferable between different substrates and consist of as least number of steps as possible. To this end, a cross-linkable amphiphilic copolymer system that is able to bind covalently to surfaces and form permanently attached networks via a one-step procedure is reported here. This system consists of brushlike copolymers (molecular brushes) made of glycidyl methacrylate, poly(oligo(ethylene glycol) methyl ether methacrylate), and lauryl methacrylate, which provide the final product with tunable reactivity and balance between hydrophilicity and hydrophobicity. The detailed study of the copolymer synthesis and properties has been carried out to establish the most efficient pathway to design and tailor this amphiphilic molecular brush system for specific applications. As an example of the applications, we showed the ability to control the deposition of graphene oxide (GO) sheets on both hydrophilic and hydrophobic surfaces using GO modified with the molecular brushes. Also, the capability to tune the osteoblast cell adhesion with the copolymer-based coatings was demonstrated.

Precisely printable and biocompatible silk fibroin bioink for digital light processing 3D printing

Although three-dimensional (3D) bioprinting technology has gained much attention in the field of tissue engineering, there are still several significant engineering challenges to overcome, including lack of bioink with biocompatibility and printability. Here, we show a bioink created from silk fibroin (SF) for digital light processing (DLP) 3D bioprinting in tissue engineering applications. The SF-based bioink (Sil-MA) was produced by a methacrylation process using glycidyl methacrylate (GMA) during the fabrication of SF solution. The mechanical and rheological properties of Sil-MA hydrogel proved to be outstanding in experimental testing and can be modulated by varying the Sil-MA contents. This Sil-MA bioink allowed us to build highly complex organ structures, including the heart, vessel, brain, trachea and ear with excellent structural stability and reliable biocompatibility. Sil-MA bioink is well-suited for use in DLP printing process and could be applied to tissue and organ engineering depending on the specific biological requirements.

Toward fabric-based flexible microfluidic devices: pointed surface modification for pH sensitive liquid transport

Microfluidic fiber channels with switchable water transport are fabricated in flexible textile PET/PP materials using a preprogrammed yarn-based fabric and a yarn-selective surface modification method. The developed robust and scalable fabrication method is based on the selective functionalization of the PET yarns with an epoxide-containing polymer that is then followed by grafting patterns of different pH-sensitive polymers PAA [poly(acrylic acid) ] and P2VP [poly(2-vinyl pyridine)]. The selective functionalization of the fabric yields an array of amphiphilic channels that are constrained by hydrophobic PP boundaries. Aqueous solutions are transported in the amphiphilic channels by capillary forces where the direction of the liquid transport is defined by pH-response of the grafted polymers. The channels are fed with liquid through hydrophilic, pH insensitive PEG [polyethylene glycol] ports. The combination of the PAA and P2VP patterns in the amphiphilic channels is used to create pH-sensitive elements that redirect aqueous liquids toward PAA channels at pH > 4 and toward both PAA and P2VP channels at pH < 4. The system of pH-selective channels in the developed textile based microfluidic chip could find analytical applications and can be used for smart cloth.

Immobilization of gelatin onto poly(glycidyl methacrylate)-grafted polycaprolactone substrates for improved cell-material interactions

To enhance the cytocompatibility of polycaprolactone (PCL), cell-adhesive gelatin is covalently immobilized onto the PCL film surface via two surface-modified approaches: a conventional chemical immobilization process and a surface-initiated atom transfer radical polymerization (ATRP) process. Kinetics studies reveal that the polymer chain growth from the PCL film using the ATRP process is formed in a controlled manner, and that the amount of immobilized gelatin increases with an increasing concentration of epoxide groups on the grafted P(GMA) brushes. In vitro cell adhesion and proliferation studies demonstrate that cell affinity and growth are significantly improved by the immobilization of gelatin on PCL film surfaces, and that this improvement is positively correlated to the amount of covalently immobilized gelatin. With the versatility of the ATRP process and tunable grafting efficacy of gelatin, this study offers a suitable methodology for the functionalization of biodegradable polyesters scaffolds to improve cell-material interactions.

Thermo-responsive copolymer coatings for flow regulation on demand in glass microcapillaries

This study presents thermo-responsive on-demand regulation of water flow rate in glass microcapillaries with a recently developed water-stable, stimuli-responsive poly(methyl methacrylate/N-isopropyl acrylamide) [P(MMA/NIPAM)] copolymer grafted at the inner walls. It is shown that the grafted coatings are stable and can withstand significant tractions under temperature variation. Such microcapillaries allow flow regulation on demand by changing temperature across the lower critical solution temperature (LCST) of the copolymer layer, which makes it swell or shrink, thus changing the bore available for pressure-driven flow. The grafted copolymer layers were subjected to different pressure drops applied to the capillary open ends, as well as to periodic temperature variation across the copolymer LCST to determine the best grafting conditions for microfluidic operation. Then, by varying the temperature, the flow rate in the capillaries was changed periodically on demand due to the swelling/shrinkage of the grafted copolymer layer. It was also shown that the entrapped air bubbles are present in the coating which can result in an apparent slip.

Adapting low-adhesive thin films from mixed polymer brushes

The concept of the responsive/adaptive mixed polymer brushes was applied to the development of the thin film coatings possessing low adhesive properties that were evaluated with AFM probes in different media. Mixed brushes composed of polydimethylsiloxane (PDMS) and polyethyleneoxide (PEO) revealed a selective layered segregation in air and water. Immersion of the sample into an aqueous environment drove PEO chains to the brush-water interface while upon drying the surface undergoing reconstruction and was occupied with PDMS. Low interfacial energies of PDMS in air and PEO in water provided low-adhesive properties of the PDMS-PEO brushes to the probes in both media due to the spontaneous and rapid reconstruction of the mixed brush.