Composites

The scaffold is a temporary supporting structure for growing cells and tissues, whose role is to mimic the native ECM [53]. It is widely known that there are various molecules in ECM, and they make up the whole complicated and transient extracellular environment. In the design phase of the scaffold in tissue engineering, a great many of things should be taken into consideration, including the fact that the scaffold under research should meet the relevant organic application, as well as simulate the function of ECM as possible as they can be achieve. In recent decades, scientists have been striving hard to carry out a large amount of research and experiments on biocomposites for developing a combined new material that consisting of at least two different materials, which are usually among metals, ceramics and polymers, as we mentioned before [54-56].

The ECM regulates a cellular dynamic behavior and intercellular communication; in the meantime, it also functions as a warehouse storing for all kinds of growth factors. Thus, the engineered scaffold should be biocompatible and bioactive to meet all the demands when replacing the abnormal tissue in the human body. In addition, other features are required for special tissue replacement or repair. For example, bone tissue engineering requires highly strength and rigidity; vascular tissue engineering requires appropriate mechanical properties, like long-time shear resistance and compatibility with blood ingredient. Certain types of bioactive ceramics (e.g., TCP and HA) and bioactive glasses (e.g., 45S5 Bioglass®) react with physiologic fluids to form firm bonds with hard (and in some cases soft) tissue. However, these bioactive materials are relatively stiff, fragile and difficult to form complex shapes. In contrast, synthetic bioresorbable polymers are easy to fabricate into desirable structures, yet they are too weak to meet the requirements of surgery and the in vivo physiologic environments [57]. Hence, biocomposites can, in some ways, help them obtain well-combined performance from mixed materials, which can achieve multi-aspects goals at the same time.

Bioactive glass containing biodegradable polymers is a commonly used composite material for scaffolds. Niiranen et al. [58] prepared a self-reinforced PL/DLLA (70:30) matrix composite containing bioactive glass (BG 13-93). They found that the addition of bioactive glass could modify the degradation kinetics of the scaffold both in vivo and in vitro, as well as improve the material morphology, dimensional stability and apatite formation on its surface. It is obvious that the bioabsorbable polymers, such as PLA, PGA, PCL, polyethylene oxide (PEO), and poly(3- hydroxybutytrate) (PHB), containing other osteoconductive fillers show great potential as bone-repairing materials in hard tissue engineering. And CaPs including HA, TCP and CPCs also play an important role in the development of scaffolds for bone tissue engineering [59]. Miao et al. [60] produced porous CaP ceramics with interconnected macropores (>200 pm), micropores (5 pm) and high porosities, and the open micropores were infiltrated with PLGA to form an interpenetrating bioactive ceramic-biodegradable polymer composite structure. In this manufacturing method, the compressive moduli of the material was significantly improved, and the bioactivity of the composite scaffolds was confirmed by the apatite layer formation in the simulated body fluid. In some cases, the addition of a polymer phase into the ceramic material might have extra functions, such as the biodegradable polymer that can act as a carrier for some special biomolecules, growth factors, antibiotics and other signal molecules, thereby increasing the capability of tissue engineering constructs [59]. Furthermore, the addition of carbon nanotubes and fibers to the composite coating will enhance the mechanical properties and induce nanotopographical surface features, which will enhance better cell attachment and survival.

The metal-ceramic composite is also used as bone grafts in clinical trials. For example, Marsich et al. [61] have been carried out experiments on adding silver nanoparticles into alginate/HA ceramic composite scaffold, and they found the new bone grafts have been endowed with antibacterial properties owing to the presence of silver nanoparticles. The results of in vitro test and the release profile of silver nanoparticles indicated the prospective characteristics of these biocompatible antimicrobial scaffolds for the future tissue engineering applications. The ceramic material can perform excellent scaffolds when adding with metal infiltration, because the stable chemical structure of ceramics ensures their highly biocompatibility all the time. On the other hand, the metal is modified by the bond with ceramics, which can show a decrease in the corrosion rate and an increase in mechanical properties. Gu et al. [62] adopted the molten metal infiltration technique to fabricate the MgCa-HA/TCP, which exhibited the inferior mechanical property (decreased by 50%) but with superior corrosion resistance (improved by 68%), compared to the single MgCa alloy matrix. This bioactive HA/TCP scaffold was also proved to have slower degradation rate due to the presence of ceramic scaffolds, which is an important part to be considered in bone tissue engineering and cartilage tissue engineering.

Apart from metal, various inorganic and organic materials are also applied to the design of composite scaffolds. For example, chitosan is greatly used in the combination of polymers to fabricate the ideal composite scaffold, because of its important role in peripheral nerve regeneration [63]. Razavi et al. [64] fabricated the tissue-engineered scaffold with chitosan nanopowders and PLGA, and found that the high chitosan content and aligned-orientation of nanofibers in biocomposite scaffold can promote differentiation and myelinogenic capacity of Schwann-like cells induced from human adipose-derived stem cells (ADSCs), which is a critical issue in nerve regeneration medicine. Collagen, as a natural polymer found in ECM, is resorbable with high swelling ability, low antigenicity and cytocompatibility [65]. Due to its poor mechanical strength, pure collagen can’t be directly used as a bone substitute material. Hence the composite scaffold of collagen and bioactive ceramics has drawn great attention [65]. Kuttappan et al. [43] summarized the current state of the field by outlining composite scaffolds made of gelatin/collagen in combination with bioactive ceramics, and Table 2.5 below shows commercially available collagen/gelatin based composites.

Table 2.5 Collagen/gelatin based composites available in the market [43]

Product

Company

Collagen/

gelatin

Additive

Application

Collagraft®

Zimmer

Bovine

Collagen Type

I (>95%), Type

II (<5%)

HAP -65% P-TCP -35%

Acute long bone fractures and traumatic osseous defects, bone void filler

GingivAid®

Maxigen Biotech Inc.

Type I collagen

HAP/p-TCP

Dental implant surgeries, sinus lift and alveolar ridge augmentation

Formagraft®

Maxigen Biotech Inc.

Type I collagen

HAP/p-TCP

Bone graft substitute

CopiOs Sponge and

Paste

Zimmer

Type I Bovine Collagen

Calcium

phosphate

Bone void filler

Ossigen®

Exactech

Collagen

Bone mineral

Bone void filler

OsseoFit®

DSM

Biomedical

Type I bovine collagen

PLLA, p-TCP

Bone voids or bone defects in the pelvis and extremities

CONDUCT® Matrix

GLOBUS

Medical

Type I collagen

Carbonate apatite mineral

Bone void filler

Puros® DBM Putty

Zimmer

Demineralized bone matrix

Bone void filler

CONFORM® Demineralized Cancellous Bone

Depuy

Synthes

Demineralized

cancellousbone

Bone void filler, use within posterolateral gutters of the spine

DBX®

Depuy

Synthes

Gelatin-

Sodium

hyaluronate

Demineralized bone matrix

Bone void filler, treatment of oral/ maxillofacial and dental intraosseous defects

Integra Mozaik™

Integra Life Sciences

Type I collagen

TCP

Bone void filler

INFUSE® Bone Graft

Medtronic

Type 1 bovine collagen

rhBMP-2

Bone void filler

Vitoss®

Stryker

Collagen

P-TCP,

Bioactive

glass

Bone void filler

OP-1 Implant

Stryker

Type I bovine collagen

BMP-7

Bone void filler

MASTERGRAFT®

Putty

Medtronic

Type I bovine collagen

P-TCP

Bone void filler

RegenOss®

JRI

Orthopaedics

Type Icollagen fibers

Magnesium- enriched HAP

Long bone fractures, Spinal fusion

(continued)

Table 2.5 (continued)

Product

Company

Collagen/

gelatin

Additive

Application

Orthoss® Collagen

Geistlich

Surgery

Porcine

Collagen

Bovine HAP

Bone void filler, reconstruction in orthop-aedic and in spinal surgery, volume extender for composite bone grafting

Bio-Oss Collagen®

Geistlich

Biomaterials

Porcine

Collagen

Geistlich

Bio-Oss®

particles

Sinus Floor Elevation, Peri- implantitis, Periodon-tal Regeneration, Ridge Augmentation

Adapted with permission from Ref. [43]. Copyright 2014 Elsevier Ltd

 
Source
< Prev   CONTENTS   Source   Next >