Mechanical improvements to reinforced porous silk scaffolds

Abstract

Load bearing porous biodegradable scaffolds are required to engineer functional tissues such as bone. Mechanical improvements to porogen leached scaffolds prepared from silk proteins were systematically studied through the addition of silk particles in combination with silk solution concentration, exploiting interfacial compatibility between the two components. Solvent solutions of silk up to 32 w/v% were successfully prepared in hexafluoroisopropanaol (HFIP) for the study. The mechanical properties of the reinforced silk scaffolds correlated to the material density and matched by a power law relationship, independent of the ratio of silk particles to matrix. These results were similar to the relationships previously shown for cancellous bone. The mechanism behind the increased mechanical properties was a densification effect, and not the effect of including stiffer silk particles into the softer silk continuous matrix. A continuous interface between the silk matrix and the silk particles, as well as homogeneous distribution of the silk particles within the matrix were observed. Furthermore, we note that the roughness of the pore walls was controllable by varying the ratio of particles matrix, providing a route to control topography. The rate of proteolytic hydrolysis of the scaffolds decreased with increase in mass of silk used in the matrix and with increasing silk particle content.

High-strength silk protein scaffolds for bone repair

“…1C). Strong interfacial contact between blended polymers within a composite is critical for achieving higher stiffness (14,32). Following a similar principle, silk was chosen as the common material for both the phases (fiber and bulk matrix) to achieve enhanced interfacial protein-protein compatibility as evident from the SEM images.…”

“…The use of ceramic materials such as tricalcium phosphates, hydroxyapatite (HAP), or bioactive glass as inclusions in polymer matrices is often used to enhance mechanics (9,(11)(12)(13). Similarly, studies using reinforcing silk particles (fabricated by milling) into a silk matrix resulted in improved scaffolds for bone applications with compressive properties in hydrated state of approximately 3 MPa, improving the ingrowth of human bone marrow-derived mesenchymal stem cells (hMSCs) in vitro toward forming bone-like tissues (14)(15)(16).…”

“…Currently, bone graft/scaffold engineering using silk biomaterials has received increasing interest as an alternative option (14,15,17,18). However, toward, this goal several biological parameters need to be met including biocompatibility, biodegradability, surface roughness, porosity, osteoconductivity, and above all high mechanical integrity (4,14,15).…”

“…However, toward, this goal several biological parameters need to be met including biocompatibility, biodegradability, surface roughness, porosity, osteoconductivity, and above all high mechanical integrity (4,14,15). However, many challenges remain to satisfy an optimally functional bone regeneration scaffold system (19).…”

“…However, many challenges remain to satisfy an optimally functional bone regeneration scaffold system (19). Perhaps the biggest challenge is the need for polymer biomaterials to meet the high compressive properties of bone, a prerequisite to function in vivo (14,15,20).…”