Substrate Material for Fiber/Tube Reinforced Scaffolds

One of the major concerns in developing novel fiber- or tube- reinforced scaffolds is the selection of appropriate substrate biomaterials. For the material properties and load bearing requirements of the native tissue are important design considerations determining the success of the reinforced scaffolds. Implanted scaffolds as space- holders to mimic the native EMC of damaged or diseased tissues or organs should possess some important characteristics for tissue engineering applications [10], as shown in Table 2.1. The basic characteristics of tissue engineering scaffold listed below are key factors to be considered during the design and manufacturing process.

At present, different types of scaffolds are compiled with their associated properties and applications. Typically, four individual groups of biomaterials, metals, ceramics, and polymers, have been proven with experimental data on their viability for biomedical materials, whose characteristics and applications are summarized in Table 2.2. For each scaffold material has different associated properties and mechanism, the choice of materials depends on the target tissue. For example, ceramics exhibit a high degree of biological activity and abrasion resistance, and have been used for bone repair for decades. In this respect, ceramics are widely used for processing scaffolds for hard tissue engineering. While, in most cases, there is a growing need for improved biomaterials to balance microstructural and mechanical

Table 2.1 Basic characteristics of scaffolds for tissue engineering applications

Properties

Remarks scaffold

Material

Bioresorbable

Foreign material and bulk degradation products should eliminate from body by natural pathways

Natural and synthetic bioresorbable polymer (collagen, PLA, hyaluronic acid, etc.)

Controlled porosity with interconnected pores

Tailor-made cellular adhesion, growth, extracellular matrix secretion, angiogenesis, nutrition, and oxygen transport without compromising mechanical strength

Polymeric hydrogels (PLG, PTFE, PLGA, PLCL) and composite materials (nano HA-collagen)

Biodegradable

Breakdown products of macromolecular degradation should not be toxic or immunogenic

Polymeric, composites, and ceramic scaffolds (nano TCP, nano HA, silica)

Controlled pore structure

To provide greater diffusivity and higher diffusion coefficient for waste removal and nutrient transport

Polymeric hydrogels and nano- fibrous structures (PLL/ PLGA, gelain microspheres, PCL)

High surface area-to-volume ratio

For increased cell density, cell adhesion, proliferation, migration, and differentiation

Nanofibrous hydrogels, nanostructured components, and micro- fluidic scaffolds

Mechanical stability

Mechanical properties should match the replaced natural tissue to withstand in vivo stimuli

Metallic and alloy based, ceramics and composite scaffolds (nanostructured titanium and its alloys, nano alumina)

Three-dimensional

templating

To assist cellular ingrowth and provide a natural three-dimensional in vivo micro-environment

Nanofibrous and polymeric hydro-gels, metallic, ceramics, and composites

Mimic natural ECM

Properties and structures should be matched with natural ECM components to coordinate with biological cues

Polymeric and composite hydrogels and nanofibrous scaffolds

Cellular compatibility

Scaffold surfaces must show cellular compatibility and should not repel cells

Polymeric and composite scaffolds (PET, PEGT/PBT)

Vascular support

To support angiogenesis and healthy regeneration

Polymeric, ceramic, and composite hydrogels and nanofibrous scaffolds

Biocompatible

Should not provoke any rejection, inflammation, immune response, etc.

Polymeric, ceramic, metallic, and composite materials

Surface modifiable

Scaffold surfaces should allow chemical or biomolecular functionalization to increase cell-material interactions

Metallic, composites, ceramic, and polymer materials (PEOT/ PBT, PEG)

Non-toxic

Should not evoke toxicity to tissues

Natural polymeric scaffolds and composites

Non-immunogenic

Immunogenic response to tissue must not be evoked

Natural polymeric, composite, and ceramic scaffolds

(continued)

Table 2.1 (continued)

Properties

Remarks scaffold

Material

Non-corrosive

Should not become corroded at physiological pH and body temperature

Polymeric, ceramic, and composite scaffolds

Sterilizable

Surfaces must be receptive to sterilization processes to avoid contamination

Metallic, ceramic, composite, and polymeric scaffolds

Degradability rate matching with regrowth rate

For gradual transfer of loadbearing and support functions to newly growing tissues

Ceramic, polymeric, and composite scaffolds (PLL/HA, PDLLA, PCL)

High water content

Helps in generating hydrated in vivo environment

Polymeric and composite hydrogels

Table 2.2 A broad classification of substrate scaffold materials

Scaffolding

materials

Advantages

Disadvantages

Applications

Examples

Metals

Strong, tough, ductile

Bioinert, difficult to make

Bone and dental implants, etc.

Tialloy

Ceramics

Bioactive, bioresorbable, high resistance to wear

Brittle, low toughness, not resilient

Low-weightbearing bone implants, dental restoration, tissue scaffolds, bone drug delivery, etc.

Nano HA Nano

tri-calcium

phosphate

Polymers

Biodegradable, flexible, low density, resilient, surface modifiable, chemical functional groups

Low stiffness, Local acid

Tissue scaffolds, drug delivery, sutures, skin augmentation, blood vessels, heart valves, etc.

Collagen PLLA PLGA

Composites

Strong, design flexibility

Varying

properties

Tissue scaffolds, drug delivery, etc.

HA/collagen

design standards, which facilitates the research on new composite materials, as mentioned below in Table 2.2.

 
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