Degradable highly crystalline polymer films: morphological regulation, heat switching, and enzymatic degradation behavior
preface
Degradable semi-crystalline polymers such as poly(ε-caprolactone) (PCL) remote claws are highly technically relevant for convertible biomaterial surfaces to affect cell adhesion at biological interfaces and implant coatings as phase change lubricants. PCL has been established in clinical applications and its enzymatic degradability has been fully demonstrated.
Specifically, PCL crystals can be used as thermally transitionable units, and exhibit changes such as stiffness and degradability when melting, the melting temperature of PCL crystals can be adjusted very close to physiological conditions, producing a polymer layer that changes its multiple functional properties when a small thermal stimulus is applied.
Statistical experiment error
Preparation, melting, and degradation experiments of OCL membranes were performed at least three times. At the air-water interface, the systematic error range for surface pressure sensors is 0.3 mN·m−1, and 0.2°C for temperature sensors. Experimental errors during diffusion of polymer solutions and environmental impurities such as dust particles at the air-water interface can lead to 1 ω irregularities in the OCL film MMA measurement.
The instrument error of heating or cooling rate at the air-water or air-solid interface is less than 0.5 °Cmin−1. The systematic error of the melting temperature at the air-water interface is the temperature range between the first sign of melting observed in BAM and the point of complete melting.
Results and discussion
OCL molecules diffused at the air-water interface are compressed to low MMA by the Langmuir trough barrier. The associated compression isotherm (MMA to surface pressure) is two different temperatures for the aqueous subphase. The compression isotherms of OCDOL and OCDME films were at slightly lower surface pressure values at a lower aqueous subphase temperature of 12°C, indicating that temperature had an effect on the crystallization process at the air-water interface.
Crystallization during compression is observed by Broust angle microscopy at the OCL membrane at the air-water interface, which indicates that as compression increases, OCL crystals become closer to each other and therefore the overall crystallinity increases. At the same time, the amorphous phase represented by the dark region surrounding the crystal gradually disappears during the film compression process. When folded chains further increase their growth front, either new crystals are formed or existing crystals grow at their transverse size.
In the threshold MMA range (short for mixedmartial arts) between 3.0 and 2.02, accompanied by a sudden rise in surface pressure, Brewster angle microscopic images show the appearance of highly crystalline OCDOL or OCDME films at different aqueous subphase temperatures (12°C or 21°C).
In mixed martial arts (short for mixedmartial arts) high crys, OCL crystals (bright regions) are tightly packed and fairly fixed, i.e. they no longer change their lateral position on the surface of the water, while amorphous areas (dark areas) are minimal, meaning that the film is highly crystalline.
In terms of morphology, OCDOL crystal size in water at 12°C is less than OCDOL crystal OCL crystal shape at 21°C is also affected by OCL functional end groups. Hydroxyl-terminated OCL (OCDOL) forms crystals with smoother edges, while OCL dimethacrylate (OCDME) forms crystals with wavy edges.
To investigate the thermal switching function, i.e., melting and recrystallization of OCL films that are highly crystallized at the air-water interface, compress the OCL sample to an MMA of 22, wait 10 min, and then heat the aqueous subphase below. By observing the membrane under the BAM, melting begins (Tm episodes; The crystal begins to melt), the melting endpoint (Tm termination; Clear BAM image without any crystals), and recrystallization temperature (T; The appearance of the crystal structure during cooling) is identified.
Highly crystalline OCL films melt at physiologically appropriate temperatures, and during aqueous subphase cooling, melted membranes recrystallize at below 45 °C, interestingly Tm episodes When high crystalline films are prepared at a water temperature of 12 °C, OCDOL and OCDME samples have lower melting temperatures. Therefore, the melting temperature range of a highly crystalline film at the air-water interface can be attributed to its higher molecular weight by varying the crystallization temperature (Tc) to compare different molecules, and the slightly higher melting temperature range of OCDOL membranes than OCDME membranes.
Enzymatic degradation of the bulk polymer takes place during surface erosion because enzymes generally cannot penetrate into the bulk polymer. Thus, the highly crystalline layer of the surface can act as a thermally convertible barrier for enzymatic degradation. Here, this effect of OCDOL and OCDME films was studied under MMA2 at the air-water interface, in the presence of a highly crystalline or amorphous (molten) state of Pseudomonas cepae lipase at the same temperature of 46 ° C.
The highly crystalline OCDOL membrane is degradable by lipase but has ca. Compared to amorphous OCDOL films, the rate is 3 times slower. Highly crystalline OCDME membranes degrade only slightly slower than OCDME amorphous membranes. This difference may be due to the interaction of functional end groups with enzymes and the degradation temperature of 46°C closer to the melting temperature range of OCMDE (48±1°C).
In addition, OCDME crystals may have a greater degree of internal disorder than OCDOL crystals due to different chain stacking. In general, the effect is not obvious. Contrary to hypothesis, the crystal barrier layer cannot effectively slow down the enzymatic degradation of OCL because the enzyme catalyzes the degradation of OCL single crystals with high efficiency. Thicker crystals or multiple layers may be required to produce an effective coating that is stable for enzymatic degradation.
summary
This study demonstrates a systematic approach to developing highly crystalline OCL films with tunable morphology, heat switching, and degradation behavior. The methods used to prepare crystals are scalable and can be applied to different biological interfaces. Future research may include the degradation of these highly crystalline coatings at different pH values in the absence of enzymes, and exploring the use of these films as heat-sensitive lubricants for surgical implants to reduce friction in contact with tissues.
