Table 2.

The constitution of gelatin–PEG and elastin–PEG precursor. The concentration of gelatin and elastin in precursor were measured by BCA method. The conjugation efficiency of amine groups and PEGDA was determined by trinitrobenzenesulfonic acid assay (TNBSA) method. (Mean ± STDEV, n = 3, p < 0.05).

Samples	Protein Ratio (%)	Protein Concentration (mg/mL)	PEG Ratio (%)	TNBSA (µg/mL)	Conjugation Efficiency (%)
Gelatin–PEG–acrylate	60.2 ± 4.5	32.5 ± 1.5	39.8 ± 4.5	160.3 ± 10.4	52.8 ± 6.5
Elastin–PEG–acrylate	56.4 ± 5.8	1.69 ± 1.7	43.6 ± 5.8	2.5 ± 0.1	59.6 ± 2.2

Note: Gelatin–PEG–acrylate solution after TFF purification and filtration with 0.22 µm membrane was stored in –70 °C for the cell encapsulation experiments as gelatin–PEG–acrylate was difficult to dissolve after lyophilization. The mass of gelatin–PEG–acrylate was achieved after lyophilization 1mL solution (with the subtraction of PBS salts: 16mg/mL). Elastin–PEG–acrylate was lyophilized after TFF purification. Elastin–PEG–acrylate was dissolved at 3 mg/mL for BCA and TNBSA measurement. Gelatin–PEG–acrylate was diluted 10 times before TNBSA assay. Original gelatin and elastin were used to prepare the standard curves of BCA assay, while lysine was used to prepare TNBSA standard curve. The TNBSA assay results of gelatin–PEG–acrylate and elastin–PEG–acrylate were normalized by the protein amount in the precursor for the calculation of conjugation efficiency.