matrix-type devices, without requiring surgical removal. [7-9] Enzymatic and hydrolytic degradation are the two major physiologically relevant mechanisms that confer degradability to hydrogel matrices. Enzymatic degradation is generally preferred in tissue engineering, where matrix degradation must be synchronized with native cell infiltration and tissue deposition. [10,11] Enzymatically degradable gels have also shown great potential for celldemanded growth factor delivery, where growth factors are released upon local proteolytic gel degradation by cells. [12,13] Hydrolytic degradation is also advantageous in controlled release applications, such as drug or protein delivery, because the rate of degradation does not depend on enzymes and can be controlled by the hydrogel's chemical and physical properties. [14] In addition, hydrolytically degradable materials could be made at lower cost compared to enzymatically degradable ones. Degradable hydrogels can be formed from both natural and synthetic polymers. Synthetic hydrogels offer advantages in reproducibility, availability, and tailoring physical and chemical properties to specific applications. [15] The synthetic hydrogel poly(ethylene glycol) (PEG) is widely used due to the advantages of being non-immunogenic, inert, and biocompatible. [16] However, the PEG polymer is not readily degradable under physiologic conditions at physiologically relevant time frames. Note that in the long-term PEG can be degradable by oxidative degradation from reactive oxygen species. [17] For short-term degradation, degradable moieties must be introduced to fabricate degradable PEG hydrogels and several techniques have been employed, such as incorporating enzymatically cleavable peptide crosslinkers [18,19] or hydrolytically degradable monomers or copolymers, such as polylactic (PLA) and polyglycolic acid (PGA) to either linear [20,21] or star PEG. [22] Each method has advantages and drawbacks. A reliance on enzymes to cleave crosslinkers can result in inconsistent degradation rates. PEG-PLA and PEG-PGA hydrogels are hydrolytically degradable, but copolymer hydrophobicity and acidic degradation products can denature proteins. [23] Hydrogels prepared from PEG-diacrylate (PEGDA) have also been shown degradable by hydrolytic degradation of the endgroup acrylate esters, when implanted subcutaneously in a rat model. [24] In another example, multiarm PEG-amine crosslinked with an ester-containing amine-reactive PEG derivative has been described as a hydrolytically degradable scaffold for Hydrogels, whose degradability can be controlled while also preserving cell viability or biomolecule stability, are in demand. Degradable polyethylene glycol crosslinkers are hydrolytically designed for use in hydrogels. Degradation is controlled by crosslinker chemical structure, such as introducing local hydrophobicity, steric hindrance, or electron-withdrawing moieties near a degradable ester moiety. Hydrogels made using these crosslinkers have gelation times from 1 to 22 min, storage moduli from 3 to 1...

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Aqueous two‐phase systems (ATPS) have found various applications in bioseparations and microencapsulation. The primary goal of this technique is to partition target biomolecules in a preferred phase, rich in one of the phase‐forming components. However, there is a lack of understanding of biomolecule behavior at the interface between the two phases. Biomolecule partitioning behavior is studied using tie‐lines (TL), where each TL is a group of systems at thermodynamic equilibrium. Across a TL, a system can either have a bulk PEG‐rich phase with citrate‐rich droplets, or the opposite can occur. We found that porcine parvovirus (PPV) was recovered at a higher amount when PEG was the bulk phase and citrate was in droplets and that the salt and PEG concentrations are high. To improve the recovery, A PEG 10 kDa‐peptide conjugate was formed using the multimodal WRW ligand. When WRW was present, less PPV was caught at the interface of the two‐phase system, and more was recovered in the PEG‐rich phase. While WRW did not significantly increase the PPV recovery in the high TL system, which was found earlier to be optimal for PPV recovery, the peptide did greatly enhance recovery at a lower TL. This lower TL has a lower viscosity and overall system PEG and citrate concentration. The results provide both a method to increase virus recovery in a lower viscosity system, as well as provide interesting thoughts into the interfacial phenomenon and how to recover virus in a phase and not at the interface.

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