Living Bacterial Sacrificial Porogens to Engineer Decellularized Porous Scaffolds

Decellularization and cellularization of organs have emerged as disruptive methods in tissue engineering and regenerative medicine. Porous hydrogel scaffolds have widespread applications in tissue engineering, regenerative medicine and drug discovery as viable tissue mimics. However, the existing hydrogel fabrication techniques suffer from limited control over pore interconnectivity, density and size, which leads to inefficient nutrient and oxygen transport to cells embedded in the scaffolds. Here, we demonstrated an innovative approach to develop a new platform for tissue engineered constructs using live bacteria as sacrificial porogens. E.coli were patterned and cultured in an interconnected three-dimensional (3D) hydrogel network. The growing bacteria created interconnected micropores and microchannels. Then, the scafold was decellularized, and bacteria were eliminated from the scaffold through lysing and washing steps. This 3D porous network method combined with bioprinting has the potential to be broadly applicable and compatible with tissue specific applications allowing seeding of stem cells and other cell types

"Protein-like" copolymers: Effect of polymer architecture on the performance in bioseparation process

Recently, a new class of copolymers, so-called protein-like copolymers has been predicted theoretically by computer simulation. In these copolymers. the conformation of the copolymer determines the exposure of certain comonomer units to the outer solution. Depending on the conformation, copolymer molecules with essentially the same comonomer composition could have pronouncedly different properties. The authors demonstrated experimentally such behavior in case of poly[(N- vinylcaprolactam)-co-(N-vinylimidazole)] (Dokl. Chem. 2001,375, 637). One more group of copolymers with protein-like behavior is copolymers of N-isopropylacryl-amide with N-vinylimidazole. Poly[(N-isopropylacryl-amide)-co-(N-vinylimidazole)] was synthesized by radical polymerization and separated into two fractions using immobilized metal affinity chromatography on Cu2+-loaded iminodiacetic acid Sepbarose CL 6B (Cu2+-IDA-sepharose). The unbound fraction which passed through the column and bound fraction eluted with ethylenediaminetetraacetic acid, disodium salt (EDTA) solution differed significantly in molecular weight, 1.4 x 10(6) and 1.35 x 10(5), respectively but were very close in comonomer composition, 7.8 and 9.1 mol-% of imidazole, respectively. The composition of bound fraction was confirmed by titration of imidazole groups. Despite close chemical composition, the bound and unbound fraction behaved differently with respect to temperature-induced phase separation at different pH values, the dependence of hydrodynamic diameter on pH and concentration of Cu2+- ions, and the coprecipitation of soybean trypsin inhibitor with the copolymer in the presence of Cu2+-ions. The differences in the behavior of copolymer fractions are rationalized assuming that the bound fraction presents a protein-like copolymer. The dependence of hydrodynamic diameter of bound (closed symbols) and unbound (open symbols) poly(NI-PAAM-VI) at different Cu2+/vinylimidazole ratios (n(Ca)/n(VI)), The polymer concentration was 4.5 mg (.) ml(-1) and pH 7.5 was obtained in all systems by using 0.010 m HEPES as a buffer. Mean values from five correlation functions are given

Chromatography of microbial cells using continuous supermacroporous affinity and ion-exchange columns

Continuous supermacroporous chromatographic columns with anion-exchange ligands [2-(dimethylanlino)ethyl group] and immobilized metal affinity (IMA) ligands (Cu2+-loaded iminodiacetic acid) have been developed allowing binding of Escherichia coli cells and the elution of bound cells with high recoveries. These poly(acrylamide)-based continuous supermacroporous columns have been produced by radical co-polymerization of monomers in aqueous solution frozen inside a column (cryo-polymerization). After thawing, the column contains a continuous matrix (so-called cryogel) with interconnected pores of 10-100 mum in size. The large pore size of the matrix makes it possible for E. coli cells to pass unhindered through a plain column containing no ligands. E. coli cells bound to an ion-exchange column at low ionic strength were eluted with 70-80% recovery at NaCl concentrations of 0.35-0.40 M, while cells bound to an IMA-column were eluted with around 80% recovery using either 10 mM imidazole or 20 mM EDTA solutions, respectively. The cells maintain their viability after the binding/elution procedure. These preliminary results indicate that microbial cells can be handled in a chromatographic mode using supermacroporous continuous columns. These columns are easy to manufacture from cheap and readily available starting materials, which make the columns suitable for single-time use. (C) 2002 Published by Elsevier Science B.V