Tissue engineering applications commonly encompass the use of three-dimensional (3D) scaffolds to provide a suitable microenvironment for the incorporation of cells or growth factors to regenerate ...

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Three-dimensional scaffolds for tissue engineering applications : role of porosity and pore size

3D Printing promises to produce complex biomedical devices according to computer design using patient-specific anatomical data. Since its initial use as pre-surgical visualization models and tooling molds, 3D Printing has slowly evolved to create one-of-a-kind devices, implants, scaffolds for tissue engineering, diagnostic platforms, and drug delivery systems. Fueled by the recent explosion in public interest and access to affordable printers, there is renewed interest to combine stem cells with custom 3D scaffolds for personalized regenerative medicine. Before 3D Printing can be used routinely for the regeneration of complex tissues (e.g. bone, cartilage, muscles, vessels, nerves in the craniomaxillofacial complex), and complex organs with intricate 3D microarchitecture (e.g. liver, lymphoid organs), several technological limitations must be addressed. In this review, the major materials and technology advances within the last five years for each of the common 3D Printing technologies (Three Dimensional Printing, Fused Deposition Modeling, Selective Laser Sintering, Stereolithography, and 3D Plotting/Direct-Write/Bioprinting) are described. Examples are highlighted to illustrate progress of each technology in tissue engineering, and key limitations are identified to motivate future research and advance this fascinating field of advanced manufacturing.

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Recent advances in 3D printing of biomaterials

3D printing with polymers: Challenges among expanding options and opportunities.

Sharing memory pages between non-trusting processes is a common method of reducing the memory footprint of multi-tenanted systems In this paper we demonstrate that, due to a weakness in the Intel X86 processors, page sharing exposes processes to information leaks We present FLUSH+RELOAD, a cache side-channel attack technique that exploits this weakness to monitor access to memory lines in shared pages Unlike previous cache side-channel attacks, FLUSH+RELOAD targets the Last-Level Cache (ie L3 on processors with three cache levels) Consequently, the attack program and the victim do not need to share the execution core

We demonstrate the efficacy of the FLUSH+RELOAD attack by using it to extract the private encryption keys from a victim program running GnuPG 1413 We tested the attack both between two unrelated processes in a single operating system and between processes running in separate virtual machines On average, the attack is able to recover 967% of the bits of the secret key by observing a single signature or decryption round

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FLUSH+RELOAD: a high resolution, low noise, L3 cache side-channel attack

We present an effective implementation of the Prime Probe side-channel attack against the last-level cache. We measure the capacity of the covert channel the attack creates and demonstrate a cross-core, cross-VM attack on multiple versions of GnuPG. Our technique achieves a high attack resolution without relying on weaknesses in the OS or virtual machine monitor or on sharing memory between attacker and victim.

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Last-Level Cache Side-Channel Attacks are Practical

Preparation of poly(ε-caprolactone)-based tissue engineering scaffolds by stereolithography.

Cache-timing attacks are a serious threat to security-critical software. We show that the combination of vector quantization and hidden Markov model cryptanalysis is a powerful tool for automated analysis of cache-timing data; it can be used to recover critical algorithm state such as key material. We demonstrate its effectiveness by running an attack on the elliptic curve portion of OpenSSL (0.9.8k and under). This involves automated lattice attacks leading to key recovery within hours. We carry out the attack on live cache-timing data without simulating the side channel, showing these attacks are practical and realistic.

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Cache-Timing Template Attacks

Crosslinking is a feasible way to prepare biodegradable polymers with potential in biomedical applications such as controlled release of active agents and tissue engineering. A synthesis route in which functional telechelic aliphatic polyester oligomers are used as precursors for the preparation of crosslinked polyesters and poly(ester anhydride)s is described. Mechanical properties, degradation characteristics and rate, and bioactivity can be modified widely by controlling the chemical composition and architecture of the crosslinkable oligomers. In tissue engineering, photocrosslinking allows to use crosslinkable oligomers in advanced manufacturing techniques like micromolding in capillaries, stereolithography and two-photon polymerization.

Photocrosslinkable Polyesters and Poly(ester anhydride)s for Biomedical Applications

A novel selective leaching method for the porogenization of the biodegradable scaffolds was developed. Continuous, predetermined pore structure was prepared by dissolving fast eroding poly(epsilon-caprolactone)-based poly(ester-anhydride) fibers from the photo-crosslinked poly(epsilon-caprolactone) matrix. The porogen fibers dissolved in the phosphate buffer (pH 7.4, 37 degrees C) within a week, resulting in the porosity that replicated exactly the single fiber dimensions and the overall arrangement of the fibers. The amount of the porosity, estimated with micro-CT, corresponded with the initial amount of the fibers. The potential to include bioactive agents in the porogen fibers was demonstrated with the bioactive glass.

Porous biodegradable scaffold: predetermined porosity by dissolution of poly(ester-anhydride) fibers from polyester matrix.

We present a cache-timing attack on the SNOW 3G stream cipher. The attack has extremely low complexity and we show it is capable of recovering the full cipher state from empirical timing data in a matter of seconds, requiring no known keystream and only observation of a small number of cipher clocks. The attack exploits the cipher using the output from an S-box as input to another S-box: we show that the corresponding cache-timing data almost uniquely determines said S-box input. We mention other ciphers with similar structure where this attack applies, such as the K2 cipher currently under standardization consideration by ISO. Our results yield new insights into the secure design and implementation of ciphers with respect to side-channels. We also give results of a bit-slice implementation as a countermeasure.

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Risto Hakala

Papers

Preparation of poly(ε-caprolactone)-based tissue engineering scaffolds by stereolithography.

Cache-Timing Template Attacks

Photocrosslinkable Polyesters and Poly(ester anhydride)s for Biomedical Applications

Porous biodegradable scaffold: predetermined porosity by dissolution of poly(ester-anhydride) fibers from polyester matrix.

Consecutive S-box lookups: a timing attack on SNOW 3G