Environmentally responsive biomaterials

Key words in situ polymerizable biomaterials, controlled biodegradation, non-cytotoxic degradation products, environmentally responsive biomaterials. 

Self-assembling injectable biomaterials also undergo gelation or phase-separation without chemical crosslinking reagents as described previously for environmentally responsive materials. Phase-separation of either hydrophobic bulk material or hydrophobic domains of amphiphilic molecules is a frequently applied mechanism by which self-assembly proceeds. 

Raman spectroscopy can be used for live, in situ, temporal studies on the development of bone-like mineral (bone nodules) in vitro in response to a variety of biomaterials/scaffolds, growth factors, hormones, environmental conditions (e.g. oxygen pressure, substrate stiffness) and from a variety of cell sources (e.g. stem cells, FOBs or adult osteoblasts). Furthermore, Raman spectroscopy enables a detailed biochemical comparison between the TE bone-like nodules formed and native bone tissue. Bone formation by osteoblasts (OB) is a dynamic process, involving the differentiation of progenitor cells, ECM production, mineralisation and subsequent tissue remodelling. 

In contrast to lipids, polymer chemistry allows various chemical modifications to introduce functionality and make polymers responsible to environmental stimuli (pH, temperature, ions, light, etc.). In biosciences, responsiveness to external stimuli is a crucial factor, especially in drug release and construction of biomaterials. 

In another remarkable example, Chilkoti et al. have developed nano-structured surfaces by combining ELPs and dip-pen nanolithography that show reversible changes in their physicochemical properties in response to changes in their environmental conditions, hi particular, these systems are able to capture and release proteins on nanopatterned surfaces by using the self-assembling characteristics of ELPs in an effort to develop advanced biomaterials, regenerable biosensors, and microfluidic bioanalytical devices [127-130]. 

Teixeira, A.I., McKie, G.A., Foley, J.D., Bertics, P.J., Nealey, P.F., Murphy, C.J., 2006. The effect of environmental factors on the response of human comeal epithelial cells to nanoscale substrate topography. Biomaterials 27 (21), 3945—3954. 

TE and cell therapy approaches aim to take advantage of the repopulating potential and plasticity of multipotent stem cells to regenerate lost or diseased tissue. TE offers a potential solution to the limits related to poor cell survival by providing extra support to protect transplanted cells and thus improving survival and engraftment. Biomaterial physical properties can be readily manipulated in response to changes of environmental factors and cellular activities. 

PKA and AP, respectively (Wang et al 2010 Zelzer, McNamara, et al 2012), as well as the triggered availability of a peptide sequence on the surface (Todd et al 2009). As peptides are natural substrates for enzymes, enzymatic response of a peptide surface appears to be an ideal way to interface a biomaterial surface with a living system. Enzymatic stimulation of peptide surfaces has the advantage that the environmental conditions required (physiological conditions) are ideal for both the peptide and the stimulus. For applications in living systems, emphasis must be placed on a well-designed peptide surface to prevent unwanted interaction with other enzymes. 

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