Biomedical Engineering Reference
In-Depth Information
crospheres are becoming increasingly popular in TE. The spherical nature maximizes the
surface area, and the small volume of beads facilitating biomolecular transport. Regarding
hydrogels, they have a similar microstructure to the extracellular matrix (ECM) and allow
good physical integration into the defect by the use of minimally invasive approaches for
material and cell/drug delivery. The biological, chemical, topography features and mechani‐
cal properties, as well as the degradation kinetics of hydrogels, can be tailored depending on
the application [65-68]. Aligned nanoscale and microscale topographic features in scaffolds
have been also reported to influence the alignment of cells. For example, this alignment is an
important requirement of functional skeletal muscle since it leads to alignment of myoblasts
and cytoskeletal proteins and promote myotube assembly along the nanofibres and micro‐
grooves to mimic the myotube organization in muscle fibres [65, 68-70]. Scaffolds are used
successfully in various fields of tissue engineering such as bone formation, periodontal re‐
generation, cartilage development, as artificial corneas, in tendon repair and in ligament re‐
placement. In addition, the incorporation of drugs (i.e., inflammatory inhibitors and/or
antibiotics) into scaffolds or specific molecules to provide adequate signals to the cells is also
possible [71] Depending on the medical applications, scaffolds requirements will depend on
its function. Hydrogels can be used as a physical barrier to protect the cells from hostile ex‐
trinsic factors before delivery, or be used as a matrix to drug controlled release or cell adhe‐
sion, growth and differentiation to further improve the secretion of therapeutic proteins
from cells. In fact cells are capable of delivering drugs in response to an external stimulus,
which is highly advantageous to maintain homeostasis for patients suffering from chronic
diseases. For the first application, the scaffold needs:
i.
to be biocompatible, by minimizing the patients' immune response, which is detri‐
mental to cell viability, hydrogel stability, and mass transport. Ideally, the scaffold
should evoke no or only minimal fibrous tissue reaction, macrophage activation,
and cytokine and cytotoxic agent release
ii.
to have controllable degradability, being the degradation products not toxic and
eliminated easily from the implantation site by the body, and
iii.
to have mechanical properties that are sufficient to shield cells from tensile forces
without inhibiting biomechanical cues to cells through mechanotransduction path‐
ways that mediate tissue homeostasis, morphogenesis, cell growth, contractility,
differentiation, and pathophysiology [70-72].
For the second applications further requirements are needed, mainly:
i.
a microstructure that allows for the influx of nutrients and oxygen toward the en‐
capsulated cells and prevents the efflux of therapeutic molecules and cellular
wastes away from the scaffold; this is assured through adequate pore size distribu‐
tion and its interconnectivity. A high surface:volume ratio should be suitable for
cell/drug attachment;
ii.
adequate drug binding affinity to allow a controllable drug released to be stable
when incorporated in the scaffold at a physiological conditions;
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