Protein interactions with peptides generally have low thermodynamic and mechanical stability. Streptococcus pyogenes fibronectin-binding protein FbaB contains a domain with a spontaneous isopeptide bond between Lys and Asp. By splitting this domain and rational engineering of the fragments, we obtained a peptide (SpyTag) which formed an amide bond to its protein partner (SpyCatcher) in minutes. Reaction occurred in high yield simply upon mixing and amidst diverse conditions of pH, temperature, and buffer. SpyTag could be fused at either terminus or internally and reacted specifically at the mammalian cell surface. Peptide binding was not reversed by boiling or competing peptide. Single-molecule dynamic force spectroscopy showed that SpyTag did not separate from SpyCatcher until the force exceeded 1 nN, where covalent bonds snap. The robust reaction conditions and irreversible linkage of SpyTag shed light on spontaneous isopeptide bond formation and should provide a targetable lock in cells and a stable module for new protein architectures.

https://www.pnas.org/content/pnas/109/12/E690.full.pdf

Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin

Increased use of reconstruction procedures in orthopedics, due to trauma, tumor, deformity, degeneration and an aging population, has caused a blossom, not only in surgical advancement, but also in the development of bone implants. Traditional synthetic porous scaffolds are made of metals, polymers, ceramics or even composite biomaterials, in which the design does not consider the native structure and properties of cells and natural tissues. Thus, these synthetic scaffolds often poorly integrate with the cells and surrounding host tissue, thereby resulting in unsatisfactory surgical outcomes due to poor corrosion and wear, mechanical mismatch, unamiable surface environment, and other unfavorable properties. Musculoskeletal tissue reconstruction is the ultimate objective in orthopedic surgery. This objective can be achieved by (i) prosthesis or fixation device implantation, and (ii) tissue engineered bone scaffolds. These devices focus on the design of implants, regardless of the choice of new biomaterials. Indeed, metallic materials, e.g. 316L stainless steel, titanium alloys and cobalt chromium alloys, are predominantly used in bone surgeries, especially in the load-bearing zone of prostheses. The engineered scaffolds take biodegradability, cell biology, biomolecules and material mechanical properties into account, in which these features are ideally suited for bone tissue repair and regeneration. Therefore, the design of the scaffold is extremely important to the success of clinical outcomes in musculoskeletal surgeries. The ideal scaffolds should mimic the natural extracellular matrix (ECM) as much as possible, since the ECM found in natural tissues supports cell attachment, proliferation, and differentiation, indicating that scaffolds should consist of appropriate biochemistry and nano/micro-scale surface topographies, in order to formulate favorable binding sites to actively regulate and control cell and tissue behavior, while interacting with host cells. In addition, scaffolds should also possess a similar macro structure to what is found in natural bone. This feature may provide space for the growth of cells and new tissues, as well as for the carriers of growth factors. Another important concern is the mechanical properties of scaffolds. It has been reported that the mechanical features can significantly influence the osteointegration between implants and surrounding tissues, as well as cell behaviors. Since natural bone exhibits super-elastic biomechanical properties with a Young's modulus value in the range of 1–27 GPa, the ideal scaffolds should mimic strength, stiffness and mechanical behavior, so as to avoid possible post-operation stress shielding effects, which induce bone resorption and consequent implant failure. In addition, the rate of degradation and the by-products of biodegradable materials are also critical in the role of bone regeneration. Indeed, the mechanical integrity of a scaffold will be significantly reduced if the degradation rate is rapid, thereby resulting in a pre-matured collapse of the scaffold before the tissue is regenerated. Another concern is that the by-products upon degradation may alter the tissue microenvironment and then challenge the biocompatibility of the scaffold and the subsequent tissue repair. Therefore, these two factors should be carefully considered when designing new biomaterials for tissue regeneration. To address the aforementioned questions, an overview of the design of ideal biomimetic porous scaffolds is presented in this paper. Hence, a number of original engineering processes and techniques, including the production of a hierarchical structure on both the macro- and nano-scales, the adjustment of biomechanical properties through structural alignment and chemical components, the control of the biodegradability of the scaffold and its by-products, the change of biomimetic surface properties by altering interfacial chemistry, and micro- and nano-topographies will be discussed. In general, the concepts and techniques mentioned above provide insights into designing superior biomimetic scaffolds for bone tissue engineering.

Biomimetic porous scaffolds for bone tissue engineering

3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting

Fundamentals of Modern Manufacturing: Materials, Processes and Systems

Propulsion system development requires new, more affordable manufacturing techniques and technologies in a constrained budget environment, while future in-space applications will require in-space manufacturing and assembly of parts and systems. Marshall is advancing cuttingedge commercial capabilities in additive and digital manufacturing and applying them to aerospace challenges. The Center is developing the standards by which new manufacturing processes and parts will be tested and qualified. Rapidly evolving digital tools, such as additive manufacturing, are the leading edge of a revolution in the design and manufacture of space systems that enables rapid prototyping and reduces production times. Marshall has unique expertise in leveraging new digital tools, 3D printing, and other advanced manufacturing technologies and applying them to propulsion systems design and other aerospace materials to meet NASA mission and industry needs. Marshall is helping establish the standards and qualifications “from art to part” for the use of these advanced techniques and the parts produced using them in aerospace or elsewhere in the U.S. industrial base.

Additive manufacturing

Additive Manufacturing

Nanoparticle-mediated targeted drug delivery for breast cancer treatment.

Additive manufacturing processes have a demonstrated capacity for flexible production of metal and polymer components. More recently, capabilities for three dimensional printing of continuous fiber...

Microstructure and mechanical properties of three dimensional-printed continuous fiber composites

Additively manufactured, short fiber reinforced polymer composites have advantages over traditional continuous fiber composites, which include low cost and design flexibility. However, these composites suffer from low strength and stiffness as compared to their continuous fiber counterparts due to the limitation of low fiber volume. In this study, we overcame this limitation by developing a vibration integrated auger extrusion system. This direct write additive manufacturing technique allowed us to fabricate short fiber reinforced thermoset composites in intricate geometries, with unprecedented high compression strength (673 MPa), flexural strength (401 MPa), flexural stiffness (53 GPa), and fiber volume ratio (46 %). Milled carbon fibers were used as the reinforcing fibers, which were considered too short to have the ability to enhance the mechanical strength of composites. However, in this study we show for the first time that milled carbon fibers have the ability to significantly reinforce the thermoset matrix and the composites reinforced with these fibers achieve mechanical performances similar to those of composites reinforced with longer fibers. We believe that a transformation takes place at high fiber volumes on the load transport mechanism within the composites, leading to higher levels of strength and a stiffness enhancement. This pseudo transformation can give rise to short fibers that act as if they are longer, which aids in the effective transfer of tensile loads from the matrix phase to the fibers. This study also showed that the mechanical properties of the additively fabricated thermoset composites match those of ubiquitous, denser structural metals, and these properties show nearly isotropic behavior. Therefore, these systems have great potential to find immediate applications where weight reduction and component complexity are both desired.

Emrah Celik

Papers

Peptide tag forming a rapid covalent bond to a protein, through engineering a bacterial adhesin

Additive Manufacturing

Nanoparticle-mediated targeted drug delivery for breast cancer treatment.

Microstructure and mechanical properties of three dimensional-printed continuous fiber composites

Additive manufacturing of short fiber reinforced thermoset composites with unprecedented mechanical performance